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Hit & Miss Gas Engine Discussion

Fairbanks Morse 3HP Z Won't start


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  #1  
Old 07-11-2016, 10:37:24 PM
ColvilleJeff ColvilleJeff is offline
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Default Fairbanks Morse 3HP Z Won't start

I have put this engine back together being very careful to follow the instructions of linking up the mag to the cam gear properly. The mag is creating a spark as expected.

The carb is producing a mix as when I put my hand over the intake side of the carb, I get covered in a light mixture of fuel. But this engine is not showing any signs of wanting to start.

I would be grateful if someone would give me some pointers to follow for the first time engine. Steps to check would be awesome.

I have opened up the sump side of the carb after filling it halfway. It leaks out the side until the fuel drops to below the outer hole where the shut off rod goes through the casting.

I have the fuel pick up turned off while I am trying to start the engine with the sump in the carb.

The engine seems to have proper compression as it is easier to turn over at the beginning if I hold the exhaust valve open until I get the engine turning.

The only other thing I can think to mention is that I am trying to start it on the left side (turning the wheels towards the back).

Thanks for any assistance
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  #2  
Old 07-12-2016, 06:03:31 AM
CBarth66 CBarth66 is offline
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Default Re: Fairbanks Morse 3HP Z Won't start

Mine has to be cranked over with a hand crank to get the rpm's up, but I have seen others not need this. Try choking the carb. with your hand to make sure you are getting fuel to the cylinder. Good luck. Chris.
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Old 07-12-2016, 10:16:11 AM
73eldo 73eldo is offline
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Default Re: Fairbanks Morse 3HP Z Won't start

This is your first old engine? How far apart was it when you got it?

Trying to start it from the inside reservoir is good because that eliminates the longer hose and check valve for the external tank. On mine I found that the valve for the external tank was not sealing well to the mixer body so I put an O ring in it so it sealed better to the case.

Its normal for it to leak gas if you fill it to the level of the shaft, there are no seals there. The idea with these engines is you would start it on gas from the internal tank then once it got running and some heat in it you would switch to the external tank with a lower grade fuel like Kerosene.

The inlet to the mixer has a spring loaded valve on it that should normally be closed. Basically the way it should work is on the intake stroke the engine begins to suck but that valve is closed so no air can get in. The only thing it can suck is fuel so it does. About the time the fuel starts to flow the suction is strong enough to open that valve and you get a sudden burst of airflow that mixes with the fuel with the burst of air which then ends up in the cylinder and the rest of the process is pretty much the same as any other 4 stroke engine. suck, smush, bang, exhaust, repeat.

If you are getting air out that inlet valve that makes me think the intake valve on the head is not seating/sealing properly during the compression stroke so some of the compression is escaping and going the wrong way.

Is your spark plug getting wet with gas?

The way I start mine is to stand on the crank end and lean over it. I grab mostly the top of the flywheels and turn it slowly till I feel its about to get past the top of the compression stroke (it gets hard to turn at that point). I then try to give it a good quick snap past the top of the stroke. Often times it will fire at that point but may not make it around again.

Another thing to check assuming this is a throttle engine is the throttle position. It could be put together wrong or something got bent and the throttle is closed.
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Old 07-12-2016, 04:35:05 PM
BobRR BobRR is offline
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Default Re: Fairbanks Morse 3HP Z Won't start

What Yr. is the engine? Bob
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Old 07-12-2016, 05:21:58 PM
beezerbill beezerbill is offline
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Default Re: Fairbanks Morse 3HP Z Won't start

A couple things to check:

Is the cam timed to the crank? This is easy to check - the exhaust should be open for the entire time the piston ascend to the top of the cylinder as you rotate the engine in the running direction. I know this is obvious but I have seen it wrong.

Are you sure the mag is timed right? The easiest way to check this is to observe when the points open - should be right before top dead center. Slight variations of exactly where before top dead center will change the running behavior of the engine but if the points open just before TDC the engine should at least run. I've been thrown off by timing marks in the wrong place.

Do you have a nice fat blue spark right at the plug, even with the engine turned over slowly?

