[Carb's Idle-adjust screw/bolt] My Idle-bolt fell out!! Can I simply replace it?

[Cerberus]

tl;dr -- if your carb's Idle adjust screw just fell-out & got lost, but you have thousands of on-hand bolts & found one that "fits perfectly" and works, are you being dumb using it / should you still just bench the unit til you get the Walbro brand screw? (NOTE: this idle-screw doesn't work by simply pressing-into a plate upon CW turns, it's unique it has a perpendicular worm-drive-gear in the hole so when you bring the bolt in/out it moves that, so I'm guessing that "fits & works" isn't good-enough here....but also have no idea what part# to get from Walbro, have googled and got nowhere..

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My carb's idle-adjust screw fell out I imagine it's because I was using the saw for notching a large Pine I felled, I was tuning the saw so I had the carb-screws-plug off (which would've prevented this!) and was doing some on-job tuning, anyways I bucked a couple logs just fine, adjusted tuning, then felled the tree & began bucking, on my 2nd or 3rd buck it felt funny so I looked at it and found it was missing its Idle-adjust screw!!

Oddly enough, saw still works!! Go Walbro (and Mastermind, as this is his build except the top-end which I had to rebuild after I broke his top-end :/ ) But I do have to give it a stab of gas on startup, as-well-as keeping throttle at like 5-10% while it warms-up for 1-1.5min, after that it works (though it will fall-out from idling, but you could use it & go through a job with it)

Anyways I do have a replacement-bolt that's the "right size" IE width, pitch etc, but when I looked closer at the hole - and saw it was true/plumb wtih the carb - I realized the 660's idle-adjust doesn't work by pushing-into a throttle plate, but instead there is a perpendicular worm-drive-gear on the bottom side of the beginning of the Idle Adjust hole, so the screw's insertion/removal from the hole is driving that worm-gear....

My replacement bolt feels good but I'd hate to find, a week later, that I ruined my Walbro carb by using the wrong screw!!!

Thanks a ton, and if it helps this is a pic of the hole & the way I was seating-to-test a bolt

 

[Cerberus]

If you look closely at the (empty) Idle-bolt-hole on the carb in ^ that picture, in the front / bottom-left quadrant you can see a dark spot in the threads, that's the worm-gear that is inserted inside the idle-bolt-hole, with gearing/threading perpendicular to the direction of the hole, so this type of idle doesn't work by a true "pushing in" of any throttle plate, but by a secondary "worm-gear perpendicular" force to the idle-plate by driving the idle-screw(/bolt), have never seen this type before (though I'm woefully ignorant on carbs, carbs & cranks are my last 2 real frontiers )

Thanks a ton, would be awesome to hear I can just use the screw I have that fits (I did not fully insert it, I didn't want to risk hurting threading on the worm-gear, but the bolt I have for it inserts smooth&proper (no forcing it, no slack, got like 2-3 turns this way before backing it out due to fears that, even though I don't feel naything wrong, that it may still be capable of damage..and this saw is my baby, and was a gift, so am not taking risks with it!!)

 

[smokey7]

If i remember correctly these saws use a screw with a tapered head that adjusts the idle. Buy the correct bolt plain and simple. If you cant buy it separate buy a used or new carb and get the screw that way. Seems like every few days you have trouble with these saws.

 

[Ronie]

Here's one on ebay.

https://www.ebay.com/itm/265068350639