# MityVac MV8500



## jsouth (Jan 31, 2008)

I just bought this mityvac,to check 2 cycle engines.I have watch how to videos on youtube.I have not yet had time to use it.How do you check 4 cycle trimmers with the mityvac.2cycle engines,the piston must be BDC.Do you have to put the 4 cycle engine on TDC. on compression stroke,like doing a leakdown test on a lawn mower.Need advice.

Thanks,
Jerry


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## Sir Thomas (Dec 7, 2013)

jsouth said:


> I just bought this mityvac,to check 2 cycle engines.I have watch how to videos on youtube.I have not yet had time to use it.How do you check 4 cycle trimmers with the mityvac.2cycle engines,the piston must be BDC.Do you have to put the 4 cycle engine on TDC. on compression stroke,like doing a leakdown test on a lawn mower.Need advice.
> 
> Thanks,
> Jerry


Not sure what you are trying to accomplish with a mityvac. If you want to check compression, just need a compression gauge that screws into the sparkplug hole and crank it a few times.


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## jsouth (Jan 31, 2008)

Sir Thomas,the mityvac can check for air leaks,around the carb. and the cylinder ,and can perform a vacuum test to see if the crankshaft seals are leaking.If the compression test show good,and air leak can keep it from running.Go on youtube and type in doublewide6 and what his channel on pressure and vacuum testing with a mityvac.

Jerry


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## Sir Thomas (Dec 7, 2013)

jsouth said:


> Sir Thomas,the mityvac can check for air leaks,around the carb. and the cylinder ,and can perform a vacuum test to see if the crankshaft seals are leaking.If the compression test show good,and air leak can keep it from running.Go on youtube and type in doublewide6 and what his channel on pressure and vacuum testing with a mityvac.
> 
> Jerry


As you probably know, a 2 cycle engine work in a completely different manner than a 4 cycle. I don't know if there is any specifications for total psi in the combusion chamber in a 2 cycle. I don't even know how you can measure for leakage in the crankcase of a 2 cycle though good or bad gaskets can affect how the crankcase controls the carb functions. I don't know if the crankcase chamber it completely sealed at all times. As you know the crankcase creates a vacume for the diaphram in the carb which in effect pumps the fuel into the combusion chamber. Maybe 30yearTech can answer that. I'd like to know also.


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## jsouth (Jan 31, 2008)

I would like 30yearTech, opinon on the mityvac.Joe Pace has a good channel,on how to use the mityvac.

Jerry


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## paulr44 (Oct 14, 2008)

http://www.mityvac.com/user_manuals/07000-06820.pdf

Four-mix (STIHL) engines, and 2-stroke engines must have a well sealed crankcase in order to operate properly. The 4-stroke engines will suffer carburetor fuel-pump issues with a leaky crankcase.

Your post seems to inidicate you need to research some basic engine functions for both 2-stroke and "4-mix" engines. None of us use combustion pressures as a reading - that's next to impossible for a bench mechanic. We use compression, leak-down and CC pressure/vacuum tests.

http://www.summitracing.com/parts/otc-5609/overview/

Leakdown tests require a different tester, preferably with 2 gauges. A leak-down test depending on OEM (some say 10%, some say 20%) will give you an audible or other means of determining a problem area. Compression tests are subjective on many engines due to compression release system. Because of the release systems, a leak-down test is more accurate in diagnosing engine problems such as worn rings, leaky valves and the like.


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## Sir Thomas (Dec 7, 2013)

If I were a professional shop rebuilding or repairing high end 2 cycle engines and could afford such equipment, I could see using this mityvac but I'm just a hobbyist repairing and rebuiding units that most mechanics wouldn't touch but throw away. I get junked machines and get them running and sell them to people who can't afford expensive yard equipment. People bring me their low end equipment and I rebuild, cutting my own gaskets and getting carb rebuild kits and have been successful.


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## jsouth (Jan 31, 2008)

I do this as a hobbyist also.By using the mityvac,I could save some time finding the cause,of troubleshooting a trimmer or a chain saw.

Thanks,
Jerry


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## Sir Thomas (Dec 7, 2013)

jsouth said:


> I do this as a hobbyist also.By using the mityvac,I could save some time finding the cause,of troubleshooting a trimmer or a chain saw.
> 
> Thanks,
> Jerry


What do they cost.


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## jsouth (Jan 31, 2008)

On ebay they very from $65.00 to $79.00.I bought mine from NAPA $76.00 and got it in the same day.

Jerry


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## 30yearTech (Sep 14, 2006)

Testing a crankcase for leaks is certainly more helpful on 2 -strokes. However unless it is a higher end more expensive unit, then many times (at least for me) it's not worth the effort. The cost to repair many of the lower end unit can be prohibitive as many can be replaced for much less then the repair costs. On many of the lower end unit, parts may only be available as an assembly and not individually, making some simple repairs expensive ones.

