Another Generator start problem.

[cahorne]

I have googled until my fingers are bloody and still cannot find a solution to my problem so any help would be greatly appreciated.
Toy hauler with Onan 5500 in the front. I did not start it for a few months and now it won’t stay running. It will start if I hold open the choke plate and run for 10-15 sec and die. It spits fuel out the carb, thus the replacement but that provided no change. It does not run at speed and seems to be lugging down under a load but I have CB’s off. Here is what I have found and completed.
NEW carb
Pulled exhaust pipe and checked for blockage
Pulled spark arrestor plug
Changed spark plugs
Checked that valves are moving
Compression check 145 and 150
Pulled brushes and checked for melt and wear.
Checked fuel pressures… solid 4 psi
Checked valve lash… a tight .006
New fuel
Grounded oil sensor

If you go not open the choke plate it will spit fuel out and occasionally backfire a bit through the carb. Typically this would mean a blockage but valves are opening and closing.
Error code is 1-5 running too slow like it is under a major load. Any fresh ideas???

 

[centerline]

im guessing the engine has excessive carbon deposit on the valve stems, which can cause the valves to be sluggish in closing, and can cause odd and varying symptoms..... one of which is the carb spitting back without the engine actually back-firing, and another is the engine seeming to lug down, without really laboring itself, even with the fuel plate wide open.....

if this is the cause, an ounce or two of seafoam in the crankcase will have you going again in about 10 minutes.....
and make sure you change the oil and filter (if equipped) within the next hour of run time...

 

[Bogie]

Have never worked on one of these, but a clue may be the backfire through the carburetor. Since you have changed the carburetor and spark plugs you might want to look at some other thing that would cause a carb backfire. The things I can think of are bad ignition coil. Cracked spark plug wires. Not sure these would apply, but improper ignition timing or incorrect valve timing. A vacuum leak (if that applies}. Worn valve train.

Just my 2¢ worth.

 

[cahorne]

im guessing the engine has excessive carbon deposit on the valve stems, which can cause the valves to be sluggish in closing, and can cause odd and varying symptoms..... one of which is the carb spitting back without the engine actually back-firing, and another is the engine seeming to lug down, without really laboring itself, even with the fuel plate wide open.....

if this is the cause, an ounce or two of seafoam in the crankcase will have you going again in about 10 minutes.....
and make sure you change the oil and filter (if equipped) within the next hour of run time...

Thank you. It’s worth a try and does make sense.

 

[cahorne]

Have never worked on one of these, but a clue may be the backfire through the carburetor. Since you have changed the carburetor and spark plugs you might want to look at some other thing that would cause a carb backfire. The things I can think of are bad ignition coil. Cracked spark plug wires. Not sure these would apply, but improper ignition timing or incorrect valve timing. A vacuum leak (if that applies}. Worn valve train.

Just my 2¢ worth.

Thank you. I did check wires and spark. It has a good blue flame.

 

[rhodies1]

Sure sounds like you have valves out of adjustment or carbon build up.
Another great product to use in gasoline fuel is a product called Mechanic,sold at Home Depot. Will clean your system.

 

[cahorne]

Sure sounds like you have valves out of adjustment or carbon build up.
Another great product to use in gasoline fuel is a product called Mechanic,sold at Home Depot. Will clean your system.

You are right it acts just like the valves are too tight but they are not and actually .002 loose. My problem with additives is the generator won’t stay running long enough to circulate through the oil or fuel system.

 

[Dahillbilly]

your valve lash may be correct/loose but the valves could be sticking in the valve guides causing them to close slowly & creating your problem. Good luck

 

[centerline]

You are right it acts just like the valves are too tight but they are not and actually .002 loose. My problem with additives is the generator won’t stay running long enough to circulate through the oil or fuel system.

if the valves have gummed up stems, they will only be loose when warm and running.... when the engine is shut off, they will seat themselves... its the sluggishness caused by the carbon build up that doesnt allow the valves to close all the way FAST enough, while the engine is running.... once the stems are clean, the valves will be snappy again, and close within the proper time frame...... and if it runs at all, its ENOUGH to get additives into the engine.... you just need to connect up so it sucks the additive, and not the old fuel....

 

[cahorne]

if the valves have gummed up stems, they will only be loose when warm and running.... when the engine is shut off, they will seat themselves... its the sluggishness caused by the carbon build up that doesnt allow the valves to close all the way FAST enough, while the engine is running.... once the stems are clean, the valves will be snappy again, and close within the proper time frame...... and if it runs at all, its ENOUGH to get additives into the engine.... you just need to connect up so it sucks the additive, and not the old fuel....

Bought spray sea foam today. I’ll pull the carb and spray in the intake while cranking and let it sit overnight to see what it does.

 

[centerline]

You need it IN THE CARB as well as the CRANKCASE or it will never work.... the carb shouldnt be removed... you are only making more work than the simple easy process that it is...