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TR5/TR250 Stumped TR250 Running Rough


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My TR250 has developed a bad stumble on acceleration, it starts and idles ok, but even the idle seems a little off, power is way down.

I realized I hadn't replaced most anything since I got the car done 8 years ago. So I got a new cap, rotor, plug wires, and then a coil. No difference, I replaced the carb floats today still no difference, but tried some shadetree diagnostics because it is at my mom's house and I didn't bring a lot of tools.

Anyway, spark is good on all, it jumps to the valve cover from the plug boot. But I pulled the wires one by one and it does what is supposed to for 4-6, but barely perceptible if at all change when I pull 1-3.

Seems like it must be the front carb. I check the float needle, seems fine, double check the diaphragm (TR4A Strombergs) they are fine. When I put my hand over front carb at idle plenty of suction and it stumbles.

Car was running well, but I have been getting an occasional stumble for a while, minor and very intermittent, became constant very quickly this summer, I have been in the middle of a move/house renovation and haven't had much time to devote to the problem (so I tried throwing parts at it.)


Geo Hahn

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Not a 6-cylinder guy, but two things I always check as part of any general diagnostics or maintenance are valve clearances and timing (including timing advance at high RPM).


Great Pumpkin - R.I.P
Just because you didn't mention it : Is there oil in the dashpots? Do the pistons move freely with the plunger out?


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Randall, didn't mention it, but yes, oil in the dashpots, pistons moving as they should. Geo, I have a Pertronix in it haven't touched the timing for years, but it wouldn't hurt to check it, I need to pull the valve cover and check valve movement etc. too, also want to run a compression test. Still think the pull the plug test results are weird and a clue.

Also double checked the plug wire/firing order.


When you were checking spark, did you also pull the plugs to check their colors?

Our GT6 gets used infrequently. It is not uncommon for one or both of its carbs to develop gum and varnish deposits in the jet assembly parts... and on their needles to a lesser degree. This mandates pulling the bowls and jet parts and cleaning everything to restore proper fuel metering. When the carbs are gummed up, the engine will often start and idle OK but will not rev or it will backfire out the carbs when revved.


Luke Skywalker
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Glemon, give the manifold nuts a quick check next time you are at your Mom's.


Marvin Gruber

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The 250 I have for sale was doing that some, it sits a lot. I screwed the jets down a couple of flats ( HS6 carbs) and it straightened out. Figured a little varnish already on needles. So maybe pull carbs piston out and check needles, if its been a while, bet the needles are black.


Country flag
Wayne, I did check the manifold nuts but just a visual as I was working on the carbs. Marv, I haven't been driving it a lot but strange that the problem seemed to get worse the more I drove it. I think I need half a day I don't have right now to troubleshoot.

There is also plenty of fuel in the float bowls and I do have an original rebuilt pump, it squirts a healthy gob of combustible stuff when I hit the primer lever, I also tried putting more gas in as the tank was quite low when it started getting bad. No difference.
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Nothing to add other than I've always been happy with spraying Gumout in the carb throats with the engine running. That can clean any deposits pretty quickly.
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