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TR6 TR6 - lack of low down power

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scott421

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Hi all ,my latest 6 is a 72 CP car with PI . At the moment the engine is not too great , it ticks over nicely but is quite lethargic up to about 2500 - 3000 rpm then goes really well . The PI set up is good and correctly timed (I know these inside out), the ignition is timed .
The car has a stainless extractor manifold and the P.O. states there was an "uprated" cam shaft . I am beginning to wonder if the cam maybe the problem in that it is incorrectly timed with the crank - ie 1 or 2 sprocket teeth out . I am going to measure the lift on the cam today and see if I can find anything re the cam timing . Any ideas either way would be appreciated - am I looking in the right direction or what should I be looking at .

My other 6 is a 1970 PI with a fast road cam . This car is very spirited right through the rev range.

Regards Scott
 
It sounds as though your distributor or timing may be an issue. If the advance is not moving at low RPM, then suddenly moves forward, allowing proper acceleration, you could have this problem.

Have you checked the timing and looked at the amount advance with the light on it to see what is happening there? Try disconnecting/connecting the advance/retard units and see what happens when you accelerate the engine.

The springs on the internal weights may be all gummed up and it may be binding inside the housing. Here is what the distributor looks like disassembled: https://www.74tr6.com/distributor.htm

Good luck and keep us posted.
 
Hi Paul , Nice site , I took everything to bits today and have started from scratch . Tappets were way out 20 odd thou ! couple of injectors , although firing were not coning properly , dizzy seemed ok but have oiled it just incase , re-did the timing , took it out and it works a treat ,
Cheers

Scott
 
One of the things I was going to mention is to do an idle vacuum test. Baseline it with a known good engine then you can refer to it, to tell you when the cam timing is out of whack, along with ignition timing, etc....
 
Hi Ron , I take it you mean the vacuum to the dizzy ? if so the PI cars dont have one . Its a good point though and one I will have to remember when I finally rebuild my Midget . Its sooo long since I have worked with carbs (and vacuum guages ).
Kind regards Scott
 
No, he means manifold vacuum; not the ported vacuum to the dizzy.

Not sure where you'd find that on a PI TR6, though.
 
Ok Thanks , will give it a look . Its between the inlet manifold and the metering unit for info .
MAny thanks Scott
 
Just for info , its the same on both cars ,
Car is running far better after yesterdays work , a bit more fine tuning and it ill be as strong as my early car.

thanks Scott
 
Hello Scott,

just a quick tip regarding a simple cam timing check. Number one on TDC firing so number six valves will be rocking. Rotate the engine one way until one valve just closes and mark the damper, rotate back until the other valve just closes and mark the damper. The two marks should be an equal distance from the TDC mark.

What sort of exhaust manifold is it, by the way?

I have a Triumph 2000 with essentially a TR5 engine, but I think the injection is later as it has six flex pipes not three no vacuum advance and runs about 7"Hg at idle.
I have a 6-3-1 manifold, cleaned up head and an SAH cam. It goes very well with a noticeable surge at 4,000 rpm and will pull 6,000 easily in second and third but a little slower in top.

Alec
 
Hi Alec , thanks re that, I will have a look tomorrow if I get a moment . Yes you have the later throttle bodies with the 6 balance pipes , a bit more awkward to set the butterflies to begin with but once all set its a piece of bun to keep in tune . 7Hg is what I am getting with both my cars , 6-3-1 manifold , ported head. Afraid I havnt measured the lift on the cam yet to see what is fitted .
Noticed a "miss" every so often under load yesterday . That is definitly electrical though so will replace the ignition components at the weekend . Hopefully by then it should be flying (or a smouldering mound of ashes).
 
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