1989 85hp Force O/B has a misfire during idol

[mightymariner1968]

Have a 1989 85hp Force O/B. After engine is warm it misfires every 2 seconds or so causing the engine to kick slightly from side to side and then eventually stall. The engine will also stall when I want to start out slowly in forward and especially reverse. Starts up right away again and will go if I engage prop right away and accelerate, other than this it runs great. Wondering if it is a trigger plate or reed plate issue. Had engine Bored 0.030 oversize and rebuilt last summer. Has approx 15 hours on rebuild. Any Ideas

 

[roscoe]

Re: 1989 85hp Force O/B has a misfire during idol

I would look to the fuel system first.<br />Specifically, I think one or both of your carbs is running lean.<br />Lean is bad for a 2 cycle motor. It will eventually burn up.<br /><br />Start by turning the idle mixture screw out, 1/4 turn. <br />If this helps the problem, great, if not, try another 1/8 turn out.<br />If still no improvement, rebuild the carbs.

 

[mightymariner1968]

Re: 1989 85hp Force O/B has a misfire during idol

Thanks Roscoe!<br /><br />I will give it a try. I have three carbs on this engine, Do you think it would a good idea if I screw each lean screw in completely and start fresh since all three carbs may differ in settings. If so how many turns should I make on each.<br /><br />Mightymariner1968

 

[roscoe]

Re: 1989 85hp Force O/B has a misfire during idol

The 1989 had different carb setting.<br />The book says to start by turning it out 3/4 turn from lightly seated.

 

[mightymariner1968]

Re: 1989 85hp Force O/B has a misfire during idol

Thanks I will give iyt a try.

 

[Realgun]

Re: 1989 85hp Force O/B has a misfire during idol

LIGHTLY SEAT the screws and try 1 turn out on all three carbs. <br /><br />Start with the top carb, turn the top screw in 1/16 turn clockwise. let idle for 5 seconds to steady idle. Engine should speed up. then turn 1/8th counter clockwise. if motor speeds up more then when you turned it in then you need to be out further if it slows then turn clockwise again 1/16th. <br /><br />What your trying to do is get the motor to go as fast as it can on 1 screw in and out. What you want is to idle as fast as it can then turn out or counterclockwise 1/8 turn and your done this should give you the best idle. You will not be running too lean either or to rich. You have to do this for all three carbs. Once you have the carbs set then you can use the idle speed screw to get to 800-850 rpm in nuetral of course.<br /><br />As you move the scre in or out let the engine idle for a few seconds to get a sdeady idle.<br /><br />On my enigine the bottom carb is out 3/4 and the middle and top are at 1 turn exactly. thats just the way it works for me and I replaced all three needles.<br />I have the 1988 85 Force.

 

[Realgun]

Re: 1989 85hp Force O/B has a misfire during idol

Oh on the bottom carb you will need a very long flat screwdriver. the idle screw hole is in the cowl "under" the catch and weatherstriping rubber.

 

[buddyle]

Re: 1989 85hp Force O/B has a misfire during idol

hello,<br />I am wondering how fast you guys Force 85 hp runs? I have 89 bayliner with o/b 85 hp, and it runs about 21 mph....i am not too happy with that at all. Any input would be great. thank you.

 

[RRitt]

Re: 1989 85hp Force O/B has a misfire during idol

take compression readings, inspect bottom of boat, and verify speedometer (and tube) are good.<br /><br /> barnacles on bottom of boat can slow you down more than you would ever imagine. <br /><br />if compression is off then you may have a 50HP instead of an 85. if compression is good then make sure carbs and ignition are good too. bad carbs and bad reeeds will cause blown up engines.<br /><br />if your speedo tube has a hole in it or if there's algae/barnacles in the pickup then you won't display correct speed.

 

[imported_LakeRunner]

Re: 1989 85hp Force O/B has a misfire during idol

Granted that you are running in salt water remove the barnacles. Arrr! If not check your compression and the speed pickup and tube.