TR4/4A Hard Start When Engine Hot

[KVH]

An old subject, sorry, but I can't solve it. Engine starts fine cold, and runs great, but won't start hot unless I wait 20 minutes.

I've tried everything. New points, floats, fuel pump, coil, timing. Still won't start from "hot" unless I let it sit.

So, here I go again: a) could it be the low tension wire from the coil to the distributor? What is low tension anyway? Mine is just a 16 gauge insulated wire;

b) could it be the condenser? I'm sure I already replaced it, but I could try again I suppose;

c) what about the distributor cap and wires? Should I replace those as well?

d) I replaced the plugs. Do I try that again?

e) my "new" coil has oil on the underside. I can't imagine that's the problem since when it was new 8 months ago there was no improvement in hot starting;

f) I checked the fuel level in the jets; it looked fine.

Something is just a total mystery. Any more ideas?

 

[NutmegCT]

An old subject, sorry, but I can't solve it. Engine starts fine cold, and runs great, but won't start hot unless I wait 20 minutes.

Have you considered vapor lock?

I've tried everything. New points, floats, fuel pump, coil, timing. Still won't start from "hot" unless I let it sit.

Re: vapor lock - When the engine is hot and won't start, put a cloth soaked in cold water over the fuel line(s) from pump to carburetors. See if that improves things.

So, here I go again: a) could it be the low tension wire from the coil to the distributor? What is low tension anyway? Mine is just a 16 gauge insulated wire;

b) could it be the condenser? I'm sure I already replaced it, but I could try again I suppose;

It can always be the condenser - but not likely if you've already replaced it.

c) what about the distributor cap and wires? Should I replace those as well?

Dist cap and wires - not likely a heat related problem.

d) I replaced the plugs. Do I try that again?

Not likely a heat related problem.

e) my "new" coil has oil on the underside. I can't imagine that's the problem since when it was new 8 months ago there was no improvement in hot starting;

If the new coil is leaking oil, that could be the cause. Try another coil.

f) I checked the fuel level in the jets; it looked fine.

Unless I'm missing something, how can you check fuel level in the jets?

Something is just a total mystery. Any more ideas?

Frustrating for sure. A couple thoughts above.

 

[KVH]

Thanks I’ll likely replace the condenser. And the coil. If the floats are set correctly the level in the jet should be a bit below the top, looking into the carb with the air cleaner and piston removed. Smarter guys than me told me to check that. Apparently, if fuel is right at the top and spilling into the intake manifold at that point, with the engine stopped,that can cause flooding.

 

[bobhustead]

When it starts fine cold, are you using the choke?
Bob

 

[robertrudolphi]

I had this problem for years with my TR6. The carbs sit right above the exhaust manifold I I believe the issue is heat sink, vapor lock...I had my factory exhaust manifolds ceramic coated last winter and that eliminated the problem for me.

 

[KVH]

Choke only needed sometimes.

BTW, I have a heat shield and all of my fuel lines are insulated with heat shield. I really doubt this is any kind of a vapor lock issue.

To me, it feels like a fuel problem, but I don’t know what else I can do in that regard. I even replaced my fuel filter, thinking that could be the problem. It wasn’t.

it seems I’ve done everything other than replace the distributor cap and plug wires. I suppose I could check that condenser again. Is the condenser really sensitive to heat?

 

[NutmegCT]

A test: After a run, when the engine is hot, cut the ignition. Spray starter fluid into the carb air intake. See if it starts immediately then.

 

[Sarastro]

You have a problem that occurs when the engine is hot. You have randomly replaced a number of parts that are not heat related. Randomly replacing parts is not a good way to solve a problem, especially when they have little or nothing to do with the problem at hand.

The problem you have almost screams vapor lock. Take NutmegCT's suggestions. If it won't start normally but will start with starter fluid, that's virtually a proof. (But be careful with that stuff--it's explosive.) Then, the problem is to cool the fuel system. I guess you've done some things; in a hot climate, it might not be enough.

 

[Hamish Racing]

Does it run rich ?
What carbs ?
H and hs6 ?
Could be that the choke is not fully opening back up to unrestricted.

if it doesn’t start up quickly when warm and takes a lot of cranking this can soak the plugs.

vapour lock is typically hot and dry carbs but sounds like you have this covered ?!

coils are a prime suspect for getting hot and failing only to work when cooler. Did you change the “type” of coil or go like for like?

 

[Jim_Stevens]

And to answer your question… “low tension“ means low voltage… 12V. Compare “High Tension” (765kV)) lines running along the freeway…. The coil takes the 12V and ramps it up into the tens of kilovolt range… high tension, creating the spark at the plug gap.

jim

 

[Jim_Stevens]

Oh, and I vote for vapor lock…

 

[KVH]

Does it run rich ?
What carbs ?
H and hs6 ?
Could be that the choke is not fully opening back up to unrestricted.

if it doesn’t start up quickly when warm and takes a lot of cranking this can soak the plugs.

vapour lock is typically hot and dry carbs but sounds like you have this covered ?!

coils are a prime suspect for getting hot and failing only to work when cooler. Did you change the “type” of coil or go like for like?

