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Idles too high to keep running

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voxboy Avatar
voxboy Silver Member Jeffrey C
Lynnwood, WA, USA   USA
Hey everyone. So, I need some advice...

I've done a lot of engine work over the past couple weeks. Everything is back on the car but now, when I start it, it idles higher and higher until I have to shut off the engine after 3-5 sec.. It was obviously not doing this before I started working on components in the engine bay. I'm sure this is user error as I have never worked on a TR6 engine. The obvious culprits are the carbs. I did my best to remove them intact from the manifold where they sat on my work bench for 2 weeks. I'm relatively confident I put them back exactly as I found them.

Is there something I didn't reconnect? Does it have something to do with the vacuum lines?

Also, If I disconnect the vacuum lines form the carburetors, it makes a marginal difference but I still can't keep the engine running for more than 5 sec.

Here's what I've replaced/repaired...
- New coolant system including aluminum water pump housing, thermostat, heater return pipe, and hoses
- Intake manifold was taken to a machine shop where it was acid washed and cleaned out. The coolant path was totally clogged.
- The heater was disconnected when I bought the car so I also put that all back together.
- New coil (Lucas GCL110)
- New alternator (Lucas Type 17ACR)
- Rebuilt distributor (has both advance and retard)
- Rebuilt radiator
- Rebuilt fuel tank (I haven't re-installed the trunk panels because it looks so good!)

Thanks everyone.

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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
I'm thinking too rich on fuel AND a vaccum leak.

Krom Avatar
Krom Paul K
San Rafael, CA, USA   USA
Jeffrey- although your post doesn't say so, if we operate on the premise that you are running the stock Stromberg carbs, check your linkage first. I say that because you are able to start the car, but it is running at high speed instead of a civilized idle level. Refer to your repair manual (you must have one to repair this car- Either Haynes or Bentley) or look at the diagrams on The Roadster Factory website. It is very simple to reassemble the manifold and carbs and get the linkage put together in such a way that your car runs at a super high idle. The carbs (and there are some people on this forum who really know about these carbs- much better than I) should have the throttle assemblies (that rotate on the side and operate the butterflies/throttle plates) bottoming out on their set screws at idle. Just start with the lever that is operated by the throttle pedal and see that the entire mechanism works freely, then report back.
PK

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voxboy Avatar
voxboy Silver Member Jeffrey C
Lynnwood, WA, USA   USA
Paul, thanks for the reply. I disconnected the throttle pedal and inspected the linkage. Everything appears fine. The throttle assemblies move freely. I took a look at my Bentley manual. There's no fault diagnosis about extremely high RPMs when starting the car. I'll keep looking online.

I raised the carb pistons as high as they could go and held them in place with a couple screwdriver handles while starting the car. Wouldn't start. Don't know if that helps.

Thanks again.

barry s Avatar
barry s Silver Member Barry Stoll
Alexandria, VA, USA   USA
1972 MG MGB GT
1974 MG MGB
1976 Triumph TR6
1980 MG MGB
You might look for an intake manifold leak, with your refurbished manifold.

poolboy Avatar
poolboy Ken D
Sandy Hook, Mississippi, USA   USA
You have a 69. Is the PCV valve firmly installed in the intake manifold ?
How about the banjo fitting; is it screwed in and both side nipples either connected to the pipes or if not are they tightly sealed or capped off and is the hose to the brake servo connected to the large center nipple ?

voxboy Avatar
voxboy Silver Member Jeffrey C
Lynnwood, WA, USA   USA
Ken, thanks for the message.

I literally can't keep the car running for more than a few seconds. I checked the manifold and torque settings for the intake manifold and it all appears tightly sealed.

When I took all the pieces off my intake manifold, the PVC valve was a bitch to remove because someone had used some kind of adhesive to attach it to the manifold. I have since cleaned it but now it doesn't attach firmly at all to the manifold. It does not screw on and I have no idea how to properly seal it.

The banjo fitting is firmly reattached. Both side nipples have tightly connected pipes. There is a vacuum hose coming from the retard on the distributor to the piping underneath the front carb that routes up to the right side of the banjo fitting. And as you can see in the pic, a vacuum hoses comes off the distributor advance to a T-divider and connects to the top of each carb.

The hose from the brake servo to the large center nipple is also firmly attached.

Is there any vacuum troubleshooting you'd recommend?

I've attached a couple pics. Hope they help. Thank you!

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dsixnero Avatar
dsixnero Dan Colanero
Westville, New Jersey, USA   USA
Jeff, make it simple, plug off all vacume lines, set dist. to 10 btdc static. Forget retard and advance for now, focus on carbs.

poolboy Avatar
poolboy Ken D
Sandy Hook, Mississippi, USA   USA
Looking at those pictures I see you've 'taken some liberties" with the emission plumbing.

