MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

TR parts and Triumph parts, TR bits, Triumph Car Spares and accessories are available for TR2, TR3, TR3A, TR4, TR4A, TR5, TR6, TR7, TR8, Spitfire and Stag and other TR models are available from British car spares and parts company LBCarCo.

Triumph TR6 - Idle too high

I just rebuilt the Stromberg’s on my '73. I replaced the bypass valve diaphragm, cleaned and calibrated the temperature compensators. All is well except the idle seems to have a mind of its own. With the idle screws backed all the way out the engine idles from 1000 to 1500 or sometimes higher. I rechecked the bypass valves to make sure they went back together correctly. Cleaned and lightly sanded (emery cloth) the sealing surface on the body. No change. Then, I re-installed the old bypass valve to see if that made any difference. No change. When the engine idles at 1500, I can cover one carb inlet and the RPM's will drop to under 1000. But, when I remove the cover the RPM's will slowly increase. Any ideas from all the experts out there??? Thanks, Bob
B Selby

Hi Bob

Are you aware of this site? Three sections on TR6 carbs.

Ken

http://www.sterlingbritishmotoringsociety.org/resources.htm
K. T. Shaddock

Will pulling up on the throttle linkage make them idle down? If so, the butterfly's are sticking. Did you replace them and the spindle seals?

BB
Brent B

Pulling up on the trottle linkage has no effect. One BF was replaced and all the spindle seals were replaced. Testing the seals with carb cleaner does not indicate any leaks. Yes, I have the three articles that were originally published at Buckeye Triumphs. I followed those steps in my rebuild.

I have even run the engine with the throttle linkage completely disconnected from each carb. With the butterfly closed, the only path (I am aware of) for gas to enter the intake manifold is via the bypass valve.

I must admit that this problem did not arise until I rebuilt the carbs. I wonder if the old bypass valves were stuck closed. Assuming the new valves are closed I can not see any other evidence of bypass.

I have heard of some owners blocking off the bypass valve ports to eliminate this problem. This would have almost the same effect as the stuck bypass valves. Has anybody tried this?

We have a club drive tomorrow AM - I may try that tomorrow afternoon.

Thanks for you help
Bob
B Selby

Bob,

Are you sure the throttle plates are seating properly on both carbswhen the throttle is released?

Did you air flow balance them?

There is a procedure to set the by pass valves. Did you try that?

Did you replace the needles and if you did are they adjusted.

The temperature compensators have a small seal. Did you replace them and are they seating properly?

As I suggested with Bryn, did you dismantle the choke mechanism and did you install the disc in the right orientation?

You may want to check the timing. It may be out since you rebuilt the carbs.

When I rebuilt my carbs. I had a devil of a time getting the timing and idle set. It was a back and forth activity but once I found the spot, it ran like a top.

Hope this helps.

Mike Petryschuk
Michael S. Petryschuk

For what it's worth - I had to disable the by-pass valves & the temp compensators to get the idle down on mine. The 3rd carb doesn't have them anyway....

BB
Brent B

Mike, thanks for the suggestions. Some of those need to be rechecked. The bypass valve is the internal adjustment type.

We had a nice drive yesterday with a few other LBC, but the 1500 - 2000 RPM idle was very annoying. It will be a few days before I get the opportunity to work on this.

Brent, did you just make a gasket to cover the bypass valve ports? What problem do you think the temp compensators were causing?

Thanks, Bob
B Selby

Bob,
Yep - just made a "blank" gasket for the by-pass valves. The temp compensators seemed to be leaking through, too, even though cleaned & adjusted with TLC. So some thread sealer was put on the plug and the adjustment screw got a couple extra turns. Both "fixes" are reversable for when I become a DPO.

BB
Brent B

Hi Bob,

I had a very high unexplained idle in the spring, my 72 has a tube over to the timing advance that was off. Too much air, reconnected, back to normal, could it be that easy?

walter
Walter Dobbins

I should have mentioned this earlier...Since the heater core is rusted out and has been disconnected for some time I did not repipe the water thru the tube on the intake manifold. Instead, I plugged the 3/8 inch water outlet at the rear of the head, plugged the inlet at the back of the water pump housing and plugged the outlet from the thermostat housing that originally supplied the intake manifold water tube. With all that said, does the lack of the heated intake manifold have any effect on the high idle of the carbs?

thanks

Bob
B Selby

Bob
I would say the water path blocked off will not affect the idle..if your normal engine temp is good then it's fine blocked off.
I would look for a vacuum leak first and check the timing..if it's advanced the idle goes up.
Check the hose to the brake booster,carbs etc.
Assuming you find no vac leak..try backing off both idle screws till they don't touch the linkage..idle still high ?? then back the dist off slowly and see if it drops to say 600 -700 rpm then bring it up to 750 - 850 with the screws...you'll have to re-balance the air flow.
This is assuming you don;t have a timing light.
Go for a drive and see how she runs

Charlie
Charlie B.

Thanks for the input, Charlie.
I did stumble on one small vacuum leak I think. Since blocking off the bypass valve ports I have been able to drop the idle but need to retard the timing a bit - she is now around 10 deg ATDC and is backfiring a little. I don't have the flutteriing noise in the carbs any more, which makes me think the bypass valves were the source of the fluttering - could those springs be weak? At this point I suspect that the bypass valves were allowing too much gas to bypass causing the higher idle and the richer burn. I have the metering needles backed out about 2 1/2 turns. 3 turns and they fall out. We will be re-torqueing the head and resetting the valves after lunch and then adjusting the carb and the timing to see if we can run without the bypass valves. Will update this later today.
thanks again.
B Selby

The by-pass valves keep the idle high by allowing air to go around the butterfly's. Another thing to check is pull the vaccum line off the carbon canister and block it off with your thumb. OK - a finger will work. If the idle drops with the line plugged off that's your source. I had 2 pieces of toothpick as restrictors in the cannister at one time. Those are gone now. I routed the valve cover line directly to the carbs. Only the gas tank vent goes to the cannister.

BB
Brent B

Another thought..make sure one (or both) of the choke linkage and the fast idle screw at the cam is moving away when the choke is pushed in...it doesn't take much to speed up the idle if it sticks.

Charlie
Charlie B.

After re-torqueing the head, we increased the bypass valve tension adjustment. The engine ran very rough with the bypass valves removed and the ports blocked. So, the bypass valves were disassembled and the adjustment screw removed from inside the cover and then adjusted to raise the back stop for the spring. Increasing the spring tension eliminated the flutter that we had heard. The old bypass valve diaphram was likely stuck in the closed position. She now idles down much better but sometimes the throttle shaft does not completely close. I am ordering new trottle return springs.

Now, I am still running rich even with the metering needles backed out 2 1/2 turns. Only theory for this is that the seat and metering needle have "worn" over the years and the clearance has increased out of the adjustment range. The seats do not appear to be easily replaceable, but I'm sure someone on the web has found a way. I may have to put up with this until I have an extra grand to order the throttle body electronic fuel injection conversion. If you have not yet seen this check out www.sidedrafttbi.com
B Selby

This thread was discussed between 20/10/2006 and 27/10/2006

Triumph TR6 index