Hesitation on acceleration

Topic: Hesitation on acceleration - FIXED!! (Read 1962 times) previous topic - next topic

Hesitation on acceleration - FIXED!!

November 07, 2009, 04:39:39 AM

I just bought an '82 tbird with the carbed 255. I am having some acceleration issues with it and could use some help hunting down the gremlins.

Symptoms:
Accelerates fine, as long as the throttle is not pressed more than a quarter way down (it will bog down otherwise). The problem is relative to the position of the throttle, not necessarily the engine speed. I can floor it, and the rpms will jump and it will run rough, but no noticeable change in acceleration.

What has been done thus far:
The guy I bought it from replaced the fuel pump and rebuilt the carburetor. Fuel filter is new as well. I ran through and checked all of the vacuum and electrical connections, and they all seem to be connected. I checked the timing and set it to 8* btdc. The pickup in the distributor has been replaced along with all of the parts from cap/rotor to spark plugs.

I have two different opinions from different people:
One says it may be an issue with the spark advancement. The other says it has to be a fuel-related issue.

So... All of the standard maintenance parts have been replaced. Beyond that, where do I start looking for problems? Also, how can I test to see if the spark advance is working? Something this old uses engine vacuum to determine timing advancement, correct?

Any help is great appreciated. I am a novice grease-monkey, so try to keep the jargon to a minimum please :hick:

Hesitation on acceleration - FIXED!!

Reply #1 – November 07, 2009, 05:16:42 AM

Our Cougar had an a hesitation awhile back and the Stator down below the Distributor Cap was replaced. No more bogging down feeling.

Hesitation on acceleration - FIXED!!

Reply #2 – November 07, 2009, 09:41:25 AM

You have a carb issue... Lack of timing advance may make it lazy and give poor fuel mileage, but WILL NOT cause a continual bog... On the older carbed models if the heat riser(flex hose) to the air cleaner is missing they will hesitate/bog badly, but once they build some RPM they will usually pull though...

What carb is on it??? If it's the Motorcraft 2300 should be a easy fix as those only have 5-6 parts(OK maybe a couple more)... If it's the Variable Venturi, only sure fix is toss it into the trash and inst a aftermarket(do not mess with a rebuilt, as its a POS design)...

EDIT, just looked in my '82 Motors Manual, the 7200vv(variable venturi) is listed for all Tbird models after '79...

Hesitation on acceleration - FIXED!!

Reply #3 – November 07, 2009, 10:04:34 AM

I'd bet the spark plugs might need to get replaced. I would throw some premium in it and advance the timing to see how it responds.

Hesitation on acceleration - FIXED!!

Reply #4 – November 07, 2009, 02:50:01 PM

I checked all of the spark plugs, and all look normal and new (as told by the seller). On the top side of the carburetor, "Motorcraft 25" is stamped on it if that helps at all.

After a quick google search and comparing images, I have the Motorcraft 2150 carb. Also, at the parts stores, the rebuild kits for this car point toward the 2150.

Hesitation on acceleration - FIXED!!

Reply #5 – November 07, 2009, 04:31:27 PM

You're correct 2150, dunno where I came up with 2300... The Motors manual is a '82 so may only have preliminary info, Ford must have swapped back to the earlier carb... The 7200 is listed as only carb for '80, '81 & '82...

Don't forget what I said about the stove pipe(heat riser), it's a must on these years that have original type carb...

Hesitation on acceleration - FIXED!!

Reply #6 – November 07, 2009, 04:43:54 PM

I checked the mixture screw settings and that is within spec. The accelerator pump is doing its job, so that is not the issue. I really can't see how this is a fuel issue with everything on the carb working as it should. What else needs to be checked?

If it is an ignition problem, could a bad coil be the culprit?

Hesitation on acceleration - FIXED!!

Reply #7 – November 07, 2009, 04:57:56 PM

Quote from: TurboCoupe50;297916

but once they build some RPM they will usually pull though...
.

The heat pipe is connected. It never "pulls through" even when rpms build. When pushed beyond about 25% of throttle it does nothing, and actually kills the power, even as the rpms stumble upward.

Hesitation on acceleration - FIXED!!

Reply #8 – November 07, 2009, 06:10:26 PM

Unless it has a plugged up fuel filter, still sounds like a carb problem... Could have a low float level, plugged up passages, or not assembled correctly...

Would be nice if you could borrow a known good carb to try...

Hesitation on acceleration - FIXED!!

Reply #9 – November 08, 2009, 04:17:43 AM

sounds lean to me,, and float level would be the primary cause of continual hesitation.

it would be nice if you were able to add fuel while driving,,as in add extra fuel manually to see if the lag suddenly went away for that moment.

that would tell me all i needed to know.

a pinhole in the float will make the fuel flow incorrect cause the float will be heavy with fuel. Cant know that until you take it apart and shake the float and listen for fuel.

Hesitation on acceleration - FIXED!!

Reply #10 – November 08, 2009, 09:21:42 AM

A pin hole in the float will allow it to absorb fuel and sink which opens the inlet valve and will flood the carb with fuel... ONLY if it were adjusted incorrectly on a rebuild, would low float height cause the bog...

Be same as a pin hole in the float of your toilet...

That said, most floats in later carbs are made of a solid plastic material and are not hollow, so can't absorb fuel anyway...

Hesitation on acceleration - FIXED!!

Reply #11 – November 08, 2009, 05:23:35 PM

I will see if I can pick up a salvaged carb somewhere to give that shot.

Hesitation on acceleration - FIXED!!

Reply #12 – November 11, 2009, 05:51:18 AM

Today I removed the carb and tore it down to inspect all of the parts. I adjusted the float level according to a rebuild manual I found online. I then worked on adjusting the mixture screws and discovered something odd (I think).

Are the mixture screws supposed to be identical to each other? If so, I think I may have found the problem. One screw goes in a lot farther than the other when I try to seat them for adjustment. I swapped the screws to see if maybe the passages were different sizes. Each screw seated the same as it did in it's original passage. Is it supposed to work like that?

Anyway, setting the float level a little higher helped, I can get about half throttle before it hesitates now. It still won't get up to highway speed though. Still need a little help. Thanks a ton for advice so far!

Hesitation on acceleration - FIXED!!

Reply #13 – November 15, 2009, 08:51:59 AM

Don't know if this applies but worth a check as had similiar hesitation problem with an 66 Olds years ago.

Check the rubber hose that connects the tank to the fuel line. Age caused it to deteriorate and caused intermittant hesitation (small crack in hose) with everything else OK. Was a @#$%^ to find as kept looking at carb, fuel pump, etc.

Hesitation on acceleration - FIXED!!

Reply #14 – November 15, 2009, 10:27:07 PM

All fixed! Turned out to be a combination of things. I reset the mixture screws where they should be and reset the timing CORRECTLY this time. Before I forgot to unplug the vacuum hose from the advance mechanism. It runs better than my 87 now.