Is the inlet valve opening OK? You should observe it opening on its own on the intake stroke. One way to check this is to set the engine to top dead center and rotate the engine in the running direction - the valve should suck open. Another way to check the inlet valve is to press it open with your finger - it should very little force (ounces, even) to open.

Are you badly flooded? One thing to try is to let the engine dry all the way out, including draining the "start" reservoir. Then dribble a few drops of fuel into the inlet (with no fuel in either the tank or reservoir) and crank the engine over. You should at least get a few pops with this method. Also, check how far out the needle valve is on the start reservoir - should be around 3/4 to 1 turn.

This is all assuming the engine is a rotary mag / spark plug fired open crankcase "Z" and not a "ZC" though most of the things to check for are the same.
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Old 07-12-2016, 11:02:19 PM
ColvilleJeff ColvilleJeff is offline
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Default Re: Fairbanks Morse 3HP Z Won't start

Wow! What great help. Ok. I will go back to the drawing board and follow each thread. You guys are awesome!

It is a Style C

The lever on the top of the crank cover is very stiff and doesn't seem to do much. The throttle rod doesn't seem to open the butterfly at all. But I have watched these engines running and started on Youtube and it doesn't look like the throttle is moving on them either.

The check valve at the fuel tank is working properly. I checked that first thing. I have tried filling the mixer bowl with fuel and it surely does run out the hole on the end until it drains to level with that.

I have noticed the intake valve doesn't seem to move much. It moves, and I can hear the engine breath in the air on intake but I don't discern any real movement of that valve.

Ok. I will try what you all have suggested and see where we are at. First with the timing. Let you all know. Thanks much.

If anyone could explain the lever on the top of the crank cover, that would be great!
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Old 07-13-2016, 12:38:37 AM
BobRR BobRR is offline
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Default Re: Fairbanks Morse 3HP Z Won't start

Most ZC with a J Mag. (none impluse)need the flywheel spun, easiest way is with a crank handle and a valve held open. Does't hurt to try a NEW spark plug. If you had this a part did you put the goveneor control back together right? Bob
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Old 07-13-2016, 05:34:22 AM
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Default Re: Fairbanks Morse 3HP Z Won't start

It's easy to get the big flat spring on the inside connected to the speed lever out of place when replacing the "hogs head" on the engine.

The end of it should press against the little rod coming out of the governor.

The throttle should be held wide open by the governor when the engine is stopped.

You will have to spin the engine to a fairly good speed for the mag to be able to fire the plug when starting.

If all else fails, try a KNOWN good plug. I've spent a few hours trying to start an engine with a plug that would fail on compression.
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Old 07-13-2016, 02:19:48 PM
ColvilleJeff ColvilleJeff is offline
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Default Re: Fairbanks Morse 3HP Z Won't start

Oooooh Ok. Thanks for that Elden. I think something must be wrong with the spring lever then. I thought I had it pushed all the way against the lid. But maybe it moved.

The other thing I noticed last night was the rod that comes down vertically from the case that pushes the throttle is all the way up and not touching the pivot. So clearly something is wrong with that too. Off comes the cover again.
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Old 07-13-2016, 04:03:39 PM
ColvilleJeff ColvilleJeff is offline
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Default Re: Fairbanks Morse 3HP Z Won't start

Z73Eldo

You were right! The cam is in the wrong position. I didn't touch the gears so I am to guess whoever put this together didn't set the cam gear to the crank correctly.

I haven't taken this apart and wonder... If I pull the two bolts holding down the assy, am I going to find that I have ruined the bearing or babbitt on the crank?

And then am I to assume all I need to do is find the beveled teeth on the cam gear and line them up with the proper tooth on the crank gear that has the punch mark on the side? But so that the exhaust is open as the cylinder goes from bottom to top?
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Old 07-13-2016, 06:10:39 PM
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Default Re: Fairbanks Morse 3HP Z Won't start

The main bearings, especially the governor end one are easy to break so be careful when lifting it to fix the cam timing.

They look like they are made of pot metal.
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