Honda CM250 Starter Clutch Issue | GTAMotorcycle.com

Honda CM250 Starter Clutch Issue

mistersouthpaw

mistersouthpaw

Well-known member
Hey everyone, picked up an '82 CM250 for the girlfriend to learn to ride on. Thing was in rough shape but i've got it running well now, however, I am unsure what is causing the issue that I am having with the starter on this bike. After adjusting the valves and complete carb overhaul and airbox cleanout it runs great (once its running) but when starting the bike it will run like it hasn't been started in a decade, barely idle with full choke, and die several times until it makes this goose honk noise and then it will start and run great. As soon as it makes the goose honk it will run perfectly fine with no choke after just previously being completely unable to run without full choke spewing white/blue smoke. I just pulled the flywheel and replaced the springs,caps and rollers - still having the same issue. I am stumped now and hoping for some insight as to what I need to fix to make this start a little easier for her (shes new). I have attached a video showing the goose honk noise it makes lol - best way I could describe it.

photos.app.goo.gl

New video by Brendan Lee

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Thanks in advance
 
That was my first thought, starter hanging up. Although it sounds more like an intake sound and blue smoke indicates raw unburnt fuel, have you checked the air intake? CV carb vacuum sound?

... a cv carb is absolutely capable of making that sound.
 
I cleaned out the airbox cleaned and oiled the filter all is good inside there, when I rebuilt the carb today it felt pretty soft (compared to my slide) when I was pushing the slide up. I think you may be on to something, but also - I do believe the starter is hanging up
 
There should be a vacuum hose on the intake very close to the cylinder head, that controls the height of the carburetor slide, pull off the hose and suck on it, that should draw the slide up and might even make that noise when it does. Another thing to watch for is plugged vent holes, anywhere bugs have tried to build a nest inside a small air intake opening. I'm thinking you have a vacuum or carb slide restriction rather then a leak, where the vacuum has to be high enough to finally draw the slide up. Maybe remove the air filter boots completely and observe the movement of the carb slides when you are starting it, or get down there close enough to hear where it's coming from, or even just put your hand on the carb and feel for a vibration or change in sound from having your hand on it.
If you are really lucky the starter might be hanging because of a carb issue.

Best luck sorting it out and let us know what it turns out to be.
 
Hmm yea I'm not seeing any intake hose on this carb - the carb is a keihin with a piston style slide.. as for vents I pulled the airbox and cleaned the crank breather vent and the drain tubes on the air box but I'm not seeing any hose blockage
 
thats actually a very nice setup, single carb is vacuum operated from somewhere, you have an additional fuel pump circuit on there, that's the thing below the throttle linkage and probably stops it from running too lean on deceleration. If there was any problems in it they should have shown up in the bottom of the float bowl first. ... if you cleaned it once and it ingests more dirt you will need to clean it again.
 
That carb is capable of making the honk sound but is that the source of the problem?
twin cylinder motor on single carb.
... compression test? that might show something.
 
Yea the additional fuel pump was in good shape, I took it apart and checked out the diaphragm all looked good.. the carbs were pretty clean overall, just the pilot jet was clogged no real issues that I could see. I have since put a filter on the fuel line as a precaution (tank is nasty but was sealed). I am just not sure where this carb gets its vacuum from it doesnt seem as if there are any blockages
 
I havent done a compression test - ill get a tester later today but it seems odd that it would run great once running, ive put almost 200km on the bike in the last two days and it feels smooth revs up well and will giddy up if you get on it (lol) with a responsive throttle.. it really just seems as if there is an issue in the starting system somewhere
 
FWIW, my wife's Mazda6 V6 makes this exact sound periodically. It's a known problem where the starter-drive hangs up momentarily and the sprag clutch is overdriven backwards. It's caused by clutch dust contaminating the drive making it sticky and slow to retract.

I think you're going to find the problem is still in the starter clutch. Is everything in there lubricated well? What oil are you running?
 
