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Tractor Pulling Discussion Forum

Missing 70

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Oppy

05-13-2004 09:38:21




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We've got JD model 70 that we recently overhauled. Bored .125 over, new pistons and some headwork. Other than that, she's basically stock.
At the pulls and under a load, it's runs great. However, when it idles it has a tendency to load up and then backfire. It's not a constant backfire, just occassionally. We've replaced with new plugs, points and cap and we're still having the same problem. Any advice you may be able to pass along would be greatly appreciated.

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MIKE

05-13-2004 13:06:03




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 Re: Missing 70 in reply to Oppy, 05-13-2004 09:38:21  
DID YOU OPEN THE HIGH SIDE JET UP UNTILL IT STARTS TO MISS UNDER A LOAD AND TURN IT BACK 1/4 TURN?



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Oppy

05-13-2004 13:23:09




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 Re: Re: Missing 70 in reply to MIKE, 05-13-2004 13:06:03  
We did adjust on the carb. while it was on the dyno but, I'm not sure exactly where we ended up on the high side jet. Thanks and I'll look into this adjustment the next time it's on the dyno. Right now she's making a good strong 50 hp. I'd like to get it up to 60-65 without getting too radical (stroking).



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MIKE

05-13-2004 13:36:07




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 Re: Re: Re: Missing 70 in reply to Oppy, 05-13-2004 13:23:09  
IF YOUR LOOKING FOR SOME EASY HORSEPOWER, THOSE JD MANFOLDS NEVER FIT GOOD, USE YOUR GASKET AND MARK THE MANFOLD AND GRIND & POLISH ALL THAT RESTRICTION OUT OF THERE EASY 7-8 HP...



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Oppy

05-13-2004 14:15:42




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 Re: Re: Re: Re: Missing 70 in reply to MIKE, 05-13-2004 13:36:07  
Speaking of manifolds. I keep hearing about using an lp version. I'm not sure I understand the thinking behind the lp and what it can potentially do for me. Do you have any thoughts on this?



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buickanddeere

05-13-2004 21:30:52




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 Re: Re: Re: Re: Re: Missing 70 in reply to Oppy, 05-13-2004 14:15:42  
Cooler mixture and less restriction. Follow Mikes advice right down the port to the combustion chamber. Take the edges and obstructions away without hogging the whole port oversize.



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Oppy

05-14-2004 09:30:51




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 Re: Re: Re: Re: Re: Re: Missing 70 in reply to buickanddeere, 05-13-2004 21:30:52  
Buick & Deere,

Thanks for the advice. Do you have any other suggestions for the miss that we are experiencing?



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mike

05-14-2004 07:22:49




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 Re: Re: Re: Re: Re: Re: Missing 70 in reply to buickanddeere, 05-13-2004 21:30:52  
the lp will give you cooler air gas mixture, but i think just grinding and polish all the hang over metal, you aree going too see a big differnce...



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Oppy

05-14-2004 09:27:47




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 Re: Re: Re: Re: Re: Re: Re: Missing 70 in reply to mike, 05-14-2004 07:22:49  
Mike,

Thanks for the suggestions. Any thoughts on a dry filter element and it's effects on horsepower. I've heard of containing it within the old oil bath housing.



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mike

05-14-2004 12:03:02




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 Re: Re: Re: Re: Re: Re: Re: Re: Missing 70 in reply to Oppy, 05-14-2004 09:27:47  
Iv been down that road when i was pulling my G, your 70 is not turning high rpms, no likes using the oil bath but it is a good system, unless u start to burn white in the stake you are getting the right amount of air, yes colder air makes more power it you are turning high rpms, my 880, cant get enough cool, if you want just disconnect the ribber couping to your hood breather, and filter that.....

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Oppy

05-14-2004 12:26:03




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 Re: Re: Re: Re: Re: Re: Re: Re: Re: Missing 70 in reply to mike, 05-14-2004 12:03:02  
I'll give it a try. Thanks again!



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Mopower

05-14-2004 04:53:07




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 Re: Re: Re: Re: Re: Re: Missing 70 in reply to buickanddeere, 05-13-2004 21:30:52  
My friend did this on a M-M Z once. Between tweaking and tuning and the port cleanup, it gained 15 h.p. No boring or stroking was done. I hope it works on mine! Have not fired the little thing up yet.



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Oppy

05-14-2004 09:39:47




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 Re: Re: Re: Re: Re: Re: Re: Missing 70 in reply to Mopower, 05-14-2004 04:53:07  
Mopower,

Thanks for the advice! We'll keep working with it and we'll make it happen.



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