# Minimum chainsaw compression for starting and running.



## Okie (Nov 6, 2015)

*What would be the approximate minimum compression for a chainsaw to start and run?*
I have a itty bitty Homelite super 2 that has about 80-90 lbs compression after about 6 pulls of the rope, spark seems ok and it won't even make a promise pop when cranking by adding mixed gas in the carb throat. I've rebuilt the carb.
It briefly started and ran at wide open throttle once for little while before I carefully installed a carb kit, thinking the carb kit would get it going at low and high speed, but now won't even make a promise pop????
Acts like it got mad at me and sulled up!!!!!!!!!
I changed spark plugs and checked ignition spark several times.

Next question: If a saw requires high compression for starting* why does a Homelite EZ with the manual compression release start and run easily at reduced cranking compression???*


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## pioneerguy600 (Nov 6, 2015)

Under reduced compression on a good tight saw the comp is still over 120 lbs, with the comp release closed it should be 140 or over. If a saw has less than 100 from the outset then it likely will be very hard to start and flood out easily.


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## ChoppyChoppy (Nov 6, 2015)

I had an ms360 with about 125psi compression. Ran fine, but if the decomp got pushed it wouldn't start. Also was fussy if I left it outside when it was cold.

I have seen saws with only 90psi run, but most wont.


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## fearofpavement (Nov 6, 2015)

This question is pretty model specific. I'm thinking 90 psi is pretty low on just about any saw. Have you checked other chainsaws to see how your compression check compares on those? (gauges can have a lot of variance)


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## AVB (Nov 6, 2015)

Okie, I see out on other forums. LOL. Not using that crane to lift that saw are you?

Usually for it takes around 100 psi for most 2 cycle to start. Pull the muffler and take a look see at the piston and cylinder for damage or just a stuck ring. You be surprise how many stuck rings I free over the years on trimmers and chainsaws.

As I said on the other forum my Little Red has 110 psi on only a couple pulls.

Those decomp valves are metered ports that allow compression to bleed off so it makes the engine easier for the operator to get the engine up to starting speed. Think of it like this try blowing a small tube. Blowing thru it slowly is easy but try blowing thru it fast and it a harder as produces back pressure. I had a Husky that I rebuilt that had over 100 psi with the decompression valve completely missing. It started and ran but ran a lot better once I install the decomp valve.


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## Okie (Nov 6, 2015)

fearofpavement said:


> This question is pretty model specific. I'm thinking 90 psi is pretty low on just about any saw. Have you checked other chainsaws to see how your compression check compares on those? (gauges can have a lot of variance)



Yes about the gauge variance readings. Automotive compression gauges would only go to about 35lbs in 6 pulls with a dry cylinder and to 125-140 with oil in the cylinder of the super 2. I finally bought a Actron cp7828 compression gauge kit after I was given a hint that most automotive gauges will read very low. the shrader valves in the cp7828 are different (weaker springs on the valves I suspect) than standard automotive compression gauges. I pulled the muffler and looked at the piston and cylinder and they appear ok and the piston only has one ring which is not stuck and what little I could see looked nice and shiny with no scratches or gouges.. I'll try adding spoonful of oil to thru the spark plug hole and see how much the comp increases on the new Actron gauge kit. I suspect it will probably increase to the 140 area indicating a worn out saw. I did not try this again because I thought 80-90 should at least produce a pop?
The saw was gave to me because it would not start.

I could not check the good running Homelite EZ compression using the manual release vs no release because I could not get the long screw in spark plug adapters into the space with the handle on the saw was why I asked about such.
I'll retest with little 10W oil in the cylinder to see how much the compression increases so as to get an idea of cylinder ring wear. Just tugging on the starter rope of the super 2 seems to indicate weak compression as compared to others saws that don't have use a compression release.


