Onan 720 help
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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=21148
Printed Date: 25 Sep 2024 at 2:25pm
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Topic: Onan 720 help
Posted By: ACJohn
Subject: Onan 720 help
Date Posted: 21 Nov 2010 at 11:44am
Picked up a 720 that seems to run strong. Throttle response is good and only smokes for an instant at startup. The issue seems to be the governor. I have read the Onan master service manual on adjustment for tractor applications, and it doesn't seem to have helped. Operators manual recommends mowing in 2nd gear, however, engine bogs and speed slows when mowing taller grass/leaves. An electric fuel pump was installed, and fuel supply is more than enough. Any advice would be appreciated.
John
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Replies:
Posted By: TREVMAN
Date Posted: 21 Nov 2010 at 12:09pm
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Time for a compression test, if you dont have 100 or better in each jug, not much power. Check your points, clean them they have a tendency to get oily, set the points, when I got my tractor it seemed to run o.k. but had no power, the points were not even close. Change plugs, who knows how old they are. See if this makes a difference. I'd check the coil and put new wires on as well. I also decarbed the heads and put on new gaskets, while I was in there I set the valves and got the carbon off of them. Dont mess with the governer until youve done these things first...These are the things I did when I got my 720, and the way it runs now and the way it ran when I got it, theres no comparsion...hope this helps, TREV.
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Posted By: Brian Jasper co. Ia
Date Posted: 21 Nov 2010 at 12:39pm
I 2nd the check/replace the points and plugs. Below 100psi compression means it's getting tired. Make sure you properly set the timing too. There is an Onan engies group on Yahoo where there are some real experts on these engines. Like Trev says, it's wise to decarbon the heads. From what I've learned from the Onan group guys is they can have carbon buildup on the head and piston that can be enough for the piston to hit the head and break the connecting rod.
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"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
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Posted By: ACJohn
Date Posted: 21 Nov 2010 at 2:13pm
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Thanks for the advice. I will replace plugs/wires (wires have straight boots and hit hood) and decarb heads. Will Seafoam do a good enough job or do I need to remove heads?
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Posted By: TREVMAN
Date Posted: 21 Nov 2010 at 3:34pm
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Remove the heads, its not an expensive or hard job. Seafoam isnt a bad idea, but the carb that was in my heads was not coming out with anything but mechanical intervention. Dont buy your gaskets from Cummins, find them on ebay they are usually cheaper. TREV.
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