View Full Version : 2 Stroke engine problem, need help please
The bike is Honda CRM250 MK1, 1989.
I bought it about a month back and it was running fine so took it for a trail ride on Salisbury Plain and drowned it in a very muddy puddle. On the way home it started to develop symptoms of an air leak as the revs wouldn’t fully die down when shutting the throttle.
It’s fine when cold, very responsive, but after it warms up the revs don’t die down.
If I raise the needle thereby enrichening the mixture the problem lessens but is still aparent, so it's just masking it rather than fixing it.
Long story short - I rebuilt the bottom end with new rod, big end, small end, mains and seals but the problem still persists. I didn't touch the bore or head as I was advised they're fine.
I have blocked off the exhaust and inlet and pressurised the cases to 10psi and slopped soapy water all over. This revealed a small leak on the reed block gaskets which I’ve sorted but the problem is still there.
I removed the airbox so I could see down the throat of the carb and the slide shuts off fully.
I've stripped the carb three times and cleaned with carb cleaner then blown through with an airline, the jets are all clear.
I reset the float height.
The Power valve and oil pump are set to spec.
I then put some Castrol R in the gearbox to see if there was a leak to crank case from it but there was no smell of the R burning.
Then I filled the cases with petrol but there's no leak from the seals.
The carb is standard jetting and all else is very much standard and was running fine before I drowned it, so I'm fairly sure it was something that happened when I filled the engine with muddy water rather than during the rebuild.
I’m now at a loss as to what to do next.
Someone from another site has suggested a mate as a good local mechanic but he seems too busy as I can't raise him so I'd be happy to take it to a recommended mechanic if anyone else knows one in the Southampton area.
Or does anyone have any suggestions? as I'm much better at breaking four strokes than stinkers.
Cheers
Millard
brassmonkey001
30-05-09, 17:43
Can you substitute the carb?
You sure it is not the throttle cable binding? Enough free play at idle?
Can you substitute the carb?
BM
I've asked to scrounge one on the apropriate forum.
You sure it is not the throttle cable binding? Enough free play at idle?
BR
Def not.
I've had the airbox hose off so I could peer down the throat of the carb when running. The slide snaps shut nicely, even when the revs are too high
if it has one, just a suggestion back the tick over right off and see if it still over revs? shit inside the where tick over screw fits? ( nah this wouldnt make it rev higher , because it mechanical) forget this one......
A take it you have checked starter jet, and seen if any crap preventing fuel flow , making it weaker?
getting hotter n revs rise makes me think yer dragging in air from manifold possibly...am not too fermilair wi yer moddle , but these are the problems ive come across wi :boobies stokers in the past....:augie
ugg
if it has one, just a suggestion back the tick over right off and see if it still over revs? shit inside the where tick over screw fits? ( nah this wouldnt make it rev higher , because it mechanical) forget this one......
A take it you have checked starter jet, and seen if any crap preventing fuel flow , making it weaker?
getting hotter n revs rise makes me think yer dragging in air from manifold possibly...am not too fermilair wi yer moddle , but these are the problems ive come across wi :boobies stokers in the past....:augie
ugg
Cheers Ugg
I checked all that.
I agree about the air leak, just buggered if I can find out where it's coming from though.
try the reed block again?
try for leaks when the engine is hot,
clean the carb all you want, it still may be the problem, they look all ok and clear but they sometimes arnt,
suzuki carbs do this a lot, substitute em and all is good
try the reed block again?
try for leaks when the engine is hot,
clean the carb all you want, it still may be the problem, they look all ok and clear but they sometimes arnt,
suzuki carbs do this a lot, substitute em and all is good
Thanks Digg
I've pressurised the cases and slopped soapy water all over each and every component/joint/seal.
I initially got a leak show up on the reed block which I sorted and it improved things slightly but didn't cure it. I did this three times and am convinced now that the reed block and inlet stub are good and air tight.
Am trying to scrounge a carb from the CRM250 forum to eliminate the carb.
cheers
millard
Cheers Ugg
I checked all that.
I agree about the air leak, just buggered if I can find out where it's coming from though.
might sound daft but try an airline on area where ye recon it might leak , n if revs rise more than its doin nah ,it could give yer an idea were its suckin in the presurised air bein blasted at it :nenau
but not direct in carb ovcourse:D
might be bollox , but could help , digger06 might say daft twat , but if concentrated air forced at a cracked area it just might show where poss leak is?
ugg
, digger06 might say daft twat ,
ugg
daft twat:D
Uncle Ricky
30-05-09, 22:25
Have you adjusted the air screw ?
might sound daft but try an airline on area where ye recon it might leak , n if revs rise more than its doin nah ,it could give yer an idea were its suckin in the presurised air bein blasted at it :nenau
but not direct in carb ovcourse:D
might be bollox , but could help , digger06 might say daft twat , but if concentrated air forced at a cracked area it just might show where poss leak is?
ugg
No it don't sound daft ya daft twat, i'll try it. :D:D:D
Cheers Ugg
Have you adjusted the air screw ?
yeah tried it Ricky, it does work as does just about everything else, it just don't stop it overrevving.
cheers
millard
brassmonkey001
30-05-09, 23:54
My thought is you've got an air leak at the carb top.
