Engine won't rev - I'm at my wits end !!

[Weston-scooterist]

Im hoping someone with more knowledge can help with my problem,

LI special
198cc small block barrel
PHBL 25mm running through drilled box with fast flow filter
Ancilotti exhaust
12v electronic ignition

A couple of weeks ago scoot just died whilst accelerating, after i stopped it started misfiring and wouldn't rev with the odd backfire, vanned it home, it wouldn't start at all now, I had just replaced a jetex with this PHBL 25 and after jetting sorted it was running spot on for about 30 miles over a few days, this same problem had occurred on the way to woolocombe with the jetex fitted after filling up but seemed to clear itself after 10 mins of full throttle on the stand, so I thought it may be the ignition.

Tested ignition, indian, LV coil was 290ohms which seemed low, so I replaced with an italian LV coil and a new pickup, all tested ok, also changed CDI.

With new ignition parts fitted the engine started first time, however anything past 1/4 throttle just bogs down on the stand, seems pretty smoky, when choke is pulled out it stalls, so I thought it might be carb.

Stripped it down cleaned all jets, checked choke and floats, all ok, spark plug is very dark.

Changed spark plug,

Checked vent in petrol cap

Checked fast flow tap

Strobed at 19

Changed fuel

Mate came round, as I was suspecting oil seal, however putting hand over exhaust stalls engine, blocking oil filler hole doesn't alter it either, he thought it was running rich as altering the mixture screw seemed to have little effect.

The whole engine and seals were overhauled 1500 miles ago with good quality seals.

Blocked exhaust ?



Any ideas welcome

[ducksta]

is manifold secured down ie not leaking air gasket fitted

[Weston-scooterist]

I put a new inlet manifold and gasket on when changing carb, that seems ok, exhaust also seems OK in that I can't detect any air leaks, but i can't be certain

[mick1]

Have you tried with no filter ? Could be mag side seal, was there any traces of oil or fuel in the stator ? Very rare but loose magnets or crack in the flywheel could be a possibility

[Weston-scooterist]

Tried it with no filter, no difference, no oil in mag housing, checked magnets, checked woodruff key, flywheel seems ok.

[mick1]

The flywheels a tricky one, not much to see really, best to swap with a known good one.

After that If it was me i'ld look at the top end (not much else to look at now i suspose), possible stuck rings. trying another exhaust wouldn't be a bad idea as well.

[Weston-scooterist]

Yeh top end is my next task I suppose, along with decoking exhaust as I don't know how old it is.

Compression still seems good though

[coaster]

Compression still seems good though

You've done all the obvious checks but I would suspect that you have a ring stuck in its grove. That will give the effect of a loss of compression when running but it may not be that obvious kicking it over. I would imaging that maybe it's started to hole the piston and some of the debris will have caused the ring to stick. A heat seize can cause this too. 19 degrees is a bit too advanced for modern fuels imho, 16 is generally considered the safe setting unless using a retrd unit of some sort.

[dennis]

Coaster, are you saying it should/would be be better if we set the timing to 16 degrees instead of 19 whitch i would imaging most on here have.

[coaster]

Yes, 16 is safer with the current fuel issues and I would disagree about 19 being normal. Maybe it was a few years ago but I think you"ll find 16 is today's 'safe' norm....discuss??