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JOHN DEERE BIG NUT CARB. QUESTION

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2 cylinder

10-14-2002 16:38:21




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I have a JD-A and JD-G both with Big Nut carbs, what kind of performance and horsepower gains can I get by boring them out to get better air flow?




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LRN

10-17-2002 07:58:02




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 Re: JOHN DEERE BIG NUT CARB. QUESTION in reply to 2 cylinder, 10-14-2002 16:38:21  
I have a late A and G also. I had the 51 from the G and the 71 on the A opened up and rejetted by Roberts. I have both tractors stroked, bored or power block and cam work also by Roberts. One thing I can tell you is Roberts know what they are doing. I would talk to him and let him tell you what to do. I've learned by spending money with other so-called experts. The dyno testing I have done with my tractors showed that a big carb on a tractor will help a litle but it is expense HP. The cheapest HP you can get is by stroking (even a small one) It also raises you compression. Just my 2 cents, Thanks

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JDG

10-15-2002 20:42:52




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 Re: JOHN DEERE BIG NUT CARB. QUESTION in reply to 2 cylinder, 10-14-2002 16:38:21  
A!!!M!!!E!!!N!!!!! Wicky



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GPULLER

10-15-2002 08:56:58




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 Re: JOHN DEERE BIG NUT CARB. QUESTION in reply to 2 cylinder, 10-14-2002 16:38:21  
You didn't say what you have done to your tractors, but I have tested Roberts Super 51 on my G. My G is stock stroke with .090 over M&W pistons, ported cyclone head and all else stock. I dynoed with stock Big Nut and then with the Super 51 and picked up 5hp. If you were going to get one hogged out send Roberts an A carb and put your Big Nut on the self.



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Jack

10-18-2002 07:33:51




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 Re: Re: JOHN DEERE BIG NUT CARB. QUESTION in reply to GPULLER, 10-15-2002 08:56:58  
Does yours have a propane manifold or gas,or Jerrys?Did you polish the intake ports?Thanks



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2 cylinder

10-15-2002 15:35:37




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 Re: Re: JOHN DEERE BIG NUT CARB. QUESTION in reply to GPULLER, 10-15-2002 08:56:58  
The 1951 JD-G is bored .090 over with aluminum high compression pistons and a flat head, plus the head and intake have been ported out, and oil bath removed. It dyno's at 70hp.

The 1947 JD-A has a powerblock .125 over with aluminum high compression pistons, the block is shortened .125 The head is ground down well into the eyebrow's, with oversize valves, three angle valve job, and the head and manifold have been ported oversize. The oil bath has been removed also. This tractor dyno's 55hp.

Both tractors have the Big Nut G carb.

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G-MAN

10-16-2002 10:38:11




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 Re: Re: Re: JOHN DEERE BIG NUT CARB. QUESTION in reply to 2 cylinder, 10-15-2002 15:35:37  
Sounds like a Robert's 71 should be way more than adequate for both of your tractors. Call him and talk with him about your needs and plans, as I found him to be extremely knowledgeable and helpful with all my questions. I don't think I've ever heard or read a bad comment about him or his business, so he seems to be a class-act all the way around.



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G-MAN

10-15-2002 07:45:02




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 Re: JOHN DEERE BIG NUT CARB. QUESTION in reply to 2 cylinder, 10-14-2002 16:38:21  
Burns is right about using the 71. My "G" came with a 71 on it and I will be sending it to Robert's shortly for some modifications and a rebuild. He can apparently do some pretty impressive things with a 71, so it would probably be a waste of a good carb and good money to hog out a good 51. He said that he can build 71s to support up to 800 cubic inches. How big are your tractors?



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burns

10-15-2002 07:05:51




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 Re: JOHN DEERE BIG NUT CARB. QUESTION in reply to 2 cylinder, 10-14-2002 16:38:21  
That depends on your engine specs. A big cube engine will need/be able to handle more cfm. Robert's Carb offers the super 51 for around 28% more airflow. Even with a stock stroke, I noticed a gain in performance with the carb but I also have all the "other" modifications done to further enhance the air flow into the cylinders. Because of the cost, Robert doesn't recommend the conversion on stock stroke tractors with all the factory equipment in place and to specs.

Also, I'd suggest keeping the 51 stock and working with the 71 off of a late A. It was designed for gas and is a lot cheaper than a big nut 51

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wicky

10-14-2002 19:18:20




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 Re: JOHN DEERE BIG NUT CARB. QUESTION in reply to 2 cylinder, 10-14-2002 16:38:21  
I think that taking carberaters and boring them out is just a bunch of wasted money and ruins them good big nut g carberaters. i have seen some that have been modified and they run worst than they did before. just my 2 cents



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