Hi all, nice forum you guys have here! I just picked up this 88 STC and it might need a bit of tuning help. It's and EVO, has the Hooker step tuned pipes, S&S Shorty E carb, Hyper Charger. Runs great, but there is a big flat spot at about half throttle. I took the carb apart to make sure its clean, which it is. It has a 066 main jet and a 025 pilot. I have adjusted the carb many ways now, but nothing seems to help this flat spot. It does not pop in the carb, so I am guessing its not lean, maybe a little rich? Does anybody have any advice? Do the jets seem to be sized correctly? Thanks for any help

 

Welcome to the forum...Your jets are too small IMO. Try a 68 Main and a 28.5 pilot. And don't forget to readjust your accelerator pump when you change the jets.

 

I agree with Stiggy, Your jets seem a little small. If you're unable to dial-in this S&S go with a Mikuni 42.

 

Thanks guys!

 

If it was my bike, the first thing that I would do is replace the intake manifold gaskets.
The old ones could be sucking air which is a no-no.

Gaskets are less than $10 bucks but installing them is a pain unless you have the proper tools.

 

Thats also a possibility. The PO mentioned he just replaced them, maybe he pinched a gasket? Would the aerosol trick work in this situation? Spray carb cleaner around the possible leak to find if and where the idles changes?

 

Yep, if you can keep the spray away from the a/c.

Some folks (I'm told) also use a propane torch (unlit),holding the nozzle near the intake gaskets to see if the engine RPM's increase.

I've just put two sets in our EVO engines, and I had an indy shop install them in my T/C 88 just this week.
THe tech told me that he has replaced them on bikes less than 4 years old but he didn't mention mileage.

On the two EVO's that I just done (one less than 9,000 miles, the other at 25,000 miles) the ones off of the engine with 9,000 miles appeared to be in worse shape than the one with 25,000 miles.

Like the tech told me, those engines go from ambient temps up to close to 300 degrees and then repeat that time and time again.
It's not a matter of will they will go bad, but when?

 

Got her all fixed up. One call to Al at S&S lead to the jets being too small as you guys mentioned. He insisted to install 072 main and a 295 intermdiate with the pipes I have. Seemed like a big jump from what jets were in there, but I took his advice. After minor adjustments to the accel pump screw, it has no more flat spots. Thanks for the advice guys!