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stumble at the hit-on alcohol
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DRR Trophy
posted
stumble at the hit-on alcohol, 750, 460 bbc. low compression 10:1
All, I have a bad stumble at the hit with this simple combo, i have large squirters and 50cc pumps both ends. Car runs good except for this, I drilled the rear squirter to a .065 drill. helped a little im out of squirt at that point. any ideas? thanks
 
Posts: 22 | Location: ohio | Registered: August 15, 2017Reply With QuoteReport This Post
DRR S/Pro
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Drill them both out!

Sounds like your to lean on the idle side which compounds the problem, richen that up too.

If you can raise the rpms before to stab it, this will also help.

Anything you can do to reduce the initial load on the motor at the hit will help too, smaller manifold, looser converter, more gear, smaller carb will all help
 
Posts: 2163 | Location: Tewksbury, MA,USA | Registered: November 03, 2000Reply With QuoteReport This Post
DRR Top Comp
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Blow out your air bleeds and then you may have to fatten idle mixture some.


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Posts: 4217 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
DRR Sportsman
Picture of 57 Vette
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Easy fix, is to turn out the idle mixture screws to richen the mixture. And if that does not fix it,try a smaller air bleed.Also make sure you have enough initial timing and the dist is locked out.

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This message has been edited. Last edited by: 57 Vette,
 
Posts: 268 | Location: Toronto Ont/Surprise AZ | Registered: August 18, 2003Reply With QuoteReport This Post
DRR Trophy
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All good advice mentioned but i wanted to add my recent experience. I had a persistent stumble where nothing I tried helped. Eventually found the pump arm springs (the ones where you adjust pump arm clearance) would compress as they were pushing the lever of the accelerator pump not giving the direct pump shot needed at the hit. I fixed it by further compressing the spring (made stiffer) using multiple small washers as shims.
 
Posts: 4 | Location: Nc | Registered: August 11, 2017Reply With QuoteReport This Post
DRR Sportsman
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Flip it upside down and see how much transfer slot is exposed before doing all the tweaks and drilling.
 
Posts: 478 | Location: here | Registered: February 12, 2006Reply With QuoteReport This Post
DRR Trophy
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[QUOTE]Originally posted by Curly1:
Blow out your air bleeds and then you may have to fatten idle mixture some.[/QUOTE)

What he said
 
Posts: 4 | Location: Melbourne, Australia | Registered: March 29, 2012Reply With QuoteReport This Post



DRR S/Pro
Picture of Eman
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quote:
Originally posted by team:
Flip it upside down and see how much transfer slot is exposed before doing all the tweaks and drilling.

Do this first. Check and adjust your pump arm springs. If needed change pump cams.
 
Posts: 1550 | Location: E TN | Registered: February 13, 2009Reply With QuoteReport This Post
DRR Top Comp
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First thing you do to figure out if it's rich or lean, is turn all four idle mixture screws to one turn out. If that makes the stumble worse, you know it is lean, as long the stumble improves when you turn all four idle mixture screws to a turn and a half out.

If it's lean go to a smaller hole size idle air bleed. No stumble with the mixture screws turned out one and a half turns, or less down to one turn, is Ideal.
 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
DRR Sportsman
Picture of FootbrakeJim
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Lot of good advice on here.
Man, that is such an undersized carb for that engine, it should have tons of vacuum and should not have stumbling issues unless something is way out of whack on your carb.
Was it converted from a gas carb? And by who?
Check float levels, then check quality and quantity of shooter squirt, (with engine OFF).
You should be getting a massive shot on any alky carb. My 468 has a 1050, shooter nozzles are .110" And that spray should begin immediately with first movement of throttle.
Is your primary/secondary linkage progressive, or 1:1? I.E: Do primaries open first, (progressive), or do all 4 blades open equally at the same time (1:1)? If progressive, you generally need more pump shot on your primaries.
What color pump cams are on it?


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Posts: 1084 | Location: Farmersville, TX  | Registered: December 05, 2002Reply With QuoteReport This Post
DRR S/Pro
Picture of banjo
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Is this a new issue?

Check the rubber check valves in the squirter pumps, it will still squirt, just not the full volume.


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Posts: 1837 | Location: San Angelo | Registered: March 07, 2005Reply With QuoteReport This Post
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