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TR4/4A TR4 misfiring under load, fouling plugs

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SMGoose

SMGoose

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New member here, one with a problem on a recently purchased TR4. I was hoping this forum could help me.

I'll try to be brief. On a cold start, it takes a bit to turn over, then rough idles for a while until it warms up. Giving it gas causes backfire and sputtering from the carburetors. Even once the idle levels out, it takes a good while until you can accelerate without stuttering.

I took it to a local shop that works on old British cars to have them set the gaps, check the timing, and tune the carbs. It didn't really help the next time I started it up. So I checked the plugs, which were fouled (dry, carbon), changed them out to no avail.

I thought maybe the fuel delivery was a problem. In checking that out, I found a gas leak from the tank outlet (right above the exhaust, no less). Ended up putting in a new gas tank and replacing the old SU electric fuel pump (I have no idea why it was in there as it's not original to the TR4) with a Facet solid-state while I was messing with it. None of these things have helped the misfiring problem. In fact, the new plugs have fouled after maybe 10 miles of driving.

I've tried to do some electrical checks to the best of my ability with a digital multimeter. Tomorrow I plan to pump the fuel into a jug to make sure it's not the fuel system. Any other suggestions would be MUCH appreciated!

Other notes that might affect the situation: In changing the fuel pump, I converted from positive ground to negative ground. I didn't notice before the conversion, but now the ammeter reads 0 once the idle is stable, but accelerating makes it jump to +30. Also, another strange thing about the car is that the coil is a Lucas CL 73 with an external resistor. This is also not an original setup for the car, correct? What type of spark plugs do you fellas use? I bought NGK BPR6HS. The previous ones were a "4" I believe. So much for brevity...
 
Welcome to BCF. First question: did the "local shop that works on old British cars" actually know what it was doing? Sure sounds like the carbs are still out of adjustment, and the backfiring seems like they're set very rich.

Was the timing checked and set to spec?

Also, is the gasoline fresh and filter clean? As it's a recent purchase, I wonder how old the gasoline is.

And ... failing coils (and distributor condensers) can give all sorts of ignition problems, especially under load.

By the way, it's normal (at least for me) to have a "rough idle" when the engine is cold and the "choke" is full on.

Just my two cents.
Tom
 
Assuming you have SU carbs, check around your throttle shafts for leaks. While at idle, spray a bit of carb cleaner where the shafts go through the carb body and see if the RPMs change drastically. If so, then you are probably drawing unmetered air and you will never get the mixture correct until you fix the leaks. Its very common to see the carbs adjusted to run rich to compensate for the extra air.
 
SU carbs or ZS? Does your new fuel pump have the proper pressure rating? What are you doing with the choke?

I don't agree that a rough idle is normal, but it does take some jockeying of the choke setting to keep it smooth. On my TR3, full choke is only for starting (and even then only when quite cold, like below 40F). Within just a few seconds, I go down to 1/2 or less, then generally back off even more after driving 100 feet or so. In general, I use the least choke that will still let the engine take throttle without stumbling.

The external resistor setup would not be original, Triumph didn't start using external ballast resistors until the 1970s. But it should work OK, if that coil requires an external ballast.

I use Bosch WR7BP plugs.
 
How new is the gas? My '3 runs way better on fresh gas...
 
Thanks for the help.

The shop should know what they're doing. I had read quite a bit about adjusting carbs but hadn't done it myself so they let me watch and ask questions. Good guys. They were rebuilding a couple MG's and a Jag at the time. Timing was checked and spec'd. (Side note: I thought if the carbs "spit," then the mixture is lean. Still learning here...)

The old tank was a little rusty on the bottom but not too terribly bad. In any case, now it has new tank, new gas, new filter and the pump is rated for 1.5 to 4 psi, 25 gph.

I have SU carbs. I haven't checked for leaks but I'll check tomorrow. I guess I just figured since the mechanics had a go at it, they must be ok. I'm going to give them a call tomorrow as well.

