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TR6 TR-6 carb question

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Bob60

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Recently bought a TVR 2500M - has TR-6 engine with Zenith-Stromberg 175CD carbs. Never owned a car with Zenith-Stromberg carbs before.

When I shut off engine after engine is warm, wait 5 minutes or so, car is very hard to start like it is getting way too much gas to the point of flooding - opening throttle all the way seems to help.

However...

When I park in may barn, I park with the front wheels up on about 4"-5" wood ramps (allows me to open the hood further - entire front of car pivots forward like an E-Type). Thus, car sits at slight angle. When in this position, it starts just fine.

My theory is carb floats are badly out of adjustment. The slight angle is just enough to prevent flooding. They were "rebuilt" before I bought car.

Before I tear into the carbs, thought I'd see if other people think I'm on the right track?? FYI: fresh points correctly adjusted, valves in correct adjustment and timing set correctly.

Thanks,
Bob
'74 TVR 2500M
various other LBC's
 
Sometimes they are hard to start a short time after the engine was stopped.
During that time the fuel in the float chamber is stagnant and sitting not too far above the hot exhaust manifold.' The fuel can percolate during that time.
The TR6 owners manual says to restart a hot engine, hold the accelerator 1/3 down while cranking.
That's going to allow the manifold vacuum to suck the hot gas and vapors out and make room for cooler gas to enter the float chamber. The engine may still run rough for a while until all the hot gas has been replaced with fresh gas by the fuel pump.
A heat shield may discourage percolation. Re-routing the fuel line won't, because it's the fuel in the float chamber that's causing the problem, not the gas in the fuel line...I tried that approach to no avail.
Might be other things contributing to the hard to start situation, such as a rich mixture, too much fuel in the float chamber, or the choke partially open. Each of those possible culprits have their own solution.
 
Hey, Bob.

I think that typically one usually needs to depress the gas pedal 1/3 to 1/2 way when starting "warm". That's really a different situation than a cold start with choke, even with the different angle.

I suppose the floats could be off, but before getting into that check the plugs to see if the carbs are too rich. If they are it would aggravate the warm start situation.
 
Bob, next time you are in there, push the choke down on each carb and see if you get some movement, they tend to stick on slightly. That's why I prefer the solid cable.

Wayne
 
Is it still easy to start with only 5 minutes on the ramps and without opening the hood? If so, then it certainly wouldn't hurt to try a bit lower adjustment on the floats.

But my guess would be that you are having trouble with either percolation (too much heat causes the fuel to boil in the carbs and fill the intake with fuel); or a float valve that is leaking just a bit and allowing the level to rise with the engine shut off.
 
You can also try using a heat shield for your carbs. After I put a heat shield in my '75 TR-6 I never had that problem again.

Dave
 
Thanks for the input.
Pulled carbs off and found floats set at 0.730. Am resetting to 0.640. I've read that one of the manuals actually gives an incorrect spek for the setting.
As per Shawn's suggestion, I'll see if the chokes were assembled correctly.
Interesting comment about the heat shield, I'll try that if things don't improve after it all goes back together.

Thanks,

Bob

74 TVR2500M
various others
 
Something to think about, Bob. Because the carbs are upside down when you set the float height, you actually raised the fuel level in the float chamber. So if the starting problem was due to too much gas in the float chamber, you didn't do anything to improve that.
I still think this was a typical case of percolation, though.
 
Bob, What Poolboy said. With more gas in the float chamber the carbs will run richer. Be prepared to lean them out if necessary. Do you have adjustable jets or needles?
 
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