Rough running @ low RPM

EnonEye

Recruit
Joined
Jan 6, 2011
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5
'96 Johnson 88 spl... always has run fantastic including low trolling speed. Now, it will not run at low RPM's but still runs great at higher RPM's (say above 2500k).
Background for what it's worth:

Last fall could not inject the fogging oil due to the shrader valve not operating properly (oil just ran over side of engine instead of inside, valve not opening obviously) but engine started and ran great all year so far up until last week. I run it weekly.

2 weeks ago I ran "out of gas." Primer bulb would not pump up and I put 2 gallons in it after getting towed in and primer bulb pumped up fine. Figured just a bad gas gauge.
Next time out it started fine cold but then began immediately with the stuttering and stammering at low RPM's. Sounds like it's running on 1 cylinder and the rest are not firing. Higher RPM's (as stated above) it runs great.

I'm no mechanic but is it worth it to put in carb cleaner and then replace plugs or just take it in to a pro? If it might be worth putting in carb cleaner (here's where I get all you mechanics pounding the desk) how do I access the carbs to squirt in the cleaner? :facepalm: My understanding is the shrader valve bypasses the carb so you can't squirt the cleaner in there. (sorry but I haven't seen a carbureter since I rebuilt the engine in my Olds442 back in 1969)

Thanx for any advice you've got. I really appreciate this type of forum before handing over my "baby" to someone else but I don't want to do her any harm either.
 

hidef

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Aug 22, 2009
Messages
1,465
Re: Rough running @ low RPM

You are going to need four carb kits. If you don't have the service manual you can order it from http://www.marineengine.com/parts/parts.php#manuals or try ebay. Spraying carb cleaner down the throats will not accomplish anything. You will have to take the carbs apart clean all the passages and then reassemble the carbs. You should also get a new schrader valve.
 

Auxlarry

Petty Officer 1st Class
Joined
May 21, 2010
Messages
304
Re: Rough running @ low RPM

I agree with hidef! You probably sucked a bunch of trash into the carbs when you ran the tank out. Good idea to install an inline filter/water seperator if you don't have one.
Good luck, the rebuild is not that hard of a job!!
 

Daviet

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Sep 24, 2008
Messages
8,958
Re: Rough running @ low RPM

I agree with hidef, your carbs are probably in need of overhaul. I would suggest that you also preform a compression and spark test to get a baseline of your engine.
 

Monte1961

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May 8, 2011
Messages
1,180
Re: Rough running @ low RPM

I agree with hidef^. Rebuilding the carb/s is not brain surgery! Although, lots of things can go wrong if you don't make a plan for attack! Before you take anything apart, even a screw, take lots of pictures. Find away to number the carbs so you know the exact position's they were in. Don't soak anything made of plastic in carb cleaner, it will melt! All other metal parts can go in carb cleaner. Allow carbs to soak for 24hrs. If you find any core/welch plugs on carb/s, they need to be removed to insure good cleaning! Just be careful not to drill past the core/welch plugs. After 24hrs soak time, rinse with fresh water and blowdry with compressed air in all holes and passages of carb. Note. Some carbs have three jet plugs. Write down or take a good picture of there location before dissembling. They should have #s on them. Buy a good quality overhaul kits. Stay away from Sierra kits! Good luck and post back!
 

EnonEye

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Jan 6, 2011
Messages
5
Re: Rough running @ low RPM

I agree with hidef, your carbs are probably in need of overhaul. I would suggest that you also preform a compression and spark test to get a baseline of your engine.
Thank you for all responses. I will be taking it into a shop as I don't feel comfortable rebuilding a carb.
Daviet... should I ask the shop to do the compresion and spark test 1st and what will that do for me?
 

Daviet

Fleet Admiral
Joined
Sep 24, 2008
Messages
8,958
Re: Rough running @ low RPM

If I were working on it, that would be the first thing I would do, then progress to the fuel delivery system.
A spark and compression test is quick and easy to do and lets you know that the basic engine functions are ok.
 

larryg

Petty Officer 2nd Class
Joined
Mar 12, 2011
Messages
119
Re: Rough running @ low RPM

gotta try if it gets messed up thats why we and the schematics are there for him .dnt be scared just do it.lol better than payin 95 an hr..
 

Monte1961

Lieutenant Junior Grade
Joined
May 8, 2011
Messages
1,180
Re: Rough running @ low RPM

Well unless you have more money than God!
 
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