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Discussion Starter #1
was wondering if someone can steer me in the right direction. I have a blown BBc 427 with 2 750 holley carbs. the boat runs great for the most part. Now every now and again when i jump on the throttle, there is a nano second of a hesitation. fuel pressure set at 7. what should my timing be ballpark? since ive had the boat, never checked timing because the boat ran so good. thx:)Unsure
 

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Discussion Starter #2
oh yeah, i removed my headers and installed zoomies. didnt like the zoomies so i re-installed headers, not sure if that makes a difference.
 

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The guys who will be able to help will want to know your compression ratio, how much boost you're making, and what fuel you use. Might also want to know aluminum or iron cylinder heads, distributor, and if it's locked.
 

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Discussion Starter #4
great, dont have a boost guage, not sure about compression, thats what sucks when you buy an engine and the guy you bought it from doesnt know anything. i am running 100LL av gas, and mallory distributor with pertronix no points. thx
 

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Discussion Starter #5
All the info i have

Mfi
Locked distributor
Iron heads
Twin 750 holleys.
100ll av gas
Gonna buy a boost guage, but will not know compression ratio
Idles at 1100
 

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What is your timing set at now?

I have next to zero experience with blower engines, so I'm not the guy to send you in the right direction... just making it easier to get the answer you're after.

In my experience, a slight hesitation off idle would be a carb setting issue. Accelerator pump, accelerator pump cam, transition circuit... something like that. But, who knows...

Oh! What blower? 8-71??? Over/under drive ratio?
 

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Discussion Starter #8
Ok. Thanks and thanks. I need to provide more info. Will check timing and accelerator pumps as well. Also its 6-71 bds and underdriven, but not sure how much. Thanks and i will play with it tomorrow.
 

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Look at overdrive/ underdrive. That will be a start.
28 to 32 is a starting place.
Hesitation with a locked advance is not a timing issue. It is a squirter or air bleed issue.
If you ease into throttle does it hesitate, or if you whack it? The throttle...
Wags

BTW, with all the info you have you are going to get generalizations.
 

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OH... 6-71 and underdriven... it ain't making much boost.
If you take off the belt, does the blower turn easily by hand, or takes some effort?
Wags
 

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Discussion Starter #12
ok from idle it responds well, if im moving good and stab the throttle, it has a real miniscule lag, then launches. my friend also suggested the squirters. so all of your advise is great.
 

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OK so its a hesitation from part throttle on.
Anytime your messing with a carb, first make sure the floats are adjusted correctly!!!
Then check the accelerator pump adjustment. There should be no play between the accelerator linkage and the accelerator pump arm, and it shouldn't be depressing the accelerator pump either. Just zero clearance.



Now you have to determine if your into the secondaries with this happens, or still on just the primaries.
If your into the secondaries, I would start my retarding the acclerater cam. If you use up part of the secondary pump shot so that less than the full shot is available when you punch it. Moving the cam to the #2 hole will delay the pump and you'll have more of a shot when you hit the throttle. AGAIN, this is only if you are into the secondaries at the time you it the throttle. Not if the stumble goes BEFORE you are into the secondaries!!



If the throttle is only on the primaries and it has a stumble when you stab it, then you may need a larger secondary shooter. I seldom buy shooters. Its easier and cheaper to buy a letter drill index set and a pin vice to open the shooters in steps.



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Discussion Starter #16
right on, now i have some homework. i will play around with it today and tomorrow, and keep you updated. thanks! Also since i didnt build the engine, is there any real way to find out compression ratio without all the specs? just for my info? im guessing my hp is around 600 maybe 650?
 

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I know.. .I know....
1) it should have the 50cc pumps on it for a blown piece. I am not a carb guy for years now... are all doubler pumpers big pumps now?
2) does it have 1:1 linkage? This will start the argument. Oh, are carbs mounted sideways... sure unless the funky adapter to mount inline.
3) It isn't a big boost piece, then... so 32* timing should be safe

Wags
 

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I know.. .I know....
1) it should have the 50cc pumps on it for a blown piece. I am not a carb guy for years now... are all doubler pumpers big pumps now?
2) does it have 1:1 linkage? This will start the argument. Oh, are carbs mounted sideways... sure unless the funky adapter to mount inline.
3) It isn't a big boost piece, then... so 32* timing should be safe

Wags
1) No, not all double pumpers have 50cc pumps. Even some Dominators don't. 50cc pumps on the secondaries may help. He says the hesitation is minor so I think he can fix it without buying the 50cc assembly.
2) It won't have 1:1 unless they've been modified.



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Discussion Starter #19
ok the carbs are both holley 4779-2. what i found is that the forward carb has NO fuel coming out of the squirter. bone dry at all parameters. so guessing the accelerator pump bad? secondarys fine.
 

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ok the carbs are both holley 4779-2. what i found is that the forward carb has NO fuel coming out of the squirter. bone dry at all parameters. so guessing the accelerator pump bad? secondarys fine.
Either the diaphram is shot, or the check umprella is shot. If it has a check ball in the bowl instead of a silicone umprella, it may just need to be unstuck and shot with some carb cleaner.
But I bet when you get it fixed it will be alot better.



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