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## Rx7man (Nov 6, 2015)

I have an old homelite XL12, it feels like it's got no compression (I didn't bother checking it), but it starts up with about 3 pulls every time... doesn't make much power in the cut though... it's funny how some saws with low compression seem to do surprisingly well, while others just quit if they have less than 140psi


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## pioneerguy600 (Nov 6, 2015)

Rx7man said:


> I have an old homelite XL12, it feels like it's got no compression (I didn't bother checking it), but it starts up with about 3 pulls every time... doesn't make much power in the cut though... it's funny how some saws with low compression seem to do surprisingly well, while others just quit if they have less than 140psi




I have seen that more on the older all magnesium chainsaws, for the most part they had longer stroke and heavier flywheels plus they had points and condenser+ coil ignition systems that made a fatter blue spark when pulled over. The newer saws with electronic ign modules seem to produce a weaker spark when just pulling them over with the recoil.


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## dsell (Nov 6, 2015)

Probably flooded. They won't pop when they're drowning. Perhaps the inlet needle isn't closing. Also, possible to pull bar oil up in the crankcase, depends on the design. The super 2 will run on 90 psi but it won't have the power it should. That's assuming it's from wear. This is from my experience of the 10 XL's I've owned. If it's scored bad, you'll probably get mixed compression results and it won't run. I've seen very misleading compression results on very badly scored saws. It should be around 120 to 130. I might have a new cylinder and crankcase for $30, but no piston.


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## Mark71GTX (Nov 6, 2015)

I would think it is probably flooded. Pull the plug and dry it out. See if it will start then.


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## smokey7 (Nov 6, 2015)

I have a motor here also. I know it has good compression, and other good parts on it. Its yours for shipping.


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## Rx7man (Nov 6, 2015)

pioneerguy600 said:


> I have seen that more on the older all magnesium chainsaws, for the most part they had longer stroke and heavier flywheels plus they had points and condenser+ coil ignition systems that made a fatter blue spark when pulled over. The newer saws with electronic ign modules seem to produce a weaker spark when just pulling them over with the recoil.


Our old Husky 65 that was bought the week I was born had 0.080" ring gap on a single ring and it still ran, but was hard to start and didn't have much power... I never took a compression reading but I'd guess around 100-110... I'm surprised it ran at all, or long enough to wear the ring that much... besides the ring was so thin around the exhaust port it was very close to snapping and hanging up, and a little scoring. That P&C became the donors for my 'wild' husky 65, since they weren't perfect I wasn't too concerned about going a little too far with the porting. 90* exhaust, 85* intake, 3/4" carb, .014" squish and 140 PSI now, it runs pretty good, though I think my squish is a little tight... I do hear the piston touch a little bit once in a while I think... I'll take it apart at some point and see if that's what I'm hearing, or perhaps detonation? Either way I'm not terribly concerned.


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## AVB (Nov 6, 2015)

Rx7man said:


> I have an old homelite XL12, it feels like it's got no compression (I didn't bother checking it), but it starts up with about 3 pulls every time... doesn't make much power in the cut though... it's funny how some saws with low compression seem to do surprisingly well, while others just quit if they have less than 140psi


Come to think of it I had a Poulan 3716 here a few weeks ago that would not start and it had 110 psi but when I pull the muffler I found why; totally trashed. The only I was getting such a reading was the excess fuel in the cylinder chamber.


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## Okie (Nov 6, 2015)

smokey7 said:


> I have a motor here also. I know it has good compression, and other good parts on it. Its yours for shipping.


I sent you a PM asking about shipping and my zip code for estimate?
74346 to Oklahoma.


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## smokey7 (Nov 6, 2015)

Recieved/responded glad to give back to the forum that has helped me out so much.


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## Rx7man (Nov 6, 2015)

I have 3 PP 4218AVX's.. the best one has about 80 PSI... it barely runs..


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## Okie (Nov 8, 2015)

smokey7 said:


> Recieved/responded glad to give back to the forum that has helped me out so much.



Another PM sent.


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## Okie (Nov 22, 2015)

smokey7 said:


> Recieved/responded glad to give back to the forum that has helped me out so much.



Smokey7:

Check you PM.

Later


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## dynodave (Nov 22, 2015)

My freebee itty bitty homelite "seemed" to spark (in air). Would not run or fire up. Opened the points gap and now "it's alive"............


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## Okie (Nov 29, 2015)

Smokey7


Check your PM's.

I still need the Homelite parts we discussed.

*Let me know something?*


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## BigDee (Nov 29, 2015)

Well I hope Smokey7 is OK.


