speed demon 575

Back at it again. Engine’s been run in on this 64 Impala and the speed demon 575 turns out to be a fantastic carb. Just wondering how to deal with the accelerator pump. When the carb is at idle and you goose it just a little there's no real squirt, so it dies. Of course if you're gentle it hesitates and comes on like it's ready to explode.

Anyone out there know why the juice does not come on right away? Looks like there must be some way to adjust the accelerator pump for immediate response without getting too rich. Speaking of which I am running a bit too rich for these platinum plugs by bosch. I've been told those plugs are just for lean running fuel injected cars. Well, I want lean but I want balance. The carb came jetted down to bout 62 on primary and 68 to 70 on secondary depending on which I choose. I'm at 6000 ft so that's a given.

Kind of excited after testing the car some, couple of burnouts etc. Checking the compression today, all 8 cylinders came out at 180 lbs. that's ok, no?

 

Set the accelarator pump arm so that there is NO play at idle and there is still a bit of travel left when the throttle is full open.

Try increasing the squirter size if the accelarator pump is correctly adjusted and you still have a big bog. I went from a 28 to a 37 squirter to cure the same problem.

180 pounds of compression is pretty good. Keep the oil fresh and it should stay that way.

 

Did you get these squiters from Barry Grant? Or are they easy to obtain from parts stores? Seems to be ok but shifts a bit early. All is new basically and I am doing my best not to ruin anything. Any more advice on the speed demon carb? I really am not sure about the center adjustment screw under the threaded spot for holding down the air cleaner.

I am just about to switch to 20W50 on the oil and have used 10W30 for the run in just to be sure things were thin and slippery for the cam etc. The ****** is now a 700 R4 that I am not quite sure of just yet.

Thanks!

 

AC delco plugs, so you can play with heat ranges to dial it in. I wouldn't use 20/50 on a fresh motor, but thats just me. Don't have experience with demon or related carbs though.

 

I think the Demon carbs are basically laid out similar to a Holley cinfiguration, so there is probably a pump arm and diaphram, cam, squirters, etc. When I set up a Holley I adjust the squirter linkage so that there is no play when the throttle is closed. I also hold it wide open and make sure there is some movement left in the pump arm (IE: it's not bottomed out at WOT-could ruin the pump diaphram). Basically I set it up so as soon as there is ANY movement of the throttle the squirter is squirtin'. After that step is done you can fine tune with squirter size and pump cam changes, although I use dragstrip numbers to dial that in. I was never able to get a good sense of progress by "seat of the pants" on the street...except maybe for tuning out a squirter-related bog. Hope that helps. If you are new to carb tuning perhaps the biggest tip is to try one thing at a time...you start fooling with everything at once and you will go in circles.

-Scott

 

Couple of things:

1) Make sure the accel pump shot comes on the INSTANT you touch the throttle - there can be no lag in the shot - or you'll bog.

2) There also may be a problem with your enrichening circuit. I'm not familiar with the way that's set up on a Demon carb, but you do have to adjust when enrichment comes in if you're running a longer duration cam than stock.

3) on the same subject - there are transfer ports in the throttle body wall. If you're running a longer duration cam, the throttle plates may be exposing too much of the transfer slots at curb idle; this would cause you to have to lean out the idle mix to compensate for the fuel flow thru the transfers. Check your throttle plate position; only a small part of the transfer slot should be exposed below the throttle plate at curb idle.

4) Fuel mix is a function of float level - make sure your float level is correct.

5) Bosch platinum plugs...

I've been using them in damned near everything I own since 1989. Love them to death; they reach a self-cleaning temp much faster than a traditional plug. Had a problem with fouling on a motorcycle; swapped out to a bosch plat and had no further fouling issues. If you're seeing a rich mix on the plug read, either the carb setup is wrong or the plug is too cold.

 

So you think I should stay with 10W30 till 2000 miles or so?

 

Holley parts are a direct fit to Demon carbs for the most part. Pick up squirters for a Holley at any speed shop.

DO NOT adjust the TV cable in an attempt to change your shift points! The travel of the TV cable should be set at installation and never changed unless it is to make up for cable strech. To adjust your shift points you should be changing the governor weights and/or springs.