spewing gas

BruceHarless · 12-27-2013, 04:49 PM

1989 2cy Marathon, just started today for the first time. Confirmed that the reed valve works by checking for suction Vs pressure at the intake.

I have a new carb, which has a narrower throat than the original. No documentation with the carb. Now the little vent pipe spews gas once the engine starts, and the engine will not keep running. I can close that off with a rubber cap, but don't know if that is safe to do. Most of all, I don't understand what causes it (or how to correct it).

The choke is, I assume, spring-loaded to NO CHOKE, right? Any realistic chance the choke is spring-loaded to FULLY ON and is flooding the carb?

1989Marathon · 12-27-2013, 04:55 PM

If it is pumping fuel out the vent, that's usually a sign that the carb float is not set correctly, and not stopping the flow of fuel once the bowl is full. Does the motor have the stock fuel pump? Not sure about the choke since I don't know what type it is. You got a pic of the carb?

BruceHarless · 01-01-2014, 03:56 PM

1989 2 cycle Marathon
I have adjusted the float twice, almost got it right but need to raise it a tiny bit more. This afternoon tried to start it-- it hit off immediately and ran good for about 10 minutes. Plenty of smoke, I chalked that up having lots of oil in the crankcase from the rebuild. Then it quit smoking and shortly thereafter quit running. Won't start now, and is not pumping fuel. (new fuel pump). I suspect that I starved it for oil and it lost crankcase pressure, 'cause now it will not pump fuel at all and compression tester shows max of 35 lbs. It was 120lbs before....

So I am going to pull the engine out again and see what I can learn. Eventually I will get back here. Thanks for helping me to here.
Bruce

1989Marathon · 01-01-2014, 04:02 PM

Check the torque on the head bolts first.
Were you pre-mixing oil/gas or using the stock oil pump?
I believe you changed the piston? Maybe it blew out a base/head gasket, or just needs to be re-torqued.

pachanga90 · 01-01-2014, 04:11 PM

If it flooded the lower-end it may have blown a crank-seal when trying to start,a backfire can cause that.

BruceHarless · 01-01-2014, 04:19 PM

In reply to:
"Check the torque on the head bolts first.
Were you pre-mixing oil/gas or using the stock oil pump?
I believe you changed the piston? Maybe it blew out a base/head gasket, or just needs to be re-torqued. "

New stock oil pump. Before it ever started, I checked the oil pump for flow, it pumped oil well. New fuel pump, too, pumped fuel AOK. All new seals and bearings in the engine, as well as crankshaft. Used old piston and rings, and had 120-125 lb of compression.

It smoked a lot for the first 8-10 minutes, then on about the 4th restart it no longer smoked. I figured it had burned off the excess. 3-4 minutes later, it quit and would not restart. The fuel filter no longer shows any fuel flow, so then I did a compression check -- 35lb max.

I will check the head bolts, thanks for that idea. Sure would be nice to find a solution and not have to pull or rebuild it.

1989Marathon · 01-01-2014, 04:22 PM

Did you lube the crank seal lips when you installed them?
Did the motor just die, or did it backfire or what?
Take a look around the base/head gasket to see if a gasket has been pushed out. Also, look behind the clutch to see if a crank seal has been pushed out.

BruceHarless · 01-02-2014, 07:21 PM

thanks for the suggestions. I have resigned myself to pulling the engine out of the cart -- just doesn't make sense to struggle with it as it is, and out it can be dealt with. Good ideas on the seals (yes, they are new). I don't understand the engine having 35 lbs of compression Vs. PLENTY or NONE, so maybe this is a seal problem.

How does crankcase pressure/vacuum relate to the fuel pump working? I don't understand what is going on in that regard.

1989Marathon · 01-02-2014, 07:26 PM

As the piston goes up and down, the pressure inside the crankcase goes from high to low, high to low....

This change in pressure is what moves the diaphram inside the fuel pump to pump fuel to the carb. If the crank seals are bad, the pressure can escape through them and cause the pump not to work.
Did you lube the seal lips during install? If not, they will be wiped out in no time.

BruceHarless · 01-06-2014, 02:19 PM

Took the engine apart - piston and rings are gone, appears I let it run dry of oil, it overheated and chewed up the top pf the cylinder and piston. I am trying to decide on repair or replacement, and am stuck with needing to know the original bore of that 1989 2 cyc engine . So far, the closest I have been given is "it looks like 2-3/4"."

This jug is 2.840" ID; the old piston is 2.820" -- is this a standard (i.e., original) size, or is it what they call 25mm or 50mm oversize"

12-27-2013, 04:49 PM	#1
BruceHarless Not Yet Wild Join Date: Dec 2013 Posts: 27	spewing gas 1989 2cy Marathon, just started today for the first time. Confirmed that the reed valve works by checking for suction Vs pressure at the intake. I have a new carb, which has a narrower throat than the original. No documentation with the carb. Now the little vent pipe spews gas once the engine starts, and the engine will not keep running. I can close that off with a rubber cap, but don't know if that is safe to do. Most of all, I don't understand what causes it (or how to correct it). The choke is, I assume, spring-loaded to NO CHOKE, right? Any realistic chance the choke is spring-loaded to FULLY ON and is flooding the carb?
BruceHarless Not Yet Wild Join Date: Dec 2013 Posts: 27