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## Okie (Nov 29, 2015)

BigDee said:


> Well I hope Smokey7 is OK.




Me too.

I've sent him couple PM's with last two weeks and no reply!

He just evaporated????

Might need to put out a missing person search or maybe a *Ember* alert?


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## Anthony Pillois (Dec 12, 2017)

Rx7man said:


> I have an old homelite XL12, it feels like it's got no compression (I didn't bother checking it), but it starts up with about 3 pulls every time... doesn't make much power in the cut though... it's funny how some saws with low compression seem to do surprisingly well, while others just quit if they have less than 140psi


your right as rain, I've got a Poulan Pro that doesn't have enough compression to blow paper towels out of the spark plug hole but I've used it for the last 2years its runs perfect for cutting wood up to 8 inches in diameter


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## Anthony Pillois (Dec 12, 2017)

pioneerguy600 said:


> I have seen that more on the older all magnesium chainsaws, for the most part they had longer stroke and heavier flywheels plus they had points and condenser+ coil ignition systems that made a fatter blue spark when pulled over. The newer saws with electronic ign modules seem to produce a weaker spark when just pulling them over with the recoil.


the newer saws with the electronic ignition can produce a blue spark by cleaning the coil and magneto and gauging them with a sheet of writing paper folded in half, most companies require them to be set with 0.10 of air gap which is about what a piece of paper folded in half is hope this helps


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## pioneerguy600 (Dec 12, 2017)

Anthony Pillois said:


> the newer saws with the electronic ignition can produce a blue spark by cleaning the coil and magneto and gauging them with a sheet of writing paper folded in half, most companies require them to be set with 0.10 of air gap which is about what a piece of paper folded in half is hope this helps



More commonly a business card is used these days to set the air gap between the module and flywheel as common card stock is in the .010 - .012 range. The modern electronic modules make less spark at lower rpm like when being pulled over with the recoil, they certainly make adequate spark to start the engine.


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## Okie (Dec 12, 2017)

I seen this post has come alive and also that I failed to report back the latest about the little homelite super 2 saw that would not start with low compression.
I had two of them little homelites just alike one ran great and this one no go. I set the problem saw back thinking I would keep it as a parts saw and few days or weeks later later picked it up cold and it fired and briefy ran cold and when I tried a prime and it flooded with no pop, let it sit 24 hrs and it would briefly run again when cold. I swapped the two carbs and the problem was the carb. A kit and good cleaning in a ultrasonic would not fix the bad carb. (and I'm usually good and repairing sall carbs but this one would not come around)
I located a ebay carb and both saws are running and cutting great one with 80-90 lbs compression and piston and cylinder looks good and it starts easily.
Summary: Bad carb would briefly allow saw to run if saw set for about 10-24 hours then would flood the crankcase/engine.


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## Anthony Pillois (Dec 12, 2017)

Okie said:


> I seen this post has come alive and also that I failed to report back the latest about the little homelite super 2 saw that would not start with low compression.
> I had two of them little homelites just alike one ran great and this one no go. I set the problem saw back thinking I would keep it as a parts saw and few days or weeks later later picked it up cold and it fired and briefy ran cold and when I tried a prime and it flooded with no pop, let it sit 24 hrs and it would briefly run again when cold. I swapped the two carbs and the problem was the carb. A kit and good cleaning in a ultrasonic would not fix the bad carb. (and I'm usually good and repairing sall carbs but this one would not come around)
> I located a ebay carb and both saws are running and cutting great one with 80-90 lbs compression and piston and cylinder looks good and it starts easily.
> Summary: Bad carb would briefly allow saw to run if saw set for about 10-24 hours then would flood the crankcase/engine.


okay the only thing that would cause the gas to go into the crankcase is the needle jet not sealing properly, as you know that's a easy fix


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## Deleted member 117362 (Dec 12, 2017)

Anthony Pillois said:


> okay the only thing that would cause the gas to go into the crankcase is the needle jet not sealing properly, as you know that's a easy fix


A plugged exhaust will also cause a flooding issue.


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## Anthony Pillois (Dec 12, 2017)

Duce said:


> A plugged exhaust will also cause a flooding issue.


i agree, but you said you looked at the piston you would have noticed that unless you were in a hurry and from the sound of your post your pretty thorough


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## undee70ss (Dec 12, 2017)

Normal compression pressures for Homelite saws. Taken from a Homelite training manual.


