TR6 TR6 - runs but no power under load?

[martin_burtt]

Last Thursday morning I went out to my 1974.5 TR6 jumped in as usual, pulled out the choke and turned the key. The car started, ran for a few moments and stalled. Tried again, wouldn't start. A bit less choke, still nothing. After letting is sit for a few moments, started again on full choke, ran for 10 seconds and stalled.

My initial thought was lack of fuel. I disconnected the fuel line at the carb and turned it over, the fuel supply seemed OK.

Checked the ignition and good spark at all plugs, timing OK, coil OK, changed distributor cap and rotor. (I have a Pertronix Ignition so no points or condenser to chnage). After significant cranking, I pulled the plugs and discovered only the rearmost plugs were getting flooded, front plugs were dry.

I dropped the bowl on the front carb, found only a little fuel in the bowl and a needle valve that seemed to be sticking a bit (I rebuilt the carbs a couple of years ago and had installed new valves then). I replaced the needle valve and the car started immediately and ran like a charm.

It idled fine and I revved it up in the driveway no problem. Jumped in for a test drive and the car had no power through second and into third. It just seemed to bog down under load and had no acceleration. It also popped and misfired a bit under load.

This morning I got a chance to work on the car again. Replaced fuel filter - no change. Replaced fuel pump - no change. Replaced coil - no change. Checked carb diaphragms - looked OK but replaced one with some slight cracking anyway - no change. Rechecked timing and confirmed advance when revved - no change. Neither advancing or retarding the timing fixed the problem. Checked compression, all cylinder equal compression.

I'm at a complete loss. Does anyone have any ideas or suggestions? The car runs perfectly when sitting in the driveway - it's as soon as any load is applied that the engine bogs down. Is it a carb problem and not getting enough gas? I gassed the car up about a 10 days ago with a nearly full tank - could it be bad gas? Ignition?

Any advice or suggestions would be most welcome.

Martin

 

[TexasKnucklehead]

confirmed advance when revved - no change.

Did you check the mechanical advance inside the distributer?

 

[Geo Hahn]

Maybe because of another thread I've got valves on my mind. Nevertheless...

Have you checked your valve adjustment lately?

 

[glemon]

Weak spark? I had a bad condensor once that had me awfully confused until I swapped it out, but you have pertronix, which is usually pretty much working or not from what I have heard.

Weak Mixture caused by a vacuum leak somewhere?

Sounds like you have been trying to track those types of things down already, not sure where else to suggest you look.

Lastly fuel delivery, but I don't think it would rev, or bog down immediately under load.

 

[martin_burtt]

confirmed advance when revved - no change.

Did you check the mechanical advance inside the distributer?

No, I haven't checked the mechanical advance. When I checked the timing with the strobe light, the timing did advance when I revved the engine. I will take a look inside the dizzy to make sure everything is OK there.

Thanks,
Martin

 

[martin_burtt]

Maybe because of another thread I've got valves on my mind. Nevertheless...

Have you checked your valve adjustment lately?

They were checked less than 1000 miles ago, but I'll put that on the list of things to check.

Thanks,
Martin

 

[TR4nut]

The way I read your note, did you just check one carb? If so, why not the other? Also, not sure what the symptom would be, but did you check float height after you changed out the needle valve?

 

[tomshobby]

Check manifold vacuum with gauge and check for leaks.
Make sure valves are opening. When my cam lobes wore down I still had good compression but the flow became limited.

 

[RagTopMan]

Any chance that you mixed up the firing order of your wires when you were changing/inspecting your plugs and distributor parts?

Don't ask me why I know that this causes the exact same symptoms as you describe (runs but no power under load).

 

[sd80mac7204]

My spitfire broke a spring in the distributor and would run just fine until you put a load on it. Would loose power because the distributor would go to full advance anytime you touched the gas.

 

[martin_burtt]

Any chance that you mixed up the firing order of your wires when you were changing/inspecting your plugs and distributor parts?

Don't ask me why I know that this causes the exact same symptoms as you describe (runs but no power under load).

Double checked and all the wires are in the correct place.

Thanks,
Martin

 

[martin_burtt]

My spitfire broke a spring in the distributor and would run just fine until you put a load on it. Would loose power because the distributor would go to full advance anytime you touched the gas.

I checked and the springs are both in place and there are no problems inside the dizzy with the mechanical weights.

Martin