Sears chain saw fuel problems

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  #1  
Old 11-28-20, 01:36 PM
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Sears chain saw fuel problems

Not a specialist in small engine repairs and this should have been a no brainer.

My fathers approx 20 year old chainsaw kept stalling. It may run for a few minutes and stop. I checked the primer bulb and it was dry. When pressed I could air. I opened the tank and found the filter rolling around in the bottom of the tank. I cut back a little line and reconnected it. The saw was running again and then stopped. I opened the tank back up and the filter wasn't connected. The line was split. Ok..... figured I'd change the line.

I took the saw apart and found all the lines to be worn out from the age. There are three fuel lines. One from the tank to the primer. One from the primer to the carb. One from the carb back to the tank. The two to the primer were the same size. The other line was smaller. If you've ever changed fuel lines into a tank you know what a headache it is.

I replaced all the lines. When I pressed the primer a small amount of fuel came up the line. When pressed a second time it stuck in and pushed the fuel back to the tank. WTF. I took the primer bulb out and it is labeled carb and tank. I had the hoses in the right locations. I decided to swap them. Now the primer fills up with gas and the line back to the carb is full of fuel..... just like it's supposed to be.

It now starts but won't stay running.
I put it aside for today and will look at it again tomorrow.

Any ideas and what exactly does the small line from the carb back to the tank do ?
I thought it was a vent but the end is in gas.

Thanks.
 
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Old 11-28-20, 02:09 PM
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The line from the fuel filter in the tank goes directly through the small hole in the tank to the top nipple on the carb thus giving the carb a constant supply of fuel when running. The primer bulb is used only for "priming" and does not play a part in the fuel flow after that function. The bottom nipple on then carb then goes back to the nipple on the primer bulb which is clearly marked "Carb". The above connections are made with the smaller diameter tubing. From the primer bulb, marked "Tank", the larger diameter tubing is routed to the large hole in the tank. The tubing goes into the tank only 1/2 to 3/4 inch. As far as getting the tubing through the holes in the tank, cutting the tubing at a slant. But no matter what you do it is still a witch. Be patient, use some Vaseline and avoid the temptation to get out the drill and drilling the hole to a larger size.

See if this helps..
Start at about 3:30
https://www.youtube.com/watch?v=kljMOd3CCZs

 
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Old 11-28-20, 02:12 PM
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May need to look at the fuel pump section and diaphragm in the carb. They may be stiff and not pumping fuel, fighting each other? Like you, I am not a small engine specialist....

Jack of all trades, master of one. I'll let you know which one, if it ever comes up.

 
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Old 11-28-20, 02:16 PM
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The line from the fuel filter in the tank goes directly through the small hole in the tank to the top nipple on the carb thus giving the carb a constant supply of fuel when running.
Are you sure of this because mine looked to be backwards.


I put the filter on the line going to the primer bulb. The filter connection looks to large for the small line that goes from the tank to the carb.

When I opened the gas tank..... it was a larger size fuel line that was split and looked like it should have been connected to the filter. The small line stuck thru the tank approx 1/2". It doesn't look like anything could or would be connected to the small line.

That video looks to be very similar to my model. I'll give it a look. Thanks.

I found another video where the lines are run to different locations.
This one looks more like the way mine was setup.... video
 

Last edited by PJmax; 11-28-20 at 02:37 PM.
  #5  
Old 11-28-20, 02:50 PM
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I just learned something I wasn't aware of.... this is not a primer bulb..... it's a purge bulb.
It draws gas thru the carb and back to the tank.
 
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Old 11-28-20, 04:04 PM
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Fuel flow = from the filter to the top of the carb, out the bottom of the carb to the primer bulb, then out the primer bulb back to the tank (no filter on that line).

Changing lines isn't too hard. Pull out the line with the filter from inside the tank. From the carb side of the tank cut the end of the new line at a long angle and push that through to inside the tank. You can usually feel that end and if you have it cut thin enough you can catch it with pliers and pull enough through to clip the end and stick the filter on. Make sure you have that end long enough to lay the filter on the bottom of the tank.

Do the other line the same way.

When you hook up the primer, make sure the suction side is coming from the carburetor and the out bound side is going toward the tank (no filter)
 
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Old 11-28-20, 04:13 PM
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If you get the new lines on and still have trouble, on a saw that old, don't mess with kits, put a new carb on it. They run about $12.00 now for a carb, fuel lines, spark plug, fuel filter, air filter, and primer bulb.
 
  #8  
Old 11-28-20, 04:25 PM
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I should be able to reroute my lines correctly using the replacement lines I ran.
Easy enough to flip them on the purge pump.

The only messed up thing is that the supply line to the carb is supposed to be the smaller line. I doubt the filter would go into the smaller line. It would really have to be well stretched.
 
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Old 11-28-20, 07:23 PM
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Small line goes with the filter then to the top of the carb.

Clip the end square and hold the end in hot water for a minute. It'll stretch over the filter.
 
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Old 11-28-20, 07:33 PM
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Ok... thanks. I'll be working on it again tomorrow.
 
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Old 11-28-20, 10:11 PM
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Yep, small line has the filter and suplies the carb and the filter should be able to lay on the bottom of the tank. The large line goes from the pressure side of the primer back to the tank.
 
  #12  
Old 11-28-20, 10:21 PM
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Yeah.... so I've been told.
I have a feeling this was worked on before because the filter was on a larger line.

