Topic: rebuilt engine wont idle

[maddog63]

I just rebuilt my 78 750 f motor it starts with starting fluid but will not idle it seems like its not getting gas. it runs for about two revs of the throttle. would this be my accelerator pump? Ive cleaned the carbs and installed a new pump but didnt adjust the tang I need some pics to show me what to do so close yet so far I a newbe at this Honda stuff but I got it from a rusted locked up motor to one that starts but wont idle.

[flybox1]

I just rebuilt my 78 750 f motor it starts with starting fluid but will not idle it seems like its not getting gas. it runs for about two revs of the throttle. would this be my accelerator pump? Not necessarily...it could be a number of things Ive cleaned the carbs and installed a new pump but didnt adjust the tang I need some pics to show me what to do so close yet so far I a newbe at this Honda stuff but I got it from a rusted locked up motor to one that starts but wont idle.

Air, Fuel, Spark...all are necessary for a bike to run
We need more info.....
Model carbs do you have?
What jets are in your carbs?
Have you bench sync'd the carbs? 
What are the IMS (idle mixture screws) set at?
have you done valve adjustment?
Set points gap properly?
Did you service the accel pump circuit...and are all jets squirting with throttle actuation?
Is your fast idle cam raising the slides as it should?
What intake are you running? [pods or airbox]
What exhaust do you have?
Battery - new, old, charged, what is the voltage at the terminals?

[madmtnmotors]

would this be my accelerator pump?

No.


The sole purpose of the accelerator pump is to help overcome the slight lean condition when the throttle is applied. At idle, or even at a steady cruising speed, the accelerator pump is dormant. The accelerator pump circuit only pumps fuel under acceleration and has no bearing on the carburetor performance at idle nor at steady rpm in any range.

[maddog63]

I went back and it starts right up but dies right away only starts on full choke. I set the valves. i have the 78 carbs. I have stock jets, bench sync'd did not mess with the accel pump except for putting in a new one. Right now no pods or airbox just trying to get it to idle. Four into one exhaust. What is the fast idle cam? the slides do move ims set at 1 1/4 turns out.

[flybox1]

I went back and it starts right up but dies right away only starts on full choke. I set the valves. i have the 78 carbs. I have stock jets, bench sync'd did not mess with the accel pump except for putting in a new one. Right now no pods or airbox just trying to get it to idle. Four into one exhaust. What is the fast idle cam? the slides do move ims set at 1 1/4 turns out.

ding ding ding

Needs the airbox to run with stock jets.   Its too lean without....supported by the fact you need choke for it to run 

[maddog63]

if i put pods on will that help?

[flybox1]

if i put pods on will that help?

not unless you properly jet for them...
just install the stock airbox/filter.  it'll work....dont fight it 

[ekpent]

 Unless those PD carbs are really finicky I have started many many 1976 or older CB750's with the round top carbs without an air box with no problems and they have idled etc. Not saying they would run great under a load but they will run and idle.
   Better keep checking to see if you have a fuel supply issue or other problems. Are all 4 spark plugs getting juice and sparking.

[flybox1]

These pd carbs run lean to begin with.  Leaner than earlier bikes.  Gotta have some resistance on the intake side, or its too lean to run.  Get the airbox on.