Holley Carb help

[bronconate68]

The problem; once motor came to temp. the Holley stumbles and dies at idle.

I finally fixed all exhaust leaks, blown out header gasket and both flange gaskets toast with the first 10 miles. The motor fired right up, start of first crank. Ran great for about 3 miles then die at a light. Took some cranking and giving it some gas to get started again. Clear fuel filter at carb mostly full. Drove back, only one stop, put it in neutral and gave it a little gas to hold idle. I pulled into my driveway and took my foot off the gas, the motor choked out right away. Drives fine when driving down the road, stumbles then stalls at stops. 800 rpms then 700, then drops then dies. Needs a lot of coxing to get started, in my driveway I finally held the throttle to the floor to get it to fire up. Any tips on Holley adjustments would be great. This is my first Holley; 770 CFM Off-road truck avenger, motor-408 stroker.

Thank you,

Nate
'68

 

[ugly74]

Checked your float level? Or it could be a blown out power valve.

 

[bronconut73]

Set your floats.
Adjust your idle mixture screws. HF vacuum gauge. Adjust to highest vacuum then readjust idle screw.
What fuel pump are you running?

 

[mlake01]

Check your fuel pressure, put a regulator on if need be and get it down to 4psi or so. Set the float levels slightly below the windows. Replace the power valve (buy a handful of these - if you're going to run a Holley, you'll need 'em).

Sounds like a lot of carb, even for a stroker, unless you plan to run the trails at 3,500 rpm ;-)





Sent from my fart smone using crapatalk

 

[ugly74]

Replace the power valve (buy a handful of these - if you're going to run a Holley, you'll need 'em).

Or better yet, buy a power valve protection kit (check ball) for like 12bucks, install it and be done worryin about power valves.

 

[baddad457]

Buy a handful ? Gee In all my 35 years of running Holleys I've NEVER blown ONE powervalve. Not one. If you're blowing powervalves, then you're tuning skills need work to eliminate backfiring. To Bronconate: go back to the begining, first set the initial timing (I like to start at 12*BTC), next adjust the idle speed screw, adjust til the throttle is closed, then back out just till it begins to open. Next screw the mixture screws all the way in, then back out 1-1/2 turns. Check the accellerator pump linkage, you want to eliminate all the slack, it should dribble fuel the instant the linkage moves. Once you've set all this, fire it up and adjust the idle speed (in gear if an automatic) next adjust the mixture screws for the smoothest idle (in gear if an auto). Check the float settings. If all this is done correctly, it should eliminate the stumble. Too little timing will do it, as will slack in the accellerator pump linkage. Ditto for the float setting if too low or too high (too low will starve it, too high will flood it) If you're running points, those can be suspect as well, they need to be set with a dwell meter, the point gap is only a starting point. Next check the distributor advance to see if it's working.

 

[pcf_mark]

Start with what baddad457 said. It is either a basic tune up issue like timing and carb settings, fuel is boiling or you have a carb that has a manufacturing defect. Holley has had some quality issues so do not rule that out once you do the basics and isolate your fuel.

I'll second the blown power valve myth - I have tuned street cars with 6-71 blowers and two carbs and never ever saw a blown power valve.

 

[bronconate68]

Thanks for the info everyone.

I'm going to start with baddad457's advice and make sure everything is set. The thing that has me baffled is that it was running just fine. I had taken it out twice with no problems idling at a stop. The fuel line from the fuel pump to the carb was to small and I had just replace it with the proper size.

I don't know what fuel pump I have but it is brand new and the clear filter at the carb shows plenty of gas. The pump is rated at 6 or 7 psi, I cleared that with the builder. The carb stats say it needs 6 psi to function properly. On my drive out yesterday the motor was running great for the first time. No stumble off the line, running smooth at low speeds (25 mph). I went through 3 lights where I had to stop and wait, no problems idled great. Came to the 4th light and slowed for traffic to make a turn and it died. Everything changed at that point.

I will be looking at the electrical side also. When I get home tonight I will see if it will fire up ok or not.

I have not had anything close to a backfire yet. I don't think it is a power valve but I still might pick up a protection kit.

Thanks again,

Nate
'68

 

[Sporto]

What about heat near your fuel line? Often times headers or exhaust pipes can have a severe impact on fuel flow to the engine. Routing lines away from these sources of heat is a great idea just in case.

