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TR2/3/3A TR3A fast idle cam connection?

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jdubois

jdubois

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On the little cam that attaches the choke rod to the fast idle screw on the front carb there are three different holes to attach the rod to (they're labeled 1, 2, & 3). Which hole is the rod supposed to go into? It's currently in the middle hole and I'm thinking it should be in the bottom one. Why are there three different holes anyway? Any insight would be greatly appreciated.
 
Mine is in the middle hole -- and it works just fine there.
SU made carbs for lots of auto makers/applications. "One size, fits all" cams are always cheaper to produce than different cams for each application.
 
Mine's in the bottom hole. It was like that when I tore the car apart, so that's where I put it back. Seems to work fine there. The next question to ask is what is the length of the rod. Maybe that changed along the way. Mine measures 3 1/2".

Edit: I could probably put it in the middle hole, as my high idle adjustment screw is almost all the way out. The end of the screw is sticking out about an 1/8". After looking at the shape of the cam, I think which hole you put it in will determine the curve of how and when the high idle comes into play. My high idle comes in quickly and at full choke runs about 1800 rpm. It doesn't come all the way down until I pretty much have the choke all the way in.
 
jdubois said:
On the little cam that attaches the choke rod to the fast idle screw on the front carb there are three different holes to attach the rod to (they're labeled 1, 2, & 3). Which hole is the rod supposed to go into? It's currently in the middle hole and I'm thinking it should be in the bottom one. Why are there three different holes anyway? Any insight would be greatly appreciated.
Click to expand...

J - one of our members (G Hahn, Dave Russell, Don Elliott, ?) once posted that the three holes may have once existed for use in different "seasons" (winter, summer, fall). Also, may have been fitted due to other variables of "slop" in the setup. I don't know.

Regardless of the hole used, the cam serves only to raise the idle speed to around 1200rpm when the choke handle is pulled out to the first "notch". So use the one that allows that amount of speed increase.

Tom
 
I'm convinced the holes were for other applications (remember SU was an entirely separate company from Standard-Triumph), possibly not even on the same carb (SU used interchangeable parts whenever possible). At any rate, I would stick with the center hole on a TR3A. Switching holes is just too much change in length. Using the top hole will result in no fast idle action at all; while the bottom hole will cause the cam to hold the throttle open all the time (unless you bend the rod by quite a bit).

The fast idle speed is adjusted with the screw on the arm.
 
I just got done looking through all the pictures of carbs on TR3s that I could find, just to see which hole that rod is in. Most of the pictures hide the postition because of the air filters. However, there were four pictures in which I could determine which hole the high idle rod was in...

Two were in the bottom hole, and two were in the center hole. :laugh: Well, that tells us nothing, except that maybe the top hole is not where it should be.

You would think that something like this would be a given.
 
Thanks for the replies, guys. Dang, I was hoping the middle hole was definitely wrong. The thing doesn't idle when cold unless I adjust the fast idle screw so far down that it interferes with the regular idle after I let out the choke. I was thinking that it looks like the bottom hole would change the position of everything such that I might not have that problem. But if others have the rod in the middle hole and it works fine, I must have something wrong somewhere else.
 
jdubois said:
... I was thinking that it looks like the bottom hole would change the position of everything such that I might not have that problem. But if others have the rod in the middle hole and it works fine, I must have something wrong somewhere else.
Click to expand...

Like I said in my first post, I have it in the bottom hole. I've seen pictures of other TR3s that have it in the bottom hole. Try it there on yours and see how it works out.
 
Well, I tried to go out and play with it this morning. But before I got very far the terminal for the start pushbutton lead on the starter solenoid fell off. The car did start up pretty easily this morning, and ran for a whole of about ten seconds at about 4000 rpm or so (I'd been screwing with the idle screws, so the high rpms didn't surprise me) before just completely dying.

Now I've got to wait for the new solenoid to come in before I can keep going. Might as well order the new clutch master at the same time, since that's failing also. :frown: I'm going to go drive my Spit to make myself feel better. At least she runs like a top.
 
This is a TR3A. You can start it with the hand-crank. Or use an old mother of a screwdriver to contact both nuts which secure the battery and starter cables to the starter solenoid. Once it starts, you can remove that huge screwdriver and the engine will continue to run - unless there is something else wrong.
 
