Carb adjustment help.

[bly]

OK, I have a new quick fuel 750 DP mechanical secondaries on 351W. Motor runs fine, idles good, accelerates decent till I hit around 3/4 to full throttle, then it craps out. I have changed squirters to 35 primary and 37 secondary, I have changed secondary accelerator pump to 50, still have problem.
If I stay in accelerator when crapping out it will clean up. No black smoke or anything just craps out, like gas is turned off.
I have good fuel pressure at around 7psi at regulator. New Holley electric pump good to 16psi and new quick fuel regulator...
Getting frustrated, thought I would ask some questions here seeing it is the weekend and quick fuel is closed and it is 75 degrees out in november, would really like to do some driving.....HELP!!

[FWB]

your running out of fuel some where, what size fuel line? is the fuel pump still
supplying enough volume when your at 3\4 throttle? what holley pump is it?
16psi isn't necessarily the only spec that is pertinent. what gph or gpm is it?
or.........are you dumping too much fuel,...... after a blast check the plugs,
secondaries might be too much for the motor.....if your runnin at 60 mph and you dump it does it still have a flat spot?

[bly]

It does fall off when running at speed and step into it. No matter what speed its at it does same thing.
I have a -8 line to Carb line then it goes down to -6. I have ran same fuel line on previous carb no problems.
It is a holley 12-150 pump 150 gph rating, that should be enough I would think, not sure though.
Havent checked plugs but will.
I was almost thinking that maybe I was running to big of acc. pump and squiters. When I got the carb I had to jet it way down. the squirters that came in Carb new were 33 prim. and sec.
Maybe I am going wrong way????

[FWB]

is anything done to the motor, meaning if its just a mild built windsor a 750 dp
will be too much carb. whats the timing set at? if you can get away with a couple of degrees advance more bump it and see if that affects the flat spot
if it does that might indicate too much carb if the flat spot move up in rpms
when it occurs.

[bly]

It is just a mild windsor....I had an old 750 holley dp before this one and was great for motor for years before I started to have problems with it, and replaced it with this Quick Fuel unit...
I will try to advance timing a smidge to see if it helps....Thanks again....

[FWB]

put a vacuum guage on it and adjust the mixture for best vacuum reading. when
you wack it up to 3\4 throttle from under the hood, do you see fuel going in
or does it spit in?

[Silverback51]

I know it's kind of basic, but did you check the float levels?

[convincor]

same problem with the old carb?
Try a different coil.

[Rick Parker]

You are not getting fuel to the secondaries. Check float, needle & Seat and any other path for fuel to the secondaries. Maybe pull the secondary fuel bowl off and look for debris inside.
You are experiencing a huge lean condition when you get into the scondaries with no fuel.

[bly]

Tried new coil, No joy...
Float levels are good.
I had Carb apart yesterday and cleaned, I thought that was the problem myself, but found no debri...
Is there a possibility my electric fuel pump is not getting enough power for pump. I just drove it, came back and the fuel press was at around 5psi it was at a steady 7 when I left, could there be a problem there???
I dont have pump ran through a relay or anything like that, Could something be amiss there?........Thanks, Brandon....

[Rick Parker]

Have you pulled the sight plugs on the float bowls, since you had it apart to verify there is fuel in the secondary bowl? The change in fuel pressure could be heat related but 5lbs is still ok.
When you are driving at a steady speed and roll the throttle heavily does it run ok for a few second (with secondaries functioning) and then go flat, or does it nose over immediately when the throttle is heavily depressed?
Where are you pulling power for the pump from? Is it mounted above or below the level of the tank?

[bly]

The Carb has sight glass for bowls, levels look good.
When driving it at a steady speed and roll into throttle slowly it seems to do better, but still craps out, when hitting it hard from a steady speed it seems to pull hard then nose over...
Im embarassed to say im pulling power from the fuse box. the pump i would say is mounted at a level plane with tank.maybe a smidge lower but not much....

[Tim Brewer]

As long as you have pressure at the regulator, you should be fine there, but if you don't, the power for the pump should go through a relay, always. What are your primary and secondary jets? Also, with the engine off and the air cleaner removed, I would manually operate the carb watching to see that the secondary side of the carb squirts as hard as the primary side.

[wtm442]

Originally Posted by bly

When driving it at a steady speed and roll into throttle slowly it seems to do better, but still craps out, when hitting it hard from a steady speed it seems to pull hard then nose over...

Check your accelerator pump lever. With engine off, and the pedal at WOT, you should be able to insert a 0.015 feeler gauge between the lever and the screw. Maybe you have way too much preload on the acc pump and you are bottoming it out and not getting a complete shot.

Another way to check is with engine off and throttle at idle position. Compress the acc pump override spring using a couple of wrenches until there is clearance (free play). Then back the screw off until all free play is removed.

Originally Posted by bly

If I stay in accelerator when crapping out it will clean up.

Could be caused by an over-rich (maybe) or a lean condition. When you are out for a ride, get the RPM's up over 3500 at a constant speed in 2nd or 3rd gear. Then stomp on the accelerator. At this RPM, the acc pump shot is all done. If there is no hesitation, the problem is in the acc pump area. If you still have the same "crapping out", it might be the power valve or something else that has been mentioned.

[bly]

WTM, I have tried hard acceleration at high RPM's, 3500 and above, still craps....
Would you be suggesting the power valve may be blown? I will check tomorrow..
I will have to check what size jets I put in sec., maybe I went to small???

Thanks again for all the help guys,,,Brandon...

[wtm442]

Originally Posted by bly

WTM, I have tried hard acceleration at high RPM's, 3500 and above, still craps....
Would you be suggesting the power valve may be blown? I will check tomorrow..
I will have to check what size jets I put in sec., maybe I went to small???
Thanks again for all the help guys,,,Brandon...

If it still crapped out when you were at a constant 3500m RPM and then mashed the pedal, it sounds like the problem is NOT in the acc pump circuits. Too big or too small a jet size would NOT give you that problem. If the power valve was "blown", it would idle like a pig with black smoke.

But maybe the power valve (or valves) are not opening. Run a vacuum gauge into the passenger compartment and check to see what is the manifold vacuum at idle, normal cruising and WOT. Write the values down. Most Holley carbs come equipped with a 10.5 "Hg power valve, so the valve opens when the intake manifold vacuum crosses 10.5 "Hg.

If you pull out the power valve, check to make sure you have the correct gasket. If you have the hi-flow valve with the rectangular windows, the gasket should NOT have the 3 centering tabs.

[jhv48]

Originally Posted by FWB

is anything done to the motor, meaning if its just a mild built windsor a 750 dp
will be too much carb. whats the timing set at? if you can get away with a couple of degrees advance more bump it and see if that affects the flat spot
if it does that might indicate too much carb if the flat spot move up in rpms
when it occurs.

I tend to agree with this one. If the carb is pushing too much air into the engine, it will crap out. One thing you can try is putting a very restrictive air cleaner (read that small) on the carb and then drive it. If the condition gets better, then you have found your problem.

That carb could just be pushing too much air for a mild 351W.

[bly]

OK guys, with much wasted time and a little money, I have solved my problem. After rejeting secondaries bigger squirters, bigger accelarator pumps, and then putting it all back to original, I pulled air cleaner off and drove, and now it runs like a banshee!!!!
I have a low profile pretty small air cleaner on it, not enough air....

Thanks to all the input I got on this, really appreciate it....Brandon.....

[convincor]

now we need to know, what filter were you running?

[392cobra]

Was it one of those tiny 9" dia. ones or the oval ones that might be 3/4 - 1" thick ??