1982 Dohc 750f stuttering on initial throttle

[Kevlar1981]

Hi all new member here I've got a 1982 dohc 750f supersport that I'm having issues with all original apart from a motad 4-1 exhaust.
Bike was a non runner in several pieces when I got it.
I've been chasing numerous issues for ages , and have worked them all down to just the one now...
Engine stutters when pulling away or at low speed when just cracking the throttle, but pulls just fine right through the range when more throttle is applied.
List of what I've done so far.....
Carbs fully stripped and thoroughly cleaned many times with compressed air and carb cleaner etc
Carbs synced
Tried 2 to 3 turns on mixture screws in 1/8th turn increments
Had low compression on no4 found to be a burnt valve so valve replaced and all others lapped and re shimmed to spec,
Ignition timing is spot on with strobe,
New plugs ngk dr8ea,
Stock airbox and filter,
No signs of any air leaks on isolators.
I'm just about out of ideas
Any suggestions would be greatly appreciated.

 

[Kevlar1981]

 

[Dyl81cb750]

Hi all new member here I've got a 1982 dohc 750f supersport that I'm having issues with all original apart from a motad 4-1 exhaust.
Bike was a non runner in several pieces when I got it.
I've been chasing numerous issues for ages , and have worked them all down to just the one now...
Engine stutters when pulling away or at low speed when just cracking the throttle, but pulls just fine right through the range when more throttle is applied.
List of what I've done so far.....
Carbs fully stripped and thoroughly cleaned many times with compressed air and carb cleaner etc
Carbs synced
Tried 2 to 3 turns on mixture screws in 1/8th turn increments
Had low compression on no4 found to be a burnt valve so valve replaced and all others lapped and re shimmed to spec,
Ignition timing is spot on with strobe,
New plugs ngk dr8ea,
Stock airbox and filter,
No signs of any air leaks on isolators.
I'm just about out of ideas
Any suggestions would be greatly appreciated.

My 81 cb750 does the same thing on initial throttle, it sputters between 1.5k and 2k rpm’s but when I give it throttle it’s fine. Please let me know if you find out the solution.

 

[jpdevol]

One of my suspicions on this symptom would be the accelerator pump, attached to #2 carb, may not be acting right (clogged or bad diaphragm). To test that, you can remove the float bowl and fill it ~ half full of gas (off the bike) and depress the actuating rod; it should shoot a spray of fuel at least 6" high or higher. If that checks out good, I'd increase Slow Jet size by one

 

[Brad C]

Hi all new member here I've got a 1982 dohc 750f supersport that I'm having issues with all original apart from a motad 4-1 exhaust.
Bike was a non runner in several pieces when I got it.
I've been chasing numerous issues for ages , and have worked them all down to just the one now...
Engine stutters when pulling away or at low speed when just cracking the throttle, but pulls just fine right through the range when more throttle is applied.
List of what I've done so far.....
Carbs fully stripped and thoroughly cleaned many times with compressed air and carb cleaner etc
Carbs synced
Tried 2 to 3 turns on mixture screws in 1/8th turn increments
Had low compression on no4 found to be a burnt valve so valve replaced and all others elevator pump

Hi all new member here I've got a 1982 dohc 750f supersport that I'm having issues with all original apart from a motad 4-1 exhaust.
Bike was a non runner in several pieces when I got it.
I've been chasing numerous issues for ages , and have worked them all down to just the one now...
Engine stutters when pulling away or at low speed when just cracking the throttle, but pulls just fine right through the range when more throttle is applied.
List of what I've done so far.....
Carbs fully stripped and thoroughly cleaned many times with compressed air and carb cleaner etc
Carbs synced
Tried 2 to 3 turns on mixture screws in 1/8th turn increments
Had low compression on no4 found to be a burnt valve so valve replaced and all others lapped and re shimmed to spec,
Ignition timing is spot on with strobe,
New plugs ngk dr8ea,
Stock airbox and filter,
No signs of any air leaks on isolators.
I'm just about out of ideas
Any suggestions would be greatly appreciated.

lapped and re shimmed to spec,
Ignition timing is spot on with strobe,
New plugs ngk dr8ea,
Stock airbox and filter,
No signs of any air leaks on isolators.
I'm just about out of ideas
Any suggestions would be greatly appreciated.

Accelerator pump may have a bad diaphragm, missing check balls, or is not set up (little metal tab that is bent to engage the pump when cracking the throttle)

 

[Kevlar1981]

Thanks I'll have another look .
I've ordered a small ultrasonic cleaner so going to give the carbs another deep clean too