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TR6 TR6 runs then dies

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jjbunn

jjbunn

Jedi Knight
Offline
The car has a pair of rebuilt Stromberg carbs. It will start with the choke out. When warmed up it starts to run very unevenly. Pushing the choke half way in improves the idle, which settles to about 1500 rpm, but it's still a little rough. Pushing the choke all the way in, and the engine dies promptly. The engine revs very freely when the choke is out.

I topped up the dashpots with 25w50 - they were low. I noticed that the twin choke cables do not have the same position at the carbs: one carb has more choke than the other.

Do these symptoms point more towards an ignition problem or a fuel/air problem?

1501759022_83486ee568.jpg
 
Lack of dashpot oil wouldn't affect idle, if anything, it would cause stumbling on acceleration. I assume you've checked that your jet needles are set correctly?
 
I know that I see clamps in that picture, but I would be looking for some vacuum leaks. After I balanced the chokes to be equal.

Check that outside line, where the two clamps are over the odd looking fitting. It doesn't seem like it would be a tight seal around that "white plastic whatever it is".
 
That is a new 3 way fitting. My new one from TRF is that color.

Notice the breather that the previous owner was using.
 
I would pull the tops of the carbs(remove the four screws). Then pull the pistons. Confirm that there are no holes in the rubber diaphragms. Look at the needles at the base of each piston. Are they adjusted in similar positions? If not, a good starting point is to have the base of the needle even with the bottom of the piston. The carbs can be tuned from there.
Do you have a book on Stromberg Carbs? If not, get one.
I would follow the book and do a step by step tuning.
Follow the others suggestions and get back to us.
 
DougF said:
I would pull the tops of the carbs(remove the four screws). Then pull the pistons. Confirm that there are no holes in the rubber diaphragms. Look at the needles at the base of each piston. Are they adjusted in similar positions? If not, a good starting point is to have the base of the needle even with the bottom of the piston. The carbs can be tuned from there.
Do you have a book on Stromberg Carbs? If not, get one.
I would follow the book and do a step by step tuning.
Follow the others suggestions and get back to us.
Click to expand...

Thanks for all the advice, which I will follow, hopefully tomorrow.

I don't think there can be much wrong, because the mechanic who worked on the engine said that it was running very well when last used, and the problem has only manifested itself when the car was turned over again recently after sitting for a while (I don't know how long "a while" is).
 
You can't go wrong if you check the basics. Somebody could have messed with the car since it "last" ran.
The more you get to know about the car, the better.
 
Yeah, check the diaphragms carefully first: hold 'em up to a light while slightly stretching them all the way 'round their circumference. Needle height (the mixture adjustment. Just opposite from SU's) is adjusted with a "special tool"... If the thing has sat for a while it may be a fuel degradation issue, too.
 
DrEntropy said:
Needle height (the mixture adjustment. Just opposite from SU's) is adjusted with a "special tool"... If the thing has sat for a while it may be a fuel degradation issue, too.
Click to expand...

The tool is Loooong hexhead allen . If you don't have one,
you can make one from a philips head screwdriver and a
bench grinder.

Yes, this seat-of-the-pants island technique works
just fine. I grinded, Banjo twisted and car drove away
shortly thereafter.

I plan on ordering the proper tool- now that I know it exists! Ha, ha.

Top off your gas tank with high test, see if that helps.

tinster
 
Tinster said:
The tool is Loooong hexhead allen . If you don't have one,
you can make one from a philips head screwdriver and a
bench grinder.
Click to expand...

The 'official' tool also has an outer collar that fits into the top of the damper tube to try to keep you from twisting the whole piston and damaging the diaphragm. I've always thought it's probably pretty hard to do that though.
 
Depends on the age/condition of the diaphragm and the little O-ring seal at the needle. I've had 'em stuck so well they required disassembly and a change of O-ring to move at all. The ring can turn to near concrete over time. This is where proper rebuild kits (J. Curto) are appreciated. Viton O-rings, not those cheezy after-market ones. The tool is a 3MM hex, IIRC.

