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Old 09-18-2012, 12:19 PM
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Demon Carberetter

Can anybody help me with Brand new demon carberetter which is a 650
vacuum secondaries which is on a 350 small block chevy which I cannot seem to get any control over the fuel.

The only way to get any colour on the plugs is to turn the mixture screws in to less than half from full stop. This leads to an off idle stumble and popping back through the exhaust. If I turn the mixture screws out more it leaves the plugs and exhaust flooded.

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Old 09-18-2012, 06:28 PM
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Lots more info may be needed. But, I suspect you have the idle speed / transfer slot set wrong, or the floats need to be adjusted. Does this carb have the idle Eze? If you don't know, check out threads on here with comment by NGTech, and do a little research on the Demon website. By most accounts these are (or can be) very satisfactory carburetors, in spite of some quality problems from years back that continue to haunt their reputation. I still have a brand new one, unused. Waiting for the right engine to be fired up.

PatM
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Old 09-19-2012, 10:41 AM
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Quote:
Originally Posted by PatM View Post
Lots more info may be needed. But, I suspect you have the idle speed / transfer slot set wrong, or the floats need to be adjusted. Does this carb have the idle Eze? If you don't know, check out threads on here with comment by NGTech, and do a little research on the Demon website. By most accounts these are (or can be) very satisfactory carburetors, in spite of some quality problems from years back that continue to haunt their reputation. I still have a brand new one, unused. Waiting for the right engine to be fired up.

PatM
Thanks Pat for reply - I am in England so it is difficult to get help and parts.

Could you make it clearer for me please by the idle speed/transfer slot set wrong.

This carburetor does not have the idle eaze - it was made previous 2001.

By the way this engine is in a 36 three window coupe.
Thanks

Chris Smith
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Old 09-19-2012, 06:24 PM
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The transfer slot is a small slot in one of the primary bores near the throttle plate. The amount of the slot showing above and below the plate shoud be approximately even at a warm idle. There MUST be some of this slot visible both above and below the throttle plate at a warm idle. The "rule" is .020 minimum each side.

Tell us a little more. What is your cam's timing specs, what are your ignition timing specs, what is your compression ratio? That'll be a good start.

PatM
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Old 09-19-2012, 07:10 PM
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Barry Grant owner's manual

May help if you don't have one:
http://www.crankshaftcoalition.com/w...ner%27s_manual

You can see the "Transfer Slot" on Pg. #3, Figure #4 here.
http://www.demoncarbs.com/Assets/doc.../LIT350rev.pdf
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Old 09-20-2012, 07:58 AM
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Suggest of replacing the power valve. It's most likely ruptured.
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Old 09-20-2012, 10:53 AM
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First thing I do with any older Demon that is having troubles is to disassemble and thoroughly clean it, then replace the gaskets. BG had a lot of issues with debris from machining inside passages and ports, and QC was pretty poor back then. Holley now owns BG and they support them well. I would guess OC will be better now too.
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Old 09-20-2012, 11:54 AM
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SSedan64 gives you two good links. Knowing that this carb is 10 years old, the advice to disassemble and clean is good as well. But, while we're at it, it would still be very helpful to understand more about your 350.

PatM
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Old 09-20-2012, 01:25 PM
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You say this is a bran new carb? In one of these posts it says 10 years old or old ? New or old try these suggestions they may help? Also make sure if the carbs new use the demon gasket included in the box!!! some over the counter gaskets disrupt the vacume slots under the carb plate and effect idle!!!! This is mentioned in other threads on this site !!!!
If your not sure about a bad or wrong power valve (opening at low vacuum signal at idle or blown) you can turn in the mixture screws on each side of the metering block all the way in till they bottom out! at warm idle if it stalls the engine the power valve is ok if the engine keeps running the power valve is most likely bad or the wrong one! but if your past the transfer slot as stated earlier this test may not work because your not running on the carbs idle circuit. Retarded timing and carb adjusting to bring idle up can cause the same conditions of popping and bog!! Try advancing initial timing and backing of idle as it increases as the timing is advanced every time you advance the timing a little your idle will speed up as you back off the idle screw your timing will retard a little. after doing this a few times your throttle plates should come back to their proper position to the transfer slot! You can also check your rear throttle plates to make sure they are closing all the way at idle! If you have a vacuum advance make sure there is no vacuum on the diaphragm at idle! If you have vacuum at idle the distributor will advance at Idle and retard at off idle throttle causing bog and popping!

