Solved: Confused - 1F running rough (and sometimes not at all) (2 Viewers)

[Fj40owen]

Thanks in advance for the wisdom and guidance here -
1970 FJ40 with a F155 Engine.
Compression 110, 110, 120, 120, 120, 120
Points checked and adjusted
Rotor checked and cleaned
Adjusted and Verified timing
Adjusted and verified valve clearance
New plugs and wires
OEM Carb rebuilt by Classic Cruisers ~12 months ago
New fuel filter, and full tank of fresh non ethanol
Verified Fuel bowl maintains at half full
Idle adjusted, no apparent vacuum leaks.

Vehicle will start and idle.
Some minor smoke when revved
When driving sudden extreme loss of power under load.
No change when vehicle is warm vs cold.

I will mention that the vehicle was driving great up until this problem suddenly started
(not a gradual thing)
Any thoughts on where to go from here?

 

[Green Bean]

Thanks in advance for the wisdom and guidance here -
1970 FJ40 with a F155 Engine.
Compression 110, 110, 120, 120, 120, 120
Points checked and adjusted
Rotor checked and cleaned
Adjusted and Verified timing
Adjusted and verified valve clearance
New plugs and wires
OEM Carb rebuilt by Classic Cruisers ~12 months ago
Verified Fuel bowl maintains at half full
Idle adjusted, no apparent vaccuum leaks.

Vehicle will start and idle.
Some minor smoke when revved
When driving sudden extreme loss of power under load.
No change when vehicle is warm vs cold.

Any thoughts on where to go from here?

How’s your fuel filter? Gas fresh?

 

[Fj40owen]

How’s your fuel filter? Gas fresh?

Yes, and edited above.

New fuel filter, full tank of fresh non ethanol

 

[red66toy]

Checked for vacuum leak?

 

[Fj40owen]

Checked for vacuum leak?

Yep, strong vacuum

 

[Sky King]

Ignition coils tend to get flaky and can exhibit on again off again symptoms.

 

[red66toy]

When was the fuel system refreshed? Before the carb rebuild or after?

 

[Fj40owen]

When was the fuel system refreshed? Before the carb rebuild or after?

After. But was regularly driven and maintained in the interim

 

[cruisermatt]

what's it got for a distributor? did you check distributor shaft for play?

 

[Fj40owen]

what's it got for a distributor? did you check distributor shaft for play?

Yea - OEM dizzy and it is tight and accurate

 

[Fj40owen]

You guys thing there is any chance there could be some minor wear to the diaphram of the fuel pump and it suffers under load? I am not sure when the fuel pump was last rebuild and may go ahead and do that as preventative maintance anyway?
As Sky King mentioned, maybe time to refresh the Ignition coil and condenser as well since I am throwing parts at it.
Maybe I will get lucky.

 

[red66toy]

You guys thing there is any chance there could be some minor wear to the diaphram of the fuel pump and it suffers under load? I am not sure when the fuel pump was last rebuild and may go ahead and do that as preventative maintance anyway?
As Sky King mentioned, maybe time to refresh the Ignition coil and condenser as well since I am throwing parts at it.
Maybe I will get lucky.

Don’t buy anything yet. Test the coil and condenser per the FSM. Under what circumstances does the fuel level stay half full in the bowl? Under idle? What about at higher rpm?

 

[charliemeyer007]

Make sure the fuel pick up is clear. Un hook the hose before the fuel pump and pull gas threw the line as hard/fast as you can (use a gas rated pump)- see if crud comes out and that the flow is good. Make sure there is nothing rattling around in the exhaust system - loose baffle in the muffler, check the carb heat deflector.

I think having some spare parts on hand is a good plan. Starter, fuel pump, alternator, dizzy cap rotor and points, plugs, air/oil/fuel filters, a pack of battery terminals, fuses. light bulbs, a change of oil and coolant...

 

[WildernessRimFab]

Some minor smoke when revved

Have your valve stem seals ever been replaced?

 

[igotta40]

when It runs rough as you describe, disconnect and cap off the brake booster hose at the intake manifold (assuming you have power brakes) and see if it smooths out.

 

[sogafarm]

I just had the same problem with my '75. I changed fuel lines and new gas tank, problem solved. As mentioned before, check for trash in fuel system. My old tank was very rusty and the starvation problem would only happen when I was driving. The rust was breaking loose as I drove it and clogged up the system. I also put in a new pump.

 

[Fj40owen]

Have your valve stem seals ever been replaced?

Not that I am aware of

 

[B y r o n]

I would also disconnect, clean, and reattach all grounds for any of the electrical components. A loose or dirty ground could cause erratic behavior.

 

[middlecalf]

Ignition coils tend to get flaky and can exhibit on again off again symptoms.

This just happened to me with my coiled/pointed 1F. Currently won’t start, last several starts took a lot of cranking, and tachometer was jumping around spastically the last couple of trips, finally pegged at max RPMs before the motor died. Coil currently tests at 1.6-2.0 ohms ( seems to vary with outside temp) on the primary side and is completely open on the secondary side. Everything else checks out ok. New coil in route.

 

[45Dougal]

Is the vacuum advance working smoothly and correctly?
Remove the cap, and try sucking repeatedly on the pipe and watch it advance and retard - maybe getting stuck or leaking diaphragm?