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Triumph TR6 - dashpot oil and levels

OK, guys, might sound dumb to some of you but I have never messed with the carbs at all..... I know, should learn. Anyway, can you guys tell me if regular 20-50 oil is OK to use in the dashpots? And what the level should be? Last weekend wehn I drove it (after the winter rest) the car bogged when it first starts in first gear. Someone mentioned that the oil in the dashpots might be low. Could that be the case? Should I see the oil to the () mark in the shaft? Rigth now I see oil waaaay down there. Thanks for the help, want to take a ride this weekend but not while the bogg is still going on. :(

Hey Abner

Yep low oil is likely. Don't use multi- weight detergent oil.

Your in a warm climate so you might start out with a plain non detergent 30 weight and move up or down. The lighter the oil the leaner acceleration mixture and reverse. Lean mixture is causing your bog likely.

Bill Brayford

Hi Abner,
I use 10w30 in mine, some guys use machine oil or tranny oil.....fill it up to the point that when you put on the damper cap you feel resistance when the threaded part on the cap is 1/4 away from the top of the cover.
Charlie Ballard

Hi Charlie and Abner

Charlie I don't use multi weight because there viscosity or oil weight changes with temperature. Detergent chemicals also don't help. You were having a bog problem last year that resolved with a light choke pull? Might be the multi weight? Single weight non detergent is best I think.

Sorry Abner forgot fill directions thanks Charlie.

Bill Brayford

Hi Bill,
I tried to sewing machine oil ( don't tell the wife ) and tranny fluid and I still had that bogging problem.
Oh well ..something to do this summer !
Charlie Ballard

When I bought my TR3A (with SU's), I used #10 oil in the dashpots in the winter and #30 in the summer. I have used 20W50 ever since 1990. I fill mine to almost the top. What I do, is unscrew the top cap, lift it about 1/2" and push the rod etc over to one side and carefully pour the oil into the top. When it's full, I push the top cap over to the center and screw it down. The excess bit overflows and I guess it gets burned off somehow.

The 20W50 oil has a flatter viscosity curve than other oils. When the oil is cold (at start-up) the oil acts like a #20 viscosity oil when it is also cold. When the engine gets hot, the oil acts like a #50 oil when it is hot. I never had a problem with multigrade oil.

BTW, when Charlie talks about "tranny" fluid, he doesn't mean 80-90 Hypoy, he means red automatic transmission fluid.

I have heard it said that bucking, etc. is 90% electrical and 10% carbs.

Don Elliott, Original Owner, 1958 TR3A
Don Elliott

Thanks all of you guys! I have not been able to do anything yet this weekend (work is getting in the way) but will let you all know what happens as soon as I fill the dashpots. I hope the bogging goes away.

Hi Guys

On the oil thing as mentioned I always use the cheap 30 non detergent hard to get now or single wieght lawn mower 30.

Charlie Sewing machine oil is about a 4 and tranny fluid equals about 10. Thats an educated guess since neither have a viscosity rating. Try the 30 single, your new diaphrams have lots of lift?

From my understanding of that carb type and general mechanics Don I think it would be better to have a richer mixture when the engine is cold and leaner hot? The single weight 30 does that since it thins a bit hot? No hard fast rule here just my experience. Cold engine runs best rich hence the choke.

I agree on the timing. Just because it runs doesn't mean its tuned? Trick is getting them both in sync. On an older vehicle a dyno, or adjust and do test runs with patience from a base point is about the best advice.

As for myself when feeling a little retarded and out of tune. I go for 2 rich mixes of single malt scotch a little sparking with the old girl and 8 hours beddybye. Tunes me up bigtime...:)


Bill Brayford

I don't think the dashpot oil really has anything to do with rich or lean. The air and fuel change at the same rate as the piston rises. What does happen is the piston (and needle) rise a little slower with heavier oil. Which, in my humble opinion, is a little slow in temps colder than freezing with the official SU oil. Not bad, just noticable. The engine sounds like it's sucking more than it should. Like breathing in with your lips close together. If you get this sound and it bothers you, use lighter oil. Never had diapragm carbs, so your mileage may vary.

