SOHC.co.uk Forums > CB500/550
Black smoke and hanging idle after a full rebuild
thomaspigeon:
@robvangulik I didn’t try this yet.
@k2-k6 and @fogrider I started to reset the carbs after work as all this news got me really excited to try. I didn’t have the time to finish but hopefully I won’t get out of work tomorrow.
I’ll probably try a idle jet at 40 just to see
Keep you updated
thomaspigeon:
Hey guys,
So good news, no more smoke and no more hanging idle! Now the midrange were weak so I lifted the needle to 3rd position from top. This fixed the problem quite well.
Low revs are struggling to pick up so I believe I’ll need to play with the mixing screw (current idle jet at 40 and I’m still 1.5 turn out). But will do this tomorrow evening if I have the time.
Also from 3/4 to full throttle its really not picking up. I suppose I’ll need to change the main jet to 100 to try maybe 105 but I don’t want to cut corners.
It’s the first time I started to get some sensations on the bike and felt like it’s actually running! I could almost take it out like this. But I’ll take the time to have it running a bit better before I go for an actual ride.
Thanks a lot for your help @k2-k6 and @fogrider! Keep you updated
K2-K6:
Good progress, and now a clear picture of individual elements to work on.
Yes to change the initial pickup in adjustment of airscrew inwards to then try like that. If you found that you end up below about 3/4 turn out from closed it would indicate that a small step up in size of idle jet would be ok. See where you get to first with this one though, and it will usually look different to with a std airbox so a little unconventional setup is to be expected in making it work.
Something that seems to help is to use R Plugs as well as R caps and set plug gaps to their absolute minimum in manual specification. It's beneficial in weaker mixture running and helps prevent the engine dropping into a flat spot at mixture margin. If you want to try that, then use NGK R 8 rated plug. It also (#8) reduces the risk of the plug tip getting too hot and being compromised.
deltarider:
--- Quote from: K2-K6 on June 19, 2021, 10:04:50 AM ---... and set plug gaps to their absolute minimum in manual specification...
--- End quote ---
This ^!!
Recently I have bought a set of 4 DR7EA plugs (I run silicone non resistor caps). When checked, I was glad to see, they were already set to the minimum by NGK: 0,6mm. Whereas the D7EA plugs, that I've bought years ago and that are still new in their boxes (for if I ever return to resistor caps), are gapped a little wider. Coincidence?
thomaspigeon:
hey,
So I went from #38 idle jet to #42 as the idle was hanging a bit and I couldn't close more the mixing screw.
I didn't have the time to play too much with it but for now it looks promising. At 1.5 turn out it's running a bit lean/ hanging idle and at 1 turn I have some black smoke but no hanging. So the right balance is in between this 2.
It feels like full throttle is not very powerful, I'm still at #100 on the main jet. But I think 105 is a bit too much as I already have some black smoke. I never had a running CB550 in the past so I don't know how powerful those engines should be.
I might have some DR8EA plugs kicking around but no R plug caps. @deltarider are you saying that I can run regular caps with R plugs?
Also last thing, engine seems a bit noisy and also jumpy when decelerating - accelerating. Like the cam chain is a bit loose. My tensioner screw doesn't seem to function properly (it doesn't do the spring return effect). Some people are doing the cam chain tensioning while the engine is running, is that a good idea?
Thanks for your help, it's getting there!
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