4 hole carb spacer for better signal, will it work?

[Mrturner1]

Hey guys, havin issues still with my new Holley 750 DP mechanical secondaries. It's on a 355 with 10.3-1 compression, RHS 170 heads, Comp 280H and has 3.73's with a mini spool and 3000 rpm stall. I'm positive this would be easier with a 650 DP but the 650 I had on the counter at the parts store got mixed up with this 750 and I didn't see the box until I already installed it. Good news is, carb will be big enough for boosted 383 later.

The issue, major stumble off idle and it even backfired out of the carb when I really stabbed it once. Right now it's got 70/75's and the shooters are .31" I think, whatever it came with. Haven't touched the shooters or pump cam, nor the PV (I think it comes with a 6.5 PV?)

It's not timing, I've tried everything with that. Backed it off, gave it more, changed springs and weights a million times. The distributor is a brand new MSD street fire and has a Moroso weight/spring/bushing kit in it. Weird thing is when I first dropped it in, my dial back timing light said 18 initial and 36 total which is great and the engine loves it. But for no reason at all a couple days later the timing light says 36 initial and it doesn't move more than a couple degrees all the way up to 4000rpm. No idea what's happening there. Got a new dial back and it showed the same. It's not runnin like there's 36 initial, it still runs just like it did when I set it all up, and it starts with ease after its warmed up and even hot, starter doesn't blink. I have a timing tape but my balancer is painted orange so I suppose I'll have to sand and acetone that and try to hit it with the timing light on "0" to be sure. I'm stumped there, could it be bushings or something like that? Wouldn't it have symptoms of 36 degrees initial?

Anyway, original question was this. I have an open 1" phenolic spacer, would a 4 hole give it a better signal since it may be too much carb for this engine and setup? Help with the other issues is also greatly appreciated. This project is very close to being driveable! Thanks guys

[Racer382D]

If you want my honest opinion, lose the RTR distributor.... I have had several issues with them recently doing exactly what you are saying.... Replacing them with a stock HEI or even a nice msd billet dist. And msd 6al box solved all of the issues.

The other thing is with a performance ignition dial back timing lights are questionable at best..... Always set the light at zero and set timing based Soley on the balancer numbers.

[Mrturner1]

Originally Posted by Racer382D

If you want my honest opinion, lose the RTR distributor.... I have had several issues with them recently doing exactly what you are saying.... Replacing them with a stock HEI or even a nice msd billet dist. And msd 6al box solved all of the issues.

The other thing is with a performance ignition dial back timing lights are questionable at best..... Always set the light at zero and set timing based Soley on the balancer numbers.

Wow, I wouldn't have guessed that the distributor could be bad, what a shame. What's the chances MSD would take it back or exchange somehow?

[Mike C]

Backfire out of the carburetor is a lean mixture issue. Try moving the accelerator pump cam to the number 2 spot so it comes in faster. You could try a cam assortment to use a more aggressive pump cam. Also think about going up in shooter size.

I have a Barry Grant Stage III 750 on my Camaro that flows 1040 cfm with all the tricks and it is more driveable with better response than the 700 cfm double pumper it replaced.

But the 4 hole would give you more velocity for better throttle response, but it sounds like pump shot to me.

[Mrturner1]

Originally Posted by Mike C

Backfire out of the carburetor is a lean mixture issue. Try moving the accelerator pump cam to the number 2 spot so it comes in faster. You could try a cam assortment to use a more aggressive pump cam. Also think about going up in shooter size.

I have a Barry Grant Stage III 750 on my Camaro that flows 1040 cfm with all the tricks and it is more driveable with better response than the 700 cfm double pumper it replaced.

But the 4 hole would give you more velocity for better throttle response, but it sounds like pump shot to me.

Meaning it's totally possible for me to get this 750 DP to run great on my 355?

[Mike C]

Originally Posted by Mrturner1

Meaning it's totally possible for me to get this 750 DP to run great on my 355?

Yes.

[Gromit]

If it is convenient, could you please show us a photo of your balancer showing the timing tape?

