Makita 7900 won't start

[foeke]

Hi guys, I'm on a loss here.
I have this 7900 that won't fire.
Full story is. The handle got crushed under a heavy branch with my hand in between.
Consequence being, my buddy replaced the handle (forgot the fuel filter), and together with my wife finished the yearly firewood collection.
The saw ran a couple of tanks alright, but then started to "not run nice". Then it shut off.
Next day it started again, but shut off again.
Now it doesn't want to fire anymore.

There is a spark, there is compression (I don't have a tester, but it's on it's way), there is gas coming in.
But even when I give it a bit if brake cleaner (acetone mixure), it won't pop.

Now I wanted to check the pistone, and found a hole in the exhaust, and the thing wont come off.
Does anybody have a "check this first" epiphany?
And an idea how to get the exhaust off?
Three bolts are off, but even some hammer time doesn't help.

 

[RED-85-Z51]

Did you get the ones down in the holes?

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[jeffbecky1]

my guess is something got in the carb while using it without fuel filter. take carb off and apart and clean it with brake cleaner. also, clean out fuel line before installing filter again

 

[foeke]

Did you get the ones down in the holes?

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Thanks! 5 bolts. . . Wouldn't have guessed

 

[foeke]

my guess is something got in the carb while using it without fuel filter. take carb off and apart and clean it with brake cleaner. also, clean out fuel line before installing filter again

Didn't think that needed checking with the industry standard "run on brake cleaning test".
I would have expected a short run of a couple of seconds when the carb is plugged.
But I'll (let it be) checked.

 

[Andyshine77]

I would definitely go through the carb. Break cleaner or starting fluid is not a good idea, a squirt of two cycle fuel mix is highly recommended.

 

[jeffbecky1]

Didn't think that needed checking with the industry standard "run on brake cleaning test".
I would have expected a short run of a couple of seconds when the carb is plugged.
But I'll (let it be) checked.

Running the saw for any amount of time without a fuel filter will quickly suck up any garbage floating in your tank and plug up the small round screen in your carb.

 

[lone wolf]

Running the saw for any amount of time without a fuel filter will quickly suck up any garbage floating in your tank and plug up the small round screen in your carb.

Or any other small place.

 

[foeke]

Just to come back with the outcome.
There was a tremendous amount of woodfibers in the carb.
So we thought we must have fixed it when we did a carb rebuild (with we, I mean my buddy, and I pitched in mental support).
But the thing still didn't even want to make a assuring bubbly sound when trying to start.
Apperantly the piston and cylinder are ex parts.
A dealer gave it his opinion and said. You might get it running, by rebuilding the top end etc. But it's very likely something else also paid the consequences of running far to lean.
And knowing my buddy, he probably never noticed it when it was leaning out.
The "I'll fix it when I'm done kind of guy".

The dealer had a new 372 XPG on sale.
He offered me a special "sorry that your saw couldn't be saved" deal.
That's now in the shed waiting for the weather to be cold.

 

[cuinrearview]

If you need a home for the 7900 I'm looking for some parts.

 

[Westboastfaller]

I would definitely go through the carb. Break cleaner or starting fluid is not a good idea, a squirt of two cycle fuel mix is highly recommended.

Industry break cleaner is the shít when all else fails but you have to strip it down, including all nylon.
Sink it in a coffee can with a lid on for a day.
It will bleach out the metal too. That is if you have the right stuff. It's been hard to get the right stuff in Canada in the last ten yrs. 3 days with the taimed down brake fluid may get you there.

 

[foeke]

If you need a home for the 7900 I'm looking for some parts.

I don't suppose you live near Germany?
It won't go in the F..it bucket.
The gas tank part is brand new [emoji26].
I'll give the repair a go. But Winter is coming. And I don't need the pressure of having it running perfectly before that time arrives.
When you actually live near Germany, please PM.

 

[foeke]

Industry break cleaner is the shít when all else fails but you have to strip it down, including all nylon.
Sink it in a coffee can with a lid on for a day.
It will bleach out the metal too. That is if you have the right stuff. It's been hard to get the right stuff in Canada in the last ten yrs. 3 days with the taimed down brake fluid may get you there.

I just use two drops of acetone, directly in the cylinder, to make stuff pop when it doesn't want to.
Acetone ignites in almost every ratio.
For example when a two stroke is flooded.