It is possible to do it the changing everything at once way. Changing both at once does work but it will never be so accurate. As you have seen with yours, it can be in the ballpark and go well enough even when it is a few jets away from correct. What i am trying to explain here is this way is the quickest i have found to get to the correct jetting right across the range. Every carb tuning maunal you read will tell you to change one thing at a time. It does take a while to do and the longer it takes the bigger the pile of left over jets!
When the pilot jetting is close but not correct any of the following happens; difficult to start when hot, random mild heat seizes while cruising, must be revved up before pulling away, poor fuel economy. And probably a few more, these are the kind of things that you could get used to and ignore
PX200E with 221 Malossi, max power at 8300rpm, VHSH30CS, 175 main jet PX200E Tourer, tuned original barrel, SIP road II, SI26/26 135 main jet, vortex 1050cc Triumph ST 600cc Honda CBR
Ahh, but I've got all those jets for the next one!!!
Being serious though; your edit about the odd niggles I'd tend to put up with is very true - I was already noticing how much better it started hot or cold - always, and how much better it was running cold at low revs, just after those few initial teaks to get the Pilot right. I do believe this is the way to do it, cost and time being precise aren't so important as getting it right. I think, although I was saying start the Pilot from scratch again, my mind was still thinking that I'd need the /140 because of the now rich circuits - just jumping the gun in my thinking, but probably not what I would have actually done when I got back to it. To be honest it still seems odd to me that we'd be going right over (on the table) to the 50/120, but I'd be better off doing the job properly, rather than guessing the outcome, so forget I said that last bit.
This is pretty much a case of rain stopped play; it's a horrible, relentless, thick, constant heavy drizzle, and everything is cold and wet and muddy, so this is not at all enthusiastic or precise. However; with the 50/140 it's a mixed bag, and I'm not really sure what it means, so maybe you can glean something from this: I have a pretty good low idle, and idle-rev-idle, and low speed/rev running is pretty good with just a slight burble at very low in 2nd, but none in 3rd. Warm starting is instant. That's with the Mix at about 2 and the Idle at about 1½. It gets difficult to be precise because I have to tweak to get it spot on, and I'd have to move it away again to count the turns. Things I noticed that aren't so good: Winding the Mix screw in much further does not increase revs, it cuts out. Progression speed (30kph in 3rd) is still only about 90ºC. I have reasonable performance, but not fantastic, and I suspect still low temps; I'm just in the lane though - first Saturday of the New Year is not a good time to be playing in the road. That's not so important as getting the **/ of the Pilot right now anyway. I'm going to post this and have a read back and a think about what, if anything, that tells us; I'm wondering if I needed to start further out with the Mix with a higher Idle. I'm also hoping to read back and see that the mix screw suggests the pilot is too rich, so I can try the 48/, but that's a guess until I have a read. Best to come away into the dry and get some advice. I'm not really going to be able to be more precise than that until I get a dry day, maybe midweek, to fiddle with the screws properly. If I get something sorted, or suggestions, I'll do some tweaking or proper temps and plugs, maybe in the morning, but I'm not inclined to play in the rain more today. It's starting great, and low-running nicely, and if anything is discernible from that little lot, I'd stay still rich. Here's a bit of film in case it helps, but to be honest, it's all a bit half-hearted and soggy this morning.
Sounds like its spluttering very slightly. How many turns out was the mixture screw. Set it on slow idle from all the way out. For ideal set up the target is 2.5 turns. This is the point where it begins to speed up. If it doesnt speed up until its all the way in then cuts out the jet is too big (if this happens it could be a dud jet and bigger than it says). See how many turns you get with the 48/140.
PX200E with 221 Malossi, max power at 8300rpm, VHSH30CS, 175 main jet PX200E Tourer, tuned original barrel, SIP road II, SI26/26 135 main jet, vortex 1050cc Triumph ST 600cc Honda CBR
I had got a bit stumped by this result; I'd read back through everything in this thread, hoping to find why it might cut out before revving high when the Mix screw was turned right in. It basically isn't revving high (not getting lean) and is just cutting out when there is no fuel, when the Idle circuit is actually closed – that's how I was seeing it anyway, and I was a bit unsure what to do next. Some of the other jets had been difficult to set up, but none had done that – the obvious big difference, since setting up those Pilot jets, being the carb mods, so I was uncertain what was going on – I know the engine is good because I've felt it, so it's only carb tweaks, which can take as long as is needed if I'm running safe, so I wasn't worried. I had decided that the only way to progress was to see for certain where exactly it was (Mix and Idle turns), and have a proper ride looking at temps and plug, and repost the above more precisely, hoping for some insight. I think I'll still do that; have a proper ride, see exactly where the screws are, redo it it carefully, making sure I was right out to start, and then if still no joy have a go with the 48/140. I'll see what I can get done during the week because I'm away next weekend.
