Blower runs fine for half a minute, then dies

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  #1  
Old 10-28-11, 08:22 AM
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Blower runs fine for half a minute, then dies

Hi,

I have a Green Machine blower, GB-50. It has a Zama C1M carb. The machine will start and idle for 30 seconds or so, then die. Or I can rev it up, and it will also die after a short period.

After dying, it will not immediately restart. If I wait a few minutes, it will restart (choke on).

If I spray in engine starter fluid (ether), it will kind of run a bit.

- I tested compression - very good.
- I tested spark - adequate.
- I have put in the RB-44 rebuild kit, except for the welch plug.
- I cleaned the fuel strainer in the carb.
- I cleaned the fuel filter in the tank, and verified that it allows sufficient flow.
- I verified carb cleaner flow through the idle jets and main jet from the needle holes.
- I have verified the fuel pump will pull up fluid from a jar.
- I have verified that the primer bulb will fill the carb.

I think all this means:
- the engine is fuel starving after the fuel chamber empties
- the fuel chamber is refilling by gravity
- the vacuum fuel pump is working
- the idle circuit works
- the main jet (hi speed circuit) works

Why won't it work properly? Any guesses, or tests I might run?

Thanks,
/John
 
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  #2  
Old 10-28-11, 09:43 AM
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Try loosening the gas cap and see if it runs longer. It could be developing a vacuum in the tank.
 
  #3  
Old 10-28-11, 10:25 AM
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I'm not familiar with Green Machine equipment but I'll assume this is a two-stroke, not a 4-stroke engine, correct? For you and all others, take note: DO NOT use starting fluid (ether) as a start aid on 2-stroke engines!!! There is no lubrication in ether; you can easily turn a reversible situation dire! Instead, go the automotive parts store and buy a trigger-type oil can and add your pre-mixed gasoline to it and use this as a start aid for your 2-stroke engines.
 
  #4  
Old 10-29-11, 11:19 AM
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Still dying...

So, a few more tests, several more carb re-assemblies, and it still dies abruptly after running well for 30 seconds or so.

Removing the fuel cap allows fuel to gravity feed out the gas line with more flow. It also seemed to let the blower run at idle longer (over a minute). But then the next time it dies again and at full throttle, it dies in 10 seconds.

I verified that the passages from the fuel chamber out the idle jets has flow, using a syringe. Same for the main jet, although it's a much smaller flow than the idle jets. I verified flow from the fuel inlet and out the fuel chamber needle, but only if the needle was opened.

I verified the one-way flows for the primer bulb. I verified the air hole for the dry side of the diaphragm.

I eliminated the gas tank and tank filter and ran it from a cup of gas. It still died.

I even used a syringe to provide pressurized gas to the fuel inlet when I ran it. It still died.

Conclusions:
- it's dying for lack of fuel.
- All passages are free flowing.
- somehow, the needle is closed, or the pump is not working.

Possibilities:
The crankcase is leaking air, preventing strong carb pumping.

Any suggestions? I have to purchase a leak down tester and make a cover plate for testing the crankcase.

Thanks for the warning about using ether on 2-stroke engines. Yes, it's two-stroke.
 
  #5  
Old 10-29-11, 09:37 PM
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Originally Posted by torrmundi View Post
So, a few more tests, several more carb re-assemblies, and it still dies abruptly after running well for 30 seconds or so.

Removing the fuel cap allows fuel to gravity feed out the gas line with more flow. It also seemed to let the blower run at idle longer (over a minute). But then the next time it dies again and at full throttle, it dies in 10 seconds.

I verified that the passages from the fuel chamber out the idle jets has flow, using a syringe. Same for the main jet, although it's a much smaller flow than the idle jets. I verified flow from the fuel inlet and out the fuel chamber needle, but only if the needle was opened.

I verified the one-way flows for the primer bulb. I verified the air hole for the dry side of the diaphragm.

I eliminated the gas tank and tank filter and ran it from a cup of gas. It still died.

I even used a syringe to provide pressurized gas to the fuel inlet when I ran it. It still died.

Conclusions:
- it's dying for lack of fuel.
- All passages are free flowing.
- somehow, the needle is closed, or the pump is not working.

Possibilities:
The crankcase is leaking air, preventing strong carb pumping.

Any suggestions? I have to purchase a leak down tester and make a cover plate for testing the crankcase.

Thanks for the warning about using ether on 2-stroke engines. Yes, it's two-stroke.

Have you done a compression test on this engine, if so what is it?
 
  #6  
Old 10-29-11, 11:52 PM
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He said the compression was good, so it's in the fuel system. I'd suspect that the carb is partially blocked somewhere, but try prying the needle valve lever up just a hair so that the needle will open a hair sooner and farther. See if that helps.
 
  #7  
Old 10-30-11, 09:03 AM
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Cheese,

I did try adjusting the needle valve lever upwards a hair. Same result, so I think it something else.
 
  #8  
Old 10-30-11, 09:52 AM
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This morning I filtered the gas through a rag and tried again. It started hard, but then ran without stopping as long as I get it above idle. It was giving off a lot of blue smoke, so I started adjusting the Hi and Lo needles. It was pretty unresponsive to the needles and was sputtering a little gas out the air inlet (I have the air cleaner off). So I think maybe I overdid the adjustment of the fuel-chamber needle lever, even if it was very little. I'm going to restore the lever adjustment and try again.

I'm not sure what has given it life. It could be:
- some partial blockage in the carb has flowed through
- I managed to seal an air leak between the carb and the crankcase
- I filtered the gas that it no longer fed junk into the carb

BTW, pumping the primer bulb works, but there is always some air being pumped, as well as gas, and there is always residual air in the primer bulb. Is that normal or is that a bad problem? Seems like it should be a closed system. Air leaks could be from the primer gasket, the diaphragm gasket, the diaphragm (pinhole), or the lo or hi jet check valves.
 
  #9  
Old 10-30-11, 11:10 AM
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Blower is running again

Well, persistence pays off and I appreciate your responses, Cheese!

After adjusting the needles and idle screw, it seems to be running well again.

Some lessons learned:
- adjusting the needle valve lever is a very fine business and it's quite likely you'll introduce a new problem (excessive richness) rather then fix an existing issue.

- be scrupulous about cleanliness. I'm not sure if that was an issue for me or not, but it could have been.

- start with fresh gas or be darn sure you've filtered out any junk.

- run the tests one by one to eliminate any issues.
-- at a system level to include as much of the process under test as possible.
-- at as low an isolated level as possible to be sure each passage is clear, or each tube is good, etc.

/John
 
  #10  
Old 10-30-11, 11:41 AM
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Great! Glad you got it and thanks for the update!
 
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