Need some fuel mixture advice

[Half-Caf]

Hey all, as some of you may have seen, I've finally got my bike back on the road!
Now with a little bit of your help I can get it running like a top.

After I had finished playing around with the idle drop, my mixture screws were probably 3 or more full turns out. The bike ran but bogged down and sputtered if I was not accelerating. When I gave it a twist of throttle it would bog, actually dip the nose down and then it would take off like no other! The bike was one big, scary bull ride

I decided that I probably had my mixture screws too far out and tried the bike at 2 turns out. The result was much improved, but the issue was still there.
I then tried one and a half turns and I believe it improved again marginally, but not much.

The bike fires up and idles great. Initially it is right at 1k, but after it warms up it rests at 1.5k.
However, my fuel mixture isn't quite right and I'm not exactly sure if its running lean or rich.

The issue occurs at pretty much any speed and any rpm (stutters a bit at a steady pace, but loooves when you open up that throttle)

The new jets are 68 and 102 (what came with the rebuild kit I bought for my 750)
I didn't see any markings on the old jets, but they appeared to be the same size.


My bike is a dohc 750f with stock airbox, uni filter, and no-name headers with a slip-on exhaust.
By the way, the muffler doesn't sound like much more than an empty can. I will be repacking it this weekend and hoping that maybe it will help.

Thoughts?

[Hellbilly429]

have you done a plug chop on it to find out if it is running lean or rich?

Also, if you don't like that muffler it is easily swapped out, didn't like mine and it quickly got replaced with a $20 Thrush glasspack

[Lucky 1]

Quote:
"I didn't see any markings on the old jets, but they appeared to be the same size."

You cannot look at jets and tell if they are the same size. Impossible.
If you have to use a magnifying glass.
If there really is no numbers on the jets they may have been drilled and the numbers removed.

Only make one change at a time.

If it was in my shop the first thing I would do is find out what size
the stock main jet and stock idle jet are supposed to be.


What is the year?
What size?
What kind of intake?
When you get the new exhaust tell us what it is.
A photo sure would help too.

1980 CB750F VB42B 15.5 FLOAT 68/98 1-1/2 mixture  STOCK SPECIFICATIONS

Twin sequentially functioning main jets.

Try to stay on one thread instead of jumping all around.

[Lucky 1]

See that plug next to the main jet?
See if that plug pops out or screws out.
That must be the other main jet.

[shinyribs]

So it runs good at WOT?...sounds perfect to me.

[Half-Caf]

Well, thanks for a couple of useful tips, but I just realized I made a pretty rookie mistake
The stock jet sizes ARE 68 and 102, but it turns out that the 68 is the primary and the 102 is the secondary...
Only if someone could have pointed this out to me a long time ago:

Half-Caf wrote

TOOLS1 wrote

The jets look like they are in the wrong holes. Could, you have switched them?

I believe I placed them as according to the rebuild guide. Can anyone confirm that?

I'm guessing that should help a bit

[Half-Caf]

But perhaps my greatest mistake was to question TOOLS!
Any mods can feel free to nuke this thread unless they would rather it remain as a public shaming to my treachery.

[JonnyNighthawk]

So the primary and secondary in your pic is backwards, correct? I know this is old but I'm new here and started cleaning my carbs today on an 82 Honda Nighthawk 750 today and got the 68 and 102 jets mixed up and not sure which goes where... The 102 goes in the same tube the carb slide needle goes in or vice versa like shown in the pic?

[TOOLS1]

You have a good eye. I believe you are right and those are backwards.
TOOLS

[JonnyNighthawk]

Sweet! Thanks!

[JonnyNighthawk]

Got the carbs back on. What a pita. Lol. Can someone tell me what this hose goes to if anything?

[JonnyNighthawk]

Goes through this bracket.