Good Fire, Fuel and Compression But! A Craftsman 18' 40cc w/n try

loger_gwNovember 15, 2011

Good Fire, Fuel and Compression But! A Craftsman 18" 40cc chainsaw w/n try to start. The bad fuel line and no filter led me to think it was only a fuel issue basically from sitting since last winter.

1. I replaced the bad fuel line, fuel, primed the engine with the bulb, and in the plug's hole later.

2. There was always a good blue spark with the original plug and one from a just fired saw.

3. The compression was good on the fairly new saw which made this A First And Frustrating.

What did I miss?

1. I look back on maybe the Carb was bad as Fuel Line But it should have tried to start, correct?

2. I switched to good gas and plug from my working saw. The other new plug fired my saw.

3. Timing was the element left, with Fire, Fuel and Compression but it was put away working.

4. Would working the carb solve anything before it's indicated as needed since it w/n fire the prime?

Any suggestions?? loger

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Loger: I know your more than competent within this problem , just a reminder to ensure a good blue spark . If not then new plug or as you have indicated a good reliable doaner plug is required. If no plug spark is evident then you coil or ignition module is faulty or you on/off switch is ! The latter can be tested or jumped to verify . If you have good spark then perhaps carb restriction or compression should be checked.

    Bookmark   November 16, 2011 at 5:26AM
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I got three hanging in my garage with the same problem. I too haven't gone through the carb. yet other than trying to just spray carb cleaner without thorough disassemble.

IMO the carb passages are plugged up only thorough disassemble, cleaning and new diaphramn will get you pass the fuel restriction issue.

I seldom remove the welch plug to get to the mid and high jets, but sometimes that's the only way to get the carb. unplugged and have chance to get it to run correctly. Problem is installing the welch plug back without the special installation tool (punch) shaped to get it to seal.

This IMO is common problem when they set with bad gas, you will see alot of them on the curb in the spring. That's were I got about 10, passed on another 10.

    Bookmark   November 16, 2011 at 5:36AM
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The saw has a very good blue spark, fresh fuel (that runs other saws), good compression. I question the chemistry of all of this being "Just Right" for the temperamental saw.

1. Is starter fluid a better option over fresh fuel as a prime in the plug's hole because it is stronger?

2. Is priming through the carb better for the chemistry and less flooding possibilities?

3. If the carb is bad from storage, why would it not try starting from a good prime?

My Basics Are Challenging Me Due To Less Time And New Technology.

Thanks! loger

    Bookmark   November 16, 2011 at 2:30PM
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Loger, carb cleaner is the preferred priming agent via the spark plug hole . If you have good commercial grade starting fluid (with lubricity additives) you could also use this agent for priming . You are correct that the flash point of starting fluid is lower and therfore a little more haz'd but effective when you us it properly as a last resort. What is the actual compression ?

    Bookmark   November 16, 2011 at 5:38PM
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All of this is my opinion so take it for what's it worth if anything?

I wouldn't use starting fluid IMO it has no lubricating properties and will wash what little oil residue is left in the combustion chamber and crankcase. IMO Carb. cleaner is much better choice it does contain some lubricating properties and closer to gasoline than Ether which IMO is close to alcohol without the water. IMO you can run the engine much longer off carb. cleaner in no load situation.

Now for your problem If you remove the plug spary carb. cleaner down the hole. pull the rope several times the comb chamber and crank case should be clear of all oily fuel residue (this would clear up you Chemisty theroy if the fuel mixture it correct or not). I always check spark by plugging into the spark plug laying if on the jug and watching for spark. Then I squirt one second blast carb cleaner down the hole, put the plug back in and attempt to start. It should fire or pop after couple of pulls.

If it fires up and rev's up some then I prime it through the carb. venturi with maybe 2 second blast. It should fire off three or four pulls rev up and die or take off on gas after the air is siphon out of the carb. If it will only fire off carb. cleaner and die after several attempt you have carb. problem. this could be reed valve (I have never experience bad one) diaphram problem not pulling the fuel up from the tank. or over rich condition (plug wet) from the needle and seat failure. If the diaphram is pulling the fuel up and it stil won't start or run then IMO you have plugged up carb. passage (very small ofices) somewhere.

After thorough cleaning All passages (including under the welch plug which houses three main jets, idle, mid, and high) assembled correctly. After all this if it still won't run IMO I would throw it in the trash and by new one Chances are if it's poulan it an't worth the bother anymore.....That's when I give up.

IMO If your doing this for customer I would be up front about it with fees and chances of solving the problem. Something like inform him of the charge for looking at the saw (checking for spark, compression check, clearing the comb. chamber, checking fuel filter/tank, and checking the spark plug) Then, what the charge would be for attempting to clean the carb. (no parts involve removal of the covers spraying out with carb. cleaner, and if that fails I would then say cleaning attempts didn't work. options are rebuild the carb and inform him of the cost of that and if still may not fix the problem. Most will not invest the labor and parts charge in an old small saw. Only use will some experience willing to attempt to fix them due to our time sometimes is worth the trouble when we get freeby discarded by someone who with no skill and will not spend the money it takes to maybe fix it. I don't blame them cause even if it fixed you still have old saw/equipment that still may not work the next time you attempt to use it or few months...

    Bookmark   November 16, 2011 at 5:59PM
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If so any fuel line sucking air from hair line crack may prevent the pulse diaphramn for working and pulling fuel up and through the carb.

    Bookmark   November 16, 2011 at 8:36PM
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Thanks ewalk & rcmoser! For the Carb Cleaner vs Starter Fluid info. I relate with this due to servicing and reading info on servicing 2-cycle outboards. A 2-cycle mix is needed in your fuel if you need to prime the engine vs possible damage. Carb Cleaner is all I own for carb cleaning purposes and never thought of it as a primer as some people say WD-40 will serve as. Now I'll have to ask if B-12 in a non-aerosol form will serve as a primer? I will usually have both due to soaking carbs with bad enough varnish in them.

I d/n use my compression gauge as I will when my thumb can hold in the compression (my rule of thumbs test that works). I have never charged for servicing an engine (which has been minimal) vs trying to help or teach worthy people (which have been big rewards since 1970 in many ways including tips and trades). Most of all, nothing is binding, no come-backs and I d/n donate my labor or work to the open public. loger

    Bookmark   November 16, 2011 at 9:37PM
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Yes B-12 in liquid form can be used for carb. cleaner. But, IMO it's hard to get the right amount in unless you got eye dropper. too much would create flooding condition possible wetting the spark plug and too little not enough to for the engine to take off and rev up (just my thoughts you probably already know this, information for the less knowledgeable noting pouring any liquid down the carb. risks chance of flooding or remote change of fire do to uncontrolled amount). B-12 also comes in aersol can also.

IMO when you have equipment that set for long period of time ususually only thorough cleaning of the fuel system is the only hope to get it going again. Again I have the best luck (as you probably know) starting at the fuel tank, fuel filter, fuel lines and then complete disassemble of the carb. Soaking or spraying with fine wire through the passages and spraying again. The reed valve (if equipment has them also provide the vacuum or pulse pressure through the carb. maybe someelse can explain if operation and function more in depth.

I use to collect parts (still have some, but got rid of majority), finding curb finds just for the parts if I can't get them going. Rarely buy new parts other than occassionally carb. kit. You just can't do nothing with bad diaphramn or spring, needle, and seat IMO.

    Bookmark   November 17, 2011 at 5:40AM
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