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TR6 Strombergs with poor idle

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SherpaPilot

SherpaPilot

Jedi Hopeful
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I have a 72 TR6 that I have owned for 32 years. Over the many years of wrenching on this car, I thought I had a pretty good feel for knowing what to do when problems arose. During the winter, I purchased a complete rebuild kit for both Stromberg CD175s. Taking my time and following several references, I cleaned, rebuilt and reassembled both carburetors on the car. Adjusting these guys was quite a chore and now 4 months of occasional work has produced a fair result but not without nagging problems. I continue to have an erratic idle. I checked and adjusted the valves, installed a new distributor cap, rotor and wires. Replaced the entire fuel line from the tank to the carbs to include a new filter. The carbs were set up IAW all the reading material I could get my hands on. The linkage was checked and rechecked. I installed a secondary return spring on the throttle return. Vacuum advance was plugged and timing set for 32 degrees BTDC. As far as adjusting fuel/air mixture, I could not get the air valves to perform as the books recommend, you know lift a little not to exceed 1/4 see it it accelerates or dies. Both carbs acted as if they were too lean. I am now adjusted 1.75 turns to the rich side. Overall the car runs great and acceleration is super. The only problem I cannot solve is the erratic idle. Once set for 850-900, it seems ok,, but as soon as the engine is loaded up on the road, it comes back with an idle range of 500 to 1200 rpm. What is going on here? Both temperature compensators checked and installed and both idle trim screws set to 1 turn counter-clockwise. I also tried the trim screws fully closed. Does anyone have any experience in fixing an erratic idle? As always, thanks for any input you can offer. Maybe I need to invest in a colortune. I forgot to mention that manifold vacuum at idle is 17 psi.
 
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Just a thought: Have you checked what the ignition timing is when the idle is too high or too low? That would at least help narrow down where to look.
 
*32 degrees", That may be it, 10 BTDC degrees would be more in the correct location.
 
Thanks for the response. I will check that out. I'm also suspecting an air leak somewhere or perhaps the crazy TR6 throttle linkage is still binding.
 
Greetings and thank you for the reply to my question. Yes, I understand the factory recommended timing (12 degrees) and have used that with the vacuum advance distributor for many years. Awhile ago, I read several articles as well as watched "University Motors" video (YouTube) on TR6 tuning and tried their advice of disconnecting the vacuum advance and advancing the timing to the new recommended setting. The theory was vacuum advanced was reduced IAW the distributor advance in order to meet US emission requirements. Some people don't like going beyond the factory settings but I thought I would try it. In my car, it seemed to perform much better. I ran the car this way for a couple of years. This crazy idle problem occurred after I did the rebuild on the Strombergs. I wish I had the spending cash to switch to a different set of carburetors. Thanks for your input.
 
That 30 to 32 BTDC figure is applied to the engine running at speed, not at idle. Let the engine warm up, then use the idle screws to bring the engine RPM to somewhere around 3500 RPM. Then turn the dizzy until you measure 32 degrees of advance. To do this you either need a 32 degree mark on the front pulley (for a standard timing light) or you use the zero degree mark and a "dial back" timing light set to 32 degrees.

Once you set the max advance to 32 BTDC at 3500 RPM, you lower the idle speed back where it is supposed to be and test drive the car. Accelerate too hard in too high a gear while listening for pinging and knocking. If you hear any, retard the timing in two degree steps and repeat your test drive until no bad sounds are heard.
 
The vacuum advance does very little compared to the centrifugal advance. So if you are running 32 degrees advance at idle, you are way over advanced at speed. I'm surprised the car can run at high RPM with the centrifugal advance working. dklawson is right on the money. Best to time the car by driving it and listening for pings than to time is at idle. Check the springs in the centrifugal advance. Mine had the wrong springs and was not advancing at all.
 
72 distributors shouldn't have a Vacuum Advance module. If the nipple on the module is pointing in the general direction of the cockpit, what you have there is the vacuum Retard module.
The problem you're having kind of sounds like a problem with the Throttle Bypass Valves.
Don't blame the carbs, per se though; afterall you said the problem started after you rebuilt the carbs....:rolleye:
 
Thanks for all the input guys, I truly appreciate it. I decided to put the car back into factory settings and see the results. There must be a ton of misinformation out there that is counter-productive. I have always had an inconsistent idle with this car. One of the reasons I elected to rebuild the carbs was because I suspected a worn throttle shaft leaking air. Guess I should have drawn a few thousand dollars from the bank and paid someone else to do this little job.
 
poolboy, I just read your personal message. Thanks for answering my questions. I'm anxious to get this project behind me.
 
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