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Delsley Jr
Delsley Jr, Mechanic
Category: Small Engine
Satisfied Customers: 688
Experience:  Handyman & Small engine repair Business owner
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I have a McCulloch 16 inch Chainsaw Model Mac 7-40. It will

Resolved Question:

I have a McCulloch 16 inch Chainsaw Model Mac 7-40.
It will not idle very well then cuts out and will not restart.
any ideas.
Rowly Crocker
Submitted: 5 years ago.
Category: Small Engine
Expert:  Delsley Jr replied 5 years ago.
HiCustomer... How old is it ? Will it restart after it cools back off ? What have you already tried ?
Customer: replied 5 years ago.

Hi Delsley

Manufactured 2006. Yes it will restart after it has cooled off but not easily

all I have checked is Plug and filter which seems fine

Rowly

Expert:  Delsley Jr replied 5 years ago.
I would suggest checking the spark at the spark plug to see if it is firing good. If it is firing good, I would check the fuel filter in the gas tank. If the filter is fine, most likely the carb is dirty or gummed-up inside of it and will need cleaned. If the spark is weak or not a good steady spark, I would say you have a weak coil on it.
Customer: replied 5 years ago.

Hi Delsley jr

I have checked the fuel filter and the carb both are in pristine condition. I should point out to you that the saw has only had about 5 hours use since new.

I have checked the plug and could see no sign of a spark, bot when iput it back together I eventually got it started and it ran for about 10 secs.

it looks like aweek coil. is that easy to replace?

Rowly

Expert:  Delsley Jr replied 5 years ago.
Has the saw got wet or damp at anytime before this problem started ?
Customer: replied 5 years ago.

Delsley

No not that I can remember it has got steadily worse ever since I bought it

Rowly

Expert:  Delsley Jr replied 5 years ago.
Ok, I would check the on & off switch sometimes they go bad and will cause problems like this. It could also be the coil is getting bad and is causing this problem your having. Coils when they go bad most of the time will lose spark when they get hot and after they cool down the spark will return and this sounds like what is wrong with your saw.
Customer: replied 5 years ago.

Hi Delsley Jr

I have replaced the coil, and it does seem to run better, but it is still difficult to restart. When I try to restart it it will fire for a few seconds then die, the only way I have managed to keep it going is to have someone squeeze the trigger the moment it fires.

Is the gap between the coil and the armature important ? if so what should it be, I set it as close as I could with out touching.

However It starts alright from cold.

Regards

Rowly

Expert:  Delsley Jr replied 5 years ago.
Yes the gap is important. I use a index card or business card to do it where they bend easy.
Delsley Jr, Mechanic
Category: Small Engine
Satisfied Customers: 688
Experience: Handyman & Small engine repair Business owner
Delsley Jr and 2 other Small Engine Specialists are ready to help you
Customer: replied 5 years ago.

That is how I set it. so thats OK. So why will it not restart?

Rowly

 

Expert:  Ranwell1 replied 5 years ago.

There are two possibilities now that could cause this problem.

 

First make sure you are using PREMIUM gas. Regular 87 octane fuel will ruin the engine on a two-cycle. You get what is known as detonation and it will score the piston and cylinder. This is especially true in the last 4 or 5 years since they changed the formula of gasoline and turned it to garbage.

 

Now as to your problems....

 

You either have low compression in the engine caused by a scored piston or cylinder.

This could have been caused by the poor gasoline as outlined above or could have been

caused by poor quality oil of lack of oil at some time in the saws life.

 

The other possibility is that even though the carburetor seems to be in good shape, it probably is not. Even if it only had 5 hours of use on it.....you probably need to COMPLETELY rebuild the carb. The diaphragms probably are a little bit stiff from sitting.

 

Please see my stock answer below for more information on this. I hope this helps.

 

 

 

As engines sit, fuel that is left in the carburetor can turn to gum and varnish and cause this and other problems.

Also, any gasoline that was left in a gas can for a period of more than 30 days must be discarded because it also has begun to turn to varnish.

More than 70% of all of our repairs in our lawn mower business are due to this same issue. You most likely have dirt, gum, varnish...etc in your carburetor plugging up the small passageways and jets in the carb. It Must be removed from the engine, cleaned very well, blown out with compressed air and reassembled using a NEW carburetor rebuild kit. ALWAYS clean the fuel tank and replace the fuel line when doing this repair or you may have to do it all over again. The inside of the fuel line disintegrates over time and these small pieces of rubber will plug up the carb too. Dirt and water from a dirty fuel tank will also plug up the carb. Find the Model, type and serial or code numbers off of the engine and take them to your local dealer to get the carb kit.

Expert:  Delsley Jr replied 5 years ago.
I would suggest checking the fuel line to see if it is getting cracks in it that would let it suck air if it is in good shape I would then recheck the carb as it may be bad. I know you checked the carb already but some parts are hard to tell if they are good or bad.

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