For instance...I do not believe the nipple on the top of the rear carb is active.
Usually on 69 carbs, it's just a threaded, blind hole with no opening to the vacuum.
Verify by sucking on it compared to sucking on the nipple on the front carb.
Compare it to the illustration in Moss.
BUT..the real problem might just be the PCV valve connection in the intake manifold.
That if not tightly sealed could produce a MASSIVE vacuum leak causing the rpms to run wild.
Get a rubber cork or something that you know you can plug that hole tightly and completely and see if the rpms come down.

AND make sure the clamps on the bottom manifold studs are spanning across BOTH the intake and exhaust manifold flanges.



Edited 1 time(s). Last edit at 2017-10-27 09:06 AM by poolboy.

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voxboy Avatar
voxboy Silver Member Jeffrey C
Lynnwood, WA, USA   USA
Ken, thanks for the reply. I wish I had enough knowledge with TR6 emissions to take liberties, but all were done before I bought the car. But you're right. I took a look at the illustration in Moss and see that there is no vacuum hose connected to the rear carb.

I think you might be on to something with the PCV valve. I'll plug it up and see what happens. If that is, in fact, the problem, how do I connect it to the manifold? There are no threads.

I'll also check the the clamps on the bottom manifold studs.

Thanks so much for your help, Ken.

Krom Avatar
Krom Paul K
San Rafael, CA, USA   USA
Fellow Members- Jeffrey poses a good question- how is the PCV secured in the early manifold? I've never removed mine, so I don't know. Is it a press fit, or is some adhesive required?

voxboy Avatar
voxboy Silver Member Jeffrey C
Lynnwood, WA, USA   USA
A quick update: I plugged up the PCV and started it up. It idled around 3000 rpm for about 5 secs before slowly climbing until I had to shut off the car. It was a different response so I was happy to see some kind of change. The intake manifold is properly secured to the engine. Just for the heck of it, I plugged the holes on the carbs where the air filter normally goes and, sure enough, the car would not start. I then plugged them individually with equal results; the car sputtered but never fully started. I can lift the carb pistons with some force and they properly fall back down. Also, the exhaust manifold gets pretty hot even after 5-10secs of the engine running. Granted, it raving super high but I thought I'd mention it

Questions:

Did I do something to my carbs by laying then on their sides for two weeks on my workbench? My throttle linkage seems to be hooked up correctly. I can give it some gas (very carefully) and it will rev higher.

Also, there is a lot of air blowing out of the valve cover hole that normally has the hose connected with PVC going to the air filter. It's a bit smokey but doesn't smell like much. Is this normal?

I had also replaced the coil and alternator (upgraded to a Lucas 17ACR and had to change the wiring). Would that make any difference?


Thanks everyone. I'm just about ready to tow it to a repair shop. I'm quickly running out of ideas.

poolboy Avatar
poolboy Ken D
Sandy Hook, Mississippi, USA   USA
Sandwiched between each carb and the intake manifold there should be a thick insulator with a thin gasket on both sides of the insulator. Do you have those in place ?
If so the only other thing I's suggest is to undo the couplings that connect the carburetors' throttle shafts to one another so that both carbs are independent of one another..
Then back out both throttle stop (idle speed) screws until their tips are barely but equally exposed, then turn both screws one complete turn in the clockwise direction and see if you can start the engine...

Krom Avatar
Krom Paul K
San Rafael, CA, USA   USA
Jeffrey- this may be redundant, but I want clarify your comment about plugging the PCV. Did you actually seal it back in the manifold, seal the manifold while leaving the PCV disconnected, or leave the manifold where the PCV fits open while plugging the PCV itself?
I'm not sure the point is completely clear, but eliminating vacuum leaks is the intent. Presuming you have ensured that the rubber diaphragm in the PCV is intact, you might get just enough teflon tape wrapped around the base of the PCV to make it a press fit in the intake manifold. That should eliminate, if only temporarily, a potential vacuum leak.
As Ken has mentioned, each of your Stromberg carbs has a throttle plate that should be closed at idle. With your air cleaners removed, confirm the throttle plates are closed. The shafts that run through the throttle plates (a brass shaft) are connected between each carb by a flexible coupling. If you loosen the small nuts on the couplings slightly, each carb will work independently. Ensure that the throttle stops on each are operating and are set as Ken has described. If you loosen the flexible couplings, when you depress your throttle pedal, it should have no impact on the carbs themselves, but the linkage will continue to flex.
If after all this, you restart and have super high revs please report back.
PK

rjc157 Avatar
rjc157 ralph c
pearl river, new york, USA   USA
If you undo the fast idle screw and the butterflies are closed can't see hoe the idle will rev so high but anyway if the car isn't concourse just get a later model manifold and eliminate all that bullshit emissions

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