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Old 08-27-2012, 07:33 PM
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Demon Carb Warped Base Plate

I got a Road Demon 650 Carb, that is what my friend said it was, for free. Problem he was having is it doesn't idle. Car starts, idle really rough, engine then dies. When he first installed it, it ran perfect. He took off the carb, and thinks when he bolted it back on he might have over torqued the nuts and warped the base plate. He installed another carb and engine idles good, so he thinks something is wrong with the carb. I installed it on my engine to see if it works and same thing idles really rough, I can keep the engine running if i put my feet on the gas but it sounds really bad. I tried putting a straight edge on the base plate and everything looks flats. Do you think having a warped base plate will make the engine idle rough? Do you think it could be something else. Don't want to spend a lot of money trying to fix it. Thank you for your help.
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Old 08-27-2012, 07:46 PM
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Quote:
Originally Posted by pukas84 View Post
I got a Road Demon 650 Carb, that is what my friend said it was, for free. Problem he was having is it doesn't idle. Car starts, idle really rough, engine then dies. When he first installed it, it ran perfect. He took off the carb, and thinks when he bolted it back on he might have over torqued the nuts and warped the base plate. He installed another carb and engine idles good, so he thinks something is wrong with the carb. I installed it on my engine to see if it works and same thing idles really rough, I can keep the engine running if i put my feet on the gas but it sounds really bad. I tried putting a straight edge on the base plate and everything looks flats. Do you think having a warped base plate will make the engine idle rough? Do you think it could be something else. Don't want to spend a lot of money trying to fix it. Thank you for your help.
I would baseline the carb back to factory specs and settings then try it again.

Be sure the power valve isn't blown/leaking.

Be sure the float level is correct.

Be sure the ends of the idle mixture screws aren't deformed from being overtightened.

Look inside the throttle plate bores to be sure the idle mixture screws weren't overtightened. The casting can break if this happens.

Check to see if the secondary throttle blades have been opened too far. Check the manual for correct adjustment of the secondary throttle blades as well as the primary transfer slot.
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Old 08-28-2012, 06:56 AM
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IF the baseplate is slightly warped; thats not too hard to correct.
Find a completely level surface such as a piece of window glass or your tablesaw table. Set the carb on the flat surface and use a feeler gauge, check and see any high or low spots. To correct the warped 'plate, you can tape a piece of emery cloth to the same surface and move the carb body in an X pattern, checking your progress often with the feeler gauge.

My suggestion is that its something else as Cobalt suggests. Also if the baseplate is severely warped; it cannot be fixed easy.
What kind of gasket are you using? Sometimes people stack two gaskets, you don't need to do this.
Are you sure the carb wasn't tightened down improperly?
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Old 08-28-2012, 08:21 AM
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Barry Grant (I assume it's that vintage) had some real problems with carbs over a pretty good length of time. What happened is they were assembled with manufacturing debris still in passages. We had their customer service rep here while Grant was in business and his fix was to disassemble and clean. Or if still bad, return for repairs. Summit stopped selling these carbs for a 2-3 years due to BG's poor customer service and refunds.