12-27-2013, 04:55 PM	#2
1989Marathon Gone Wild Join Date: Oct 2010 Posts: 6,730	Re: spewing gas If it is pumping fuel out the vent, that's usually a sign that the carb float is not set correctly, and not stopping the flow of fuel once the bowl is full. Does the motor have the stock fuel pump? Not sure about the choke since I don't know what type it is. You got a pic of the carb?
1989Marathon Gone Wild Join Date: Oct 2010 Posts: 6,730

01-01-2014, 03:56 PM	#3
BruceHarless Not Yet Wild Join Date: Dec 2013 Posts: 27	Re: spewing gas 1989 2 cycle Marathon I have adjusted the float twice, almost got it right but need to raise it a tiny bit more. This afternoon tried to start it-- it hit off immediately and ran good for about 10 minutes. Plenty of smoke, I chalked that up having lots of oil in the crankcase from the rebuild. Then it quit smoking and shortly thereafter quit running. Won't start now, and is not pumping fuel. (new fuel pump). I suspect that I starved it for oil and it lost crankcase pressure, 'cause now it will not pump fuel at all and compression tester shows max of 35 lbs. It was 120lbs before.... So I am going to pull the engine out again and see what I can learn. Eventually I will get back here. Thanks for helping me to here. Bruce
BruceHarless Not Yet Wild Join Date: Dec 2013 Posts: 27

01-01-2014, 04:02 PM	#4
1989Marathon Gone Wild Join Date: Oct 2010 Posts: 6,730	Re: spewing gas Check the torque on the head bolts first. Were you pre-mixing oil/gas or using the stock oil pump? I believe you changed the piston? Maybe it blew out a base/head gasket, or just needs to be re-torqued.
1989Marathon Gone Wild Join Date: Oct 2010 Posts: 6,730

01-01-2014, 04:11 PM	#5
pachanga90 I Refuse To Get Stuck!!! Join Date: Jun 2010 Location: Hilton,NY Posts: 5,427	Re: spewing gas If it flooded the lower-end it may have blown a crank-seal when trying to start,a backfire can cause that.

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01-01-2014, 04:19 PM	#6
BruceHarless Not Yet Wild Join Date: Dec 2013 Posts: 27	Re: spewing gas In reply to: "Check the torque on the head bolts first. Were you pre-mixing oil/gas or using the stock oil pump? I believe you changed the piston? Maybe it blew out a base/head gasket, or just needs to be re-torqued. " New stock oil pump. Before it ever started, I checked the oil pump for flow, it pumped oil well. New fuel pump, too, pumped fuel AOK. All new seals and bearings in the engine, as well as crankshaft. Used old piston and rings, and had 120-125 lb of compression. It smoked a lot for the first 8-10 minutes, then on about the 4th restart it no longer smoked. I figured it had burned off the excess. 3-4 minutes later, it quit and would not restart. The fuel filter no longer shows any fuel flow, so then I did a compression check -- 35lb max. I will check the head bolts, thanks for that idea. Sure would be nice to find a solution and not have to pull or rebuild it.
BruceHarless Not Yet Wild Join Date: Dec 2013 Posts: 27

01-01-2014, 04:22 PM	#7
1989Marathon Gone Wild Join Date: Oct 2010 Posts: 6,730	Re: spewing gas Did you lube the crank seal lips when you installed them? Did the motor just die, or did it backfire or what? Take a look around the base/head gasket to see if a gasket has been pushed out. Also, look behind the clutch to see if a crank seal has been pushed out.
1989Marathon Gone Wild Join Date: Oct 2010 Posts: 6,730

01-02-2014, 07:21 PM	#8
BruceHarless Not Yet Wild Join Date: Dec 2013 Posts: 27	Re: spewing gas thanks for the suggestions. I have resigned myself to pulling the engine out of the cart -- just doesn't make sense to struggle with it as it is, and out it can be dealt with. Good ideas on the seals (yes, they are new). I don't understand the engine having 35 lbs of compression Vs. PLENTY or NONE, so maybe this is a seal problem. How does crankcase pressure/vacuum relate to the fuel pump working? I don't understand what is going on in that regard.
BruceHarless Not Yet Wild Join Date: Dec 2013 Posts: 27

01-02-2014, 07:26 PM	#9
1989Marathon Gone Wild Join Date: Oct 2010 Posts: 6,730	Re: spewing gas As the piston goes up and down, the pressure inside the crankcase goes from high to low, high to low.... This change in pressure is what moves the diaphram inside the fuel pump to pump fuel to the carb. If the crank seals are bad, the pressure can escape through them and cause the pump not to work. Did you lube the seal lips during install? If not, they will be wiped out in no time.
1989Marathon Gone Wild Join Date: Oct 2010 Posts: 6,730

01-06-2014, 02:19 PM	#10
BruceHarless Not Yet Wild Join Date: Dec 2013 Posts: 27	Re: spewing gas Took the engine apart - piston and rings are gone, appears I let it run dry of oil, it overheated and chewed up the top pf the cylinder and piston. I am trying to decide on repair or replacement, and am stuck with needing to know the original bore of that 1989 2 cyc engine . So far, the closest I have been given is "it looks like 2-3/4"." This jug is 2.840" ID; the old piston is 2.820" -- is this a standard (i.e., original) size, or is it what they call 25mm or 50mm oversize"
BruceHarless Not Yet Wild Join Date: Dec 2013 Posts: 27