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Old 02-09-2005, 20:28   #1 (permalink)
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750 Carby/jetting.

Can anyone who has a 750dp on their rig let us know if they run a hydo or solid cam, and what jet works best for their car.
I have a 750dp Mighty Demon with std jets of 75 and 83. On the dyno i was told it was "slightly" rich, but have been advised by some others in the know, to go a bit bigger in the jetting for the combo i have. What are you guys running???
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Old 02-09-2005, 20:41   #2 (permalink)
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Re: 750 Carby/jetting.

That sounds odd? No point going richer if the mixtures shop up well on the dyno. A 750 demons supposedly bigger than a 750 holley isn't it? I run 74's in the front and 86's in the rear and it's currently rich as buggery. It was fine with the weiand and that jetting. Thats what the 279rwkw's were done on.

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Old 02-09-2005, 22:09   #3 (permalink)
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Re: 750 Carby/jetting.

Sounds like you're too big on jets there xdclevo. I've got 378 cubes, almost same cam as you with 750DP and running 71-74 in primaries (weather depending) and 80-84 in secondaries.

If on the dyno your mixtures were too rich then unarguably it is too rich, and you need smaller jets. Doesn't really matter what others advise for your combo because it obviously doesn't mean shit compared to a proper analysis like an AFR reading on the dyno.
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Old 02-09-2005, 22:20   #4 (permalink)
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Re: 750 Carby/jetting.

It all depends on if your drag racing it. I run 75 in front and 83 in rear with air cleaner and hell of alot bigger with no air cleaner.
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Old 02-09-2005, 23:27   #5 (permalink)
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Re: 750 Carby/jetting.

I'm running a 750HP DP 73 prim, 74 Sec @ 210rwkw any bigger jets I lose power!
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Old 02-09-2005, 23:42   #6 (permalink)
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Re: 750 Carby/jetting.

Quote:
Originally Posted by xdclevo
Can anyone who has a 750dp on their rig let us know if they run a hydo or solid cam, and what jet works best for their car.
I have a 750dp Mighty Demon with std jets of 75 and 83. On the dyno i was told it was "slightly" rich, but have been advised by some others in the know, to go a bit bigger in the jetting for the combo i have. What are you guys running???
U have to watch this with a demon carby.The Demon has very linear fuel curve compared to say a Holley and if too rich on a Demon, the car will run like a slug.
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Old 02-10-2005, 01:57   #7 (permalink)
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Re: 750 Carby/jetting.

Quote:
Originally Posted by FPVGT
U have to watch this with a demon carby.The Demon has very linear fuel curve compared to say a Holley and if too rich on a Demon, the car will run like a slug.
After doing some hard runs and checking the plugs again, they look as though it is quite lean.
Also, after that last dyno run, i discovered my aircleaner airsupply was "very" poor. Since then, i have improved a lot, and also now run the K&N extreme lid on top. Definatly getting a lot more air now.
I have some 77 and 85 i will try, and see how it goes.
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Old 02-10-2005, 02:39   #8 (permalink)
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Re: 750 Carby/jetting.

750HP Pro with mild hydraulic and stock heads: Had 77/78 with a rich 12:1 AFR on the dyno. Running 72/78 at present. Bit milder combo than yours though.

Everyone's combo is different, and each engine as you know needs its own individual tune, considering all the variables. The "throw away line" from "those guys" saying go a bit richer on the jetting when you've had a direct "rich" AFR reading on the dyno already.............hmmmmm?

It's good to have those spare jets available whilst on the dyno and see the direct AFR and HP change. Would be good to get it on there again for 30 minutes and see the results. Keep us posted.
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Old 02-10-2005, 03:03   #9 (permalink)
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Re: 750 Carby/jetting.

Quote:
Originally Posted by xdclevo
After doing some hard runs and checking the plugs again, they look as though it is quite lean.
Also, after that last dyno run, i discovered my aircleaner airsupply was "very" poor. Since then, i have improved a lot, and also now run the K&N extreme lid on top. Definatly getting a lot more air now.
I have some 77 and 85 i will try, and see how it goes.
Sounds like another trip to the dyno xdclevo. They can set it up in the ball park, then you can play around going up or down a little front or rear and see what it likes.
Increasing the air flow will change the tune. My last dyno tune was done with the pipes dropped. The car ran well at the strip and as I run around on Lpg I left the jets the same. When I have run petrol with the pipes on it's rich as, black tail pipe, poor idle, fouled plugs etc. I really need two carbs!
If your new air cleaner has uncorked your motor, i.e more air I would think you would need more fuel also, bigger jets.
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Old 02-10-2005, 03:16   #10 (permalink)
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Re: 750 Carby/jetting.

Once you car is setup on the dyno, take off the aircleaner for another power run, just so you know what difference it makes to HP and AFR.
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