Author Topic: 78 750 carb questions  (Read 356 times)

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Offline WaleFab

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78 750 carb questions
« on: September 15, 2014, 05:59:39 PM »
Heya guys, Just signed up after repeatedly coming to this site for information. Ive hit a point that I need some finite advice.
Ill run through what Ive done and whats up.
Carbs are PD42b. Dismantle and rebuild and cleaning of all stock components. (needled not effected other than removed and cleaned) mains are 115 if i recall correct and idle is 45?
I have a Vince and hines 4-1 wrapped.
Stock airbox
New points and condensers, gapped at .013, timing is correct.
Rectifier gaps have been set to factory settings.
New plugs, same as ive always ran.

That said, im at 3 full turns out on my mixture screws.
Bike runs better than it ever has in my possession, and picks up good.
I still feel that its a bit lean, though if i go to 3.5-4 turns Im getting smoke out the exhaust under full crack throttle.

The bike runs very well once its warmed up and can be a bit of an effort to start initially.
If I really haul ass on it then come to a stop light the bike seems hungry, as im assuming something with the float is off and its not allowing gas to replenish as fast as it should?

I think thats all for now...

Does idle mixture screw on carb 2 move or adjust? I know that carb is the master thought id think it should still be adjustable.
When i screwed the idle screw for carb 1 completely in, by bike continued to run. Carbs 3 and 4 choked out and bike died. (getting blow by on screw #1? worn out?)
All carbs are synced very well to one another it seems on the 4 gauge setup...

Thanks in advance. Ill post some pics of my girl once I finish painting it this week. its been quite the process over the last year haha.




Modern mind / classic heart
'78 CB750 Cafe Mono / GSXR build

Offline Stev-o

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Re: 78 750 carb questions
« Reply #1 on: September 15, 2014, 07:25:12 PM »
Welcome Wale.  The later CB's were lean sock and you have aftermarket exhaust.  Does the V&H have a baffle?
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........