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Old 07-24-2007, 08:25 AM
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Road Demon & Where's the gas going?

I originally started this with a PM to our on-line tech from Barry Grant.

I decided to post to the board so that everyone could learn and benefit or offer their knowledge and suggestions.

I bought a Barry Grant 625 cfm Road Demon carb with electric choke and vacuum secondaries.

I installed this carb on a newly rebuilt (not by me) Chevy 350 that has been bored .060 and has a mild Crane cam installed and dished pistons. I used a 1" aluminum spacer (for an additional vacuum outlet) on top of an Edelbrock RPM intake.

I checked to see that the throttle plates were fully closed (about .020 opening at idle slot) with the choke fully open and off the high idle cam before installing the carb.

In preparation to the initial engine start-up for the cam break-in, I filled the fuel bowls thru the bowl vents until fuel was visible halfway up the sight glass of each bowl.

Three days later when I was ready for the initial start-up I noticed that no fuel was visible in the sight glass of either fuel bowl. I removed the carb and saw that there was fuel in the bottom of the intake. I removed both bowls to check for debris and found nothing. Very clean internally. I checked the tightness of the base screws to the main body and found then slightly loose. I tightened them back up and re-installed the carb. I filled the bowls thru the vents again.

Initial start-up went fine. Fired right up and I ran the engine to complete the cam break-in. Shut the engine down. Changed the oil and filter. Fired the engine back up. Started immediately. I adjusted the idle to 700 RPM in Drive. Drove around the block. Open headers used for break-in so I didn't go out of my neighborhood. Carb responded very well but is running rich. I have not done any adjusting of the air/idle screws yet. Pulled back in my garage and shut it down.

Three days later I have again noticed that the fuel level in the bowls is down below the bottom of the sight glass. I checked this every day and it was a very gradual loss. Not from evaporation from any heat buildup. Throttle plates are closed.

Where's the gas going?

The photo is before the air cleaner was installed with temporary exhaust headers for cam break-in. I have ceramic coated lake pipes for the final exhaust.
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Last edited by Frisco; 07-24-2007 at 08:33 AM. Reason: added photo
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Old 07-24-2007, 10:35 AM
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carb

What did the tech guy tell you yo do???

I know this sound like a pain but,,,buy a brand new carb to intake gasket. Install it then run the engine until up to temp. Park the car a wait a few hours, carefully remove the carb and see if the gasket is wet with fuel...

If it is PM me and i'll chat with you about what could be the problem

Keith
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Old 07-25-2007, 07:20 AM
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Quote:
Originally Posted by k-star
What did the tech guy tell you yo do???
Sent me a PM back asking how well the engine re-started. I replied back and he has not answered.



Quote:
Originally Posted by k-star
I know this sound like a pain but,,,buy a brand new carb to intake gasket. Install it then run the engine until up to temp. Park the car a wait a few hours, carefully remove the carb and see if the gasket is wet with fuel...

If it is PM me and i'll chat with you about what could be the problem

Keith
I did this when I removed the carb the first time. There was no gas on the gasket. The gas didn't show up in the intake until a couple of days had gone by. No gas externally or at the shafts. Only in bottom of the plenum.

The carb sits flat on the intake and the spacer. There is no rock. All mating surfaces are flat.

I guess I could go back to a Holley. I thought I'd give the Demon a try. It is a good looking carb although from what I've seen posted on this site it doesn't seem to be a very good choice. I am very puzzled by the lack of response from the tech guy that comes here. He must be really busy.
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Old 07-26-2007, 07:10 AM
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Back to the top.

Anyone?
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Old 07-26-2007, 08:25 AM
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Quote:
Originally Posted by Frisco
Back to the top.

Anyone?
1. Retighten bowl screws & power valve;
2. replace bowl, metering block, & power valve gaskets,
3. clean the air bleeds
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Old 07-26-2007, 08:42 AM
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Quote:
Originally Posted by Not A T 25
1. Retighten bowl screws & power valve;
Bowl screws are tight. I did not check the tightness of the power valve with a wrench. It seemed to be tight otherwise. Since there is no power valve in the rear bowl and it also loses gas after sitting, this does not seem to be a possible area of concern except for the front bowl. I will check this out.

Quote:
Originally Posted by Not A T 25
2. replace bowl, metering block, & power valve gaskets,
I have not changed any of the gaskets as they seemed OK. No gas is leaking to the outside areas of the carb. I do have gaskets on order at this time.

Quote:
Originally Posted by Not A T 25
3. clean the air bleeds
I saw nothing internally that would cause any blockage or stop the flow of gas or air. The carb actually ran well for the "out of the box" factory settings. Very responsive. It is a little rich and I have not adjusted the air/fuel screws yet. The only adjustment I have done to date is the idle speed has been set to 700 RPM with the trans in Drive, choke fully open, engine at operating temps, and the air cleaner installed.

Thanks Not A T 25 for your reply.
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Old 07-26-2007, 08:43 AM
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In the summer months, gas evaporates very quickly. Cap the vent tubes and watch the gas level in the site glass. Of course, you can't drive with the vents capped but it is a good test to check for evaporation.
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Old 07-26-2007, 08:46 AM
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Quote:
Originally Posted by 454C10
In the summer months, gas evaporates very quickly. Cap the vent tubes and watch the gas level in the site glass. Of course, you can't drive with the vents capped but it is a good test to check for evaporation.
Thanks for the suggestion. This is easy to check out.
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Old 07-26-2007, 09:39 AM
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Quote:
Originally Posted by Frisco
I have not changed any of the gaskets as they seemed OK. No gas is leaking to the outside areas of the carb. I do have gaskets on order at this time.



I saw nothing internally that would cause any blockage or stop the flow of gas or air. The carb actually ran well for the "out of the box" factory settings. Very responsive. It is a little rich and I have not adjusted the air/fuel screws yet. The only adjustment I have done to date is the idle speed has been set to 700 RPM with the trans in Drive, choke fully open, engine at operating temps, and the air cleaner installed.

Thanks Not A T 25 for your reply.
I do know that a bad gasket can cause a fuel bowl to leak down into the manifold and BG has had problems in the past with chips and contaminants in the carbs so taking some carb cleaner and blowing out the air bleeds would be a wise thing to do. Are the carb bowls dry or just below the site glass? If they are dry I doubt very much that it would be evaporation.
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