Q-500 Racing Discuss AMA 428, AMA 424, and any other variants of Quickie 500 racing

Carb coming lose

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Old 04-10-2008, 10:17 AM
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BUDMAN27
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Default Carb coming lose

Been having some truble with my Super Tigar .40 carb coming off in flight. The little half moon bolt has started to eat into the metal as you can see. My buds at the flying field have thier ideals on how to fix. Just wondering what you guys thought I should do other than buying new stuff. Thans in advance.
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Old 04-10-2008, 10:37 AM
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luv to race
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Default RE: Carb coming lose

Bond it in the case with high temp RTV, maybe JB Weld. There is obviously a tolerance issue. We are to guess that the carb is a lose fitting in the case hole.. yes? So..that gap should be filled. Does the little nut work itself lose during flight, allowing the carb to come out? Maybe use some red loctite on the nut after you tighten it up?
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Old 04-10-2008, 10:53 AM
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daven
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Default RE: Carb coming lose

Clean thoroughly and JB weld her in for good.
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Old 04-10-2008, 10:57 AM
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Default RE: Carb coming lose

No you don,t have to guess Randy. It is a little lose. I,m relucktant to use JB Weld ,because I used it on a Nelson outer shell before and it came apart. Maybe some good lock tight will do the trick. It just bothers me to see how much metal is geting gouged on the side of the carb neck. I wished Super Tigar would of done the same thing that OS did and put two screws to hold the carb on.
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Old 04-10-2008, 11:42 AM
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Default RE: Carb coming lose

Nelson "outer shell"? what's that...? are you talking about the muffler? If that's the case, I'd guess the surface wasn't cleaned well enough. Especially if the engine/muffler had been run before. The bonding surface would be extremely contaminated, and would need major cleaning if and expoxy was to adhere (JB Weld included). But in the carb area of an engine, raw fuel and oil would be easy to clean (as Dave recommended).

However, I'd try to use the little tightening bar that is in the motor. If the nut coming lose is the issue, loctite the nut and tighten the crap out of it. Did you notice if the nut works itself lose? I assume that when you land the carb is hanging out of the engine, right. And the little bar/nut thing is still there? If the little bar/nut is still tight... gluing the carb in may be the only option (other than just buying a new engine).
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Old 04-10-2008, 12:55 PM
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Ed Smith
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Default RE: Carb coming lose

It could be that the carb body is so worn in the clamp position that the locking bar will not lock it. As the lock nut is tightened it pulls the bar through too far and runs out of thread and locks against the end of the thread rather than the carb body. If you see what I mean.

Try wrapping a piece of shim around the carb body. You will be surprised what a piece of 0.002" shim will do. Or, a washer under the locking nut to push the nut away from the thread.

Or as Randy says, screw it, buy a new engine!

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Old 04-10-2008, 01:07 PM
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ChrisAttebery
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Default RE: Carb coming lose

Use 5 minute epoxy. Clean the parts thoroughly with acetone first.

In the early 90's I had a Picco 80 that was doing this on a regular basis. John Finch from RCBM wrote an article on speed secrets around the same time. One of them was that he glued his carbs in his motors because of the very problem you describe. I tried it and it worked. End of problem.

When you need to remove the carb just heat the case gently with a propane torch. The epoxy will soften right up.


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Old 04-10-2008, 02:07 PM
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Default RE: Carb coming lose

Hi!
If the carb comes loose ...then you haven't tighten the bolt enough! Also be sure you balance the prop.
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Old 04-10-2008, 04:04 PM
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Default RE: Carb coming lose

Thanks Chris I think out of all the salutions mention so far I like yours the best. Jaka I have the bolt tighten. If you look close at the pic (sorry its a little out of focus) you will see it has a gash in it from it beating the H out of it self. I just beleave this is not a good way to hold a carb in.
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