'Amazing Reving CRM' MK11 (I've got one now :-( )

[Jonorow]

i can bring the spare carb for you to check? doubt it has a different float but has the inner pin seized? that mightrestrict the float travel. jon

[drillam]

Well the engine starts easier and no longer screams off into the stratosphere of its own accord but there's still a problem with the revs not dying down.
Throttle response is good initially but as it warms up the revs still stay on the high side after a blip of the throttle. I can force them down by holding it in gear and slipping the clutch. Once down at tick over speed it stays stable until I blip the throttle then it'll stay on the high side.
Adjusting the pilot screw has little or no effect.
It bogs down slightly when taking off from a standstill or accelerating from low speed, whereas before it was very lively.
So my feeling is an air leak which is accentuated as the engine warms up.
I'd like to do a leak down test as I've found this a good diagnostic tool in the past on four strokes but have held back until now as I have a fear of popping the crank seals if the crankcases becomes pressurised. Can anyone tell me if this is a possibility on 2 stroke engines please? I've done other engines in the past as I said but find that the air pressures involved, usually around 100psi, is enough to force the piston down the bore if the locking arrangement of the rear wheel is not done right first time and usually takes a wee bit of trial and error on some bikes. Clutches can slip, well they tended to on my Nortons but to be fair they were over half a century old, and rear drum brakes were not as good as discs so I might be worrying unnecessarily
So if I inadvertently force the piston down the bore will the air pressure simply escape through the exhaust and /or transfer ports? or is it likely to pop the seals before it can escape?
I'm displaying my ignorance of 2 strokes again so some advise would be good.
cheers
Millard

[drillam]

Looks like this site has answered my question

http://groups.google.com/group/rec.craf ... 11b31a5455

Seems I would need to make up a crankcase pressure tester to around 6psi.
My thoughts on the leakdown test was that the bore/head seals might be the cause of my air leak but on reading through the above link it would appear to be more likely the bottom end. Also this method would test the rubber intake stub/reed block and associated gaskets.
looks like a good place to start.

[fallenmikethebike]

If you are certain that the throttle is not sticking, in any of it's component parts, and the bike ran sweetly prior to the 50 yds front crawl you inadvertently subjected it to.
The most likely cause would appear to be a mixture issue, among which causes may be one or many.
Leaking crankcase , mating faces.
Seals to crank.
Incorrect jetting, [too small]
Inlet Manifold, leaking in un-metered air.
Cylinder base gasket leaking.
Mike

[fallenmikethebike]

i can bring the spare carb for you to check? doubt it has a different float but has the inner pin seized? that mightrestrict the float travel. jon

No every things moving fine, i will bring mine along as well then for a comparison, many thanks.
Mike

[drillam]

I had at first thought of doing a leakdown test but after reading the thoughts of folks far more knowledgeable than me on two stroke engines I realised that the pressure required from the airline to do a cylinder leakdown test would pop the crank seals. So the next line of attack was to shamelessly pinched this idea from another site

http://www.thumpertalk.com/forum/archiv ... 06699.html

and adapt it to suit what I had lying around the shed.
So I took my leak down tester and hooked it to the compressor and wound the regulator down to around 9lbs or so. Then attached it to the hose which goes into the plug hole.

http://i14.photobucket.com/albums/a340/ ... C01699.jpg

The idea is to block off the exhaust and intake ports and pump air into the plug hole with the piston at BDC, thereby pressurising the combustion chamber and the crankcase all the way up to the reed block and inlet stub, which I'd guess would have to be the most likey candidates for a leak.

Then made up a blanking plate and gasket for the exhaust port;

http://i14.photobucket.com/albums/a340/ ... C01688.jpg


and a plug for the intake stub;

http://i14.photobucket.com/albums/a340/ ... C01690.jpg

pump in the air and then go all around the joints with a paintbrush slopping soapy water everywhere and voila,, gotcha ya wee bugga;

http://i14.photobucket.com/albums/a340/ ... C01697.jpg
http://i14.photobucket.com/albums/a340/ ... C01694.jpg

So the next job is to remove the reed block and make new gaskets, then with luck report back tomorrow that all is well, fingers crossed.
I'll keep you informed.
cheers

[drillam]

f**k, f**k, f**k, f**k, f**k, f**k, f**k,

No difference, starts fine but as soon as it warms up the revs stay high after closing the throttle.

