TR2/3/3A Kangarooing on light throttle

I have a problem I'm struggling to diahnose.

It happens when gently accelerating or travelling slowly (so light throttle) particularly in low gears. The car starts to jerk/kanagaroo. The solution is to dip clutch/raise throttle, and perhapos change up a gear. If I accelerate harder the problem isn't there.

My suspicion is the carb setup. I have twin H6s which I rebuilt (leaking fuel) and then set up after doing the timing and valve gaps. Getting the balance exactly right was fiddly, and then when doing the mixture I struggled to tell the reaction to the lifting pin. I may be doing myself a dis-service but I think the mixture could be rich or lean.

Question is how do I tell, other than trying to leave the choke out a little.

Or am I being paranoid, and the problem is elsewhere. Any ideas?

Regards

John

To some degree, this is normal with manual-transmission cars in low gears. The throttle response in low gears is very sensitive--so you get on the gas a little, the car suddenly goes forward, and the motion pushes you backward and causes you to get off the gas a little, then the car slows suddenly, and you are pushed forward, and the process repeats. If you haven't seen this in the past, it might be that your carbs were fairly far out of adjustment, and you just weren't getting enough power at low speeds.

From here, I can't tell if you are experiencing this normal effect or if it's something more. Is there someone who can drive it and evaluate it for you?

My rule of thumb is that if you don't find a fairly sharp response to moving the mixture nuts, then something else is wrong. Of course, you need to double-check that the jets are following the nuts, sometimes they need an extra boost upwards after leaning the but.

So, check timing, valve lash, and carb sync before trying to set mixture.

Also, what are you running in the dashpots? I tried a range of oils some years ago, and found that very thick oil would cause symptoms similar to your description.

Hi all. Thanks for the responses. I've just been out to try and focus on the problem. Firstly, it is worse when cold, when the car was thoroughly up to temperature it was much less noticeable, which says to me too rich. I locked my foot in one place, but the kangarooing just got worse, which says it isn't the throttle sensitivity, although I do feel the throttle return spring is too weak.

When I got back I tried the mixture. When i push up either lifting pin briefly on either carb, the engine speeds up. The rear carb is now almost there in that lifting the pin has almost no effect either way, but what I wanted to do was to get the mixture so it was weak (lifting the pin makes the engine slow down) and then work it back towards rich to find the right point. I can't get to weak with either carb. When I rebuilt the carbs I put in new needle valves in the flaot chamber and did the 7/162 bar setting, and spent some time making sure that was right.

The oil in the damper is a light machine oil, and I know the springs are in......

I'm obviously doing something wrong here, but can't see what

Bucking is one of many symptoms of a lean mixture. Doing it more cold than hot also confirms lean, as a cold engine requires more fuel, so any lean condition is amplified.

+1 with Randall on checking the dashpot oil. When I first got my TR4a (with HS6 carbs), it would stumble at lower revs and I had to keep the choke pulled to smooth things out. I found that the dashpots had some very thin oil in them. I replaced it with 20 weight oil, and the car was transformed!

Jim

Like Randall suggest, the carbs are the last thing to set when doing a tune up, and John maintains the mixture is lean and it sure sounds like it. I would add that often the problem is ignition on these cars. What I do is have the plugs out to see what they look like and usually have a couple sets of plugs on hand to replace and questionable ones; usually the back ones foul first. Anyways, I set the points at 15 on feeler gauge and the plugs at 25. The points should be set first because they affect the timing. It sounds like you have the valve lash correct.

One of my thoughts are you have 1 or 2 fouled out plugs. Another thought is your distributor is malfunctioning perhaps the plate the points sit on is bouncing around. If that little loop on the vacuum advance comes off the plate, the timing floats around and could give you the Kangaroo effect you created with such great visualization. . Plus if you have a different coil and distributor I would try them.

I have H6Ss on my TR3 but have had little luck with the typical approaches to setting them. I found the ColorTune to work well with one in the front, and another in the rear cylinder.

But, as another completely different point of view I want to mention how my car used to 'kangaroo'. It would do it on a fairly flat road that had a short dip in it. Many roads around Houston fall into that category. Anyway, if I would 'dip' with light pedal, as one would do when maintaining highway speed, the car would lunge forward and back causing enough change to make it difficult to overcome with my foot on the accelerator. It seemed like the engine or transmission was 'winding' up and down. It turned out being related to the HVDA 5-speed and especially the springs in the clutch plate. With the TR6 style clutch, numerous springs isolate the spline of the clutch plate from the disc, and if weak, can cause the car to lunge. The springs eventually wore through the retaining plate, came out and ruined a perfectly good drive. The new clutch disc (provided by Herman) has much beefier springs and retainers.

