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Post by henri on Apr 23, 2015 16:08:58 GMT
i prefer the idea of the kytronic (not sure on spelling) cdi's , they have a screw head switch with i think 6-8 settings you can have different maps on , rather than trying to map at side of road wi-fi-ble ,do it at home with more care/thought n time in it . tho could be my general wi-fi/puters/bluetooth/gps phobias showing thru again , H
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Post by sime66 on Apr 24, 2015 12:59:08 GMT
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Post by henri on Apr 24, 2015 15:53:13 GMT
kytronik , thats the spelling , the mappable cdi looks good to me , but the spark magnifier on its own is a waste of money ,in my opinion , seen same kind of thing every 2-3 years ,claiming the same performance boost n mpg savings ,an they never work ,maybe this is the 1 that does but i doubt it , H
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Post by henri on Apr 24, 2015 16:00:08 GMT
just read the modern vesp chat sime linked ,seems they all rate the spark booster ,might have to re-think my above comments , H
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Post by vespasco on May 8, 2015 20:23:57 GMT
Update: After hi rpm pinking/fuel starvation issues, i finally cured the problem! So far anyway! Before i had the stock Rally fuel tap Then fitted a BGM FastFlow. It took a while to realise but the BGM FF was problematic on reserve.. it just would not let enough fuel to the chamber and i suffered fuel starvation at higher revs...causing pinking problems amongst other things. Tried another BGM FF...same problem but slightly better Refitted the stock tap... Ok upto around 7000rpm+ then fuel starved. Fitted SIP FF - checked for leaks first. Seems good. Finally!!!! I can actually ride WOT throttle again!!  Ive been Faffin around with jetting for ages..changing one thing at a time..in the end it included changing atomizers, idles, slides, carbs, taps, exhaust, etc... I could get it sweet at low and mid but fail at WOT Ive always left the timing where it is, 19°, i want to advance the timing not retard, so stuck at the jetting etc... Once the SIP FF was fitted the jetting didnt take long, but still needs a tweak, (i was getting rusty nuts in the rain)... Ive now seen that rev counter go well past 8000rpm!! And stay there with out getting too hot Finally!!! I spotted a couple of things that didnt help me when jetting.... After losing most of my Dellorto jets (the ones i needed anyway) i bought a complete set of BGM ones.... The finish is a little poor tbh. I can also say the differences between the main jets and atomizers made by SIP Performance, BGM, SPACO, and Dellorto.... Well, always use Dellorto is all i can say!!! Quality! Theyre all slightly different to each other! I noticed a slither of brass which must have came from the slot in the top of the MJ was 1/2 blocking the hole.. This was on a few of the jets...it seemed to happen when i slotted it in so never noticed it before i put it in. I keeped thinking my MJ was blocked,,along with no fuel!!made for poor running Once the motor was able to actually run WOT i swapped my homemade pipe to the SIP mkll. It was starting to sound too hot. Im glad i changed it, the insides were rusting away! And was like a set of maracas when i took it off! The SIP mkll was the smoothest of the exhausts i have. So ive got that on for now. It wont be long before the mkl is back on though! So the set up now , for the moment is; Si24, 142 BGM main jet, 52/140 idle, stock no.4 slide, BE3 - with the top holes slightly enlarged, 160ac which ive opened up a little,,likely around a 170 now, SIP road mkll, 19.5° Its a little rich between 4000 - 5500rpm, which is why i opened out the atomizers top holes.. Theres still room for improvement  Now i can properly start getting it running sweet at all rpm. Once it stops raining. And re fit the si26! and probably the sip mkl with it Im determnined not to have to buy an ignition gadget!! I also fitted the new fren 'aqua' brake shoes... The pads must have been thinner on the new ones than the ones i took off! as when i tested them without any adjustment, they barely worked! Visually they looked about the same! Ive also ordered an Indian brand FF fuel tap for £8 as a back up! Hopefully i wont need it now. It looks like a SIP copy in the pics. Overall,, this bunny is happy = |
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Post by pxguru on May 9, 2015 17:03:25 GMT
What I am reading is that it is all going well now. The only thing that worries me is the bigger main AC. The more air that goes in there the less draw on the main jet. Makes it susceptible to run weak at WOT when the weather changes. Rarely is there ever a need to go away from the 160.
