loading up during idle

[SKEETER150HP]

i have a 79 blackmax 150 v6 that runs great at running speed but when i go through a no wake zone and run it real slow it acts like it is loading up or fouling plugs. after going through a no wake zone it will not plane out unless the passenger gets up front of boat. once it planes out it seems to be running great. i have had it in to two shops and had it looked at and they say everything is fine? the boat is a 16.5 bass boat with a twenty one pitch at 4500 ft above sea level. i will try a 19 pitch but hoping to hear other possible ideas ....thanks

 

["G"]

Re: loading up during idle

When my 115 Merc did exactly what your 150 is doing it was a combination of ignition problems discovered separately. (Of course I had already done a compression check when I did my tune up). One was a coil that had a bad ohms reading. It worked at high idle but not at low. Once the bad coil was replaced it did help and the engine seemed to run better. Then one day shortly after my coil problem was fixed, the stator just up and quit while on a fishing trip. The kicker got me home but it sure did ruin my day. Since the stator replacement no issues with idle problems. It really did fix the whole idle issue.

I contacted the Merc Tech line about it. They told me to look into the timing/synchronization but I had already done that. Besides that they were having me check float levels etc. I told him I had done a carbs off tune up but was fairly adamant the floats were out of adjustment or maybe it was primary timing. A second testing on that assured it was not.

How I figured out the coil was bad was; I looked at my plugs after a day of boating. Saw that one was carboned up, traced it back and found a ohm reading low. I thought it possible the top carb was out of adjustment and I checked/adjusted them too.

Anyway... hope you find a different issue than mine, stators are spendy!

 

[Faztbullet]

Re: loading up during idle

Does it do this after you run it or the first time off the trailer?

 

[SKEETER150HP]

Re: loading up during idle

when first off trailer it does fine and first thing in morning it does fine, it just does it after idling for awhile or going slow in a no wake area

 

[Faztbullet]

Re: loading up during idle

Check the recirculation valves under the carbs (small black hoses attach to them) If they are plugged are stopped up it will cause fuel to puddle in the intake and cause it to load up. The older valves used a nylon check ball/disc and it may be swelled due to ethanol use, the newer use a steel/brass construction. After you use it and its acting up, pull the hoses with a set of long needle nose pliers and see how they spray, it should spray out in fine mist , if it dribbles out or sudden blobs the valve is bad.

 

[SKEETER150HP]

Re: loading up during idle

thank you for responses guys, ill give those ideas a shot

 

[j_martin]

Re: loading up during idle

Normally that engine would be jetted at .002 - .004 oversized for idle jets, .002 - .004 undersized for mains. from stock at that altitude.

Stock size depends on carb model more than application.

hope it helps
John