Revs yes, power no

[de_prooij]

Good evening, I have a problem with my 1979 cb750KZ where I would like to ask your help for.

The bikes starts pretty well, and in neutral (when warm) it revs up all the way. When I start driving the power seems to be completely gone. In gear 1 and 2 in the end (the old Daf66 from my mom was faster) it revs up all the way, but in the other gears the air resistance seems to win... It might be that the main jets do not come in.

I have disassembled the carb completely and cleaned them ultrasonic. The air filter is clean. The battery charges normally.

Does anyone have an idea on how to find a sollution for my problem? Does this problem sound like a Spark/timing problem, or like a fuel problem?

 

[Travis]

It might be running supper rich or your plugs are fouled (or something else completely). What do the plugs look like? What jetting do you have in the carbs? Have you done any modifications since it last ran well?

 

[de_prooij]

It might be running supper rich or your plugs are fouled (or something else completely). What do the plugs look like? What jetting do you have in the carbs? Have you done any modifications since it last ran well?

Thanks for the reply!

The plugs are new, I'll pull them tonight to look at colors. No modifications from my side. I pretty much brought it back to live. The former owner had it stand still for several years. The jetting is original.

I'll also check whether the needles work properly.

Thanks so far!

 

[tommycarl]

Probably a silly question, but.... are you sure it's running on all 4 cylinders?

 

[fatoldo]

I have a very similar problem. Looking into it also. If I come up with anything I will be sure to post it to you

 

[hondsx]

using old stock coils could be fowling out a plug at times or causing non total combustion for that cyl.
just2cents

Lar

Good evening, I have a problem with my 1979 cb750KZ where I would like to ask your help for.

The bikes starts pretty well, and in neutral (when warm) it revs up all the way. When I start driving the power seems to be completely gone. In gear 1 and 2 in the end (the old Daf66 from my mom was faster) it revs up all the way, but in the other gears the air resistance seems to win... It might be that the main jets do not come in.

I have disassembled the carb completely and cleaned them ultrasonic. The air filter is clean. The battery charges normally.

Does anyone have an idea on how to find a sollution for my problem? Does this problem sound like a Spark/timing problem, or like a fuel problem?

 

[hondsx]

agree, check (graph) coils for continuous power at plugs at all times, unburned fuel, more fowling, catch 22...

just2cents

Lar