Gents,

Something is haunting me... been on the dyno recently to get my Motorcraft 2100 adjusted, as well as the ignition. It was all way-off and after the tune-up, it made a hell of a difference. But, I'm still experiencing a slight problem, which has been described earlier, but I didn't seem to find the exact same problem and it's solution.

When I drive normally, the engine runs fine and my smile could reach the moon.... But, after taking a roundabout, or waiting at a stop-sign, the engine stumbles on acceleration when I easily step on the gas. When I " floor " it, it doesn't stumble.

The carb has been professionally cleaned and the accelerator pump diaphragm has been replaced. What else could cause this stumble ?

Thanks, it's not a big thing, but just a PITA.....

Best regards,
Martin

 

Two items that erased this issue for me:
Check your fuel filter for blockage. (My screw-on type canister was full of gunk from the tank float)
Are you running points? (I replaced my points/condenser, and ensured the dwell angle was correct).

This has made my red-light stumble disappear. Hope it helps.

 

Stumbling on light acceleration from a stop is probably due to being just a hair too lean at idle. The hard acceleration adds fuel from the acceleration pump, but you don't get that squirt of fuel when you open the throttle slowly during a light acceleration.

 

Hi Treverd,

Fuel filter is absolutely clean and I'm running a electrical ignition, so that should be OK. Also, it was tuned up by a very renown local guy. But, during the tune-up, I forgot to mention the stumble....

Could it be that during braking, the fuel filter empties itself back into the fuel line maybe ? So it creates a lean environment in the carb ?

Thanks !
Martin

 

Hi Turbo Dog,

Thank you too for answering ! My idle screws are already 5 full turns out....

Best regards,
Martin

 

5 turns out or 3 turns out...you still need to know if you're rich or lean. I'm not familiar with the passage layout in a 2100 carb, but most carbs have a port just above the throttle when it is closed. Those are the first to allow fuel in during an easy acceleration. Did you check your emissions levels while on the dyno?

 

TD, we didn't check for emission levels. Might give it a try to open up the screws a bit more, maybe it helps. Have no idea how long the screws are, in other words, how much turns can they make before they fall out ?

 

I don't know but you can find out. One other thing you can try for that stumble is to bring the base timing forward 2 or 3 degrees and see if it makes any difference.

 

did you run full 12v to electronic ignition ? or just use the factory wire off coil ?

 

There is an adjustment on that carb for accelerator pump throw. Reset it for more squirt.
Lean accelerator pump is a common cause of acceleration bog.

 

To be honest, I need to take a look at the 12V connection to the coil, I'm not sure what is used.

And for the reset of the throw, it's now in the far most hole. More leverage, more squirt I presumed :-)

 

We'll get you going, Martin.
Do only one thing at a time, test, move on.
There are two holes on the accelerator pump lever of the 2100. You are on the outer, you say. That is the lean throw. Unhook the rod, put it into the rod tip back in the lever hole closest to the carb body. That will richen and probably take care of the lean bog on acceleration.
Let us know.

 

Thanks a lot guys for all your help ! This afternoon, I reset the throw into the hole, closest to the carb-body. No difference, but it made me think twice... When I took off the aircleaner, looked inside the throat of the carb, I noticed the pump is squirting too late. After approx. two-thirds of it's stroke, it starts squirting. That must be the problem ! Haven't looked at it any further, as I was invited for a dinner at the local beach, so had to set my priorities to food and drinks instead of accelerator pump problems....

 

Yes, with engine OFF, look down throat of carburetor, there should be two squirts of fuel IMMEDIATELY when throttle is blipped. "Normal" accelerator pump rod adjustment is to use the inboard side on the forward holes, and the 2nd hole from the top (for temperatures 40F through 80F)

Are you employing a vacuum gauge for engine tuning and carburetor disgnostics? If not, why not?

Also, setting float height causes some confusion, even with people who speak English. Keep in mind the initial dry "bench setting" for the _float height_ is just an arbitrary baseline setting.

It must be fine tuned, this is done by measuring the actual wet _fuel height_ in the bowl. This distinction is very often conflated or confused. I just repaired my lawnmower for this exact same reason. The technician set the float WAY too high, and this caused flooding and sooty plug. Dang kids!

With the engine fully warmed up, let it idle for two minutes on level surface and then shut the engine OFF.

If you are careful the air horn and gasket can be removed (4 screws) and then observe the height level of the fuel in the bowl.

Most (many) applications specify 29/32nds _fuel_ height from the fuel to the machined flat surface of the top of the fuel bowl carburetor. A U.S. Washington Quarter is pretty close to 29/32" and is handy to have compared to a machinist's rule.

Note that the actual float height is irrelevant at this point, the fuel height is what is important and will affect jetting and idle, transition circuits, everything. If you have to adjust the float arm, it's best to remove float completely and bend the arm carefully.

If you are REALLY careful, and keep an extinguisher handy close by, you can even idle the engine with the 2100 air horn removed and watch the fuel level for a few minutes to check for proper operation. 29/32" fuel height should be maintained. Do this outside, not in the garage, for safety. The float height may have to be set quite low to reach the correct fuel height. This is OK.

Finally, 5 turns out on the mixture screws is not correct. The initial "bench setting" is 1.5 turns out from fully seated. Then they are turned in (clockwise) for maximum RPM consistent with a smooth idle at the same time, and backed out as necessary for smooth idle, though still "lean drop". Typically 1/2 to 1 full turn out (every engine different) is optimum.

 

I like the idea of using a quarter to help with the float adj. It's a lot easier than the machinist's ruler.