OK, Another Hesitation Question

Mustang Jim · Oct 1, 2010

I've searched the forum to see if I could find a previous post that would solve my issue, but nothing seems to match.

My 64.5, 260V8 starts fine and idles fine, but hesitates badly on acceleration. I've replaced the plugs, wires, distributor cap, rotor, pertronix ignition (now a pertronix II), ignition coil, fuel pump, fuel filter, rebuilt the carburetor, adjusted the accelerator pump, adjusted the timing and yet I still have hesitation on acceleration. When I step on the gas, it's like I just took my foot off the accelerator for a few seconds and then it picks up... not smoothly, but it begins to accelerate ok.

The problem started after the car sat in my garage for a year. I think I ran it maybe 2-3 times over the year. Back in the spring, I was determined to bring it back to its old "glory". At that time, I noticed the fuel line was clogged as I could not start it. I blew out the fuel line with compressed air and got it started. So far so good, but then I noticed the hesitation. So, that's when I started to do all the work I mentioned above to no avail.

What do you think? Maybe crud in the tank? I've used a few tanks of gas since. Vacuum leak? Something else? I love working on this stang of mine, but this is frustrating! Any ideas?

Thanks,
Jim

Realmongo · Oct 2, 2010

Since it sounds like you covered all the normal bases and the car sat for a long period and ran fine before that, I would guess that you have some carburetor passages that are plugged by hardened gas/dirt deposits. You may want to consider sending the carb off to a place like Pony Carburetors for a complete remanufactoring and engine test/setup.

Az Pete · Oct 2, 2010

That type hesitation is normally caused by a fuel delivery issue as you depress the pedal. Going from the normal cruise circuit with a small amount of gas being used to a need for more gas, it relies on the accelerator pump to deliver that needed jump. If that is not in perfect time, you get a hesitation......either to much gas and a puff of black smoke out of the pipes or to little gas and no indications. I had a Holley 600 do that for about 1000 miles until I got it just right.

Have someone follow you to see if there is a puff of black smoke when you step on the gas.

This all may be caused by junk blocking the internal carb circuits or a improper adjustment.

D.Hearne · Oct 2, 2010

Checking the accellerator pump is easier just by removing the aircleaner assembly and moving the linkage while looking down into the carb throats. The instant you start moving the linkage, you should see fuel come out of the squirters. Retarded timing will also cause a hesitation. Are you setting the timing at the 6*BTDC setting the factory recommended ? If you are, then bump it up to about 12* BTDC. Every Ford I've ever owned liked 12* a whole lot better than 6.

Mustang Jim · Oct 2, 2010

Guys, I think I found the problem. I only had about 30 minutes to play around with it today, but it appears that the PCV valve is not sitting tight in the grommet and it's sucking in air. I pulled the PCV valve, temporarily plugged it and the car accelerated fine with no hesitation. I thought the PCV valve was tight enough in the grommet, but I guess not. I should have some more time tomorrow to check this out. I hope that's all it is.

Az Pete · Oct 2, 2010

The PCV valve sucks air from inside the engine most of the time based on vacuum when accelerating or not. I kind of doubt that is the problem..............

Mustang Jim · Oct 2, 2010

AZ Pete, you're right. I had some time tonight, so I picked up a new grommet for the PCV valve and replaced the old dried out one. Still have the same problem. I readjusted the accelerator pump 3 times, advanced the timing, retarded the timing.... and still the same thing.

Hmmm..... What's next?

Az Pete · Oct 2, 2010

Does the car accelerate if you gently push on the pedal to gain speed? Also, have you looked at the advance mechanisms? Check to see if the weights inside the distributor are free to move and also check the vacuum advance to see if it is functioning.

I also recommend setting everything to the correct setting....then work one item at a time. If that does nothing, put it back and try another adjustment. I still lean towards a fuel delivery issue from my past experience. Took me forever to solve it.

What carb you using?

KStang65B · Oct 2, 2010

Put a glass fuel filter in just before the carb filter and drive it a bit. See if it fills up with junk.

The previous owner of my 65 had the same problem. He put in a new tank but the filter an carb kept getting clogged with junk. I put in a filter with clear glass and it immediately filled up with orange junk.

I'm assumed rust from inside the fuel lines. I ran it off a jug of gas for a quick drive and it ran perfectly. The gas was a bit chunky when I drained it but the tank had no rust.

KStang65B · Oct 2, 2010

Also, check your u-joints. Bad u-joints will feel like a hesitation or slipping of the trans.

Mustang Jim · Oct 3, 2010

If I accelerate real gently, there is little to no hesitation. I checked the vacuum advance on the distributor and it held vacuum. Also, the vacuum assembly moved fine as I did the test with the distributor cap off. I've replaced the fuel filter twice and both times it appeared clean. Junk in the fuel tank? I'm thinking that could be. I hate to pull the fuel tank, but I'm not sure what's next.

D@mn, this is frustrating!

Realmongo · Oct 3, 2010

It still sounds like clogged internal passages in the carburetor from sitting.

rbohm · Oct 3, 2010

the advance mechanism that you need to check is not the vacuum advance, but the mechanical advance. it has to operate freely if the engine is going to accelerate properly. you can check this by taking the cap off, and turning the rotor one way then the other and see if it snaps back like it should. it should also move freely. if not then you need to pull the plate and free up the the advance weights.

Mustang Jim · Oct 3, 2010

OK, next weekend here's the plan:

Rebuild Carburetor (again)
Disconnect fuel line and blow out with compressed air
Drain fuel tank
Check mechanical advance on distributor

I hope nobody minds, but I might be back with more questions next weekend.

Thanks,
Jim

Az Pete · Oct 3, 2010

When you do the carb, get the can of cleaner you can put the large parts in and soak them as required. Then use air to blow the carb lines out.

Mustang Jim · Oct 11, 2010

Great news! Problem solved!

I took the carburetor apart and cleaned it again. Upon closer examination, it looked like one of the venturi passages was clogged. I guess I missed it the first time around. Anyway, after a good soaking, I put it all back together and took it out for a test ride. NO MORE HESITATION! I feel like I'm driving a different car.

Thanks everybody.

Jim

OK, Another Hesitation Question

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