More carb trouble x 4 - adventures in CB restoration

[bblass]

Good news! A little copper gasket sealant and my engine now longer seeps oil. Bad news! Now I have a carburetor that's not getting fuel and a cylinder that's not firing.

My number 4 carburetor is not getting fuel like the others. There is minimal in the bowl after turning on the petcock. I've checked the line and it's clear. I've checked the passage into the bowl and it's clear. I've replaced the pilot jet, main jet and synced the carb. Cylinder is making 180 compression, carb is pulling 20CmHg at idle just like the other 3.

If I spray carb cleaner or starter fluid into the intake of cylinder 4 it fires right up. This leads me to believe that my issue is the vacuum in the fuel line isn't strong enough to get fuel all the way into bowl 4. This strikes me as odd since bowl 3 is working fine and on the same t junction.

Internet research on similar problems has mostly lead to people having a short coil. I swapped mine and the boots. Same issue; it has to be the fuel.

Does anyone here have any experience with an issue similar to this one? I'm starting to think I should just replace all the fuel lines with clear vinyl and go from there. Thanks!

[yamahamer]

Have you checked the float setting? Sounds like the float is shutting off fuel too soon.

[bblass]

Have you checked the float setting? Sounds like the float is shutting off fuel too soon.

Yes, that was my first thought too. I set it to 26MM and even played with adjusting it further down. Rod that the floats are mounted on is smooth and burr free.

[01YZF6]

Is there an air fuel mixture screw for that  1 carb?

Also, not sure on that carb, but my float valve seat on one of mine was severely clogged, preventing fuel to paas through or allow the float needle to seat/lift properly.

Are you able to sync the carbs too?

[bblass]

There is an air fuel mixture screw. I've got it set at 1 turn out like the others and synced the carbs. It has to be either that the fuel doesn't have enough pressure to get to the fourth carb bowl or something with the float needle. I inspected the jet and it moved under compressed air but that doesn't necessarily mean much. I'll swap it with another carb tomorrow night and see if that's the culprit. Thanks for the lead!

[01YZF6]

Year and make of bike?

[bblass]

Year and make of bike?

1975 CB750K

[bblass]

Update, swapped the jets and floats on carbs 1&4. Now both are working fairly similarly but now cylinder two is low and 3 is running way hotter. Hoping a good sync will fix this

[IceCold4x4]

Just had a thought... Ate the floats taking in fuel? Not an uncommon problem. And would definitely change the actual float height even though they'd measure out the same...

[bblass]

Fuel is getting into the bowl. After syncing and fiddling with the carbs a little more 3 is running hot, 4 is running about 10 degrees cooler, 1 is a little behind 4 and 2 is still barely firing if at all. Rechecked the floats last night. Think I may go back to the stock jets on number 2 and see what that does.

[merc16]

Any updates ?

[bblass]

Yes, sorry. I committed the cardinal sin of internet forums and didn't post a resolution when I finally found one.

I took the carbs apart again and cleaned them again. Then I double checked everything as I was putting it back together. Honestly not sure what I had done different but it works well now.

The stock air box was too restrictive for the extra 100ccs, high compression pistons, head work and better exhaust. I had to add velocity stacks to the pods in order to get any midrange. It now runs great but cylinders 1 & 2 foul occasionally on startup. At some point I need to go down a size on the mains and it should correct the issue.

For now, it's a fun little round town bike and a great conversation starter. A few of us from the North Alabama Vintage Motorcycle Club page are riding our project bikes to Carrigans Thursday night @ 6:30. You should come join us.