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MG MGA - Moonlighting-TR Help

A couple weeks ago I posted about a '75 TR6 a friend was looking at.

Well he bought it and I'm helping him out a little. Yes I know I should ask the TR forums, but I haven't found a good one yet and for whatever reason I trust you guys more.

Here's the deal. The car sat for 3 years. They towed it to a service center drained the gas and put in clean gas, started it up and that was that.

Upon arriving home he found that the car wouldn't keep an idle below 1300 rpm, it would stumble, the front carb would back fire, and it would eventually die. The car will however drive reasonably well.

Here's where I got involved.

I checked the timing and checked for vacuum leaks in the emissions system. All OK.

I used my color tunes and have diagnosed that the car either has fuel starvation or a very lean mixture. I've disassembled the fuel pump (which is mechanical),cleaned it, and put it back on. I've also checked the fuel flow up to the carbs and they appear fine. (Fuel pump pressure is rated only 1.5 to 2.5 psi which is too low to test with the testing gauges I can borrow from Autozone.)

I was about to pull the carbs to clean out the float bowls (Zenith Strombergs)when he threw me a diagnostic curve ball.

After I had cleaned the fuel pump the car was able to keep a rough idle down to 1000 rpm without dying. However he ended up driving it during a rain storm and told me that the performance was horrible while doing so. He hasn't driven it since.

What are your thoughts? Is this a bad coil? Is this electrical. Is this coincidental?

Other clues,

Before going into storage the car was converted to a pertronix ignitor system (no coil replacement though) and the carbs were rebuilt. Both were done at a local shop, so presumably everything ran OK before it was brought home for storage.

Thanks as always,

Tysen
T McCarthy

Was it miss firing or just down on power. Bad distributor cap or plug wires can cause missfire when damp. Also, humid air is less dense than dry air so performance will be down slightly on a humid day anyway, and if the carbs aren't up to snuff, could change the mixture enough to make a big change in performance.

PS sitting with gas in it for 3 yrs could gum up the carbs completely so could need another carb overhaul.
Jeff Schultz

Personally the first thing I would do would be to do a compression test. There is a possibility of burnt out valves with those symptoms.
Naturally that is a start of the diagnosis but should be the first part.
Robert (Bob) Midget Turbo

Tysen-
Very common that cars sitting get gummed up carbs. That's consistent with what you've found so far. Biggest problem causing those symptoms is deposits on the needle and jet right at the normal fuel level - the gas gums as it evaporates when sitting. That makes it way lean at or near idle, but only a little lean further up, again consistent.
Get some fuel system/fuel injection cleaner, lift the carb pistons and squirt some right where the needle enters the jet. Put the rest in the tank at about double the recommended dose - usually the whole can is stated for 20gals, so that's about the right amount. Let the carbs sit for an hour or so, then start it up and drive it. In 50 miles or so it most likely will be cured.
If idle problems continue after that, remove carb pistons and examine the needles under magnification. Sometimes corrosion will etch the needles right at fuel level, though this has not been as much of a problem in the last 15 years as in the 80-95 period. But that makes it rich at idle, not your symptoms.

DO NOT spray carb cleaner so that it can get on the ZS diaphragms - it eats them!

FRM
FR Millmore

FR wins the prize!

Thank you for the help.
T McCarthy

This thread was discussed between 09/09/2009 and 11/09/2009

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