[Mrturner1]

Originally Posted by Gromit

If it is convenient, could you please show us a photo of your balancer showing the timing tape?

I haven't installed the timing tape yet, been busy with work and was also teetering on whether or not I want to sand down the paint so the tape will stick.

[Mrturner1]

After Googling it, these MSD streetfire distributors sound like a big piece of junk. There are ALOT of people having issues with them.

[Mr Handy]

If your thinking of a new Distributor I recommend a D.U I. from Performance Distributors. Made a good difference in how my 350 runs. I did a lot of research on dizzys and this is the one I settled on. Heck they tune the dizzy and it is calibrated to 24* total at 3000 rpm. I'm running 12* initial. It also seems to be the only new Dizzy that is calibrated ere in the US.

I think you should be able to get the 750 to run mo problem. A 4 hole spacer can't hurt. if you get a spacer get a 1" spacer. That seems to be the optimal thickness.

I had an issue with backfiring through the carb and the problem was that the distributor clamp was a POS and warped not holding the distributor tight. I dug a stock clamp out and have been fine ever sense... It was also a skip white dizzy and I switched to the DUI.
If you are running 18* initial and only getting 36* total mechanical there is something wrong unless you have the advance limited. 18* initial seems like way to much especially if you are running vac advance.

[Mrturner1]

Originally Posted by Mr Handy

If your thinking of a new Distributor I recommend a D.U I. from Performance Distributors. Made a good difference in how my 350 runs. I did a lot of research on dizzys and this is the one I settled on. Heck they tune the dizzy and it is calibrated to 24* total at 3000 rpm. I'm running 12* initial. It also seems to be the only new Dizzy that is calibrated ere in the US.

I think you should be able to get the 750 to run mo problem. A 4 hole spacer can't hurt. if you get a spacer get a 1" spacer. That seems to be the optimal thickness.

I had an issue with backfiring through the carb and the problem was that the distributor clamp was a POS and warped not holding the distributor tight. I dug a stock clamp out and have been fine ever sense... It was also a skip white dizzy and I switched to the DUI.
If you are running 18* initial and only getting 36* total mechanical there is something wrong unless you have the advance limited. 18* initial seems like way to much especially if you are running vac advance.

I put the Moroso spring and weight kit in it with new bushings which is why I have 18* initial. I will definetly look into the DUI distributors. I was also thinking about an MSD pro billet with a 6A box, but I'm leary of MSD now

[Mrturner1]

Is MSD really as bad as I'm reading about or is it just limited to the StreetFire HEI distributors? There are a lot of stories out there about these things being junk. I was thinking maybe now is as good a time as any to upgrade to an MSD Pro Billet HEI with a 6al box, but not if MSD's stuff is all Chinese crap like this street fire

[hugger6933]

I've had good luck with all my MSD stuff though I never have had [to my recollection] a dist like yours. I think you have a lean condition off idle, and yes the 750 will work while a little big it will do once tuned out. Check the power valve those blow out any time you have a backfire and it will cause troubles. Try another power valve and then maybe work on adding some more shot at the pump by moving the pump cam or adjusting the pump arm.

[Mrturner1]

Originally Posted by hugger6933

I've had good luck with all my MSD stuff though I never have had [to my recollection] a dist like yours. I think you have a lean condition off idle, and yes the 750 will work while a little big it will do once tuned out. Check the power valve those blow out any time you have a backfire and it will cause troubles. Try another power valve and then maybe work on adding some more shot at the pump by moving the pump cam or adjusting the pump arm.

Well after reading back over this I suppose a lean issue is possible even though it's a 750 DP on a 355. I'm gonna try and move the pump cam and see if that helps.

Another thing that's a little frustrating is that the RPM's drop about 400 to 500 rpm when I put it in gear. I know a little drop is normal but mine seems like to much

[69chevytrucker]

1 i had a StreetFire HEI it died after about 4500 miles put on my engine so i would say no good.
2 a 750 dp is more carb then you will ever need on a sbc engine the most cfm a sbc would ever need is about 535 cfm so your good there.

