721D RPM change

tew45

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I have a 2004 721D that the RPM drops after a quick turn. It doesn't stop but just drops down then recovers quickly. The tank can be low or full and the add on clear line filter is nearly full. What will cause the RPM change?
 

shiftsuper175607

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I have a 2004 721D that the RPM drops after a quick turn. It doesn't stop but just drops down then recovers quickly. The tank can be low or full and the add on clear line filter is nearly full. What will cause the RPM change?

not enough info to work with...seems fuel related....but?
 

tew45

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I really think the fuel filter may have an issue but I thought someone else had a similar experience and could shed a little light on the subject. The fuel cutoff is working with no problem. Filter has a little over 200 hrs on it.

The problem again: Mowing thick or thin grass, engine full speed, tank full or low, and make a fast turn right or left (seems worst with left turn) then after 1 or 2 seconds the RPM will drop to at least 1/3 of full RPM then after approximately 1 or maybe 2 seconds the RPM will return to normal. It is not really a problem but it is beginning to be aggravating since the tension pulley on the PTO belts just fell off and I'm ordering parts.
 

tew45

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I changed the fuel filter today while doing the weekly maintenance and after mowing a short time the problem is still there. Is there a filter screen in the fuel tank that is removable? I mow around 20 acres and this is getting to be a pain. I can make a fast turn right or left, fuel tank fill or low (makes no difference still RPM drops) I can make a slow turn with no problems but when fast I can count 3 seconds and the RPM drops and recovers.
 

bertsmobile1

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It is a problem in the carb.
Rapid turns cause the fuel to rise inside the float bowl which lifts the float which cuts off the fuel which causes the fuel level to drop which makes it harder for the venturi to suck the fuel into the emulsion tube so you slow down for a second or two.

In reality the mower is working outside the operational parramiters of a float carb.
And the only real solution will be to fit a diaphragm carb or a fuel injected engine

This is assuming you are talking about a Kawaka FH 721D because we have no real idea who or what you are talking about, which particular Grasshopper you are talking about if in fact is is a Grasshopper and no idea what particular engine is giving you grief.
 

BlazNT

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This is a diesel engine for sure. In Grass Hopper D in the model name always designates diesel. I'm thinking it is a wire shorting out during the turn and then moving back to original position or as you turn something is moving to the wire and shorting it out.
 

tew45

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This is a diesel engine for sure. In Grass Hopper D in the model name always designates diesel. I'm thinking it is a wire shorting out during the turn and then moving back to original position or as you turn something is moving to the wire and shorting it out.

Well I found the problem. I think someone else mentioned this in another post. I did not know if there was a check valve or a filter on the bottom of the fuel pickup line but I removed the fuel line from the elbow and unscrewed it and the fuel line was just a 1/4 inch plastic tube with no filter. I checked the tube for restrictions and found a little wad of grass in the elbow. I removed the grass and blew out the line and reassembled the fuel pickup. I was low on diesel but I decided to try and see if the problem was cured anyway. I mowed a 1/4 acre plot and used many fast turns--no problems-- except the usual hesitation when the fuel is low. I like it to have that low diesel hesitation so I know to fill up with fuel before i have to walk home and get the container. Thanks for the help!
 

173abn

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I'm glad you found the problem.this will help others troubleshoot if they have similar issues...russ
 

thehemikid

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On my 2003 721D there is a second filter after that upper inline filter. The second filter has a fuel shut-off lever on it for its filter change. I think this filter acts as a water trap also. When mine was having some irregular rpm deals,...but not in the turns like yours,...it ended up being that longer lower filter being a bit clogged.
 
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