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Hanging Revs

Tommicky

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Hi guys, new here so bear with me.

1993 cb750
Mostly stock except I cut exhaust pipes and added shorty slip on’s with packed mini baffles
Electrical has been converted to LED with diode added
Everything else is stock mechanically, only cosmetic work has been done. Gaskets all around despite lower engine parts.
3,655 original miles
Rode it 50 miles since purchase, ran out of oil from failed gasket on the ride home after buying. Ran “ok” besides that. I did ride it again afterwards for a few miles on the new exhausts with no problems

112 main jet
35 idle jet
Idle fuel mix is 2 1/2 turns out
Stock needle settings non adjustable unless I add a washer
Stock airbox
Rubbers are all soft with no cracks
Carbs cleaned and synced
Good spark, 175 compression all 4, no vacuum leaks I can find, new battery, new sparks, new coils, fresh gas, petcock operating good, floats needles and jets all new, no float sticking, enrichment circuit is good even new valves.



So I have a hanging rpm issue. This does not happen every time but definitely gets worse as it warms up. And oddly it is intermittent, I went for a ride and it was somehow just fine, came home parked for an hour then bam, came back.
Idles good, starts up first try, but if I blip the throttle it goes up to about 5k and won’t come down for about 2-3 mins. I can not figure this out and starting to think it’s an issue with the aftermarket shorty exhausts I put on. They’re kind of “open pipe” style but I do have them packed and baffled.

My question is, has anybody installed these before and would my jetting be too lean? 112 She eats gas like nobodies business, mileage is terrible honestly.

I’m wondering if since cutting the pipes to put these slip on’s.... would that take away from back pressure so much that the slides in my carbs just not open the whole way? I can imagine then that my jetting would be correct or very close, but still don’t understand how it can be fine one ride and then completely unridable the next time I start up? What would cause such an intermittent lean symptom like that? I’ve never experienced something that’s so inconsistent so I can’t really track down what is causing this.

Any and all help, somebody tell me if I’m at least thinking about this correctly and it’s an exhaust issue. I can’t go back to stock “they’ve been cut”, so I need to stop wasting money and figure out where to go from here.
 
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