Anyway, I just wanted to point out another possibility and understand that if you have the original style TR3 clutch, you will not have the springs as I mentioned.

Cheers,
Jer

Good point. But the stock clutch does have springs, they are just correctly matched to the torque of the motor.

HI all,thanks for your inputs, they are all appreciated. Interesting the comments about running lean. I ended up taking off the cleaners, disconnecting the lever from the bottom of the jets fully, seperting the carbs on the spindle and starting again.

Balance between carbs was close, 7 vs 7.25 on my gauge, so i just tweaked that. The big difference was the mixture, the rear most carb was weak, lifting the pin stalled the engine whereas the front one was pretty close, a bit rich if anything. So, lifted both pistons, screwed in both jets and then out by 12 flats, and went through the tuning again. The exhaust still sounds a little bit uneven, but it is a lot better than it was. The pistons both drop to the plate i.e the needle isn't binding. Kangarooing is now gone. Good point about the colortune - I think I have one of those on the shelf, but I'd forgotton. That would give me some certainty, but also allow me to see the sensitivity on the adjusting nut.

So, firstly I obviously got it very wrong first time I did it - mea culpa. I think the problem is that I was adjusting the carbs with the lever spring disconnected (so no upward pressure on the bottom of the jet), but without the lever being disconnected (split pin) from the bottom of the jet. In that position the carbs always seem to be too rich.

I thought the lever was purely to do with the choke, and detaching the spring would negate its effect. Clearly it does more than that.

I have a 4/OD gearbox coming this week to swap the 4 speed, so I'll have a look at the clutch. I'm hoping it was new when this was rebuilt - that was 8 years ago but only 350 miles since, which is where most of my problems are coming from. My general experience is that the more you use a car (appropriately serviced), trhe more reliable it is.

Also managed the repair a three way tear in my roof using a vinyl repair kit. I had to ignore most of the instructions and use common sense, but you can barely see where it was now.

Konrod said:

So, firstly I obviously got it very wrong first time I did it - mea culpa. I think the problem is that I was adjusting the carbs with the lever spring disconnected (so no upward pressure on the bottom of the jet), but without the lever being disconnected (split pin) from the bottom of the jet. In that position the carbs always seem to be too rich.

I thought the lever was purely to do with the choke, and detaching the spring would negate its effect. Clearly it does more than that.

Click to expand...

Yeah, that spring is the only thing that pulls the jet head up against the mixture nut. Without it, turning the nut leaner does nothing at all, as the jet will just stay down. Then later of course, when you hook the spring back up, the jet moves and changes the mixture.

In fact, I like to pull up on the jets a bit after turning the nut leaner, just to make sure they move as far as possible. Sometimes they can hang up so even the spring doesn't move the last little bit. That's especially a problem if someone has tried to stop the jet glands (the cork rings) from weeping, by stretching the spring inside that puts pressure on them.

There are regularly a number of questions related to setting carbs and timing on our cars. Always interesting and informative. Is the workshop manual procedure the best starting point or is there a source that combines some of our collective wisdom? Cheers, Mike

Randall has perhaps hit the nail on the head. The workshop manual says to disconnect all of the choke connections, including the lever under the mixture adjusting nut (or at least, that is the way I've read it) before adjusting the mixture. It seems that is perhaps wrong.

The other interesting point I noticed was the lifting pin. You can use that with the aircleaners on, but of course you can't see the pistons. My lifting pins cause a full deflection of about 1/8" if pushed fully home, which causes a different result to lifting it by the prescribed 1/32". I've scribed a mark on my lifting pins so I don't overcook it, but I can see colortune being the way to go.........

That's odd, my manual says specifically to leave the spring connected.


Still a good idea to pull the jet up after leaning the nut, though, IMO; especially if it didn't seem to make a difference. I won't say having the jets hang up is a common problem, but it definitely happens sometimes; especially if a DPO (or DCO) tried to 'adjust' the springs.

The later manuals were updated to say to lift the piston by 1/8" (rather than 1/32"). But I still don't lift it by the full available travel, rather just a small amount from where I can feel it contact the piston.


Sorry, Mike, I don't have a good answer to your question. To me, the TR2 workshop manual, even with the TR3 supplement, is a very early document. There were a lot of changes that were only updated in the "Instruction Book", later known as Practical Hints for the Maintenance of the Triumph T.R.3