Ok, I'm about to order my carb and kit to switch from TBI. I've decided on a Speed Demon Carb. Every VE calculator I've done basically points to the 575cfm. Which is where I was leaning. Then I bought the new Camaro Performers mag. today, and surprisingly there was an article about a 305 buildup with some aftermarket vortec heads that probably flow a little more then mine, and a comp cam that is comparable to the LT1 that I am running. But they went with the 650 Speed Demon on it. So now I'm torn between the two. They made 372 hp and 350 tq with their setup. Mine should be close in comparison, I would guess 25-30 hp less maybe?

Any idea which carb would be better suited? Plus I am pretty new to carbs, so the easier it is to tune the better.

 

The 650 would give you more room for growth, without hurting much at this point. You should have plenty of stall to get you into your power band and stay out of the bog zone of a mechanical secondary.

 

What are the engine, & driveline specs of the combination you're working on?

 

Check his sig.

 

Yep, haha.

Stock bottom end, LT1 Cam out of a 96 Camaro, Vortec heads milled down .035, Edelbrock Performer RPM intake, stock rockers, 2800 RPM stall, Trans Go shift kit, mid 3.?? gear ratio with limited slip (not stock and not put in by me). And I live in denver, so high altitude. Future plan would probably be a nitrous kit.
Oh and I ordered the 650 yesterday, so hopefully you don't frown on it much. Also is a dual feed line a good idea? As long as it doesn't hurt driveability I would like to plumb that in at the same time.

 

if its a dual feed carb, you will need a dual feed line.. a single inlet to 2 outlet will be fine..

 

If you ordered a dual feed carburetor, you'll need a dual feed fuel line. If you're going to be going to a larger displacement engine in the future a 650 will be a good choice, if this is pretty much where you're staying at a mile high the 575 would most likely give you better drivability.

 

So I would probably be looking at rejetting the 650 for good driveability? Also, I am guessing that the speed demon is a dual feed correct? Everything should arrive tomorrow from jegs. So I'll be starting the project this weekend.

Thanks

 

Yes, you will need to jet down a bit for your elevation. Yes, it is a dual feed carburetor.

 

Is there a good size to start with for this elevation? My carb tuning is minimal at this time, any good starting points would be very helpfull. Oh and it is the 650 that i went with, if that helps.

Thanks again

 

At your elevation you'll probably need to go down 3 jet sizes in both the primary, and secondary sides of the carburetor.

 

Ok, well I did the swap today and everything seemed to go pretty well. Only problem I ran into was the fuel pump not running after the motor starts. So I spliced in a key on power wire directly into the pump. I've got it running pretty decent, it ran pig rich for a few minutes. I got it leaned out to where it idles smoother then TBI ever did. My only driveability problem is the off idle acceleration from a stop, or if I down shift. It boggs for a second then catches back up and pulls hard. If I lay into the throttle while moving it has excellent power.

So I'm currently playing with leaning out the 4 corner screws and adding alittle to the fuel floats. I think it runs out of fuel as soon as I hit the throttle then catches up. I might be wrong here but thought I'd post for some input.

And a couple times that I ripped into it, it had a really high idle right after it. It was coasting at about 2500 RPM's with my foot not on the gas. At that point I didn't have the air cleaner on cause I was just going down the street and back. So nothing was hanging up. But it later went away????
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Oh and with the BG 3 port AFPR I cant get lower then about 7.5 PSI. Why is that?

 

the high idle is from being rich.. from the sounds of it, its really rich.. if possible, i would change the jets.. i run around 6.5ish psi on my mighty demon.. the regulator should be able to go down to 5psi.. just keep tryin to adjust it.. turn the screw, rev the motor.. idle doesnt move a whole lot of fuel so reving will help reset the pressure

 

I noticed my carb only has 1 screw on top, in the bowl area. Some of the pics I've seen have 2 screws on top. This is on exact opposite sides with the air cleaner stud in between them. I'm not talking about the float adjustment screws, but 2 gold screws on the top of the carb. Am I suppose to have both of them? Hopefully that wasn't there at one point and now it fell down the carb. That would be alot of not fun.

I also ordered the new set of jets.

 

if you see any open threads then it is possible that something get loose.. heres a pic of my mighty 750.. i'm guessing its the large gold ones cause i have the smaller screw-in air bleeds that are also gold..(i think thats what it is) but i have no idea what those large ones are for.. my guess would be just to hold something on, obviously.. the baseplate perhaps??

 

I believe they hold theh squirters down. Does the speed demon maybe only have a squirter on the primary side? I don't see any fuel coming out of the back side, but I'm not under the hood when accelerating hard.

I still can't figure out why my idle won't come down very well after doing a wot pull. I can drive around no problem at normal throttle, but soon as I get on it, it idles high. I've got the idle screws leaned out as far as possible without making it stumble. And fuel pressure still won't come down any lower.

 

you will have to rejet to fix the idle problem.. the 650 speed demon has 2 versions there is a twin squirter version and a VE series.. try PMing the BG tech guy..

 

Yeah, mine is the VE, so I only have one squirter. I ordered the new jets so they should be here by wed. My freakin fast idle screw fell off out of no where, i was looking at the intake and all of a sudden i see a screw laying on the intake. Don't know how it fell out being spring loaded and all. That is the worst thing to ever try to put back in. I'm still working on it.

 

Well I rejetted it today. Seemed to take care of the off idle stumble. But I still can't adjust my psi below 9, so I might try another gauge to see if it went bad. I still have a high idle problem after doing a hard pull, I don't know what could be causing that. I might try another return spring to see if that helps, but it seems to go back to normal if you shut it off and restart it.

With the smaller jets would it be a good idea to raise the floats alittle? It seems alittle on the lean side at the moment, it kinda has a spot at about 3500 rpm that it seems to have a lull.

 

i'm no guru at tuning carb so i cant give you a definite answer on the floats.. but i still believe the high idle is from being too rich.. but then again, i have never had my motor lean out.. its always been filthy rich..

seems weird why a BG fpr wont bring down the pressure.. if the new guage doesnt work, you could try take the pressure regulator apart and clean it.. that took all the problems out of my holley regulator.. a nice cleaning with brake cleaner.. or was it carb cleaner?