What did I do wrong? 79 CB750F carbs super lean

[Whozaa]

Hello all,

I'm new to this forum so let me give you guys a little background. I had a 78 GL1000 a couple years ago. I bought it not running and nursed it back to health. (should never have sold it ) Well about a month ago I had a hankering to tinker again, so I found myself a 79 CB750F that I just couldn't pass up. I heard it run before I bought it, but it was with a different set of carbs. It seems to have a solid motor, so I'm not worrying about that yet. The carbs however, look like they've had the hell beat out of them. I ended up buying another dead set of carbs off ebay and basically made one good set out of the two bad ones. I followed the same process that worked for my Goldwing, meticulously pulling apart every single piece, changed every o-ring, seal and diaphragm, reset the float levels, blowing out each passage, etc.

So I get the carbs back together and back on the bike. Right away they leaked out of the float bowl bleeders, but I tracked that down to the float needle/seats. I figured some dirt must have gotten in the lines, so I flushed everything out which fixed the bleeding. I fired up the bike, but it seems to run extremely lean. It will only run with full choke. I can leave the choke off if I keep reving it. The problem seems to be common to all 4 carbs, which makes me think I did something wrong in the rebuild.

So really I have 2 questions:

1) Should I expect the bike to run this lean with stock jets. It has a leaky 4-1 exhaust and no airbox. I have the airbox, but haven't reinstalled it yet. I know its not going to run perfect like this, but I didn't expect to need the full choke just to keep it going.

2) When I pulled out the mixture screws, they were missing their flat washers. I couldn't figure out how to reinstall them correctly. The service manual and microfiche aren't very clear. So right now they go like this: o-ring on the screw first, then flat washer, then spring. Is this right? Would it affect my issue?


Wow! This post really rambled! Well thanks in advance to anyone who can help me out.

-Whozaa

[Re-run]

Well actually your carbs require a vacuum to operate correctly, vacuum being supplied by using the choke.
I suspect that if you put in a filter and fit the airbox, you will have better results.

[Whozaa]

Yeah, I thought about that. I just didn't think it would be THAT drastic of an effect. My 'wing never behaved like that. I know its a different bike, but the carbs were very similar. I'm going to try putting the airbox on tomorrow night and see if it helps. I don't have a filter for it though.

[Re-run]

Well your 78 carbs are probably a lot like the 78cb carbs and as such, the airbox is not vital to operation.
you should probably get a filter though as without it, you might not have much better results.

[woodsrider250]

Rerun is right....The 79 CV's NEED the box.

[Whozaa]

Hey thanks to both you guys. I'm going to put the air box back on. I'm working on getting a filter, but in the mean time I've noticed that I'm missing all four of the boot clamps and the filter wavy spring thingy! The air box was off when I bought it and I didn't think to look at it that closely.

Until then, any ideas about the proper mixture screw stackup?

[Re-run]

I am not sure what the stock settings would be, the manual would have that but I would concentrate on getting the carb boots or at least trying to make some with some radiator tubing or something similar first and getting a filter of some sort.