Car Missing down track

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Car Missing down track

Postby JamieDumanski » Tue Apr 09, 2019 2:06 am

YouTube video below

Hey there everyone. I have been chasing an issue and looking for some advice. As you can hear in the video the car is missing. It is a Huddleston 7.90 Sniper Lite, 3 1/2. Has a 40mm carb. Holeshot clutch. I have had everything from .085 to .106 main jet in every incremental increase. The result is the same. I
wouldn't say anyone is better than the other. I raised the float to ensure it isn't running out of fuel. However, it happens sometimes at the hit and other times as soon as 10 feet out. Then the rest of the way. The plug has been NGK BR6HIX, BR7HIX and BR8HIX all set at .025 Gap.

Carb Specs
Huddleston
96 Main Jet
59 Pilot
1.1 Low side
plugged high side
Brass screw (idle mixture) is 1 1/4 open from full closed

Head temp
170 start
245 finish

Exhaust temp
830 start
1260 finish



Could it be ignition? I am changing from the standard 5HP coil to the Briggs PVL and a ARC flywheel. Any other thoughts of things to look at?

Thanks so much!

https://youtu.be/BNdlOtshB2M

Photo of computer run. You can see the RPM isn't smooth and the dips represent the pop or miss
https://www.dropbox.com/s/7n2zg3708foipzn/IMG_1802.PNG?dl=0
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Re: Car Missing down track

Postby WILD BILL » Tue Apr 09, 2019 5:58 pm

From the vid it sounds like it's lean popping.

Also, Based on those starting line temps I'ld say it's lean there too. I like to see my head temps in the 155-160ish range and EGT's in the upper 6 to low 700 range.



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Re: Car Missing down track

Postby Kern Family Racing » Tue Apr 09, 2019 11:07 pm

We have the same HP 7.90 setup and here is where we are. We had the same issue and I can tell you right now that it is in your carb. It is a transition pop from going lean to rich. Our main jet is a Holley 89 so you are a bit rich on the main jet. Your starting line temps should be no higher than 150 CHT and we launch at 140. Exhaust temp at launch is 600-650. If you look at the air intake all 3 air bleed holes should be PLUGGED. Huddleston used a rubber plug on the hole in the 8 o’clock position that falls out eventually. We just used a screw and loctite to plug the hole. Put a screw in air bleed plug in the main jet air bleed in the 6 o’clock position. Idle mixture screw about 1 3/4 turn out from all the way in. I have the paperwork directly from Huddleston for all the settings. Took us a while to figure out what was happening, but it was just too lean at launch. FYI, you will probably have to turn up your idle a little bit once you make the changes.
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Re: Car Missing down track

Postby WILD BILL » Wed Apr 10, 2019 6:34 am

Not sure how the 40mm is but my 42's I have the pilot bleed wide open and use the screw only to control the mix.

I think if I were to plug it it would effectively disable the air screw. Never tried it though so just my theory smiley-oops .
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Re: Car Missing down track

Postby JamieDumanski » Thu Apr 11, 2019 11:39 am

Kern Family Racing wrote:We have the same HP 7.90 setup and here is where we are. We had the same issue and I can tell you right now that it is in your carb. It is a transition pop from going lean to rich. Our main jet is a Holley 89 so you are a bit rich on the main jet. Your starting line temps should be no higher than 150 CHT and we launch at 140. Exhaust temp at launch is 600-650. If you look at the air intake all 3 air bleed holes should be PLUGGED. Huddleston used a rubber plug on the hole in the 8 o’clock position that falls out eventually. We just used a screw and loctite to plug the hole. Put a screw in air bleed plug in the main jet air bleed in the 6 o’clock position. Idle mixture screw about 1 3/4 turn out from all the way in. I have the paperwork directly from Huddleston for all the settings. Took us a while to figure out what was happening, but it was just too lean at launch. FYI, you will probably have to turn up your idle a little bit once you make the changes.



Thanks for the great reply! Any chance you can share that paperwork?

What about your pilot jet? Mine is a 59. What is yours?

Thanks!
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Re: Car Missing down track

Postby JamieDumanski » Thu Apr 11, 2019 11:41 am

With the idle mixture screw that you have at 1 3/4 turned out from closed. Is out richer and in leaner or the opposite. In leaner and out richer?

Thanks again!
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Re: Car Missing down track

Postby WILD BILL » Thu Apr 11, 2019 6:03 pm

On the 42mm's, IN is RICHER,OUT is LEAN.

Easiest way to see is turn the screw a little and watch EGT's and RPM. Leaner will cause both to rise and richer will cause both to fall.

EGT typically resounds the quickest followed by RPM then CHT.
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Re: Car Missing down track

Postby Kern Family Racing » Mon Apr 15, 2019 11:05 pm

Our pilot is a 59. I will try to get out there and take a pic of the paperwork. You can PM me your number and I will text it to you.
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