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John Deere Tractors Discussion Forum
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620 LP HARD TO START

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Kenny N AL

07-19-2007 17:36:45




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My brother has a 620LP that he can't get the engine started unless the tractor is pulled. He had the starter rebuilt and it spins the engine ok. You can spin it until the battery is drained but the engine won't start (never even tries to start). You can pull the tractor 6 feet and it will start right up. Any suggestions on getting this tractor started without pulling it?




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Kenny N AL

07-21-2007 06:41:22




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 Re: 620 LP HARD TO START in reply to Kenny N AL, 07-19-2007 17:36:45  
Thanks for all the suggestions. I think we will focus on the firing first, because the engine has good compression, just had a valve job, and some of the major LP delivery components have been replaced. The tractor runs excellent and strong once it is pull started, so we're thinking it may be poor spark at the plugs when cranking with the starter. The previous owner replaced the generator with an alternator, so there may be some additional wiring issues. I think my brother wants to put everything back original, because it obviously worked when it was built.

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lonzo

07-20-2007 16:21:08




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 Re: 620 LP HARD TO START in reply to Kenny N AL, 07-19-2007 17:36:45  
I had two LP's that wouldn't start and i did everything these guys said to do and nothing helped, i finally found the intake valve guides were so loose that they were sucking air and diluting the vapor, replaced the guides and ran like a clock, these guyes have some very good ideas,don't over look anything.



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CLW

07-20-2007 07:25:27




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 Re: 620 LP HARD TO START in reply to Kenny N AL, 07-19-2007 17:36:45  
Kenny it sounds like it is not getting the 12v needed to start. Get a jumper wire and connect it to the Neg. side of the batt. if it is still wired as Neg. ground. Then try starting the tractor. When the engine starts turning touch the other end to the Neg. side of coil. This will bypass the Resistor and a possible(open) Ign. switch. If it starts, start checking backward until you find the open problem. This same thing happened on my 630LP and it was the Ign. switch. If you need a wiring diagram email me and I will send you one.

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2cylinderlp

07-19-2007 22:08:00




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 Re: 620 LP HARD TO START in reply to Kenny N AL, 07-19-2007 17:36:45  
Might help if you told us more. Once it is started does it run properly? Are you sure it is producing spark when the starter is engaged? Maybe there are some other things wrong with fuel delivery and the starter just can't spin it fast enough. In order to start easily, there needs to be oil in the oil bath air cleaner. The throttle should be just a little off idle. You shouldn't need to use the choke. The choke button really isn't a choke anyway. It is just the opposite. It functions to lean the mixture. It might be needed in cold weather because of thick oil in the air cleaner making the mixture too rich. You shouldn't need to use it in summer weather. You would start the engine with the vapor valve open. You don't need to worry about the converter vaporizing the fuel because it is already vapor that is coming out of the vapor valve. For just moving the tractor around and even light duty work, the vapor valve is all that needs to be open. For heavier loads the engine needs more fuel than what might boil off just from ambient temperature. So then you open the liquid valve and close the vapor valve. Liquid fuel goes to the converter that is heated by warm coolant from the engine. The warm coolant in the converter will assist in more rapidly boiling off fuel vapor to be burned in the engine at higher power settings.

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Carl NY

07-19-2007 19:00:09




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 Re: 620 LP HARD TO START in reply to Kenny N AL, 07-19-2007 17:36:45  
Check the compression on each cylinder. My guess it is very low.



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Gerald J.

07-19-2007 18:52:14




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 Re: 620 LP HARD TO START in reply to Kenny N AL, 07-19-2007 17:36:45  
Might need bit more effective choking. Might need the intake manifol gaskets.

It should be started with the gas valve from the LP tank open and the liquid valve closed. It has to warm up the coolant so it can be used to vaporize liquid. Once its warm enough the liquid valve is opened and the gas valve is closed.

When stopping, close the liquid valve and let the engine run out of fuel.

Could be an air filter restriction too.

Gerald J.

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