Guys, what would be the best weight to use down here in SoFl where it never gets cold? I was just peeking in there yesterday and the oil appears low. By the way, I like Don's method--the stuff you read about how to tell the oil level in the carbs has never made any sense to me.

JL Bryan

We up here in Canada wish you would stop on this "where it never gets cold?" stuff:)
It probably would be best for you to lean (no pun intended) towards a heavier oil viscosity.
The Charlie/book method of checking dash-pot oil level is correct. If you do not feel resistance as Charlie puts it, then maybe you have a problem in there.....bad O-ring??

Abner, You should follow this procedure also. Keep in mind that the oil level should not really change. If it drops then maybe you have bad O rings.
Also if you have not touched your carbs then you need to get intimate with them. It is important to keep the 2 carbs synchronized. Maybe you are out of sync. The procedure for sychronizing the 2 carbs is very easy and is well documented on the WWW (go to past thread mentioned below). I highly recommend getting the carb sync tool and learning to use it. I check my sync at least 3 times per summer. It is very easy to do and adds to enjoyment of my 6.
Finally, In a past thread, I have posted an "alternative" method to removing the clip holding the O ring in place. IMHO, it saves scorring the walls of the dash pot. Go to the Archives (2002) and you will find a thread titled "Tech-Tip Correction"....Aug 19,2002.
Rick C

Then there is the dreaded by-pass-valve...but that is another story:)
Rick Crawford

Sorry, "The procedure for sychronizing the 2 carbs is very easy and is well documented on the WWW (go to past thread mentioned below)."
The link for the carb adjustment is
Rick C
Rick Crawford

Sorry, Rick. You can pay me back when we hit our 90+ temps and 90+ humidity days and nights from about May to October! You can't even check the oil without sweating all over everything.

I did get my carbs synced, although without the little tool, about 3 months ago. It was kind of fun except it was a pain in the butt getting the air filter cover back on with the gaskets. At least it gave me a sense of accomplishment! I probably need to redo them.

JL Bryan

JL - All the snow has just about gone here in the Montreal area. I've actually got a bit of water showing around the edge of my pool. But the ice in the middle is still about 2 ft thick ! Up here for the winter we leave the pools full. Its going to 55 deg. F here today.

The Expos are leading in their Grapefruit division - did you notice ? Spring is about here when they come up here to play ball.

For Jim, we saw huge flocke of Canada Geese this morning in never ending and always shifting "V" formations at what appeared to be 10,000 ft altitude. I wonder who tunes their carbs ?

Once you sync your carbs and put the air filters back on, remember that now you have the filters back on there is less air going into the carbs, so you are probably running a bit richer.

Don Elliott, 1958 TR3A
In August 2001, I drove to Colorado & back = 5220 miles in 3 weeks. It was 37 deg. F when I awoke from my tent in the State park.

BTW, the TR6 gang had a previous record of 925 entries. We are almost there again.
Don Elliott

Are you saying that at some point we get reset to Zero? Do we loose the archives? It appears that we have already lost a year (from what I recall) of the archives.
Snow all gone and out raking the lawn. Birds a chirpin in the morning..YA HO spring is here!

John, I have been in FL and AZ in the summer. I know what you mean. The unisyn tool makes life so easy and is "visual" accuracy.
Rick C
Rick Crawford

RicK - Our BBS web-mechanic in England, Mike Plumstead chops off the oldest threads every now and then and the total comes back down a 100 or so.

Write and ask Mike about those missing archives. His addreess is :-

Don Elliott, 1958 TR3A
Don Elliott

Hi Tom

Correct damper will not affect rich/lean overall, except when accelerating?

Remove the oil rev. the engine and watch the air mixture cylinder pop up rather than rise. Engine takes a big gulp of air because the fuel can't get there fast enough. Leans out when you want rich and may bog or at least drop in power momentarily.

Down draft carbs have the accelerator pump to compensate. Sidedrafts use the damper?

As far as the weight to use as mentioned there are no hard rules. Engines compression/condition/temperature/aircleaners carbs float level etc. etc. all will make some difference.

