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Carb Backfire...now gas overflows into intake!

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Old 06-14-2018, 04:02 PM   #1  
doorgunner
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Default Carb Backfire...now gas overflows into intake!

Holley 600 cm carb has been great until backfire happened after replacing dist. coil.

The cylinders must have been loaded with fuel from cranking with the bad coil. I installed the new coil......BIG BACKFIRE.

I removed the air filter and cranked the engine over a few seconds.....fuel started pouring into the carb throat from the nozzles.

I removed the front and rear bowl plugs to check the fuel levels......gas poured out of the sight holes.

The float adjustment screws on top of the bowls have no effect.....the fuel overflows/gushes out of the sight holes and nozzles when cranking.

IS IT POSSIBLE THE FLOAT ARMS ARE NOW BENT SO THAT THE ADJUSTI G SCREWS ARE NOT CONTACTING THE FLOAT ARMS AND NEED TO BE RE BENT?
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Old 06-14-2018, 04:22 PM   #2  
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The backfire created a whole lot of pressure that had to go somewhere. Check for ruptured power valve, blown gaskets, etc. Power valve bit the dust on me about a year ago when I had the timing way off and made it backfire.
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Old 06-14-2018, 04:24 PM   #3  
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as stated above you have to remove both bowls and see what damage occurred, wonder if the floats were crushed.
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Old 06-14-2018, 04:43 PM   #4  
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Originally Posted by ronarndt View Post
The backfire created a whole lot of pressure that had to go somewhere. Check for ruptured power valve, blown gaskets, etc. Power valve bit the dust on me about a year ago when I had the timing way off and made it backfire.
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as stated above you have to remove both bowls and see what damage occurred, wonder if the floats were crushed.

The power valve and bowl gaskets are still good. The floats are made from solid material and can't collapse.

Im thinking because the float adjusting screws have no effect that the extreme pressure jammed the float ARMS against the needles causing the ARMS to be BENT to the point that the adjusting screws will not close the needles in either bowl.

Does this sound POSSIBLE to you?
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Old 06-14-2018, 05:40 PM   #5  
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Which 600 Holley? The DP or the vac secondary spreadbore?
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Old 06-14-2018, 05:43 PM   #6  
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Are you draining the bowl before you try and adjust the floats?
Long shot but wondering if your oring on needle and seat isnt fubared?

Last edited by cuisinartvette; 06-14-2018 at 05:44 PM.
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Old 06-14-2018, 05:56 PM   #7  
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The needle & seats may shot, those o-rings can disintegrate and that little viton tip can get screwed up. I don't know about bending float arms but you might've boogered up that tip cranking down hard. They are cheap. I'd replace them after I dried the car out and cleaned the plugs.

One note about those floats. I made a driveway gasoline fountain when I my Holley 4160 over the winter. The floats that were in it were yellowish and did not have a spring on the float arm - and no way to put one in. Now there are two new black Holley floats in there with the proper springs. Holley said that was a product bulletin a long time ago.



Good luck
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Old 06-14-2018, 06:10 PM   #8  
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Quote:
Originally Posted by maj75 View Post
Which 600 Holley? The DP or the vac secondary spreadbore?
Quote:
Originally Posted by cuisinartvette View Post
Are you draining the bowl before you try and adjust the floats?
Long shot but wondering if your oring on needle and seat isnt fubared?
Vac secondary/yep....drained bowls/needle tips and o-rings look new/will post pics when I get home tomorrow night

Thanks.....any more ideas are welcomed.
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Old 06-14-2018, 06:19 PM   #9  
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The needle & seats may shot, those o-rings can disintegrate and that little viton tip can get screwed up. I don't know about bending float arms but you might've boogered up that tip cranking down hard. They are cheap. I'd replace them after I dried the car out and cleaned the plugs.

One note about those floats. I made a driveway gasoline fountain when I my Holley 4160 over the winter. The floats that were in it were yellowish and did not have a spring on the float arm - and no way to put one in. Now there are two new black Holley floats in there with the proper springs. Holley said that was a product bulletin a long time ago.



Good luck
Hmmmmm.....the carb is less than two years old But I don't remember seeing the spring on either float. The needle tips are I was easy on screwring down the threaded needle tubes.
Can I buy a repair kit at OReilley/etc. ?
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Old 06-14-2018, 07:37 PM   #10  
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Hmmmmm.....the carb is less than two years old But I don't remember seeing the spring on either float. The needle tips are I was easy on screwring down the threaded needle tubes.
Can I buy a repair kit at OReilley/etc. ?
If the carb is that new Iíd be surprised if you had that spring problem. Mine is an Ď80s vintage. That said, yes you can buy the little springs on eBay for a couple of bucks but the problem wasnít they were missing it was that they werenít there in the first place and there was no way to put them on. The replacement float arms had small notches that allow you to put the springs in.

I had two needle/seat problems. One was a disintegrated secondary before I rebuilt it and the other was just two days ago. Thatís why I responded to this thread. I must not have tightened the set screw enough and it backed out and man, flooding can happen quick. It sounds like you have a needle/seat problem and maybe, maybe a float problem but why both at once? Sounds weird. The nut is the adjustment and the screw locks it.

I saw some mention of a power valve. No help here with a car that isnít running but Holley told me that when you are setting the fuel/air mix at idle if you can screw those two adjustment screws all the way in and the car still runs then the power valve is blown. Something to check later.

When my was really flooded it was hard to tell what was going on. I pulled the needle/seats, removed the sight plugs, disconnected the fuel line, cranked it over to clear the cylinders, cleaned the plugs and put a fan on it. Let it dry out real good.
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Old 06-15-2018, 07:36 AM   #11  
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With bowls off, you can eyeball up whether they close needle valves or not. And set float level. I also blow in the fuel inlet. Now turn bowl upside-down and blow. That checks needle sealing. Pull floats and throw them in a bowl of gasoline. They float or sink? Which bowls, side or center pivot? I have a bunch of side-hanger bowls-carbs I am not using.

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