Varitronic starting issues when hot

[Jeff t]

Anyone had issues starting when hot, i have checked everything fuel related, carb, reeds, even pressure tested thinking electronic issue. Set up old version Imola, phbh 30mm , franspeed exhaust.
Thanks

[Rich Oswald]

Anyone had issues starting when hot, i have checked everything fuel related, carb, reeds, even pressure tested thinking electronic issue. Set up old version Imola, phbh 30mm , franspeed exhaust.
Thanks

Are you using an air filter of any sort?

[Jeff t]

No runs open mouth

[gp200ts1]

Rings worn?

[hullygully]

stator readings when cold & then when engines hot would help bud

[Rich Oswald]

Rings worn?

+1

[Jeff t]

Its not done a lot of miles, is there any test i can do without taking the headoff, compression test? Only not done one before.

[Fast n Furious]

Its not done a lot of miles, is there any test i can do without taking the headoff, compression test? Only not done one before.

You can use one of those typical £15 Fleabay automotive compression tester kits.
These kits typically use an M14/M10 plug to PCL adaptor. This adaptor then screws onto the gauge hose (where the one way valve is.) The usual problem here is that there is insufficient room to click the PCL fitting together because the cable guide that's connected to the choke lever, gets in the way.
Be aware though, that in effect, the adaptors actually raise the volumetric capacity of the combustion chamber slightly. So, the compression reading will show around 5% lower than it actually is. Not much I know, but hey ho. At kick start speed I would expect a reading of 65PSI or better. ( remember to keep the throttle open to allow the engine to breath!)
Don't be tempted to use the extension hose adaptor that comes with these kits because these will significantly increase the effective compression volume resulting in a dramatic incorrect low reading!

[Jeff t]

I bought a compression tester but couldnt fit without the rubber hose so decided to strip down and check the rings anyway. The piston was pretty clean with hardly any marks past the rings but that might reflect how little i have used it since it was last stripped down.
Measured the ring gap and its about 0.43mm on a 64mm piston which reading Sticky’s book doesnt seem that bad, so now not sure if to rebuild as is or fit new rings. Any thoughts.

Thanks.

[Fast n Furious]

.25mm (10 thou) would be the normal gap for 64mm new rings.

[Jeff t]

Thanks new rings it is then.

[Adam_Winstone]

But I don't expect a 0.43mm ring gap to be related to your starting issue as, like you noted from Sticky's manual, that is far from worn out.

[Jeff t]

Yes and looking on Cam lam website it says minimum ring gap 0.3mm and max 0.7mm for Imola small bloc so still not sure !!

[Adam_Winstone]

You say that it's not done that many miles... could it be as simple as getting to know its starting requirement when hot?

I ask this as a pal of mine, who has decades of Vespa riding experience, was going on about how his Lambretta was a poor starter from hot. We then ended up at the petrol station together and I then witnessed kick, kick, kick, "It's not starting again now that it's hot."

Clearly the bike was flooding so I asked him if he always turns his fuel on before starting, to which YES was his answer. I told him that he should try starting with his tap OFF as he'll have a full float bowl already and that he might find it starts better without turning the fuel on. I had also noted that he had a tendancy to turn the throttle whilst kicking.

Rather than letting him replace the plug with a dry one, his usual fix, I asked him for a go, turned his fuel off, kept the throttle closed and it fired up within a couple of kicks. A change of technique was all that it needed.

I'm not trying to teach anyone to suck eggs here, just illustrating how a change of technique can make all the difference, especially when hot starting.

It seems as though you've covered most other things... but double check that the choke cable has enough play to close off 100% then in the off position, which is a common problem that can cause hot start issues.

Good luck.

[Warkton Tornado No.1]

As Adam intimates, hot starting can often be an issue, probably never more prevalent than with the PH carburettor many of you patronise.

Unlike the earlier VH, the PH range does not have an in built overflow, so the cold fuel soaks up the heat after the engine has run & there is a tendency to flood, although it only takes a little excess for flooding to occur, probably exasperated by a downdraught inlet. If an air filter is fitted, the problem is exasperated further. Likewise, that other ‘trait’ of having an engine set up too rich - & then some - will not help matters.

[Jeff t]

Thanks for all the tips all taken with the right intent. I have tried diffent methods but as i dont use it regular as i use my S2 most of the time my normal starting method is no choke or throttle, if i think about it like putting away after use i turn the fuel off for a short time but couldnt say i do that all tne time.
My gut feel after ruling eveything out and all the detail i know that i might have missed explaining, is it goes back to when I fitted the varitronic, had it dynoed but it ran awful and he couldnt set up mid range. So i think its carb related or im really unlucky and its electrical. Plan is to rebuild double check eveything then check elelctrics although not sure where to start but know a man who might know then get it set up on the dyno.

Thanks again for the help.