Author Topic: Stuck Choke / Rich Mixture  (Read 1137 times)

Offline Rosebud

Stuck Choke / Rich Mixture
« on: July 29, 2017, 06:43:50 PM »
I noticed an unusually strong exhaust smell a couple of weeks ago. When I inspected the spark plugs I discovered that my formerly golden brown plugs and tailpipe have become black and sooty. Turns out that the choke mechanism on the bottom of one of my SU HS4s isn't fully releasing after engaging the choke. My carbs were new 4k miles ago so I shouldn't think they're in need of rebuilding.

Question #1: What's the best way of freeing the sticking choke mechanism? I can push it back into place but it still hangs up about one-eighth of an inch after pulling the choke knob again. Can I clean and lube it in place or do I need to remove and clean & lube? What kind of lubrication; silicone, oil, grease, dry graphite?

Question #2: All 4 plugs are equally sooty. I would expect that only the two plugs fed by the offending carb would be sooty. Maybe both carbs are running rich?

Because all 4 plugs are sooty I thought I better make sure both carbs are properly adjusted. I have never done this before. I synchronized the carbs using a Uni-Syn device and I'm now ready to adjust the mixture. Following Haynes, it says "To begin, press the piston lifting pin upwards." It goes on to say that "the pin is omitted on later models." Swell.

Question #3: From the diagram it looks as if I should easily see and/or feel the lifting pins. I cannot, so I'm assuming my carbs don't have a lifting pin. Now what? Haynes doesn't offer any help beyond telling my to press the nonexistent lifting pin. How do I go about adjusting the mixture w/o a lifting pin?

Thanks!
Rosebud
...the sled, not the flower
https://www.facebook.com/PoserMotorSports

Offline MiniDave

Re: Stuck Choke / Rich Mixture
« Reply #1 on: July 29, 2017, 06:55:41 PM »
Instead of a lifting pin, use a 1/4" blade screwdriver and insert it under the dashpot (air filter off), then rotate it from horizontal to vertical - that does the same thing that the lifting pin does.

I would spray a little Kroil on the choke mechanism and operate it with the choke knob and see if it frees up.....any penetrating oil should do it. I'd spray some carb cleaner on those plugs and blow them off before reusing them

With the balance tube in the manifold between the carbs, I would expect them to all be pretty much the same after a run....as that's what it's for....to balance the mixture somewhat..... you have two carbs as much for more airflow as anything.
1989 Cooper Racing Green
2009 Clubman S
1969 Jaguar XK-E FHC
2004 Audi Allroad 2.7 TT

Offline Rosebud

Re: Stuck Choke / Rich Mixture
« Reply #2 on: July 29, 2017, 07:12:47 PM »
Instead of a lifting pin, use a 1/4" blade screwdriver and insert it under the dashpot (air filter off), then rotate it from horizontal to vertical - that does the same thing that the lifting pin does.

Thanks Dave. That was exactly what I was looking for. I recalling seeing the screwdriver method on YouTube but I didn't make the connection. BTW: I purchased Rosebud in your very city 10 years ago. What are the odds?
Rosebud
...the sled, not the flower
https://www.facebook.com/PoserMotorSports

Offline MiniDave

Re: Stuck Choke / Rich Mixture
« Reply #3 on: July 29, 2017, 07:15:34 PM »
Wow, who did you buy it from, I may know them......
1989 Cooper Racing Green
2009 Clubman S
1969 Jaguar XK-E FHC
2004 Audi Allroad 2.7 TT

Offline Rosebud

Re: Stuck Choke / Rich Mixture
« Reply #4 on: July 29, 2017, 07:31:17 PM »
Wow, who did you buy it from, I may know them......

Rick Goetz. Know him?
Rosebud
...the sled, not the flower
https://www.facebook.com/PoserMotorSports

Offline MiniDave

Re: Stuck Choke / Rich Mixture
« Reply #5 on: July 29, 2017, 08:08:38 PM »
Yep!
1989 Cooper Racing Green
2009 Clubman S
1969 Jaguar XK-E FHC
2004 Audi Allroad 2.7 TT

Offline Rosebud

Re: Stuck Choke / Rich Mixture
« Reply #6 on: July 29, 2017, 10:33:34 PM »
Yep!

Wow, that's quite a coincidence. If you see Rick, tell him I said hello. And thanks again for your help.
Rosebud
...the sled, not the flower
https://www.facebook.com/PoserMotorSports