• Enter the March CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!

Carbs spitting out fuel from intake when cranking over

DoorBuster2

CB750 Member
Messages
9
Reaction score
0
Points
1
Location
Rockford Illinois
Title basically says it all; I've been rebuilding my 1978 CB750A for the past three months, and I think it's finally in a shape to run. I rebuilt the carbs with the carb rebuild kits, and cleaned everything, and replaced all screws. I put it in, hopeful it would start, and as it was cranking over with choke fuel started to spit out of the carb intakes. Without choke, it doesn't spray as much, but with the choke or throttle fully opened it sprays a ton of fuel (fuel comes out where the airbox connects).

I don't think its a stuck fuel pin or float because the day prior I had reset the float to its correct height (something like 0.571 for the A model) and made sure everything was moving.

Any thoughts on what could be wrong?

*** I did submit this to another fourm, and then found this one instead that deals with SOHC 1978's in particular. Sorry about double posting
 
I'm 99.9% sure I did it right when I rebuilt it. I've been watching hackaweek and Peter Anderson for the rebuild process, and followed everything to a T. Could it be that the carbs are over flowing with fuel and leaking out the top into the main body?
 
Well of course it could be all 4 doing it is pretty odd.

HAS to be floats or something close associated if so.
 
So I just pulled the carbs out, had a little drainage bucket underneath and filled them up with fuel, to the point where should've overflown had they not been functioning properly. However, everything was fine with no leaking out the top, and the floats seamed to be hold the fuel.
 
I mentioned ethanol use in another post to you over this. If you simply move the rack around to knock the sticking needles loose they will appear to work perfect like you just found out. Until they sit long enough to then stick again.

Pull a bowl. If you see any red residue in there then rust from ethanol, it will go through and past any OEM Honda filter made and make the needles act up too. The problem will come and go to drive you mad.
 
Sorry I should have clarified, I pulled the bowls and they were clean. Needles were also clean. I then put them back on and filled them, with no leaking anywhere. I put the carbs back on the bike and cranked it over. Nothing. I sprayed some carb cleaner into it to get it started, made one or two little pops like it was trying but then continued to crank. I definitely have spark, could this still be a fuel delivery issue?

When I cranked it, I had the choke pulled and there was no fuel spraying out, so it looks like the issue was solved. Not sure how though. As her usual though, its refusing to start. Any suggestions on what to check? Thanks!
 
You likely wet fouled the plugs if there was that much fuel coming out. New plugs. Why it's only spitting a bit like wants to but won't. Pull plugs and if wet looking you are there.

You still haven't mentioned ethanol in fuel and the problem with needle sticking will likely continue if so. They miraculously begin to 'work right' until they do it again. The rust does not have to be there to do that.

Ethanol in fuel is the biggest screwover the corn states have ever given to the rest of us, it is garbage.
 
Then you are NOT getting fuel to engine, the only choice you have left. Not rocket science.

Having trouble with some posting.............like this.........

'...it sprays a ton of fuel...'

......referring to carbs earlier. Excess fuel like that does not simply disappear, if we assume the engine is properly timed then it should have inducted it to foul the plugs and what every engine on the planet does if I work on it. Meaning??????? amount of fuel overdescribed or something else?

Your posting is beginning to argue with itself and always problems there. Plugs being 'completely fine' argues there was no heavy fuel to ever begin with.

Not trying to start an argument but it is what it is. I have no trouble ever starting engines, they usually crank up instantly, often within 2 seconds.
 
How do I get fuel to the engine then? I have fuel in the carbs, they are full, I have vacuum sucking air in (stuck my hand on it and definitely was sucked in). I'm really at a loss of what could be impeding the flow.

By "spraying out", it was spraying the other direction. Out of the intakes, and presumably not into the engine. I get that. Now, when I go to crank it over with full choke I don't get any spraying out of the intakes. So its either going into the engine, and not doing anything or not going into the engine. My main question is why won't it go into the engine. I've rebuilt these carbs so many times and I know for a fact every single needle is 100% clean.

As for the fuel, I've only put in 83 with no ethanol, as its an option in my state (costs about 10 cents more), as I've heard about the fuel clogging it.
 
Last edited:
If the engine is viable and will start then you can shoot a 1 second shot of starting fluid into each intake and then close the chokes to trap it and try to start. It WILL try to pop and run long enough to eat the ether at least and not doing so screams something is wrong. Where is the IGNITION timing, NOT cam timing?

'83' fuel if the octane number is too low for that engine FYI.
 
Back
Top