TR2/3/3A The Newest Bug to Fix...Now with Video!

[CJD]

Dave, I'm still not seeing a problem here.

The little 4 banger was not designed for the heavy draw of an electric fan, so the RPM will always drop when that many amps kicks in. You are increasing the load on the motor without re-adjusting the idle...so it will necessarily drop. Most carbureted cars that had heavy draws, like fans/AC/etc. used a solenoid to bump up the idle speed when the heavy hitters came on line. Without that a drop in idle speed is inevitable.

I grew up with only carbureted cars, and I do not ever remember having one that would idle as long as yours does without clearing the carbon with a rev every several minutes. Remember that modern FI cars run closed loop, reading the O2 levels and constantly adjusting for variations in load and they even vary the air bleed for a rock steady idle. Carburetors do not have a feedback loop. You set it for a speed, and that's what you get. No temp or altitude adjustment is inherent in the carb. Thus, if you let it idle for extremely long periods...which 15 minutes is extremely long for a carbureted car...it is natural for it to load up or lean out.

When a load comes on a carburetor, the idle slows, lowering the vacuum. Lower vacuum will not draw the same fuel as it did with a free idle. Well...I could go on, but bottom line...if I have a carbureted car that will idle for 15+ minutes before it loads up, I am happy. Altering the basic design to add heavy draw fans, and your idle is absolutely incredibly stable.

 

[M_Pied_Lourd]

Hi John,

Understood, but the car would get to a point where it wasn't drive able. I couldn't pull up to a stop light without it idling...it would just die at idle like it did in the video. The last drive I took, I barely made it back home and it stalled out in my driveway. This drive had very few and very short stops. Temperature never went above approx 195 but still had the stalling out issue.

Cheers
Tush

 

[CJD]

Hi John,

Understood, but the car would get to a point where it wasn't drive able. I couldn't pull up to a stop light without it idling...it would just die at idle like it did in the video. The last drive I took, I barely made it back home and it stalled out in my driveway. This drive had very few and very short stops. Temperature never went above approx 195 but still had the stalling out issue.

Cheers
Tush

I would read that as vapor lock. The solutions to that would include some/all of the following fixes:

1) get rid of the mechanical pump, as it transfers heat from the engine block to the fuel.
2) either insulate the fuel line or re-route it away from the engine and coolant hoses.
3) install a heat deflector under the carbs.
4) try a different brand fuel that has higher tolerance to vapor lock.
5) Increase fuel pressure to 14 psi at the tank, and then use a regulator at the carbs to reduce the pressure back to a carb-friendly value.

Any time I parked my TR3 while hot, it would vapor lock on the next start up. Not badly, but enough that it would sputter and pop for a couple minutes until I got cool fuel through the lines. Even in the best of conditions, these cars are on the verge of locking.

 

[TuffTR250]

I did most of the items John suggests but none of the fuel pump steps. As John mentions when parking it while hot it tends to vapor lock and sputters for a few minutes. I have found that fully choking it when starting hot will even it out very quickly. One other thing I did is to fabricate a front damper. I believe that helps a lot by not letting the engine compartment get quite as hot while driving. The heat does build up quickly when stopped. I have noticed that even when it is very hot here in Raleigh, in city driving if I can get up some speed between stop lights the damper drives enough air up into the radiator and engine compartment to cool it down just between stop lights. Doesn't help in stop and go driving so for that I turn on my electric fan override switch. Attached are pictures of my air damper.
Regards, Bob