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SOS: Carburetor screw likely in engine

Millertime

New Member
Joined
May 5, 2022
Total Posts
8
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Location
Denver, Colorado, USA
Idle rev still way too high, so I decided to look at the carbs again. Popped off the right carb today and low and behold, one of the throttle plate screws was missing. Not sure if this is the root cause, but this is surely a big problem regardless

Had a mechanic come work on the bike about a week ago and was able to watch everything he did. when he was putting the carb back together, I noticed the screws would not screw tightly. I pointed that out as a concern and he said "Dont worry about that at all, no way that thing comes out". Well, he clearly was wrong--and a horrible mechanic.

Since it is the throttle plate screw, I feel like the only direction the screw could have gone is into the engine. Really want to check with you guys before I do anything, however. Where should I start?

Secondarily, it looks like I will need a new throttle plate and screws. Have looked quite a bit and it doesn't look like any of the carb rebuild kits available on the internet have plates. Any and all help is appreciated.
 
I would start by looking in the intake and sparkplug hole. It might be worth getting a cheapo boroscope that works with your phone. Or you could fish in the hole with one of those bendy magnet rods - I'm assuming the screws are magnetic. I would definitely want to make sure it's not in the cylinder before turning the motor over.

You may need to look on eBay for a used throttle plate. It's sometimes worth buying a parts only carb body for things like this.

It'd be a good idea to add your bike model/year to your signature. What model is it?
 
There's a good chance the screw made it all the way thru into the exhaust, at least I hope it did. The screws are magnetic so a small wand extendable magnet thru the plug hole and in the intake port would be good to try.
The bore scope would also be a good check.
You might remove the other screw and use it in the other hole to tighten and verify if the shaft threads are stripped in which case a fresh shaft will be needed. That also allows you to measure the screw for length and diameter. Small screws are available from https://belmetric.com/search-result/?search_query=JIS
Look at the edges of the throttle plate for any damage, damage means replacement.
 
There’s also a thread on here about different types of loctite/threadlocker.

If you can re-stake the screws like they did at the factory, that’s ideal. Be *very* careful not to bend the throttle shaft.

Otherwise I’d stick to the purple version. Some prefer the red, but you’ll be quick to ruin the head if you forget it. I’m still not clear on the breakaway torque when heated either.

They’re very small screws.


-Ed
1972 CL350
1985 VF700F
 
If the screw was ingested while the engine was running, I would quit looking for it. It either made it through or is already digested. Not likely to be found either way.
 
Miller - I have a box of carb stuff. I *might* have a throttle plate in there.

I should be back at my garage on Thursday. I’ll make a note to look for it then.


-Ed
1972 CL350
1985 VF700F
 
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