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String Trimmer Problem


SKIP's Avatar
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08-01-03, 09:18 AM   #1  
Shindaiwa String Trimmer

My Shindaiwa has given me years of excellent service (since 1985), with only minimal maintenance required. Lately it has developed what seems to be a fuel problem. It'll start and run fine for 20 or 30 minutes, until I stop it to adjust the strings. When I restart it, it lopes. Last time out it even died - quickly, as if the switch was thrown.Cleaning the carb (Walbro) and adjusting the screws got it running fine - for about 10 minutes.

I got it running again and was holding it in different positions to see if the pick-up tube was the culprit, when I noticed something I had never seen before. The pick-up was bubbling furiously. How in the world can gas and air go in opposite directions through the same tube at the same time?

I took off the gas cap and sniffed, but it only smelled like gas. (Boy, I'd hate to be one of them huffers.)

I'm going to dig into it some more when I get a chance. So far, I've got it penciled in for December. In the meantime, does anyone have any experience with this kind of problem, or any suggestions about how to figure it out?

 
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08-02-03, 08:23 AM   #2  
Carburetor Problem

Hello Skip. Welcome to the Small Engine forum.

Lets focus on possble problems.

Ignore the bubbles & directions of air and fuel flow in the lines for now. Try running the engine with the fuel cap off. If the engine continues to have the same problem, the vent hole in the fuel cap is likely restricted or plugged.

If this is the case, a vacuum will be created and fuel will cease to flow and air will be drawn into the fuel line. If this is not the case of a restricted vent hole in the cap, it is likely the carbs diaphram is defective. Replacement is the only solution.

There could be carb fuel flow restrictions within the carb. These are caused by stale fuel. Carb internal cleaning is required and the installation of new carb parts.

How the engine runs just prior to stalling may indicate flooding or an excessively lean fuel to air ratio. This needs to be mentioned in your reply. It helps to determine more accurately the cause.

Most likely I haven't covered all of the possibilities. The other resident small engine service and repair professionals may be able to offer additional suggestions, advice & help.

Check back on your question several times over the next few days for additional replies.

Small engine repair parts, generic repair manuals and additional help are all available at all local small engine repair shops and or lawn mower repair shops in your area. Shops and dealers are listed in the phone book directory.

Suggestion:
Read all already asked questions and the replies offered in them on this same type of problem for additional help & information. Doing so will provide additional possible causes and the solutions to correct them.

If you need further assistance, use the REPLY button. Using the reply button moves the topic back up to the top of the daily topic list automatically & keeps all communications in this one thread.

Regards & Good Luck.
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08-02-03, 09:24 PM   #3  
Hello SKIP!

One thing to add here, other than what has already been mentioned: Are you sure the fuel lines are connected to the proper spots on the carb? One of the carb fittings should be a fuel return, or a crankcase pressure line that pressurizes the tank with air to keep positive pressure on the supply line.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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08-04-03, 06:02 AM   #4  
The trimmer runs in its loping manner until it suddenly quits. It seems to run okay without the gas cap, but I didn't try it that way under load. Each time I start it, I need to open the fast idle screw another half turn. (I usually run out of patience before the screw comes all the way out, but it's been close.) The gas is fresh. I disassembled the carb and blew cleaner through all the ports and orifices, and checked the condition of the various needle ends. The diaphragm appears to be in good shape.

There is only one line connecting to the carb. The gas cap has no vent hole, but the tank does have what appears to be a vent tube supported by a bracket next to the carb. It's connected to what appears to be a check valve. I tried to blow through it. No dice. Couldn't suck any air through it either. (I tried some of my best jokes, which I've been told really suck, and still no luck.)

The spark plug is new, the muffler is clean, the wire connections are tight, and the insulation has no breaks (that I could find).

At this point, I'm suspecting that thing that I think is a check valve. The symptoms indicate that it's not getting enough gas, and no vent would cause that condition. I need to check with a Shindaiwa guy to see what that part is. It's a model T-20 that I bought in 1985, so that valve could be worn out.

 
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08-04-03, 08:45 AM   #5  
As an update to my update, I found the part in question (pn 20035-85522), and it's called a breather. A Shindaiwa parts man will have one for me tomorrow for $6.77 plus a cut for our congressmen. He told me that it is a check valve, and that I should be able to pass air through it (in one direction).

Hopefully, I'll have it on tomorrow night, and will post a "success" reply on Wednesday.

 
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08-05-03, 10:02 PM   #6  
I hope that does it! If your old one is clogged, you definitely need it. Let us know!


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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08-07-03, 06:53 AM   #7  
I picked the new part up Tue, and checked it before I paid - it did allow air to pass in one direction. Hooked it up that night and the trimmer worked fine for about 2 minutes, and then went back to its loping mode. Some things I observed: 1) loping occurs under load - all sounds normal w/o load; 2) motor position has no effect; 3) loosening the gas cap has no effect; 4) bubbles no longer came from pick-up; 5) the primer bulb fills with gas on its own, and then bubbles - it has never filled before without being pumped.

I fought with the thing, polishing the weeds until it would die, re-priming, re-starting, more weed rubbing, over and over - then, just when I was wondering how far I could throw it, it started and ran like it was on steroids, had more power than it's had in a long time, was cutting milk weeds as big as my thumb like butter. Some of the weeds saw it coming and just surrendered, committing hari-kari rather than submitting to such a vicious onslaught.

By then it was too dark to cut any more and I was out of weeds, so I will have to wait until the next episode. I think I must have a piece of crud in my carburetor that's intermittently blocking a check valve. Or maybe that gypsy curse is finally kicking in. I should know more after this weekend.

 
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08-07-03, 08:36 PM   #8  
Hehe, I think you are right about the crud. Sometimes making one run enough will pull whatever blockage is in the carb through.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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08-18-03, 03:23 PM   #9  
I finally got around to trying my trimmer again. (Last time it got dark and I ran out of weeds just as it started running good.) This time I waited until the temp got to over 100 - just for grins - and fired her up. Ran great, no problems. Started and stopped it several times, ran with different string lengths, etc. - all good.

Ready for the next problem.

 
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08-18-03, 08:57 PM   #10  
Glad it's running good! Good job


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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