[jameskirk1]

Thought that this might help some one out at one point or another; and I also know that "BG-Tech" may read this as well so they might put it in their memory banks...

I've got a 625cfm Road Demon Jr. on my mouse equipped S-10. It hasn't EVER ran right at idle. Truly awesome response at all other engine speeds, but ALWAYS a rich idle that I could never figure out or tune out of it. I had initial timing set everywhere from 6 to 18 degrees before; no help. The air bleeds were clean. The power valve wasn't leaking. I reset the butterflies/transfer slot so many times I could do it in my sleep. I could shut the idle adjustment screws in all the way and it wouldn't die. I sent Barry Grant Tech e-mails, and read a LOT of posts on this forum, but to no avail...

I FINALLY FIGURED OUT WHAT IT WAS!!!

I had pulled down and cleaned the metering plates and bowls off numerous times on both the primary and secondary side to clean/inspect thoroughly. Something I never did was pull the base plate off of the main body. Well, I was at my wits end, and decided to pull this off as a last resort, just to check before I ordered a fuel injection system (ha ha)...WELL, from the Demon factory, the gasket that seperates the baseplate from the main body was "off"!!! It was scooted over and "rotated" by a few degrees, and this was allowing the idle discharge port to pull all the extra fuel mixture it wanted from the transfer slot!!! (The sealing surface between these two holes is less than a 1/8") So I "re-aligned" it, and have put many test runs on it since, and let me tell you, it truly runs great. I have cured my problem.

I'm not bashing Demon, it is an AWESOME carburetor, worth every penny. And I figured even if I helped even one poor soul scratching his head out there, it would be worth writing about...Cause that's what forums are about.

-=James=-

[Tech @ BG]

James,

Sorry about the troubles you had. If there is anything we can do to help you in the future please let us know.

[machine shop tom]

A friend of mine had the EXACT same problem--same symptoms, etc. He finally returned the Demon and put a 750 Vac Holley on it and was happy ever after. Seems like some pins to keep the gasket in place would be in order. (Hint, hint!).

tom

[k-star]

Tom brings up a good point... Every demon carb that i have worked on has not had any locating pins in the base plate. what is the reason for this????

Keith

[Miket]

I am very happy to see this post. I am on my Second Demon---A Mighty Demon that BG Tech suggested I get after using a Speed Demon...reason for the change....loading up at idle.

Guess what? It still loads up with my new Mighty Demon...now it may be the problem you mention above or the BG Tech guys may be right when they suggest I should be running 18-22 Degrees BTDC. But I am going to check this out tomorrow...I will let you know what I find.

and thanks.

[k-star]

You should go thru that carb and check all the gaskets, and pv, bolts etc to make sure they are all tight. Also to make sure there is no debris in the carb anywhere... Does it have the idle air adjustment in it?????

The timing deal will really help you out if it's retarded.. do you have the right heat range plug it in also?????

Keith

[Miket]

Originally posted by k-star
You should go thru that carb and check all the gaskets, and pv, bolts etc to make sure they are all tight. Also to make sure there is no debris in the carb anywhere... Does it have the idle air adjustment in it?????

The timing deal will really help you out if it's retarded.. do you have the right heat range plug it in also?????

Keith

It does not have the idle eaze feature. I will have to go back through the carb. Timing is at 16 BTDC...I don't consider it retarded but BG says it should be more----which means I have to to do somehting with MY HEI. Plugs are correct.

[k-star]

If you have that much initial timing i don't really think the timing is the problem. Have you been keeping fresh plugs in it as you go along tying to solve this problem????

I had a 750 demon on a customers car that was leaking fuel on the secondary side thru the pv cut out. I never got the problem solved and he sent the carb back to summit for a refund. He got a 650 demon now to try on it. I was in that carb 8/10 times and i never found the problem..

Try running the car and then pulling the carb while the engine is still warm and see if the mounting gasket is wet with fuel. and also sit the carb on the bench on some paper towels and see if it makes them wet.

keith

[Miket]

Originally posted by k-star
If you have that much initial timing i don't really think the timing is the problem. Have you been keeping fresh plugs in it as you go along tying to solve this problem????

I had a 750 demon on a customers car that was leaking fuel on the secondary side thru the pv cut out. I never got the problem solved and he sent the carb back to summit for a refund. He got a 650 demon now to try on it. I was in that carb 8/10 times and i never found the problem..

Try running the car and then pulling the carb while the engine is still warm and see if the mounting gasket is wet with fuel. and also sit the carb on the bench on some paper towels and see if it makes them wet.

keith

BG TEch said it should be timed at 18-22 BTDC...can't do it with my HEI right now. I will try the other suggestions today.

