TR2/3/3A Mild street cam and Idle?

Anyone running a mild street cam and find they have to set the idle at 1200 rpm to avoid a some what irregular idle or is it just my car?

I've got a pretty lumpy cam (282°) and have to keep the idle at about 1000-1100 rpm.

I run a Kastner D Cam (284 duration) with a milled head and 87mm pistons. I can idle once engine is warmed up at 1000rpm but only after I had the carb bodies sleeved to avoid air leaks and installed a Pertronics in the dizzy. The Pertronics did the most for an improved idle. I'm running about 30 degrees advance as well.
JVV

My previous TR3 wouldn't idle below 1200 even with a stock cam!

"karls59tr"...as a matter of interest, did you have your engine and clutch assembly fully balanced

TR3driver said:

My previous TR3 wouldn't idle below 1200 even with a stock cam!

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Did you have to use the clutch and drive train to shut it off? Mine would run on terribly at anything over 900. (Perhaps that's why the manual gives instructions for ed-carbonizing?)
Tom

malbaby said:

"karls59tr"...as a matter of interest, did you have your engine and clutch assembly fully balanced

Click to expand...

No I didn't do the balancing.

It did have a tendency to run on sometimes. I just got in the habit of always letting the clutch out right after I turned off the switch (with my foot firmly on the brake). With a little practice, I got to where it was so smooth that I didn't know if it would have run on or not.

That engine definitely had issues. It was supposed to just be a temporary solution while I rebuilt another engine to go in, but somehow the rebuild never happened. And the "junkyard dog" was still getting.me to work and back every day when the car got totalled.

TomMull said:

Did you have to use the clutch and drive train to shut it off? Mine would run on terribly at anything over 900. (Perhaps that's why the manual gives instructions for ed-carbonizing?)
Tom

Click to expand...

I shut the TR3 off the same way Randall describes. It runs great otherwise so I don't want to mess with it. One day I do need to have the SU bodies rebored for shaft inserts...maybe that's part of the issue of a higher idle along with a non stock cam?

Could be, but 'performance' camshaft grinds almost always compromise idle quality. Optimizing the needle profile to match the cam can help, some, but higher idle rpm is usually necessary.

I don't know, but I suspect that modifying the timing curve for more advance at idle would help, too. I believe the stock curve is deliberately late at idle (eg 4 BTDC instead of 10 or 12), to help prevent kickback while hand cranking.

I doknow. If it runs on with no ignition...then one would think it could idle slower with the ignition on...right?

All those idling 1k and above...it's important to realize you are operating outside the idle circuit for the stock H6's. That could be compounding the idle issues if you don't mod the carb to take it into account. We used to drill the butterflies to let in the extra air so the butterfly would drop back to its intended idle position. Then it may take drilling the mixture passage for increased idle fuel.

Explain please as I've never heard of this for SU's and what mixture passage are you referring to? The Jet if drilled would provide additional gas flow across the full range of the needle I would think. Maybe changing the needle to one with more flow at idle would work. I don't know what other passages could be drilled.

My idle is at 1100 rpm's. 287 duration 89mm pistons and a lite flywheel. There is a noticeable
lump at idle. I kinda like the sound when driving thru a parking lot nice and slow. Even the Mopar Guys like the sound.

Des Hammill states the following as reasonable idle rpms in his book on Weber and Dellorto carbs: (He states that this info is appropriate regardless of carburetaion.)
:

Standard cams about 240 degrees duration and 30 degree overlap, 500 rpm; Mid performance cams about 265 - 270 degrees duration 50 degrees overlap, 800 rpm; medium performance cams about 270 - 290 degrees duration 70 degrees overlap, 1000 rpm; Racing cam 290 - 320 degrees duration 70 degrees overlap, 1200 rpm. He also states that modified engines require a considerable amount of spark advance, 16 - 18 degrees @ 1200 rpm.

I run a TR3 with 280 duration 70 overlap cam and high ratio roller rockers which give a mathematical lift of .427"lift @ valves. It has twin Weber DCOEs, milled head, and Mallory dual point ignition. It requires 32 degrees total advance and at least 16 degrees to idle at 900 - 1100 rpm. The car shakes a little at idle and will not run decently with less advance. It seldom runs on when switched off. I have run this set up for a good 20+ years.