The International CBX Owners Association

Hi Guys
I'm still struggling to get my bike to run right. When cold and warming up, everything is OK. As soon as I put some miles on it, the idle becomes erratic and the engine sounds noisy with knocking from the primary chain and clattery top end. Once cooled down, everything sounds quiet and smooth again.

My question is, if carbs were the issue, would the idle be poor from cold as well?

Out on the road the bike rides very well, pulls smoothly and goes really well for about 5 miles then starts feeling harsh and wont idle smoothly. I've check all my coil and plug connections. I haven't balanced the carbs yet as I'm not convinced this will make any difference.

Could the ignitors cause this problem. The bike has been off the road for 25 years.

Engine has been fully rebuilt.
Cheers
Martin

If you have an infra-red temp gauge point it at each header pipe when idling and see if they are the same temp. If one is much cooler than the others it may not be firing and that will cause rough running. From there you can trouble shoot.
If your engine has been rebuilt I assume the carbs have been disassembled including the pilot jets and everything thoroughly cleaned? If that's the case a carb sync is your next job. It really makes a difference. Ross

Hi Ross
Thanks for the info.
Yes, carbs were stripped an thoroughly cleaned. Started bike tonight and it idled perfectly for about 4 minutes then started missing. I am going to get carbs balanced anyway but not sure if I have an electrical issue.

Best Regards
Martin

I don't think you have a carb issue. The way you describe it, the problem starts when the motor/system warms up.
What changes?
Resistance in wiring changes with temperature.
It could be your coils, which are bad and fail when the temps increase.
My guess is, it is an electrical issue.

robsgreen wrote:Hi Ross
Thanks for the info.
Yes, carbs were stripped an thoroughly cleaned. Started bike tonight and it idled perfectly for about 4 minutes then started missing. I am going to get carbs balanced anyway but not sure if I have an electrical issue.

Best Regards
Martin

Is this running off an aux bottle, or your gas tank? If the latter, did you clean it? Are you running a fuel filter? If so, is it clean, and flowing properly?

Hi Guys
Bike is running off gas tank through a brand new honda fuel tap. Ive checked all connections on my new coils, checked the advance retard assembly, ran it with the fuel cap off to see if there was a blockage. pulled every electrical connection and cleaned and re-assembled. I feel it is electrical,timing perhaps? the guy who owned the bike before, removed all three triggers on the pulsar unit. Whilst I can set up one accurately by the F mark on the crank, I cannot do the other two other than to put them back where the witness marks are on the back plate. Not ideal but I think I need a TDC plug gauge to accurately set the other two up. bike would then need strobing to set the timing spot on. Even still, Im not convinced this is the issue. I will fit an inline filter as well just to make sure fuels is not been contaminated. Bike rides great to start with and then becomes hot and bothered. Its really frustrating but Im running out of ideas. cheers Martin

Are all the choke plates opening completely? One of the float valves not sealing completely? Hopefully, Dave or Mike might have some good input.

So you did not clean the tank, did not install a filter with your cleaned carbs? If that's the case I'd complete that project before you imagine you have some new problem on top of the old one.

The tank looked very clean and as the Fuel Tap has a filter built in I presumed this would be OK? I have no carb leak issues. If it was contaminated fuel / blockages, wouldn't this show up all the time? I take your point though and maybe I should clean it out to make sure. Plugs by the way are showing normal running coloring. I expected one of them to give a pointer to whats going on but they all look the same. I have booked a classic Japanese bike specialist mechanic to come and balance the carbs and set up the timing. He might be able to shed some light on the problem hopefully. I run the bike on unleaded super and did add Redex fuel treatment.

My bet is still on a bad coil or igniter

I am leaning that way.Ive still got the original coils which I changed because they were cracked but it may be worth swapping them over to see if there is any difference. I looked at the ignitors and they are leaking but I guess that means nothing. They will be next on the list after Ive had the mechanic over ( unless he pin points it) I'll let you know what happens. . I also drained off two of the carbs into a clear plastic container and also turned the fuel on and ran a pint of fuel out just to see if any crap came out. Thought that if there was sediment in there it would show up but fuel was absolutely crystal clear. Thanks for all your help

Hi Guys

Just an up-date on my rough running CBX

Put my original coils on to see if this made any difference and solved the problem of the rough running. I only changed them as the bodies had cracks in them but its proved that one of the new coils is faulty. New better quality coils are on the way as I've been told that I should change them if there are cracks in the bodies.

In Addition

I had set up my carbs up during their rebuild as per the manual and was very sure I had a got a them pretty close to balanced as the bike ran and idled well. I was convinced there would not be much improvement if I had them balanced with vaccum gauges. How wrong I was!

Classic Bike mechanic came and fitted up the gauges and the carbs readings were all over the place. It was fantastic listening to the engine change as he dialed them in. The engine has gone super quiet, no rattles from the clutch and best of all, the throttle response is now really crisp. No substitute for proper balancing.

Bike than sounds and runs brilliantly

Cheers

martin

Martin: Glad you got it sorted and thank for the testimonial about the virtues of gauge syncing the carbs. You saw first-hand exactly why to do it.

Dave

Thanks for the follow-up, Martin.
Now you get to enjoy your work.