[Grumpy old man]

I went to 411 speedway with my brother in law Gordy Foust last night and during intermission I was telling him about your carb issues (Gourdy had the worlds fastest 66 Chevelle and was the 1st guy to run a promod over 200 mph at an NHRA sanctioned race and worked for both Holley and Edelbrock ) his suggestion was to change your power shot down to a smaller shot and to hook up a manifold vaccumm garage to see just how far it's dropping when you punch it . He asked if you were local and he would have it fixed in less than 5 minutes . Post or PM me all your current specs and settings and he said he would work it all out for you .He also said every backfire thru the carb can destroy the power valve . Google gordy foust 66 chevelle and look at his dual quad nitrous set ups .he knows what he's talking about .he's a fuel system expert .

[Mrturner1]

Originally Posted by Grumpy old man

I went to 411 speedway with my brother in law Gordy Foust last night and during intermission I was telling him about your carb issues (Gourdy had the worlds fastest 66 Chevelle and was the 1st guy to run a promod over 200 mph at an NHRA sanctioned race and worked for both Holley and Edelbrock ) his suggestion was to change your power shot down to a smaller shot and to hook up a manifold vaccumm garage to see just how far it's dropping when you punch it . He asked if you were local and he would have it fixed in less than 5 minutes . Post or PM me all your current specs and settings and he said he would work it all out for you .He also said every backfire thru the carb can destroy the power valve . Google gordy foust 66 chevelle and look at his dual quad nitrous set ups .he knows what he's talking about .he's a fuel system expert .

PM sent, and there is some other odds and ends in post #1, hopefully enough info. Thanks for helpin out, I'm ready to start driving this thing to work!

[davepl]

I -think- all the modern Holley carbs (like the newer HP line) have power valve protection, but it's definitely something to check. Hopefully it saved you during the backfires.

[GASoline71]

Originally Posted by davepl

I -think- all the modern Holley carbs (like the newer HP line) have power valve protection, but it's definitely something to check. Hopefully it saved you during the backfires.

They do. Every Holley carb built since 1994 has blowout protection built in.

But a really hard huff through the carb can still blow one out. But it would be a pretty violent backfire to do it.

Gary

[Mrturner1]

Well I can't do anything until I get the timing issue fixed, and I'm leaning towards an MSD pro billet and 6al box, but that's about 700 bucks after tax and shipped. Lot of money, but I'd like to be done with this problem.

[Mrturner1]

Ok I got an MSD pro billet HEI today and installed that so all my timing and spark issues are gone. I decided to try a smaller power valve since the one that came with it was a 6.5. I tried a 4.5 and the stumble got worse. I can't imagine needing a bigger power valve, but I'm certainly no expert. Timing is 18 initial, 18 mechanical in at 3000 rpm, and the instructions say the vacuum advance puts in 10*. I tried both ported and manifold vacuum and BOTH make the truck idle up when I connect it.

[GASoline71]

Did that carb come with a DVD in the box?

Gary

[Mrturner1]

Originally Posted by GASoline71

Did that carb come with a DVD in the box?

Gary

Nope didn't come with one, thanks for the links though

[Mike C]

So, the "Bog" when you stomp on the gas is not from too MUCH fuel, it's too LITTLE fuel. The accelerator pump and squirter are to fill in the hole left when the large throttle blades open.

Rich and lean are from a jetting perspective, but it can still have a lean backfire when you punch it because of the "hole" in the a/f curve that the pump shot didn't fill even if it is jetted correctly.

A larger squirted or more aggressive pump cam can do wonders.

Ported vacuum source should have ZERO vac at idle. If you aren't at zero something is wrong...

[GASoline71]

Holley accelerator pump cam tuning:

https://www.youtube.com/watch?v=k2-RY2JqWek

Accelerator pump tuning:

https://www.youtube.com/watch?v=k-Nx5HEzvlY

Adjusting fuel and float levels:

https://www.youtube.com/watch?v=ge-mIk6nEYQ

Power Valve tuning tips:

https://www.youtube.com/watch?v=mE_xTUXQJQ8

All these videos are on the Carb Tuning DVD that Holley sends with all their new carbs.

Gary