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MG MGA - MGA running problems

Hi guys,

I tuned the car yesterday with a Colortune and an SU carb toolkit. I synchronized the carbs and balanced the mixture, but today the car was very, very hard to start. Even when pulling the choke out all the way, it still took a few cranks to get going and wouldn't stay on until the engine was thoroughly warmed up.

Any ideas?
Rich

Try richining up the mixture a bit. Sounds like she's running lean.
Baz

Hi Rich. I would do a complete tune up BEFORE fiddling with the carburettors any more. Worn plugs, points, or condensor, bad distributor cap or wires, incorrect valve clearance or ignition timing can make an engine hard to start and run poorly also. Usually carburettors are NOT the problem. Cheers! Glenn
Glenn

Good suggestion. I checked the plugs yesterday, they don't have many miles on them but the mixture was running too rich when I replaced them (covered in black soot). I cleaned and re-gapped them and they are in good shape.

I'm running an electronic ignition system now, so there isn't a point system or condensor to worry about. However, I haven't checked the timing, so I guess that's my next step.

Pulling out the strobe light now...
Rich

Yikes, looks like the timing was WAAAAAAY off.

About 25 degrees before TDC at 1000 RPM. I advanced it to 16 degrees before TDC and it runs a lot smoother and idles nicely at 700 RPM. Starts right up, too. I'm pretty sure that was the starting problem, because I had accidentally retarded the timing to about 30 degrees and it was nearly impossible to start. Ran real rough too.

Also, I double-checked the spark plug gap and it's supposed to be around .026" ... I had remembered the wrong gap setting and had it around .035". I have a high voltage sports coil, but that's probably still too wide of a gap.

So tomorrow I re-gap the plugs and check the carb mixture again...
R Stokes

Its good to see the "COLORTUNE" Transparent TUNING Spark Plugs are still carried by "MOSS MOTORS" & others! In the 1960s-1970s I used TWO AT THE SAME TIME, one in CYLINDER #1 and another in CYLINDER #4, adjusting both carburetor adjustments alternately in VERY SLOW INCREMENTS to get EXACTLY THE SAME SHADES OF "BUNSON-BURNER BLUE" IN BOTH CYLINDER #1 & #4. I assume they are still good up to 5,000 RPM, but FOR TUNING ONLY, not for driving down the road! In the "GOOD OLD DAYS" I checked the "COLORTUNE" against my "HEATHKIT AIR/FUEL RATIO METER" which used a "Balanced-Bridge Circuit" with a RESISTOR in one leg & THERMISTOR exhaust GAS SENSOR in the other leg. HEAT varying with COMBUSTION EFFICIENCY allowed A/F Calibrations of about 15-1 to 10-1 Air/Fuel by Atomic Weight. (Whew! Long sentence. But now you know how it used to work!). Sure enough, "HEATHKIT" was RIGHT: When you adjust LEANER than 15-1, the meter DOES INDICATE FALSELY that you are running TOO RICH! It was OK for tuning my MGA-1600, Austin America {BLMC 1275 Sedan), and M.G. midget 1275 to the "Factory Recommended" "SMOG CONTROL" 14.7-1 A/F Ratio, but SURE ENOUGH at about 15.5-1 A/F Ratio, the stupid meter indicated I was GOING RICHER when I was tweaking it LEANER!
OLD BILL-67

Rich,
I would try setting the plugs at 30. With a Lucas Sports coil and a pointless ignition system the plugs will do the job at that gap.

Ray
Ray Ammeter

Ok, I don't think I'm home free yet. Do these symptoms mean anything to you guys?

1. Car still won't start without the choke on. Not even a little.

2. There's a loud "popping" noise, almost sounds like back-fire about once every 5-10 seconds until the car is warmed up.

3. Acceleration is very sluggish until the car is hot. When it hit 200 degrees or so, it finally started to accelerate like it should.

Maybe my timing is still off? As I mentioned above, I retimed it to 16 degrees before TDC at 1000 RPM with the vacuum pipe disconnected. It was at about 25 degrees previously, and it seemed to accelerate better there.

-Rich
Rich

Adjust your valves. If your intake valves are tight, you could backfire on startup.
When you adjust them insure that the valves are not binding in the head. Remove the valve cover and rotate the engine while watching the valves. Rotate until the #1 intake valve opens and closes. When it starts to close, turn the engine until the crankshaft is at TDC, and note whether the valves are both closed on #1 cylinder. The valves on #4 cylinder will both be fully closed when the #1 piston is at TDC. If the valves are not closed, your timing chain is not lined up properly. Remove the distributor cap. Rotate the crankshaft in the backward direction until you are at 7 degrees before TDC. The distributor rotor should be at the 11 oclock position, which should be the #1 firing position.
mike parker

I would try moving the timing to halfway between where you are now. Then do 2 degree increments each way to fine tune. And it sounds like you're still lean.
Tom

I had very similar problem about a year ago, after I hadn't driven it for a month or so. It was really hard to start, and missed a beat every 10 seconds or so until really warmed up. It turned out to be the spark plugs. The plugs only had a couple hundred miles on them and looked good, but did have a little soot on them. I cleaned the plugs, checked the timing and adjusted the carbs, but it still was hard to start. I replaced the plugs and it started easily, and ran fine even when cold. You can't always tell the condition of the plugs by looking at them.



Jeff Schultz

Mike,

I've been working on my MGA timing this summer. I've been confused a few times. Here are some "facts" I've found.

Timing and rpm can be measure two ways- at the distributor and at the crank. To make matters worse, you sometimes see a mixtur of the numbers- distributor advance at crank rpm. The conversion is easy- dizzy number times 2 is crank number. Personally I think a lot of the static vs dynamic discussion is the result of mixing dizzy and crank numbers.

The MG manual static timing is by crank degrees. Dynamic timing is by crank degrees. Distributor specs are in distributor degrees. MG published distributor specs using distributor rpm. The MGA dizzy is zero advance to 150 rpm (300 crank rpm), 1.5 degrees at 300 rpm (or 3 at 600 crank), 7 at 650 (14 at 1300), and full 12 degrees at 1500 (24 degrees crank advance at 3k engine rpm)

Between the differences of static vs dynamic timing, the standard advance curve, and a little wear, the 25 at 1000 crank numbers aren't too far off. If your car "chuffles now, it is probably late enough that the mixture is still burning when the exhaust opens.

I am just completing an ignition test machine. I'll try and snap a few pictures this weekend and post their location here. Why an distributor tester? My fuel pump quit last year and I used the time to "fix" other stuff. It hasn't run right since. The distributor advance is the last in a series of "back to square one" moves this summer. Hopefully I will have it purring for Wheels and Wings.

Have fun,
Bill

PS- I don't use the e-mail attached to this account- only check it once every few months. If I don't respond to a personal e-mail, that is the reason. Sorry
Bill Eastman

Hi Guys,

A big improvement today. I made the following changes:

1. Inspected the front carb and found the jet was loose. I centered and tightened it down.

2. Set the timing back 2 degrees to 18 degrees at 1000 RPM.

3. Changed the dashpot oil from 10W30 to 20W50.

4. Manually set both carbs to the exact same depth using a vernier caliper (I didn't use the colortune to adjust the mix yet though).

I finally am getting some power out of this thing. Nothing to write home about yet, but it doesn't stall out on the traffic lights anymore.

It's still running quite hot - 220 degrees after a 5 mile drive. My guess is I'm still a little lean.

Tomorrow I'll get some new plugs and Colortune it again, and see where that takes me.

-Rich
R Stokes

This thread was discussed between 31/08/2005 and 03/09/2005

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