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Stihl 045AV Chainsaw - Fuel Blows Back Thru Carb


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09-09-07, 12:40 PM   #1  
Stihl 045AV Chainsaw - Fuel Blows Back Thru Carb

Hi,

I have an 045AV Stihl Chainsaw that I picked up recently - mainly for parts, but it seems like it is in good enough shape to get running again.

When I try to start it, it hits for just a couple or three seconds. The most obvious symptom is a good bit of fuel being blown back through the carburetor.

Although I did not think it the issue, I did put in a carb-repair kit to eliminate that as a possibility. No go.

This gets me to thinking that it is a timing issue. On the other hand, I recall reading somewhere that these things may have some sort of reed induction. If it does, that seems to be the most likely culprit.

I do not have a repair or parts manual. Would replacing the reed valve involve splitting the crankcase? Any other suggestions would be welcome.

Thanks, Mark

 
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09-09-07, 04:09 PM   #2  
I don't know if an 045 is a piston port or a reed port intake so I can't tell you if you have a possible faulty reed or not. What I can suggest is taking the muffler off and apart and inspecting the exhaust port and muffler for blockage from excessive carbon buildup. While your there, have a close look at the condition of the piston and cylinder through the exhaust port. Perhaps someone will post in with first hand knowledge of the intake port design on an 045.

 
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09-09-07, 06:13 PM   #3  
Hey Puey,

What you said gave me an idea, so I popped the carb off and looked from the intake side. There is nothing but open air to the piston. I see a little scoring, but nothing horrible. What I can see of the lower ring (if there are more than one), looks OK.

There is a small protrusion at the top of the intake port that makes me wonder if something is supposed to be attached to it -- like a reed. Uh oh. I was a motorcycle mechanic back in the 70's, so I am familiar with a piston-port design. See no reason for the bump.

Thanks for your suggestion, Mark

 
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09-09-07, 08:37 PM   #4  
I don't think you're missing anything...I think your exhaust is stopped up.


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09-09-07, 08:50 PM   #5  
Hey Cheese, I sure hope ur right. LOL

I'll take a gander at it tomorrow. Looks like a new exhaust on it. Who knows. Maybe a dead rat or sumpin.

Mark

 
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09-09-07, 08:55 PM   #6  
Even if it's not the exhaust causing the problem, I don't think it's the lack of reed valves. I don't think this saw has them. Usually I find gas blowing out the carb to be a sign of an exhaust restriction though.


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09-09-07, 09:55 PM   #7  
OK Cheese.

I could not stand to wait, so I removed the exhaust pipe. It has been bashed some, but I blew through it and would not call it obstructed.

I got a better look inside the cyclinder. As with the intake side, I see some scoring, but nothing horrible. Rings look OK. Guess I will round up a compression gage and see what I get. Reckon a good bit of blow-by might spew fuel back through the carb.

I believe it to have electronic ignition, but my older one (I bought in 1976) has points.

Let you know what I find out.

Mark
Mark

 
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09-12-07, 09:07 AM   #8  
Checked compression: 130 PSI so that is OK.

Got the flywheel off and it is electronic ignition. Someone obviously has worked on it. On the inside of the flywheel, there is scoring where the coils were definitely rubbing on the flywheel itself. I loosened the coils and one moved in a good amount. Would this cause any issues by itself?

Also, the stator plate was rotated as far counter-clockwise as it would go making it fire as late as possible. It looks like there were some parts replacements/repairs done in there and maybe not done so well.

Do not know what an entire stator assembly runs for one of these things.

 
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09-12-07, 10:57 PM   #9  
Sounds like a mess. The scraping on the flywheel got my attention the most. Check side play on the crankshaft.


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09-13-07, 03:14 AM   #10  
The flywheel is not scraping now. The primary coil either was replaced or something done to it. When I loosened the screws and pushed it towards the center, one end moved a good bit inward so it was not set in there correctly.

I do not have a service manual, but plan to put the stator in the middle of the adjusting slots. Any thoughts on checking the timing other then to get it running and see how it does?

 
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09-13-07, 08:02 PM   #11  
I don't think I've ever had to deal with that aspect of one of those saws. A service manual would come in handy here, lol. If there is no way you can see to judge the setting, go by old screw marks where it was set before, or give it a shot with your best guess. Other than that, I don't know.


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09-14-07, 07:19 AM   #12  
Hey Cheese,

I usually put things back like that too, but when I even look closely, there is no way to tell where it was originally.

Sometimes I put a small screwdriver on top of the piston and flip the flywheel past the timing area. If a spark is relatively easy to get, I can kind of tell when it is at least good enough to run -- or, at the very least, it is firing before top dead center.

I got a new spring connector for the top of the spark plug. Any suggestions on how to get it into the new cap? I poked the wire through and tried to pull it back from the plug side, but it just keeps coming off.

Got a lot of putting back together to do, but I'll let you know how it turns out.

Mark

 
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09-14-07, 07:58 PM   #13  
I usually get those clips on by pushing the coil wire through the rubber boot, and out the other end, install the clip, and pull the wire back into the boot along with the clip. Sometimes you might have to bend the wire on the clip a bit to make it more hooked.


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09-14-07, 08:45 PM   #14  
Well Cheese,

I got it all back together and it is like I did not do anything. Back to square one. Unless this thing does have reed induction, I don't get it. Ugh.

I have assumed the fule is coming back through the carb. Maybe it is coming from somewhere else. Leak somewhere maybe.

 
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