# Checking with the RPM Gurus.....



## Opfoto (Jan 3, 2013)

I bought a couple of these as was suggested previously to check the RPMs on my Craftsman #247.88790.

Digital Engine Tach Tachometer Hour Meter Inductive for Motorcycle Motor FC0 | eBay

According to the manual on page 31-32 it lists the Engine as #LA318SA-156554, with everything I have read (various Tecumseh manuals) online it keeps referring to the Tecumseh microfiche page 30 for RPM settings. As it goes that is hidden somewhere inaccessible on the interweb.

Using the above meter I have the following settings on my unit without the adjustable carburetor.

Full throttle (after warmup) 3450rpm
Low throttle (No Load) Idle 1650-1750 rpm

Running thru the gears without using the auger it runs:
1st -3rd gear @ 3200=3300rpms
4th-6th gears @ 3300-3400rpms

Running thru the gears with the auger but NO snow throwing (we have no snow!) it runs:
3400 no matter what gear I put it in

I did not check the RPMs in reverse at all.
It sounds good...No hesitations, No sputtering, No backfiring, No surging.

I am willing and very happy to leave it alone UNLESS the gurus here tell me I have something way out of whack. I don't want to blow this up....


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## nt40lanman (Dec 31, 2012)

These engines typically top out at 3600 but I like to keep them as low as I can to increase longevity. I think your numbers look OK.


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## nwcove (Mar 2, 2015)

your "unloaded" rpms look ok to me, plz post back if it snows and you get a chance to see what happens under varying loads.


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## Kiss4aFrog (Nov 3, 2013)

Your machine, your choice. Here are some vids to see how to go about adjusting it.

https://www.google.com/search?q=donyboy73&ie=utf-8&oe=utf-8#q=donyboy73+adjusting+high+speed


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## pfn (Dec 24, 2010)

I have an 3 yr. old Ariens Pro and recently installed the same tach. My RPM have never reached 3600 either. I'm running at about 3300. 
Interesting.


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## Kiss4aFrog (Nov 3, 2013)

I'd like to have the max available and then you can chose to run it anywhere you feel comfortable with.
Just my :2cents:


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## skutflut (Oct 16, 2015)

Kiss4aFrog said:


> I'd like to have the max available and then you can chose to run it anywhere you feel comfortable with.
> Just my :2cents:


3600 RPM is whats listed in the service manual at the following link:\

http://previewer.org/?pdfurl=1qeXpu...fRncjL2OLS39TexOXdztPdyODZzNrfytrS25PkzMuSreY

Running it a bit slower is probably a bit easier on the engine, but you will lose a bit of throwing distance due to slower impeller speed. All the other figures look ok. Be more interesting to see how well the governor does holding it at or around 3400 when its tossing heavy snow.

Of course, there is another school of thought here. If you baby that engine, then it will never wear out and you won't have an excuse to get a new/different snowblower. When I get tired of an engine, I bend the governor spring so it revs to about 6000 rpm, and then after about 4 minutes, you get to go shopping


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## GoBlowSnow (Sep 4, 2015)

I'm using the same Tach on a similar if not same engine, and mine seems to do quite well between 3450-3500.


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## Opfoto (Jan 3, 2013)

t40lanman - thanks for the confirmation of 3600, I thought that I heard that somewhere

nwcove - Thanks and will do, I know my luck is running out!

Kiss4aFrog - Thanks for the video link, Have watched a few of his videos and he is very helpful. As I stated I really don't want to blow this up.

pfn - I think I can adjust it higher but not sure I want/need to....

Kiss4aFrog - I agree know the limits then choose.....

skutflut - I have read that manual and still cant find the "suggested" RPMs. They describe how to measure the RPMs when they are at a certain voltage...etc not really what I was hoping for but thank you for providing the link. 

GoBlowSnow - Thanks for your confirmation, it appears as though my settings are inline and not something to worry about.

I am going to leave it as is and report back when I get to throw some snow

Thanks to everyone for providing me the links and opinions .... I appreciate it!


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## pfn (Dec 24, 2010)

Opfoto said... "pfn - I think I can adjust it higher but not sure I want/need to....".

I'd like to have something to check my tach against. I ran my machine yesterday to see what it read with no load. I couldn't get a good read as the tach was all over the place. It wouldn't settle on any number long enough. I don't recall having that problem when I was moving snow. I wonder if the tach as issues.


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## KennyW in CT (Feb 24, 2015)

Older units with many hours I'll set them for 3400 under load, which usually equates to around 3450-3500 with no load. 
There will be times, however, that even at 3400, the machine won't throw as good as it will at 3600 so I try to test the performance as well. 
Never exceed 3600. I hate when a customer complains it doesn't throw as far as when he brought it in then I try to explain you cannot run these things at 4500 rpm either!!.

I also adjust the high speed mixture screw (if it has one) while the auger is on to eliminate any hunting issues. I find that you really need the engine under load to adjust the high speed mixture correctly.

Now if I can just keep the Harley owners from putting the low speed rpm at 250 so it sounds like a Harley (potato-potato...) I would probably see less engines coming in with thrown rods due to lack of lubrication! Oh, and that's if they even check the oil level. (yes, that small puff of blue smoke every time you start that 40 year old machine up means that a minute amount of oil just left your engine!)


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## ELaw (Feb 4, 2015)

Those tachs can be a bit finicky. 

Try using more turns of wire around the plug wire, and also make sure the turns are tight to the plug wire. Or if you have a lot of turns and they're tight already, try fewer.

Basically what that does is alter the amount of signal going to the tach. If the tach gets a weak signal (pickup wire loose or too few turns), it'll have a hard time computing the RPM. But the signal can also be too strong and overload the tach... so you have to fiddle to get the right amount.


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## Town (Jan 31, 2015)

pfn said:


> Opfoto said... "pfn - I think I can adjust it higher but not sure I want/need to....".
> 
> *I'd like to have something to check my tach against. *I ran my machine yesterday to see what it read with no load. I couldn't get a good read as the tach was all over the place. It wouldn't settle on any number long enough. I don't recall having that problem when I was moving snow. I wonder if the tach as issues.


There is an alternative to the engine tach, a digital laser photo tach. Here is an example: Amazon.com : CE Compass New Digital Laser Photo Tachometer Non Contact RPM Tach : Car Electronics

The idea is that you stick a small reflective strip on the pto and point the device at it for a reading of rpm. To get a reading of the loaded rpm you may need to remove the starter (if you have an electric starter) and affix the reflective strip on a flywheel cooling fin.

Just a thought to confirm your actual engine (and impeller) speeds rather than counting pulses.


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## RedOctobyr (Mar 2, 2014)

If the tach has a ground wire, make sure it's grounded to the engine. 

KennyW, good reminder about setting idle speed appropriately, thank you.


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## KennyW in CT (Feb 24, 2015)

When in doubt, a Vibrotach works every time!

https://www.rcpw.com/briggs-stratton-parts/genuine/19200.html?gclid=CPKo2MnD3soCFQsjHwodVgcI8Q


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## pfn (Dec 24, 2010)

KennyW in CT said:


> When in doubt, a Vibrotach works every time!
> 
> https://www.rcpw.com/briggs-stratton-parts/genuine/19200.html?gclid=CPKo2MnD3soCFQsjHwodVgcI8Q


Neat! I've saw something similar years ago. I didn't know they were still available.


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## jason7mm (Aug 27, 2013)

I've got one, they are incredibly accurate


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