TR6 Perfectly tuned TR6 wont start when hot.

[ttpiper]

I have a 76 TR6. Recently I encountered some hesitation on acceleration, checked the plugs and determined the car was running pretty rich so decided to do a complete tune up. I replaced the plugs, wires, dist cap and rotor. Read a bunch of threads on the best way to tune. I set the timing using the vacuum method set to 17 to 18 Hg, which put the timing at 900 rpm around 12 deg BTDC. Then I checked the carb mixture only to discover the needles were set to the richest setting. I leaned out each carb using both colortune and lifting the piston methods, sync'd the carbs and readjusted the idle. Took the car for a test ride and it ran better than. I shut the car off and then immediately started it again with no problem. I shut it off and let it sit for about 20 minutes. I tried to start the car again and it wouldn't start. In desperation mode I returned the carb setting to being rich. Still would not start. I advanced the timing beyond the 12 deg BTDC and was able to get the engine to start and make it back home. I then proceeded to retune to my previous settings, went for another test drive, it ran perfect, brought it home. Waited 20 min and again I barely got it to start. The next day while the engine was cold I tried starting it (with choke) and it started right up and ran fine. My conclusion was some kind of vapor lock was occurring.

It's a bit frustrating to have a perfectly tuned engine that wont start when hot. Any suggestions besides putting a heat shield between the manifold and the carbs?

 

[sp53]

Probably the coil.

steve

 

[poolboy]

I doubt it's vapor lock...."vapor lock" (a commonly used term) prevents the fuel pump from supplying fuel to the carbs.
You can check that by disconnecting a fuel line down stream of the pump and if you see gas pulse out when you hit the starter for one or two seconds, it's not vapor lock.
If the problem is fuel related, it might be fuel percolation in the carbs float chamber...heat from the exhaust manifold boiling the stagnant fuel in the float chamber.
If that's the case a heat shield can help if heat insulation material is added to the shield.

 

[ttpiper]

I doubt it's vapor lock...."vapor lock" (a commonly used term) prevents the fuel pump from supplying fuel to the carbs.
You can check that by disconnecting a fuel line down stream of the pump and if you see gas pulse out when you hit the starter for one or two seconds, it's not vapor lock.
If the problem is fuel related, it might be fuel percolation in the carbs float chamber...heat from the exhaust manifold boiling the stagnant fuel in the float chamber.
If that's the case a heat shield can help if heat insulation material is added to the shield.

I believe your right on with it being a fuel percolation issue. I see lots of different heat shields out there. Are there any in particular better than others?

 

[poolboy]

I'm only familiar with 2 and both are made by ARE and sold by Moss if not direct.

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But in my experience it did not work 'naked'.,,but once I added real heat insulation to the floor, no more percolation issues.

JEGS 32033: Heat Shield Mat [12 in. x 24 in.] - JEGS High Performance

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[DrEntropy]

Check your float bowl check-valves & float adjustment for leakage too. Over-full and with heat sink, fuel could be perked into the intake. Results in a "flooded" condition on restart attempt.

 

[Sarastro]

First, you really should use a timing light for setting the timing. Other methods won't be accurate.

Second, the car should at least start and run even if the ignition and carb adjustments are way off. So, messing with those won't help. The problem is elsewhere.

These things are invariably an issue with fuel vaporizing where it shouldn't. Call it percolation or vapor lock if you will. Today's fuels fizz like ginger ale, even at moderate temps, and vapor bubbles build up quickly. I had this problem in my Bugeye Sprite, and fixed it by reorienting the fuel lines so there were no upward arches; vapor bubbles could then float to the top, into the carbs, and out the vents. Plastic fuel filters are especially revealing--I've seen them completely filled by vapor, and you wonder how fuel could get through them at all.

A heat shield may help, but don't expect it to be a magical solution.

 

[poolboy]

Nothing magic about it...If properly applied it's simply a practical solution to the prevention of PERCOLATION in theTR6's ZS carb float chamber.

 

[ttpiper]

Update - I purchased a heat shield to keep the ZS float bowl cool. I also added a couple layers of insulating material to the heat shield per Ken's suggestion. I still am experiencing the same problem with the car not starting once it warms up. The last time this happened I had only driven the car a mile or so down the road and it was a cool day out.

I keep coming back to the fact the carbs were originally set to run rich. In fact they were set all the way CW meaning they were set to the most rich fuel/air mixture possible. When I adjusted the carbs to the correct mixture, the car would not start after it warmed up. I have since adjusted the carbs back to be on the rich side but not fully CW like I first discovered. The car now starts when the engine is warm. This has led me to believe there might be something amiss in the carb's Temperature Compensator that's making the mixture too lean to start the car. Once the carbs cool down it starts with no problem. Does this make any sense?

 

[poolboy]

You can disable the Temperature Compensator and see.
Remove the plastic dust cover and turn the tiny nyloc nut fully clockwise...that'll prevent it from opening

 

[glemon]

When you try to start it from hot are you giving it gas (pressing on the throttle)? I have found my old British cars often like the throttle opened when starting from hot, the old carbed cars are less than perfect in adjusting to changes in temperature and operating conditions.

 

[ttpiper]

Disabling the Temperature Compensators on the ZS seems to have solved my problem. My TR is running better than ever and I can easily start it back up when hot.