Wow ! Another TR3 'daily driver', and right down the street from me ! I
live in Lakewood, and drive between Long Beach and Paramount every day on my
way to work in Redondo Beach in my TR3A.
Anyway, my idle probably wanders +/- 200 rpm from time to time, I never
worry about it too much and it always wanders back. The biggest effect
seems to be from under-hood temperature, but I've also noticed differences
from tank to tank of gas, I suspect from varying amounts of MTBE in our SoCA
fuel.
Some things to check :
1) Worn throttle shaft bushings can cause erratic idle. I'm not sure, but I
think part of the problem is that the throttle plate drags on the throat.
Before I rebushed the carbs, I had to always blip the throttle to get the
idle to come down. However, it may be that the shaft just leaks less when
it's seated against the rear of the bushing, and more when it's against the
front, since the gap would be exposed to manifold vacuum in one position and
only venturi vacuum in the other.
2) Wear in the linkage can cause idle problems. Particularly the round pegs
in the end of the links can wear oblong, so that if you tighten the
adjustment screw to snug them up (keep them from falling apart at
inopportune moments), they bind at the ends of the normal travel. The cure
for this is to replace the joints, but a work-around is to pull the return
springs on the carbs up tighter. Which of course makes the throttle shaft
bushings wear faster <g>
3) Vacuum leaks can cause high idle. The TR3/A doesn't have a lot of places
to leak, but check where the intake manifold meets the head, and where the
carbs meet the manifold. One way to check is to squirt some WD-40 on the
suspected area, and listen for any changes in engine speed.
4) Poor jet centering can sometimes cause erratic idle speed. If the needle
is binding against the jet, it can sometimes stick and hold the piston too
high, which will affect the mixture. If this is the case, you should
probably replace the needle and jet, as any wear will cause mixture problems
(which can be a source of overheating problems).
5) You might check the valve clearances. My engine seems to sometimes idle
fast when its time to set the valves.
Randall
59 TR3A daily driver
65 Sports 6 project
et al
avhodge@iwon.com wrote :
>
> I have been driving my 1960 TR3 to work for the last 2 weeks.
> From Long Beach, CA to Paramount, about 5 miles each way.
> Tuesday the idle jumped up about 500 RPM. The choke does not appear to
> be stuck. I've had the car since November and put about 2000 miles on it.
> Any idea what might cause the idle to jump up?
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