If it’s running well at all throttle positions now then all is good. You are certainly going to know if there is ever an issue and can re jet when, if ever there is a need.
You have a final MD run to post as a comparison?
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Post by sime66 on May 9, 2015 18:39:39 GMT
You have to admire the persistence to get this spot-on; hope you have a good, trouble-free summer, and can resist the urge to keep tweaking and just ride it!
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Post by vespasco on May 9, 2015 19:48:15 GMT
No MD yet...i just put the si26 back on now its going better. And its much better too Although i put the same jets back in the si26, which was for today at least... 160AC, Be3, 142mj (140mj was ragged edge) and a 52\140 idle. I went on a long run it was ok. But it was scary over taking as my fuel started cutting out, so just kept at 60mph. Ive been using the BE2 to good effect too of late, at least in low/mid range. (I know it will be leaner at WOT) Ive also have my slightly opened out 160AC. And the slightly opened out BE3 I have my box of jets with me at all times, and the screwdriver i need to change is by my feet, and ive been riding without a side panel to make it easier to quickly swap jets. I leave the motor running, undo the 4 x screws and swap whichever jet im checking out at the time. I totally see what youre saying guru ji .. about the large AC. It just helps make it ridable for now, while im trying other combinations/trying sort out my fuel issue. And im still working on it. One eye is constantly on the CHT gauge... Which was acting a weird earlier if you ask me. I remember i used to ride WOT on dual carriageways, and the temps would be pretty constant once i settled at a constant speed, dropping a couple of degrees if anything... Today i watched the gauge slowly rising from the normal temps ive had all today, 280°f, to 305°, ,, i could also feel the motor reacting too,,,then it would clear it self and drop down to 280 again! After more investigating im leaning towards an air lock issue.... Ive thoroughly gone through the carb looking at ways to get more fuel in there ... And discovered, possibly, another little modification thats worth doing..or which ive done anyway to try help the problem. The inlet hole in the spaco cosa float bowl top, which ive already drilled out to 3mm (if you do this mod. don't drill the brass needle sealing pad)!! Fuel comes from under the little round mesh filter, which ive taken out in the past, and then goes into the feed hole that gets drilled out to 3mm and fed through the needle valve, into the bowl,etc etc I noticed the casting for this hole was sticking above the filter. Meaning if that hole was lower then i could effectively gain more fuel, as the fuel feed level would be lower. So i dug out an old Dellorto top and guess what... Bingo!  So i used a small file and done this..  I think its helped... But when i tried, (with barely any fuel in the tank), it was missing when i gave it throttle. I filled up, bled the fuel line by slightly unscrewing the carb bowl float top and letting the fuel flow out. In 2nd the rpm went upto 8900rpm! 3rd upto around 8300rpm 4th it struggles to hit 7000rpm although its not quite set up yet. Its getting there. Im fitting the SIP mkl tomorrow. Its just this fuel issue... I ve shortened the fuel line, lenghened it too! Checked the routing... Will pop the tank off again and look at other ways.... The pipe through the side of the carbbox maybe a good idea.??! Im gonna look into it more, ive seen it mentioned before somewhere.. I dont mind custardising my already custardized (originally a 150 Super) carb box  On my custardized Rally for that matter. Holes can be filled easily enough Im not ever planning to rely on a fuel pump. I love the simplicity of the vespa... I know it can work... I just need a good fuel supply! The SIP FF tap is the best so far!! Hopefully ill get some more dynos soon but its so windy. The ones ive done are still reading more torques that PS, which i like so thats good to know. I missed your post there sime! I started writing this ages ago and got distracted! Believe me, just ride it is where im aiming for but it aint been as easy as it normally is! |
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Post by vespasco on May 10, 2015 14:07:36 GMT
Ive been swapping jets.
Im happy the main and idles are ok.
