Reed valve / fuel pump failure

[The Moosehunter]

Had my 800 series slow down and stop when out last. Thought it was a fuel pump failure. Have taken the pump off, the diaphram seems fine although it just doesn't pump fuel. Fuel does get through when disconnected from carbs and primed. Compression fine on top 3 cylinders all around 165psi ( can't get to lower one ). How could I find out if it's a reed valve problem ? What would the symptoms usually be ? Or any other ideas please.

 

[NathanY]

Re: Reed valve / fuel pump failure

If it was a reed valve problem it would affect the bottom two cylinders that feed off the bottom carb. More than likely you lost your bottom cylinder due to timing or running to lean.

 

[The Moosehunter]

Re: Reed valve / fuel pump failure

It's not that I don't have compression of the bottom cylinder, it's just that my guage will not fit behind the casing.<br /><br />Does the fuel pump run on compression from all 4 cylinders or just one ?<br /><br />If a reed has gone wouldn't that affect all 4 cylinders not just the lower ones.<br /><br />How many valves are there ? I do not have a manual yet to tell. When I do get one could somebody estimate how long it should take a reasonable home mechanic to get the power head off (assuming all bolts undo OK, not that they will I'm sure ). Are there any speciallist tools that I may need prior to ruining, I mean removing the head.<br /><br />Thanks for any replies in advance

 

[mellowyellow]

Re: Reed valve / fuel pump failure

I suggest you look for an air leak in fuel<br />system before you go any further... maybe a<br />cracked hose or fitting. try a portable tank<br />and a new primer bulb as well.<br />good luck,<br />M.Y.

 

[JB]

Re: Reed valve / fuel pump failure

Howdy, Moosehunter.<br /><br />A reed valve failure would only affect the one cylinder that those reeds feed, unless that is the cylinder whose crankcase operates the fuel pump. Then it would not pump fuel to any cylinder.<br /><br />Compression would not be affected.<br /><br />Does the fuel pump pump fuel into a plastic bottle if you disconnect a carb line and place it in a bottle?<br /><br />Let us know what you find.

 

[The Moosehunter]

Re: Reed valve / fuel pump failure

I have replaced the fuel hoses in the motor and the ones from the tank seem fine. The bulb looks quite new although I can't be sure.<br /><br />Is it possible that a seal or something has blown in the crankcase area ? Is this common ? I must admit I'n no expert on 2 strokes but without sufficient pressure I guess it won't even allow a little bit of fuel in. <br /><br />Even if the fuel pump is knackered or the lines are leaking, should you be able to keep the carb bowls filled by using the primer bulb, allowing you to get some life out of the otherwise large useless paperweight.

 

[jim dozier]

Re: Reed valve / fuel pump failure

You can pump the fuel bulb by hand to check for a defcient fuel pump. However, sometimes a leak in the fuel pump diaphragm will cause fuel to be injected directly into the intake port of the cylinder to which it is connected causing that cylinder to run rich (in which case pumping the fuel bulb may make it worse. I believe fuel pumps are only connected to 1 cylinder. They just use the alternating vacuum and pressure that occurs in the intake port to run the fuel pump diaphragm. Using two 1-way (opposite) check valves, fuel is sucked in, then pushed out to the carbs.<br /><br />Make sure you are getting fuel to the pump. Check all lines and connections all the way to the tank. If the pump is pushing gas to the carbs, your problem is in the carbs. Reed failures happen, but not often. They are probably last on your list. When the engine bogs down, try pumping the fuel bulb to test the pump. Then try choking the carbs manually (enrichening) to see if the carbs are running lean.