Problem with primer

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  #1  
Old 07-21-03, 04:51 PM
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Problem with primer

I have a Stihl string trimmer (model FS76) with a walbro diaphram carburetor (Model WT 227D). I was having a starting problem, so I rebuilt the carburetor with a K10-WAT kit. It has both a primer bulb and a mechanical choke. Before tearing it down, the primer bulb would work good. Now afterwards, the primer bulb wont work at all. I've got several Walbro service manuals and I followed them very closely. The new fuel pump diaphram isn't rubber but some kind of light brown material. I have even went back to the original...no luck. There are two extra holes in the newer one...but I can't see where that would make any difference. I'm not certain why, but I have a very low batting average on these diaphram carburetors. Any help and suggestions would be greatly appreciated. Does the carburetor have to be completely assemblied or will the primer bulb work with just the gas lines connected.
 
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Old 07-21-03, 05:25 PM
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Are you sure you don't have the two fuel lines mixed up. Try switching them around.
 
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Old 07-21-03, 06:09 PM
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Primer bulb situation

I have a Stihl string trimmer (model FS76) with a walbro diaphram carburetor (Model WT 227D). I was having a starting problem, so I rebuilt the carburetor with a K10-WAT kit. Before tearing it down, the primer bulb would work good. Now afterwards, the primer bulb wont work at all. I've got several Walbro service manuals and I followed them very closely. The new fuel pump diaphram isn't rubber but some kind of light brown material. I have even went back to the original...no luck. There are two extra holes in the newer one...but I can't see where that would make any difference. I'm not certain why, but I have a very low batting average on these diaphram carburetors. Any help and suggestions would be greatly appreciated.
 
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Old 07-21-03, 08:06 PM
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Hello: Jack

I combined your two postings into one but did not edit either. I would appreciate a small favor if you would so kind. Please use the reply button to update your question and or post replies back into it.

Doing so will keep all the threads together in one topic and make it much easier to read and follow along. Would greatly appreciate it. Thanks.

Do not feel bad about your statement "I have a very low batting average on these diaphram carburetors." You're not alone...

Diaphram carbs can be very annoying, time consuming, fustrating and not every mechanic gets an overhaul of this type of carb done right the first time...LOL!....

Try the suggestion offered by racer. Most likely may solve the problem. A very commonly made error by mechanics too.

If you need further assistance, use that 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.
Web Site Host & Small Engine Forum Moderator. "Accurate Power Equipment." Small Engine Diagnostics Services & Repair.
 
  #5  
Old 07-21-03, 08:15 PM
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Thanks fellows for your responses...I think the hoses are right because of their different lenghts. Should the primer bulb work if only the hoses are connected?
 
  #6  
Old 07-21-03, 10:05 PM
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Hello Jack!

Whether it will work with one line connected depends on how the primer operates. Some primers do nothing more than pump air into the tank, which pressurises it and forces fuel into the carb. Some primers pump fuel from one end, and suck it in the other, basically filling the carb with fuel and flushing fuel through it. The pressure side of the primer should be connected to the fuel line that runs into the tank and has no filter on the end. The fuel line with the filter is the suction side.
 
  #7  
Old 07-22-03, 06:22 PM
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Thanks for all your replys...but I feel that I may have a leaking crankcase (seals). What is the best way to pressurize the crankcase? I have a small handheld pressure/vaccuum pump. BTW this engine doesn't have a reed valve (its piston ported). Also, whenever you press the primer bulb, aren't you suppose to see gas squirting in the carburetor? Incidentally, I got the primer bulb to fill up with gas. After close examination, I noticed the gasket on the metering side was completely by-passing a small hole in the carburetor body. When I went back with the original gasket, it started working again. I guess you really have to watch those gaskets and diaphrams. I maybe chasing thin air but I want to try to prove someting about this crankcase.
 
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Old 07-23-03, 11:26 PM
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Will it start now? If so, with it running, spray some carburetor cleaner around the crankcase seal and see if the engine speed picks up noticeably. If so, it is leaking. I don't see many Stihl products with crankcase leaks, for what it's worth.
 
  #9  
Old 07-24-03, 07:55 AM
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Cheese,
That's my main problem, it won't start. Big fat blue spark though. Even when sprayed with starting fluid-no go. After pulling starter rope for a while, whenever I pull the plug-bone dry, not even a smell of gas. Incendiatally, what is the purpose of the un-filtered fuel line. Is it suppose to help pressurize the fuel tank?
 
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Old 07-24-03, 08:23 PM
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Yep, it either pressurizes the tank, and/or is a return for the excess fuel pumped by the carb.

Try using a few drops of gas instead of starting fluid. By your description, I think you may have a restricted exhaust. Remove the muffler, or pull out the spark arrester screen if equipped, and clean it out. I bet it's clogged.
 
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Old 07-25-03, 02:44 AM
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Cheese,
Are there any publications available (possibly on the internet) that give you helpful hints and tips on these two cycle machines (trimmers and blowers)? I have several books by Intec and a very good service manual from Walbro. Also, do you know of any schools or workshops? I do good with 4 cycle engines but just can't seem to "get it going" on these 2 cycle engines.
 
  #12  
Old 07-25-03, 05:41 PM
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I'm sure there are, try your library. I don't know of any, but I know they exist. 2Strokes are different animals, and can be aggravating at times, but once you get used to them they aren't so bad. The most common problems I see with 2 strokes are carb problems and restricted exhausts. Deteriorating fuel lines are also common.

Reading up on them will help, but hands on is the best teacher. We will be here to help when you run into one that stumps you. Did you check the exhaust on the trimmer?
 
  #13  
Old 07-26-03, 04:43 AM
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Cheese,
The exhaust looked fine. Thanks for your comments.
 
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