Topic: About to do a carb synch, quick question.

[750K]

I had a local honda shop rebuild my motor and carbs over the winter, things run pretty good although I think a bit more attention to the carbs will make the difference. Motor is way snappier, smooth and real quiet compared to before the rebuild but I have a slight hesitation when rolling on the throttle. Once under load and past 1/8-1/4 throttle things smooth out and I have no lack of power between mid range and when at highway rpms.

A bit of background on the bike. 77 cb750k stock motor, Pd carbs with the stock airbox and a 4-1 header. Prior to the rebuild the bike idled fine, ran well through mid and high range. I've been running through it getting caught up on all the maintenance the PO didn't do over the last year I've owned it.

I re-checked and set the valves and points, which helped a bit. Plugs 1 & 3 are lean, plugs 2 & 4 are tan and look pretty good. I'd like to do a synch and adjust the mixture, seeing as pulling the choke out a touch when the bike has warmed up pretty much eliminates the stumble and the color of the plugs I'm guessing I'm running a bit lean and I'm sure another carb synch won't hurt.

So is it mixture screw out to richen? How many turns out is the stock mixture screw setting, my clymer says 1 1/2 turns out from all the way in as a preliminary setting. Thanks for any input.

[TwoTired]

The 1 1/2 turns spec is for the stock bike.  The 4 into 1 makes the bike NOT stock and stock settings can't be relied upon to bring the carbs into proper tune.
A 4 into 1 almost certainly has less back pressure than the stock pipes, and will need enrichment of most, if not all, of the mixture settings in the carbs.
You may be able to get by with only opening the idle mixture screws out some more.  It's worth a try and cheap to do.  Clockwise to lean and counter clockwise to enrich.

You should also revisit the accelerator pump, ensuring that the two check valves open and close to only allow fuel to pump in one direction ad not allow drain back.
Also, the pump diaphragm has two "ears", the holes in the ear need to be the same diameter as the holes in the body.

Do check the carb vacuum sync, so that all the cylinders can fire with equal strength at any throttle setting, and all the plugs can show the same deposit pattern.

Cheers,

[750K]

Thanks TT, I'll start with the sync and get the mixture adjusted and go from there. I'll run through the excelerator pump if the sync doesn't cure the stumble.

Last spring the carbs were tuned as part of my spring tune up, right after I bought the bike and things ran great. The 4-1 has been on the bike for years, so jetting seems fine. The carbs were completely taken apart, soaked and cleaned. Jets and needles were left as is once cleaned up, new orings and gaskets were put in. 

Im pretty sure it's going to be a matter of a proper tune And set up, I remember doing all that on my wife's cb400t last year. I tore down, cleaned and rebuilt everything on her carbs. Tuning wasn't too bad, but this will be the first set of 4 carbs I've set up. Thanks for the help.

[750K]

What a differance, today I rechecked the valves, adjusted the cam chain & sync'd the carbs. No more stumble rolling on the throttle, idle smoothed out and it pulls hard and smooth. I richened the carbs up a 1/4 turn on 1 & 3, will dial in the mixture next. Sprayed the carb boots with wd40, doesnt look like i have any air leaks which was nice to see.

Things were pretty out of sync, I'll be having a chat with the shop owner next time I'm in the area...