I follow the old rule. For every action or change there is a reaction. Rarely what I expect? So I go to plan B.


Bill Brayford

JL in Florida - I'd use the summer weight engine oil for your dashpots - from the same can of oil that you use for your engine. Logically, I ask others why should one go out and buy a special oil that's not on the shelf in your garage already ? These cars are simple. Keep it that way !

Back in 1958 when I was much younger (but I'm still young) and I bought my TR3A brand new, the rule was to use your winter engine oil grade in the dampers during the winter and to use summer weight engine oil in them during the summer.

At that time, detergent and multi-weight oils like 10W30 or 20W50 did not exist. Only straight weight SAE #5 or #10 for winter or SAE #30 for summer. I don't even think #40 was available then.

Maybe that's where Bill got the suggestion about single grade SAE #30 non-detergent oil for the dashpots.

I use summer weight (Castrol 20W50) in my dashpots during the summer and store my TR for the winter. But maybe SU's are different.

Don Elliot, 1958 TR3A (with SU Carbs)
Getting anxious again !
Don Elliott

Hi Bill,

I am not an expert. And these carbs are a puzzle, aren't they? Kinda like a motorcycle carb. Makes you wonder why they don't just run a cable out the top instead of making the piston vacuum actuated. Except for the delay from the damping. I always thought the accelerator pump wasn't needed because of the variable venturi design (more velocity thru the smaller opening draws more fuel).

I'm open to anything here, I'd like to understand these puzzling carbs better.

Pertaining to the thread, I think the "whatever oil you use in the motor for the season" rule is on target.


Hey, Tom. The "cable" you speak of opens the butterfly throttle valve. That increases the level of vacuum in the throat which, because of the drillings in the piston body, lifts the piston. The damper delays the lift so that the higher vacuum pulls in more fuel to give the richer mixture for acceleration that "constant area" carbs get with an accelerator pump.

As the piston rises the vacuum in the throat decreases, but the area for fuel flow increases because of the needle taper. The design is for the mixture to equalize back at the original valve before the throttle was opened.

I've tried different viscosity oils in the damper and have settled on a heavier weight (15W-50) based on perceived better performance.

Brent B
Dan Masters

What a great deal of info........ Thanks guys! And I'm still frustrated! It is not until tonight (if there is no honey-do's) that i will be able to fill the dashpots (thanks Charlie for the directions). Ive decided to use the same as I run in the engine which is 20-50. Lets hope the bogging goes away!
Rick, thanks for the suggestion on getting in touch with the carbs....... I'm still aprehensive about doing that.... don't want to mess the whole thing up, hahahhaa.
Let you all know soon.

Hi Abner

Well since we beat the oil to death...:) Before you get too carried away other than topping up dampers get a bottle of fuel injector carb cleaner. For the TRs tank you will only need half when full and take it for a drive. May be just old gas and crud. If you have a fuel filter in the line you might want to change it. Clamp the hose both sides before you remove.

Tom I don't pretend to be an expert either but as RickC suggests. I have had to get intimate with them a lot in the last 40 years for one reason or another. Yep Don old school for the single weight. If I find something works I stay with it..:)

By the way at WOT (wide open throttle) all engines will read 0 vaccum. Its the variable air speed venturi action due to passages that lifts aircylinder and fuel.

Sort of the same concept just different. Don't want anyone with a new vac gage thinking that dropping vac is causing carbs to starve? I was taught the concept young by an Uncle with a beer in one hand and an airhose in the other. Asking if I wanted a drink? There is a trick with the thumb.

Don't try this at home. That was when beer was 5 bucks a case not 35!


Bill Brayford

It's just always been a puzzle to me why they use the butterfly at all. Motorcycles don't have the butterfly in the carb (unless they stole an SU for their Harley).

Woooooooo Hooooooooo!!!!!!!!!!
No more boggin! Thanks guys, it seems it solved the problem, had a short sweet drive last evening around town.

Tom--I believe SU's were in fact a factory installation on some HD motorcycles (I've seen them on ebaY when searching "SU carb").

Rick O.
Rick Orthen

This thread was discussed between 27/03/2004 and 31/03/2004

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