Back when I used to spanner for a living we'd spray something all around the carb and manifold to locate an airleak on a running engine, but I can't remember what. :blast
WD40? Carb cleaner? Brake cleaner? :nenau
Been a long time...:rob
Muddy water scoured the carb slide & body you're leaking air through your carb top work. Carb gets hotter, gap gets bigger, more air finds it's way in, bypassing jets.
brassmonkey001
31-05-09, 00:01
Muddy water scoured the carb slide & body you're leaking air through your carb top work. Carb gets hotter, gap gets bigger, more air finds it's way in, bypassing jets.
That's exactly what I thought.
I knew it wasn't BB King.
My thought is you've got an air leak at the carb top.
Back when I used to spanner for a living we'd spray something all around the carb and manifold to locate an airleak on a running engine, but I can't remember what. :blast
WD40? Carb cleaner? Brake cleaner? :nenau
Been a long time...:rob
Starting fluid, ( Ether) revs increase slightly if you spray it around the area & there are leaks. Be careful though....
brassmonkey001
31-05-09, 00:04
Starting fluid, revs increase if you spray it around the area & there are leaks. Be careful though....
Easy-start? Yeah, could well have been. :thumb2
That's exactly what I thought.
I knew it wasn't BB King.
High 5 Lucille :beerjug:
Muddy water scoured the carb slide & body you're leaking air through your carb top work. Carb gets hotter, gap gets bigger, more air finds it's way in, bypassing jets.
seen a lot of carbs scoured badly but work ok, worth a try though, is there a seal on the carb top?
ps, blowing through your carb with compressed air isnt a good idea,you can lodge debris in the carb drillings, the jets look clear but the actual carb could be (partially) blocked
My thought is you've got an air leak at the carb top.
Back when I used to spanner for a living we'd spray something all around the carb and manifold to locate an airleak on a running engine, but I can't remember what. :blast
WD40? Carb cleaner? Brake cleaner? :nenau
Been a long time...:rob
I'll try Easy-Start on it today, cheers BM
seen a lot of carbs scoured badly but work ok, worth a try though, is there a seal on the carb top?
ps, blowing through your carb with compressed air isnt a good idea,you can lodge debris in the carb drillings, the jets look clear but the actual carb could be (partially) blocked
Digg
yeah there is a seal in the top, I'll check it.
When I blow air through I can feel it exiting the other end of the drillings.
slacken or remove the throttle cable
turn your idle mixture in to stop then out 1 turn
back your idle stop screw right out till you can't feel the slide touching it.
now what happens ?
i think it'll be your carbslides worn and leaking air past when shut tho'.
had a guzzi lm did the exact same thing - thats what 40k miles on open bellmouths does tho.
To see if the revs would increase by finding the air leak I sprayed some Easy-Start all around the carb, reed block and inlet stub, no difference. I removed the air filter and spayed it directly down the carb but killed it the first time. Second time I sprayed a bit less and the revs calmed down a bit. I'm assuming that what happened here is that the mixture was enriched temporarily by the ether in the spray, so for a short while getting rid of the weak mixture. Dunno if it helps though, still haven't found the scource of the leak, if there is one. Pinning all my hopes on an increase in pilot jet size now as suggested by a coupla guys on the CRM250 forum.
so you went through water and now u need a bigger pilot jet??the jet didnt shrink in the water,:D
it points to a partially blocked carb drillin if it helps, if the carb then clears ul be runnin rich then
so you went through water and now u need a bigger pilot jet??the jet didnt shrink in the water,:D
it points to a partially blocked carb drillin if it helps, if the carb then clears ul be runnin rich then
yeah I know mate, it's just that a coupla the guys on the CRM forum are very insistant that I try it, so for a few quids worth of new jet i'll try. But as you say, I reckon it might just mask the problem. Don't know what else to try apart from a carb but can't raise a loaner yet.
well its worth a try as you say , you can always change it back if it clears
so you went through water and now u need a bigger pilot jet??the jet didnt shrink in the water,:D
it points to a partially blocked carb drillin if it helps, if the carb then clears ul be runnin rich then
Just to clarify, it wasn't just a soaking in water, it was a very muddy puddle, this was the result
http://i14.photobucket.com/albums/a340/drillam/Honda%20CRM250/Salisburymud1.jpg
http://i14.photobucket.com/albums/a340/drillam/Honda%20CRM250/DSC01626.jpg
it wouldn't start untill I removed and cleaned the mud off the spark plug electrodes. I know I should have van'd it home but was out in the middle of the Plain so didn't have a lot of choice really. That's when the symptoms started to show, on the ride back to the van, steadily became more noticeable.
