TR2/3/3A The Newest Bug to Fix...

Hi Guys,

Spent the past week on a new problem...at least I think it's a problem....

The background

I can idle the car for about 12 minutes before it starts to run rough from what I think is fuel percolation/vapour lock.

The car never goes about 195 F as I have an electric fan on a new wizard aluminum rad that kicks in at about 185 F. The problem happens when the puller fan kicks on it brings quite a bit of hot air from the radiator into the engine bay. The fan works to pull the temperature back down to about 170 before it cycles off. The problem is in the interm between the cycles. The car has never overheated because the carbs start to run rough and eventually it won't idle well before it shuts off if I don't give it any throttle.

I think from what I've read, the car seems to be operating at about a fairly common temperature range when idling.

I can't get the car to run any cooler at idle...I've checked timing, installed a 165 F thermostat and added a drilled plug to the bypass hose. I've flushed the block twice and refilled with 50/50 water coolant. I've checked mixture on the carbs and made sure needles are not binding etc...

I should mention that I am running a stainless header that I have wrapped with header wrap. I'm sure this contributes to some Under hood heat as well, but like I said, temp guage never goes above 195 F.

I'm not sure how this will effect the drive ability of the car as idling in the garage is one thing...actual road testing/driving it, this might be a non issue unless I get stuck in heavy traffic.

Any thoughts on a cure for my rough idle? I was thinking a heat shield might be helpful for the stock SU's but though I would ask here first.

Cheers
Tush

A long shot, but is there a chance that, while idling, the fan kicking in draws enough current to affect the ignition somehow?

Hi Andrew,

Thanks for the suggestion. I think with a generator it might, but I have an alternator conversion on this car, so have lots of juice.

Cheers
Tush

Maybe it's the mixture. The carbs will load up during idle. Combine that with heat and a bit rich mixture..maybe.

Did you go with the electric fuel pump?

Thanks guys,

Could be PB. I need to take it for a good run to clean it out, come back and read the plugs. I've only checked mixture according to the book and the piston lift test so far...as an experiment though, I leaned it out quite significantly with the mixture nuts turned most of the way up with no change in operating temperature. Ran poorly though and had a flat spot when revving it.

Karl, I went back with a mechanical pump...electric pump is on stand by for now.

Cheers
Tush

Is this happening with bonnet closed or open at idle? I think I'd go for a run to see what plugs look like. Suspect you will have not have problems when driving due to extra air flow. Does your car have an air shroud? Cheers, Mike

Perhaps Andy Mace is onto something, particularly since the problem occurs when the electric fan comes on. I'd check the ignition system thoroughly and even try a different coil. (My mentor, back in the very early 1960's would throw a fit if I attempted any carburetor tuning before I could guarantee the proper state of electrics; and this advice has stayed with me). Also, re-check the valve clearances, and, I know you've done this, make sure there's enough oil in the dashpots.
Tom

Thanks Tom, I do have a spare coil. Wouldn't hurt to try it out. I'll go through a valve adjustment again. Yes, daspots are filled.

Cheers
Tush

Hi Mike,

Bonnet closed, idling in the garage. Yes, I have the 3A rad deflector fitted.

For now I think I'm going to try and override the fan thermostat and keep the fan running all the time to hopefully help keep it cooler, longer.

I'm off to a show this morning hopefully if the weather holds out...ill see how it runs.

Cheers
Tush

If it only happens after 12 minutes of straight idling...I'd say you have one of the best running TR3's around! I can't imagine being at a stop in traffic for that long without having a chance to move and rev it a bit.

I bought some Thermo-Tec fuel line cover and pushed it onto the fuel line from the carb end all the way to the fuel pump. I also covered the pipe between the carbs. As I recall I bought their 1/2 inch cover material. It was tricky getting it around all the curves and it looks a bit bulky, but it has helped with the vapor lock I was getting when I stopped and turned off the engine to pop into a store for a quick stop. When I came back out and started the car, I had to choke it to get it to start and run. With the Thermo-Tec cover, it is much better.
Regards, Bob

I'm with Andy on this, point of reference is my 4A with electric fan and alternator. At idle when the fan kicks on it pulls a lot of amps and the alternator is working harder putting a drag on the engine and the rpm's drop slightly. Maybe enough on your car to cause the rough idle. I'd set the idle up a bit and see what happens.

Does the current for the fan go through the ignition switch? If you don't have a relay to handle the current, I would be looking at overall voltage drop. A typical radiator fan only draws 8 amps, which draws only perhaps 1/4 hp extra from the motor; shouldn't be enough to make more than a tiny difference in rpm. And my TR3 idles just fine with the generator doing nothing at all, both headlights and the rad fan on.

Does the exhaust smell rich and/or puff black smoke? Those would be signs that you do indeed have percolation. Adding one of Joe A's heat shields helped a lot with my percolation problem, tho I might try to add more insulation to it the next time I am in there.

PS, another test might be to temporarily disconnect the alternator and see what happens then. You should be able to run for an hour or more on just the battery even with the fan on. If not, a bad battery might be the problem. Even alternators don't put out unlimited current at idle.

Hi Randall,

Thanks for jumping in. The fan is wired through a relay. I have added a secondary fuse box for power to the fan. I do have a 10si Alternator conversion installed.

The exhaust does seem to blow a little black if I try to clear the carbs when it starts to run rough.

Hard to believe that I'm getting percolation when my temp guage/fan thermostat says that I'm running at 185 F. Should take more than that dont you think in your experience?

I think I'm going to attack this from an electrical perspective and start eliminating that from the equation first.

Here is what I'm planning to do

Swap distributor from 1 running pertronix to the other running points (I'm wondering if my pertronix might be on the way out)
Swap cap/wires/rotor
Swap Coil

I plan on doing these one at a time to see if any one thing fixes the problem.

After that, I'll go back to fuel and will do a stationary test as mentioned in another thread with an electric pump and Jerry can hooked up directly to the carbs.

Worse comes to worse, I have another set of SU's that I can swap out to see if I get the same issue.

It might take me a couple of weeks to go through all the tests but I'm pretty patient/persistent . I will report back after each test/change that I make to the car.

Thanks Again,
Tush

To me, the black smoke pretty much proves you have a mixture problem rather than electrical.

The temp gauge reports coolant temperature (obviously), but that doesn't have a lot to do with the temperature at the carb jets. Those jets are hanging out above the exhaust manifold, which gets much hotter than the coolant. My coolant was never going over 190F (where the fan comes on), but I noticed before installing the shield that the rubber float bowl mounts looked burned from exposure to heat!

Gasoline also boils much easier (lower temperature) than water. The boiling point even changes from summer to winter and with geographic location, so may depend on when & where you filled the tank last. I couldn't tell that it made any difference to the TR (CA has funny rules about car fuel anyway), but you might try a different brand/grade of gasoline and see if that makes any difference. I used to have an Audi 100LS that ran noticeably better on Amoco unleaded premium than anything else.