[DoubleVision]

I run a road demon Jr. 625, it`s been a good carb, I did have to clean out the idle circuits though. I had spoken to many techies on the phone, and not only at BG, but other places as well, they all recommened high spark timing, I had my timing set as high as 16 degree`s and it was still a dead player slug out of the hole, but none of them asked, or ever mentioned, which vacuum port the vacuum advance is suppose to be connected at, I had it connected to a ported source, or one that pulls vacuum off idle, after a recommendation from BOBCRMAN, I set it at 12 degree`s BTDC with vacuum advance disconnected and plugged, then connected it to the manifold source or full time vacuum, I rechecked the timing with it connected, the timing at idle was right around 24 degree`s BTDC, I drove the car and what a huge difference, it has outstanding low end, and good midrange, something it never had before, vacuum advance at idle is needed since the idle is lean and usually off idle is lean, leaner mixtures burn slower than do richer mixtures so more spark timing is needed. In one case where we were running a 400 with 6 inch rods and a comp solid 260 duration cam, we set the base timing at 20 degree`s, since we used such a big cam vacuum advance can`t be used, so we made up for the lack of it just by advancing base timing more.

[Tech @ BG]

Originally posted by machine shop tom
Seems like some pins to keep the gasket in place would be in order. (Hint, hint!).

tom

We haven’t used locating pins in the baseplates of our carburetors for a number of years, nor has Holley®. Until these comments here we had not heard of these types of complaints. We track all of the feedback we get from our customers to evaluate what we are doing, to determine how to improve our products. We have not seen these as a problem in past, but passed on the feedback we’re seeing here we will look into possibly making a change.

[Miket]

Originally posted by DoubleVision
I run a road demon Jr. 625, it`s been a good carb, I did have to clean out the idle circuits though. I had spoken to many techies on the phone, and not only at BG, but other places as well, they all recommened high spark timing, I had my timing set as high as 16 degree`s and it was still a dead player slug out of the hole, but none of them asked, or ever mentioned, which vacuum port the vacuum advance is suppose to be connected at, I had it connected to a ported source, or one that pulls vacuum off idle, after a recommendation from BOBCRMAN, I set it at 12 degree`s BTDC with vacuum advance disconnected and plugged, then connected it to the manifold source or full time vacuum, I rechecked the timing with it connected, the timing at idle was right around 24 degree`s BTDC, I drove the car and what a huge difference, it has outstanding low end, and good midrange, something it never had before, vacuum advance at idle is needed since the idle is lean and usually off idle is lean, leaner mixtures burn slower than do richer mixtures so more spark timing is needed. In one case where we were running a 400 with 6 inch rods and a comp solid 260 duration cam, we set the base timing at 20 degree`s, since we used such a big cam vacuum advance can`t be used, so we made up for the lack of it just by advancing base timing more.

I am in the same boat vaccum wise. Seems the logical answer to this (assuming theres nothing wrong with the carb) is to head towards a programmable ignition system.

[Chevymetal]

James,

Sounds like your gaining experience to become part of the BG Tech staff one day yourself!

That is how everyone learns the 'secrets' of hotrodding, and that's having problems and then figuring them out.
Good job

[Miket]

Well,

I pulled my demon off (sounds bad doesn't it?) and checked for a damp or wet base gasket---nope dry as a bone. I checked the transfer slots and noticed that the secondaries were a little closed---I opened them to make sure they matched the fronts and all were at spec. I then removed the base plate and found that two to three holes were 1/4 covered by the gasket. I was unabled to tell if the gasket moved or wether it was drilled wrong. Seems that if making these carbs work correctly is as delicate as it appears, maybe some extra care or double checking of the base gasket might be worthwhile. I gently opened up the holes on the gasket enough to see all 360 degrees of the holes in the baseplate...carefully to not let any debris into the hole itself.

I reassembled the carb on the motor...cranked it up. It seemed to idle better---though still rich....but better.

With my combo (below) I still believe I need to be higher with idle timing and will plan on moving to a new ignition system.


ZZ502 with the following mods:

Decked block for 10-1 CR
File fit rings
Crane Solid Roller cam 615/630 300 dur
Matched springs
Crane Race Roller Rockers
HD P-Rods
Ported GMPP Oval Port alum heads
Port matched Edelbrock Victor JR intake
HEI Dist with upgraded module

[Tech @ BG]

Miket

Most likely opening the secondary butterflies is what has helped clean up your idle slightly. If you'll contact our technical department at (706) 864-8544 we should be able to walk you through this.