throttle hestitation on 901

Anonymous-0

Well-known Member
Tuned up a 901 Ford with new plugs, points, rotor, condenser, cap, & wires. Runs OK except for a momentary hesitation when I open the throttle. Owner tells me it wasn"t present before. The carb is a TSX 662 Marvel Schebler. I"m not familiar with this particular carb but would expect this to be normal since there is no accelerator pump. Is it?

The power needle initial setting is 1- 1 1/4 turns but the tractor couldn"t pull itself up a small grade set at 1 1/4 and doesn"t reach max power until it"s about 2 turns. Again is this normal?

Finally, I can"t seem to get a rich idle mixture by turning the idle screw in. My tach/dwell meter fluctuates wildly at both the dwell and RPM settings so I"m not sure what RPM it"s idling at. Is the 400-450 RPM spec critical?

Points set at .025 and timing is on the mark although again I'm not sure of the RPM.

I"d appreciate any help from you Ford experts.
 

Sounds like your carb could use a good cleaning. A sticky float valve would cause your hesitation and a partially clogged needle valve for the venturi would prevent an over rich mixture. Both common problems with gassers that sit during winter.
 
There is no such thing as "normal" carburetor adjustments (number of turns) as many factors are involved.

The point dwell should not fluctuate. Doing so is an indication of worn distributor bushings.

The 450 RPM idle spec is important when setting the ignition timing.

Stumble or hesitation upon rapid throttle opening is common if the engine is not fully up to operating temperature. Once up to temperature, the engine should not stumble upon rapid acceleration if all is as it should be but most will. Richening the main jet slightly MIGHT help.

Dean
 
if advance and dizzy are good, including timing, and it lacks power, and hesitate. TRY a lil enrichment on the main.

post back,.
 
The idle mixture screw will have little no effect above a certain throttle opening.

Due to wear of the throttle shaft and bore, most have no effect even at idle speed.

The idle mixture screw is not the cause of engine stumble upon acceleration.

Dean
 
(quoted from post at 08:11:28 04/18/14) Tuned up a 901 Ford with new plugs, points, rotor, condenser, cap, & wires. Runs OK except for a momentary hesitation when I open the throttle. Owner tells me it wasn"t present before. The carb is a TSX 662 Marvel Schebler. I"m not familiar with this particular carb but would expect this to be normal since there is no accelerator pump. Is it?

The power needle initial setting is 1- 1 1/4 turns but the tractor couldn"t pull itself up a small grade set at 1 1/4 and doesn"t reach max power until it"s about 2 turns. Again is this normal?

Finally, I can"t seem to get a rich idle mixture by turning the idle screw in. My tach/dwell meter fluctuates wildly at both the dwell and RPM settings so I"m not sure what RPM it"s idling at. Is the 400-450 RPM spec critical?

Points set at .025 and timing is on the mark although again I'm not sure of the RPM.

I"d appreciate any help from you Ford experts.

First things first.
Since you tuned it up and it changed behavior, look there first.
Like said, if you set the timing, but not at the proper RPM, the timing is wrong.
Verify the advance weights are clean and working (does the mark move under the light when you increase rpm?)
If ok, check your manual for the proper spec at the high rpm (easier). Mark the specified degree on the flywheel for max advance. Bring it to the specified high rpm and time the max advance mark. When it drops to idle, it will be where it is supposed to be with a properly working advance mechanism.
(and the proper timing at working rpm is more important that the idle setting anyway IMHO)

When timing is right, if the carb is good and clean, set the adjustment at the book starting points.
take a drive, when warmed up, coast along at near idle in gear, pull the throttle to full quickly. If it stumbles, enrich the main a little until it doesn't. If 1/2 to a full turn won't make the stumble go away, your carb or fuel supply system needs a rebuild/clean.
 

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