As for the choke, I pull out all the way to start, then when it turns over, push in halfway. Then gradually all the way until it doesn't die. Once i can bump up the rpms with the accelerator without too much misfire, I'll drive, but I don't use choke at all while driving. I just drive it a few times around the block and it stumbles with too much throttle or after shifts. Should I keep messing with the choke while driving? Am I not letting it warm up enough? After it's warm it runs better, but I don't push it very much. And it shakes like the dickens when I kill the ignition.

What do you guys think about the amperage thing on acceleration? Thanks again!
 
I remember my first TR4 very well. Right after I bought it, I had all the kinds of problems you're describing. I took the car to a shop and they were of no help. I remember one of the guys saying it had to be rings. Far from it. It was just fuel.

On yours, I doubt you should worry about the ammeter. Just yet anyway.

Can you just check that the shop didn't miss the point gap or timing in any wild manner? You really shouldn't feel that a rough idle is normal.

Check the basics right off the bat: Your distributor cap and rotor must be good. A bad cap can cause fits and can confuse anyone, and can show extreme symptoms. So check the cap, rotor, wire connections from the coil to the distributor, and then check the point gap to see if it's really .015. Then since it's so easy, check the static timing by rotating the crank and pulley (maybe yank on the fan in neutral) until the hole lines up with the pointer and the rotor points at piston 1, and see if the points are just starting to open.

Of course, this is just guesswork, but I'd be darn sure you first rule out the easy items like the rotor, points, timing, distributor cap, and those plug wires. A bad plug wire can also cause fits. I once had one sparking out the boot back toward the fuel line. Be sure the wires from the cap are all going to the correct piston/plug, and since you've been running I doubt that's an issue.

The only other things that comes to mind and which are easy are: a) You say you have new tank. Did gas flow freely though your fuel line? Is it clear and unblocked? You must know from attaching that electric fuel pump. It should have really flowed from the free end; and b) why the electric pumps at all anyway? I know I've got no right to question that, and others here love electric pumps, but I hope the problem isn't with the pump--because I'd imagine that could be hard to nail that down as the culprit.

Let us know how it all goes and ask away if you have more questions. Someone wiser than I might jump right in.

PS I'm assuming you've removed your air filters, checked that the carb pistons rise and fall freely, and that your choke is not somehow stuck. At least do a quick check on that side.
 
New plugs fouled after 10 miles of driving? Fouled how? Gas? Oil? Wet? Dry?
Basic rule - if its got spark and got gas and they get there at about the same time - she's got to run.
Basic rule 2 - 96 1/2% of the time, its an electrical problem. Unless the floats are sticking, chances are the carbs are ok. Is there any gas dripping from the carb? I've been driving LBCs and other cars since 1949 and I've only had two fuel-related problems: on 2 VW Rabbits - kaput fuel pump relays, and once on a TR6, I neglected to fill the Stromberg pistons with sufficient oil. ( See below). British car owners are notorious for fiddling with their SUs or Strombergs WAY too much. I haven't touched mine in the 17 years I've owned my TR6 and except for a sticking float needle in carb #1 (solved with a rap from a screwdriver), I've had no fuel problems. I use drygas every winter to prevent moisture condensation. I still have the original gas tank and fuel lines.
Basic rule 3 - these cars are very sensitive to correct point gaps. Make sure they're set between .014 & .016. I use an old Lucas point gap feeler gauge perfect for the job.
Basic rule 3 - SU/Stromberg carbs are basically simple devices asking only that you keep the pistons filled with oil. Dry pistons can cause problems like you describe. Ask me how I know. I use 30 weight engine oil.
All the other stuff that's been posted so far is excellent advice. Just don't go crazy and start pulling everything apart all at once. Go slowly and logically, eliminating one thing at a time. And - let us know in detail what you find out. BTW, where are you located? Maybe someone here can help out.
 
I'm with pdplot- ignition system is still a suspect here. I had similar issues with my 4 when I first got it, new points/condensor fixed things up. A weak spark can give you idling issues, fouling, missing under load..
 
