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77 cb750a isnt getting fuel on cyl #4

Paradox1559

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Hello, I'm a new member/owner, and I love this bike. Its super clean and only has 45k on a single owner. However my #4 cyl isn't getting fuel, but the carb is.

I have a sinking feeling I need to pull the carbs for cleaning, but I would like some advice first.

Thanks in advance
-rich
 
It would seem to be a small brass nipple in the air passage. It has a lot of pressure behind it if I try to spray carb cleaner through the passage. The hole is very small, how can I clean it?
 
Most spray carb cleaner does very little by itself. Carb clean and compressed air are the only way to clean without damaging jets. The best way is to remove the carbs so you can remove the jets and emulsion tube for proper cleaning.
 
Wohoo its running pretty good, however cyl#4 is running 10 degrees cooler than the others. And there is a slight hesitation at start off, with a slight amount of sputtering. I'm probably going to run it with some seafoam for a bit, so she can clear her throat. Then i'll do some fine tuning.
 
Nope, those are air jets. The pilot is inside the fuel bowl. As carb sits on the bike the higher smaller OD long brass jet between the float sections. NOT the main jet which sits lower in the fuel.

Can be the accelerator pump discharge hole on that one carb affected too. The others working but one not. With fuel in the bowls you work the throttle and the same fuel stream must squirt out of all 4 of the holes into the carb bores with the choke open. The discharge port is likely that stub that sticks up that the choke plate almost hits at fully closed. It has a hole facing forward that you can't see looking into back of carb.

The pilot appears to be a #35, they can be carefully opened up like the #38 or #40 these engines commonly use, with a piece of guitar 'E' string wire, the smallest wire one uses. The wire is about the size of that hole or around .013". You're putting steel wire into a softer brass jet, go about it in a haphazard way and you can scrap the jet but be careful and it's fine.
 
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If needed Jets R us makes different press in pilot jets for these carbs. Regardless what people say you can replace these press in pilot jets. I use a small pliers, you just have to work them slowly and they will come out, you just gotta use some common sense and a little twisting while pulling. Most of the time they come out pretty easy. I have removed them often on these style of carbs, never had an issue with one not coming out. The press in with little force, I have a small piece of hardwood that I put on the jet and use a very small hammer and lightly tap till they are in.

Yes the accel pump will cause a big stumble on these and its hard to get the accel pump circuit to bleed all the air out. I normally do it on the bench before mounting it on the bike so you dont flood the engine. You have to keep the accel pump float bowl full and keep opening the throttle till it squirts.

I suspect you still have a pilot jet partially restricted if you still have a little bit of a miss at idle and its running a bit cooler. The pilot jet causes the most issues because they are the easiest to plug and the hardest to remove and clean well.
 
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