Is it a Triumph or a Singer [sewing machine]?

[Member 10617]

On another topic -- having given up on persistent oil leaks -- here is another bothersome "problem."

My car, at idle, runs like a sewing machine. Chuga-chuga-chuga. At normal speed on the road, it runs smooth and fast. No skipping, no misfiring, "perfection." (Or so it seems.)

I have tried everything to improve the idle (checked spark plugss and wires, balanced carbs, set idle, set air/fuel mixture, etc., etc.), but to no avail. chuga, chuga, chuga.

Any idea what may be going on and what I might do about it?

chuga, chuga, chuga....

 

[TR4nut]

Ed-

How low of an RPM are you going at idle? More than one thing can give you that chuga chuga chuga thing, quite often not easily fixable for an older car especially at low RPMs. Air leaks in the carbs at the throttle shaft is one spot, also your distributor may be a contributor - the idle is very sensitive to any advance so if you have just a little wear there you can get an irregular idle. If you can smooth out at 900-1000 rpm, I'd just call it good!

 

[TomMull]

Dashpot oil ok and fuel mixture properly set? Tom

 

[Roger]

What happens if you snap open the throttles when there's no load? If it accelerates cleanly you could be a little rich at idle. If it stalls, a bit lean maybe.
I'm not sure how to interpret 'chuga', but it sounds like a rich idle to me.

 

[hondo402000]

maybe a vacuum leak?

 

[Geo Hahn]

I sorta consider idle to be like a heartbeat -- the most important thing is to have one.

You could put a timing light on it at idle and see if the mark wavers... that would suggest some wobble in the distributor/bushing which could affect idle if you are using points.

 

[Member 10617]

The RPM is usually around 900 to 1000, but lately it has fallen off a bit. I increased it back to 1000, and it is doing a little better

I believe my distributor needs to be replaced or rebuilt> I believe I will get a rebuilt one from The Roadster Factory some time this winter. I am using points, and I have had some trouble with the advance in the past.

I also have two carb rebuild kits that I will install this winter.

I'll double check the dashpot oil.

Looks like it is going to be a project-filled winter!

 

[DNK]

Instead of a new one just send yours to Jeff at
https://www.advanceddistributors.com/
Better than brand new

 

[Moseso]

+1 on Advanced Distributors, from another happy customer.

 

[CJD]

Hey Ed,

That idle is a bit high. You may be uncovering the vacuum port during idle, which can make things inconsistent. The book recommends 500...mine is smooth at that after a year off. See if it can be lowered. If it cannot, then we can start trouble shooting...

John

Ps...smooth, but still sounds a lot like a sewing machine.

 

[TR4nut]

John-

500 rpm.. lucky dog! My tired TR4 is typically 700-800.

Randy

 

[Member 10617]

My car tends to stall out at anything less than about 700 RPM. Holds best at 900-1000 RPM. But I have read elsewhere that 1000 is a bit high.

I have spoken with Jeff and am considering sending my distributor to him. My only thought is that I'd like to have one in the car while he is working on the one presently in it. Some say there is an advantage to having a backup distributor.

CJD--

What would I be doing to uncover the vacuum port at idle? Any way to prevent this if I am doing so?

 

[CJD]

Well, haven't had mine on the road yet...so now you guys have me wondering if I oughta go ahead and raise my idle now!?!

Ed... If you look at the diagram on pg 14 in the "fuel" section of the service manual, you'll see that the port for the distributor is just on the air filter side of the butterfly. So normally it receives no vacuum at idle, but does once you open the throttle. If the butterfly is opened too much at a higher than normal idle, then the port starts to see vacuum with a closed butterfly, which can lead to an inconsistent idle.

May not be a factor, but just one more thing to check...

John

Oh, a simple check is just to disconnect the vacuum line and see if the idle changes...

 

[TR3driver]

Another thing to check is whether the tachometer is accurate or not. It's not unusual for them to read high at idle, so your 800-1000 may actually be 400-600.

Personally I'm with Geo, though. As long as it doesn't die at stop signs, I'm happy with wherever it idles reasonably smoothly. I used to have a "3/4 race" cam that didn't like to idle below 1200-1300 (and I wish I still did, that engine ran great at higher rpm).

I don't see that anyone mentioned valve lash. Having a valve too tight can make them idle rough.

Another unlikely but possible problem is a float valve that doesn't quite shut off when hot, or a float that doesn't quite ride high enough. But those should show up as rich mixture when the problem is happening.

 

[Member 10617]

Randall,

I recently had the tachometer rebuilt, so I assume it is accurate.

At 900-1000 RPM, my car doesn't die at stop signs (or stop lights), and even at about 700 RPM, although it sounds a bit sick, it doesn't completely stall out.

Oddly, the idle is not bad at all when I stop momentarily for signs and lights while running, but if I stop and idle for a minute or so for some other reason, it gets "sloppy." I'm hoping the work I intend to do on the distributor and the carburetors, including the floats, will result in improved performance.

The last time I took the car into the shop, they found that a valve (all of them are new because the engine was rebuit) was too tight. But the fix them made didn't affect this irregular idle problem.

Another -- possibly related -- problem is that the car will diesel on me at times, especially if I have been driving at low RPMs for a few moments before shutting down, like driving into my driveway.

The flip side of all this is that the car has fantastic pickup on the road and runs a smooth as it ever has. It really feels like a new car when I'm doing 45 to 55 mph (my upper limit).