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720 LP Has got us stumped.

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Bob F.

10-03-2001 04:50:55




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We have a 720 LP that was overhauled a little over a year ago. It got new pistons, rings etc and at first ran great. It has steadily gone downhill from there. At first it started easily and idled well and also ran good under load. It is now at the point where it starts hard and when it gets warmed up it misses and won't idle and keeps dying. It we can nurse it up to full throttle and put it under some engine load it does straighten out and runs a little better.
To this point we have tried new plugs, points, rotor and distributor cap and have taken the LP gas regulator off and had it rebuilt and bench tested and set to specs. We have had some people more knowledgeable than we are try different carbeurator and timing settings. Some of these things have helped temporatily but soon it goes back to running as badly as ever. You guys (and gals) have proven to be very helpful in the past and as we are stumped at this point any help you could give us would be appreciated.
Thanks in advance.

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John Bayer

02-08-2003 14:50:31




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 Re: 720 LP Has got us stumped. in reply to Bob F., 10-03-2001 04:50:55  

Check your vavle clearances. Did you get the head reworked during the overhaul? If clearances are good do a compression check to make sure they are both in sink. Let me know what you come up with.



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DP

10-03-2001 17:15:26




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 Re: 720 LP Has got us stumped. in reply to Bob F., 10-03-2001 04:50:55  
Just a thought Bob. Check that your diaphram in the regulator isn't leaking by. Had a 630 lp some years back that was acting a little like that. If its giving the wrong mixture, it will start hard and run rough till you work it hard enough to burn the amount of fuel that it is being supplied with. Might be worth checking. Good luck to you, Don



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twopop

10-03-2001 20:41:24




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 Re: Re: 720 LP Has got us stumped. in reply to DP , 10-03-2001 17:15:26  
I feel DP and G taylor are on the right track.if you are not getting the right amount of vacuum,the regulator will not supply the right amount of fuel.you need to look for air leaks and holes in the diaphram,or pugged port in carb.



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G Taylor

10-03-2001 11:08:47




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 Re: 720 LP Has got us stumped. in reply to Bob F., 10-03-2001 04:50:55  
A long shot possibility is a intake manifold or carb leak to atmosphere. Another is valve train wear/failure.



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Mark A

10-03-2001 06:18:12




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 Re: 720 LP Has got us stumped. in reply to Bob F., 10-03-2001 04:50:55  
Forgive me if I am being too basic, but do you start the tractor on vapor, and only turn on the "liquid valve" after the tractor heats up? Our old 630 needed to run on vapor a good while before turning on the "liquid valve".



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Clooney

10-03-2001 06:10:39




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 Re: 720 LP Has got us stumped. in reply to Bob F., 10-03-2001 04:50:55  
Bob, the stranger might have a point there. The LP 720 uses "by-pass" starting & uses a 6 volt coil with 12 volts from the starter by-passing the ballast resistor during cranking. Just as a test try running 12 volts to the coil after it is started & see if it runs better, if so you probably have the wrong coil on it. On the other side if you have the correct 6 volt coil & someone has eliminated the ballast resistor & you now have 12 volts running to a 6 volt coil it will burn the points quickly & the coil will overheat & poor running results. As a test check the voltage to the coil during running & see if is the required 6-8 volts or the incorrect 12-14 volts.

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The Stranger

10-03-2001 05:33:03




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 Re: 720 LP Has got us stumped. in reply to Bob F., 10-03-2001 04:50:55  
I know this is going to sound a little weird---but have you tried a new coil? Or made sure the polarity of the one you have now is correct? It doesn't sound like a fuel problem to me, I think you have an ignition problem. If it was me, I'd sure try a new coil.



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Bob F.

10-04-2001 04:31:05




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 Re: Re: 720 LP Has got us stumped. in reply to The Stranger, 10-03-2001 05:33:03  
Guys:
Once again Thanks Again for all the suggestions and leads for me to check out. Just when I think that I've checked everything I find that I probably have just scratched the surface. Help like this is what makes this site so great.
Thanks yet again:
Bob F.



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