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| Joined: | 12-27-2022 |
| Location: | Beaverton, Oregon USA |
| Posts: | 37 |
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Back again. Still trying to understand this car.
Car starts easily when cold with choke. Runs great. Very difficult to start when the engine is warm. I don't use the choke when warm (tried it no help). It would usually take 3 or 4 tries before it starts recently had to wait 30 min before it would start. Once it does, it runs rough for a minute or two then fine.
Tom
This is a very old thread, but I wanted to document an alternate response to this issue for other members on the board.
The hot start problem is CARBURETOR related, not emissions, vapor lock or ignition. After the carbs heat soak for a while, they are hot enough to significantly heat the air passing through them during a hot start. The hot air is less dense, and contains less oxygen, and therefore needs less fuel to combust properly.
The problem is that carburetors are stupid, and add fuel based on the VOLUME of air, not the density. That means during a hot start the mixture is pig rich, and difficult to ignite. Once the engine fires and enough cool air passes through the carbs, the carburetors cool off and no longer heat the air, and the density of the air increases, so the mixture leans out and the car runs normally.
The Zenith engineers knew about this, and added a temperature compensator to the carb, but by now they are way out of adjustment if they are working at all.
First, get the baseline mixture correct. Do NOT use the lift the slide method, it is much too sensitive to technique, and most people lift the slide way too much, so the engine tries to stall and the tuner assumes that the mixture is too lean. He then adjusts the mixture richer. This aggravates any hot start issues even though the car runs fine when cold and when cruising. Therefore use a color tune, CO2 analyzer, O2 sensor or plug cuts to get the mixture correct. Once the mixture is correct, the plugs will be a light tan color after a spirited drive with the engine fully warmed up.
If this is not enough to solve hot start issues, you will need to adjust the compensators. These are the white assemblies on the side of the carbs, about the size of your pinkie finger. Make certain the carbs are at ambient temperature when adjusting them, they must not be warm to the touch. Remove the two small screws that hold the cover on the compensator. Do not lose them, they are number 5 screws, which you will most likely not be able to find at the hardware store (usually stores stock number 4 or number 6 screws, but not number 5).
Under the cover is a bi-metal strip with an adjustment screw. The strip opens an air bleed to lean the mixture when the carb gets too hot, thus preventing a hot start failure. Tapping *lightly* on the black plastic plug at the end of the the strip with your finger, back off the screw until the plug can be felt to move when lightly tapped. Then tighten the screw until movement can no longer be felt and tighten the screw 1/8 turn further to preload the plug. Replace the cover and adjust the other carb in the same way.
This will eliminate 95% of all hot start problems. It worked on my TR6, it worked on my TR7, and it worked on my TR8. All of them had hot start problems when first acquired. So try this before you go chasing ignition or vapor lock gremlins.
Cheers,
Vance
Last edited on 12-31-2022 05:50 pm by Darth V8R