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Idle too high

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RJS

RJS

Jedi Warrior
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Hey Everyone,

My idle seems a bit high (1,100 RPM) and can't seem to lower it. The mixture with the jet adjusting nut is spot on (I use a Colortune with great results). Throttle/idle adjusting screws are backed all the way off. Fast idle screws properly adjusted and not touching the choke/fast idle cam.

If I "blip" or "snap" the throttle the idle will drop to a nice 800RPM for about a minute. But, then slowly creeps back up to 1,100.

Could it be the float levels need adjusting or the float needles are leaking?

The ignition, timing and everything else are all within spec.

Thanks

Bob
PS: '66 TR4A with a pair of SU HS6's
 
If you have a high idle it means you are still getting air and fuel. Make sure you can cut off the air supply by first seeing that your throttle discs are adjusted right and covering the throat when the throttle is off. Pull the carbs off, Loosen the slotted screws , slightly and slap the discs closed with the shaft will seat the disc. Now you know that the carb will mechanically shut air flow off. Of course the discs are chamfered to seal the bore when closed . When you reassemble the linkages make sure they allow the discs to close when at idle. Now you at least know the carbs will shut off the air supply if nec. pointing to a vacuum leak if your idle still won't adjust down. I'm driving either a TR6 or TR3 to work today ! Hope yer doin' the same.
 
All good suggestions, but I think I would start by disconnecting the throttle linkage at the carbs, to see if perhaps it is binding somewhere and holding the throttles open slightly.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I'm driving either a TR6 or TR3 to work today ! Hope yer doin' the same.[/QUOTE]
Not me, it's my day off!

Got a TR3 rear hub off the shaft last night, gonna see if I can repeat the trick with the other side.
 
For what it's worth my 69 TR6 wouldn't idle below 1300 until I discovered the diaphram in the PVC valve was shot. After replacing it, the car immediately idled at 900 - 950.
Chris
 
Back in the day (mid-60's), my TR3A idle was an ideal 900 RPMs. My recent acquisition of a '61 TR3A is also idling high at 1200 RPMs. If my mechanic lowers it, I'll find out how and will post the results. Otherwise, I'm fine with it as-is.
 
I had that problem with my TR3. It may be that the jets are binding and not returning all the way once the choke has been pulled and the return springs are too anemic to pull them back. I temporarily solved this problem by adding an extra spring to the linkage connected to the horn bolt. The real solution was to replace the the dried out cork jet seals with lightly lubricated o rings. Once I did that I didn't even need the extra return spring and the idle always dropped back to normal.
 
I suspect it is too much air or a vacuum leak rather than too much fuel. With PCV disconnected, she idles at 900 RPM. But, this is with the idle/throttle screws backed off all the way already. So, there is either an existing vacuum leak or the throttle butterflies are not closing fully (throttle linkage misadjusted or butterflies need to be adjusted on the throttle shaft).

When I add the PCV back on (which is designed to be a controlled vacuum leak), the idle jumps to 1,100. Even still, I should be able to adjust that back down with the idle adjustment screws. But, that 1,100 is with the idle screws backed all the way off.

I will inspect further later today. Question, can I inspect to see if the throttle butterflies are closing fully by pulling the air cleaners and peering down the carb throat?

Bob
 
It's really tough to see that way. You really need a light on the other side of the throttle plate, so you can see where the light shines through.

You could try spraying a little WD-40 or carb cleaner around the carb bases and manifold/head joint with the engine idling. If the idle changes, you just found a vacuum leak.

But the "drops and creeps up" still sounds like something binding to me. If it's not the linkage, it could be that the throttle plates are not aligned properly, or that the shaft is worn enough to droop out of position.

Something else to keep in mind, your dash tachometer may not be exactly accurate. It's very common for them to read high when they get old.

The engine in my TR3 doesn't much like to idle below 1000 (indicated) anyway, so I just let it idle a little high. Some day I might investigate, but all I really care about is that it doesn't die at stop lights.
 
We seem to have a rash of these this year. Do you think the new fuels are causing havoc with the rubber diaphragms in the carbs?
Not a carb expert at all, just saying
 
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