PX poor starting when warm

[sime66]

Thanks for the greetings guys. Anyway, now that we’re all best mates:
Last year the scoot ran pretty well really; my first year back for a while. It’s a 1983 engine, 1984 frame PX150E (Arcobaleno, non-elestart, non-autolube, don’t think EFL?) with a 177 kit and sito+, and is now on 46,000 miles. I’m using a B6HS and 2% RockOil Synthesis 2 Racing oil. I’m in Cornwall, I did Builth Wells without a hitch, then our local rallies (R.F.T.S. Newquay, and R.T.T.R. Torquay); I had a minor breakdown and replaced a CDI unit, which sorted that; I put on a Sito+ and had the jetting checked and confirmed as well set up for my 177kit and Sito+. As the year went on and warmed up, I started having trouble starting when warm. Later in the year I did Isle of Wight – did thrash it a bit coming home; I did Weston and Woolacombe, and loads of other Club rides and ride-outs. All the while towards the end of the year she was running lovely, but just didn’t want to start when warm. Always started from cold, despite freezing and damp weather. I did 4000 miles last year and rode all winter, and although only short journeys really over winter, the problem seemed to be OK, I imagine because it just wasn’t getting hot. Now at the first hint of the weather warming up a bit, I’m back to bump-starting at petrol stations and car parks. It isn’t a big problem, but my rally-year will be so much more pleasant if I’m not the numpty who won’t start every time we stop for petrol. The general consensus here amongst those who know seems to be rings, although I don’t really think performance is down. Anyone got anything to add as ideas for investigation? The problem for me is that it could be so many things and I’m not clever enough to know where to start or what to look for.

[Rudi]

hi,
if the rings are ok you should feel some resistance in the kick starter... its not a professional method but no compression will be felt in the kick starter.

one other thing that comes to mind is maybe the carb is warped, and then air leaks in. does the scooter idle fine? when its hot do you see a change in the idle (increases)?

[sime66]

Hi Rudi, thanks for the reply,
I’d say that resistance is OK when cold, or when it does start. If I have to kick it a few times when warm without starting, I’d say the resistance is noticeably reduced (which is when I resort to bumping). Something warping when hot seems to be logical to me. I wondered if it might be the cylinder head because during last year the problem was once narrowed down to a loose (stripped) cylinder head nut. That’s been sorted now, but I have a nagging suspicion that permanent damage might have been caused then. That is just my hunch though, and doesn’t seem to impress those in the know in our club. The other factor which makes me suspicious about the rings suggestion is that performance is good, and mates who have ridden it say that it pulls really well compared to theirs.
I’m going to make a point of comparing cold and warm tick over tomorrow too, and investigate the carb seating.
Thanks again – some things for me to think about and check.

[mickymidas]

Could be as simple as head needs re-sealing . Take head off , use a mirror or peice of glass with wet and dry on top , lapping paste or wd40 will do. Rub head around in figure of eight , clean off and re-seal with gasket blue. tighten head nuts up opposite to opposite and best to use torque wrench so not overtight and risk warping the head...Used to happen a lot on my old rally 200 engine, before i was educated about unevenly overtightening head bolts .( tell tale oil leak from head )

[kru251]

Due to running OK, when cold I'd say almost 100% it is rings/piston/bore wear. Had this with a Lammie. Perfect when cool. Pig to start when hot but once going performance was OK. Rebore, new piston & new rings made ALL the difference and all was right in the world again.

[sime66]

Thanks everyone,
I’m going to check out the carb seating and tick-over hot/cold (Rudi), just to quickly remove it as a suspect or deal with it. I did notice it was slightly moist/oily on the cover around the idle screw, but don’t know if that’s normal. I’ll torque-check the nuts and cylinder head for signs of leaks/oil, and maybe do the re-sealing (mickymidas). If all is tight and clean though, it does look like it’s rings etc.(kru251), which was the most popular vote here too. That just begs the question whether it will be OK to limp through this year, or if I’m risking more damage by putting it off. (I don’t expect an answer to that; I think I know, just wish I’d done it at the end of 2012 season now!)
Thanks again, I've got several things to check, but it looks like inevitably it'll be piston/rings/rebore before all is well again.

[sbwnik]

Change the rings. I'm assuming you torqued the head up properly after the stripped thread?

I'd also give the head a quick skim, but I'd not use anything like blue or instant gasket, it shouldn't need it when lapped in. Piaggio don't use it, and I don't know any engineers that do - most say to stay clear IME.
It's not a Lambretta
Torque the carb up too.

If that doesn't sort it, then I'd look at the pick up and coil on the stator.


All that said, a little voice is reminding me that my 177 was run on a B7 for round town, B8 for longer runs. You have checked the plug, haven't you?

[sime66]

Thanks sbwnik, you have touched on some of my other doubts!
The head nut was replaced by the side of the road just by feel, but done properly with torque wrench later. Since then I’ve just checked that they’ve stayed tight.
There is no blue or anything there at present.
I Will certainly torque the carb.
I deliberately listed my plug in the first question because I did have my doubts. It is correct, and I have checked. I also asked in the club, and it was confirmed as OK and the advice was that if all was going well, then don’t change it. I was beginning to wonder if this qualified as ‘all not being well’, so time to try something different. I just put a new B6 in even though the old one was fine. (I had a slight doubt that one side of the isolator was slightly darker than the other, but haven’t followed that up yet). I have a new B7 I could try, but don’t want too many variables at once though. It’s going to get colder again next week, so might wait for that change until my problem comes back when it is warmer again, and I’ll then see if the colour is constant on the plug too.
As for the stator and coil, I had gleaned that the electrics side might be the culprit, hence my comment that I wasn’t sure which of the several possibilities to start with. This is something I know even less about, and I’ve read about it, but that seems to be something to investigate after the cylinder.
It definitely sounds like the first job is check all torques, and second job is rings.

