new engine carb jetting

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new engine carb jetting

Postby jr drag dad » Sun Aug 05, 2018 7:55 pm

Ok guys, I HAD a 140x400 raptor,,,,, Last Friday After 3 years of running, the block has aquired a crack around the du (main bearing flywheel side) bushing and has pushed the bushing out into the side seal cutting it,,, I put together a 200x563 Blockzilla and am using the same 33mm Mikuni,,, The engine idles fine and "cracking" the throttle slightly is very responsive. The problem is when I rev it up and return to idle it is "hunting" and revs up and down by itself for a few seconds... I think it needs a bigger pilot but it has what I think is already big,,,, The pilot is a .065 , The main is a 185 , left side air bleed is .8 and right side is 1.0 ,,,,,,,, We run mostly at 6000 feet adjusted altitude ??????? Any ideas ????
jr drag dad
 
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Re: new engine carb jetting

Postby Kern Family Racing » Mon Aug 06, 2018 4:58 pm

If you have not removed the pumper rod and blocked it off, get rid of it and it will stop most likely. I have a BZ1 with a 33mm and I am at 932’ elevation. I am still on the rich side with a 55 pilot and a 0.5 air bleed. Idle mixture screw underneath is out 1 1/2 turns from closed. I have a 180 main and a 0.7 air bleed. My CHT at launch is 155 and egt stays just under 1200. With your altitude you, should be way leaner than you are right now. I would also check for vacuum leaks. Make sure your gasket on the air horn isn’t bad, o-ring and washer on idle mixture screw good, and if you bought pilot jets from Viperizer in the last year, trash them because they are not drilled all the way through.
Scott and Jack
Kern Family Racing
 
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Re: new engine carb jetting

Postby jr drag dad » Tue Aug 07, 2018 5:27 pm

Thanks so much for the reply,,, The pumper had been removed,, , I started it up and sprayed carb cleaner around the manifold and carb with no rpm increase,,, I tried another 33 with smaller jets and got the same results only worse,,, went up on the pilot in the second carb and smaller on the air bleed a few times and the hunting is much better. gonna keep tinkering and hope we can get it better..
jr drag dad
 
Posts: 56
Joined: Mon May 08, 2017 12:35 am

Re: new engine carb jetting

Postby Kern Family Racing » Thu Aug 09, 2018 11:07 am

Pull your pilot and check the hole. If it looks like a tiny pinhole, then it is a bad pilot (most likely a gas jet). It should look like the opening of the jet and roughly the size of the equivalent drill bit. If you happen to have a .050 drill bit, then slide it all the way through. If it won’t go, then it is a gas pilot. I spent a lot of time and money and ultimately ruined a good engine because of the bad jets.
Scott and Jack
Kern Family Racing
 
Posts: 116
Joined: Tue May 31, 2016 7:12 am
Location: Greenfield, IN

Re: new engine carb jetting

Postby jr drag dad » Sat Aug 11, 2018 5:14 am

LESSON LEARNED ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, DO NOT try and tune on anything but the track........ with all the popping and hunting I "ASSUMED" it was lean... I was running it with no load.... Went to the track and watching temps with a digatron I adjusted and ran 5 9.31@70mph ,,,car is deadly consistent
jr drag dad
 
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