Runaway throttle - AC 170 Gasser
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Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=57176
Printed Date: 28 Aug 2025 at 2:43pm
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Topic: Runaway throttle - AC 170 Gasser
Posted By: Tony-MD
Subject: Runaway throttle - AC 170 Gasser
Date Posted: 20 Sep 2012 at 1:36pm
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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?  |
Replies:
Posted By: NoMoneyAC
Date Posted: 20 Sep 2012 at 1:58pm
| I would clean and set carb and check linkage first. |
Posted By: Russ-neia
Date Posted: 20 Sep 2012 at 2:47pm
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Could also be a broken governor spring or broken governor weight. ------------- The innovators offer what others will imitate. |
Posted By: Tony-MD
Date Posted: 20 Sep 2012 at 4:06pm
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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
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Posted By: Lonn
Date Posted: 20 Sep 2012 at 4:39pm
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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 |
Posted By: Tony-MD
Date Posted: 20 Sep 2012 at 6:09pm
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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) |
Posted By: jnicol6600
Date Posted: 20 Sep 2012 at 6:30pm
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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 |
Posted By: AlVee
Date 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. |
Posted By: DaveCinIN
Date 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. |
Posted By: Brian Jasper co. Ia
Date Posted: 21 Sep 2012 at 9:01pm
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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 |
Posted By: Turbooutlaw
Date 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. |
Posted By: DrAllis
Date 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 ??? |
Posted By: Kurzy
Date Posted: 30 Nov 2018 at 7:20am
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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
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Posted By: WD45Diesel57
Date Posted: 30 Nov 2018 at 11:35am
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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 |
Posted By: jacasper
Date 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. 
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