Is the carbon on the plugs black or brown? Fact that they are dry tends to indicate not rich. Try replacing the condenser. It's a cheap part that is hard to diagnose other than by replacement and will produce anomalous symptoms. What does the spark look like during bad running? Should be bright and jump 1/4 inch to ground. As for fuel mixture, try starting from scratch. Close the mixture nuts (turning the wrench toward the radiator). When snug, back each nut off ten or so flats (one of the available manuals specifies a strating point, I think, of 14) and see how it runs. A properly adjusted carb will increase idle speed slightly when you lift the piston 1/8 inch with the blade of a flat screw driver. Is there oil in the dashpots?
Bob
 
SMGoose said:
As for the choke, I pull out all the way to start, then when it turns over, push in halfway. Then gradually all the way until it doesn't die. Once i can bump up the rpms with the accelerator without too much misfire, I'll drive, but I don't use choke at all while driving. I just drive it a few times around the block and it stumbles with too much throttle or after shifts. Should I keep messing with the choke while driving? Am I not letting it warm up enough? After it's warm it runs better, but I don't push it very much. And it shakes like the dickens when I kill the ignition.
Click to expand...
As far as general driving technique, I start driving immediately, using just enough choke so the engine will take throttle smoothly. I do try to be reasonably gentle with it, but I have to turn left across a busy 4-lane road, so that generally involves full throttle. And in just a couple of miles, it is warm enough to release the choke fully.

4 psi is a little on the high side, the original spec was 1.5 to 2.5 psi. Might be OK, but watch for signs that the fuel pressure is overcoming the float valves, especially when the engine is hot. The use of 'Grose Jets' seems to aggravate the problem.

One thing I didn't see mentioned, have you (or your mechanic) checked the valve adjustment? Valves too tight can really mess up the mixture, it is one of the first things to set when doing a tune-up.

The shaking after you turn off the key is known as "running on", and is generally a sign that the engine isn't tuned right (although it might be just high idle rpm). It's also not especially good for the engine, so I would suggest leaving it in gear, with your foot firmly on the brake, and using the clutch to kill the engine just after you turn off the key. With a little practice, you should be able to do this so smoothly that you don't even know if it would have run on or not. My TR3A had a tendency to run on from time to time (never did get the idle rpm down where it belonged), so I just used this technique every time.

No disrespect, but I have seen "professional" mechanics overlook many things. The only solution seems to be doing it yourself. One thing to check is that the carburetor pistons move smoothly and easily. Take off the air filters and lift each piston in turn to the top with a finger (engine not running obviously). You should feel a definite resistance to lifting the piston, but it should move smoothly to the top with no binding or roughness. Then when you release the piston, it should fall quickly and smoothly to the bottom, and land with a distinct click. If you don't hear the click, chances are that the jets are not centered properly, which will cause no end of grief in trying to adjust the carbs. The piston position controls the mixture needle, which in turn controls fuel flow; so it is essential that the piston move in response to any small change in air flow.

Also, if the carbs have been run for a long time with the centering not quite right, it is possible for the needle to wear a groove on the inside of the jet; which will mess up the mixture curve. In extreme cases, you won't be able to set the idle mixture lean enough; but the cruise mixture will be so lean that the engine will overheat and EGT will be way too high. My Dad's TR3A had this problem so bad that the exhaust manifold would glow red after a freeway run!

No charge or slight discharge at idle is normal. If you get the idle rpm down to the book 500 rpm, you may even see the red light glow. The generator just doesn't work at all with the engine below 1000 rpm or so, and won't reach full output until it is turning fairly fast.

However, it shouldn't stay at 30 amps for more than a few seconds. The generator is only rated for 21 amps continuous, and will overheat if it puts out much more than that for very long. If the ammeter stays at +30 for any length of time, it probably indicates a problem with the control box, battery or generator (in roughly that order).
 