I would just try the 48/140. If that ends up 3 turns out then then you know the 48 is too lean and go back to the 50.
You are right about the cutting out. By that point you have already passed the correct setting.
PX200E with 221 Malossi, max power at 8300rpm, VHSH30CS, 175 main jet PX200E Tourer, tuned original barrel, SIP road II, SI26/26 135 main jet, vortex 1050cc Triumph ST 600cc Honda CBR
I'll do that then, thanks. I reckon I got myself a bit lost there; I'll have a go with 48/140, make sure I'm right in better conditions and without rushing it, and report back when I've got something definite.
On a Summers day when you know what to do and have all the jets to hand, this would still take a few hours to do properly. Then maybe another two times over a few weeks, once ridden for a while. You can see how quickly it gets close enough to leave alone!
Apart from the foul weather another thing that has slowed you down is the change of tack. Orignally I understood you wanted double safe jetting but now you have had a taste of the "light side", you now want ideal, but single safe jetting for the extra power it gives. This will take a little longer with this weather but will be done soon enough.
Try the 48 and see how many turns to where is starts to speed up.
PX200E with 221 Malossi, max power at 8300rpm, VHSH30CS, 175 main jet PX200E Tourer, tuned original barrel, SIP road II, SI26/26 135 main jet, vortex 1050cc Triumph ST 600cc Honda CBR
As long as you chaps don't lose interest while I'm messing about, it doesn't matter how long it takes; I can use it 'safe' (I can tell by temps, plug and performance), and with time and tweaks I can get nearer to the beast that started to reveal itself; it's fair to say I got a bit of a taste for it – but still engine-safety first! All the time I'm tweaking and having to think about it, I'm learning it a bit better without having to read back through this marathon thread for snippets of info. I put the 48/140 in this morning, I'll take the mix out to 4, set the Idle, and wind the mix in and see where it gets to before the revs pick up this time. - Hopefully I'll get something more sensible to report back; if so I'll do the other stuff (idle-rev-idle, slow running etc) before thinking about Progression chops again. She's going to be a little beauty! - No worries here........
(You're gradually changing where my mix should end up as I lower my jet – is that to keep it safe in case I go too small?)
I expect the 48 to be perfect or just a bit too small. Need to be cautious with this one. Just touch where the revs pick up and stop there. Count the turns and see how many.
PX200E with 221 Malossi, max power at 8300rpm, VHSH30CS, 175 main jet PX200E Tourer, tuned original barrel, SIP road II, SI26/26 135 main jet, vortex 1050cc Triumph ST 600cc Honda CBR
Caution is my natural state. Reckon it's time to get a few more jets to keep this job moving now we're all back into the swing, and because I have a few days and this weekend of not being able to do much on it. There's not many 48/s available; I've got the /140 & /160. Shall I get 48/100? 50/100? 50/120? I wasn't expecting to need /100s, but a bit pinned down if 48/ is good. If I'm getting any I might as well get a few while I'm at it, any suggestions or best guesses?
Weather conditions: Precip: Clear Sky (0%), No rain Pressure: 997mb Temp: 6.6ºC Wind: W @ zero knots
Well that was refreshing Quick 45 minutes out. Finished with a wide open blast round the bypass, 5 miles dual carridgeway mostly at WOT, peaked at 81mph (GPS), turned onto the sliproad showing 305 degrees F. Not bad for an old iron barrel Polossi! This has to be slightly richer jetting to keep the temperature down.
PX200E with 221 Malossi, max power at 8300rpm, VHSH30CS, 175 main jet PX200E Tourer, tuned original barrel, SIP road II, SI26/26 135 main jet, vortex 1050cc Triumph ST 600cc Honda CBR
Not bad, but if you need any jetting advice to get it running properly don't hesitate to ask!
(Sorry; bit of role reversal there.)
