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Hit & Miss Gas Engine Discussion

Fairbanks Morse 10HP Z early pattern running poorly need help!.


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  #1  
Old 08-23-2017, 10:23:10 PM
Nathan K. Nathan K. is online now
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Default Fairbanks Morse 10HP Z early pattern running poorly need help!.

Hi All, I seem to need some help with this one!.
I am having trouble getting my 1917 FM 10HP Z to run smoothly. It seems to have good spark, I can just barely pull it over compression with petcocks closed and it doesn't seem to have much blowby just a small leak on the igniter also it starts great with priming or the right amount of choking but it just won't run nicely. Spark timing is right on the marks, valve timing is as close as I could get to the recommendations i found on here opening ~30deg before bdc and closing ~5deg after tdc but it still will only fire very irregularly. So does anyone have any ideas to help with my nightmare?, all help apreacated.
Nathan.
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Old 08-23-2017, 10:37:20 PM
Lvolling Lvolling is offline
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Default Re: Fairbanks Morse 10HP Z early pattern running poorly need help!.

Sounds fuel related if it runs when priming or choking. Check valve not stuck, fuel pickup clean, check carb,or a very loose intake valve guide may cause it.
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Old 08-24-2017, 09:22:43 AM
Arlie Levy Arlie Levy is offline
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Default Re: Fairbanks Morse 10HP Z early pattern running poorly need help!.

Intake valve spring too weak.
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Old 08-24-2017, 10:33:31 AM
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Will Batty Will Batty is offline
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Default Re: Fairbanks Morse 10HP Z early pattern running poorly need help!.

Nathan

Good to hear you got it running!

I know my 10 hp Fairbanks is not the early style like yours but I had to do a lot of messing around with the intake valve spring adjusting tension with washers and trying different springs before I got mine to smooth out. I never did get to run smooth with the original spring I had to go to a lighter spring and my engine was like yours with lots of compression to. The fine tuning can take some time to get sorted out but you will get it!
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Old 08-24-2017, 03:50:06 PM
Andrew Mackey Andrew Mackey is offline
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Default Re: Fairbanks Morse 10HP Z early pattern running poorly need help!.

Make sure the snifter valve in the front of the mixer does not have a too weak a spring behind it. If too weak, the mixer will not draw gas properly. How is the clearance on the intake valve stem? Too loose and you will have a too lean a mix at idle. Exhaust valve spring strong enough? A too weak spring will not close the valve properly. You might want to make your exhaust valve clearance a bit bigger, to open it later (25 degrees before BDC) and close earlier (about TDC). Have fun with your Z. They do not like to idle well - the mixer was designed to work best under load. it will take a lot of fiddling to get it to idle evenly and slow!
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Old 08-24-2017, 05:21:15 PM
stufforbud stufforbud is offline
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Default Re: Fairbanks Morse 10HP Z early pattern running poorly need help!.

I find running mine with the choke plate under the air intake about 3/4 closed make it idle perfectly, hitting every time.
Bud
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Old 08-24-2017, 06:59:11 PM
Kirk Taylor Kirk Taylor is offline
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Default Re: Fairbanks Morse 10HP Z early pattern running poorly need help!.

Quote:
Originally Posted by Nathan K. View Post
Hi All, I seem to need some help with this one!.
I am having trouble getting my 1917 FM 10HP Z to run smoothly. It seems to have good spark, I can just barely pull it over compression with petcocks closed and it doesn't seem to have much blowby just a small leak on the igniter also it starts great with priming or the right amount of choking but it just won't run nicely. Spark timing is right on the marks, valve timing is as close as I could get to the recommendations i found on here opening ~30deg before bdc and closing ~5deg after tdc but it still will only fire very irregularly. So does anyone have any ideas to help with my nightmare?, all help apreacated.
Nathan.
Just a random thought.........
I know on the smaller engines, there is a brass tube that extends from the bowl assembly to the throttle plate and serves as a fuel nozzle. I am guessing that the larger engines use a similar method. If the tube gets broken off, the engine will start but not run worth a hoot.
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Old 08-25-2017, 04:22:12 PM
Nathan K. Nathan K. is online now
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Default Re: Fairbanks Morse 10HP Z early pattern running poorly need help!.

Thanks for the help so far,
Just to clarify when running at ~270rpm it will miss way more than it fires(it only seems to fire twice if speeding up, gov. seems to be working).
So It makes no difference if using the start or run side of the mixer which was just cleaned also the early mixer doesn't have the spring loaded plate. If I open up the needle valve or close the choke it will flood it out so it can get fuel, the fuel tube was broken off so I replaced it with one that just goes though the throttle plate notch but not sure exactly how long it should be?. My engine has the early intake valve cover/piston valve damper, I did pull it off and try pushing and pulling on the spring but it didn't seem to help but I can try playing with it again and also change the valve clearance(does anyone know the proper clearance?).
Will, yes I did get it going for the show this spring as it is 100 now and near where it used to work at an old mine and the former owners got to see it running but now I need to get it running better for another show!. A friend also has a 10hp like yours that runs almost perfect so I was hoping mine would too!.
Nathan.
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Old 08-25-2017, 05:23:11 PM
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Joel Mosley Joel Mosley is offline
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Default Re: Fairbanks Morse 10HP Z early pattern running poorly need help!.

Another common reason for 8 cycling or the failure to fire on each compression stroke is a weak Exhaust valve spring. You could try pulling out on the valve while the engine is running, stretching the spring out, putting spacers under the valve spring or buy a new spring. A weak spring can allow the exhaust valve to lift off of it's seat on the intake stroke. You can also look at the exhaust valve while the engine is running and see it you can see it flutter or suck in slightly on the intake stroke. You may not see it, but it still may be lifting off of the seat and sucking air through the exhaust. If it does, you need a stronger spring which may help solve your problem.

Good Luck.

Last edited by Joel Mosley; 08-26-2017 at 12:59:34 AM.
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