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## Anthony Pillois (Dec 12, 2017)

undee70ss said:


> Normal compression pressures for Homelite saws. Taken from a Homelite training manual.
> 
> View attachment 618297


I agree that's what it should be under normal circumstances but a saw can run with considerable less compression you just have to tinker with them I've been repairing small engines for over 40 years and in most cases low compression usually means you are going to use it under less of a load


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## Okie (Dec 12, 2017)

undee70ss.

Thanks for posting the *normal training manual compressions* for Homelite chainsaws. I saved it too my Homelite computer reference file and also printed it off for my shop file.

But I've seen several saws (when all else is ok) that will start easily, run strong and cut ok when the compression is below the recommended per the book (taking the reading with a accurate gauge) If I see the piston and/or cylinder is scored I don't bother trying to save the existing. I've seen some EZ Homelites that run real good with 135 lbs compression for example. Even if compression is real good* I take a peek at the piston/cylinder to see if any cancer is inside. (and is usually the first thing I check)*

I've got an old good running 30 year old 028 Stihl with a 16 inch bar that I use every season for firewood and when checking compression it should not even start or run. (probably would not pull a 20 inch chain but does real good with a 16 inch aggressive cut chain)

Sometimes a guy* will get pleasantly surprised how good a saw operates when compression is low*, therefore I do take compression readings with a grain of salt. (and I do not trust the picture of very high compression readings I see on ebay of saws for sale) Too much puffing and buying a used as is chainsaw on-line is in the same category as buying a pig in a poke.


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## Anthony Pillois (Dec 12, 2017)

Okie said:


> undee70ss.
> 
> Thanks for posting the *normal training manual compressions* for Homelite chainsaws. I saved it too my Homelite computer reference file and also printed it off for my shop file.
> 
> ...


I am doing a video for utube tomorrow using a Mac 1010 with 150 ppsi compression and a Poulan pro 5020av with less than 50 ppsi compression not even enough to blow paper towels out of the spark plug hole and yet I have used it for 2 years I hope y'all check it out tomorrow afternoon


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## alderman (Dec 13, 2017)

Rx7man said:


> I have an old homelite XL12, it feels like it's got no compression (I didn't bother checking it), but it starts up with about 3 pulls every time... doesn't make much power in the cut though... it's funny how some saws with low compression seem to do surprisingly well, while others just quit if they have less than 140psi



I was going to post this also as my old XL12 is much the same. Now I'm kind of curious so may put the gauge on it just to see what it really is. 


Sent from my iPad using Tapatalk


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## Anthony Pillois (Dec 13, 2017)

alderman said:


> I was going to post this also as my old XL12 is much the same. Now I'm kind of curious so may put the gauge on it just to see what it really is.
> 
> 
> Sent from my iPad using Tapatalk


i plan on posting a easy to understand comparison on compression between a Mac1010 and a Poulan Pro 5020av the Mac 1010 has 150 lbs of compression and the Poulan only has 30 lbs of compression and after all the research the Poulan isnt suppose to run but after tomorrow people will see low compression isn't the end of the road for the saw


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## TrevorH (Dec 13, 2017)

I generally go with 110+ is good, 100-110 is maybe weak depending on the saw, and 100-90 is probably bad, 90- is definitely something wrong. But always do a muffler check too


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## TheTone (Dec 13, 2017)

Looking forward to seeing a 30 psi saw run.


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## Anthony Pillois (Dec 13, 2017)

TheTone said:


> Looking forward to seeing a 30 psi saw run.


I tried to get it uploaded on utube but it wouldn't upload so I put the video on Facebook, look under Anthony Pillois and check out the post and you will see the Poulan pro 5020av run


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## Anthony Pillois (Dec 13, 2017)

I just got the video on utube so if you search utube for low compression under Anthony Pillois you will see the Poulan Pro 5020 crank and run


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## undee70ss (Dec 14, 2017)

Anthony Pillois said:


> I just got the video on utube so if you search utube for low compression under Anthony Pillois you will see the Poulan Pro 5020 crank and run


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