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Gas EZGO Gas EZGO Marathon, Medalist, TXT and RXV.



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Old 09-30-2021, 12:13 PM   #1
Justinh722
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Default 1986 Marathon. No power unless muffler removed

I’m fairly good with small engines in general but I’m new to carts. I’ve been working on a 1986 marathon with the robin 244cc engine for an older woman who paid $2700 and was only able to drive it a week before it died on her.

I’ve tuned it up and checked all the basics. There were signs of leaking at both crankshaft seals so those have been replaced. I did replace the carburetor with an aftermarket but it runs the same. Reason for replacement is the Mikuni has loose throttle linkage and looks like someone tried fixing it and ruined it. Cart is getting fuel. Previous owner had bypassed oil injection so I emptied the tank and put some non-ethanol in and mixed it 128-1.

I’ve had this here for about a month now researching to my wits end. Belt drags a little at idle but nothing major. Does make the cart hard to push. Verified the pulsar coil has the correct resistance as well as the primary and secondary windings in the ignition coil. Pulsar is adjusted right at the middle. I marked the slots when removing during seal replacement. It runs okay and builds RPMs in both forward and reverse but only with the muffler removed. But when running in forward it makes a clattering noise. Muffler was barbecued in a hot fire for 3-4 hours. Seems to have more air flow when blowing through it from the tail pipe to the flange. I’ve yet to check the exhaust port on the engine for any kind of carbon blockage. I’m currently testing the cart with the rear up in the air and the drive belt removed while making sure I don’t over-rev it.

I thought I would give this a shot to get some other suggestions while I’m out checking on that. Engine has 125 psi of compression. Air filter is completely plugged so I have one on order and I’m currently just running it without for testing purposes. Spraying carb cleaner in the intake kills the engine so the issue is definitely air flow. Does she need to spend the money on a new muffler or has anyone else not had luck with the barbecue method for the muffler? I’ve yet to run into a small engine repair that has stumped me like this aside from completely disassembling the engine and checking everything. The noise in forward has me concerned a bit. Any guru’s out there familiar with this issue?
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Old 10-12-2021, 10:11 AM   #2
Justinh722
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Default Re: 1986 Marathon. No power unless muffler removed

I’ll post an update for anyone curious. The muffler had an internal breakage that caused the baffling to get hung up not allowing the exhaust gasses to exit like it should. So requiring a new muffler and with all the reliance mufflers being on backorder, it looks like I may have to just buy a muffler and fabricate my own. The factory muffler is 12 1/2” long by 6” in diameter. I found a farmall tractor muffler 13 inches long and similar diameter that I can just close off one end and weld in a flange to the side and figure out the tailpipe routing.

Unless anyone knows of a better option as the powerband of the engine comes from the header design I believe it should work.
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Old 10-12-2021, 10:54 AM   #3
crash12888
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Default Re: 1986 Marathon. No power unless muffler removed

Keep us posted on the outcome and noise level, Everyone is always looking for options with the older carts.
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Old 10-12-2021, 12:19 PM   #4
trig123
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Default Re: 1986 Marathon. No power unless muffler removed

Quote:
Originally Posted by Justinh722 View Post
I’ll post an update for anyone curious. The muffler had an internal breakage that caused the baffling to get hung up not allowing the exhaust gasses to exit like it should. So requiring a new muffler and with all the reliance mufflers being on backorder, it looks like I may have to just buy a muffler and fabricate my own. The factory muffler is 12 1/2” long by 6” in diameter. I found a farmall tractor muffler 13 inches long and similar diameter that I can just close off one end and weld in a flange to the side and figure out the tailpipe routing.

Unless anyone knows of a better option as the powerband of the engine comes from the header design I believe it should work.
I have a used muffler from a 1987 with the 2pg engine I would sell
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Old 10-16-2021, 01:34 PM   #5
Justinh722
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Default Re: 1986 Marathon. No power unless muffler removed

I just built the muffler last night and welded the 1 1/4” pipe with the old flange through the hole I made in the muffler outer core and the inner baffle. I then tack welded a 3/4” tailpipe about the same length as the old muffler. It has more flow than the broken one and sounds decent aside from the leak around the tacked on tail pipe. I chose to tack it in case I wanted to remove it and go with a 1 inch pipe. But if the stock muffler is 1 1/4” through the core and 3/4 coming out and it’s supposed to run normally, then I have a different issue as it still doesn’t have any acceleration even with a new muffler. Just strange how it runs great and can build rpm quickly and fast without the muffler. It still has the noise when running it in forward. I’m completely stumped.

