TR4A Misfire

[Peter Harper]

Help what do I check next. I have a misfire that started Thursday doing 60 MPH on a motorway coming back from a nice run to Stokes Bay at Lee-on-Solent. On getting home I changed the plugs and she ran well for a 20mile trip to a Hampshire hostelry to meet other Triumphs. Friday misfire after a quarter of a mile stop and she will accelerate normally for about the same distance. On starting without moving it will rev normally not under load if I hold it at 3000 revs it starts to misfire after obout 20 seconds.

 

I have checked the following I have again changed the plugs, all plug leads and ht lead. I have pertronic electronic ignition so I reverted back to Points ,no cure. I checked the levels of petrol in the SU float chamber both seem ok at the same level, I checked the dash pots are topped up, and the pistons in the su carbs rise and fall on acceleration. The fuel level was under a quarter so I put 4 gall of super in from a gerry can ( fuel Bought Today )I have run the car with the fuel cap open in case of venting problems. Still misfiring, I veer towards a fuel supply problem I am using a standard mechanical (AC ) fuel pump but how can I check if it is delivering enough. Or am I barking up the wrong tree.

 

Any help or suggestions would be welcome.

Thanks Peter

[ianc]

From the symptoms, you might be suffering from the petrol tank shedding fine particles of rust into the fuel, which, under reasonable load, rise to block the gauze filter in the bowl of the pump. As soon as the engine stops, the particles settle into the bottom of the bowl, so the engine is able to restart.

Remove and examine the filter bowl. If this shedding should be the problem, see my article in Section K3 of the Technicalities CD.

If you go for "sloshing" the inside of the tank, be aware that Moss now recommend a 3 stage process using:

- Fuel Tank Cleaner Degreaser

- Fuel Tank Etching Fluid

- Fuel Tank Slushing Compound

Similar products are available from other vendors.

When I had the problem in 1997, I cleaned the inside of the tank thoroughly (see article) and used just the Fuel Tank Slushing Compound, and this treatment seems to have lasted some 12 years.

 

Another possibility is electrical breakdown of the rotor arm - all too frequent with the modern Lucas items, it seems. Essential to purchase two (one spare, in case you damage/lose the first) from Distributor Doctor - see TR Action.

Ian Cornish

[Peter Harper]

Thanks Ian that is a good idea I have an inline filter as well which I have checked but not the one at the fuel pump I will try now, Thanks Peter

[stuart]

You could also try a re-location of the coil to the inner wing and also check the short jumper wire from coil to dizzy.

Stuart

[Peter Harper]

Ian I have cleaned the filter at the fuel pump ( what a job when you have no pit to see what you are doing) Unfortunately no cure, Stuart I also checked all leads to dizzy and coil all clean bright connections. I have not moved the coil to the wing as the pertronix leads are not long enough and I checked and refitted the engine earth strap.

 

Looking on the gloomier side could a valve have burned out?

 

Any nore checks or suggestions.

 

Peter

[Dazzer]

Hi

 

I would swap the coil as I think Stuart is on the right track.

 

I've just come back from a rally in France, two days into the rally I developed a misfire at a slightly lower RPM than yourself but very similar symptoms. I swapped out everything, points, condenser, rotor arm, dizzy cap etc. I to thought a burnt out valve. However, after an eight hour high speed drive ( it cleared itself at 3200 rpm) I returned home, and as a final check I swapped the sports coil off our Triumph 2000.

 

Completely cured. I then placed the TR4 coil on the 2000 (just to see that the sports coil wasn't masking a problem) and sure enough the 2000 developed a misfire.

 

A lucas sports coil is between £20 and £30, buy one and affix it on your inner wing like the rally boys, if it turns out to be something else.

 

I'm definitely running with two coils from now on.

 

Cheers

 

Darren

Edited June 19, 2010 by Dazzer

[Roly]

I had a misfire that took me a while to track down.

It was dross that had collected above the needle valve in the back carb.

It was not until I unscrewed the needle valve that I saw the debris above it.

 

When I had the misfire start I could usually limp home, and by the time I got round to taking the tops of the flat chambers off to check if there was fuel, they were full. Presumably by the time I looked, fuel had seeped into the fuel chamber and all looked OK.

