1985 Marathon losing power

LP8484 · 04-10-2017, 08:13 PM

I bought an'85 Marathon and it needed a new starter generator. I installed that along with an air filter, fuel filter, spark plug, and with the exception of forward ended up being reverse and vice versa the install was no issue. But besides that once it was running I made about 6 laps on my street and then it was obvious the RPM's significantly dropped off even as the pedal was fully depressed until the point it didn't have enough power to make it up my driveway. When I checked it out the starter generator was really warm. Could I have gotten a premature bad one? Or could I have damaged it when I had the directions backwards?

LP8484 · 04-11-2017, 11:48 PM

Figured it out. Disconnected the header pipe off the muffler and the engine took off. I guess it's time to replace the 32year old muffler

Skoal82 · 04-12-2017, 01:45 AM

Look up in the search function of the forum for barbecue a muffler
The price on a new muffler is probably pretty expensive if you can find one.
Yours is probably just built up with unburnt fuel and oil and a good hot bath in a fire should clean it out.
Worth a try before buying a new muffler.

LP8484 · 04-17-2017, 08:36 PM

I already had ordered the new muffler before seeing your reply Skoal, thanks for the input though! Although even after the muffler install I was able to drive it around the block and it ran great for the first half then I started having stall issues unless the choke was played with. That was pretty much the only way I got it home. I currently have replaced the muffler, battery, starter generator, spark plug and set proper gap, new air filter, and fuel filter. I am currently premixing my gas and oil at a ratio of 128:1 and added seafoam at the recommended 128:2 as per the can instructions for a 2 cycle. I have not disconnected the oil tank or lines, could I be drawing air from that throwing off mix?? My next step was to pull it out and plug the oiler off then clean the carb which I hoped the seafoam would assist with. Ive seen posts with different oil mixtures people say 70:1, 100:1 etc etc.

Skoal82 · 04-19-2017, 05:26 PM

Their is a fitting on top of the carb for the oil, make sure you seal that off.
As for the mix I think anything from 80-1 to 128-1 should work fine.

Spicyunicorn · 04-20-2017, 05:34 PM

have you done a compression check?

LP8484 · 05-20-2017, 04:43 PM

Sorry it has taken me so long to reply it's been busy around here. I did a compression check and it's registering around 85. On an 85 marathon what can I expect to see before I should start looking into taking the engine apart

BrewCityMusic · 05-20-2017, 04:58 PM

120 is good, the Factory says rebuild at anything under 100, although I have run old 2-strokes that were in the low 80's (but as You're finding, without a whole lot of "pep") ...

Make sure You are holding the gas pedal to the floor when testing ("Wide open Throttle") in order to get a truly accurate reading. If You are, and it's still in the 80's, I'd think about a top end kit, they're cheap and easy to install. While You've got the engine out though, don't forget to invest $15 in a set of crank seals too, I've seen a lot of top-end jobs on the old 2-strokes result in alately blowing out the old seals, which neccessitates ANOTHER engine removal, LOL

04-10-2017, 08:13 PM	#1
LP8484 Not Yet Wild Join Date: Mar 2017 Location: South Carolina Posts: 12	1985 Marathon losing power I bought an'85 Marathon and it needed a new starter generator. I installed that along with an air filter, fuel filter, spark plug, and with the exception of forward ended up being reverse and vice versa the install was no issue. But besides that once it was running I made about 6 laps on my street and then it was obvious the RPM's significantly dropped off even as the pedal was fully depressed until the point it didn't have enough power to make it up my driveway. When I checked it out the starter generator was really warm. Could I have gotten a premature bad one? Or could I have damaged it when I had the directions backwards?

04-11-2017, 11:48 PM	#2
LP8484 Not Yet Wild Join Date: Mar 2017 Location: South Carolina Posts: 12	Re: 1985 Marathon losing power Figured it out. Disconnected the header pipe off the muffler and the engine took off. I guess it's time to replace the 32year old muffler

04-12-2017, 01:45 AM	#3
Skoal82 Gone Wild Join Date: Mar 2015 Location: Central mn Posts: 1,036	Re: 1985 Marathon losing power Look up in the search function of the forum for barbecue a muffler The price on a new muffler is probably pretty expensive if you can find one. Yours is probably just built up with unburnt fuel and oil and a good hot bath in a fire should clean it out. Worth a try before buying a new muffler.

04-17-2017, 08:36 PM	#4
LP8484 Not Yet Wild Join Date: Mar 2017 Location: South Carolina Posts: 12	Re: 1985 Marathon losing power I already had ordered the new muffler before seeing your reply Skoal, thanks for the input though! Although even after the muffler install I was able to drive it around the block and it ran great for the first half then I started having stall issues unless the choke was played with. That was pretty much the only way I got it home. I currently have replaced the muffler, battery, starter generator, spark plug and set proper gap, new air filter, and fuel filter. I am currently premixing my gas and oil at a ratio of 128:1 and added seafoam at the recommended 128:2 as per the can instructions for a 2 cycle. I have not disconnected the oil tank or lines, could I be drawing air from that throwing off mix?? My next step was to pull it out and plug the oiler off then clean the carb which I hoped the seafoam would assist with. Ive seen posts with different oil mixtures people say 70:1, 100:1 etc etc.

04-19-2017, 05:26 PM	#5
Skoal82 Gone Wild Join Date: Mar 2015 Location: Central mn Posts: 1,036	Re: 1985 Marathon losing power Their is a fitting on top of the carb for the oil, make sure you seal that off. As for the mix I think anything from 80-1 to 128-1 should work fine.

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04-20-2017, 05:34 PM	#6
Spicyunicorn Gone Wild Join Date: Jun 2015 Location: NW Iowa Posts: 1,669	Re: 1985 Marathon losing power have you done a compression check?

05-20-2017, 04:43 PM	#7
LP8484 Not Yet Wild Join Date: Mar 2017 Location: South Carolina Posts: 12	Re: 1985 Marathon losing power Sorry it has taken me so long to reply it's been busy around here. I did a compression check and it's registering around 85. On an 85 marathon what can I expect to see before I should start looking into taking the engine apart

05-20-2017, 04:58 PM	#8
BrewCityMusic Hammer Down !!!! Join Date: Jun 2010 Location: Lake Geneva, WI Posts: 2,681	Re: 1985 Marathon losing power 120 is good, the Factory says rebuild at anything under 100, although I have run old 2-strokes that were in the low 80's (but as You're finding, without a whole lot of "pep") ... Make sure You are holding the gas pedal to the floor when testing ("Wide open Throttle") in order to get a truly accurate reading. If You are, and it's still in the 80's, I'd think about a top end kit, they're cheap and easy to install. While You've got the engine out though, don't forget to invest $15 in a set of crank seals too, I've seen a lot of top-end jobs on the old 2-strokes result in alately blowing out the old seals, which neccessitates ANOTHER engine removal, LOL

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