# Increasing engine rpm on B&S 420



## Town (Jan 31, 2015)

The Ariens Pro model 926065 with the 420 cc B&S is spec'd by Ariens for 3,600 rpm +/- 100 rpm. Has anyone increased the engine rpm to 3,700 rpm using the governor control? Is it an easy change, and how did you do it?

Thanks for any input.


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## UNDERTAKER (Dec 30, 2013)

*WHY?????????????? Would you want to do that???? *


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## micah68kj (Oct 8, 2011)

POWERSHIFT93 said:


> *WHY?????????????? Would you want to do that???? *


*Yeh. Why?*


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## Kielbasa (Dec 21, 2013)

That was the first thing that popped in to my head. Why?


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## Town (Jan 31, 2015)

POWERSHIFT93 said:


> *WHY?????????????? Would you want to do that???? *





micah68kj said:


> *Yeh. Why?*


Many engines from the factory run slower than their spec'd engine speed. In my experience setting the engine to the top of the spec'd rpm range gives better engine performance and therefore more throughput of snow. 

The LCT 414 cc engine in AX form is spec'd for 3,700 rpm but mine was running 3,450 and did not perform as well as I expected/wanted. By changing the governor setting the engine ran at 3,700 rpm and performed very much better. I kept that setting for almost 5 seasons. The LCT/AX engine manufacturer spec'd the 414 cc engine with rpm at 3,900. Near the end of season 5 I upped the governor to 3,925 rpm and it ran better, sounded even better and performed better with snow throughput. 

A friend has the B&S 420 cc in an Ariens Pro and has not used it in the winter yet, but has some demanding conditions. The thought is that the engine may be short on rpm and so perform below par. I cannot get access to his engine's governor system since he lives far away. The internet has nothing that I can find so far on the B&S 420 governor system. Now in the fall is a better time to check on stuff, rather than wait until winter snow and cold.

My thought is that some of the experienced people on this forum would know the system and be prepared to share their knowledge.


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## Zavie (Sep 23, 2014)

Until someone posts and exact answer about the 420cc, Taryl covers it generally in a video only he can do:


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## Zavie (Sep 23, 2014)

POWERSHIFT93 said:


> *WHY?????????????? Would you want to do that???? *





micah68kj said:


> *Yeh. Why?*





Kielbasa said:


> That was the first thing that popped in to my head. Why?


Because.... "There's your dinner":wink2:


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## Town (Jan 31, 2015)

Zavie said:


> Until someone posts and exact answer about the 420cc, Taryl covers it generally in a video only he can do


Thanks Zavie I usually don't watch those ******* videos after the first few scenes. But that is the best video I have ever seen on how the governor system works and why and what you have to do to correct any problems that may be there. Quite excellent. He is one smart guy, and able to get the principles across completely, not halfway as usually the case.

So the question is whether that B&S engine uses the same spring adjustment process as the Ariens B&S 420 in the Pro.

Thanks for posting.


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## Zavie (Sep 23, 2014)

I'd be very surprised if it didn't have the exact same system.


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## legarem (Sep 9, 2017)

Zavie said:


> Until someone posts and exact answer about the 420cc, Taryl covers it generally in a video only he can do:https://www.youtube.com/watch?v=XbFyGRixoGA&t=409s


You made my day. It's a long time I didn't laugh like that. These guys are crazy. I suspect they smoke something before doing this video:smile2:


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## rslifkin (Mar 5, 2018)

The B&S 420cc is easy to adjust. There's a high limit stop screw for the throttle lever. Adjust that to get a little more throttle travel and you'll get more RPM with no impact on idle speed. 

I have my 420cc set for 3700 RPM with no load. Barely drops with the augers engaged, drops a little under snow load.


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## Town (Jan 31, 2015)

rslifkin said:


> The B&S 420cc is easy to adjust. There's a high limit stop screw for the throttle lever. Adjust that to get a little more throttle travel and you'll get more RPM with no impact on idle speed.
> 
> I have my 420cc set for 3700 RPM with no load. Barely drops with the augers engaged, drops a little under snow load.


Thank you so much for sharing your knowledge, expertise and experience with your B&S 420. I think my Subaru engined tiller uses the same technique for adjusting engine speed. 

Surprising your engine speed drops when augers engaged and under snow load. My laser device shows my engine speed is same with augers engaged or not. When moving forward into snow engine sound stays the same and when snow load increases the governor increases throttle opening which changes engine noise but there does not appear to be any slow down in engine rpm or the stream of snow coming out the chute, just the volume increases. My observations would be very subjective in snow performance since I have no digital information.

Thanks for your solution.


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## rslifkin (Mar 5, 2018)

A mechanical governor will always have some droop. So if it's at 3700 at no load, you'll probably be down to around 3500 by the time governor has the throttle wide open. Without a fancy electronic governor, you can't do much better. If it tried to maintain exactly 3700 all the time, the governor would be too sensitive and it would end up hunting and surging rather than maintaining a steady RPM.


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## melson (Feb 9, 2015)

Most of these small engines are designed to achieve maximum HP around 3600. But HP and torque aren't the only metric in the ability to throw snow. There's also the rpm factor. Because all moving parts are tied to engine rpm then the throw distance is a direct result of rotational speed. Generally speaking, if you want to throw farther then increased engine rpm is an easy and effective way.
However, engine life and component wear-and-tear may be negatively affected (*may be*, depending upon several factors) by higher-than-intended engine speed so this is a trade-off that should also be considered.


