poor running issues

[johnny650]

well you know how it is when you have tried everything and nothing you do seems to make the slightest difference .....well I'm there.

Last week I fitted a new small block 200cc cylinder kit to a freshly built gearbox.
22mm jetex 118 main , 5899-2 atomiser , 50 choke , 48 pilot 200 slide, foam filter and AF 42mm clubman and it started and ran ok for about a 5 mile test run although it was clear that it needed some work with the jetting and tuning etc.
Since then it flatly refuses to run at all !

It will start most of the time and there always seems to be a spark but when I try to ride it it will only ride at idle speed even with the throttle wide open ???

Putting the choke on whilst riding WOT makes no difference whatsoever even though it feels like a fuel starvation issue.....

Double checked the points gap and the advance (19 BTDC) ok
Swopped plugs 4x no change
Removed inlet and exhaust and fitted new gaskets. no leaks
Drained fuel tank refilled fresh petrol,
Checked flow rate through gas cock 600ml per minute ? presume adequate .
Swopped 4x spare carbs with various jetting ...no change.?!

The only issue that I am aware of is the compression is too high at 130+PSI I can stand on the kickstart and it is really hard to kick over even with my 17 stone on it....


Every time I check the plug it looks like its not getting enough fuel but I can see the fuel flowing through the clear pipe and large fuel filter and 4x different carbs cannot all be faulty . Its like the engine isn't pulling fuel from the jets

I'm so frustrated with this that i have prepared a 185cc cylinder kit to fit tomorrow but its extremely annoying not to find the cause of this problem . I hate to quit on anything but crikey its doing my head in

[Muppet]

try the same set up with a standard air box and and filter or cover the foam filter you have with tape just leave the end of the filter free of tape so it has more resistance to the air flow and it might start and run

[Martin20]

Feel your pain Johnny! Having very similar issues with my Special! Was running OK(ish), but needed new clutch, so did that and treated it a 42mm AF Clubman, hoping it would give me an extra mph or so. Had standard exhaust on before, which although I had washed through with caustic soda a few times, was probably not at it's best! Built scoot back up, started first kick, felt great through all gears apart from a little hesitancy up to 1/4 throttle. Past that, it felt really good. Over the next few days, problems became worse, until it became impossible to ride. Swapped to another 22mm Jettex I had in garage, no change. Put original netted back on, tried various jetting options, nothing! Started to think air leak, so at the weekend, stripped exhaust off and refitted with new gaskets/sealer. Left 24 hours to cure, then started it yesterday morning, and same issues. Stripped it all down again, head off, barrel off, new gaskets all round. Started eventually last night ,still the same. Only thing I can think of now is the new exhaust! Going to try it with my standard one again today, if only to hopefully eliminate that as being the problem! Will keep you posted!
Martin.

[johnny650]

try the same set up with a standard air box and and filter or cover the foam filter you have with tape just leave the end of the filter free of tape so it has more resistance to the air flow and it might start and run

good suggestion Muppet ..

I did try both a foam filter and the standard hose/airbox without much change but I didn't think to restrict the air flow because it seemed like a fuel delivery issue
.
If there is too much air then presumably the engine won't be able to suck the fuel from the jets through the venturi. I am beginning to wonder if the GP manifold is part of this problem.....it has a massive port also the cylinder had had the inlet port widened excessively so much so that the GP manifold would barely cover it.

i'll try restricting the air flow first ......

[johnny650]

Feel your pain Johnny! Having very similar issues with my Special! Was running OK(ish), but needed new clutch, so did that and treated it a 42mm AF Clubman, hoping it would give me an extra mph or so. Had standard exhaust on before, which although I had washed through with caustic soda a few times, was probably not at it's best! Built scoot back up, started first kick, felt great through all gears apart from a little hesitancy up to 1/4 throttle. Past that, it felt really good. Over the next few days, problems became worse, until it became impossible to ride. Swapped to another 22mm Jettex I had in garage, no change. Put original netted back on, tried various jetting options, nothing! Started to think air leak, so at the weekend, stripped exhaust off and refitted with new gaskets/sealer. Left 24 hours to cure, then started it yesterday morning, and same issues. Stripped it all down again, head off, barrel off, new gaskets all round. Started eventually last night ,still the same. Only thing I can think of now is the new exhaust! Going to try it with my standard one again today, if only to hopefully eliminate that as being the problem! Will keep you posted!
Martin.

blimey Martin ....sounds like you are going through the same grief as me .

I have practically exhausted every thing I can think of now. I am starting to consider things like excess crankcase pressure, blown drive side seal, coil breaking down under load, debris /rust trapped in the tank petrol tap filter , blocked exhaust etc ....

I think I am about at the end of my tether with it so I'm preparing everything this morning to remove the engine and strip it . I think I'll almost certainly replace it with the 186cc I aquired this week.
Really looking forward to the day I can just kick it over and charge off down the road with no issues .
Let us know how you get on with yours.

[johnny650]

hey !........I've just remembered something really weird that happened when I first fitted the exhaust manifold and spun the engine . A load of bits of paper flew out the end of the manifold ???????????? wtf ?

I didn't think any more of it but supposin a mouse had made a nest in my exhaust over the Winter and riding the scoot has shifted the nest to the end of the exhaust and blocked the tailpipe ...

Did I say that i was getting desperate

[johnny650]

well here must be the reason for the engine not running ...an oil leak into the crankcase.

This is the interesting thing though.....there was no oil on the spark plug and apart from a small oil leak from the base gasket there was no real evidence of this . Because the scooter wouldn't actually run.......... the oil never got combusted so there is no carbon on the plug or the piston crown. either.

I'm now not sure if the excessively high compression was pressurizing the crankcase or if the drive side seal has actually blown or even been installed the wrong way round....... so I'm going to have to remove the flywheel to check the mag seal and remove the cover to check the drive side seal. I'll probably end up replacing it anyway to be on the safe side.

I'd be gutted if I fitted the 185 cylinder only to find there was still an oil leak and smoke pouring out the exhaust.

Still looking on the bright side I've learnt a lot today. Always do a pressure check on the crankcase of a new build !

And on a nice day like today with swmbo away for a couple of days I'm as happy as a pig in the proverbial .<a href="http://s130.photobucket.com/user/peanut ... c.jpg.html" target="_blank"><img src="http://i130.photobucket.com/albums/p261 ... 4kvrtc.jpg" border="0" alt=" photo oil in the crankcase_zpssj4kvrtc.jpg"/></a>
<a href="http://s130.photobucket.com/user/peanut ... v.jpg.html" target="_blank"><img src="http://i130.photobucket.com/albums/p261 ... okzsfv.jpg" border="0" alt=" photo happy as a pig in shhh you know what_zpstpokzsfv.jpg"/></a>

[johnny650]

ahhhhhhhh common guys ............we need more than 10 seconds to edit a post for crissakes........ jeez I hate trying to edit a post or post an image link on here if this doesn't work I'm giving up

<a href="http://s130.photobucket.com/user/peanut ... c.jpg.html" target="_blank"><img src="http://i130.photobucket.com/albums/p261 ... 4kvrtc.jpg" border="0" alt=" photo oil in the crankcase_zpssj4kvrtc.jpg"/></a>[/photobuckvid]
<a href="http://s130.photobucket.com/user/peanut ... v.jpg.html" target="_blank"><img src="http://i130.photobucket.com/albums/p261 ... okzsfv.jpg" border="0" alt=" photo happy as a pig in shhh you know what_zpstpokzsfv.jpg"/></a>[/photobuckvid]