Walbro Carb repair

[Peter Clare]

Can anyone advise me of the best way to retain the screw which holds the throttle butterfly to the shaft to prevent loosening due to vibration. I would normally use Loctite but don't want it to get into the bearing surface . There is nothing in the Walbro manual so I assume this is not normally dismantled , but I have some accident damaged carbs to repair.

[nickhenderson]

Hi Peter,
Walbro stake the back of the screw by machine at the factory to prevent loosening. No manual mentions removal, so marketing intend it to be a throw away and replace with new item.

Tinkerers though, like to dismantle things and often remove this screw for various reasons, plate modification, worn shaft etc. They often overlook the "staking" and just force the screw out, damaging the shaft thread in the process. Much better to use a Dremmel or suchlike to carefully grind the screw flush with the shaft (thus removing the staked portion) before removal with a good fitting driver.
Really the only way to refit is to use as you say, Loctite or similiar. I use a needle to place a droplet inside the shaft on the internal threads prior to re-fitting the plate and screw.

I then go and sit with the carb in my hand and operate the valve every couple of minutes for maybe 10 minutes!
Why?
To identify if the Loctite has wicked along the shaft and into the body. A freely operating shaft says no, but one that gets stiff says yes. This early detection then gives you the chance to quickly remove the screw and plate and shaft before it all sets solid!!!
Really you only need a tiddly bit of threadlock for it to work. Others apply it after screw fitment to the rear of the screw allowing it to wick in, but depending on viscosity used, thread fit, temperature etc, this method could be highly subjective.

I hope this helps.

[Peter Clare]

Thanks for your advice Nick - I'll follow your recommendations.