Thats what it sounds like to me which is why I replaced the caps springs and rollers, I also noticed some wearing on the the starter gear but put it back into service after looking at the cost of a new one. I am running motul 3000 10w40. When I reinstalled the starter gear I put some motor oil around the starter gear.

My starter gear had the same wearing as this one - as did every other used gear that I saw on ebay - s-l1600 which gave me confidence because the wearing on the ones on ebay were worse than mine and the part is roughly a quarter of what I spent on the bike

Also the starter motor tends to keep whirring a bit after the bike is running
 
mistersouthpaw said:
Hey everyone, picked up an '82 CM250 for the girlfriend to learn to ride on. Thing was in rough shape but i've got it running well now, however, I am unsure what is causing the issue that I am having with the starter on this bike. After adjusting the valves and complete carb overhaul and airbox cleanout it runs great (once its running) but when starting the bike it will run like it hasn't been started in a decade, barely idle with full choke, and die several times until it makes this goose honk noise and then it will start and run great. As soon as it makes the goose honk it will run perfectly fine with no choke after just previously being completely unable to run without full choke spewing white/blue smoke. I just pulled the flywheel and replaced the springs,caps and rollers - still having the same issue. I am stumped now and hoping for some insight as to what I need to fix to make this start a little easier for her (shes new). I have attached a video showing the goose honk noise it makes lol - best way I could describe it.

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Thanks in advance
Click to expand...

Refer to this link, page 177:

https://ia801909.us.archive.org/30/...l-Nighthawk-78-a-03-Service-Manual-Clymer.pdf

I have the same bike and had the same issue. Your starter-drive is not disengaging properly and is likely dragging the motor. You can solve the problem by taking off the left cover and doing a bit of lubrication with some oil and white grease. If I recall correctly this is a bit tricky. You can actually order a new assembly on ebay. As long as the bike starts I wouldn't worry too much, but I believe I had a couple of broken springs or something in the drive (been a couple of years since did this job). BTW, I installed a kick start assembly from a CM200 Twinstar, just got a machine shop to drill out the right side cover for the shaft and seal. Works like a charm and kids love the kick start look.

As for the white smoke, that is normal for the Honda upright twins with a Keihin carb. Basically you've got a bike that has not been run much and when it is cold there will be oil seepage past the rings. They should seal once the bike heats up, and the more you ride it the less you will have the problem as the rings reseat themselves. From a start before tuning, the carb should be two full turns out from seated. After the engine has been run to hot, you should tune the carb to max RPM then adjust the idle accordingly. The carbs on these bikes are temperamental and the slide is sensitive to dirt. Disassembling and cleaning it is a very good idea because if there is dirt in the slide the bike will not run properly. Also, on the right side of the carb there is a vacuum hose. Be absolutely sure it is clean, unkinked and unobstructed or again, you will have problems.
 
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Just to clarify I have lubed up the 38T starter gear sprocket and still had no luck.. you think I should just go ahead and remove the starter and give that some grease? Also this carb has no vacuum hoses on it - just had the fuel hose.. I have searched and see no nipples for a hose where is your vacuum hose?

Edit - ill just leave the starter for a bit and see if it causes any problems but where is your vacuum hose located? I'm either missing one entirely or something
 
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mistersouthpaw said:
Just to clarify I have lubed up the 38T starter gear sprocket and still had no luck.. you think I should just go ahead and remove the starter and give that some grease? Also this carb has no vacuum hoses on it - just had the fuel hose.. I have searched and see no nipples for a hose where is your vacuum hose?

Edit - ill just leave the starter for a bit and see if it causes any problems but where is your vacuum hose located? I'm either missing one entirely or something
Click to expand...

Yeah, if you've already lubed it and all you get is the noise you can disassemble the actual starter and try lubing it or just get a new one.

As for the vacuum hose, I was befuddled because it didn't appear in any of the diagrams of the Keihin carb. I only remembered it because I have one on my Harley. Couldn't understand why 400km after each carb cleaning the bike would sputter under load, and when I opened up the carb it was full of fine dust. Here's where it is:

PICT0903.jpg
 
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