Fresh top end ,still no power SOS

[steelhorse79]

I just rebuilt my 89 marathon because of no power on inclines. It had 90psi before the tear down. I found one ring gone and piston badly chipped. I did new seals (both sides),new piston & rings,new cylinder.I also put on a 40.7" x 1"-3/16 new belt and new starter belt. Fresh plug and 40:1 break in fuel, adjusted floats and cleaned carb 3 times,turned pilot screw 1 turn out. Fuel pump has been changed to external mount by previous owner,i believe this year had one mounted on the engine.Here are my symptoms, press gas ped and engine fires and rpms come up and belt engages , after about 30 seconds rpms come down (gas ped still floored) and engine struggles. If I wait a minute and try again same result. I placed hand over carb intake while engine struggles and rpms will come up and run better but after 15 -20 sec power loss. pulling out the choke a little will make it run better for 10 seconds then back to the same.I took it for a ride and it is doing the same thing it did before the rebuild. I haven't checked the compression again but turning the crank by hand It is much stiffer, will check tomorrow. New carb time? or new pump? The previous owner said the pump was replaced . Any input would be a great help, I'm very frustrated.

[Marathon Man]

Maybe a fuel pressure problem or possible clutch issue ?

[steelhorse79]

It does the same thing with belt off. starts fine runs strong for 30 seconds then starts to die. If I let off on the gas ped and try to start it right away it will struggle but if I wait a minute then try she will fire right up and run for the 30 seconds .I assume its starving for fuel.

[Dave Box]

The first thing you should do is to check the compression to make sure that you didn't break a ring.

After that I would check for a multitude of fuel delivery issues. For example have you pulled the line to the carburetor to ensure you are getting adequate delivery? I would also be concerned at this external pump mount business, air leaks in this area will kill the engine. Is there a fuel filter in the line? If so you have the symptoms of partially blocked filter.

You say you have cleaned the carburetor but did you tear it down to the last nut and bolt? For example the nut that holds the bowl on is the main jet. Did you clean that and did you unscrew the main nozzle and clean that?

If these symptoms are what you had before the rebuild then we have to look at what has remained constant.

Let us know and we will get you fixed.

Dave

[steelhorse79]

I will check comp tomorrow and let you know but just turning the clutch by hand it was much stronger then before. I did dismantel the carb and clean all jets. Why would it throttle up and run well for 30 seconds then struggle? I'm thinking the pump is not keeping up with demand. I was just looking at the site sponsors and saw a high flow B&S pump that will work with stock carts. Dont know if I should try that or find the right pump for that year?

[steelhorse79]

I forgot to mention i put a new filter on but now that I think about it there may be a second filter between the pump and carb. I will start with that. I will keep you posted.

[madoc1]

to check the pump, pull the line to the carb and check and see if you are geting a steady stream. it will pulse a little, but you will know if you are getting enough. just a long shot, but are sure you installed the piston correctly? ie with the piston port in the right direction.

[steelhorse79]

I hope so, port facing reeds (intake)Arrow on piston top facing fan side.I will check pump flow and compression this afternoon and report back.I did notice the original piston had 1 small port and the new one has 2 small ports, but my reserch tells me the 3pg engine has the 2 port. The previous owner claims a golf cart mechanic worked on it, but I doubt his abilities as alot of things I found are questionable.

[Dave Box]

I would think that the piston is in correctly as the engine does run albeit briefly. As both Madoc and I stated pull the line right off the carburetor and crank the engine. You should see a healthy jet of fuel. This will give us a clue as to the performance of the pump and any filter that might be there.

Dave

[steelhorse79]

Just found some bad news, comp is at 85psi. Heres the thing I purchased the top end kit from buggies unlimited and discovered the casting inside the piston was so rough that it would not fit on the needle bearing, I measured the old with a micrometer and carefully filed each side evenly untill I got the same as old piston. Then when installing rings I felt they were not seating fully in the piston. My past experience with 2 stroke motorcycle rebuilds the rings always seated flush with the piston and expand slightly to meet the cylinder. These rings would not seat by hand and I had to very carfully tap with a rubber mallet to install. the rings were located on the center pins good and seem to be seated in piston.I smeared assembly lube all on the inside of cylinder to help rings seat. I'm thinking as the engine heats up the rings dont expand just stick in the groves and lose psi.I'm hoping the cylinder is still good and I can order another std piston from a different company and do it all over again. This morning I started the cart on jack stands and it fired off well and actually ran decent , after about 60 seconds of full throttle it started losing power again. Thats when I took the comp test. I will wait untill its cold and try the comp test again to see if its higher. Is my piston and ring installation decription normal for these engines?