I put a HPD pipe,cutch kit, K&N, air box mods on my wifes Trailblazer. I got it done with only one day to spare before Cochranton, so I didnt get much time to tune it. To be safe i used the 160 Main with the clip 4 notches down from the top. Well we got to Cochranton on Thursday night so I had some time to spare. In HPDs instructions it said to run the 150 with temps above 40 Deg so since I had the 160 in I thought I would be safe lowering the needle 2 notches. It seamed to clean up the throttle responce in the midrange and the temp was close to 75 degrees, so I figured I was safe. WRONG! About 3/4 of the way through trail B she burned down. I am sure it was because of all the 1/4 - 1/2 throttle trail work combined with the low needle position, I was stupid to move it.
Anyway I tore it down and had the cylinder taken .020, and I also had the head taken .020.
My question is what are you guys with similar setups running for jetting? I am thinking of starting with a 165 main and the needle all the way up. Is this to conservitive?
Thanks Drew

 

If you have a 34mm carb from an 400 or can find one from someone who has replaced. This would to me be the best fix. right now in my TB with everthing Im running 230 jet. Hope this helps

 

If you have a 34mm carb from an 400 or can find one from someone who has replaced. This would to me be the best fix. right now in my TB with everthing Im running 230 jet. Hope this helps

 

The needle is just too lean. You really need to go to the next richer needle. Saw exactly the same thing happen to a Blaster that was run at Cochranton. The Blaster was basically stock with a slightly milled head and a 2nd over Wiseco. This was the 2nd time in a month that it seized up. For some reason there have been a rash of mid-range burndowns on many diferent types of engines lately. I'm beginning to wonder???? I've personally witnessed this when there is an air leak or the needle is not on the right clip or just plain too lean of a needle. I really think that it's tough to tune the mid range with unleaded fuel and those stock plugs. They just won't give you a good reading.

 

Ok call me the greenhorn but what exactly is midrange burndown or for that matter burndown in general. Beefy250