Its the 1/4 throotle range... From around 3200 - 4800 rpm range thats still giving me problems.
It 4 strokes like a gattling gun
Without the air filter fitted its nice and smooth.
Any suggestions as to what i can do to keep the filter and getting it back to a nice smooth low speed cruising ride?
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Post by henri on May 10, 2015 15:49:42 GMT
different slide , as the rev range your saying is problematics where the slide cut-outs n pockets at rear are having a effect , a leaner pilot jet might help ,
the cut-outs n pocket influence the pressure difference on either side of slide which is what draws fuel up the pilot circuit , as it switches from pilot jet to atomiser in control , does the 26/26 have a old style no pocket slide or more modern pocketed 1 , ive heard of people filling in the pocket with jb weld to richen its effects , never tried it myself ,
am not sure wether its a larger cut out to richen or lean ,will have to dig out my amal carb manual as it explains it well in there . H
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Post by vespasco on May 10, 2015 21:06:34 GMT
Id sure like to see that Amal slide guide Ive always believed more pockets = more air?! And as i knew i was going to have this problem i kept the stock no.4 in there, as its got lots of pockets. I have a 'flat' slide with no pockets,,well, it has a tiny one for the progression, on top..ive not bothered trying it yet, thinking it would be richer... But may do now,,,, would richen everything else up, could then come down a size on the jets!!?? I swapped the sip road mkll for a sip mkl this aftenoon..ive been looking forward to doing that I have a sip shim in there this time too...nice and tight now The mkl is a much nicer sounding pipe if nothing else... And it revs out just a litle further too. It seems to breath a bit more free-er than the mkll Ill post some MDyno comparisons later.. Its getting closer to perfect! I may well try a leaner idle, maybe going down one on the MJ aswell. But everything i seem to be doing is making it leaner! I need it nice n rich at wot... Im struggling to get a digestive coloured plug, when ive always been more of a bourbon man myself! Ive sliced off a few layers of mesh around the air filter, leaving just one thin layer,,, thats helped a lot. Now the only rough ride i have is between 3300 and 4300 rpm and is not as bad as it was but still annoying. Doing all that would lean it out more maybe?? But by removing the air filter, and top lid, would that actually lean the mix? As the mix is still regulated by the air correctors!? In my head, its the same as the fast flow taps, it just feeds more fuel to the jets which then regulate the amount. I need a fast flow air feed!!... I used to use a similar air filter before, with most of the mesh removed,,it was ok on the previous set up. Cruising today at no more than 60mph, on/less than 1/2 throttle..temps ok. Sounds very nice again. Feels good. Cruising at 53mph and its only just on 1/4 throttle. I looked in my tank before i set off, it was about 1/2 full, meaning about 20 miles before i hit reserve normally, so went to fill up at a garage 20 miles away! Just cruising! No mad blasts, etc.. I got to the garage and then saw id hardly used any fuel so didnt actually fill up!!..done another 10 city miles...didnt like that too much ,,with the 4 stroking...so went to fill up again, squeezed in less than my normal 5litres... Rode home in a sensible fashion, no problems..smile on face...until i have to cruise between 33mph-43mph  Or my fuel level drops...its not so bad now, with the SIP FF. ive gone through the fuel feed thoroughly..from tank to venturi, checked for bubbles, checked connections, routing etc. Ive done all i can to improve it. Ill just have to keep the tank topped up as often as possible! But generally , its back and sounding sweet..pulls well to 65mph. Anything more than that and it just eats fuel !!! I wont be cruising at over 65mph anymore!! Too expensive!! Winding it through the gears quickly makes me have to hold on tight anyway!! And its a lot smoother so long as i dont let the revs drop below 4200rpm Ive also changed my 2 stroke oil, just to see what effects it has on the plug colour...one reason being,,,ive been getting lean looking plugs recently although i haven't actually checked the plug on this current set up... Which is: SIP mkl, si26, with 160ac, BE3, 148mj! (Slightly rich atm), 52/140 idle. The list of things to try is getting shorter...thankfully...the sip mkl and si26 will defo stay! Although i may swap the slide! Depending on what gems H can unearth on the slide guide I do however have another head, same total volume but with slightly larger combustion bowl, which i think would suit this set up a little better!? Any comments on that? Im not going to be constantly tweaking without any riding. Tweaking is not so much fun when you have to go up and down the same old road, not too far from home! Im very keen to smooth out this little annoying problem in the 3300-4300 rev range tho' ! Any suggestions welcomed |
