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TR2/3/3A 1959 TR3 engine rebuild problems

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mt10flyer

mt10flyer

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First post. I rebuilt the engine and am having a hard time getting it to run right - dang it.

Symptoms: Hesitates, backfires on initial acceleration no matter how I have it timed, and does not produce much torque.

Equipment: New everything in engine, new Pertronix Flamethrower dissy, new old style fuel pump, stock rebuilt SU's.

Data: Compression 135psi on all cyl, checked and recheck value clearance, vacuum measured off front carb just above nil at idle, approx 15in at rpm, centered jets and equal coordination observed during accel, equal vac at idle, mixture test ok, I know the timing marks on the crank and cam are correct.

What am I missing? Sheesh.

Oh...and thanks in advance.

David
 
Backfire out the exhaust or the intake? My most common mistake on a new rebuild is getting the wire sequence wrong.
 
Distributor 180 degrees off?
 
Sounds like either ignition timing or cam gear is one tooth off. Have you tried substituting the points distributor for the petronix? That is what I would try first.
Robert
 
The backfire is through the carbs. At TDC the dissy rotor is pointing to #1. 1-3-4-2. I may throw the old dissy back on and see if that helps. The low vacuum reading at idle seems odd. Does anyone know what "normal" vacuum off of the front carb fitting should be?

I don't think the cam is a tooth off. When I aligned the marks on the cogs I turned the crank by hand several revolutions to verify that the marks came around and lined up properly.
 
Take note that at the Dissy cap the wires are not in a linear pattern. Pull the cap and look inside. Or perhaps the union that holds the two carbs together isloose
 
Backfire through the carbs usually indicates lean condition and/or ignition timing problem or messed up firing order...assuming that the cam timing is OK. Could also be a vacuum leak as smaceng suggests (which would cause a lean condition).
 
Hmmm. Fuel starvation would have the same leaning effect. That is something I haven't considered.
 
Intake....my guess is firing order or cam. If it was really lean enough to cause the intake backfire, then it would be a bear to start cold. Backfire with lean will be under load.

Have you checked the valve clearances? A stuck valve or no valve clearance will cause intake backfires. After that, a large intake leak will do it.
 
Got it...and I AM a looser. It was firing order [hangs head in shame]. 1-3-4-2. Yup. No problem...but it is in the counterclockwise direction. On the MG rebuilds I have done I remember [perhaps falsely] the rotor going clockwise. Anywho, after getting it right she runs like a striped ass ape. Thanks for the help...and now you can make fun of me.
 
Don't beat yourself up - it once took me two days to find a bad ground! That's what we are all here for - to help each other when we get stuck and have questions. I'm in the middle of putting everything back together from my winter tear down......I'm sure I'll be posting for help soon!
 
Like I said...my most common mistake on rebuilds! Easy to confuse with everything going on getting it going. At least it's easy to fix!
 
I guess the fuel pump is new....but is it one of the DEFECTIVE new fuel pumps out on the market???
On the original pump the factory pinned the pump arm into place.The new pumps the pin is dropped into
a grove and swagged over to hold it in.This can and does fail quite soon giving very low fuel pressure.
To check it while starting,pump the lever under the pump to bring the pressure up.If it runs fine for a few seconds
you have a turd on your hands.....
MD(mad dog)
 
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