Hey Guys, Maybe someone on this board can help tune my Holley 750 DF/DP. First off the engine, 400 pontiac bored 30, trw flat top pistons, crane hydraulic 560 lift w/ 1.65 steel rockers, 1968 #16 heads ported, bowled, 3 angle valve job, holley street dominator. The carb is a holley 4779 750 DP/DF like I said prior with a proform center section, primary jets at 72, secondary at 84. Next the problem, engine just does not want to idle, when you think you have it, it gradually slows down and shuts off. When you increase the throttle screw for a higher idle it seems to hold but fluctuates up and down about 200 rpms. Any help will be appreciated. If you need any other information, post here and I will try to get the answers for you. Thanks in advance for your help guys. http://forums.performanceyears.com/g...n_confused.gif http://forums.performanceyears.com/g...n_confused.gif http://forums.performanceyears.com/g...n_confused.gif

You Have To Be Willing To Take It To The Max!

Hey Guys, Maybe someone on this board can help tune my Holley 750 DF/DP. First off the engine, 400 pontiac bored 30, trw flat top pistons, crane hydraulic 560 lift w/ 1.65 steel rockers, 1968 #16 heads ported, bowled, 3 angle valve job, holley street dominator. The carb is a holley 4779 750 DP/DF like I said prior with a proform center section, primary jets at 72, secondary at 84. Next the problem, engine just does not want to idle, when you think you have it, it gradually slows down and shuts off. When you increase the throttle screw for a higher idle it seems to hold but fluctuates up and down about 200 rpms. Any help will be appreciated. If you need any other information, post here and I will try to get the answers for you. Thanks in advance for your help guys. http://forums.performanceyears.com/g...n_confused.gif http://forums.performanceyears.com/g...n_confused.gif http://forums.performanceyears.com/g...n_confused.gif

You Have To Be Willing To Take It To The Max!

Sounds like a vaccuum leak. Check all parts to make sure they are flat & sealing. Did your carb do this before you added the Proform main body.

Scott, I don't think so, but its been at least 10 years since I used it. Upon using the proform center section, I replaced everything outside of the centersection, so it is practically a new carb. I will check for vacuum leaks. Thanks.

You Have To Be Willing To Take It To The Max!

Sounds like maybe intake leaking. Spray some carb cleaner along the top and bottom of intake gasket and see if rpms increase.

With hydrallic .560 cam you are most likely in the
transfer slot on the Holley carb. When you turn the screw to lower the idle the fuel you had from the transfer slot goes away. You also probably have limited control of the idle screws.

Try raising the angle of the rear throttle blades first slightly and lowering the front blades to get more idle air flow. evenly open up all 4 idle
mixture screws and see if you casn get the carb rich enough to idle correctly.

remove the carb and look at the position of the blades on all 4 barrels. If more than .040 of the
transfer slot is exposed on the front or rear,
drill .090 holes in the throttle blades and reset
the throttle blades for < .040 transfer slot to be visible.

90% of the time poor idle with a non stock cam is
due to idle blade position being wrong. Tom V.

http://kurtsplates.homestead.com/files/UR2SLO.jpg

Poor idle only can come from transfer slots over exposed but fluctuating sounds like vacume leak. If your idle mixture screws work correctly I wouldn't mess with throttle blade settings or be drilling holes........

The fluctuating idle with the increased idle speed is probably coming from the power valve.
Check the power valve rating and also make sure it's not bad.

johnta1
Pontiac Power RULES !!!
www.wallaceracing.com
http://wallaceracing.com/johnta1plate.jpg

I too have been having similar problems with my combo for longer then I can remember. I can achieve a stable idle after the car warms up for about 10-15 min. (no choke provisions), but my car idles very rich. It is rich to the point that I get gasoline in my fuel. I have tried everything to lean it out, but when I do the car just will not idle. My car only produces about 7-8in.hg. at around 900rpm. My engine builder says it is because of the camshaft duration, but I don't buy it. I have seen plenty of cars with way more radical camshaft/engine combos. that idle just fine. But enough about my problems. Have you checked your vacuum to see how low it is or if it fluctuates? Are you allowing plenty of time for your motor to warm-up. I know these are basic questions but you have to start somewhere.

