CARB/fuel symptoms

[jlew]

hello all, wish I was riding

1980 CB750C DOHC
Stock Airbox, V&H 4-1

had some major idle issues after this winter so I pulled the carb bank and started on cleaning them up.
I broke the carbs down to the bank (didnt split) and started methodically inspecting/cleaning/replacing.

soaked the bank in pinesol for 2 days, grabbed some tooth brushes and went to town.
cleaned out all passages/ports with a bunch of random width wires and a jewelers magnifiying eyepiece and blew copious amounts of air all over under and in.

polished the float seats till they were mirrored, chem dipped all the other metal parts (with mouse sander taped to can) and scrubbed them clean.

jets must've been replaced previous owner (which was a decade ago) but they had quite a bit of shine to them still, barely any corrosion. jets are STOCK size (i think 102/65). (new rubber plugs on the slow jets)

set air screw to 1 turn out (maybe 1.5 turns?) did a bench sync, replaced all rubber parts (air cutoff, diaphrams, orings)

all in all a succesful 'rebuild' (not a full rebuild cuz i didnt break the bank but close enough).

popped the carbs back on (that was by far the most difficult part, getting the airbox boots to seat).

so I go to fire up the bike and barely hit the start button and it fires up and purrrrrrrrrrs. had to adjust the idle a bit but went out riding and i'm getting an odd 'bog/studder' when I roll on the throttle. its great at lower speeds and ok if i gently roll the throttle but really giving it a twist bogs down.

any ideas from the collective good? I have no qualms tearing them apart again, it was actually quite fun and I bet i can pull em, take em apart and have em back on the bike now in an hour or 2.

 

[Rich Ard]

Did you sync them with a vacuum gauge?

 

[jlew]

That would be a negative ghost rider, just a bench sync.
I already picked up 4 gauges this morning on my way into work and will hopefully get it hooked up tonight and will post the results.

but correct me please, I have always been under the impression that sync issues will be more readily apparent at idle then when on throttle, and i've got a smooth idle; but my mechanics exposure is from growing up on a farm wrenching on tractors. apples and oranges right?

2nd gear twist it hard it takes off quick, when rpms shoot up it starts to bog, then idles down slowly.
but i'll get the guages up on it hopefully today and go from there.

 

[Rich Ard]

Always good to start with a baseline - and it may be that you'll be surprised at further pep when they're in sync

 

[mechdesign2k4]

Bench synch gets u close. Vacuum synch must be done, it helps in all ranges not just idle. A few things scare me about your cleaning process. Carbs must be torn down completely. Use carb dip instead of pinesol, blow out with compressed air after. Replace all orings inside the carbs. Usually the bowl gaskets too. Unless worn, the brass bits are reusable. While your carbs are soaking its a good idea to check the valve clearences. If they are off you will not get that bike running right. How are the carb to head rubber manifolds? They should be soft and pliable. No cracks...


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