No go above 4500 RPM

Chad Hartzell · Posted: Mon Sep 16, 2002 8:29 am Post subject: No go above 4500 RPM

Had something weird going on yesterday...

1st note: completely disassembled carb prior to practice and used carb cleaner on all jets, fuel filter, etc... Also went through power valve and cleaned thoroughly.

Practice- Took about 1/2 a lap for the motor to "take off". For the most part if I held it at 1/3 to 1/2 throttle, it would run, but only up to approx 4500 rpm. If I floored it, nothing. Then after about 1/2 a lap, it took off. Then, cuts off at the end of the straight. Pulled the choke to see what happens- no improvement. This was with a 165 jet with needle clip in "2" position. Air screw at 1 1/2.

1st change- went to a 160 jet.

Qualifying- Again, took about 1/2 lap to come to life. Again, cutting off at end of straight, but not as bad.

2nd change - upon conferring with another driver who was running a 158 jet, I tried the same.

Pre Final - No complaints, except, cutting off the end of the straight again and stumbling for a bit, probably losing .3 to .5 per lap. Would reel in the drivers ahead of me throughout every part of the track except the straights.

NOTE: When it was running max RPMs for the day were 12000 - 12100.

3rd change - I'm thinking I was running too lean and needed to give it more gas, thus, the cutoff at the end of the straight. Thought I'd do a little too much to see if there was a big difference, and went to a 168. Still at "2" clip and 1 1/2 on the air mix.

Feature - Motor never got above 4400 RPMs, 1/3 throttle, 1/2 throttle, full throttle.... nothing.

I'm going to take this thing apart again and see what I can find. Here's my guesses:

1. Problem with fuel pump - Would I be the only person in the history of man to actually have a bad Mikuni fuel pump? (I know one racer who's driver shifter for 13 with never a pump problem). I doubt there it a problem here, unless there is something blocking fuel flow.

2.Something is "blocking" the main circuit- but this was cleaned thoroughly Saturday, and I filter all fuel going into the gas tank.

3. There is a small troll that originates from Austria that lives inside my carburetor. It lives off of gas/oil mix, and is not letting my carb get everything it needs.

Any thoughts? And thanks in advance. If anyone can help solve it, I'll furnish a frothy beverage in Vegas...

Chad

Dick George · Posted: Mon Sep 16, 2002 8:56 am Post subject: No go above 4500 RPM

a low battery will kill these things too.

Chad Hartzell · Posted: Mon Sep 16, 2002 9:45 am Post subject: No go above 4500 RPM

Good point, however, it was a brand new battery, bought & ran Saturday, and charged all night Saturday for Sunday.

However, could something in the harness cable be on the blitz?

Chad

Andy Seesemann · Posted: Mon Sep 16, 2002 2:34 pm Post subject: No go above 4500 RPM

Chad,

Look in the pipe through the silencer end....

I'll bet its blocked.

ANDY SEESEMANN

Mike Moya · Joined: 18 Jul 2001 Posts: 213

Hi Chad, I'd say it's the troll. They live in EVERY Rotax carb. They only come out when you're racing, hardly ever on practice days. I like my Rotax, but love the Leopard!Bye

Nick Weil · Posted: Mon Sep 16, 2002 10:04 pm Post subject: No go above 4500 RPM

Chad,
We had the EXACT same thing happen to a customer recently. We took all of the individual components apart one at a time, reassembled and still could not find the problem. We took the carb apart one more time and disassembled it, paying EXTREME close attention the the needle valve and the floats. We reassembled it an everything was fine. I think the needle valve rubber tip was sticking in its seat.

Nick Weil www.speedquestkarting.com

Chad Hartzell · Posted: Tue Sep 17, 2002 4:14 am Post subject: No go above 4500 RPM

Andy / Nick,

Thanks for the responses. I went completely through the carb last night. Nothing looked wrong, no chunks of anything found. I did notice that the orange tip of the needle valve looked as though it might have been sticking / gumming up onto the jet itself as the was a slight bit of orange residue from the rubber tip.

I will check the pipe. It's the only thing I haven't looked at...

CH