stumbling
 

I have a holley 870 on a world 427w in the higher gears fom say 3 thru 5 if I press down on the gas the car stumbles and sometimes back fires from the side pipes. I not sure if it is ignition or carb related or just bad fuel any help would be appreciated Im at my wits end with this car.

Vacumn secondaries need to be adjusted.

thanks motor head it ran fine through the first half tank of gas and started acting up on the second half if it was vacumm secondaries would it have acted up right away?

Maybe the distributor shifted a bit...and retarded the timing...?...

If the distributer shifted wouldnt that effect the idle because it idles fine.

One of the bleeds may be clogged -- very, very, very common. Blow out all eight of them (idle and high speed bleeds). Four on the primary side, four on the secondary side. Put a clear bag over the carb when you blow you cleaner down through them 'cause it will squirt back up in to your eyes as the high speed bleeds are a little smaller than the plastic tube that comes with your carb cleaner. I've written about this many times on here. In fact, you should clean your bleeds every year or so -- it can make a huge difference. This post has easy to follow pics: http://www.clubcobra.com/forums/fe-t...long-post.html

..............or what Patrick said .

will try that Patrick thanks

How long had the car been sitting with old fuel in the tank?

Wastehauler, please take time to post if Patrick's advice worked for you. I've had the same issue going on myself for sometime now. Even after carb was suppose, rebuilt, by local mech. here, couple weeks back. Still same issue.

Ran fine one day, then started the slight stall thing going on, when going through gears, during normal driving.

Thanks Patrick, going to give this a try,,,,,,,,,, when time permits.

My 2 cents:

I would get a fuel sample from the tank and analyse ethanol/water percentages.

Replace all flex hoses with alcohol (ethanol) compatible hose.

Flush lines after assembly from rear to front prior to fitment the carburettor.

Strip and rebuild carb as necessary. Blow all passages clear with air, ensure air bleeds are clear, ensure accelerator pumps operate correctly (no stuck outlet check valves etc).
Ensure float levels are correct. Throttle plate to transfer slot relationship is correct, all mixture screws at 1.5 turns out.

Adjusting Your Holley
 

You know, I tried something a little new this year on adjusting my idle mixture. I had changed out my S/H air filter for one of the K&N Xtreme jobs and, of course, had a thread with pics on the fab job to make it sit flush and fit inside the Turkey Pan. The increased air flow necessitated a carb adjustment. Instead of using my vacuum gauge, or watching the RPMs as I monkeyed with the mixture, I fashioned a little cardboard circle to go around my screwdriver, similar to a cam degree wheel, so I could easily adjust both screws exactly alike. Here's the new part: I adjusted the mixture screws so that they were exactly the same amount out from seated and the distance was an amount so that when I removed the rubber plug from the vacuum port (manifold vacuum) at the front base of the carb, the RPMs did not go up, nor did it go down - it stayed exactly the same (no vacuum advance on the distributor, btw). The car has never run better. I was told this little trick by an ancient Ford technician who said he swore by it on Fords with longer overlapped cams and Holleys on top. BTW, in measuring the mixture screw distance out from seated, it is just over one full turn. Soooo, if you have absolutely nothing better to do, pull the plug off your vacuum port while idling, if the revs go up, or if they go down, try this trick and see if you like the results.

WE replaced the Holley "870" with a quick fuel SS850 and replace the stock 6.5 power valve with a 2.5 because vacuum is at 5 PSI. This gave wastehauler a choke for the first time since having this car. It now starts and idles at 1000 after a warm up. We also changed the original GM style(coil in cap) mallory dist with a MSD, with street fire box and solid coil. Originally the car ran great . More responsive and smooth. Then after a few minutes the stumble was back. It turn out the spark plug wires were heating up and causing resistance to the plugs.
A new set of plugs and wires did the trick. Seat of the pants results with the Quick fuel is un believable.
R & R Tunning found the problem with the plugs and wires.
After he drove the car he suggested Drag Radials !!!

vacuum at 5"? that must be some engine!

Its a 427w from world products with the man o war block for the first time I can really feel the potential of this engine as far as the quick fuel carb its like putting fuel injection in the car so snappy and responsive with instant starts and idling of which I never had with my holley 850. I highly recommend the quick fuel.

Patrick

I did clean the air bleeds, along with bumping up timing a touch.

1 mixture screw was out 1 and 1/2 turns, other 1 and 1/8 from seat, per using vacuume gauge. Both now at 1 1/8 just for testing.

Car ran much better, 40 mile trip. Hardly any stumble, if any at all. So I'm really unsure just which adjustment helped the stumbling issue. But thanks for the idea anyway.

I've always tried mixing at least 1 (avgas, racing), to 5 gal 93 in the car. And maybe even wonder if timing wasn't my biggest problem. But don't understand why the stumbling would have started for no reason other than the air bleeds.

Car seems to be back to it's old self now,,

Thanks again.

Patrick

I did clean the air bleeds, along with bumping up timing a touch.

1 mixture screw was out 1 and 1/2 turns, other 1 and 1/8 from seat, per using vacuume gauge. Both now at 1 1/8 just for testing.

Car ran much better, 40 mile trip. Hardly any stumble, if any at all. So I'm really unsure just which adjustment helped the stumbling issue. But thanks for the idea anyway.

I've always tried mixing at least 1 (avgas, racing), to 5 gal 93 in the car. And maybe even wonder if timing wasn't my biggest problem. But don't understand why the stumbling would have started for no reason other than the air bleeds.

Car seems to be back to it's old self now,,

Thanks again.

A common mistake.

Obtaining highest vacuum first with one screw has the engine idling on near correct A/F ratio, then you end up not knowing where you are.

Far better off starting at 1-1.5 turns out and knowing where all the screws are while targeting highest manifold vacuum.
It is as much an art as a science.

Now, back to the original thread please.