Engine "loads" when I roll on throttle under load then accelerates

S

stillbuster

New Member
I hate for my first post to be a question but my "search foo" is weak.
1979 CB750K
Was a rolling couch when I purchased, removed all comfy stuff from the bike, plans for a cafe project.
The bike is stock with exception of:
Replaced 2-1 headers with MAC 4-1 exhaust
new plugs and plug wires
clubmans
No mods to air intake

When I ride the bike I can be in any gear tooling along about 1/3 throttle 4-5000 RPM then when I roll on the throttle the RPM's jump about 1500, the bike gets gets louder like it is winding up then begins to accelerate.
It seems to build/load then accelerate.
I have pulled the plugs and they are a nice light brown creamy color on the electrode but black almost wet around the top flat part of the threads.
What is the cause? And what is the fix?
Starving for fuel?
Thanks
 
So it revs up without accelerating? Might the clutch be slipping?
 
Yes you are correct, it Revs up without accelerating.
It must be the clutch because it feels as if I am feathering the clutch and then begins to accelerate.
I will check my clutch adjustments and see what happens.
If after adjusting the clutch if this continues is this a sign that I need a clutch rebuild?
 
Possible. It's fairly easy to pull the right crank case cover and remove the clutch. Measure the plates to see if they're in spec. If they're still good, you may just need new clutch springs.
 
Also... make sure you're not using any special oils such as Royal Purple or any of the fully synthetic stuff. Wet clutches don't like those.
 
You just answered my next question. The older gentleman I purchased the bike from proudly proclaimed he had just serviced the bike with Royal Purple synthetic and how expensive it was.
Maybe it hasnt done any permanent damage.
 
Ah, yeah, I'd try a conventional motorcycle-specific oil just to eliminate that variable. If it still happens after that, it could be the clutch.
 
It's unlikely to do any permanent damage. The problem with it is that it's just too slippery. With a wet clutch, the plates are literally sitting in a bath of oil and if you use synthetic oils, there isn't enough friction to effectively transfer the power from the engine through to the transmission.

Drain out what you have and fill it back up with some standard mineral-based oil. Run this for a while and you should notice an immediate difference. It will likely improve again after the next oil change, though it may not be noticeable. Your owner's manual should specify the grade used, though I'd wager it being 10w-30 or 10w-40.
 
Use a cheap diesel oil, they have higher detergent content.
Shell Rotella is JASO MA spec for wet clutch, 15w/40
Early plates can be used with some synthetics
Royal Purple do make oil suitable for motorcycle's, if the car oil was used that could be the problem (it's around $70.00 worth of oil, put it in your car next oil change)
'New' clutch plates (around 1990 on) don't care as they are different material composition
 
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