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Post by almar on Feb 16, 2024 15:30:01 GMT
My 1980 CB400 has developed a problem.
The right hand cylinder, (looking forward over the bars), does not run properly. On tickover it does not run. In the worshop reving the engine still doesn’t always make it fire up. Running on the road once the revs top 4k it fires and continues to run until I allow the revs to drop below 4k when it either cuts out or “hunts”.
There appears to an adequate spark on tickover and fuel is reaching the carbs.
Has anyone experienced this or can offer advice?🤔
All suggestions gratefully received!
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Post by johnfcbn44dx on Feb 16, 2024 17:50:05 GMT
Suggestions
Check spark plug cap, cut 3mm of the end of the HT lead and screw the cap back in, if the cap looks ok
Renew the spark plug.
Check the HT lead back to the coil, especially where it enters the coil, any splits, put a dab of silicon, and wrap with PTFE thread tap whilst it is still tacky.
Ensure no corrosion at the coil mounting / bolts / earth against frame.
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Post by almar on Feb 16, 2024 18:58:41 GMT
Thanks for the quick reply and suggestions. I was proposing to renew plugs and caps as they may still be the original 43yr old units but will also check the HT leads and coil etc.
Will order the plugs, caps and some new HT leads ASAP.
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Post by CTB on Feb 16, 2024 19:20:11 GMT
You can’t remove the leads from the coil unfortunately
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Post by almar on Feb 17, 2024 8:18:55 GMT
Thanks for that. It brings two things to mind.
1. Does the coil and lead come as a single unit?
2. The fact that, with the spark plug out of the engine and lying on the block, there is a good spark indicate that it may be more likely a fuel problem.
There is fuel to the carb so could it be a blocked jet?
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Post by duffer on Feb 17, 2024 9:00:14 GMT
A visible spark is not an indication of a good electrical system. Keep checking and swaping stuff.
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Post by almar on Feb 17, 2024 13:07:01 GMT
Thanks, that’s what I intend to do.
If, after replacing the ignition system, it still has the same problem I fear it will be take the carbs to a specialist as I don’t feel competent to strip and reassemble them. I will have them completely refurbished while they are out. To try to avoid future problems.
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Post by johnfcbn44dx on Feb 17, 2024 15:17:49 GMT
Thanks, that’s what I intend to do. If, after replacing the ignition system, it still has the same problem I fear it will be take the carbs to a specialist as I don’t feel competent to strip and reassemble them. I will have them completely refurbished while they are out. To try to avoid future problems. Could try chucking some Redex in the fuel, prior to any complexity.... How is the plug colour with the new plug? When it comes. |
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Post by buster on Feb 17, 2024 19:20:43 GMT
is anything obstructing the choke link mechanism in between the carburettors? it could be worth checking that the butterflies (at the rear of the carbs) are operating as they should
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Post by almar on Feb 19, 2024 16:39:17 GMT
Thanks again for the extra points. buster. Choke mechanism/butterflies both moving freely. johnfcbn44dx will try the Redex or equivalent when I can get it on the road again. Going away for a couple of weeks starting tomorrow then will order new plugs , caps and will probably renew the coils also. Getting the ignition system good, then moving onto the carbs. Plug colour, when coming back from a run on both cylinders, is good. |
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Post by BritPete on Feb 19, 2024 17:19:03 GMT
Thanks again for the extra points. buster . Choke mechanism/butterflies both moving freely. johnfcbn44dx will try the Redex or equivalent when I can get it on the road again. Going away for a couple of weeks starting tomorrow then will order new plugs , caps and will probably renew the coils also. Getting the ignition system good, then moving onto the carbs. Plug colour, when coming back from a run on both cylinders, is good. I have a pattern coil from David Silvers on SME and works fine |
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Post by almar on Feb 21, 2024 8:00:34 GMT
Thank you for the info re replacement coils.
I use David Silver a fair bit for spares so will contact them on my return home.
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