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Post by sime66 on May 10, 2015 21:22:23 GMT
Im struggling to get a digestive coloured plug, when ive always been more of a bourbon man myself! It's like a trip down memory lane here tonight, with Guru Ji's puzzles, and reference to the biscuit scale!  I was wondering if you could do something with the filter mesh; I was going to suggest making some holes (after something you wrote in one of your last few posts, but I can't be bothered to read back and find it now), but decided it was a bad idea anyway - I had one before that looked like it had deliberate holes in it - some sort of bodgery I suspect. Anyway, this is far too involved and precise for me, so I'm sloping into the background again to watch quietly - sorry to interrupt  |
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Post by pxguru on May 11, 2015 6:10:43 GMT
Are you using the drilled BE3? and where did you drill it?
Get the main jet running digestive first. Make sure you do the jetting after 5 miles at WOT to get it properly hot.
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Post by vespasco on May 11, 2015 8:18:28 GMT
Ive modified the be3, jusy slightly, by opening up the larger top hole. But i also tried a BE2, which didnt help a great deal. Drilling holes in the airbox lid! Or the top of air filter itself. ! Yes it would help! Thats a maybe My range of jets only goes up to 150! Im suprised im even using a 148 tbh! Ive been trying to get that plug to change colour believe me!! I was wondering if its the modern fuel and highly efficient oil im using??!! I may just well change to the other slide i have, to richen everything up (the low/mid range anyway) and start again. With leaner jets. It wont take long to do. I found another slide too, with just a cut out underneath. I think its for the Rally. But itt looks a bit worn. |
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Post by vespasco on May 11, 2015 17:56:43 GMT
Quick update.. I changed the slide, holy crap, what a difference!! Thats staying  To be fair, there was a slight backwind, flat road. Yet im still having the same problem, 4-stroking around 3200-4200rpm and showing a lean plug after that range. the lower the fuel level in the tank, the more chance i have of fuel starvation. (The run recorded above was with a full tank). Ive kind of given up on the jetting...its got to be something else..although.... I can get the idle set, ive tried a few difference ratio idles, from 50-120/140/160, 52-140, 55-160. I have the 50/140 in right now... This gave me least 4 stroking. What i did notice is that, at WOT the MJ needs a 148, 145 possibly/ragged edge. With this MJ in, it 4 strokes as above Put in a 135MJ or less and its nice and smooth...138 - same problem. And with the 135MJ in fuel would starve after 7000rpm, way too small Im not sure what that tells me as yet.... Carb too small?? Try a 48/140 idle? Polini air filter!!?? The sip road is staying Ive been racing the hell out of this today, until it started to pink then i had to ease on the brakes quickly. and it really shifts upto 60mph+ and stays there too. Thats at half throttle, more than that and it pinks. Im going to try my other cylinder head as a last resort, with a larger combustion bowl, less squish band. But first im going to retard the ignition a touch, its soo quick (if i keep the revs over 4200rpm). I think i could actually retard and not loose too much performance. It would do me good to limit it like this otherwise ill be twisting that throttle open at every opputunity! I was hoping to leave it as high as possible. Upto now, its great upto 60-65mph. Quick, quiet-ish, economical, sounds sweet, even if the plug doesnt look it. 62mph in 3rd :0 (8100rpm) I saw the rev counter go to 9100rpm (in 2nd gear) :0 Plug chop at 1/2 throttle/cruising 60mph+ shows custard cream! I got one plug check in after WOT, also custard cream colour, with a grey tint!!! Not so good! Is it possible i have a tiny leak in somewhere!!?? |
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Post by henri on May 12, 2015 7:44:34 GMT
wish i'd read this before pouring thru amal carb manuals n bsa service sheets this mornin, then tryin to convert the info from a round slide piston ported 2 stroke carb or 4 stroker to a vespa rotary set up. with a proviso i could be wrong ,this is how i think it operates on a spaco, the pocket at rear of slide is to cause a swirling air movement that causes a better mix an directs at pressure depression better over the opening of bleed screw hole/mixture screw end . am not sure wether filling/increasing the pocket would lean or richen , i believe filling would richen .
