1979 cb750k slow acceleration 1-4k rpm

[sdew99]

Hi all,

My cb750 seems to be bogging especially around 2500-4500 rpm under acceleration and deceleration. About 5k and up there's no issues and it seems to accelerate fine. Carbs were cleaned recently and the slow idle jets were removed and cleaned. Plugs look ok to me?

Tia

 

[brettp]

I don't know if others will agree but those plugs seem on the lean side.
Are you running stock intake with stock jets?

 

[sdew99]

I don't know if others will agree but those plugs seem on the lean side.
Are you running stock intake with stock jets?

Kind of what I thought. Yes, but running 4-1 delkevic exhaust. Also measured the fuel volumes out of the carb bowls and it's concerning lol.

 

[brettp]

In which order did you drain the bowls? Because all 4 carbs share the fuel line up to the petcock. The first bowl you drain will have the fuel from the bowl and the fuel in the line to the petcock.
You may have a need to do a valve adjustment seeing as all the plugs look similar.

 

[sdew99]

In which order did you drain the bowls? Because all 4 carbs share the fuel line up to the petcock. The first bowl you drain will have the fuel from the bowl and the fuel in the line to the petcock.
You may have a need to do a valve adjustment seeing as all the plugs look similar.

Started with cylinder 4 and worked towards cylinder 1. The fuel line was already off so would have just been from the brass tee down. Checked the valves a few hundred km ago and they were all between 3-7 thou.

 

[brettp]

Hmm. Seems like your float heights are all over the place. Need to fix that. Float height will influence your fuel mixture so don't make adjustments to anything until your float heights are done

 

[sdew99]

Hmm. Seems like your float heights are all over the place. Need to fix that. Float height will influence your fuel mixture so don't make adjustments to anything until your float heights are done

Ok. So I took the carbs off the bike, geared up an auxiliary tank and filled the carbs. Drained them, and all were 50 ml plus/minus 2 mL. My float levels are also bang on. I am thinking the hose going from my fuel tank was partially kinked causing the restriction of gravity flow which was why my first volumes were so off. Also discovered my accelerator pump was leaking badly because I had forgot to put the o-ring in where the bowl meets the body(around check valve for pump). That's all for today haha.

 

[Doohan]

#3 plug seems to be the leanest and carb #3 only has 15ml.