It looks as if you already have solutions or proposed solutions for just about anything that can go wrong with your carbs or ignition.
All I will say is get rid of all of it. You can put a pertronix module in the Lucas distributor but then you may have sloppy bearings or sticky advance
mechanisms. A new, electronic distributor can be had pretty cheap these days.
As far as carbs go, if you want the performance of the DCOE webers for 1/2 the price and no tuning headaches get the Mikuni HSR 45's, they bolt right on the TR4 manifold.
I haven't had a single carb or ignition problem for over three years. If your going for originality then just disregard my .02
best of luck,
jim g.
 

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Thanks a lot guys. First some answers to questions:
-All plugs are fouled equally and it's dry black carbon.
-When the mechanics tuned them, they pulled old oil out of the dashpots and put in SU carb oil. So that should be fine. Piston was moving nicely.
-The mechanical fuel pump was removed and an electric SU installed before I got the car. I don't know much about the mechanicals and I heard the Facets were good, so I just got one of those.

Here's what I've done this morning:
-Let the fuel pump flow into a jug and there's plenty of flow there: 20 oz in 30 seconds. The rubber hose that runs from the old fuel line through the engine compartment to the carbs is 1/4", not 5/16" like the back end was.
-I pulled the distributor cap checked all that out. I'm about to head to the parts store to get a gap tool (like I said, I'm new at this!) and while I'm there I'm going to buy new points and condenser just in case.
-Attempted to look at timing using this as a guide https://www.vtr.org/maintain/Setting-the-Ignition-Timing-on-a-TR.pdf but could not find the hole in the pulley. Will try again later. Also, it wasn't very smooth and at some points in the rotation very difficult to rotate. When the mechanics did the timing, they used a strobe while it was running. Would that upset the timing in a TR4 as it says for the 2 and 3 in that article?

Ok off to the parts store...
 
I just checked the condenser with an ohmmeter and it checks out. The points gap, however, was about .08. The rotor and cap show a little bit of wear so I'm debating just changing everything out. Lesson learned on doing it right yourself. There still might be a vacuum leak, but I'll check that after I get this sorted out.

jimg: is the Flame-thrower distributor the one you speak of?
 
I wanted to provide a bit of encouragement. I went through the same process recently on needing to trouble shoot timing and fuel related issues on a TR I bought that had also been sitting for a while.

Once your car is all set up, it should be good to go and not require constant adjustment. Going with the aftermarket items can be a good choice, but also staying with the standard points, condenser, and SU carbs will work just fine.

I have a couple of TR's. The TR4 I finished restoring awhile back, and have not messed with the SU carbs or even needed to reset the timing. Once you learn how, it can be fun to go through the tune up process when needed.

With the plugs being black and dry, this is a good. It means that the car is running rich.

If you get through the items mentioned in the other treads and still have an issue, the other very common wear point that will effect the car's idle and also mixture are worn throttle shafts on the SU's.

I would focus on the items mentioned by the other folks to make sure these items are all set and working correctly. Part of the "fun" of owning a new for you Triumph is figuring out what was done by the previous owner. Once you go through these items, I expect that your TR4 will be running like a champ.

Steve
 
Thanks, Steve. And everybody, for that matter. This site has been a godsend. It started up and idled better after the points were changed so that's a good sign. It's not all the way there but I ordered a new cap, rotor, wires and plugs and will set the timing as well. I'm feeling pretty good that that will work.
It's funny. Any other car and a tune-up would have been my first thought, but after the fuel leak and the mechanics and the uncertainty of an unfamiliar car (& unfamiliar carburetors), I guess I psyched myself out. Well I hope, anyway! I'll let you all know the verdict in a couple days.
 
SMG,

That point gap is of course really off, so fix that first. Some around here say the gap can really be horribly off, and yet the car will run, but, still, fix that. Be sure all your wires in the distributor are intact. Good shape. The wire from the Terminal Bush to the points must not be shorted.