R

 

[SHX669]

Good adivce/info all around in the above posts.
I'll triple that power valve myth thing - I've blown one in 42 years - and MOST Holleys have had a power valve blow out protection built in for at least the last 10 years - probably longer.
SHX

 

[baddad457]

Thanks for the info everyone.

I'm going to start with baddad457's advice and make sure everything is set. The thing that has me baffled is that it was running just fine. I had taken it out twice with no problems idling at a stop. The fuel line from the fuel pump to the carb was to small and I had just replace it with the proper size.

I don't know what fuel pump I have but it is brand new and the clear filter at the carb shows plenty of gas. The pump is rated at 6 or 7 psi, I cleared that with the builder. The carb stats say it needs 6 psi to function properly. On my drive out yesterday the motor was running great for the first time. No stumble off the line, running smooth at low speeds (25 mph). I went through 3 lights where I had to stop and wait, no problems idled great. Came to the 4th light and slowed for traffic to make a turn and it died. Everything changed at that point.

I will be looking at the electrical side also. When I get home tonight I will see if it will fire up ok or not.

I have not had anything close to a backfire yet. I don't think it is a power valve but I still might pick up a protection kit.

Thanks again,

Nate
'68

6-7 PSI pressure may be too much. It takes very little flow to keep a carbed motor happy ( I doubt the line you replaced was too small), pressure however is a different story in replacing that "small" fuel line, you could have overloaded the float's ability to control the fuel flow, thereby causing the new problem. Start it up, run normally it a block or two, then check the sight plug to see if it's got too much fuel in the bowl. A sticking needle/seat can also cause havoc, flooding the engine. Just off hand, it sounds like you've got too much fuel in the carb's bowls.

 

[SHX669]

All three of my Holley manuals say to run 5-7 psi fuel pressure - you also need volume.
SHX

 

[broncnaz]

Id say you have eiterh bad needle seats or the float level is off. I'll echo the power valve setiment although I have seen 1 bad one its rare. Not to mention your carb already has power valve blow out protection. If your power valve was bad you would most likely be blowing grey or black smoke out the tail pipe at idle.
Also since it runs fine sometimes that points to either float level or needle seat issues. one thing I always had problems with was the offroad needle seats they always had issues I swapped them out for the standard needle seats and the issues went away. Really the offroad needle seats are more for high speed offroading then for fairly normal use.

 

[baddad457]

you also need volume.
SHX

Nope. I'm running a 35 gal/hr pump feeding three carbs at WOT. At 30 gal/hr, that would be enough to feed an engine getting 2 mpg at 60 mph.

 

[ugly74]

Oh yeah, my mistake on the new carbs already having the power valve protection.
All mine were resurrected from abandoned paperweights. I aint dun never did buy no new fancy carb;D

 

[bronconate68]

I started it up after work and it fired right up. It didn't seem to run as smooth but it was still running strong. I'm going to start with baddad457's advice and take the carb tuning back to point A. I'm also going to follow broncnaz's and Ugly74's advice and check the needle seats and float levels.

The fuel line I removed didn't keep the fuel filter full at idle, it even ran dry once or twice. The line was old and I had to bend it by hand to get it connected. The bends weren't pretty and I figured they might cause me problems. So now I have plenty of fuel and I'm going to let it prove to me that the fuel pressure is incorrect if that is the case. The fuel line is not near anything that should heat it beyond reason.

Thanks everyone for all your help.

Nate
'68

 

[pcf_mark]

How is your fuel filter situation? Maybe you need to swap them out. I have seem the glass ones rust and flake apart and get stuck in the needle and seat. Wander down the fuel filter aisle to find a plastic clear one you can pop in.

 

[bronconate68]

How is your fuel filter situation? Maybe you need to swap them out. I have seem the glass ones rust and flake apart and get stuck in the needle and seat. Wander down the fuel filter aisle to find a plastic clear one you can pop in.

I only use the plastic clear ones. I had a glass filter fail on me and almost start a fire. I wont use one of those again. All filters (3) are new and the clear one was new yesterday even though the one I had was barely used. They are inexpensive. Thanks.

 

[baddad457]

It's seldom that any filter will completely fill, unless you rotate it to bleed off the air bubble as it's running. Air bubble = not a concern, completely dry ? that's another story.

 

[bronconate68]

I'll clarify that I use the plastic clear at the carb, the others are the normal canister type.

With the new fuel line the clear filter is full with the air bubble. I'll find out Wednesday how resetting the carb to point A works out.