the cut out on slide if it works like amal 1's would lean the mix if increased/cut more .
i have heard of people filling slide pockets with jb weld, but the consequences of it falling out due to vibration/thermal expansion means i wouldnt advise trying it ,
but if another slide improved it reckon tryin another slide might cure it all the way , trick is knowing which way the progression of slide numbers goes /what there codes mean . havent looked yet but there must be some info somewhere on slide progressions. or pulling slide youve got an shaving the cut-out an trying again . measure up between 1st n 2nd slide an whichever way the numbers progress seems to be the way to try ,eh , H
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Post by vespasco on May 12, 2015 12:44:19 GMT
Thats brilliant. Thanks H.
Ill have another scan through that Later.
I was thinking last night, the first thing i should do is retard ignition.
Then theres more fettlin' with the atomizers. Im sure, in theory at least, i should be able to improve upon it. Open out the existing holes, or drill some more, smaller than the BE2 tho'!
I found the no. 5 slide improved the 4 stroking problem just a little bit but more than anything improved air/gas flow and vastly improved throttle response.
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Post by pxguru on May 13, 2015 5:42:12 GMT
It does sound like you are nearly there. 77mph even with the wind behind is pretty impressive for an old Rally I have had the same problem in the past but managed to sort it. Did you drill out the hole between the float bowl and the main jet? On some SI carbs its not as big as it could be. Should be about 2mm diameter right through to the main jet. Where is the throttle when it is bogging at mid range rpm? Check the float bowl and then we can drill some more holes in you atomiser! |
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Post by henri on May 13, 2015 8:14:46 GMT
had a thought this morning , maybe your at the limit of what a spaco slab carb can be tuned with your state of engine tune , they are a bit basic an it might always be a compromise from here . maybe time to save pennys n be a good boy an see what santa brings nxt chrimbo , say a mallosi inlet n 24mm dell' , pbhl, for instance . or if ya win lotto a polini set up, H.
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Post by vespasco on May 13, 2015 21:15:42 GMT
Thats i wondered H. That the carb is getting beyond its limits. Yet im determined to make the si26 work. It kinda does work, without the air filter, so thats why im sticking at it. In my mind the 135MJ is max for the si with basic jets/filter etc. Anything above that and i get problems. Using a 'proper' carb would be taking it even further! And going faster! And yes, run much nicer no doubt. Then id be considering a proper pipe.... But i really dont need anymore speed! Its supposed to be a tourer after all! 77mph was suprise. And i plugged chopped that run! My ignition is next to the luggage hook, under the seat! And it was well lean innit The porting really has opened it up, without loosing too many torques/ if any The 77mph run in the opposite direct pulled to 65mph but struggled to make use of the extra throttle i had left. If i ducked down a bit more i could have gained a few more mph but why bother! I do have to duck a little just to hold on Fuel supply wise, ive checked the entire fuel supply as far as i can see, but so far, only up to the main jet stack. It gave me problems to start with, mainly as the fuel level in the tank went down. Ive probably made more mods to the fuel supply/carb than anything else on the motor Sip fast flow. Good 7mm inner diameter fuel pipe at correct length (short as possible). Good Routing of pipe. Good No air bubbles. Good Cosa float bowl top (Spaco) with 5.2mm needle Inlet from float top to needle opened up to 3mm and also lowered, as previous post. Inlet passage way to main jet stack opened up to 2mm, wiggled about it. Thats the nearest sized drill bit i had. I had read that 2.1 mm was the norm. The BE3 mixer ive been using has the upper holes reamed out slightly, not as big as another mixer i have. (An E2) I had tried the BE2 but it didnt do too much to get rid of the problem. I