That's a nice blast for first week in January. You're 305ºF/152ºC, after 5 mins WOT, 82mph (130kph); - on the plug? That's about as hot as you want to be then?
…....I've had a read back through, and in the CHT gauges thread, here:
You had 300ºF as the upper safe limit; I'll put it here in full because it's interesting how it all fits in with this thread where it's at now, and the jetting changes and range of temps across the throttle range I'm getting:
You will not regret having a CHT gauge. They are a lazy way to get the jetting right. And if you keep an eye on it, it might just prevent a seize up, dodgy fuel issues or forgetting the 2 stroke!
I also go by 300F (150ºC) as the maximum with the sensor on the spark plug. I think this to be quite hot enough for the road. I have the SIP speedo one and have the sensor on one of the head bolts which is a bit cooler than the spark plug but doesn't get broken quite so often.
Here is the theory bit. The basic idea of a Carburetor, is to supply a constant ratio of fuel air mixture regardless of the position of throttle or quantity of air drawn through it. The ratio of fuel to air determines how hot the flame will burn. More fuel to air (bigger jet) will make the CHT colder and less fuel to air (smaller jet) will make it run hotter. This might be opposite to what anyone first thought.
When you find the right one and have the CHT gauge all set up, try riding at each of 1/8, 1/4, 1/2, 3/4 and full throttle for at least 30 seconds or so each. And you are looking for better than 250F (120ºC) and near to 300F (150ºC) across all the throttle positions. This is especially useful with a needle carb where there are many more adjustments.
And (because maybe it ties in with my temps rising momentarily after coming off WOT):
Running hotter is more powerful but dangerous over 300F (150ºC). Probably not a bad thing to be careful but measured at the spark plug, you could take it to over 200F (95ºC) round town and 250F (120ºC) on the motorway and still be in the cautious limit. It is important to check CHT across all throttle positions carefully. Even running perfect wide open can still seize up when you shut the throttle at speed, if its lean in the middle.
It's good reading back a year or so, and what was written then is making more sense now.................
was looking around for t5 jetting info an found this on modern vespa forum , some interesting reading ,just for info now , modernvespa.com/forum/topic115912 , H
if its got wheels n makes a noise I wanna play with it, skateboards included coz "skate-punks rule",
H, I don't think this was written about the SI carb. I think it has been copied and modified to suit from something with an air screw. The setting up of a mixture screw is not done like that.
PX200E with 221 Malossi, max power at 8300rpm, VHSH30CS, 175 main jet PX200E Tourer, tuned original barrel, SIP road II, SI26/26 135 main jet, vortex 1050cc Triumph ST 600cc Honda CBR
Sime, Problem with my iron Polossi is it hasn't quite got enough cooling for its power. If it was jetted to run ideal it would just seize up at WOT. In the three years this Polossi has been running I have found that keeping the MJ slightly over gives me enough miles to have some fun with it. If I held it open a few more miles it would have seized up. If I drop back to cruise at 70mph it cools down to about 285 deg F and will run forever. You will not have this issue with your iron barrel. Yours will hold the 300 deg F at WOT as the cooling will manage.
PX200E with 221 Malossi, max power at 8300rpm, VHSH30CS, 175 main jet PX200E Tourer, tuned original barrel, SIP road II, SI26/26 135 main jet, vortex 1050cc Triumph ST 600cc Honda CBR
Weather conditions: WET & WINDY – as bleedin usual! (Just doing errands; not an enginny run, so no weather or engine data)
Yes, I understood the point, pxguru, and was just thinking aloud really; it's a perfect example to me of how you're jetting to balance/optimise your performance and cylinder temps. And that, what was to me at the time a theoretical thread last year, now makes lots of sense because I'm doing the jetting; seeing the performance and temp balance, and now have a CHT gauge to see exactly what's going on – not just at WOT, but across the throttle range.
You could jet leaner, get more power, but seize because you'd be exceeding 300ºF for long WOTs, because your C.I. Polossi hasn't got the cooling for its potential power, so you're slightly rich to compensate for it, and lose a bit of its power as a result.
I'll be at max 300ºF (150ºC), and won't be jetting to the limit when I get it sorted, or riding long WOTs as a rule, or too concerned about the top speed other than for curiosity anyway – even if I had the same insufficient cooling for power problem, which I don't because mine has much less power. - But this is my temp limit for when I get to the stage of seeing what jetting vs 'Beast' I'll end up with...........
