Help MC22 loud thunk when starting

check and clean connections through from the starter motor, solenoid and battery - also check your earth strap

 

So new battery worked for about two days (started the bike about five or six times over those two days). Had to bump start it just now and it's turning over, then just runs out of juice. No more thunking (yet), just doesn't quite have enough to get it started?

Strangely it was 14.95v idling (about 1.8 to 2k rpm), dropped to 14.8v at 5k rpm, and dropped to about 13.6v when off (will try to get another reading later once it's stabilised a bit more).

Could it be that the reg/rec isn't working properly and it's killing the battery with that output voltage?

 

Absolutely, overcharging a battery will boil it and it will not hold a charge. Anything above 14.5-15v is suspect and you may start popping globes, fuses and worse, computers or instruments.

Replace your reg/rec with a good unit, I would suggest an FH020AA kit from roadstercycle.

 

Hello,
My 1990 MC22 does exactly the same thing. Sometimes when the engine is cold it turns over a couple of turns and then a CLUNK, he starter gets stuck. I do not know the cause. However, when this happens, I put the bike in 2nd gear and push it back and forth to get the engine to turn a little. This movement somehow disengages the starter gear from the engine. After this procedure the starter normally turns fine. If not, I repeat the procedure until it does. This behavior has never showed up when the engine is warm.

 

that sounds like a flat spot on the starter motor armature contacts - I had a van which sometimes needed a push to get the starter motor past the flat spot - new brushes in the starter motor fixed the issue

 

I think I'm gonna go insane.

Finally had another chance to have a look at it and I'm nowhere better - might be worse now in fact! I installed the new reg/rec and charged up the battery and it's doing this now:


I pulled the starter out and it seemed to spin freely (both directly hooked up to the old battery and connected where it should be on the bike, just not against the flywheel(?) ), but when I put it back it just sounded like it didn't have enough power to turn it over properly. I have another bike (VTR250) that shares the same battery so I played musical chairs with the three batteries and all three start the VTR but not the CBR. I've also put in a new starter solenoid and jumped the two pins and it's still the same.

I also can't seem to push start it anymore; had it in 4th - 6th and it would just gurgle while I was running alongside it but the second I stopped it would die.

Beginning to worry that it's something in the engine...

 

Sorry @GreyImport, forgot to try that. Have just done so now and there's no fuel there; did it in like maybe fourth gear and walked it up and down the drive a few times. Stuck my finger in there too and it was dry as a bone.

 

looks/sounds to me like the starter is pulling to many amps...If you can, check the battery voltage sag when you try to start with a multi-meter...it could be the starter motor is under a lot of weight/torque and drawing big amps, the starter is dying and pulling excess amps or the battery's aren't rated high enough.....

 

@GreyImport I'll give the trimming a go when I get a chance - I'll have to figure out how to get a bit more clearance with the leads as it's pretty crammed in there, guessing I'll need to pull the airbox and move the radiator or something. Spark plugs looked a bit darker than when I last saw them so I guess it's running rich, should I throw a new set in for good measure?

@Wozza, I've put a multimeter on and tried to start it if that's what you're meaning by voltage sag? If not let me know what I'm looking for so I can get it on video.


@Murdo I tried to start it hooked up to my car (while it was off), but still the same sort of thing unfortunately.

 

I can bump start it now but it won't idle, only if I rev the cahoots out of it. It could just be that I bumped the throttle stop screw when I was removing the carbs to get to the starter, or I need to use the choke? 28 degrees + push starting + pudgy software developer physique means that I'll give it another go tonight because damn that's tiring. But that does at least mean that it's not completely locked up? Might have to pull the starter out again and take it to an auto-electrician to test for me because god knows I have no idea what I'm doing.

 

yeah thats what I meant...Thats a big sag Id almost say the batt has a bad cell or 2, but as you have tried other batts then id say the starter maybe the issue...normally Id also try with the plugs out/coils unplugged (and any other non accentual electrical systems) and see if that helps, then try and turn the motor over (plugs out)by hand either by a socket on the crank or by spinning the back wheel in a high gear to make sure the motor isnt seized or hydo locked....The reason the bike is now a pig to start is with that low a voltage at crank the spark is getting snuffed out or isnt even firing so it just flooding with unburnt fuel.....

 

Be careful with starting without coils/plugs connected, there is a posibility of damaging the TCI unit

 

Hit the kill switch

 

I've lost track at this stage. Is the bike still running?
If not, I might be way out here, and don't want to lead anyone astray, but is there any chance a main bearing is dry or spun, and when it is heated up by rapid rotation of the journal, closes the clearances and acts like a band brake and clamps down on the crank? I've seen amps climb through the roof because of lube failures in bearings in other machinery. the result is having the bearings heat up to the point the thermo-couples would shut it down. If there were no safe guards, the bearing would heat up, burn what oil was in the wedge, and temps climb until the distortion in the bearings created such interference that the machine would seize.
In a bike, we can't see the black / scorched oil discharging, there's no thermo couples, and we can't read bearing temperatures with an infra red thermometer. However, I'd bet if the crank was stopped in a hurry it would give a thud.

 

I like where @Bab is at, and I thought failed brushes and contacts in the start could be an issue (turns easy unweighted, lacks power when loaded). Spark plugs out and in gear, you should be able to turn the motor over fairly easily by the back wheel. If it is stiff to turn, then it'll be as bab said.