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Help with 89 or 90 20 hp merc

F

Frerman91

Member
Hello, I have a 89 or 90 20 hp merc that was stored with fuel in it for aprox 8yrs when I pulled it out I cleaned the plugs and fuel filter and added new fuel. Started on 3rd pull it seemed to run well. When I took it out this past weekend I noticed it had a moderate miss and stumble during the 1st quarter of the throttle but ran well from there to wot. On the 2nd day the stumble/miss got worse and started to stall at idle through the 1st quarter of the throttle but again good from there to wot. Seems like the idle circuit Is plugged up runs seemingly rich during low idle operation but good above that. Any suggestions ?
 
It's amazing it runs at all, or doesn't overheat (since you didn't say you changed the impeller).

Jeff
 
yes jeff, I agree. I will be doing that shortly. I spoke with my local dealer and they suggested running a cleaning additive before attacking the carb.
it pumped strong and cool otherwise I wouldn't have put it in the water. do you agree with the dealer or should just get the kit.
 
Amsoil Quik Shot candidate. Alternatively Amsoil PI. Works for me very well. Non oxy fuel only, brother. Make sure the pump has a separate hose, or insure the last purchase was non oxy......do the math on the pump. Otherwise, run out the first gallon into another can, or preferably your car or truck. I don't take 'em apart unless I really have to.
 
thank you timguy, amsoil products are not readily available to me. it was stored with ethanol fuel in it for 8 yrs. the wp impeller has not been changed since I bought it in 97 so im sure its overdue. it has non ethanol in it now. not sure what you mean about the 2nd hose. and what am I running into another can fuel or water ? what can I use to soak the carb in to clean it.
 
Okay, to clarify, the gas pumps often don't have a "dedicated" hose for non oxy. So if the last purchase was ethanol, you will get the first gallon coming out the hose and pump as ethanol, even if you switch over the selection to non oxy. Spray the carb and infected parts with fuel injector cleaner. This is stronger than carb cleaner. Some plastics will be damaged by it even. Sorry about Amsoil, these products have been a lifesaver to me. Check on line, perhaps you will find a local small engine shop that stocks them.
 
yes, the place I get fuel has a dedicated pump. I'm using berrymans tb cleaner. its in a chemdip bath as we speak. I just hope this is the problem. it looked reasonably clean
if not what could cause low idle miss.
 
ok, I have cleaned the carb installed new parts and reinstalled . after running and setting the mixture it seems to run a bit better at times but there is a spot at about 1/3 rd throttle where it still misses and sputters pretty bad. any ideas.
 
what new parts were installed? Did you buy a complete carb kit with the primer and fuel pump assembly? Is the carb base gasket on correctly? Is the pulse port for the fuel pump on the block clean. Did you soak the carb or just spray stuff at it? There is no mechanic in a can!
 
yes, I purchased and installed a complete kit, it was soaked in berrymans carb cleaner (not spray) for 48 hrs and followed up by a rinse with injector cleaner ad blown out with a compressor. everything appeared clean and clear.
 
Have you done a compression test? Have you changed the waterpump impeller? Have you done a spark test? Spark should jump 1/2" air gap.
 
just completed the comp test it was 105 psi, the impeller was next not done yet. im getting new plugs shortly and will do the spark test. how do you do the spark test with the plugs not having electrodes. will it sill jump the gap between the plug and block.
 
Well it should not be pumping good cool water that would suggest a thermostat problem. The other thing is that is that is a chrome blind bore motor very expensive to rebuild. They do not like to be overheated that is an expensive lesson.
 
Ok, sounds like a thermostat is in order. In addition to the impeller. I changed out the plugs due to cracking in the ceramic part and it seems to run better but I'm currently running it in a barrel so I need to get it to the lake to see for sure. Thank you
 
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