 

After clearing the blockage I had a couple of repeat misfires and had to clear again. This was depsite installing a filter and changing the fuel hoses. So there muust have been some loose residue somewhere between filter and carb.

 

Hope this helps.

 

Roly.

 

Its now been alright for the last few months.

[ChrisR-4A]

Hi Peter, I had an extra filter a few years back, it was the glass tube type and although it looked clean the mesh had closed up, maybe due to unleaded fuel, anyway the only way to be sure is to take it off and try blowing through it. To check the mechanical pump at cranking speed it should deliver about an eggcup full of fuel at each pulse or half fill a jamjar in 6/7 secs. If this all seems ok remove the rocker cover and check all valve clearances are at least at or above the minimum.

Hope this helps.

Chris

[Peter Harper]

Thanks for your suggestions, Roly I have already stripped and cleaned the float chambers and needle valves. Chris I have removed cleaned and replaced the inline filter then removed the element to see if it improves things no improvement.

 

Darren I will replce the coil when I can get hold of a replacement and the rotor arm likewise.

 

Thanks to all for your sugestions they are really appreciated. I will report back when I have tried the last two ideas.

 

Peter

[Peter Harper]

I have managed to borrow a Rotor arm and a different coil and the misfire is no better, infact now worse with spluttering and backfires from the first firing and there appears to be an adequate fuel supply.

 

Where do I go from here would a compression check show a burned out valve I would appreciate your colletive ideas or suggestions.

 

Thanks Peter

[Dazzer]

Hi Peter

 

Yes a compression test would detect a burnt out valve, especially if it's the lack of compression that's causing the misfire.

 

You'll be looking for consistency in the readings, usually about 150 to 160 on all cylinders. However, the 4 pot is pretty robust and will still run without misfire with inconsistent readings.

 

As a matter of course I checked the comp on a TR4 recently, which was running on all four without a hint of a misfire and the readings were 160, 145, 150, 125.

 

I would think you will have a very low reading on one cylinder to give you the misfire, if indeed it is mechanical.

 

When you checked the exchange coil and rotor was this still on points and condenser? or had you reverted to the electronic ignition? The electronic ignition might be using a high output coil not suitable for points and visa versa for a standard coil, also check (if the comp test is OK) that the coil you borrowed was not a ballast resisted type and working on the vehicle it came off.

 

It's just when you say it seemed worse with the new coil, just to be safe.

 

Hope this helps

 

Cheers

 

Darren

[67_gt6]

Hi Peter

 

Another possibilty - if you are using the emissions gear ie the Smiths Emissions valve that goes into the inlet manifold, make sure that none of the hoses have split. They tend to split on the underside nearest the exhaust manifold where it is difficult to see. If one of them has split it can lead to a weak mixture and a persistent misfire.

 

Andy

[graeme]

Peter,

 

Have you checked the timing? It is possible that the dizzy has come loose and is turning randomly. Or another possibility, the internals of the dizzy could be loose or even seized.

 

Cheers

 

Graeme.

[Peter Harper]

Thanks for further suggestions I will have another play after work on Tuesday

 

Peter

[67_gt6]

Hi Peter

 

These are the issues that have given me misfires over the last few years:

 

Rotor arm

Failed coil

Distributor cap - reading back over the thread not sure if you haver had a look at this? Check for carbon on the points.

Split hose on emissions gear

Inadequate fuel supply - inline filter had developed some kind of vacuum lock

Leads

 

Andy

[Peter Harper]

Hi folks My misfire was as Roly had a piece of detritus blocking the fuel before the needle valve working like a flap valve blocking ithe flow on high demand. I found it when I decided to try and rev the engine to clear itself of its maladies and I gave up after a lot of spluttering and backfires I happened to touch the exhaust manifold on no 4 cylinder it was only warm but 1 and 2 were hot. The penny dropped and a carb strip down and cleaning with an air line solved the problem. I made the Wessex meeting last night with 21 other Triumphs.

 

A happy bunny again.

 

Thank you for all your suggestions and help It is a great forum

 

Peter