It's a nice number, and I understand where it comes from (as opposed to the pot-puck of the temps around the forums); when you chaps were saying my 139ºC the other day was too hot for my short WOT, I accepted it without knowing how you knew, (and it felt great!) although I knew from the plug it was hot/lean – now the numbers all tie in better in my mind, which will help me understand and remember.
(Anyway, what's this ºF lark, you chaps? We've been metric for 50-odd years now)
The only problem I find with a CHT gauge is sometimes you spend more time looking at your temps than the blinking road.Especially if you think you are on the lean side.
px guru ,if ya wade further down theres a good-ish debate about atomisers in dell/spaco carbs ,an the actions of the holes in them . its all big-mouth yanks arguing,but there is some good info.especially if ya ignore the idiots trying to compare them to weber downdraught emulsifiers. H
if its got wheels n makes a noise I wanna play with it, skateboards included coz "skate-punks rule",
H, Some of these yanks say some good stuff and some don't! There is a lot of info here but not all correct, in my opinion. The funny thing is the video for 4 stroke Weber atomisers do work the same way as the SI ones. That part is right!
PX200E with 221 Malossi, max power at 8300rpm, VHSH30CS, 175 main jet PX200E Tourer, tuned original barrel, SIP road II, SI26/26 135 main jet, vortex 1050cc Triumph ST 600cc Honda CBR
really , bugger ,means once again its back to basics for me to try n understand the theory better .as much as i hate the worry n danger of "seat of pants" jetting ,its what i'm use too an the scientific methods baffle me .H
if its got wheels n makes a noise I wanna play with it, skateboards included coz "skate-punks rule",
these SI carbs are a real enygma, I m wortking now for more than 2 years about all sort of combinations to sorted out the best compromise. I even contacted DELLORTO France Italy and UK to have answers.
I was asking about the relationship between air corrector and throttle slide (actually there are 9 different just for the 24/24 si + 4.1 and 4.2 created by SIP) The only answer I had was from Matt Cooper at Dellorto Uk and even this answer was not really satisfying : "higher is the n° of the throttle slide, weaker will be the mix..."
Changing the air corrector jet affects the main jet at wide open throttle. In the mid range the air corrector has little effect and the mix is related to the main jet and mixer tube.
At wide open throttle a smaller air corrector will richen the mix (it reduces the air and can also increase suction to pull more fuel) and larger air corrector will weaken the mix
So, the more important : we know that the idle jet is providing lubrication from idling to wide open throttle.The problem with people who seize up is that they usually just upjet their main jet, and that's not enough...
For me the answer for my POolossi was a 26/26 Pinasco Si carb. MJ is 140, IJ is 50/120 (2.4) 1 turn and half mixer BE3 Air Corrector 150 slide throttle n°4 modified to open fully T5 air filter (larger with venturi inside ) Float chamber with 5.2 mm needle (cosa) enlarged fuel hose connection
No rubber connection to the frame, I changed it for a Polini moss air filter
But, what is working on this engine is totally different on every engine I did build so...
Hi Geoff. Your Polossi set up is interesting for comparison with others, but as you say yourself, it is specific to your engine. You make two other main points as well though: I think we're all agreed that a bigger air corrector will make the mix leaner; I hadn't read or heard that this would only be true at WOT, and that the MJ and mixer would be more significant in mid-range, to me it seems that it must be relevant at all times the MJ stack is active and must be affecting the mixer, however I think it's true to say that we rarely change the air corrector (maybe because the emphasis is not on WOT riding, if your information source is correct?); I've picked up a 185 in my recent 2nd-hand scavengings, but I don't expect to use it, in fact I haven't even started to adjust my mixer/atomiser tube or slide yet either, which brings me on to your second point; Yes, we agree, and these last few pages of this thread concentrate on the important fact that the MJ should not be changed alone if the lower and mid-range are to be adequately jetted to. In fact we've gone so far as to say that the Pilot should in fact be set up before the MJ, not just as well as it. Actually we're setting up the Pilot Jet in two stages; the Idle circuit and then the Progression circuit (as it is a one-piece mini jet-stack with two variables and serves both those circuits); both before the Main Jet, and then the mixer/atomiser tube. - The bottom of previous page (12) lists the order in which I've been trying to do my new engine, which has pretty-much started again from scratch since I drilled my carb channels.
