Holley carburater pullover on 520 Gitzu

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Kenny627
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Holley carburater pullover on 520 Gitzu

Post by Kenny627 » Sat Mar 21, 2015 10:47 pm

Have a Gitzu 520 with a 600 cfm Holley carburator. At an idle it drips out of the squirters. When you put it to half throttle it pours out of the squirters. Put a new Holley on it and it does the same thing. It is using more fuel and running rich. Any advice on how to fix this? Heard about putting a MA 45 on it and was wondering if it would work.
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trailerdon
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Re: Holley carburater pullover on 520 Gitzu

Post by trailerdon » Sun Mar 22, 2015 8:37 am

Went to a 650 on mine "mechanical secondary". Made a big difference. That being said, on yours have you adjusted the fuel / air mixture ? to rich is not the end of the world, to lean an you roast a cylinder

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Re: Holley carburater pullover on 520 Gitzu

Post by broncobill » Sun Mar 22, 2015 9:02 am

You can modify manifold to run a HA6 which is a side draft carb. I hear some people are having good results with a 650 Quick Fuel carb.

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Re: Holley carburater pullover on 520 Gitzu

Post by loudmouse » Sun Mar 22, 2015 9:07 am

I have experienced this on several large aircraft engines and was not able to stop it no matter what I did. The correct fix would be a larger carb to lower the signal to the boosters. I also do not recommend using the vacuum secondary single feed holley as u will empty the back bowl and the engine will lay down on power from running lean.
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John Fenner
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Re: Holley carburater pullover on 520 Gitzu

Post by John Fenner » Sun Mar 22, 2015 9:13 am

Too much carb. A tuned 450 or 550 holley would be best for that engine.
I never finish anyth,,,.

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Deano
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Re: Holley carburater pullover on 520 Gitzu

Post by Deano » Sun Mar 22, 2015 9:25 am

Are you running an unregulated electric fuel pump? Or if it's internal, maybe it took a dump.

Generally, Holley carbs are designed to use and run most reliably with 7 or 7.5 psi.

Pressure much beyond that and all kinds of weird things can happen that will make one look defective.
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Kenny627
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Re: Holley carburater pullover on 520 Gitzu

Post by Kenny627 » Sun Mar 22, 2015 9:50 am

The psi at the carb is running 5-6 lbs. we used two different guages. This problem just started recently. I bought a brand new carb and it is doing the same thing. I just did not want to keep throwing money at it to try and fix the problem.
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John Fenner
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Re: Holley carburater pullover on 520 Gitzu

Post by John Fenner » Sun Mar 22, 2015 10:26 am

What kind of pump do you have?
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Re: Holley carburater pullover on 520 Gitzu

Post by nbooth » Sun Mar 22, 2015 10:30 am

Boat uses athird more fuel than before.carb was rebuilt because I noticed squirters just dumpin fuel in motor.this boat is 12 years old.never had a problem till now.

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Re: Holley carburater pullover on 520 Gitzu

Post by nbooth » Sun Mar 22, 2015 10:32 am

It has a carter electric

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Re: Holley carburater pullover on 520 Gitzu

Post by John Fenner » Sun Mar 22, 2015 10:33 am

Float levels set right?
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Re: Holley carburater pullover on 520 Gitzu

Post by nbooth » Sun Mar 22, 2015 10:51 am

Yes.rebuilt and tuned by loudmouse

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Re: Holley carburater pullover on 520 Gitzu

Post by nbooth » Sun Mar 22, 2015 11:01 am

I have a video of what its doin if anyone would like to see it.

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Re: Holley carburater pullover on 520 Gitzu

Post by John Fenner » Sun Mar 22, 2015 11:07 am

Sure
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Re: Holley carburater pullover on 520 Gitzu

Post by loudmouse » Sun Mar 22, 2015 11:22 am

A 500 is way to small on a 520
15' Alumitech deckover LSX TT Oxbox 84" JX 4-blade
Gas required Water optional :dontknow:
Built and Tuned by Me
14'X8' JW, Chevrolet 122CID LNF Turbo Engine, Ox box, 80" NGR 3 blade

Life is short, eat your dessert first! :downtown:

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Re: Holley carburater pullover on 520 Gitzu

Post by cdid » Sun Mar 22, 2015 11:32 am

I run a vac sec quick fuel 650 on mine and other than my mag issue that card has done great
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Re: Holley carburater pullover on 520 Gitzu

