Brian66

My '66 with a 302 is experiencing some periodic "miss" at idle and hesitation on low throttle conditions. The hesitation appears to go away under moderate/strong throttle and higher revs, and also no sign of it when cruising on the highway. Starting from a stop with light to moderate throttle and giving some light to moderate throttle when already rolling will give some hesitation.

As for some details, I have appx 3k miles on a new Weiand intake and Edlebrock 1605 carb, and points/plugs/wires were also replaced at that time. The symptoms have just started in the last couple weeks (within last 100 miles or so), and I have since installed new cap, rotor, and fuel filter with no improvement to the miss/hesitation.

One other thing is that, especially when warmed up, I will get a pretty good "hiccup" in the idle now and then when idleing at a stop light.

Any other ideas at what might be causing this or what I should look at?

urban_cowboy

Sounds like the primary and/or the accelerator pump/nozzle is either too rich or too lean for your application. Time to start checking plugs. Have you had the carb professionally tuned or dyno-tuned?

Brian66

The carb has not been professionally or dyno tuned. It has been re-jetted (mains and secondaries) for my elevation (6,000ft) per the Edlebrock chart (don't remember the specs).

I will pull some plugs this weekend and report back what I find.

urban_cowboy

Keep in mind that the reason people like Edelbrock carbs is they tune simply. That does not mean that you still do not need to check the tune from their suggestion. After all, not all 302s need the same about of fuel at the same time. You are doing the right thing checking plugs.

Stepman

Also check your points for burning and check the dwell. 3k is about time for an adjustment.

Brian66

Point taken on the carb tune. Adjustments beyond the jets are also probably beyond my expertise, so I will probably look into having a shop fine tune the carb and timing. In the mean time I will still check the plugs this weekend and report back with what I find.

I really want to move away from the points (perhaps a pertronix, Mallory 85 series, or Unilite), but to keep peace in the house the Mustang budget needs to take a break.

jonward786

yeah, dont go by what the edelbrock manual says you need, go by what your plugs say you need.

i had the EXACT hesitation you are describing on my car for a long time. the only time it would stumble/hesitate/miss was at slow accelerations or cruising at low speeds.


increased jet size and problem solved. my plugs were also white as chalk...

Brian66

I guess my only question is wouldn't I have encountered these symtoms right after adjusting the jets? The miss and hesitation just came about a couple weeks ago, in the last appx 100 miles. It was kind of sudden also, it was running great, then one day after driving it to work (which I only do about once a week) and making a stop on the way home, after that stop it ran badly on the way home (had to shift into neutral at lights a couple times to keep it going). It has not run as bad since, but that is when the miss and hesitation started.

Edit: I may answer my own question by guessing that if the carb is mis-adjusted the affect on the plugs could have built up since the jetting, which is just now affecting how it runs. But I did check several plugs a month or so ago when repairing a header, and while they were a little black with carbon, overall they looked ok (to my eye). They "may" have seemed a little wet, however, but that would go against the way I jetted the carb (smaller), I would think.

urban_cowboy

Like I said in another post today. Carb tuning is dependent on temperature, altitude, and humidity. Even if you carb was tuned just right, when one of these things change or if these change enough, it will adversely affect a carburetor. I am not saying that is what happened, but I run three different tunes (summer, winter, and spring/fall) for that very reason.

Like others have suggested, you should also check your timing and ignition. That too can play havoc with a tune if something changed.

Brian66

Thanks for the info, there is definately lots I need to learn about tuning (both carb & ignition).