H, you ain't doing so bad by the seat of your pants are you; I don't think all the theory really compensates for that experience.
Chaps; you do realise that those are not all Yanks in that thread – one of them is a currently-elsewhere comrade of ours, have another look and see if bholinath's avatar looks familiar............ (I 'outed' him back in November -page 6)
I haven't got much done with the scooter this week, and I'm not around much this weekend; fingers crossed for Doulsy and Loon-e with their projects though.
It is easy to see here how the fine tuning and core activity make it all so confusing. The problem with this SI carb is that there are so many choices. It only seems simple. If you end up with a scooter that does everything it should, is a joy to ride and never siezes up, then who's to say the jetting is wrong? But sometimes one little niggle that won't go away means going back to the start and beginning the jetting all over again!
PX200E with 221 Malossi, max power at 8300rpm, VHSH30CS, 175 main jet PX200E Tourer, tuned original barrel, SIP road II, SI26/26 135 main jet, vortex 1050cc Triumph ST 600cc Honda CBR
Here a copy of the informations by Matt COOPER at DELLORTO UK :
"Throttle slides - the higher the number the weaker it is up to 8th throttle
There are two different types of idle jet, 9982 has an adjustable air calibration. This affects things in the upper part of the idle range, there is a chart here:
With the atomisers, we haven't got much information except that the holes at the bottom supply more fuel to the lower rev. range and higher ones to the upper rev range"
For those who would like to contact him to deepen the question : Matt Cooper @ Eurocarb Ltd <sales@dellorto.co.uk>
Seems like you are getting yourself really confused Geoff. There are just too many choices and a lot of interaction between parts. For example if you change the throttle slide, then you need to change every other jet to match with the new slide or at least go through the entire carb calibration and plug chopping sequence from the beginning to confirm that it will not sieze up on you at any one particular throttle position. Changing throttle slide (on an SI carb) is not a final tweak when you are finished jetting.
What I am trying to do with Sime here, is work through the simplest sequence to get an SI carb set up on a non-standard engine. At the end it will run perfect and not seize up.
PX200E with 221 Malossi, max power at 8300rpm, VHSH30CS, 175 main jet PX200E Tourer, tuned original barrel, SIP road II, SI26/26 135 main jet, vortex 1050cc Triumph ST 600cc Honda CBR
Px Guru, I absolutely agree with you, don't get me wrong. I was just digging in my mail box and sharing the informations I had 2 years ago, it was the opportunity to give you the contact of this guy Matt Cooper.
I perfectly understand what you are doing with Sime, no worries. As I told you previously, I m wortking now for more than 2 years about all sort of combinations to sorted out the best compromise with these SI Carbs. And while I was investigating I found disturbing informations.
During the years, Vespa changed the 24/24 SI set up. The following show you the different interactions (I added the T5 and the cosa 200) These informations have fueled my curiosity. That's why I did contact Dellorto to try to understand
model year Air Corr. mixer tube MJ IJ Slide P200 1987 160 BE3 116 55/160 (2.9) n°9 P200 E et Px200 1988 160 BE3 116 50/160 (3.2) n°4 P200 E et Px200 1989 160 BE3 116 55/160 (2.9) n°4 P200 E et Px200 1989 160 BE2 118 55/160 (2.9) n°4 Px200 E 1989 190 BE4 116 50/120 (2.4) n°4
T5 1986 120 BE4 110 50/100 (2.0) n°5
Cosa LX 200 1987 160 BE6 92 48/140 (2.9) n°8 Cosa Lx 200 1988 160 BE3 92 48/140 (2.9) n°1
My point of view is you must have all the data of a problem to try to solve it. In this case, the engine never changed, it was always the same base.
Last Edit: Jan 11, 2016 16:00:12 GMT by rgcgeoff29
I wouldn't be surprised if there were a few Friday afternoon ones in that list too. Bound to be a few more variations.
Over those years there had been very slight changes to the heads and exhausts. Also fuel changed quite a bit. It wont affect what we are doing to much here as we will be detemining what is required by how it runs, rather than using a spec sheet. Doing it in the right order is the key to getting it done quickly. Its not the only way of getting there but it is more scientific.
PX200E with 221 Malossi, max power at 8300rpm, VHSH30CS, 175 main jet PX200E Tourer, tuned original barrel, SIP road II, SI26/26 135 main jet, vortex 1050cc Triumph ST 600cc Honda CBR