new turbo tuning-need help

[Trxster]

Ok, got my sled up for a tuning day yesterday and had some problems. Ended up I had a leak on the crossover tube. Once I got that fixed it ran ok but seems to bog a bit when I give it a quick throttle burst or at the top end. I could not get the rpm's over 9500 which was not due to clutching but rather do to it bogging or stumbling. The boost gauge holds pretty steady at -5lbs at idle and doesn't bounce around like it did before I located the leak. Anyone have any ideas?

Could this be leaky carb caps which would not allow the slides to open quick enough or all the way???

I am jetted at 132.5, fuel screw 1/2 turn out, needles were at 1 from top and I am running at about 5-6000 feet. Also, I was dumping the exhaust straight under the tunnel but didn't like how loud it was so I am puting my glasspack muffler on it. Do you need to change jetting without muffler?

 

[rxrider]

What boost are you getting at WOT? If you cannot get the rpms up your engine could be detonating caused by lack of fuel, lean condition. Be careful and do not push it until you have figured it out. The STM carb caps are a must with a turbo, I'm getting them too.

My friends Apex with MCXpress did detonate because of too little fuel, when he gave it WOT boost went to 12 lbs and stayed there, rpms went to 10500 and after a few seconds it dropped to 9000 and would not go any higher. He did not understand what was happening to his sled, so he did a few more passes and there she went into deto.

 

[Trxster]

I kept my boost at the minimum of 7.5 lbs. When I tried to give it more than 3/4 throttle it wouldn't go up to 10k, it just started stumbling around 9k like it was rich or something so I backed it off quickly. I was trying to be gentle as a butterfly but it is hard to test things without giving it some boost. Also, It sure sucked the gas down quickly yesterday. Could this be due to additional vacuum leaks or could it be due to carb slides not opening?

 

[rxrider]

Whose turbo do you run? My take is that it is going lean, it could be leaking in the T-s where the hose going from intercooler to carb float bowls connects to the carbs.

I am at 140 mains, needle 3 position, pilot screw out 2 turns, I'm going to 145 mains asap running 16 lbs of boost. With 135 mains my sled started crackling and missing after 3-4 seconds of wot from a stand still, this was at 14 lbs of boost. I went to 140 and it is running pretty good now at 16 lbs, but I feel that it is still a little too lean for my boost level thus going to 145 mains.

 

[cameljockey]

wideband

 

[rxrider]

WBO2 - You bet, I'm desperately in need for one. But I need more $$$ for all the mods the sled needs LOL. I can hardly affort to buy gas to ride with all the goodies that is going into the sled .

 

[srs8288]

Need help

Let me know if you figure it out, I am having the same problem with my Stage 1 MPI supercharger. Thanks

 

[Blue shadow]

To get the stumbling out I had to put back the stock carb springs.The silver ones are to weak and cause the slides to come up to fast.

 

[Trxster]

Interesting....mine wasn't very quick on the low end until I put the silver springs in!!!! Now it is like it was before the turbo. My wideband was reading in the 9's with the 132.5's, so I dropped it to 127.5's and Wednesday it did pretty good....had to drop the needles all the way and the a/f ratio was in the low 10's with no bog. So I put on 125's and put the needles back to stock and we'll see how it is tomorrow. I am pretty sure it was a rich bog, not a lean bog. The t's and caps don't leak and I am only running 8lbs of boost right now.


I think that you guys with the superchargers are in a totally differnt world because you are starting out under a bit of boost and go up from there so your low/mid range jetting would probably be a lot different from ours. Same with someone running 16psi.....a lot differnt that me at 8psi.

Rt

 

[srs8288]

Supercharger lag

I have great midrange, no upper end. From 3/4 throttle on I have nothing and I am only turning around 9,000 rpms wide open. I just went to 130's and will try that. I only have 7 1/2 pounds of boost. Sure can get discouraging.

 

[Silverbullet]

Re: Supercharger lag

I have great midrange, no upper end. From 3/4 throttle on I have nothing and I am only turning around 9,000 rpms wide open. I just went to 130's and will try that. I only have 7 1/2 pounds of boost. Sure can get discouraging.

There was a small run of SC that slipped above 8 or 9k....So check that and I'm at 127.5 w/ a straight 47 helix turning 10,200 to 10,500 depending on fuel and conditions..