[kru251]

SBWNIK.

It's not a Lambretta

Still a bleedin' two stroke whatever!!!!!!!!! ;D

[sbwnik]

Chuck a B7 in it, a B6 is for standard engines. No harm in trying... it may run a little rough at first though, it'll need a bit longer to get properly up to heat.

[pxguru]

Deciding the right plug heat rating is often a bit trial and error but for your set up I would agree with Nik on this one, no less than a B7. If you run a B7 for a while take a decent picture of it and we'll tell you if the cold plug is running hot enough!

Sounds like the warm starting is the rings, an air leak or both. If it was mine I would take the barrel off, new nice thick base gasket, fit new rings and do a heavy polish on the head to set the squish correctly but that's just me! ;D

[sime66]

A great load of advice, thanks everyone.
The B7 is going in for sure immediately.
On the weekend I'm going over the carb, cylinder, and exhaust with a torque wrench.
I'm organising new rings, and when I do that we'll have a good head polish before getting it all back snug. and properly squished down!
I'll report my progress soon.
Cheers all

[sbwnik]

Polishing the head won't set the squish correctly, it'll decrease it a touch! It's the distance between TDC piston and the head at the edge... polishing the head will skim it slightly, thus closing that gap.

Just a point..... That said, I'd still do it, just be very gentle with it, I use a drop of oil on the head when I do it (and I mean 'a drop') as it can help to show when you've flatted it right - the oil gets evenly distributed. I know of people who do the same with a fine grinding paste, but that always strikes me as being a bit dangerous.

[sime66]

B7 seems to be the business. Started easy hot and cold, ticked over lovely hot and cold, ran smooth and responsive – nothing discouraging about it at all; good call.
I understand what you mean about thick gasket and heavy polish Vs fine polish only, and keeping the squish correct.
Cheers again.

[sbwnik]

A thick gasket would raise the port timings



Just being picky now....!

[sime66]

She’s all torqued up now, and running lovely with the B7, almost want to leave well alone, but going to do the rings and head polish too before Tenby. Precise squish settings and port timings are a bit too technical for me, I see you getting very in-depth and losing me completely in other recent threads, although I do have a read-up when something is mentioned that I don’t know about. It’s only a tatty, well-ridden, 30yr old scoot with a few tweaks, that’s all. Anyway, since my attention has been drawn towards the carb, I’m thinking of putting a P200 carb on it instead of fiddling with the existing one, (which I can get to know better by overhauling it afterwards). I take it that’s a wise improvement and worth it? I have been reading here and elsewhere about the jetting; is it an obvious automatic choice of jets (PX177, sito+, 24/24E), or is it trial and error? Also do I need a new/different air filter and box?

[sbwnik]

Si24/24E should be ideal. Stick it on with the standard jets and see how it runs - you may need to tweak it slightly to do it, and I'd take a punt on a second hand Dellorto rather than a new Spaco, they tend to be better quality IME.

[sime66]

It is a pukka Dellorto SI 20 20D on there at the moment - just checked. You reckon not to replace with a Spaco at all? I guess I'll let it be known that I'm in the market for an original Dellorto SI 24 24E non-autolube then, and keep this one until the right 2nd hand replacement comes along. It does have to be non-autolube does it, or can something be plugged up? Different gasket? I'll look it up myself, but I'm curious why I have a D now, and the one I'm after is an E. Anyway, thanks very much again for all the info; I'm well on the way to getting my old girl purring! Once I'm sure what I'm after I'll stick an ad in the Wanted section, but if anyone else reads this, and has one, I'll be happy to hear from you.

[sbwnik]

Any Si24/24 Delly will do the trick. Spaco are very hit and miss, some are good, some are great, but a lot are downright awful.

Make sure you use a non autolube gasket, and you should be fine.

[sime66]

Understood, thanks; I'm on it.

[waspman]

I have a 1999 PX200e kick start model (non electric start) and starting especially when it had cooled down was a mission, i.e. when it had sat at work all day or even a couple of hours. Ambient temperature during this period was between 15 - 25 degrees C. It is tuned, decoked, new plug, HT lead, plug cap, air filter cleaned, new needle valve and carb cleaned out, no flooding issues etc and otherwise it runs really well. Furthermore it starts well hot and stone cold. I have finally worked out the technique that works consistently.

Open the fuel tap, (which I shut off if not running), give it full choke, NO throttle whatsoever, it should take 2 or 3 kicks max and it will fire up. At this point give it throttle and let it run for a few seconds before pushing the choke off. I noted with mine there was virtually no smoke which suggests to me that the fuel evaporates or dissipates or at least components of it do whilst sitting from hot to cool to the point where the motor is essentially dry of fuel from the crankcase to the combustion chamber. Notably the difficult starting is after it has been warmed up well and truly.

Stone cold give it full choke, same deal as when cool. When hot do not give it any choke but give it a bit of throttle.

I would now classify it as easy to start simply by using this technique and coincidentally its like most other 2 strokes I have had be it a lawn mower or chainsaw etc. Choke and lack of throttle seems to work on them all.

[sbwnik]

Just leave the fuel on....