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Discussion Starter #1
HOLY SMOKES FOLKS!!

Okay.. Today I replaced some VERY tired vac lines because I'm certain that they are original and were loose as can be. That's all I did. Now the engine idle is crazy fast and the idle adjustment screw won't bring it down to normal. It was running just fine before I changed 3.. stupid.. little.. vac.. lines.

Don't get me wrong.. I love this car but holy crap.. She's wearin me out.

HELP!

Thnx in advance to you brilliant people!! LOVE YA!

Phiilip
 

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Hmm... idle screw isn't lowering the idle?? strange. These cars as you know have lots of little gremlins. Holy crap is an understatement . My Idle is a bit high in my opinion but the mechanic turned it up because when i would drive at speed, say on the highway, then get off the exit and then lets say I arrived at a stop light, the **** thing would stall out, I didn't think turning up the idle was the solution but I guess its a lot cheaper than some other crazy solution. I digress. If you pull off a vac line does it stall?
 

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Discussion Starter #4
Hey Guys,
I did pull off one vac line and it did not stall.
And yes it did backfire a couple of times when I was trying to throttle it out of fast idle.

I'm gonna mess around a lil bit more later today and see what becomes of it.

Phillip
 

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I once accidentally disconnected one of the short U-shaped vacuum hoses from the carb and the engine would race on start-up and continue to rev above normal RPM and misfire or backfire if I pressed the accelerator pedal. Once the engine warmed up it would settle down to normal RPM and the misfiring ceased. I removed a couple of spark plugs and noticed that they had white deposits signifying a very lean mixture and that's when I started to look for vacuum leaks and discovered the disconnected vacuum hose. In my case it was one of the short U-shaped hoses between the weakening device and the carbs. Hopefully you have a similar issue which could be easily rectified.
 

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Discussion Starter #6
I once accidentally disconnected one of the short U-shaped vacuum hoses from the carb and the engine would race on start-up and continue to rev above normal RPM and misfire or backfire if I pressed the accelerator pedal. Once the engine warmed up it would settle down to normal RPM and the misfiring ceased. I removed a couple of spark plugs and noticed that they had white deposits signifying a very lean mixture and that's when I started to look for vacuum leaks and discovered the disconnected vacuum hose. In my case it was one of the short U-shaped hoses between the weakening device and the carbs. Hopefully you have a similar issue which could be easily rectified.
I'm experiencing the same thing. I checked the spark plugs and it looks like I'm running a little lean. I also put the old U shaped vac hose back on and didn't seem to change anything.
After a bit of warming the engine will settle down to a slower idle.. If this does not fix itself..I can live with it

Phillip
 

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Still sounds like you still have a vacuum leak somewhere, maybe the hose to the distributor advance mechanism or possibly the 2 narrow hoses that fit under the carb air intake. Another possibility is that your choke cam is sticking but that would cause black sooty spark plugs. The weakening device could also be stuck, you could try spraying some WD 40 into it as that sometimes helps free it up.
 

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When you adjusted the idle screw did u see the shaft move as you loosened it? If not you may have to adjust the linkage to the accelerator pedal to let the adjuster go down ,if it has no free movement
 

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Discussion Starter #9
Thanx for the heads up guys.. I'll do more sniffing around for vac leaks and possible linkage issues. I'll post my finding. :)
 

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There has to be something basic about this problem
Old vac lines car runs OK
New vac lines car does not run OK, so something along the way during the pipe replacement has introduced the problem. Run the car and spray WD40 around the lines you changed if you hear a change in engine revs then the lines or line is drawing in air and burning the WD40.
Are you absolutely sure you changed the vac lines and reconnected in the proper order?

Pretty certain as the problem has been introduced it will be a simple fix
 

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Logic would dictate that your observations are correct motorman. I'm just thinking out loud here and wondering if the carburettors had been previously adjusted to run as well as possible compensating for the old leaking vacuum hoses and may now need to be readjusted to the correct settings since the vacuum leaks have been fixed? I would be reluctant, however, to fiddle with the carbs until I was confident that the vacuum hoses were good and the distributor timing was set correctly.
 

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Discussion Starter #12
Okay Boyz and Girlz,

Here is an update..
I checked the timing.. It was Ok
Replaced that crazy U shaped vac hose between the carbs
Adjusted the carbs
Found the issue of the fast idle. I adjusted the choke linkage.
Now.. She.. Purrrrrs
 

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Well done Philip. Those choke linkages need an occasional light oiling (WD40 or similar) of the moving parts but don't get any oil on the choke cam face itself as this can cause it to slip. The accelerator pedal linkages need an occasional squirt of oil too. Happy motoring in your purrrring Silver Shadow, Larry.
 

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now since reading the solution to the problem, I think I'll give my linkages a squirt of oil and see what happens...see my previous post and tell me if you think this might help mine as well.

Thanks all
 

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Hi JohnnyC, It's good practice to occasionally lubricate the choke mechanism with a light oil (but not the cam face) and the accelerator pedal linkage between the carbs and the pedal too but I don't think it will solve your stalling issue. If your choke is not opening fully when the engine warms your spark plugs will probably have a black sooty appearance. Your problem sounds like it's something to do with fuel supply, maybe carbs not balanced or carb floats set too low but I'm only guessing. When you say that your engine idle was OK but the mechanic turned up the idle screw to solve your cutting out problem are you sure your revs were right beforehand? If you get a multi meter with a tach reading and attach the positive lead of the meter to the negative connection on the coil and the negative lead from the meter to a good earth you will be able to determine what the actual revs are, the manual states that the engine should idle at 650 RPM when warm with the choke fully open . I have my carb screw set to 600 RPM or slightly below that and that's where I think it idles best for my application but each engine has its own peculiar sweet spot in my experience.
 

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Also JohnnyC, check the breather hose from just below the oil filler cap to the top of the carb intake, there's a mesh filter at the lower end of this breather pipe which needs to be cleaned out occasionally.
 

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will do, once I tinker I will report back with what I find...I'm thinking of ordering the gauges to check if the carbs are balanced properly, I suspect not.
 

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On HIF7 carbs it's not generally considered a good idea to tinker with the mixture screw, the mixture setting is done at the factory using specialised test equipment and once set a cap is placed over the screw to stop people fiddling with it. If you mess with that you might never be able to set them right again without specialised CO2 measuring equipment. There's a nut on the lever between the front of both carbs that you can loosen to balance both carbs in unison, then carefully retighten the nut without moving the levers. Before you start give both carb pistons and the area in which they travel a good clean with methylated spirit or carb cleaning fluid and top them up with oil. Clean the carbs one at a time to reduce the risk of mixing up which piston goes in which carb as they are individually manufactured as a set. Also check that your air filter is in good clean condition.
 
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