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misfire, sanity and banging your head against the wall


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Hi all, just wanted to share an issue I've been struggling with for a few months now, that has caused me to question not only my sanity, but my own ability to problem solve.

 

At the back end of last year I was putting my tr4 away for the winter, flushed and replaced the anti freeze, greased up. Took her out for a quick blast to mix the coolant fully before putting her to bed.

 

was a few miles from home and giving it some beans, and she developed a horrendous misfire, managed to struggle home, just.

 

Was going to replace points anyway as I like the reliability of the electronic ignition. So new plugs, leads coil and accuspark ignition module.

 

Started her up and ran perfectly, in fact better than before, discovered the rear wheels would actually spin!

 

fast forward to January, out for a run in the nice weather and the misfire returned, stopped and she idled ok started again misfire on acceleration.

 

Got home again on two cylinders.

 

checked compression, all cylinders 160 psi, suspected fuel, tested fuel pressure and flow, 3psi and filled my fuel can quite quickly, so no issue there.

Checked pistons moved freely and needles not bent, all okay.

 

mindlessly tapped the float chamber of thecfront carb as I listened to her misfire and she picked up on to all 4 cylinders, installed a couple of grose valves in to float chambers, found a piece of plastic bag the size of a 10p piece behind the seat of the rear carb(no idea!). No change.

 

still misfired, checked everything again, compression, electric, float valves, fuel flow, piston movement, mixture, timing. Could find nothing wrong, was about to throw in the towl. Was now at the point where you just replace things as you have no idea, send distributor to Martin Jay, carb rebuild, soul destroying, what could it be?

 

Again fast forward to today, tinkering tune up, noticed the front carb was running very lean, how had I missed this, had it moved, had I messed it up? Adjusted mixture and balanced carbs, running very ssmoothly, reved the engine, and back to misfire, only this time it mised at idle not on acceleration, I could now see the problem, front carb was not working, took the air filter off and lifted the piston with my finger and there was the problem.

 

the needle had fallen out of the piston and was blocking the jet. Upon inspection the needle was a tight fit in the piston and clearly was falling out and then sticking back in to the piston as it dropped back at idle hiding the problem and when I took the piston out the first time it looked fine. Dropping the jet to adjust the mixture had allowed the jet to drop down so the needle could not put itself back in to the piston.

 

refit tighten screw all works as it should, sanity back, self esteem back, desire to burn out tr4 gone.

 

Thank god, was loosing the will to live with this issue.

 

Mark

Edited by MRG1965
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Hi Mark

 

Had the same problem last year and did the same as you, in the end took it to TR Revington who found and blocked jet in rear carb, now goes like a rocket the best in the 4 years that I have owned it.

 

Regards

 

Geoff

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  • 3 weeks later...

HI All, just a quick update.

Even though I got the car running and she seemed to be back to full health, I was not convinced I'd found the truth about what had happen or why and it was bothering me.

So I had the carb pistons out Sunday night and had a detailed look at them and could see that there was little except the grace of god keeping them in place in the piston.

After a conversation with the nice customer services people at Burlen ltd (sucarb.co.uk) I've have discovered the underlying issue and why it would have returned to bite me in the @#se.

 

The HS6 carbs fitted to my car TR4 are of the of the biased type and not the fixed needle type as per gods intention. But they did have the original TW fixed needles in, which have been modified with a little tophat and spring doodad (AUD 3307) to convert them from fixed to biased needles, but the person who did the conversion forgot or did not know that they needed a little touch of solder to keep them in place, as I discovered when one fell in to the jet and blocked it. So mystery solved and one less reason for me to be concerned on my way to Lemans in a few months time.

For piece of mind I might just fit the BAD biased needle, which look to be almost identical to the TW profile on the minty lamb site, but with two additional stations making them 1/4" longer. And if I'm going to do that might as well put new jets in and be done with it.

 

Mark

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Hi Mark,

10/10 for tenacity and sleuth like abilities.

 

It must be very satisfying that you have found the cause.

 

For LeMans - get your car on the road do lots of miles before departure. You van't beat miles for winkling out the iffy problems.

 

Roger

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Hi Mark,

10/10 for tenacity and sleuth like abilities.

 

It must be very satisfying that you have found the cause.

 

For LeMans - get your car on the road do lots of miles before departure. You van't beat miles for winkling out the iffy problems.

 

Roger

Hi Roger, yes plan to be out and about as much as possible to build confidence. It's been a fun time (I think), but glad I've finally found the root cause, you learn new stuff everyday and what don't kill you makes you stronger, they just don't mention the pain, frustration and sleepless nights you have to go throught :-)

 

Mark

 

Mark

Edited by MRG1965
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A few years ago in France my 4A was running like a pig in the mountains. It would run slow but didn't like fast at all.

Back at the chateau I had a look around the engine and only after taking the carb filters off I noticed that one of the SU pistons wasn't lifting.

The clamp on the butterfly cross shaft had slackened off so only one carb working - arrrgghhhh.

 

Roger

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