1990 Johnson 88 Spl- Idle Problems

[PheasantsForever]

This is my first forum, so please excuse my ignorance if I am posting in the wrong place here.
I have just purchased a fishing boat, and it has a 1990 Johnson 88 Spl motor. Prior to purchase I hooked up the muffs, and the engine ran good through all cycles. I put the boat in the water for the first time, and the idle seems to low to me. Idling at 700 on the Tach. When putting the motor into gear-Forward or reverse it will die. I can counter this by shifting quickly, and giving it a lot of fuel. It will jump/jerk to get on plain, then I idle it back and it runs fine for a minute or two. After a couple minutes it will sputter and die again. Runs very well through all speeds except at idle. I will start by cleaning/rebuilding carbs. Any information on a good source for parts would be much appreciated. Also what else should I be doing to fix this problem while I am cleaning the carbs?
Again this is my first time on a forum so if I need to redirect this I will be happy to do so.

Thank you

 

[oldboat1]

Welcome! Can buy your carb kits here at iBoats.

Make sure you disassemble the carbs and soak everything metal, follow with soft wire in all openings then carb spray. Doesn't hurt to have a parts diagram in front of you.

 

[flyingscott]

Compression test before you spend any money!

 

[interalian]

Compression test and cylinder drop test. You could start by raising the idle a hair and see if it helps.

 

[PheasantsForever]

Compression testing tonight. I will post what I find.
Also everything I am reading says that it is not as easy as turning an idle screw to bring idle up?

From what I am reading I will have to adjust the timing along with the carbs? have any of you been through this process, and if so do I need a timing gun?
Thanks guys for any info I will get back with the compression readings tonight.

 

[flyingscott]

No timing needs to be adjusted for the idle. Don't adjust anything until the drop test and compression test are done.

 

[interalian]

If the compression and drop test show OK, idle is simply a matter of removing the throttle cable, adjusting the idle screw then resetting the cable at its new position (so it has the correct tension and pulls back fully to idle). Timing at idle isn't a reference - whatever it is, it is.

 

[PheasantsForever]

Compression test results looking from back of motor.
Top left 119
Bottom left 119
Top right 120
Bottom right 120

That is good news. I can't find my muffs at the moment so couldn't do drop test yet.
Now that compression isn't an issue I can start spending some money. What do you suggest I do first to fix the idle/shifting problem?

 

[interalian]

That's good compression. What do the plugs look like?

700rpm should be OK for idle. Mine works at 500.

Once you've done drop test, you may also do the 'business card' test. With the silencer cover off, you should get a fine mist of fuel sprayed out from the front of each carb when idling. If one hole is dry, it may have a blocked idle circuit. Carb rebuild (including removing the welch plugs to clean all passages) would be my next thing. Get OE kits if you can - they're best.

 

[PheasantsForever]

Thanks I'll that this weekend. Post more when that is done and we get back in the water

 

[PheasantsForever]

To update I have completed all the testing that you guys have suggested and what I have read other places. All passed with great results. Am I correct in assuming that that compression readings I got are really good for the age of the motor? I have decided to take the boat to a local marine that I trust. Hopefully they can figure something out. I have tested compression, Drop Test, and rebuilt carbs. Also replaced plugs and wires. Am I forgetting something that would affect the idle RPMs?

Thanks