Carb question

« **on:** February 27, 2014, 09:02:33 AM »

I'm still learning about Carbs and I just picked up a Holley 750cfm DP and I am rebuilding it, the question is I pulled off the bowls and metering blocks, should one side have larger jets? And currently it has 98's in one metering block and 90's in the other, what would be good jetting to start? The motor is a .30 over 396 steel crank, forged pistons 10:1, mild cam maybe 525 lift, 1.7 full roller rockers and a Victor JR. Intake, it spins a "B" cut impeller around 5300.

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« **Reply #1 on:** February 27, 2014, 09:50:16 AM »

I think that's a good start. Unless you have a jet kit with a good assortment of jets you're kinda stuck. I'd see how it runs and go from there. Somebody might chime in and personally know of better sizes and you could get those but I think you're good to go.

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« **Reply #2 on:** February 27, 2014, 09:09:17 PM »

Do you know the history of this carb? Did it come on the boat (did someone already set it up to run on this engine)?

Depending on the Holley List# it likely came with 70/71 primary jets and 80 secondary jets.

I'm a believer in using the original Holley jetting as a baseline then adjust from there as needed.

90/98's in a 750 sounds to me like someone had the wrong size carb and was trying to make due with what they had.

Good luck, and keep the updates coming (I'd like to know where you end up at the end).

« **Reply #3 on:** February 27, 2014, 09:38:38 PM »

Quote from: crewchief22 on February 27, 2014, 09:09:17 PM

Do you know the history of this carb? Did it come on the boat (did someone already set it up to run on this engine)?

Depending on the Holley List# it likely came with 70/71 primary jets and 80 secondary jets.

I'm a believer in using the original Holley jetting as a baseline then adjust from there as needed.

90/98's in a 750 sounds to me like someone had the wrong size carb and was trying to make due with what they had.

Good luck, and keep the updates coming (I'd like to know where you end up at the end).

No I just picked up the carb, and the jetting was already like that & it had the power valve block offs in it, so I just put the baseline 6.5 in it. No history on what this carb was on before. I plan on taking some other jet sizes with me and try to do some extensive tuning in the next month or two, also doing a new intake manifold. So kinda back to square one.

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« **Reply #4 on:** February 28, 2014, 06:03:41 AM »

The power valve block off is the reason for the drastic change in the jetting. Usually around a 10 jet size adjustment is a starting point when adding a PV block off.

Like I said before, you'd probably be better off going back to the original Holley baseline and start adjusting from there.

Post the List# and I'll check to see what jets were correct from Holley.

« **Reply #5 on:** February 28, 2014, 06:15:51 AM »

Quote from: crewchief22 on February 28, 2014, 06:03:41 AM

The power valve block off is the reason for the drastic change in the jetting. Usually around a 10 jet size adjustment is a starting point when adding a PV block off.

Like I said before, you'd probably be better off going back to the original Holley baseline and start adjusting from there.

Post the List# and I'll check to see what jets were correct from Holley.

The choke horn is milled off

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« **Reply #6 on:** February 28, 2014, 06:27:01 AM »

Crewchief22, feel free to give me a
call/text or anyone for that matter who has advice or guidance

(562) 277-3431 - Chris

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« **Reply #7 on:** February 28, 2014, 10:23:23 PM »

Quote from: Riverlife_ on February 28, 2014, 06:27:01 AM

Crewchief22, feel free to give me a
call/text or anyone for that matter who has advice or guidance

(562) 277-3431 - Chris

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Hey Chris, it was kind of late when I finally got on and saw this, so I'll try to give you a call tomorrow.

« **Reply #8 on:** February 28, 2014, 10:52:24 PM »

90-98 sound way hi for a 750, and with the power valves blocked, it should be pretty much the same both front and back... with the pv in the primary block the primary jets should be abt 8 sizes smaller than the secondaries.... The jets should prob closer to 72-80 with a pv... Also if you bought it used, be sure the air bleeds haven't been screwed with, cuz that will have your head spinning no matter what trying to tune

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