With the air cleaner off, you could also pin the piston with a finger to try adjusting the needle. If it takes more than that to keep the piston from turning with the Allen wrench, the O-ring is likely rock hard and useless as a seal anyhow.
 
OK I have been trying the simple things first, working first on the idea that it's more likely to be an ignition/electrical problem than the carbs.

I removed all the plugs and re-gapped them to 0.03" (the recommended gap for the sports coil). They were a tad too big before. All the plugs were black sooty, indicating too rich a mixture (right?)

I checked that the plug leads were wired to the plugs and distributor in the correct order (!)

I then started the engine, and let it idle with full choke for a while. Then I pulled each plug wire in turn, noting that the engine slowed a little for each. There was a difference for each plug, so I think that indicates the distributor and HV are OK.

Then I pulled the air filters off the carbs, and checked that each piston moves freely. They did. I then tightened all the hose clamps. Some of them were not as tight as I would have liked.

I also tightened some loose fittings on the accelerator linkage, which seems a very Heath Robinson affair to my untrained eye.

At this point, with the choke half way in, the engine was idling at ~1500rpm with some roughness, but I had the impression more smoothly than before.

However, I looked at the gauges, and the Temperature gauge was up in the red. So I turned the engine off.

Next I will lift the tops off the carbs as suggested and see if I can detect any problem there.
 
You may find the cam activated by the choke is not set evenly with the two carbs. Pretty simple check and reset if needed. Once that is set you should be able to adjust the main idle screws to lower the RPMs to 8 or 9 hundred unless there are other problems.
 
Running hot and rich? If not already done, throw a timing light on it and check the settings then try adjusting the carbs before ripping into them.
 
The plugs are going to be black since the car has only been running on choke.
 
jjbunn said:
I also tightened some loose fittings on the accelerator linkage, which seems a very Heath Robinson affair to my untrained eye.
Click to expand...
The stock accelerator linkage is kinda wierd and floppy/loose, there's a built in (intentional) "lost motion" process in it that is designed to make sure that the linkage cannot hang the throttle open and thus avoid inevitable catastrophe.
There are a lot of adjustments you can make to it; I personally adjusted most of the lost motion out of mine to "tighten" it up
 
TR6oldtimer said:
Running hot and rich? If not already done, throw a timing light on it and check the settings then try adjusting the carbs before ripping into them.
Click to expand...

I took the tops off each carb, inspected the rubber diaphragms , and the heights of the needles. Everything looked good, and seemed to confirm that the carbs had been rebuilt (the rubber looked very new). The needles were very clean, and they were not rigidly fixed in position, but could be wiggled a little.

I don't have a timing light. Can I make my own? I do have a tach/dwell meter, but have found it hard to use in the past.

I'm very reluctant to start getting in and dismantling the carbs unless there's strong evidence they are bad.
 
jjbunn said:
I don't have a timing light. Can I make my own?
Click to expand...
Possibly, but not worth the effort, IMO. Snoop around a little on eBay, you should be able to pick one up for $20-$30
https://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&viewitem=&item=260166635568
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I'm very reluctant to start getting in and dismantling the carbs unless there's strong evidence they are bad. [/QUOTE]
I'm inclined to agree. Have you tried blocking off the line to the brake booster yet ? They sometimes fail "just sitting" and can cause a major vacuum leak.
 
TR3driver said:
jjbunn said:
I don't have a timing light. Can I make my own?
Click to expand...
Possibly, but not worth the effort, IMO. Snoop around a little on eBay, you should be able to pick one up for $20-$30
https://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&viewitem=&item=260166635568
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I'm very reluctant to start getting in and dismantling the carbs unless there's strong evidence they are bad.
Click to expand...
I'm inclined to agree. Have you tried blocking off the line to the brake booster yet ? They sometimes fail "just sitting" and can cause a major vacuum leak. [/QUOTE]

Oh! That's something I will try next :smile: Thanks.
 
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