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TR4/4A Tuning the TR4A

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KVH

KVH

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Okay, I've got the timing and points correct, and I think I've got the carbs right. I'm not seeing any air or vacuum leaks. The car is really running great. I opened the jets up 8 flats. Problem: still idling erratically. Swings from 1000 to 1200 rpms at idle. Is there any rule of thumb here? I'm tempted to buy a new distributor I'm seeing on EBAY for a mere $98.00. Looks perfect. But if my problem is simpler, I'd like to try that first. thx
 
Your best bet with a distributor is to get yours rebuilt. If you buy a cheap one, that is what you are going to get. If you get yours rebuilt for about $150 ( that is what it cost me) you will have a sturdy unit that is set up for YOUR car, not some fictional general type engine. I was set to buy a new Lucas unit from a major supplier and was told by the supplier pretty much what I just stated above.
As to finishing the tune up, I usually found that the 8 flats was the starting point and I usually had to go back a couple to get it to where I wanted it. Did you syncronize the two carbs?
Charley
 
Yes, I'm sync'd with my old Unisyn device. It's just that uneven idle. Might just have been too hot. I've got a new bushing and dog gear for the distributor. May take into the local machine shop and see what they say.
 
uneven idle speed? sure sounds like a vacuum leak to me.

Spray some carb cleaner all around the base of the carbs, manifold, etc. I'm betting you have a leaking flange or seal somewhere.

Tom
 
You might put a timing light on the engine while it runs at idle -- see if the timing mark moves about rather than holding steady. That can be a clue that the distributor bushing is allowing some wobble in the shaft (when causes slight changes in the points gap which causes slight changes in timing which causes slight changes in idle speed).

Some address this by installing a Pertronix which tolerates some wobble as it eliminates points gap from the equation. Even a well know rebuilder often prefers this approach than dealing with that bushing.

That said, I prefer to stay with points and maybe you do to. If you find a local shop that can & will replace that distributor bushing I'll be interested in hearing about it (haven't looked or asked myself so I can't say if that will be easy to get done locally).
 
Geo Hahn said:
That said, I prefer to stay with points and maybe you do to. If you find a local shop that can & will replace that distributor bushing I'll be interested in hearing about it (haven't looked or asked myself so I can't say if that will be easy to get done locally).
Click to expand...

Once upon a time I replaced the bushing, just pounded it out and pounded in the new one.
 
Darrell_Walker said:
Once upon a time I replaced the bushing, just pounded it out and pounded in the new one.
Click to expand...

I was under the impression this was a 'ream to fit' situation (which is not to say that a replacement might not work w/o reaming). But then, I have never done this nor had it done.
 
Geo Hahn said:
I was under the impression this was a 'ream to fit' situation (which is not to say that a replacement might not work w/o reaming). But then, I have never done this nor had it done.
Click to expand...

It seemed to fit as-is. Though this was 30+ years ago.
 
When you get the distributor rebuilt they also redo the springs inside the distributor. Which I am led to believe is a big thing in trying to get the distributor running correctly. But that is more at the upper revs than at idle.
Charley
 
Jeff at Advanced Distributor is an outstanding choice, have used him for years. BUT - make sure as suggested you don't have vacuum leaks first.
 
charleyf said:
When you get the distributor rebuilt they also redo the springs inside the distributor. Which I am led to believe is a big thing in trying to get the distributor running correctly. But that is more at the upper revs than at idle.
Charley
Click to expand...

Actually, the spring(s) are as important at low RPMs as high. Two springs are in there. One spring should retard the timing all the way to 4 degrees at rest and gradually allow the amount of advance to increase until the second spring slows the advance rate to the full 30 degrees at red line. If the springs are worn or stretched by a few mm, the timing at rest may not return 'home', and cause hard starts. -The "timing" can be adjusted to offset the inability of the spring(s), but I have seen tremendous improvement with new springs and proper advance. -just my two cents, and I agree that shaft wobble should be minimized, as well as vacuum leaks.

Idle speed will change considerably with slight changes in timing, so the effect of those springs should not me understated.
 
OK so I'll check the carb shafts and intake manifold for leaks. Anywhere else? The exhaust manifold and flange at the exhaust pipe should be irrelevant I hope.
 
Geo Hahn said:
You might put a timing light on the engine while it runs at idle -- see if the timing mark moves about rather than holding steady. That can be a clue that the distributor bushing is allowing some wobble in the shaft (when causes slight changes in the points gap which causes slight changes in timing which causes slight changes in idle speed).
Click to expand...

I'm back. Still aiming for a smooth running engine. Can't get the idle to stop jumping. It's not terrible. Just about 200 rpms of change. I know it's not right, however, and I've never had this problem previously. I can't find a vacuum leak, but something must be wrong. Two hundred up; two hundred down. Any chance it's the condenser? Likely not. I may pull the distributor but I really don't think that's it. The timing sticks fairly well within a few degrees.
 
KVH, Have a look at the butterflies and make sure the are closing. If they are not centered all kind of weird things happen, they should close completely with the idle screw off the stop.

Wayne
 
When I found my carb bodies/bore to be not perfectly round compared to the butterflies, I had a constant idle, but could not get the idle low enough. If your shafts are worn, and wobbling around, the idle would vary. If you hold the butterflies closed against the idle screw, does the idle still wonder a few hundred RPM or stay steady? -In order to see if the butterflies closed the whole way, I had to remove the carbs, turn out the idle screw and hold the carb up to the sun, looking through the bore to see how much light came around the butterfly (between the closed butterfly and carb bore). It doesn't take much light to have a high idle.

Another thing you might check is the spring that pulls the breaker plate (from the vacuum module) simply slides onto a cone shaped post on the breaker plate. If the end of that spring is stretched more round, and not fitting tightly against the post, the plate might randomly wiggle back and forth -which changes the timing a few degrees, and could effect the idle speed.

While you are checking out that spring, be sure the smaller spring on the mechanical advance weight under that plate always returns the advance the whole way -that spring needs to be under tension at rest. You can check it by gently rotating the rotor against the spring/weight force, and when you let go, it should snap back 'home'.
 
KVH, your symptoms sound familier to me. Take the valve cover off and check for proper valve adjustment , you may have one are more too tight. You'll never be able to adjust the lopey idle out of it if so.
 
If you have a PCV valve, you might try disconnecting it and plugging the manifold opening, to see if it affects the idle.
Berry
 
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