SOHC.co.uk Forums > CB350/400
Bike over heating after 40 mile ride
Ken4004:
Had an issue with the bikes engine overheating after going up a step hill so when I stopped at traffic lights the bike died, left it 20 mins and I was able to ride the 20 miles home.
I suspect this is due to either the bikes engine overheating running a bit lean and or timing slightly out.
I did think the bike was running a little rich so because I had run out of adjustment on the air screw I decided to move the carb needle up one notch to lean it out but I think that was too much of an adjustment so will put them back to the middle position.
I have been able to do this without removing the carbs , a little fiddly but possible and means I can complete the task in under two hours for all four carbs which
Isn’t too bad.
So the plan is adjust needles
Reset air screw to standard position
Recheck points
Reset timing and strobe
And finally sync carbs
Probably would be an idea to check the valve clearance as well while I am at it.
Still running the bike in after engine rebuild so covered 280 miles, I think there is a bit of a flat spot on performance after 5000 revs so hopefully all the work about will improve this, I did consider changing the plugs because I am using NGK DR8ES plugs and the manual says DR8ES-L so not sure what difference that will make.
I did also check the ignition auto advance assembly for the points to see if that was sticking but it seemed to be OK last time I looked and using the strobe I could see it advancing when the revs increased.
Sorry about all the waffle probably just thinking allowed while typing this, I think another problem is that I am normally riding my Triumph 1050 so I might be confusing the sluggish throttle response with the fact that the performance of the 400 is so much lower so comparing 120 horses with 37 so I really need to ride another bike to make a good comparison.
That’s my day planned out unless the wife has a job for me !
Well you will be glad to here I finished waffling for one day !
TrickyMicky:
If you raise the needles upwards, that will make the mixture even richer. The needles are tapered, so the higher position admits more fuel earlier as you open the throttle.
Mikep328:
A flat spot beyond 5k RPM is essentially the opposite of the way these bikes typically act so clearly something is not as it should be. I'm curious about the "running out of adjustment' comment re the air screws. The normal adjustment range is fairly narrow and "running out of adjustment" sounds to me like the low speed circuit is clogged/otherwise not functioning properly.
As far as above 5k RPM, retarded ignition timing could cause poor high speed response. Retarded ignition will also cause overheating. A clogged muffler can cause both as well.
I agree that returning everything to the stock settings is the best way to start the troubleshooting process. Of course that assumes that the various components - ignition system/carbs are all adjusted to spec/working correctly. So that might require carb disassembly for a thorough cleaning/setup. Carb float level and fuel flow from the tank should be checked as well as the vent on the tank's cap. A clogged cap vent can cause a lack of power under high engine load - sometimes it can be bad enough where the engine will idle but not run well in local low-speed traffic.
FWIW re fuel flow - I once had an issue with an add-on aftermarket fuel filter causing a restriction. Removing that filter eliminated the problem. I no longer add any fuel filters; I rely on the ones that came OEM! Re that - pull the OEM filter from the tank and check its condition/replace if necessary.
In any case, good luck!!!
exvalvesetdabbler:
How was the fuel level in the tank? Was it on the verge of needing to be on reserve? And the strep hill altered how the fuel sits in the tank
Regards
Dave
Ken4004:
Hi Guys thanks for all the replies let’s answer the questions
I dropped the needle once notch because it was running I thought a bit rich so will move it back to the middle position so stock position
I believed I had run out of air screw adjustment because I adjusted it in small intervals and went out for a ride and I believed it was still running rich.
I had completely stripped the carbs and cleaned everything, fitted new carb kit all except the original needles because they looked good ( what was I thinking school boy error)
I took the carbs apart and fitted the new needles and put the cir clip one notch up to make it run leaner I should have really just fitted the new needles and then tried it.
I have read that regarded ignition can cause overheating but it did look good when I strobed it but will definitely recheck.
I have a pre filter on the tank so this can be removed and see what happens
The fuel cap vent being clogged is a good possibility as I have never checked this .
And finally I did have plenty of fuel in the take when I went up the hill the bike stopped when O was on the level just pulling up to the traffic lights, I also like the sound of the muffler being blocked as it did have quite a lot of loose rust in it which I thought I had cleaned out which is not easy to do.
Well you have given me a lot to think about but as I said first get it back to stock adjustment then carry on from there cheers guys I keep you updated regards Ken
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