I wouldn't time it with a strobe. Instead, just static time it. If you have a test light (or care to buy a bulb of just pull a bulb out of the front turn signal and get some spare wire), just connect one line from the light to a good ground, and the other line to the side of the coil that goes to the distributor. Be sure you're at TDC with the rotor pointing at piston number one. Loosen the clamp nut on the distributor base, and with the ignition key turned on, slightly rotate the distributor so the light just comes on as the points just begin to open. Be careful of course not to yank the distributor upward. After the test light just begins to glow, stop, re-tighten the distributor and you're done--except that to be 4 degrees BTDC you must now turn the vernier adjustment dial so one more notch line on the vacuum body shows. Each notch is apparently 4 degrees.

Check the contact and spring up in the "underside" of the distributor cap. Be sure it's there, and clean. Replace that rotor. Sometimes a rotor is just manufactured wrong and you may not see it.

Granted, none of this may fix your problem but you need to rule them out. Look at those plug wires. Be sure you do have the correct plugs. A good condenser. Don't drop any little screws or anything down into your distributor. Then, for me, I'd look at those SUs last.

Finally, if your TDC mark on the pulley is gone, I'd wonder how your shop used a strobe. Others here know better, but to find TDC I think you're looking for when piston #1 is at its highest point on the compression stroke (each piston has two strokes, compression and exhaust) and without the mark on the pulley you'd probably have to determine that point and mark it with a white marker. You'd do that by removing the valve cover and watching the #1 piston valve reach its highest point, when the distributor rotor is pointing to #1. You can pull the crank fan slowly by hand to get to the right point. I pull mine with a rag 'cause it's really difficult with the plugs still in.
 
I agree. I think part of the challenge of a "new" old car is knowing where to focus. This is where the folks on this website are so helpful. They have given me the confidence to dive deeper on resolving issues that would have taken so much longer with many more frustrations along the way.

Yeh these cars can be "easy" to work on. I found that the "easy" part would not be possible without everyone's help from this site. It is great to have a site available like this for TR's and other LBC's. Without the help, I wonder how many more TR's would be sitting in garages collecting dust vs. out on the road or going through various levels of restoration.

Good luck!

SMGoose said:
Thanks, Steve. And everybody, for that matter. This site has been a godsend. It started up and idled better after the points were changed so that's a good sign. It's not all the way there but I ordered a new cap, rotor, wires and plugs and will set the timing as well. I'm feeling pretty good that that will work.
It's funny. Any other car and a tune-up would have been my first thought, but after the fuel leak and the mechanics and the uncertainty of an unfamiliar car (& unfamiliar carburetors), I guess I psyched myself out. Well I hope, anyway! I'll let you all know the verdict in a couple days.
Click to expand...
 
" This site has been a godsend"

I sure agree on that statement - for *many* reasons!

You mention you "checked the condenser with an ohmmeter and it checks out." Could you expand on that? A condenser is like a mini-battery - I wondered if you removed it from the distributor, and how you tested it. After over a month of engine problems, I tested and discovered my condenser was bad. Replaced it and no further problems.

Also, you discovered the bad point gap. Didn't the shop check that earlier?

Thanks.
Tom
 
Tom, I removed the condenser from the distributor, put one lead on the wire end and the other on the condenser body. The ohms rose until it read OF. I switched the leads and it did the same. I had heard that's how you do it, anyway. Would you agree?

The bad points were also sitting at a little bit of an angle to one another when open. That probably didn't help. I have no idea why the guy didn't tell me to just replace them. I watched the process but didn't want to get in the way so I didn't get very close.

I also found the TDC mark on the pulley with a bit more light today. The PO had the engine rebuilt and it was a subtle indention but it's definitely the mark because the pulley is also a little warped at that point from the force of the indention. I'll tackle it all at once tomorrow when I pick up the rotor/cap/wires.

Considering all this, I feel like I really should check the valve adjustment while I'm at it, like Randall said. For the valve cover gasket, can one be found at the local parts store? I'd like to not have to pay $7 shipping for a $4 gasket.
 
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