Post by loudmouse » Sun Mar 22, 2015 11:42 am

The carb is a 3310 600. I Rebuilt it to the best it could be for the carb we were working with. Run great. Cranked very good cold or hot. The problem is fuel pull over! The New one does it also just as I said it would. The only way to stop the problem is to go larger to decrease the signal at the booster and vacuum on the squirters. Anti siphon squirters were tried(not my idea), lowered fuel level in bowl, added a small weight to ball under squirter, changed the needlle to the old heavy style instead of the ball in the squirter, attempted to change bowl to a check ball instead of rubber valve but it is a single feed carb. Those 600 single feed carbs are not meant for performance of any kind. That said a 650 or 700 dual feed properly set up for it's intended engine should stop the pull over.
My guess is that most if not all of the larger aircraft engines using this small of a holley carb is experiencing fuel pull over to some degree and increased fuel usage! Hope this helps others finding their high fuel consumption problem.

FWIW, a larger carb was recommended. Now maybe it will get one.
15' Alumitech deckover LSX TT Oxbox 84" JX 4-blade
Gas required Water optional :dontknow:
Built and Tuned by Me
14'X8' JW, Chevrolet 122CID LNF Turbo Engine, Ox box, 80" NGR 3 blade

Life is short, eat your dessert first! :downtown:

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Re: Holley carburater pullover on 520 Gitzu

Post by John Fenner » Sun Mar 22, 2015 11:57 am

Drill out the air bleeds? Emulsion circuits clean?
I never finish anyth,,,.

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Re: Holley carburater pullover on 520 Gitzu

Post by loudmouse » Sun Mar 22, 2015 1:13 pm

The air bleeds have nothing to do with the squirters
15' Alumitech deckover LSX TT Oxbox 84" JX 4-blade
Gas required Water optional :dontknow:
Built and Tuned by Me
14'X8' JW, Chevrolet 122CID LNF Turbo Engine, Ox box, 80" NGR 3 blade

Life is short, eat your dessert first! :downtown:

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Re: Holley carburater pullover on 520 Gitzu

Post by John Fenner » Sun Mar 22, 2015 3:51 pm

Got the cam set on accy pump too tight.
I never finish anyth,,,.

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Re: Holley carburater pullover on 520 Gitzu

Post by John Fenner » Sun Mar 22, 2015 3:53 pm

Vibration and harmonics will build pressure in the circuit. I assumed that it was booster from op.
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Re: Holley carburater pullover on 520 Gitzu

Post by loudmouse » Sun Mar 22, 2015 7:38 pm

No its pull over from the squirters
15' Alumitech deckover LSX TT Oxbox 84" JX 4-blade
Gas required Water optional :dontknow:
Built and Tuned by Me
14'X8' JW, Chevrolet 122CID LNF Turbo Engine, Ox box, 80" NGR 3 blade

Life is short, eat your dessert first! :downtown:

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Re: Holley carburater pullover on 520 Gitzu

Post by dusty burch » Mon Mar 23, 2015 9:51 pm

loudmouse wrote:A 500 is way to small on a 520
If you do the math a 500 is to big ....c.i.×max rpm divide by345 equals cfm× .80percent efficient
% thats how you figure out cfm so in other words a 500 holley find a buddy with a good running carb and runn it one time and see if it isthe carb stuff like this drives you crazy hope you get it

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Re: Holley carburater pullover on 520 Gitzu

Post by John Fenner » Mon Mar 23, 2015 10:46 pm

X 2 Dusty!
I never finish anyth,,,.

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Re: Holley carburater pullover on 520 Gitzu

Post by loudmouse » Mon Mar 23, 2015 11:40 pm

If u want to ride ur 520 with a 500 2b and think thats all that is needed then great. Ur happy and that is what matters, BUT it will pull way more pitch with a larger sized carb. WHY? Because more air will fill the cylinder. When too small of a carb is used high manifold vacuum is created at WOT. This causes a loss of cfms(restriction) available to fill the cylinder. Just as this situation is proving by the pull over. Air speed is too fast thru the venturi or vacuum too high. Thus the fuel is Siphoned out the squirter. BTW volumetric efficiency @ 3000 rpms should be near 100% if the carb, intake, cam and exhaust are matched to the engine size. Any restriction will reduce power. Holley carbs are sized(rated) at 1.5# of vacuum and that is the cfm size. But it is widely known that dropping WOT vacuum to .5# will increase HP a considerable amount. And reducing WOT vacuum from 5lbs to below 1lb is a very sizable hp gain.
15' Alumitech deckover LSX TT Oxbox 84" JX 4-blade
Gas required Water optional :dontknow:
Built and Tuned by Me
14'X8' JW, Chevrolet 122CID LNF Turbo Engine, Ox box, 80" NGR 3 blade

Life is short, eat your dessert first! :downtown:

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