Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: richardnlambert on August 01, 2022, 06:04:59 PM
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Hi all
I have a issue with number 1 cylinder not firing I have tried a number of thing listed below and now starting to think engine rather than ignition or fuel
The engine sounds good when warmed up but remove plug 1 and still sounds good no change bike tends to overheat after a run.
New coils leads and plugs
Took lead off plug no difference in engine running
Swapped number 1&4 over good spark
New carbs
Cleaned carbs a number of times
Checked valve clearance
Plug is black ( scooty carbon) all rest light brown
Compression check incorrect way throttle not open
1= 70
2-4 = 100
Compression check correct way
1 = 145
2 -4 = 125
Check temperature of manifold
1 = 60
2 -4 = 150 approximately
Used easy start direct into inlet manifold no difference
Any help ideas would be appreciated
Thanks
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Is number 1 sparking or just not firing when in ?
Compression is a tad low, should be around the 175 psi mark.
Have you done a leak test on the head to see if any valves are bent ?
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The spark plug sparks outside The compression test was weird as it was higher than the 3 other cylinders with throttle fully open but lower than the others when closed, not sure how to do a leak test
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The temp on the down pipes suggests that there is not enough fuel getting through. Are all the float heights right and were done in the correct way ?
To do a leak test, the head has to be removed .
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I adjusted the floats using clear tubes looks like the head has to come off then
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I would expect number 1 exhaust to get hotter if there is fuel, the black plug is interesting as it's obviously firing albeit not properly. Do you have another plug lead you could try before taking the head off? I'm thinking the spark could be failing under load.
When I first fired up my 400 before the restoration the compressions were on the low side but all four exhausts were red hot.
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To me this suggests the pilot circuit is suffering a blockage and needs to be looked at, the soot on the plug is not unusual in this situation, before you remove head check everything else again, compression reading is not too bad considering that cylinder is not up to temperature.