In one way i'm glad because on investigation the big end and mains were shot and woulda given way sometime soon.
here's the big end bearing
http://i14.photobucket.com/albums/a340/drillam/Honda%20CRM250/DSC01666.jpg
thanks for all your suggestions so far.
millard
Outtomunch
31-05-09, 17:57
so you went through water and now u need a bigger pilot jet??the jet didnt shrink in the water,:D
it points to a partially blocked carb drillin if it helps, if the carb then clears ul be runnin rich then
Gotta say it sounds like that to me too.
Went through similar with my TDR (except it was like that when bought, not due to muddy puddles :D).
After the third complete carb strip down, clean, float height set it all suddenly worked ok :mad: Given the piccies you showed my money is on still having some shite in the carb :nenau
Good luck though, sounds like a right 'mare :mmmm
Andres
Carb cleaning services...
www.bestultrasonic.com
Ive had 5 crm250s, presently got enough bits to build 2 in the garage. If you want anything give me a shout. Im clearing it all out cheap now as i need the space.
Mine was doing something quite similar and it was something simple - the clamp strap that tightened the airbox around the carb had snapped and air was leaking in. Replaced and hey presto. Back to perfect running low down.
The crms a tough little cookie and can take immense abuse without problems.
Like i said though, gimme a shout if you do want to swap anything. I had a spare carb if it does turn out to be a heavily worn carb (doubt it). Definetely wants a good clean out though. I just chuck my carbs in a bowl of fresh petrol and use a brush on it, whip the jets out, blow through them in your mouth. JD
Other things to check though, powervalve operating correctly? Not got it adjusted wrong have you? is it functioning?
Paul
still sounds like a crank seal leaking
Steve :oonyack
Could be, were these replaced during the rebuild? - sorry just re read your initial post where you stated you had.
It would be the very last thing i would check though.. for the obvious reason that its frickin expensive and annoying stripping it down again.
2 strokes only ever go wrong in 2 ways - BIG TIME or something really simple yet annoying haha :D
Other thing is...crms are fickle little buggers sometime. My last mk3 was rebuilt with top bits, but did something similar to what you describe. Could never stop it as it seemed to just be what the engine wanted to do. I turned the idle screw right out so it was just pop... pop..... pop...but wouldnt idle when cold without the choke (not left that on have you! Mine used to rev its tits off if the choke was left on more than 30 seconds)
once warm though it would just sit there ticking over lovely.
As a starter though, put all the jetting back to standard (unless you have a full dep on it). Make sure the air filter is oiled (otherwise itll run lean)
Take it out for a spin and do a plug chop. Thats the simplest way of seeing how its running.
Paul
still sounds like a crank seal leaking
Steve :oonyack
That's what I was thinking, all that shite in the engine has scored the smooth sealing area on the crank:nenau
Shep
Carb cleaning services...
www.bestultrasonic.com
Cheers alimey
I might just invest in one of those. had a look on ebay and there's some to be had for around £30, dunno if they'd be any good at that price though.
Could be, were these replaced during the rebuild? - sorry just re read your initial post where you stated you had.
It would be the very last thing i would check though.. for the obvious reason that its frickin expensive and annoying stripping it down again.
2 strokes only ever go wrong in 2 ways - BIG TIME or something really simple yet annoying haha :D
Other thing is...crms are fickle little buggers sometime. My last mk3 was rebuilt with top bits, but did something similar to what you describe. Could never stop it as it seemed to just be what the engine wanted to do. I turned the idle screw right out so it was just pop... pop..... pop...but wouldnt idle when cold without the choke (not left that on have you! Mine used to rev its tits off if the choke was left on more than 30 seconds)
once warm though it would just sit there ticking over lovely.
As a starter though, put all the jetting back to standard (unless you have a full dep on it). Make sure the air filter is oiled (otherwise itll run lean)
Take it out for a spin and do a plug chop. Thats the simplest way of seeing how its running.
Paul
I'm gonna strip the carb again and this time carefully poke through all the drillings with soft copper wire rather than carb cleaner and airline.
Was thinking on it over the weekend and as I've checked out all the other areas where air could leak in but it's still running weak then I'm coming to the conclusion that rather than an over supply of air it's likely to be an undersupply of go juice.
Probably be wrong again but it's worth a try.
That's what I was thinking, all that shite in the engine has scored the smooth sealing area on the crank:nenau
Shep
Shep
I did a pressure test on the cases and combustion chanber and it's all good, I also filled the cases with petrol up past the level of the crank seals and it was dry as a bone on the outside.