thought it was going to be the answer! (I still have a spare, un adultered be3) Im happy, now, that enough petrol is reaching the venturi. Just not necessarily at the ratio with air. And i havent ruled out inlet timing modifications. It would be nice to open it out a little earlier. But it already has 107°/74° atdc timing, 181° total. What would happen at low revs if i made that, at least 116°, the same as the transfers close? Could i go even more without upsetting the smooth running? But total duration would be a little too much at 190° total duration. For my 'tourer' ... wouldn't it? Im happy to do that without being off the road for too long, if its going to improve things. Idle to 1/8 throttle (3200rpm) is good/ok. (Although the si24 is a little smoother) The throttle picks up on the main stack cleanly at a little before/around 1/4 throttle (4300rpm) The progression period in between is where there is a problem. 50, the smaller number on the idle jet is the lowest i have. So im thinking a 48/140 is worth a try. It would be nice to be able to use a 160ac on the idle but i find i have to wind the idle mix screw way out, which makes it richer!! So, i hear a hint at an atomizer-modifier Id really like to try that. A guess only, smaller holes somewhere above the existing upper holes on the be3?? I also have a good range of other atomizers if they would be better to modify? (They have gradually smaller upper holes than the BE3, in order of leanest/most hole area - (BE)2, 3, 1, 5, 4 has no holes. 6 also has no upper holes but has more lower holes. Im intrigued |
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Post by henri on May 14, 2015 10:02:15 GMT
the only stuff ive seen on modifying atomisers is on the bretta forums , the basic theorys should translate to vespas i guess , will try an find it again , think it was lambretta club uk forum , tho there might of been something similar on scootererotica aswell.
so if i come across another cheap 24mm pbhl dell or similar your not interested ,ive got 2 recent but have plans for both i'm afraid ,i owe ya a favour as i dont know if you spotted it but a identical polini mandolin went for 39 on flea-bay last week, not my one ,thats for the vbb/cosa franken scoot .
or theres keihin copys OKO's 24-26mm with manifolds on kraut flea-bay for 60 euros , H
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Post by vespasco on May 14, 2015 11:26:20 GMT
Im a little reluctant to not use a stock set up but never say never ! I think id go 28mm if i went down that route. I'm still intrigued about what mods. to do on the atomizer. Where drilling the atomizer is concerned, I meant to write 'drill larger hole/s' in my previous post.. But seems like guruji had the same problem and found a solution!?! Seriously, no worries about the Polini pipe. Youre happy, im happy Everybody happy, tra la la la la laa |
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Post by henri on May 14, 2015 13:52:11 GMT
think theres a 28mm on kraut-bay too similar type of euros ,or if ya feeling crazy cud see if my mate will part with his 32mm oko lammie carb , its big enuff to suck passing pigeons in , nothins funnier than seeing a bretta exhaust spitting feathers ,well apart from the usual watching owners push em down hard shoulders that is,
havent looked at atomisers yet ,tho the rainy day might give me time yet ,do remember the talk was of model/watchmakers drills being used ,as there available in 10ths of mm differences , drill with sharp end an use undamaged/unused shanks n fine paste to ream/finish-polish holes ,H
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Post by pxguru on May 14, 2015 14:35:42 GMT
If you do decide to get a bigger carb it will need to be a 28mm PHBH.
Do you think you have affected the float level? If the BE2 didnt make it run better then drilling the BE3 wont help. Your float level must be too high. Anything but the original float level and they run c**p.
On my ported standard 200 barrel a few years ago I was running a 160 main jet (drilled myself. Biggest I ever found was 150). I think if you need a main jet any bigger than this it won't run on an SI carb. Mine with the 160 worked fine right across the rev range but needs the normal float level.