I have way too much time in this owners cart. New crank seals and new carb and new fuel pump and lines…compression is good. New air filter and fuel filter. Pulsar and ignition coil all test fine. My only other option is to remove the engine again and tear it down and check everything. She doesn’t like to spend money so it becomes an issue when I have to try and repair it at little cost the way it is.
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Old 10-16-2021, 03:18 PM   #6
CP241
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Default Re: 1986 Marathon. No power unless muffler removed

You have to keep in mind, it is a 2 stroke. It needs that back pressure in the muffler to run right. You can’t just go put on any ol muffler and expect it to run like it should. You may be able to adjust the carb and make it work… but with an opened muffler and stock carb jetting it’s gonna run crazy lean and not last long
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Old 10-16-2021, 04:44 PM   #7
Justinh722
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Default Re: 1986 Marathon. No power unless muffler removed

It’s not so much an opened muffler as it’s still restricted by the inlet and outlet. I mentioned it’s more free flowing than the bad one simply because the other one had broken off inside and plugged it up. The issue is that it should be running with the muffler regardless. I can tune an engine if it turns out to be too lean but the pipe that’s more restrictive to the tune of the engine is the header pipe before the muffler. The warning should have been if I were to just drive the cart without a muffler at all and risk a melted piston. I’m wondering why it’s still not running correctly with the same back-pressure the stock muffler would be giving it. It’s being starved for air somewhere. You would have made a valid point had I said that the new muffler was causing the engine to over rev or run hot. When opening a muffler you are introducing more air. More air would mean it needs more fuel. It will only run well with the muffler removed. The carb is sucking plenty of air, but not enough for it to run correctly.
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Old 10-16-2021, 04:58 PM   #8
CP241
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Default Re: 1986 Marathon. No power unless muffler removed

You are correct, and technically you “can” even run a 2 stroke with a straight pipe.

These small engines are not your typical small engines, however. They are tuned very specifically and even the smallest little air leak, airbox missing, or even a Chinese carb that looks just like a real carb can make or break it. I’m not saying you won’t be able to make it work with a different muffler, but it’s going to take a lot of tweaking given the finicky nature of these little motors. The stock muffler is designed for these to work with the stock carb and stock airbox and etc. even the slightest change in any of the makeup results in huge tuning problems, and again I’m not saying you can’t or won’t be able to make it work. But it’s gonna take some tweaking. I’d start by putting a fresh plug in it, run it, and then pull and read the plug. Then adjust accordingly.
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Old 10-18-2021, 05:27 PM   #9
Justinh722
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Default Re: 1986 Marathon. No power unless muffler removed

Thanks for the help. I’m just at my wits end and about to tear it all down and see what’s going on with it. The piston is installed correctly. Compression is good. No noise in reverse. Noise in forward not sure if it could be a main bearing issue.
The subframe that the engine sits on…is it supposed to move completely up and down? I’m able to grab the engine and lift it up and down a good few inches or so.

The carb I ended up getting was a Chinese pos and I compared the main jets and the jet in the aftermarket carb was slightly bigger. So moving back to the stock carb and using couple pieces off the Chinese one I was able to get it to run decent. It will top out and gain speed after it gets going. In forward I can get it to move from a stop a little easier than reverse. But in reverse the engine just won’t rev at a stop like it’s a low speed jet issue. If I hold wide open it will build up and finally take off. I noticed both the oem carb and the aftermarket had the float adjusted under 1mm when it should be between 1-3. I have it at about 1.5mm now. Wondering if I should lean it out a bit to 2. Even with the rear wheels in the air, it won’t pick up speed down low right away.

The Drive belt is dragging causing the secondary clutch to move but that shouldn’t be the issue as the primary should still hit harder with throttle. Even with belt removed it just picks up slow then goes to wide open throttle just fine. I’m convinced the issue is tuning or timing but the noise in forward has me concerned. Adjusting timing on these would require removal of the flywheel to adjust the pulsar and then assemble and check again and repeat…correct?

The drive belt is worn but still a tad over an inch wide. Measured at 45 1/2” long using string around the outside diameter. I would have gotten stock carb but the woman paid 2700 for the 1986 cart and literally no maintenance was done to this thing. She said she can’t afford to put too much into it. I hate using any Chinese parts. Starter belt is at its tightest adjustment point. So it seems she needs to get a new mikuni carb, new belts, and ultimately a rebuild. Fuel is mixed 128-1 non ethanol. It’s clearly running too rich at low speed but opening the air jet doesn’t help much.
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Old 10-18-2021, 07:06 PM   #10
Justinh722
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Default Re: 1986 Marathon. No power unless muffler removed

I just checked the timing using an inductive light and forward timing is lining up on the mark just a little to the right but the reverse timing is so far off it’s maybe 4 inches to the left of the mark. What would cause this? This would indicate the timing being retarded which would explain the very slow acceleration and higher top end power.

EDIT: pulsar coil is reading 156 ohms. Secondary coil orange to green reads 4.5 ohms and secondary orange wire to plug boot is 11k ohms. All within range. How can the ignition timing in reverse be far off when setting one direction correctly automatically puts the other in range.
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