We’ll, I have HS6 carbs, and found a hole in the underside of my coil. I’m not rejoicing yet. Trust me. Going on two years hunting this down. I’ll replace the coil. And condenser. I’ll check the plugs, too. Vapor lock is possible but seems like sort of “out there.” I’ve got 3 TRs, and never had this issue before. It’s just a simple old 60s LBC, no different from my others. Unless my heat shield is making things worse. I’ll also replace a fuel line that seems old and worn, but I doubt that’s it, either. I hope I can report success soon. Thanks for the ideas!!

 

[KVH]

Back to vapor lock and fuel issues for the “hard start” issue—does the fuel line on a TR4A IRS go thru the tunnel T Shirt where the exhaust pipes are, or is the set-up different? Mine looks same as live axle, right thru the T Shirt. Seems close to the exhaust pipes which is why I wrapped the line in protective foil. Thx all.

PS I have not test driven the car since I made my other “possible“ fixes.

 

[karls59tr]

Back to vapor lock and fuel issues for the “hard start” issue—does the fuel line on a TR4A IRS go thru the tunnel T Shirt where the exhaust pipes are, or is the set-up different? Mine looks same as live axle, right thru the T Shirt. Seems close to the exhaust pipes which is why I wrapped the line in protective foil. Thx all.

PS I have not test driven the car since I made my other “possible“ fixes.

Where do you buy the protective foil?

 

[KVH]

I used two different types, both from O’Reilly auto parts. One is a tape that is wrapped around the line. The other which seems better, is a sleeve that closes with a Velcro strip. If I could do it over again I would probably use the sleeve everywhere.

 

[Sarastro]

I was surprised by the hole in your coil. If the case of the coil was punctured, there should have been a lot of oil leakage, as most coils are oil-filled for electrical insulation and heat removal. A few are potted in epoxy, but those (like the Bosch "blue" coil) tend to be pretty expensive. If you have a hole and have lost all the oil, you really should replace the coil regardless of the present problem.

I suppose it's possible that might be the problem, but then I'd expect it to misbehave while operating, not just starting.

 

[KVH]

It was definitely in the manufacture. Looked like the inside element was slammed down into the “can.” The underside had four hits protruding from the inside, and two were leaking. Very small leaks, but noticeable, And probably leaking more when hot. The fluid that was leaking was sort of an oily bluish color.

I’m a realist. I have doubts this is my problem. Yesterday the car ran and started fine, but I’m going to take it out for another bit of abuse and see what happens.

If I were to pick a culprit at this time, I would still be concerned about vapor lock and my fuel line being too close to the exhaust pipes, and whether a different routing of the fuel line should’ve been attempted when the engine and transmission were removed and rebuilt three years ago.

At one point near the far rear of the frame there is actually under 2 inches of space between the line and the exhaust, and I just can’t imagine that’s OK, even though I used some insulating foil.

This is an IRS model, and I’m not seeing any other way to route the line. It is routed almost identically to the routing on my live axle TR4A.

 

[Sarastro]

I see you are in Arizona--the hot part in the south or the not-so-warm north? If the former, you have a climate at the extreme end of the environment the car was designed for. So, even with some care to offset the effects of heat, it may not be enough.

The problem with vapor lock is not vapor bubbles in the lines. The fuel pump can push fuel past that. The real problem is that small bubbles get lodged in places, like the float valves or valves in the fuel pump, where they are not easily pushed out. But, that being the case, it may be hard to fix the problem. I have an electric pump and fuel-pressure regulator, which avoids having a pump mounted on the hot engine, and I'm sure that helps, but occasionally I still have some trouble starting after running the car on a hot day and parking it. Maybe the simplest option is just to keep a water bottle in the car and pour some water on the pump and carbs when you encounter the problem. If nothing else, it will confirm the cause of the problem.

Definitely, replace the coil. If you've lost any oil from it, it will cause problems sooner or later. Probably sooner.

 

[NutmegCT]

If I recall, loss of oil in that ignition coil causes the coil to overheat, as there's insufficient oil to carry away heat from the internal windings to the outside.

Just sayin' ...

 

[KVH]

Just as a postscript, my starting problems are gone. I'm fairly certain the issue was my coil that had two holes on the underside. Car starts every time. Somehow, I think the hotter engine on restart required a stronger coil, and mine must have been on its last legs. The holes were a by manufacturer defect. No doubt about it.

(My next project is some kind of engine platform for when I reattach the engine and transmission--on the floor of my shop.)