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Post by vespasco on May 14, 2015 18:23:06 GMT
I have the same stock float height. Ive even measured the fuel level (level/just above the top of the lowest hole) Heavier float? I have a 150mj, my biggest! I may even have a 1.6mm drill bit too!?! Im sure i have a 1.5mm, which if done by a wobbly hand may end up 1.6mm And a load of old too small main jets to destroy! I mean modify. Im going to keep enlarging the top BE3 holes, little by as little as i can. Then try drilling smaller holes above them! Slowly increasing the size of the holes, until i reach nirvana!? I always thought a 28mm carb would be best. But hadn't a clue which one i should have tried tho'. I never looked into it that far. Dellortos are quality too. I realise that much But its not going to be on my shopping list just yet. Theres a few more things left to try, finding time for one. So the main question for me atm is: Would i be chasing my own tail if i , for eg, didnt use an air filter to overcome the progressional bog, As id have to up the main jet even more? |
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Post by pxguru on May 15, 2015 4:29:34 GMT
Sounding like you are running out of options. Try drilling a 160 main jet to at least make sure it floods at high rpm. You could try a smaller air corrector like 140 if that doesn't make it flood. Once you get the main jet where you want it then work on the atomiser drilling. SI carbs don't handle high rpm (8000+)very well. Might be something to do with your crank 107/74 is for high rpm. Yours should ideally be just like Sime's at 125/55. See how it runs without the air filter fitted. Mine ended up running without it |
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Post by henri on May 15, 2015 7:56:05 GMT
pbhb carbs are good an used a lot in smally-world , but do have a rep for being hard to impossible to set up a good tickover on ,my belief is thats coz a 130cc engine just isnt drawing enough air at low rpm for carb venturi size , on a 210cc that shouldnt be a problem , H
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Post by vespasco on May 17, 2015 9:53:57 GMT
Ive been revising some more but am struggling to find an answer.? Hopefully someone here can help?
Its to do with the inlet timing i have.
My crank and inlet gives 107°/74° duration.
My transfers close at 118° BTDC
Should i cut the inlet so the inlet opens earlier? Like 118°. To match the trans closing?
(The motor is more of a tourer than a rev freak)!
Would having a total duration of 192° would be too much for me???
If i were to open the inlet on my piston and cases a touch more would this help with the blowback im suffering (ie...the common stuttering at around 4000rpm
The answer maybe in simes thread but im struggling to find/remember/understand!
More coffee!!!!
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Post by henri on May 17, 2015 12:44:30 GMT
i'm struggling to remember myself ,coffees not workin today, i think it wasnt vespa orientated so probably jap/disc valve stuff , but there was a correlation between venturi size/initial comp an inlet tract length that at certain rpm/gas speeds you got a sort of bounce back blow back, with a gap off 11deg theres a decent pressure drop so charges get sucked in fast when inlet opens .if you open the inlet to close the gap the engine could get a bit breathless at higher rpm's when inlets open for a shorter time period .will have to wade through the yamaha/jap 70's tuning stuff ,the info's in there somewhere on how much lead you need between trans closing an inlet opening .might be sometime as them japs are wordy beggars ,make german tuners look monosyllabic,
memorys dredging up a inlet duration of 185 is fine ,not sure why or where its from so not sure , heads hurtin now ,will think on it later . H
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Post by henri on May 17, 2015 14:56:00 GMT
sorry mate ,ive had a look an just keep getting bell n jennings stuff ,would help if i could remember the 2 jap guys names or which technical website i found it on . it was in a paper they did for yamaha in bout 73 about initial compression an piston pumping effects , basically they found a initial comp of 1/1.5 is best ,with 1/1.4 to 1/1.6 being high n low borders , less n the charge dont move up transfers fast enuff , higher an it saps power from pumping action an blows seals quicker , all of this isnt really helping you i guess .just tryin to avoid sayin sorry i'm such a numpty an not "bookmarkin" the stuff .at the time i waded through it an thought "god i'm not going to want to repeat that marathon " , an didnt bookmark , DOH!!!.
an realised the 185 figure i gave above might be a exhaust duration memory , brains not all there today i'm afraid , maybe a touch too much argon n bright lights this week , or beer last night , probably both . H
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