Yes, it does look as if you've been very thorough, but the fault does sound like an air leak and the seals could leak only while the crank is rotating, you've checked most other things so far:nenau
Good luck anyway, these type of faults are always a pig to find, timings ok I suppose?
Shep
Yes, it does look as if you've been very thorough, but the fault does sound like an air leak and the seals could leak only while the crank is rotating, you've checked most other things so far:nenau
Good luck anyway, these type of faults are always a pig to find, timings ok I suppose?
Shep
no adjustment on the timing, it's right or it's fukked.
no adjustment on the timing, it's right or it's fukked.
Ah! that sorts that then:D
Stripped the carb and poked every orifice through with a piece of copper wire then blew through with 100psi. All clear but no difference.
Let it warm up then blipped the throttle and let it run at that for a while. There's no tacho so difficult to say what it revs at when they don't die down but it's nowhere near screaming, just a very high tickover.
Cut it and here's the plug
http://i14.photobucket.com/albums/a340/drillam/Honda%20CRM250/DSC01702-1.jpg
Took it for a run and going up hill on 1/2 to 3/4 throttle in third, cut it coasted in and here's the plug
http://i14.photobucket.com/albums/a340/drillam/Honda%20CRM250/DSC01740.jpg
It goes real well out on the road, no fuss , no drama, just goes like stink. I'm almost tempted to ignore the tickover problem, if it wasn't for the cost of the possible consequences
whatdya reckon?
First plug chop looks absolutely spot on to me. Nice brown colour.
Second one looks a bit sooty but its not that bad. Id maybe do a couple more just for some comparisons but to be honest.... doesnt look too bad.
Not worth stripping the engine for it.
Cheers alimey
I might just invest in one of those. had a look on ebay and there's some to be had for around £30, dunno if they'd be any good at that price though.
They also do this Mill...:thumb
http://www.bestultrasonic.com/index.php?cat=CARBURETTOR_CLEANING_SERVICES&ActinicSID=2ead1f4e5e9a4be0ade24b4b1e7aa693
Ps Are you sure your reeds/seats are not damaged & shutting off tight..:nenau
Well I finally today got around to trying the next size up in pilot jet, No 48,,
Guess what ????
No difference.
So in went pilot jet No 50.
While I was waiting for the engine to warm up again I thought I'd turn the tickover speed down a wee bit and bingo, problem dissapeared. Not what you're thinking, it's not as simple as having the throttle stop screw wound in too much, here's what happens:- when the throttle stop is wound back to a fairly low tickover speed the revs die down nicely when blipped, but turn it up just a touch, and I mean much less thean 1/8th of a turn (literaly a few degrees) and the revs increase very slightly as you'd expect but when you blip the throttle the revs stay on the high side, just as before. I can still force them back down to a nice low tickover by slipping the clutch, in gear, brake on. Into neutral clutch out and it stays stable, as it always had during this process.
So I went back to the standard pilot jet, size 45 and same thing happens.
So what do you think's happening here? Any clue as to why a few degrees on the throttle stop should induce a problem but back off a few degrees and it's cured? Just like an on off/switch - "Problem/No Problem"
Answers on a postcard please !!!!! :nenau
Anyway, fuggit, I'm off green lanning up by Alton/Basingstoke this evening wi Mike (Dolly Rocket) and a few others so I'll let you know if it survives, or not.
Millard
Damaged throttle stop screw? or if it hits the end of the slide a damaged slide?
probably a step/indentation worn on the angled bit of the slide where the stop hits
bugger it, just ride it till it dies.
probably a step/indentation worn on the angled bit of the slide where the stop hits
Yep yer right Digg.
tried to rectify it but didn't make a lot of difference. Think I'll try a new slide.
http://i14.photobucket.com/albums/a340/drillam/Honda%20CRM250/DSC01787.jpg
http://i14.photobucket.com/albums/a340/drillam/Honda%20CRM250/DSC01792.jpg
http://i14.photobucket.com/albums/a340/drillam/Honda%20CRM250/DSC01794.jpg
Took it out to a horsey event wi the TRF on Sunday. Great day out on trails we wouldn't normaly be allowed on wi bikes. Did about 78-80 miles and it behaved itself well, so fairly pleased wi it. Just a wee bit o fettling and it'll be there.
bugger it, just ride it till it dies.
I'm wi you mate :D
:beerjug: Crms for ever! rraaahhh
Anyone want a wr400? i sold my crm to buy it thinking it would be a beast compared to the crm. Ive since decided all 4 stroke offroad bikes are for puffs.
Pint of premix for me landlord. :thumb
back your idle stop screw right out till you can't feel the slide touching it.
now what happens ?
.
got there in the end :D
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