SOHC.co.uk Forums > CB350/400
My 1975 CB400F restoration project
Laverda Dave:
--- Quote from: Johnwebley on March 05, 2024, 08:52:11 AM ---While the carbs are off, worthwhile to check the float heights,
+1 on that suggestion. I don't know why but these carbs can be a bit of a nightmare especially if they have been messed with in the past. I have used Keyster kits in the past and it was those that caused all my issues together with sticking floats where the float pin had been very slightly bent by p/o's. Stick with the original brassware wherever possible even if you have to give it a good clean. And obviously whilst the carbs are off the bike give them a good going over and bench sync.
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K2-K6:
--- Quote from: ozzybud on March 05, 2024, 01:00:13 AM ---The P.O. of this bike said he put a re-jetting kit in. He said it included instructions to drill extra holes in the exhaust, Throw away the air cleaner cover and new Main Jets and likely messed with the factory needle Position. ( I cringed a lot when he told me of this) Why didn't Honda think of this?
I rode the bike prior to tearing it down just to do some test and tune and make sure the engine was solid.(about 100 miles) It ran great pulled hard and had equal compression in all 4 cylinders.The carbs did not require synchronization. Plugs 1,2,3 were dark tan #4 was light tan.
The only changes i have made to affect engine performance was install the repro exhaust.
Took it for a longer ride yesterday about 10 miles. ran great at first after 5 miles it started missing on some cylinders. when i got home # 1 was coldish.
removed the plugs 1,2,3 were black and sooty fouled or on there way to fouling.#4 was fine
I removed and cleaned the plugs. All of the idle mixture screws were out 4-5 turns? what? almost ready to fall out... lol Reset to 1.5 turns out.
Took it out today with similar results ran good a little longer.like 7 miles. removed the plugs and they looked similar.
I am assuming at this point that the P.O. removed the #75 jets for something larger. I ordered 4 OEM Used #75 jets and a gasket o-ring set.
I will Check out everything else when i get the carbs off.
Is there anything else I am missing? I spent a lot of time on my CB360 getting it to stop fouling plugs. It ended up being the Chinese needles were smaller diameter and a little bit shorter than oem.
Any suggestion would be appreciated.
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As already given in other posting, these are extremely sensitive to such small changes, volumes, jetting accuracy of manufactured parts etc.
Not over sensitive, just really accurately specified and built, resulting in very good running when all is in order. Fine tooth comb is the way to go through them to understand just whats in there and getting back on track, not dismissing even the smallest observation.
A thread here http://www.sohc.co.uk/index.php/topic,14609.0.html that looks at what the practical implications of jetting on them may be of interest.
ozzybud:
--- Quote from: McCabe-Thiele (Ted) on March 05, 2024, 09:15:52 AM ---Your photo had me confused (I'm easily confused) - is it a close up of the old silencer end?
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Yes it is the silencer end
Cb750r:
I chased my tail jetting my 750 for quite some time, what really frustrated me is a lot of carb tuning states to get the main jet sorted first and work your way down…
In my scenario to get it to run right wide open was too lean at idle and to get it to idle the main was super rich, I played with countless needle positions and float heights and in the end a bigger idle jet sorted things out.
I will second what others have said about non genuine brass, even in sport bikes I’ve jetted I try and avoid non genuine jets/needles.
Just another thought, where are you elevation wise? We have from sea level to fairly high base elevations in the pacific west coast to deal with, and small bikes have less hp to deal with jetting that’s off for your ‘base’ elevation. My snowmobile actually had a dial to lean out jetting as I climbed to keep it running optimally as I climbed. I’ve also had dirt bikes with ‘mild jetting’ changes from stock that are widely used elsewhere but would foul plugs at my elevation. Maybe your bike was ‘ok’ or slightly rich at sea level and you’re too high for it to run well now?
ozzybud:
--- Quote from: Cb750r on March 05, 2024, 03:04:26 PM ---I chased my tail jetting my 750 for quite some time, what really frustrated me is a lot of carb tuning states to get the main jet sorted first and work your way down…
In my scenario to get it to run right wide open was too lean at idle and to get it to idle the main was super rich, I played with countless needle positions and float heights and in the end a bigger idle jet sorted things out.
I will second what others have said about non genuine brass, even in sport bikes I’ve jetted I try and avoid non genuine jets/needles.
Just another thought, where are you elevation wise? We have from sea level to fairly high base elevations in the pacific west coast to deal with, and small bikes have less hp to deal with jetting that’s off for your ‘base’ elevation. My snowmobile actually had a dial to lean out jetting as I climbed to keep it running optimally as I climbed. I’ve also had dirt bikes with ‘mild jetting’ changes from stock that are widely used elsewhere but would foul plugs at my elevation. Maybe your bike was ‘ok’ or slightly rich at sea level and you’re too high for it to run well now?
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I am at or near sea level
Seattle Washington
My plan is to get everything back to stock settings and jet. #s then go from there. I have 4 OEM #75 jets on the way
After what I went through on my CB360 I am leary of using anything other Than OEM especially the needles.
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