TR2/3/3A Slight surging at Idle?

[karls59tr]

Hello all Can anyone advise what carb adjustment needs to be done to settle a few hundred RPM surge at idle?
Karl

 

[CJD]

Generally, a smooth but surging idle is a sign of being lean. Try unscrewing the nuts a flat or two and see if it helps.

 

[Madflyer]

Yes CJD sounds lean. Is it more at start up or at temp. It could be a vacuum leak. What does it do when you open the oil fill cap on the rocker cover ?? does RPM change and up or down. ??

 

[sp53]

you car does that with the filler cap?

 

[Madflyer]

Yes you lose vacuum mix goes off dis loses vacuum timing changes. It may not be your problem it is just a test I do you can gain or lose 200 RPM. It tell me two things timing a bit off and or mixture off. The RPM will always change. If the RPM goes down maybe 50 RPM your about right.

As to your problem look at your fuel pump

 

[Graham H]

That's a new one on me?

Graham

 

[karls59tr]

I haven't done the filler cap thing yet but I believe the slight surge issue is due to the fact that I did not renew the throttle shafts when I rebuilt the carbs. The car runs fine otherwise. I have to keep the idle up around 1200rpm or she stalls out at lower idle but that just might be an inaccurate tach. CJD: I'm reluctant to richen the mixture as the plugs really foul up if the car idles for any length of time. (Might be the fast road cam contributing to the fouling as someone I talked to with a cam said their car runs "pig rich" at idle!).
I have done the old school "plug checks' at the side of the road and the plugs are a nice tan color around the center electrode so the black powdery carbon does burn off after a good run.....still powdery around the threaded insulator though.

 

[CJD]

Our TR3's just use road draft for the crankcase ventilation, so removing the oil filler cap doesn't really affect mixture like on later cars with a PCV system.

Karl, if you have a hot cam with long duration the idle roll will be normal...along with the need for a higher idle.

 

[sp53]

I think you will find Karl the surge is air coming in from a secondary source, like the throttle shafts. This throws fuel air adjustments off too much and makes adjusting the idle down very difficult because it is sucking in too much air no matter what. Basically you end up chasing the timing back because the engine is trying to increase RPM with the extra air and setting the fuel up to get the proper adjustment for the extra air mixture with fuel makes for more fuel at idle to run correctly.

 

[karls59tr]

I think you will find Karl the surge is air coming in from a secondary source, like the throttle shafts. This throws fuel air adjustments off too much and makes adjusting the idle down very difficult because it is sucking in too much air no matter what. Basically you end up chasing the timing back because the engine is trying to increase RPM with the extra air and setting the fuel up to get the proper adjustment for the extra air mixture with fuel makes for more fuel at idle to run correctly.

This may sound like a redneck fix but ....what if nitrile or rubber O rings were epoxied flush to the carb body where the throttle shafts enter the carb body? A drop of oil where the O rings sit on the shafts. Carbs are now sealed from intruding air!

 

[Madflyer]

Spraying a non combustible fluid around your carbs and shafts, if RPM stables will confirm leak. and hot cams can lope at idle. those cams are for high RPM's and the above is correct higher RPM need at idle or may may dog out of the whole. Listen to a dragster motor full gas then clutch. Our LBC are happy to run at 2000 RPM's and peak at 4000 RPM low RPM are not efficient above will go flat so we add a cam say changes the curve. My TR 6 has a cam that comes in at 3,500 RPM on paper and you can feel it so 1200 at idle. There is a system to all this that our old cars were left behind todays cars adjust many times a second. We set it up for the middle and drive on.

 

[sp53]

Should help some and I think I tried it. Extra air getting in is the same as giving the car a little gas at the pedal. That is all the gas pedal does is let more into mouth of carb. I found to get the idle down the distributor needs to fully return and there can be no air getting in except at the carburetor mouth.