The C4 and 4 Mix units may benefit from this, but I can't recall ever needing to test for a crankcase leak on one (at least not yet). The other 4 stroke trimmers with a separate wet oil sump would probably not need to be pressure tested, as the most common place a leak would occur is between the carburetor and cylinder head. If you removed the carburetor to install an adapter plate to test, you would likely either seal or create leaks. The best way to test for a leak in this area on a 4 stroke would be spraying brake parts cleaner around the suspected leak while the engine is running to see if it has any effect on the unit.


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## Sir Thomas (Dec 7, 2013)

30yearTech said:


> Testing a crankcase for leaks is certainly more helpful on 2 -strokes. However unless it is a higher end more expensive unit, then many times (at least for me) it's not worth the effort. The cost to repair many of the lower end unit can be prohibitive as many can be replaced for much less then the repair costs. On many of the lower end unit, parts may only be available as an assembly and not individually, making some simple repairs expensive ones.
> 
> The C4 and 4 Mix units may benefit from this, but I can't recall ever needing to test for a crankcase leak on one (at least not yet). The other 4 stroke trimmers with a separate wet oil sump would probably not need to be pressure tested, as the most common place a leak would occur is between the carburetor and cylinder head. If you removed the carburetor to install an adapter plate to test, you would likely either seal or create leaks. The best way to test for a leak in this area on a 4 stroke would be spraying brake parts cleaner around the suspected leak while the engine is running to see if it has any effect on the unit.


I agree. Unless you are a hobbyist with a thick wallet, this would be an unecessary expense. I wouldn't mind having one, another toy to play with but I'm retired with very little extra money to spend money on one. 
My take. I take everything apart clean it, replace gaskets (make my own), rebuild the carb if necessary, put it back together and test for spark and compression. If it doesn't work, junk it and use it for parts. I have more time than I have money and what I charge is barely enough to pay for parts and a little set a side for tools that I can use.
If it's something I'm working on for someone else, and I do the above, I just start all over and check everything. Right now, that money I'd spend on that would be better spent on a pilot bearing puller. 
I'm not trying to be nasty, just stating the fact.


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## paulr44 (Oct 14, 2008)

FYI, on the 4-mix motors if they have a CC leak the fuel pump doesn't work right. I adjusted the valves on one as I've done many times, when I was putting the valve cover on I knocked the gasket slightly askew, and didn't run worth a crap. Now I always replace the gasket and am mindful of it's position, considering the importance of it's sealing ability, and it cost less than $2.


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## paulr44 (Oct 14, 2008)

http://www.hobbytalk.com/bbs1/showthread.php?p=4500583#post4500583
http://www.hobbytalk.com/bbs1/showthread.php?p=4500501#post4500501


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## Rentahusband (Aug 25, 2008)

Sir Thomas said:


> I agree. Unless you are a hobbyist with a thick wallet, this would be an unecessary expense. I wouldn't mind having one, another toy to play with but I'm retired with very little extra money to spend money on one.
> My take. I take everything apart clean it, replace gaskets (make my own), rebuild the carb if necessary, put it back together and test for spark and compression. If it doesn't work, junk it and use it for parts. I have more time than I have money and what I charge is barely enough to pay for parts and a little set a side for tools that I can use.
> If it's something I'm working on for someone else, and I do the above, I just start all over and check everything. Right now, that money I'd spend on that would be better spent on a pilot bearing puller.
> I'm not trying to be nasty, just stating the fact.


I pretty much do the same as you Sir Thomas.


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## mikel m14 (Jul 27, 2009)

jsouth said:


> Sir Thomas,the mityvac can check for air leaks,around the carb. and the cylinder ,and can perform a vacuum test to see if the crankshaft seals are leaking.If the compression test show good,and air leak can keep it from running.Go on youtube and type in doublewide6 and what his channel on pressure and vacuum testing with a mityvac.
> 
> Jerry


It's a neat tool. I recently bought the mityvac mainly to test carbs. I tested two zama carbs on stihl trimmers this week, both wouldn't bring fuel up into the primer bulb(purge). The only test they failed on was depressing primer bulb(fuel line hose input), wouldn't move from 10psi. Ultrasonic cleaned 1 carb, put it back together and retested. Passed all test this time. Also tested fuel tank and that failed. Sprayed fuel lines and fuel cap while pumping mityvac and a big bubble was forming under fuel cap. Replaced fuel cap(held 4psi), installed carb and it started up and I let it idle for around 40 minutes until it shutoff. Turns out spark plug also needed replacing, now it's good to go. One thing I did notice is that the carb leaked(mityvac testing) when put back together but stopped leaking(retested) after running fuel thru it. I'm guessing because everything was dry when reassembled.

On 4 stroke I use a leak down tester that has 2 guages. The mityvac will only go to 30psi.


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