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TR4 Misfire

I have owned wetliner TRs since 1962 , my present TR4 since 1984 and thought I knew the engine fairly well. But I have a problem and have run out of ideas for fixing it.

The car has always run well on SUs and a Facet fuel pump, and for the last 10 years or so with an electronic 123 distributor, but recently it has started to misfire badly.

Starts promptly hot or cold, idles well and revs freely. Seems to run normally on very light throttle and will maintain 50mph on the level, but as soon as the throttle is opened to increase speed or climb a hill the misfire cuts in.

General Mechanical

Overall good condition. 

No induction leaks. At idle 21"Hg vacuum.

Cold/dry compression test, all cylinders read 160psi.

Valve clearances checked and adjusted to 0.012”

Fresh petrol 95 octane good fuel flow with/without filters.

Fuel flow not measured but flow and pressure seem OK

Fuel tank removed and flushed, but fairly clean. A small piece of plastic was found in the tank outlet union which I thought was the cause of the problem, but this has proved not to be the case.

Fuel pipes blown through with compressed air.

Float levels checked.

Jets and needles inspected and seem OK

SU carbs set slightly rich.

Run with/without air filter

Ignition

New plugs

New ignition leads

New coil

New rotor arm

New distributor cap

Alternator disconnected. Short Vee belt running water pump only.

Hot wired with +12v direct to coil

New earth wire, distributor body to engine.

Extra earth wire engine to battery negative.

123 Distributor returned to Dutch factory, some electronic parts replaced.

All these changes and checks have had no effect on the misfire.

What have I missed, what else can I try?

Dick Goodey


 

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Symptoms are consistent with a weak spark.
Did you replace the condenser?

Even new ignition components can be faulty, especially
coils. I assume rotor arm is a top quality item, e.g. from
the Distributor Doctor.

AlanR

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To AlanR

Yes, at first I thought it was an ignition problem, but the car has been fitted with a 123 electronic distributor for many years. No condenser. The 123 is built in a Bosch body and uses Bosch cap and rotor arm, original and recent replacement. Have never heard of Bosch producing duff stuff.

To Dave

No loss of power before misfire problem so I doubt worn cam (I had that with a fast road cam about 10 years ago, now running a standard TR4A profile). I will measure valve lift next time I take the cover off.

Thanks to both

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Did you replace all the ignition components one at a time (giving each a test run).

If not, have you still got all the old parts. If yes then refit them one at a time plus the test drive.

Usually it is only one components that goes iffy.

 

Roger

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17 hours ago, alaric said:

 

Starts promptly hot or cold, idles well and revs freely. Seems to run normally on very light throttle and will maintain 50mph on the level, but as soon as the throttle is opened to increase speed or climb a hill the misfire cuts in.

 

Sounds to me like something limiting the fuel flow. I had a similar problem, only cured by removing the float chambers and float valves, then turning the engine over on the starter (mine is a mechanical fuel pump). I'd already blown through the fuel pipes but I think there was something stuck in the fuel duct inside one of the carbs, that air wouldn't shift.

When you rev the engine with air cleaners removed, are both pistons lifting?

Pete

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Check the two coupling links that join the throttle spindles, they sometimes partially break but look to be complete until you open the throttle wide, at this point one of the carbs shuts down and you get the misfire, ... this happened to me on both my TR and a Triumph 2000 (Stromberg carbs but the same link system).

Cheers Rob

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This is what you call a misfire !!!!

 It was fuelling. !!

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I have had a 123 on my 4A for 12 years and not a single problem so far. However, I always carry the original Lucas distributor and leads as belt and braces. Just a thought Dick - if you still have the original distributor why not try it, if it has no effect on the misfire at least you will have eliminated the 123 as a potential culprit.

Tim

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  • 4 weeks later...

Finally cured the misfire. It was a white gunge, consistency and appearance similar to silicon sealant. Not really sure what it was, but presume it was introduced in a bad batch of fuel?

The bulk of the gunge was in the pipe between tank and carbs and because it was semi fluid it allowed only small quantities of fuel and compressed air to flow.

After several attempts I believe I have finally got rid of it.

Thanks for all the helpful suggestions. 

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16 hours ago, alaric said:

No Slosh Seal. Never heard of it until now. Just Googled to find out what you were referring to. 

What is the link between Slosh and white gunge?

Someone posted a while ago that they'd had a fuel blockage due to slosh sealant peeling off and clogging the fuel feed.

Pete

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