FH641V Long carnking when cold

ExmarkDon

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I have a FH641V with about 400 hours on it. When cold and not run for a day or two, it cranks for a long time before starting. Once it starts, I could immediately shut it off and it would start right up again. It seems like there is no fuel in the float bowl when fully cold. Once it has started up for the day, it will start immediately for the rest of the day, even if it cools down. I don't see any fuel leaking from the carburetor, and don't seem to be getting any in my crank case. I have disassembled and cleaned the carburetor, changed out the fuel pump and fuel filter without fixing the problem. It is like the fuel is getting sucked out of the float bowl as it cools down. Any ideas? Thanks in advance for your help.
 

ExmarkDon

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Re: FH641V Long cranking when cold

A similar question recently came up here. Maybe the replies to that will help.


Thanks Darryl, The post you referenced was leading in the direction of the choke. I forgot to mention that this engine is in an Exmark Laser Z. The choke and throttle on this machine are on separate controls. I have checked for full choke with the air cleaner off, and it seems to be working OK. When getting ready to run this machine for the season, I think I will open the float bowl drain before cranking to see if there is any gas in it. Thanks again, Don
 

bertsmobile1

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One problem that can manifest itself this way is a loose fuel line or a bad diaphragm in the fuel pump.
This allows the fuel to drain back from the pump.
so when you try to crank the engine the fuel pump is trying to pump air.
It is not designed to pump air so it takes a long time to draw the fuel through the fuel line to charge the float bowl.

The other thing that I have come across is bad / dirty float needle making it sticky so reluctant to open till there is a reasonable amount of fuel pressure behind it.
The fuel pump only pumps 5 to 10 psi and a good fart can go 15 psi for a comparrison so it does not take much build up on the needle to stop it opening.
 

bertsmobile1

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And of course I forgot overheating.
If the cooling fins are clogged dirty the engine can overheat .
This causes the oil to thin more than the mower is designed for so the oil drains away from the rings.
Thus when you try to start it some time is needed for oil to build up in the ring grooves and make a sufficient seal to suck fuel again.
 

Darryl G

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Edit: Never mind. I didn't see that Bert had replied and was involved and this is a bigger issue than I can help with.
 
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ExmarkDon

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Let me back up a bit. My Exmark is a year 2000 machine that I got really cheap with the knowledge that it may need an engine. It only had about 200 hours on it, which I believe based on the condition of the machine. When I got into the engine, it was pumping oil out the top bearing seal. Checking with a dial indicator showed that the crank had about .060" of play (it should be about .004"). I think what happened is that at some point the engine was run low on oil (which makes sense since it was missing the "O" ring under the oil dip stick and two of the plugs on the bottom of the block had cuts in the "O" rings). The upper bearing was the first to go dry, got hot and wore open, and ruined the top oil seal, bearing and crank journal. So I completely disassembled the engine. The bores and pistons were good, as was the block. The crank was worn down about .015" on the upper journal and the upper bearing was worn open about .050". I checked every other part and all measured within specs. The engine was good with the exception of the upper crank bearing and worn crank journal. I have a machining background, so I made a new bearing about .025 undersize on the I.D., pressed it in and then turned the upper journal diameter of the crank to get .003" clearance to the bearing. This repair has worked out good for over 200 hours. I have removed the shroud and checked the end play of the crank with a dial indicator several times, and it has not changed since the rebuild.
Since this machine was so old, bit by bit, I have been replacing anything that might fail due to age. I replaced the plugs at the time of the rebuild (several years ago). I have since replaced all of the fuel lines, fuel filter and pump, and all vacuum lines on the engine. I do not think that it has overheated at any point since I have regularly removed the shroud to check the end play of the crank and would clean the fins etc. at the same time. It really runs great, once it is running.
If I run one of the fuel tanks empty, and switch over to the other, it cranks about 15 seconds or so to get fuel into the engine. Does this seem normal? It is about the same time it takes to get it going on a cold start if it has not run for a day or so. It makes Berts idea about the fuel lines draining back into the tank sound possible. When it is time to start this machine up for the season, I will have to disconnect the fuel lines going back from the engine to see if they have air in them. Thanks again to Bert and Darryl for your input. Don
 

bertsmobile1

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Although I rarely see one fail, there is a check valve in the fuel pump, assuming you have an impulse pump.
This keeps a small positive fuel pressure on the fuel line from the pump to the carb.
When it fails it can take some time to build up enough fuel pressure to raise the float needle off it's seat
A really easy check is to put an inline fuel tap between the tank & the fuel pump.
If nothing else it will make replacing the fuel filter cleaner & easier.

Turn the fuel tap off when you have finished mowing then back on the next time.
Starts up quicker then a defect in the fuel line / pump is confirmed.
A cheap and well spent $ 10
 
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