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djwarner

Solution to Creeping Mixture/Idle Speed Screws

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I've had a continuing problem with the idle speed or mixture screws changing position over time despite the spring tension to hold them. Thinking back to the days when all cars had carbs, this was a common cause of deteriorating idle between tune ups.

 

As polution controls became common, the idle mixture screw was set at the factory and locked in place with a non-removable cap. But these are impossible to find today.

 

I envisioned making my own caps out of plastic when it occurred to me that a similar piece already exists in the form of electrical wire nuts with shrouds. I purchased some at Home Depot - 2 to 5 # 14 wire size. I punched out the spring locks from the back side with a 1/8" punch and trimmed the shroud to match the screw surrounding. My idle speed screw has a hex head instead of a knurled screw head, so I cut a slit in grabbing area to weaken it.

 

Here is what I came up with:

post-26587-0-16400200-1439568524_thumb.j

post-26587-0-98901800-1439568556_thumb.j

post-26587-0-28624500-1439568590_thumb.j

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I know, I know - Weber DGVs are neither fish nor fowl, but the came with the car when I bought it. I've been reading in this forum how these carbs are for family sedans and taxicabs ever since. But to date no one has offered a free set of SU's and associated linkages, air cleaner, etc.

 

I will have an interesting post about recent modifications in another posting.

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I've had that problem on numerous different brands of carbs. Holleys were a particular problem.

 

Edit: The solution I used is to use Loctite " Green " #290  Blue #220 This is a wicking compound of low strength. It is designed to be used on pre-assembled fasteners. It works excellent on idle screws. Prevents, the setting from changing from vibration, but still allows adjustment by operator.

 

http://www.henkelna.com/industrial/green-threadlockers-pre-assembled-wicking-13227.htm

Edited by Chickenman

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I'm no expert on the topic, but the green 290 is not a low strength lock. It's actually a "medium/high" strength wicking lock. I think if you use the 290 and get it applied correctly, you could be very sorry. I'm think the wicking grade 220 blue would be a better choice if you were convinced that you needed a wicking grade.

 

http://www.henkelna.com/us/content_data/339213_11656_LT4985_ThreadlockerGuide_v6_F_LR.pdf

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My Bad. You are quite right. Looking in my Toolbox I see that it is Loctite #220 that I use. The wicking action is nice, as you can just set the mixture screw and then apply the Locking compound without disturbing the setting.

 

I got confused as the Loctite Web link lists wicking formula's as a Green color, but when you go to the actual page, it separates them into Blue ( #220 Low strength ) and Green ( #290 Medium-High strength ) colors. Good catch!!

Edited by Chickenman

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Yeah, I only know that because I made the mistake of using the wicking green once on a small screw and then tried to take it apart without heat. Prior to snapping that screw off, I had always assumed that red = high, blue = medium, and green = low. Not so. And I paid the price. :o

 

Interesting that on the page for the wicking grades they say that it's easy removal and ideal for small screws. What I think they mean is: "It's easily removable with the application of heat", and "It's ideal for small screws because you don't have to hold the small screw in your hand and make a mess out of everything trying to apply the locker to the screw threads before assy. You can apply it after assy which might make it easier to apply." That's my read anyway.

 

I agree that the wicking grade is the best choice for the carb stuff so you can apply the thread lock last after you have all the adjustments made where you want them. But I do think if you don't any of the wicking stuff, the ubiquitous blue medium strength non-wicking grade (blue 242?) would probably work OK instead. Take the screw in question partway out and put some on the exposed threads and then quickly try to get it "close" to where you ultimately want it before the threadlock sets up. Then after that point, do your tuning. It won't hold as well, but I'm thinking it would probably be good enough.

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