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## Town (Jan 31, 2015)

rslifkin said:


> A mechanical governor will always have some droop. So if it's at 3700 at no load, you'll probably be down to around 3500 by the time governor has the throttle wide open. Without a fancy electronic governor, you can't do much better. If it tried to maintain exactly 3700 all the time, the governor would be too sensitive and it would end up hunting and surging rather than maintaining a steady RPM.


That is not my experience. Perhaps you have a weak governor spring since that will have too much travel to maintain adequate pressure and responsiveness so I can see engine speed dropping, push mowers often have that problem. Also slop in internal governor mechanism will drop engine rpm when load changes quickly and quite likely hunt due to erratic movement recovering from the slop. LCT has a very strong governor spring so reaction is very quick and steady. If the load exceeds the hp then engine rpm is going to drop.


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## Town (Jan 31, 2015)

melson said:


> Most of these small engines are designed to achieve maximum HP around 3600. But HP and torque aren't the only metric in the ability to throw snow. There's also the rpm factor. Because all moving parts are tied to engine rpm then the throw distance is a direct result of rotational speed. Generally speaking, if you want to throw farther then increased engine rpm is an easy and effective way.
> However, engine life and component wear-and-tear may be negatively affected (*may be*, depending upon several factors) by higher-than-intended engine speed so this is a trade-off that should also be considered.


I think most engines develop their maximum hp above 3,600 rpm. Manufacturers suggest an engine speed below max hp so the engine will last longer. Increasing engine rpm from 3,600 rpm to 3,700 rpm is usually within the manufacturer spec range and will improve performance noticeably. Adding more blades (i.e. 3 to 6) will speed the ejection of snow and send it a bit farther so throughput is improved and you can go a little faster for the same quality of snow removal. Increasing engine rpm beyond 3,700 to 3,900 will increase performance a little more again at the expense of engine life.

I know that an 11 hp Tecumseh OHV can be increased to over 3,800 rpm and last for 15 years and still be running perfectly. A stock 8 hp Tecumseh SV lasted 30 years before getting tired with less usage than the 11 hp. So engine durability is quite good even when used extensively. 

Increasing the impeller speed beyond that of engine speed requires a pulley ratio change and many experts here have spoken about their engines being able to run high ratios to improve performance which will put additional loads on engine and gear box. If you want to improve performance beyond the manufacturers specs then some extra wear is to be expected. No one has indicated any failures as a result of their changes. What is life without some risk.


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## rslifkin (Mar 5, 2018)

From what I can extrapolate based on the Briggs 420cc torque curves that are published, peak HP is likely somewhere in the 3700 - 3800 range. 

As far as governor response and droop, yes, a stiffer spring or different leverage ratio can reduce droop. The Briggs 420 governor does seem to have a bit more droop than I'd like out of the box, but I haven't played with it to see if I can make it more sensitive without causing it to hunt at times.


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## BNSFguy (Nov 2, 2019)

Yea. On the LCT 420 CC engine maximum torque is made at just over 3000 RPM's. Maximum HP isn't listed but I'm sure that's made at a higher RPM. I was curious as to the max RPM's on this LCT 420 CC and what it's supposed to be at. Mine reads 3650 RPM's at full throttle. I believe to change RPM's on the LCT is different than the B & S.


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## Town (Jan 31, 2015)

BNSFguy said:


> Yea. On the LCT 420 CC engine maximum torque is made at just over 3000 RPM's. Maximum HP isn't listed but I'm sure that's made at a higher RPM. I was curious as to the max RPM's on this LCT 420 CC and what it's supposed to be at. Mine reads 3650 RPM's at full throttle. I believe to change RPM's on the LCT is different than the B & S.


Do you want to change the governed engine speed? It requires removal of the front gas tank shielding for access to the governor arm. On my 414 cc engine the spring is mounted to the "middle" hole on the arm as stock, but the fixed end of the spring on the engine cooling cover can vary in stock form. Stock rpm on mine was 3,450 rpm, laser measured. The Ariens AX 414 cc spec is 3,600 rpm +/- 100 rpm so 3,700 rpm is within stock spec. The LCT site lists the 414 cc engine at 3,850 rpm +/- 50 rpm so 3,900 rpm is also stock, but for the generation before mine.

In the attached pics the gas tank has been removed for clarity. The attached first pic shows stock position, while second shows the setting for 3,700 rpm. To increase to 3,900 rpm the spring fixed mounting needs to be moved ever so slightly away from the governor arm to further tension the spring.

I like the engine running at 3,900 rpm better than 3,700 rpm and way better than 3,450 rpm which has no power to speak of.


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## BNSFguy (Nov 2, 2019)

Town said:


> BNSFguy said:
> 
> 
> > Yea. On the LCT 420 CC engine maximum torque is made at just over 3000 RPM's. Maximum HP isn't listed but I'm sure that's made at a higher RPM. I was curious as to the max RPM's on this LCT 420 CC and what it's supposed to be at. Mine reads 3650 RPM's at full throttle. I believe to change RPM's on the LCT is different than the B & S.
> ...


I'm going to run mine the way it is from the factory and see how it feels. But I do want to know how to change it if I want to increase RPM's closer to LCT spec. My only hesitation with doing so would be concerning the warranty. I have 5 year warranty that just started on this brand new machine and I'd be worried about bringing it in for service, if I ever need to, and have them void my warranty. I might have to wait awhile. I'll see how it runs.


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