CB 125 S Keihin carb factory settings.

J

jamesromeos

New Member
Finally getting back to my project. 1975 122mm CB 125s. I found a factory carb from the PO. He had installed a mikuni POS on it. my issue was the bike would not ever start on choke with the crap carb. It would run and Idle fine with the choke off, even on cold days. I got the factory keihin carb sent to me last week. on the right side there is a nearled nickel looking screw in the carb, and down to the left lower there is a brass screw that can be screwed in so far it is recessed. I cant get the bike to run other than a sputter at WOT. any detailed instructions on how to set the carb back to stock specs? pics would help/
Thanks in advance,

Jim
 
You need to read the factory service manual.
Literally step by step instruction of what you want.

Unless you have a pod.
Then just burn/crush the bike.
 
Keep spitting fuel out of whatever that brass hole is on the upper right. No info in factory manual
 

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"no info in factory manual"

Service manual, not owners manual.

Sounds to me like you need to adjust the valves, among other things.
 
Fuel does not leak due to valve train issues.
Fix one problem at a time and know that there are often more then one problem.

These bikes run like shit and don't like to start without a factory airbox and filter.
 
When an intake valve is tight, it hangs open.

When an intake valve is tight, it causes hard starting.

When an intake valve is tight, it hangs open.

When a piston rises on the compression stroke, the intake valve is supposed to be closed.

If the intake valve isnt closed all the way on the compression stroke, it can push fuel right out of the carb.

These engines are notorious for the valve clearance tightening. The reason I know this is because I've built almost a dozen of them. Regardless of whether or not it is pushing fuel out, which it most certainly can, you should adjust the valves.
 
You know what I strongly dislike about these forum's? The ignorant rude answers. I have a service manual, and i have a haynes manual, it tells me plenty about jetting, springs, needle valves, choke component's, floats, bowl's, o rings, spacers....the one thing I cant figure out is what that port does....hence my question on this forum. It seems if anyone knew what it exactly is, there would simply be posted an answer, not snide remarks.
 
jamesromeos said:
You know what I strongly dislike about these forum's? The ignorant rude answers. I have a service manual, and i have a haynes manual, it tells me plenty about jetting, springs, needle valves, choke component's, floats, bowl's, o rings, spacers....the one thing I cant figure out is what that port does....hence my question on this forum. It seems if anyone knew what it exactly is, there would simply be posted an answer, not snide remarks.
Click to expand...
It's an air bleed. When vacuum is present, it helps pull fuel through the main jet and into the engine. If your intake valve is tight, it can allow excess fuel to be pushed back out that hole
 
also, be sure not to tighten the carb any more than it takes to seal it up, or it will distort the housing, cause binding and leaks.
 
rotate the crank in the direction of engine operation, watch the intake rocker go down, come back up, and as it comes back up, keep pressure on the flywheel to keep it from overotating as it reaces top dead center. the instant the intake rocker becomes idle, start watching the timing marks, line them up, and you're there. The other option is to have someone watch the piston through the plug hole.

Make sure you are not at top dead center on the exhaust stroke. If you follow my instructions you'll get it.
 
jamesromeos said:
Small screwdriver in cylinder, find tdc?
Click to expand...
Do not stick a screwdriver in your cylinder. As explained above (read the posts carefully so I dont have to say it all again), there are TWO top dead centers for a 4 stroke engine, it is imperitive that you are on the compression stroke.
 
jamesromeos said:
Best way to adjust the valves? From what I see a tappet adjustment with feeler?
Click to expand...

The manual walks you though that too!

The push was to get you to look at what is what with the carbs, rather then just refer to the "thing" on the side.
Still have not confirmed if you are trying to run this bike sans filter.
 
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