 |
PM |  | |
Quote | | |
Reply | | |
Full Topic | |
| Joined: | 04-07-2022 |
| Location: | Oregon USA |
| Posts: | 96 |
| Status: |
Offline
|
Separate, and not vacuum related...
If the Thermal Compensator is suspect or not working, then don't bother fixing or replacing it. Simply adjust the plunger in all that way such that it can never unseat/ open the port. The Thermal Compensator is a 'seasonal' thing, providing a slightly richer mixture during the warm-up cycle in cold weather. Most 907 powered cars get put in storage and aren't driven during 'real' Winter. If that's the case for you, then restoring the Thermal Compensator is a waste of effort.
Regards,
Tim Engel
Tim,
Your description of the compensator function is a bit off. I do not recommend removing or disabling them for reasons I shall explain.
The thermal compensator does not enrich the mixture, it LEANS the mixture when the carburetors heat soak. It does this by using a bi-metallic strip that moves a small pintle. When the pintle moves, it uncovers an opening, allowing a small amount of air to bypass the jet and join the air fuel stream as it enters the intake manifold. This additional air results in a leaner mixture.
Why do we care about heat soak? When the carburetors get hot after a drive cycle, they will heat the incoming air. This reduces the air density and since carburetors add fuel based on the VOLUME of air (not the mass of the air), the carburetor is now over fueling. This can make the car hard to start, and can result in rough running for a couple of minutes until enough cool air passes through the carb to cool it, which allows the air density to return to normal.
If you are experiencing difficult hot starts, or rough running after a hot start, the temperature compensator is not working, or is misadjusted (opening at too high a temperature).
This issue manifests when the engine has fully warmed, and is then shut down for 15-30 minutes, and then restarted. It is particularly evident on hot days when the ambient exceeds approximately 90F.
The Lotus engine does not have the carbs over the exhaust manifold like Triumphs or MGs. So this tendency is not as severe as it might be. If you live in a cool climate, I suppose you might never experience it.
If you experience this issue, then restoring or adjusting the compensator is warranted.
Vance
Last edited on 05-28-2025 02:13 am by vnavaret