I did the pressure test again last night when I realised that the new reed block gaskets had not cured the problem but this time could find no bubbles. I went all round the inlet stub, reed block, base and head joints, and all of the crankcase joints which is exposed (outside of the gearbox) and saw no evidence of leaks.
I'll remove the airbox today so I can confirm that the throttle closes fully when I shut off the twistgrip, but other than that I can't think what else would be causing it. Everything points to an air leak but I can't find one.
The only other place I can think of is the crank seals but they're new. Perhaps I damaged them on assembly. Might be time to remove the gennie and clutch again and check. f**k,


[quote="fallenmikethebike"]:( If you are certain that the throttle is not sticking, in any of it's component parts, and the bike ran sweetly prior to the 50 yds front crawl you inadvertently subjected it to.
The most likely cause would appear to be a mixture issue, among which causes may be one or many.
Leaking crankcase , mating faces.
Seals to crank.
Incorrect jetting, [too small]
Inlet Manifold, leaking in un-metered air.
Cylinder base gasket leaking.
Mike[/quote]

Mike
The jetting is standard


I'll do the pressure test again today, very carefully in case I missed something. If nothing shows up then it's off with the clutch and gennie to check the new seals. Although I'm not sure they would be affected by heat expansion like a joint face would.

Getting seriously dogged off now.

[Jonorow]

unless it is smoking badly i wouldnt worry about the clutch side but you should be able to see if theres a problem on the rotor seal. try smearing it with grease, might help to isolate it more.
might also be worth smeering some silicone around all the joints. if thats fine then you might be a carb issue again.
dont change things untill you find the problem though.

[knackeredMk1]

Are you sure that the powervalve is moving

[drillam]

[quote="Jonorow"]unless it is smoking badly i wouldnt worry about the clutch side but you should be able to see if theres a problem on the rotor seal. try smearing it with grease, might help to isolate it more.
might also be worth smeering some silicone around all the joints. if thats fine then you might be a carb issue again.
dont change things untill you find the problem though.[/quote]

A mate suggested that I drop a wee bit of Castrol R in the box as the smell is very distinctive if it burns.
I have some in the shed for an old cammy Norton I used to have so it's worth a try.

"Are you sure that the powervalve is moving "

yeah definately. When I give a it a burst of higher revs it it moves then goes back to rest on tickover.

[Jonorow]

does the revs change when you adjust the air screw? if not youu need a bigger pilot jet.

[Jonorow]

or is it a smaller jet? cant remember but wind out the idle screw and see if it changes as you turn out the air scew

[drillam]

[quote="Jonorow"]or is it a smaller jet? cant remember but wind out the idle screw and see if it changes as you turn out the air scew[/quote]

Jonorow, it has no effect, but it has got standard jetting.
I think the needle is non standard though, it's a J35D. Initially I thought it had four slots but I should have learned by now to wear me specs, it's got 5. Clip was in the second from top before but I'm moved it to the middle now which should have raised it a touch and made it a wee bit richer. I did it not to try to cure the problem but to try to return to as close as possible to original spec.

Also it runs fine for the first few minutes until it warms up, only then do the revs fail to return to tickover speed. This keeps me thinking that it's something expanding with the heat and opening a wee space for the air to get in?

I keep thinking back to that fact that everything was running fine before I drowned it, so surely it's something I've done rather than a problem I inherited with the bike?

[fallenmikethebike]

Generally, a blocked or lean pilot jet would give a reluctance to tick over, i.e. higher revs, but, you also get starting issues with this symptom, does it start OK?
Winding in the mixture screw, [which meters the air] would have the effect of richening the mixture.
Although not a cure, try a 50 pilot jet, or richer still, also, re-oil the filter, get it slopping wet, seal the mating face with some grease , which is a good policy anyway, load up the air box with some clean foam/ sponges, i.e. restrict air flow.
Now give that a whirl, if it starts behaving, the problem, though not necessarily the solution is revealed.
Hows the plug colour during these episodes?
Lower the clip, on the needle , again this makes for a richer mixture.
Mike

[drillam]

[quote="fallenmikethebike"]Generally, a blocked or lean pilot jet would give a reluctance to tick over, i.e. higher revs, but, you also get starting issues with this symptom, does it start OK? "

Mike
yeah it starts real easy hot or cold

"Winding in the mixture screw, [which meters the air] would have the effect of richening the mixture.
Although not a cure, try a 50 pilot jet, or richer still, also, re-oil the filter, get it slopping wet, seal the mating face with some grease , which is a good policy anyway, load up the air box with some clean foam/ sponges, i.e. restrict air flow.
Now give that a whirl, if it starts behaving, the problem, though not necessarily the solution is revealed.
Hows the plug colour during these episodes?"

Plug colour is fine.

"Lower the clip, on the needle , again this makes for a richer mixture.
Mike[/quote]"

Will do.

I just did another pressure test and really slopped soapy water everywhere, on every joint and gasket, there's not a bubble in sight.
Just off to replace the exhaust and carb now and to check that the carb slide is not sticking when it heats up.
I'll lower the needle right down to see what effect it has.
Will report back soon.
Thanks for your answers once again.
Millard