Jester

Last edited by painted jester; 09-20-2012 at 01:33 PM.
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Old 09-20-2012, 02:21 PM
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Hey Jester. I agree. Perhaps when the sun rises in the UK, we'll learn a little more about the current ignition timing and the camshaft he's using. I suspect with a clean out, a resetting of the Throttle plate/Transfer slot position, and some timing adjustment things will improve. But I'd caution not to advance timing if it brings total timing up too high.

PatM
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Old 09-20-2012, 02:41 PM
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Quote:
Originally Posted by PatM View Post
Hey Jester. I agree. Perhaps when the sun rises in the UK, we'll learn a little more about the current ignition timing and the camshaft he's using. I suspect with a clean out, a resetting of the Throttle plate/Transfer slot position, and some timing adjustment things will improve. But I'd caution not to advance timing if it brings total timing up too high.

PatM
I agree pat I was wondering if this is the new Demon since Holley took over production or the older Barry Grant production? A picture of his set up would help too!

Chris

Last edited by painted jester; 09-20-2012 at 02:51 PM.
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Old 09-21-2012, 10:49 AM
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Hey Jester
It's not a recent, or even current carb. Post 4 identifies it as pre-2001. Hence, no Idle Eze. But, it still could well be brand new. I have a 750 Speed Demon, never used, VHS instruction video, no Idle Eze. It sits on a motor I haven't yet started. I'll be retiring in late Novmber, and I figure the Demon will become "used" before new year's eve.
The OP is in the UK (note the spelling of carburetor) so his clock is a lot different. But I do wish he'd post back with responses regarding his cam and ignition timing.

PatM
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Old 09-21-2012, 12:51 PM
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Quote:
Originally Posted by PatM View Post
Hey Jester
It's not a recent, or even current carb. Post 4 identifies it as pre-2001. Hence, no Idle Eze. But, it still could well be brand new. I have a 750 Speed Demon, never used, VHS instruction video, no Idle Eze. It sits on a motor I haven't yet started. I'll be retiring in late Novmber, and I figure the Demon will become "used" before new year's eve.
The OP is in the UK (note the spelling of carburetor) so his clock is a lot different. But I do wish he'd post back with responses regarding his cam and ignition timing.

PatM
My wife spells the same way like I spell "tire" she spells it "tyre" so did my mother.

I've ordered bran new Demons in the box with Quality problems !! One the front right jet wasn't drilled there was no hole in the jet, one the base plate was warped, another had filings in the bowl from machining! Demon was a great product at the start but near the end the quality control was terrible! Barry Grant had a great product in the beginning but I think The employees let him down Or whoever he contracted to do the machining and assembly and inspections. In my speed shop I hated to see a car come in that wanted or had a Demon! Since the 80s Ive probably installed over 100 demons even the inline 4! and had no problems at all till the last 4 or 5 years of production!!! Then it was like they were cutting corners and turning out faulty products or actual sabotage on the line !!!

From what I heard I dont know if true or not! He was overwhelmed with returned merchandise at the end. Its funny how just a few trusted workers can ruin the reputation of the man that hires them!!!! At one time Demon was as good as it looked it was a beautiful piece of engineering and design and was easy to tune in!

The reason I mentioned sabotage is because I had a new Road Demon out of the box that when installed flooded over and I couldn't adjust the float when I pulled the bowl There was a cigaret butt in it That was intentional!!!!All the problems Ive had with Demon were minor to me and could be repaired very easy like drilling or replacing the jet, or cleaning out the machining filings, or removing the bowl and removing the cigaret butt!!! But a laymen that expects to bolt on a new carb and just set the idle and go would probably return it if he had a problem that most shops that know carbs would fix on the spot!

The home builder that just buys one will probably never have a problem!! but lets say demons sold were 1,000,000 and only 10% had a minor problem and were returned that would make 10,000 people complaining and 10,000 carbs that Grant would have to fix and return that probably have nothing wrong to begin with except the person that sent it back doesn't know how to install or tune a carb. 10,000 people complaining can bring down a reputation of a good product quick!!!!

Jester
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Old 09-21-2012, 05:58 PM
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Demon Fuel Systems, look up your carb installation setup and troubleshoot here.

I love my Speed Demon carb, I admit everything has to be just right, but when it is
Set the floats, transfer slots, get it back to basic setup then tune with a vac gauge.

The OP is in the UK (note the spelling of carburetor) so his clock is a lot different.
We spell carburator the same as you, he just made a spelling error.
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Old 09-24-2012, 01:17 PM
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Hi Malc

You know, I'd have sworn way back when (in the dark ages, perhaps) I had a TR3 manual that spelled carburetor using two "t"s. It wouldn't be the first time my memory failed me. And since I'm using an "e" where you've used an "a", well, it's clear neither my spelling nor my memory is very good.

Thanks for the update, though.

PatM
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