# some basics



## 1930 (Apr 14, 2013)

I was hoping someone could fill me in on the proper way to diagnose problems with small engines. I am assuming there is an order of attack and that it is much like automotive Air/fuel/spark but is their a roundabout standard gauge of compression that I should be looking for? 

I have compression gauge for automotive, I have the kind that has the adapters that screw into the spark hole and the rubber tipped hold on and crank style but I am assuming that for small engine none of my automotive adapters will fit so I may be left with the rubber tipped style. 

Problem with that is I have noticed there are some applications where I would not be able to get that bulky tool in where it needs to be because of metal framework so I am wondering what some of you guys use. 

Again what might I expect for a compression reading if there is a standard number. 

I have some 2 cycle and 4 cycle engines if that makes a difference. 

Also what is the best way to check spark intensity, isnt there a gauge that can be pressed onto the wire to test this. I ask because I have seen on some of my engines a pretty dim spark, not rich deep blue like I am thinking I need to see but that could be because of the daytime sunlight and my eyes getting old. 

Thanks


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## 30yearTech (Sep 14, 2006)

Compression is compression and it's the same for automotive and small engine's. The majority of spark plugs are the same thread size, so your screw in gauge will work on most applications.


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## 1930 (Apr 14, 2013)

30yearTech said:


> Compression is compression and it's the same for automotive and small engine's. The majority of spark plugs are the same thread size, so your screw in gauge will work on most applications.


Compression is compression, thanks................ I have not tried my automotive compression fittings on these engines but it sounds like I had better try, again I had assumed that they would not have worked. Thanks for the tip.


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## Don L (Jul 14, 2012)

Since most four stroke engines use an internal compression release it can be hard to get a good reading with a gauge.My technique is to stick a finger or thumb over the spark plug hole and crank the engine,if you can't hold the compression back with a finger it is probably good enough to start so you can run other tests.(Note;if you use your own fingers for this make sure the spark plug cable is far enough away from your finger so you do'nt get shocked and do'nt stick your finger so far into the spark plug hole as to let it get pinched by the piston.) 
Safety first.
:thumbsup:


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## Rentahusband (Aug 25, 2008)

I learned how to make a leakdown tester from you tube with parts from Home Depot. It helped me diagnose a leaky ex valve on a 5hp Tech.


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## 1930 (Apr 14, 2013)

Don L said:


> Since most four stroke engines use an internal compression release it can be hard to get a good reading with a gauge.My technique is to stick a finger or thumb over the spark plug hole and crank the engine,if you can't hold the compression back with a finger it is probably good enough to start so you can run other tests.(Note;if you use your own fingers for this make sure the spark plug cable is far enough away from your finger so you do'nt get shocked and do'nt stick your finger so far into the spark plug hole as to let it get pinched by the piston.)
> Safety first.
> :thumbsup:


This is what I have been thinking and thanks for the info.


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## 1930 (Apr 14, 2013)

Rentahusband said:


> I learned how to make a leakdown tester from you tube with parts from Home Depot. It helped me diagnose a leaky ex valve on a 5hp Tech.


Thanks for the tip, I will have a look see on you-tube


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## Rentahusband (Aug 25, 2008)

I purchased a Mighty-Vac compression test kit for compression testing. I remove the valve on the appropriate hose and use the hose for my home made leakdown tester.


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## 1930 (Apr 14, 2013)

Rentahusband said:


> I purchased a Mighty-Vac compression test kit for compression testing. I remove the valve on the appropriate hose and use the hose for my home made leakdown tester.


Mightyvac, I think that is a Harbor Freight tool? I recently purchased one of these to help with a brake bleed on my truck, I will have to check this out further


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## Rentahusband (Aug 25, 2008)

1930 said:


> Mightyvac, I think that is a Harbor Freight tool? I recently purchased one of these to help with a brake bleed on my truck, I will have to check this out further


This is not a vacuum device. It is an actual compression testing kit, with various attachments for different size spark plug threads. Automotive/sm engine.


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## Jeff194307 (Dec 28, 2004)

A very simple way to trouble shoot a non running engine is to sray WD40 into the carb and attempt to start if it runs for a second, the you know that you have spark and compression, then you turn your attention to the fuel delivery system.


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## 1930 (Apr 14, 2013)

Jeff194307 said:


> A very simple way to trouble shoot a non running engine is to sray WD40 into the carb and attempt to start if it runs for a second, the you know that you have spark and compression, then you turn your attention to the fuel delivery system.


I have never tried WD-40 but have always grabbed the starting fluid or brake cleaner can


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## Don L (Jul 14, 2012)

I use a two stroke mixing oil bottle fitted with a gear oil bottle cap I've put a pin hole in filled with gas.Makes a handy little squirt bottle that do'sent spill gas everywhere,just use with caution.
I also use gear oil bottle caps on motor oil bottles,they fit most oil bottles and work much better than funnels.


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## 1930 (Apr 14, 2013)

Don L said:


> I use a two stroke mixing oil bottle fitted with a gear oil bottle cap I've put a pin hole in filled with gas.Makes a handy little squirt bottle that do'sent spill gas everywhere,just use with caution.
> I also use gear oil bottle caps on motor oil bottles,they fit most oil bottles and work much better than funnels.


I have been told recently and it makes sense to be very careful using starting fluids or anything that could possibly wash the oil off of engine parts that may really rely on the oil being there during start-up such as especially 2 stroke engines


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