Mid range issue
 

I had my Reds engine pinched after compression started to fade. I broke it in again and have tuned it in the parking lot and it was running great. The power and speed were back. On the track it was a little weird though. Coming off the 90 degree left hander heading onto the the straight the engine would start picking up RPMs just fine, but 1/4 to 1/3 of the way into the RPM band it sounded like it would go rich and struggle a bit. Keeping the throttle pinned, the engine would clear out and would accelereate normally again. It would do the same thing every lap. I'm not sure if the bottom or top is too lean or too rich because as I said, it was running great in the parking lot and on the track, bottom end from idle seems good and top end seems good, but not the part in the middle. In the parking lot it rockets out of the hole even after idling for a while. Thanks for any help.

It sounds more like a clutch issue than a tune issue to me. In a parking lot your tires have so much grip the clutch engages differently than it does in dirt. Check your shoes and springs.

Check your clutch, fuel tubbing and tank

Really sounds like a clutch issue. Are you by chance running an adjustable clutch?

Where did you have it pinched?
Take the engine out and do the 3-o'clock test.

I had the same thing happen to me once on a fresh pinch, and it had accidentally ingested some dirt through the filter I discovered when I took it apart it was full of grains of sand :(

Yes, its a Buku clutch. Normal weight shoes. What should I check for? Overall condition of the clutch and bearings are fine.

I will check. I really hope its not that.

Dirt ingestion does not cause mid range bogging. It's your clutch.

Yeah it's your clutch. Read the instructions that came with your buku clutch. It should explain what you are experiencing. I think they call it lag.? Not sure on the term they use but I had this happen to me a while back. Read the instructions and it will clarify it for you. Pm me if you don't figure it out.

Loss of compression = bogging. Or do you not correlate dirt ingestion to loss of compression?

In the past when I have tuned an engine in a parking lot it was way off on the track. How was the temps compared to before? I would just try it richer first and then leaner and see which way you need to go.

Rex

While dirt will effect the compression, wouldn't that (loss of compression) effect the overall performance range of the engine & not just the mid range.?
No compression, no power, low, mid or up high in the revs.

Fyi : if you tune in parking lot or grass low will be a lil too lean on the track

leave 2-3 hrs rich on lsn when parking lot or grass tuning , you will be good on the track

got to compensate for the wheelspin/freerev of the dirt which will expel the fuel/oil mixture in the block at low rpm/idle faster than it will on grass or asphalt


clean shoes and bell , leave clutch pretty loose , set your stagger only about 1/4 turn apart from each other , adjust tighter in 1/16th turn increments until clutch just stops bogging your particular engine down , lasts a long time like this and runs awesome

Loss of compression (dirt ingest) will effect the engine throughout not just the midrange. It effects mostly the high end due to blow by especially if there are scratches in the P/S. It will not cause bogging only in the mid RPM range. The engine will be extremely difficult to tune at all and also will be prone to constant flame outs. I believe you had Mid range bogging and also that your engine had dirt in it but that was not the cause of your bogging.

My ST-RR EVO
I know this is an old post but how you managed to solve your issue? Or just changed the motor?