1984 merc 90 hp stalling at idle

[Bill Collector]

Please excuse any mispellings I'm on my phone. I found a cherry in a barn in nh. Original owner, no salt water, kept indoors it's whole life and no salt. It sat 4 years and before that had very little use. I drained the tank and removed and cleaned the csrbs. Bottom carb was packed with crap. Reassembled and used the boat 5 times with little issue besides the idle. Boat runs strong and is fast and smooth throughout shifting and throttle range. After it's warm it won't hold an idle and I'm noticing gas in N the water around the engine. Enough to be concerned with. I trimmed up the motor and gas leaked out of the carbs so I know that's a problem. Carbs are jetted 1.5 turns out. Once warm it will start if you put it in neutral and goose it while cranking, then have to Rev it and do the quick move into gear. Will run like hell after that but I need to fix this. Bought 3 carb kits and carbs are on my bench waiting for rebuild. My question is are my symptoms in line with leaking float valves? Ie - need to rebuild them.

Of note- new bulb, new plugs, new gear oil and compression is great.

 

[gm280]

Bill, I realize you stated you removed the carbs and cleaned them. But your problem seriously points to the carbs yet. When you clean carbs, did you disassembly them completely? If not, you need to because the small jets and passages can be clogged and everything look great. But the fact that you are having idle issues points to the idle circuit. That means the low speed jet section and passages. So I suggest you go back into the carbs using carb spray and compressed air. But remove everything this time and install carb kits. Then reinstall and adjust them until it idles properly... JMHO!

 

[Bill Collector]

Thanks for the reply. Yes I removed them and cleaned them and ran the boat and now I've removed them again with in tensions of installing new kits. I figured after sitting for all those years I'd suck something in there at some point.

 

[racerone]

Maybe there was a reason it sat all these years.--Maybe a nice looking motor but what are the compression numbers ??

 

[Chris1956]

New carb gaskets are mandatory for a good result. It is very smart to replace the floats and inlet needle and seat, as well, if you want a good result. You will also need to set the carb float height properly and adjust the idle mixtures on the water, in gear, with the motor warm.

 

[Bill Collector]

Thanks for the replies. Compression is 116 across all 6. How many turns out do I start with when tuning? They are at 1.25 out now prior to rebuild. Kits are taking forever to get to my house.

 

[Silvertip]

When you get to the point of adjusting the idle mixtures, you do one carb at a time, reset idle speed if necessary, then repeat this process several times to get it right. If you have this right, the engine should idle fine and not sputter or gag when you hammer down. Idle mixture adjustment is not a one-time thing. It needs to be repeated at least twice to get it right.

 

[Bill Collector]

Ok I have the carbs completely rebuilt. I started the mixture screws at 1 turn out and went in increments up to 2 turns. I've found 1.5 turns out seems to be the sweet spot. I adjusted th e only idle screw there is on the throttle mechanism near the fuel pump and it's idling nice on the hose. Water testing today.

 

[Chris1956]

Bill, 1.5 turns out is the starting point. You will likely need to richen the carbs a bit to get to the correct mixture for smooth acceleration and reasonable idle. Make all adjustments 1/8 turn at a time, 1 carb at a time, starting from the top carb, and testing acceleration after each adjustment.

 

[Bill Collector]

I've run into an issue. Started motor in the water and warmed it up. It's running, but fuel stream coming out throat of carb 1 and 3. Looks like my floats are stuck or not adjusted right. These are the carbs with the floats free floating in the cylinder on the left of the carbs, not in the undermounted bowl. My plan is to remove the starter and just remove the top of the carb, needle and seat area, make sure float isn't stuck and levers are level when the needle is upside down. Ordering new floats too. Any more suggestions?

 

[Chris1956]

OK, sounds like sidebowl carbs. The dual carb float levers need to be adjusted to give the correct float height and drop. Invert the carb cover. Bend the lower lever until the upper lever is parallel to the carb cover. Now turn the carb cover right side up. The distance between the two lever ends should be 1/4" Bend the lower lever (other lever) until that is achieved. Make sure the spring on top of the float is intact. Make sure the floats are not cracked or dissolved. It probably makes sense to replace all the floats, inlet needle and seats.

 

[Bill Collector]

Thanjs agajn for the tips. I dis everythIng that was suggested and here i am. Ok completed the tuning, had boat running great for a month. Last night trying to teach a 7 year old to ski I lost my hole shot. I can drop it in gear and very very slowly accelerate stopping every few half inches on the throttle and the engine will pick up and it will run like hell after that, right to a 50mph wot. but stalls right out if I go for the hole shot. I'm afraid to mess the settings which took me quite a while to settle on and get me to where I am today. Should I just go back to 1.5 turns out and start from scratch? It seems I'm 1/8 turn out further on the top carb than the bottom carb but im in work and cant get exact settings at this time.Help!

 

[Chris1956]

Normally you would not need to readjust the carbs, unless something unusual happened. Check the fuel filters for debris, and make sure there is no water in the fuel. Check compression and spark at idle. Inspect the fuel pump diaghram. If it leaks, it can cause the cylinders to misfire at idle and run fine at high speed.

 

[Chris1956]

And yes, top carb is usually set more rich than lower carbs. That is pretty normal.