Also something to think about, is with large cams more initial timing has to be run to get a good idle. I'm runnig approx. 20 degrees initial and approx. 36 total with a solid 265 int. and 276 dur. @ .050 with 619 lift. When I first installed cam, I got the same symptoms as you guys got but when I set initial at 20 degrees, I can now idle it at approx. 900 rpm's. Before that I had to set it as high as 1200. But we are talking a whole different type cam. Checking for vacume leaks and timing first will cost you nothing and about 15 minutes of tinkering....

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by gto70:
It is rich to the point that I get gasoline in my fuel.<HR></BLOCKQUOTE>

Man, I hate it when that happens...... http://forums.performanceyears.com/g.../icon_wink.gif

Chance favors the prepared mind.

You caught that huh Goatman. I meant to say oil.

Hey Guys, Thanks for the help, it turned out to be an intake manifold leak. I tried closing off the heat crossove ports with sheet metal but looks like I failed. Purchased Felpro 1233 intake gaskets and solved the problem.

Thanks again for the help

You Have To Be Willing To Take It To The Max!

As a suggestion to people posting carb issues on the board, it would really be nice if you would describe all of the changes to the intake system
before you post about a carb problem.

Carbs get blamed many times for other issues which
could easily be addressed if the board members knew the WHOLE story. Tom V.

http://kurtsplates.homestead.com/files/UR2SLO.jpg

No "Grasshopper", One must be able to seperate the two.........

Quote:

"No "Grasshopper", One must be able to seperate the two......... "

Lerry, explain. Thanks. Tom V.

http://kurtsplates.homestead.com/files/UR2SLO.jpg

The indications told me intake gasket leak because the fact the idle FLUXUATED and he stated that just as he thought he had it, it would stall. Telling me that WHEN he thought he had it (as he stated), the car then reached a hot enough temperature to expand the metals and start gapping the space between the gasket or gaskets. That is the point where the engine would die. Transfer slots overexposed (usually) will still let the motor idle at a higher rpm. Even though the idle mixture screw don't do a whole hell of alot...

Tom a "Grasshopper" LOL!

Ya, that's like calling Ccass a "Hobbyist"

And Pontiac Dude a "Shadetree Mechanic"

Or Goatman "Controversial" Oh wait, scratch that one... http://forums.performanceyears.com/g.../icon_wink.gif

http://forums.performanceyears.com/g...on_biggrin.gif http://forums.performanceyears.com/g...on_biggrin.gif http://forums.performanceyears.com/g...on_biggrin.gif http://forums.performanceyears.com/g.../icon_wink.gif

http://forums.performanceyears.com/g.../icon_razz.gif

Chance favors the prepared mind.

Quote:

"because the fact the idle FLUXUATED"

I guess I did not pick up on that one as EVERY
engine (Pontiac) I have owned, the idle fluxuated!

(At about 5 inches of vacuum and .600 lift, I was never smart enough to get that quarter to balance
on the intake manifold).

Most of the time the hammers were shaking off the walls, the neighbors were complaining about the
noise from the open headers, and the cops were driving by to visit, have some coffee, and "shoot
the *****."

I guess I am a "Grasshopper!" Too dumb to take
that "bad" camshaft out of the engine and put on
of those "good" 17-18" inches of vacuum camshafts
in the engine so the idle would not fluxuate.

Tom V.

ps If I had known he had one of those "good" cams
in his engine I would have immediately ruled out the transfer slots as the air flow requirement
would allow closing the blades below the slot.

http://kurtsplates.homestead.com/files/UR2SLO.jpg