Current/former Holley Street Demon users on Pontiac engines. Your experiences?
 

After finally getting my 65 drivable I'm working on getting it to run right. There is a 750 Street Demon on it now. It runs but not great.

Before going any further please no "throw it in the trash" and "Put a Holley on it" or "Put a QJ on it".

Though ultimately I do believe one of those changes would be needed to "get the most out of it" IF I choose to go in that direction.

Right now I'm interested in getting the Street Demon to run the best it can on the street. There are quite a few big block street Mopar users that seem to like the carb, They rave about the response and drivability.

Searching the archives I see quite a few folks were using the SD at one point I was wondering what your experience was at the end of the day?

1. Still using it as it was out of the box
2. Rejetted it
3. Threw in the trash
4. Took it off the Pontiac and put it on a small block Camaro

Though 3 and 4 are pretty much the same thing.

Could you please detail the not running great comment for us so we might offer some help?

Idled smooth but idle to WOT would just die. Part throttle is ok, doesn't feel like a 455 at all.

I did the initial adjusting/test. Accelerator pump shot, step up rods/springs, secondary air door and there were improvements in certain areas but there was something not right.

I opened it up last night and one of the floats was set 5/16" too low and the other almost 1/8" too high. I corrected that but couldn't put it back together because the gasket that goes between the top and the body was split between the float bowl and the secondary throat.

Both of those issues were not conducive to a properly functioning carb. It'll take a few days to get the gasket in and get it assembled. When it's back together I'll have more of an idea of how it should have been running out of the box.

Right now I was just looking for other folks experiences with a functioning SD as I haven't had on yet :)

I had posted and noted after decades on this forum.
The Demon carb works as good as any other carb.
As long as it's given the same attention as any custom built unit Qjet included....no magic there!
I'm currently tuning a Demon now :thumbup:

Definitely think you'll have a wait and see approach after you get your new gaskets. I spent a long time trying to get a 1407 ecarb to function well on my 455 and float changes were some of the most prominent changes to feel that I could make.

I don't know squat about the SD carbs, so I can't comment further than my experience there. Hopefully those changes help you out.

What intake and is there sufficient clearance for the "goggle" secondary plate to fully open?

JLMounce, did the Edelbrock eventually work well for you? What type of changes were required?


I'm currently running a Performer RPM. With the 2 gaskets and steel spacer the rear blades open/close fine.

Total timing?
Just wondered if you might have advanced the timing after the previous situation?

Timing is at 32 total by 3k. Currently I'm attributing the issue to the float level and torn gasket, mostly the low float level.

Just for an update. I set the floats correctly and put the carb together with the new gasket. Other than moving the accelerator pump to the top hole, which I had done to work out the lean hesitation all else is stock on the carb. Drove it to work this morning and it's working much better. I'll continue to test it and check the plugs when I get home. Seems responsive but need to get it out on an open road for a better idea.

A few notes on the carb. Those bottom screws holding it together are ridiculous, why put them there other than going for the "clean look".

The choke is giving me some issues as well, having trouble getting the top step to engage. It engages at the second step. Still working on that though it's not a deal breaker as by the time I really need the full fast idle the car will be put away for the winter.

They also have a cover on the choke and where is the screw? On the bottom. With the cover on you have to work blind on the choke mechanism. At least that cover can be left off while setting it up. After it's complete I'll drill the cover and tap the choke housing to put a screw in from the top.

The plastic bowl has a raise ridge running down the center of all the walls. To improve gasket seal I imagine, That ridge is sharp and caused the tear/cut in the first gasket. It also cut the new gasket in a different location. No leak that I can determine but I'll order another gasket and dress that ridge down a bit to prevent the cut.

I'll work on tuning it a little, then move on to getting the trans and rear end sorted out. At least I can enjoy it on nice days for a few more weeks.

Those "Bottom Screws" have been on the Holley 4 BBL and 2 BBL carbs for at least 50 years with no one else complaining about them.
They call the carb a Modular carb.

The only issue on the Bottom Screws is making sure to leave out the two Bottom Screws in the center of the Throttle Plate Assy (see picture #2) so that IF they ever came loose they would not drop into a Open Plenum Intake manifold.

At one time Holley offered a Thin Steel Plate that went between the carb base and the intake manifold to keep the screws out of the intake/engine.

Holley revised the latest Throttle Plate Assembly parts so the holes are not even drilled.
(Look at Picture #1 No screw holes next to the alignment pins on the baseplate)

Tom V.

See Pictures attached.

True but the Street Demon isn't based on a traditional Holley.

On a 'Holley" you can access the jets, floats, needles & seats, bowl gaskets, accelerator pumps without having to remove the carb from the intake .

On the Street Demon you can't access any of the above without disconnecting hoses, linkage and the carb.

http://forums.maxperformanceinc.com/...ictureid=13573

That's the thermoquad "Demon", LOL. THey sold quite a few when they came out, lots of advertising. Another copy of another "Real" carburetor....

Right. As opposed to the Holley "Demon" which is a copy of another "Real" carburetor. :)

Ah my neighbor had one of those Holley carbs on a 1966 mustang we never could get it to operate right being near 25 years ago I forget the details but I think it all was float related and basically a design issue that could not be resolved

Holley did not make them very long

.

Not the same carb. These have been out for 6 or 8 years I believe. Still in production today. Both Carter and Holley did offer 3 barrel carbs in the 60's though

Since these are based on the Thermoquad they are pretty popular over on the Mopar boards.

Mopar buddy gave up on the Street Demon on his 383 stroker. Using a wide band even he could just not get it consistently tuned in. Swapped to an annular booster Holley that dialed in better for him than the down leg version.

After 2 years he just swapped to a Hilborn stack FI adpated to EFi and using a Holley controller and even better control

So it looks like this will become another "throw it in the trash" and "Put a Holley/QJ/FI Unit on it"

Just giving you his results I have not personally used one. Or get a wide band and see what the actual AFR is to help your tuning each circuit. Basically ANY type carb that will help you tune the idle, transition, power and WOT circuits.

Doesn't have to be, BUT I'm not sure you will find many here that would want to even try to diagnose it.:eek: All the manufacturing irregularities that the AFB clone E-carbs have, make them a waste of time. Not sure how the demon's have been faring:rolleyes:

I have a friend that has some nice cars. LOL, None of them really run near their potential. I just keep my mouth shut. I've tried to explain that not every carb will work properly on every engine.
Save yourself some grief, Shaker455 isn't too fay from you, have him build a Q-Jet of Holley for you, specifically tailored for your engine...:guitar: