Runaway throttle - AC 170 Gasser

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I just picked up a '72 AC 170 gas machine (G-226). The engine was rebuilt and then the previous owner replaced the carburetor (Zenith) soon after. When I got it on Saturday it would start and run (with some minor misfire) but would shut off when you pull the throttle all the way down. I fixed that with a low idle adjustment. Now it idles nice - but not down in the 500-550 RPM range the manual calls for. Seems to work and idle best at 700-800 RPM and I am OK with that. 
The real problem is this: If you just bump the throttle (and it's real stiff) it runs all the way up and pegs the tach. You have to really work with it to get it to hold in any range over idle and even when you get it set it will start to "creep" until it runs away again. 

I got the hood off yesterday and changed the plugs (fixed the low idle misfire) and now I am ready to tackle the high side. I want to get the high idle set right so it doesn't run up past about 2200 RPM but I'm a little confused about where the high idle screw really is. The manual says it is on top of the cover where the governor is - there is an allen screw there with a lock nut but no amount of adjusting seems to make a difference. 

I am going to crack open the case to inspect the governor spring today but thought I'd throw this out and see if anyone else has seen/had this issue and has any advice for me. 

Appreciate any ideas. 

Tony

==EDIT==
Adding a pic of my new baby (proud new papa) just off the trailer Saturday - who doesn't like pictures?

Edited by Tony-MD - 20 Sep 2012 at 1:58pm

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Tony-MD Members Profile Send Private Message Find Members Posts Add to Buddy List Bronze Level Joined: 20 Sep 2012 Location: Maryland Points: 23	Post Options Post Reply Quote Tony-MD Report Post Thanks(0) Quote Reply Topic: Runaway throttle - AC 170 Gasser Posted: 20 Sep 2012 at 1:36pm
	I just picked up a '72 AC 170 gas machine (G-226). The engine was rebuilt and then the previous owner replaced the carburetor (Zenith) soon after. When I got it on Saturday it would start and run (with some minor misfire) but would shut off when you pull the throttle all the way down. I fixed that with a low idle adjustment. Now it idles nice - but not down in the 500-550 RPM range the manual calls for. Seems to work and idle best at 700-800 RPM and I am OK with that. The real problem is this: If you just bump the throttle (and it's real stiff) it runs all the way up and pegs the tach. You have to really work with it to get it to hold in any range over idle and even when you get it set it will start to "creep" until it runs away again. I got the hood off yesterday and changed the plugs (fixed the low idle misfire) and now I am ready to tackle the high side. I want to get the high idle set right so it doesn't run up past about 2200 RPM but I'm a little confused about where the high idle screw really is. The manual says it is on top of the cover where the governor is - there is an allen screw there with a lock nut but no amount of adjusting seems to make a difference. I am going to crack open the case to inspect the governor spring today but thought I'd throw this out and see if anyone else has seen/had this issue and has any advice for me. Appreciate any ideas. Tony ==EDIT== Adding a pic of my new baby (proud new papa) just off the trailer Saturday - who doesn't like pictures? Edited by Tony-MD - 20 Sep 2012 at 1:58pm

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NoMoneyAC Members Profile Send Private Message Find Members Posts Add to Buddy List Silver Level Joined: 04 Apr 2012 Location: Kansas Points: 78	Post Options Post Reply Quote NoMoneyAC Report Post Thanks(0) Quote Reply Posted: 20 Sep 2012 at 1:58pm
	I would clean and set carb and check linkage first.

Russ-neia Members Profile Send Private Message Find Members Posts Add to Buddy List Silver Level Joined: 11 Sep 2009 Location: NE Iowa Points: 489	Post Options Post Reply Quote Russ-neia Report Post Thanks(0) Quote Reply Posted: 20 Sep 2012 at 2:47pm
	Could also be a broken governor spring or broken governor weight.
	The innovators offer what others will imitate.

Tony-MD Members Profile Send Private Message Find Members Posts Add to Buddy List Bronze Level Joined: 20 Sep 2012 Location: Maryland Points: 23	Post Options Post Reply Quote Tony-MD Report Post Thanks(0) Quote Reply Posted: 20 Sep 2012 at 4:06pm
	Thank you gentlemen. I checked and rechecked linkage and it seems fine. I opened the governor housing and everything looked intact - there were no 'floating' pieces, the spring was intact and connected and the weight looked ok. I disconnected linkage at both ends and the spring feels strong. I am beginning to suspect a bad (or badly installed) throttle cable. It is extraordinarily stiff - you can't move the throttle up or down easily with one hand, you have to bump it. I know that may be independent of the runaway issue so there is likely a secondary issue with the governor as well. I am mechanical enough to work on this and eventually get it (with the help of the experience of others here) but I am beginning to worry that if I keep tinkering with it I will either make it worse or drag it out until it's too cold (for me) to work on it. I may have to punt and find a tractor mechanic around here ~casting eyes down in shame as I type~ Maybe a couple more days.... -Tony

Lonn Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 16 Sep 2009 Location: Назарово,Russia Points: 29781	Post Options Post Reply Quote Lonn Report Post Thanks(0) Quote Reply Posted: 20 Sep 2012 at 4:39pm
	The link to the carb isn't rubbing on the block is it? I know you said you checked but just wondering if you check that link.
	-- --- .... .- -- -- .- -.. / .-- .- ... / .- / -- ..- .-. -.. . .-. .. -. --. / -.-. .... .. .-.. -.. / .-. .- .--. .. ... - Wink I am a Russian Bot

Tony-MD Members Profile Send Private Message Find Members Posts Add to Buddy List Bronze Level Joined: 20 Sep 2012 Location: Maryland Points: 23	Post Options Post Reply Quote Tony-MD Report Post Thanks(0) Quote Reply Posted: 20 Sep 2012 at 6:09pm
	I went out and checked it again (never hurts and I'm up to try anything to get her right) and it is good. It's close but definitely not rubbing. I'm inclined to bend/shorten the carb link even more (it's set right according to the manual - 1/16" off the gov link when pulled to full throttle) to simply restrict the amount of travel and keep it from reving so high.
	-Tony '70 One Seventy (G-226)

jnicol6600 Members Profile Send Private Message Find Members Posts Add to Buddy List Bronze Level Joined: 02 Jul 2011 Location: Sullivan Co. IN Points: 174	Post Options Post Reply Quote jnicol6600 Report Post Thanks(0) Quote Reply Posted: 20 Sep 2012 at 6:30pm
	are the governer weights free to move in and out on the shaft?Sounds like what it would do if they were stuck. nice looking tractor by the way Edited by jnicol6600 - 20 Sep 2012 at 6:31pm

AlVee Members Profile Send Private Message Find Members Posts Add to Buddy List Silver Level Joined: 12 May 2011 Location: Iowa Points: 271	Post Options Post Reply Quote AlVee Report Post Thanks(0) Quote Reply Posted: 20 Sep 2012 at 6:46pm
	Just curious it wouldn't be a motor out of a combine and have the combine governor in it just a thought.

DaveCinIN Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 12 Sep 2009 Location: Kouts, IN Points: 629	Post Options Post Reply Quote DaveCinIN Report Post Thanks(0) Quote Reply Posted: 20 Sep 2012 at 6:47pm
	I don't know about a One Seventy, but my One Ninety XT has a wing nut for the throttle lever tension. Too loose and the rpms will drift down, too tight and the lever is stiff.

Brian Jasper co. Ia Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 11 Sep 2009 Location: Prairie City Ia Points: 10508	Post Options Post Reply Quote Brian Jasper co. Ia Report Post Thanks(0) Quote Reply Posted: 21 Sep 2012 at 9:01pm
	Sounds like the governor arm is out of adjustment. Disconnect the link from the carb. Open the throttle on the carb fully and open the throttle lever on the tractor. The link should over travel the carb by about 1/8". Bend the governor arm as needed.
	"Any man who thinks he can be happy and prosperous by letting the government take care of him better take a closer look at the American Indian." Henry Ford

Turbooutlaw Members Profile Send Private Message Find Members Posts Add to Buddy List Bronze Level Joined: 17 Nov 2018 Location: New York Points: 7	Post Options Post Reply Quote Turbooutlaw Report Post Thanks(0) Quote Reply Posted: 30 Nov 2018 at 6:38am
	Hi, this is kind of an old post (2012) but I have the same exact issue with my gas 170. It’s identical behavior! I greased up all the throttle hinge points and it’s still stiff after working it like crazy. Think it is just the design. Anyway, I hate the bump and tune method because you do always end up over reving the motor and that can’t be good for it. It’s also really frustrating to constantly tap the throttle down as you work and it starts to run away. Curious what the solution finally was or if anyone else knows what the deal is with the AC 170 gas and the runaway throttle. Edited by Turbooutlaw - 30 Nov 2018 at 6:39am

DrAllis Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Access Joined: 12 Sep 2009 Points: 20557	Post Options Post Reply Quote DrAllis Report Post Thanks(0) Quote Reply Posted: 30 Nov 2018 at 7:13am
	Ignore the 1/16" and 1/8" linkage dimension. Engine off and hand throttle set wide open. Remove the cotter pin on the link rod directly behind the alternator. Pull the link rod out of the vertical governor arm. If the vertical arm moves rearward, bend the link rod down in the middle to make the rod shorter so it just slides back into the hole. Oil each end of the linkage and make sure everything is very free. The effort required to move the hand throttle is stiffer than most, because there is no counterbalance spring to help you. There is a friction adjustment bolt inside the instrument panel area. An OLD throttle cable can make things very stiff. You'd think those cables would last longer than 50 years wouldn't you ???

Kurzy Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 02 Nov 2009 Location: WSS, Montana Points: 808	Post Options Post Reply Quote Kurzy Report Post Thanks(0) Quote Reply Posted: 30 Nov 2018 at 7:20am
	Howdy Tony-MD, Just restored a 67 One Seventy gas. Throttle was hard to move too! I took both choke and gas cables off, hung long way and put oil on till dripped out other end. What a difference! Now under your power steering cowl is a throttle control. Its two friction washers, can loosen or tighten throttle. My works like a pro now! Just might help you too. Thanks Kurzy

WD45Diesel57 Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 20 Jul 2010 Location: Varna, Ont. Can Points: 646	Post Options Post Reply Quote WD45Diesel57 Report Post Thanks(0) Quote Reply Posted: 30 Nov 2018 at 11:35am
	had the same issue on my series one D15 ended up governor was sloppy so I put couple washers between the governor bearing and fork and it smartened right up, too much play between will cause runaway rpm
	1-B's, 2-C, 2-CA's,2-WF, 1-WC,1-G, 3-WD's, 2-WD45, 1-RC, 1-D17 Diesel, 1-D14, 2-D15,1-D17 row crop,1-D19 gas and All Crop 40,60,66,72,90 and 100

jacasper Members Profile Send Private Message Find Members Posts Add to Buddy List Bronze Level Joined: 31 Dec 2019 Location: Minnesota Points: 1	Post Options Post Reply Quote jacasper Report Post Thanks(0) Quote Reply Posted: 27 Jan 2020 at 12:18pm
	I had the exact same issue that Tony described. I took apart the governor and upon inspection everything seemed fine. All the linkage moved properly on both sides of the governor. After some frustration I decided to take the carburetor off and I found that the throttle shaft snapped inside the carburetor. So it would open the butterfly valve but wouldn’t pull it back.