69 E Type High Idle

I got my last problem fixed ( see sputtering E-Type) several weeks ago and we have taken a couple of day trips with everything running well. Last week I pulled the car out of the garage and removed the radio/console to repair the wire from the radio to the drivers side speaker then drove the car back into the garage. All uneventful. Yesterday after replacing a couple of instrument panel light bulbs I started the car and as soon as it caught it shot up to 3500-4000 RPM and would not come down. I have checked both the operation of the choke mechanism and the throttle linkage, both seem to be working properly. What's my next step?


Thanks,
dj

Something is jammed in the linkage. I would disconnect the rod from the triple carb shaft, tie the shaft to idle with a spring (make DANG certain you didn't go full, wide-open throttle), start it up.
If idle normal, start looking for something jamming, carpet, wire, insulation.
Work the rod you disconnected up and down to check for free movement.

I agree - have another look at the throttle linkage. That Rube Goldberg (Heath Robinson actually) configuration on a LHD car has lots of places that can bind.

If you still think it is not binding you can remove the air intake plenum (two wing nuts and the 3 clamps on the air filter can) and take a peek into the carbs. You can lift the piston and use a flashlight to look at the butterflies (throttle plates) and see if they are closed when the throttle is at rest (they should be).

While you're peering in there you might also see what they look like when the throttle is fully depressed (engine off of course) as it is not uncommon for the linkage to get so far out of adjustment that one does not get full throttle when the pedal is floored.

I'm thinking you have 2 Stromberg carbs but it is best to mention what carbs are on there when inquiring about that system as many have converted to the triple SUs -- though in this case the pursuit of a solution is pretty much the same.

Linkage appears to be fully functioning. Linkage to the secondary throttle is secure and secondarys are free to rotate. BTW, yes I have dual Strombergs. Carb pistons move up and down with little effort and while holding them up, the throttle plates appear closed. Choke cable functions and choke plate at the end of the cable rotates. However working the choke plate with my finger there was a significant difference in the feel. One felt very smooth almost no feeling at all, the other had a scratchy grindy feel to it. Not exactly sure how this works but whats the chances of having a choke stuck partially open? It would fit the sequence of events.

Thanks
dj

That is a possibility.

When I got my car the PO had worked on the carbs and like everything else he attempted to get it ready to sell he did it exactly wrong.

Who knew you could assemble the choke backwards? That plate with the little holes can go on either way. I had to start it with no choke and add choke to keep it running. Drove me nuts until I took those assemblies apart to see what was wrong.

Certainly worth examining both of them.

I would also check to make sure that you have no vacuum leaks. Take a can of carb cleaner and spray around every gasket between the carbs and the head. If there is a leak, you will hear the idle speed change.

I feel like a bit of a dope because the cause was fairly simple. There are a couple of sort of wavery, springy like connectors (I love this technical talk) that connect the front and rear carbs. Somehow one of them slipped a bit resulting in one carb remaining slightly open when the other was closed down.

Now use a unisyn and actually balance them at a specific rpm

At least you found & solved the problem -- feel good about that. Those little accordions are pretty important -- as you just proved.

DonJ said:

Linkage appears to be fully functioning. Linkage to the secondary throttle is secure and secondarys are free to rotate...

Click to expand...

BTW - In case you don't know: Many owners just prop those secondaries open to leave a clearer intake path. They swear it is an immediate and noticeable performance improvement and I share that opinion having done that.

Later, when I had the manifold off, I took the opportunity to remove the secondary throttle plates and the shafts - plugging the holes of course. That is even better but most of the easy gain can be had with a simple 5-minute fiddle that holds them open all the time.

Here is a post by Pete Crespin with specifics and some follow up on the '5 minute fix':

https://forums.jag-lovers.org/av.php?1546489n69