120 force missing/bogging at take off

[wet dog]

20' bayliner capri with rebuilt 120 force L-drive was working fine while breaking in new engine. used 25:1 oil mix for first 10 hours and it ran fine, just lots of smoke. now it hesitates at takeoff and sputters out of top carb at 3/4 throttle, sometimes not making it on plane. top plug is continually fouled, black soot, even after swapping from another cylinder. I do have good spark. thinking it must be carbs but I took them off and they look clean. could excessive oil continually cause just one plug to foul? Does the black soot on top cylinder mean it is not firing? It does occassionaly get going and once running WOT it does fine.

 

[wet dog]

Re: 120 force missing/bogging at take off

I do have spark on all for cylinders, but discovered 1 & 2 are not firing (no change in idle rpm when 1 & 2 plug wires are disconnected). Carbs have been off a couple times and cleaned, reeds are good. at WOT occasionally all four cylinders will fire, I think, as rpms change and speed increases sporadically. could it be timing issue? I adjusted throttle linkage recently to allow butterfly valves to open completely. WD40 sprayed into top carb when idling does nothing.

 

[trophy17]

Re: 120 force missing/bogging at take off

my 1994 force 70, is kinda doing the same thing, it boggs down when i first push the throttle down and then finnaly "catches"up to itself and then runs fine. Did you find anything out about this? is it the carb? the fuel(ethonal) just not sure. Have just replaced my stator, trigger and switch box, so my power is all there. stumped in tallahassee.

 

[pnwboat]

Re: 120 force missing/bogging at take off

The symptoms that you are experiencing are typically caused by weak spark, fuel delivery problems,or bad reeds. You've checked out the reeds, so that isn't the problem. If it was weak spark, the plugs would look very clean due to the fuel mixture not igniting. The fact that you have fouled plugs probably means the mixture is being ignited but the mixture is too rich. Maybe the top carb is running too rich. I would start off by doing a "Sync and Link" to make sure both carburetor butterflies are perfectly sync'd together. I would then take a look at the top carb. Most likely a bad or sticky needle valve, or the float is adjusted too high. The other thing to check is the fuel recirculation system. Make sure the hoses and check valves are working and not clogged. I would also add a low cost in-line fuel filter in between the fuel pump and carbs if you don't already have one.

If everything checks out OK, the I would take a look at the CD modules/coils. Swap them around and see if the problem (removing plug wires from 1 & 2 w/no affect on idle) moves.

 

[fishin1789]

Re: 120 force missing/bogging at take off

I've got the same problem with my 20' Maxum with the same motor. I've went thru the fuel system with no improvement. I'll be checking the recirculation system later today then it's on to the electical items. "IF", or hopefully "WHEN" I find my culprit I'll let you know! I hope you have a Clymer manual on this engine, You're gonna need it! When mine gets running right again, IT'S FOR SALE! These L-drives should come with a set of wrenches and a manual, sorta like an old Harley! Good Luck!

 

[JAKER95XR]

Re: 120 force missing/bogging at take off

I got the same issues on my 95xr force.I rebuilt the carbs twice,fuel pump and checked the recirculation system.I looked at the reeds there good.I also replaced every fuel line on the boat,also checked the tank for fuel pickup and correct venting all good.New plugs and thermostat.On the spark side of it,all new,stator,trigger,voltage reg,rev limiter and fly wheel.Im begining to think the only cure for it is the bottom of the river.I got MORE PARTS ordered if i find something I'll let you know.