I checked out this video and it was set up exactly like mine.
video: start at 14:25
 
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Old 11-29-20, 12:04 AM
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Here ya go. A way to check if you have it connected right or not:
https://www.youtube.com/watch?v=uCC1qO75zDk

You may question if your check valve is working properly.

I think this will get you to where you want to be. Forget small and large lines, just work on the routing and go from there.
 
  #14  
Old 11-29-20, 07:53 AM
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For sticking the lines through the case I would cut them at an angle like I described. That way the fuel line is pulled to a smaller diameter as it goes through the hole in the tank.

If you use a larger line for both routings through the tank case you can have a problem at two points. One is the hookup at the carburetor and a potential air leak and the other at the hole in the case. If it was made for the smaller line and you pull a larger diameter line through in you would restrict the fuel flow through the line.

In the case do you have two different size holes for the lines?
 
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Old 11-29-20, 11:05 AM
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Yes.... I have two different size lines. The one near the fill is small and the other is the larger one.
This is from that video I linked to above.

Filter on large line


small line on purge bulb



My carb has two brass connection pins.... not that right angle black piece.
 
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Old 11-29-20, 06:58 PM
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It won't affect operation if the filter is connected to the larger line as long as that line is long enough to hit the bottom of the tank and is connected to the correct fitting on the carb and the other lines are connected to the right ports and all fit snugly.
 
  #17  
Old 11-30-20, 06:57 AM
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Yeah, that's a different routing of the small line. I don't know why they have the two different size lines on any of them. It's pretty common, but it seems more so on chainsaws. The filter would fit a lot easier on the larger line but the upper brass fitting is usually sized for the smaller line. It couldn't be to just distinguish one line routing from the other. There's a lot of other ways to do that. Interesting.

The one thing I've noticed over the years there's a lot of difference in the size of the smaller line. Not only the O D, but the I D has bounced around. I'd guess that comes in with the source.
 
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Old 11-30-20, 08:11 PM
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Here is a theory: Could have used lines both the size of the larger one, not sure WHY they choose to use a small and larger one.
However, looking at the flow of the fuel and sequence of operation, here is my thoughts.
When using the purge bulb, you are sucking fuel from the tank, through the filter, through the larger line, through the carb, into the purge bulb, back into the tank through the smaller line; a check valve is in this path to prevent back flow of fuel. This sequence is just to prime the carb with gas. Flow can only be as fast as fuel will travel through smaller tube, but doesn't matter as it is just to prime carb.
Once engine is running, the diaphragm in carb creates a sucking action to pull fuel through filter and larger tube. In order to supply the correct amount of fuel, the larger tube needs to be used, the smaller one may not be able to supply the volume needed.

 
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Old 12-02-20, 05:05 PM
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Thanks for all the help. I did reconnect the lines correctly. Now the chain starts on the first or second pull and stalls as soon as the trigger is pulled. Restarts easily will idle fine for several minutes. Pull the trigger and it stalls. Looks like it's time for a carb. The unit is 20 years old and had been pretty reliable. Looks like the parent company was Husqvarna or Poulan.

My Sears saw is a 358.360460
The OEM carb would have been 545081885.
The new replacements aren't the same. Apparently the filter box needs to be modified or buy the carb and filter box as a kit. The lines are on opposite sides of the carb.

In looking around.... I found eReplacement to offer the kit. About $30 with shipping.
eReplacement carb

Any thoughts ? The rebuild kit is inexpensive but is it worth the time to rebuild it ?
I'm fairly certain the diaphragm is shot by the way it's acting.






Thanks N.E. Wolf for the pictures.
 
  #20  
Old 12-03-20, 05:42 AM
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If it's starting well, Pete, I would try adjusting the mixture screws first. The screw farthest forward should be the low rpm screw. When you get it started turn up the idle stop screw a little. That gives you a few more rpms to work with. Then set the low mixture screw for max rpms.

See how the saw transitions from low to high with those settings. You may have to play with the low mixture screw a little to get it to snap off like it should..

If that takes care of it, turn the idle stop back down to have the chain barely moving at idle.
 

Last edited by marbobj; 12-03-20 at 06:14 AM.
  #21  
Old 12-03-20, 09:21 AM
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I'll try adjusting the mixture. It involves removing the red and blue limiter caps.
 
  #22  
Old 12-03-20, 12:39 PM
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You may get what you need inside the range of the caps. A little goes a long ways on those things.
 
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Old 12-03-20, 05:05 PM
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I tried adjusting with the caps in place right after repairing the line.
I tried feathering the throttle and adjusted them slowly but didn't notice any change.
 
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Old 12-03-20, 07:31 PM
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You'll have to take the caps off, then. The L screw (front one) usually affect the transition from low to high rpms.
 
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Old 12-11-20, 02:38 PM
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Just wanted to post the final outcome. I did end up buying the replacement kit from eReplacement. It came with a Wabro carb and the needed (modified) air filter housing to match the new carb. The new choke linkage would hit the old air filter housing so they came up with an "improved" version. Idle needed to be adjusted and a slight mixture adjustment but runs great now.

Thanks for all your help. It is appreciated.
 
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Old 12-11-20, 06:04 PM
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Bravo !!!! And Merry Christmas to ya, Pete !!
 
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Old 12-12-20, 02:02 PM
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Good, glad you got it going. Thanks for the update!
 
 

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