Job 3 - Idle issues

[Marlboro]

OK, bearings and new wiring all done on the trailer, time to move on to the fun stuff.

Noticed last year that the motor was hard starting (89 johnson gt100), and towards the end of the year it was having problems idling especially when put in gear. I started it on the hose the other day, used a technique I found on some forum, raise the fast idle lever, hold the key in for an 8 count, release and turn on. Worked great, motor fired right up (the first start of the year). So I think the starting issue is ok.

As for idle, after warming up the engine for a minute or so with the lever up, I tried to close it and just have it idle on its own, no dice. Would bump the gas with the key and it would shoot to life but just die soon afterwards. I know you can't set the idle out of the water, but I did turn the screw a bit just to see if I could get it running on the hose, went one turn and stopped, no luck. Last year, it would idle fine but would be trouble as soon as I put in gear.

Background: Bought the boat last season. PO had converted to pre-mix with the original VRO still pumping the fuel. Long story short, I was convinced by a tech to ditch the VRO and just instal a regular fuel pump which I had him do. First trip out seemed fine, was cruising along and I could just feel the slightest "miss" almost like something tugged at the boat for a split second, as soon as I slowed down and came to idling speeds I started having stall problems. The tech said he had to remove a carb to instal the fuel pump. Maybe dislodged some crap in the carb???

I know I'm not giving you much to go on, I'm picking up a compression gauge this weekend to check those numbers and I will verify spark. I figure the carbs could use a rebuild. I'll update the thread when I get some compression numbers.

 

[Jimway]

How old are the plugs? Two cycles tend to run lean midrange, hope it wasn't too lean.

 

[Marlboro]

Plugs at the time might have had 2 hr's on them.

 

[JT Patroni]

The summer of 2012 I had a similar issue with stalling when going back to an idle. Took a ride over to Rockport and it kept stalling at low idle. Made it back to Wellesley Island, and pulled up to the dock and it stalled for the last time. Never to start again. (Johnson 3L 200 hp) Problem - Timer base went bad. $650 later and it was fine. And relieved that I made it back to my dock.

Have the timer base checked. Special gauge for that test that I don't have.

Good luck!

 

[Marlboro]

Thanks Jim, I'll investigate this more.

 

[wired]

Ive seen that push in the enricher thing for 8 seconds before . I'm not sure how that is supposed to do anything without pressure in the fuel system. Ive always pushed it in while turning the key as the discharge nozzles wont actually spray unless the diaphragm operated pump is pressuring up the system.

At this point I'd be pulling apart the carbs for a good cleaning, float adjustment and especially a link and sync and timing adustment.

 

[Marlboro]

I hear ya about the 8 second thing. However, it worked like a charm. I'm leaning towards a good carb cleaning and rebuild as well. Probably been a while for this engine. Rebuild kits are cheap and its another task I've never done so I would like to tackle it. I haven't looked at timing adjustments in the manual yet so definitely some research for me to do.

Thanks for all the replies.

 

[Marlboro]

update

Finally got around to picking up a compression gauge and a spark tester. Started engine on the muffs to bring it up to temp. Motor did idle today without help but it is rough. Ran a compression check on the cylinders, all within 10psi of each other. Spark test showed a nice blue spark across a 7/16" gap.

Along with my tools, I ordered up the rebuild kits for my carbs. I'm thinking this is the next step and I plan on going at them tomorrow. I have a factory manual and some youtube vids to help me along. Any tips anyone would like to share before I tear into this??? I have reviewed the link and sync procedures in the manual, doesn't seem too bad, but I'll be back with questions for sure, especially around timing.

 

[jumbofordman]

Ive seen that push in the enricher thing for 8 seconds before . I'm not sure how that is supposed to do anything without pressure in the fuel system. .

On a Merc carb motor, when you squeeze the bulb until it's firm it fills the float bowls in the carbs. When you hold the key in it opens a solenoid that drains a little bit of gas from the bowls to the cold start enrichment circuit. Doesn't require any pressure, it's all gravity.

 

[Marlboro]

OK, I'm stumped. Putting first carb back together, manual says invert carb and fill idle circuit with Iso and check for a leak at point "a". How the hell do I do this?

 

[Marlboro]

Point "a" being where the emulsion tube comes through the body from the idle circuit. Think the tube is a press fit into the body so a leak could occur. Anybody ever check this when rebuilding carbs?

 

[Marlboro]

Update

Just thought I would update the thread, finished rebuilding the carbs on the weekend. With the carbs off, I looked over the re-circulation lines, they were not run correctly per the manual. The fuel line used for them had definitely seen better days so I changed them. Check valves tested fine. Put it all back together, linked and synced the carbs. I don't have a timing light but I do have a dial indicator so I thought I would just confirm TDC on piston 1. It was bang on. Put the muffs on and let her rip. Result: started up immediately, idled and sounded nice. Lowered the fast idle lever and it idled fine. Took the boat down to the river and went for a great ride, although it was choppy as hell..... Shook something loose and my bilge pump and gauge lights aren't working but the engine was running great! Hopefully get to enjoy some boating now.....