A mildly warped base can be compensated for with 2-3 gaskets
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Old 08-28-2012, 09:01 PM
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I checked with my friend and he said he never adjusted the carb but i will check the settings. I have the carb off the car and was tinkering with it. If I give it full throttle sometimes it will stay open and other times it will return back to close. Is this how it's suppose to be? The gasket I am using is a rubber type of gasket. I will do the feeler gauge to see how warped if any it is.
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Old 08-29-2012, 01:17 AM
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I agree with Irelands Child. I had the same problem with one of their carbs on a new build before going to the Weber IDAs. I fought with that thing trying to get it to run right for months. One day I got so frustrated, I disassembled the entire thing. I found aluminum chads in almost every machined passage. After taking the time to clean everything out and blowing out all passages, it ran like a top.
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Old 08-29-2012, 04:29 AM
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I third what Ireland said. I had bought a new 625 Road demon jr.
When I first got it and set it up it ran good and idled fine. I ran it for months without issue. Then one day out of the blue all of a sudden it wouldn't idle anymore. So I removed it, got a few cans of carb cleaner and set to clean it out. I blasted the idle circuits and found them full of CNC shavings from the machining process. There was so much of it packed up in there I couldn't figure out how it idled at all. Once I got them cleaned out and made sure I blasted all the other passages she went back to idling smooth and ran great.
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Old 08-29-2012, 06:43 AM
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Does anyone else remember when Barry Grant blew his top and blasted people (I think it was on YellowBullet)? Said some pretty vulgar things about his customer base and said that his carbs were well made and these problems were isolated incidents. Yet; every single person I know who has a Demon carb; had these problems. To the OP: let us know how this shakes out.
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Old 08-29-2012, 11:45 AM
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BG customer service was as poor as their QC! When BG went bankrupt it was no surprise, as he had some serious issues within. Now that Holley rescued BG and owns the company, I expect the service and QC issues will be a thing of the past.
I always use a straight edge on the carb bases and turn the carb upside down to check. I can put a light behind and easily see if there's a warped base.
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Old 08-29-2012, 02:46 PM
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BG carb woes

I bought one of the BG Road Demons at a reduced price - it must have been like the Holley deal, where a carb has been returned for warranty and they disassemble it, clean it and sell it again for $100 off. Anyway - it worked well out of the box and was easy to tune but....

I got a bad tank of gas and the needle and seat assemblies went to sticking - alcohol in the fuel maybe? Didn't work with BG's brand of Viton? After reading about other's difficulties with the leftovers in the passages - tore it clear down and never found a thing. Put new (steel) needle and seat assemblies in it and it settled down and worked right.
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Old 08-29-2012, 02:53 PM
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Quote:
Originally Posted by pukas84 View Post
I got a Road Demon 650 Carb, that is what my friend said it was, for free. Problem he was having is it doesn't idle. Car starts, idle really rough, engine then dies. When he first installed it, it ran perfect. He took off the carb, and thinks when he bolted it back on he might have over torqued the nuts and warped the base plate. He installed another carb and engine idles good, so he thinks something is wrong with the carb. I installed it on my engine to see if it works and same thing idles really rough, I can keep the engine running if i put my feet on the gas but it sounds really bad. I tried putting a straight edge on the base plate and everything looks flats. Do you think having a warped base plate will make the engine idle rough? Do you think it could be something else. Don't want to spend a lot of money trying to fix it. Thank you for your help.
Check the gasket, body to baseplate if itīs the wrong one out of a rebuild kit it wonīt idle.......experience....
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Old 08-30-2012, 02:57 AM
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When I heard that Holley had bought BG my feelings were just the opposite.
I've said it many times, Holley's quality control is just about a joke. Over the last 15 years I've installed just as many new holley's as the next guy on various peoples vehicles. Every single one I installed new out of the box had parts missing. At one time I had bought a new 600 Holley for basic street daily driver duty. It was missing parts when I got it. So after I got that straightened out, I finished tuning it and drove it. Very very rarely would I ever kick in the secondaries which were vacuum operated. Within a year, I started having problems with the carb. Me and a friend of mine stripped it down and found the throttle shaft bushings on the secondary side were completely worn out. They were made out of really cheap plastic. So I thought no problem, I'll call Holley up and get some more. Wrong. Holley didn't offer them and neither did anybody else. So I was forced to remove the throttle base and throw it away and find another one to replace it. By the time I found one my G/F suprised me by buying me a Demon and I never fooled with Holley's again.
However since the demon came with it's own set of issues, I went back to what I started with, a Quadrajet and that's all I'll use now.
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Old 09-19-2012, 07:42 PM
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I checked the baseplate with a window glass, and yup its warped. I had an extra gasket so I doubled up the gasket and now it idles. If I rev the enging it sounds good but if I rev it up slowly the engine starts to stumble. Still didn't clean out the passages, wanted to see if putting the two gaskets would work.
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Old 09-20-2012, 01:11 AM
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Assuming the window glass is without flaws.

Iīd check it with a steel straightedge, horizontally, diagonally.
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