Don Elliott said:
Once it starts, you can remove that huge screwdriver and the engine will continue to run - <span style="font-weight: bold">unless there is something else wrong.</span>
Click to expand...

There is :cryin:

That's a good point though, I could use a screwdriver, or easily enough wire up an external switch for it across the terminals.

One of the things I like about the spit is the push button directly on the solenoid itself to make it easy to start the car from the engine compartment.
 
Ok, besides learning a new way to weld, the screwdriver across the terminals worked, after I remembered I still had to have the key in the run position! The car still didn't want to stay running, so I kept looking around noticed the mixture adjustment nuts seemed awful lean (but I'm clueless about SU tuning). I screwed them both all the way lean and then backed out twelve flats again. After that, the car will keep running for a while but no matter what I put the throttle at, it doesn't want to go any faster than about 500 RPMs. This is with a cold engine and the choke fully out. If I put the choke in it dies. Suggestions? Still too lean?

(BTW, this car hasn't run in about eight months. When it was put away it didn't run right.)
 
jdubois said:
One of the things I like about the spit is the push button directly on the solenoid itself to make it easy to start the car from the engine compartment.
Click to expand...
The TR3A had that originally as well. I like it too. But even without it, you can just connect a jumper from the hot terminal to the side terminal. Using a screwdriver like that is a good way to ruin the solenoid terminals.
 
jdubois said:
This is with a cold engine and the choke fully out. If I put the choke in it dies. Suggestions? Still too lean?
Click to expand...
Too lean (meaning not enough fuel), but not mixture adjustment. Those nuts should do nothing when the choke is pulled out; and choke full out should be way, way too rich once the engine fires off.

I would start by visually looking to see that the choke is pulling both jets down by roughly the same amount. Full stroke on the knob should get you at least 1/4" between the head of the jet & the nut, or else there is a problem with the linkage.

If that looks good, my next step would be to pull the fuel line off the front carb, and briefly check fuel delivery. The book gives a spec somewhere, but I would just check for a good, strong spurt of fuel as the engine cranks, rather than a dribble. Then lift the carb lid to check for stuck float, blocked float valve, etc.

It's also important to check that the carb pistons move totally freely in their bores. You should feel resistance when you lift them with a finger (engine not running), but when you drop them, they should fall quickly and smoothly, landing with a distinct click. The least little hangup or tight spot (especially at the bottom of the travel) will make it impossible to get the mixture adjusted properly (as the mixture is very dependant on the piston position vs air flow).

BTW, here's a shot of the fast idle linkage for reference. The fast idle adjustment screw is incorrect, but the rest is OK.
 
Thank Randall, I'll give all that a look-see. I did clean/check/re-fill the pistons and they seem to be ok. But I'll check fuel delivery and the float bowls.
 
Do you have enough fuel flow. I had a similar situation (but it just developed on an otherwise fine running car that had been trouble free for years). Turned out I had both the class sediment bowl in the fuel pump full of crud and the little screens on the input to the carb bowls full of crud. It would start then die if you touched the throttle. I think if my idle was a bit higher it would have died too.

Besides blocked fuel flow the fuel pump output might be a problem. If the new ethanol gas has done in your pump diaphragm that might be it.
 
Thanks Adrio, after Randall's suggestion to check fuel delivery it occurred to me to check the pump for as well. It's good to hear that could be the issue. I've got to put my two year old to bed, and then I'm going to head down to the garage and see what I can see.
 
Ok, I didn't get a chance to check the fuel flow out of the pump because I'm not allowed to make noise at night, per the wife. But, this is what I did notice-

There was a little bit of sediment at the bottom of both float bowls and in the fuel pump sediment bowl, but nothing too disturbing. The filter above the sediment bowl was almost completely clean.

The float bowl cover on the front carb seems to have slightly stripped threads where the valve seat screws in. It still holds pretty tight, but doesn't 'cinch up' like the rear one does.

There is a little spring loaded peg on the bottom of the carb pistons. I'm not sure what it's purpose is, but it stops the piston from fully contacting the bridge. The rear one gives about 0.025" clearance between piston and bridge and the front one gives about 0.005" clearance. I'm not sure which one is correct, or if that discrepancy matters.

Any of this sound fatal, or should I just proceed with checking fuel flow tomorrow morning?
 
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