520 govenor question

bill finn · May 16, 2016

while dyno testing the 520 we are reading 24hp at rated rpm. i noticed that the throttle shaft is not wide open.so we pull the dyno down to lug the engine and the throttle does not open anymore. If I move throttle shaft manually to wide open I pull 31hp. Also the govenor leaf spring adjustment rod is adjusted all the way up the rod to as tight as it can adjust. I have also turned the load screw out several turns and still get no change on hp or any black smoke. It runs like a watch and 31hp would be acceptable for this tractors condition. why is the govenor not moving carb to wide open throttle under heavy load? could the govenor leaf spring be week over time and give problems? Float height is set at 1/2" with a fuel level tube, book says 3/4". Valves are set at .021 cold, book says .020 hot. This is the first run after a complete valve job.
anybody have an ideas?

toot · May 17, 2016

Yes those springs become weak over time. Since you have access to the dyno, play with your timing settings as well to achieve max hp. Make sure your advance in your distributor in not froze as well. That tractor, if in good running condition should be putting out more than 31 hp. As far as the carb, Has it ever been off and worked on? it has fixed jetting and that load screw is used for adjustment, but there are things that can be messed up regarding the seat, and the taper on the screw end.

bill finn · May 17, 2016

carb was professionally rebuilt by Roberts not to long ago. I did play with timing and felt like we got it where it runs the best. I will look at the advance tonight. Do you think the governor internals could keep me from achieving WOT? As far as the load screw is concerned I have been turning it out(4to6 turns) to try and add fuel and have no black smoke. tractor runs very nice.

Bob · May 17, 2016

Sounds like the length setting of the rod between the governor and the carburetor is not correct. It's been a LONG time since I worked on one of these and I can't remember if that setting is made by adjusting the actual rod or the position of the governor lever on the governor shaft. Either way, the result is the same... the carburetor throttle lever needs to hit it's "wide open stop" just before the governor arm runs out of travel in that direction.

At this point, the governor weights are fully retracted "inwards".

Also, wear (a flat spot) on the radiused ares of the governor weight "fingers" would be something to check for.

Kent Petersen · May 17, 2016

Have you checked the carb to gov. auj with engine off throttle wide open auj likeage i/2 a hole short of going in the hole on the carb shaft also wide open

bill finn · May 17, 2016

of coarse, what a great idea. I had not thought of that and will be checking when I get home tonight. Thanks to all for the help

Bob · May 17, 2016

Please let us know what you find with the linkage.

bill finn · May 17, 2016

sure will

bill finn · May 17, 2016

well the linkage was off considerable. I checked the dist advance buy twisting rotor and make sure it springs back, seemed ok. disasembled the carb and inspected everything, also blew carb cleaner thru all vent and fuel holes.I still get no smoke, even if i pull choke out(on dyno under load). i have moved load screw and cannot figure out how to set it. No matter where i put the screw i see no change in hp. tractor is pulling 30hp with what i will call alot of blowby. I am sure the rings are worn, now that the valves are new the blowby is worse. Tractor runs good so unless we get another idea to try we will not be looking to overhaul at this time. I sure would like to learn how to adjust that load screw.
thanks to all for the help

Mike M · May 18, 2016

Hum? A lot of blow by. Can't say I didn't warn you awhile back.

" Oh one more thing. Since the head is off anyhow. I'd also pull the pistons out because I have seen several of the 620 models with broken top piston rings. Seems these models using thinner rings and aluminum pistons don't hold up well when past "normal" overhaul limits like a cast iron piston with wider rings will. Pretty much anytime I pulled a head off I'd also pop the pistons out and if nothing else bad found hone it and install new rings. " Quote.

buickanddeere · May 18, 2016

Odds are the cam and followers are also worn with reduced lift and duration.

bill finn · May 18, 2016

I am sure all the predicted wear is spot on. Unfortunately not all tractors are going to get a complete engine overhaul. It does run very nice and will spend the summer pulling a chicken fence around the yard. My obsession for doing my best will have to take a back seat to economics. I still need to learn how to adjust the load screw, which hopefully wont cost any money.
thank you all for your help

toot · May 18, 2016

If you feel you need more fuel you can get different load screws thru robert's. Each jet is slightly sized differently, but I have only done this when the tractor has had some increased mods to engines for pulling. For example the all fuels have more jetting due to the heavier fuels used.. just be careful not to over jet or tank your fuel economy. Have you done a compression check? at cranking speed with throttle wide open should be in the 140 range.

ET · May 18, 2016

Were you able to get the specified high speed no load rps out of the tractor before putting a load on it? You will never get rated hp without it.

bill finn · May 18, 2016

according to the tac on the dyno we are running just under 600 rpm no load, I think 585 is book spec. 535 is rated pto speed and I have not verified accuracy with a hand held tac. so there could be some discrepancy, the dyno is only new to us.

520 govenor question

bill finn

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Bob

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bill finn

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