1998 Force 120 - Running Rough / Stumbling

[buzzbomber]

Sup Everyone,

Had the boat out last weekend, ran it around for about 8 hours stop and go. On the way back to the harbor with one mile to go outboard started acting up. It started running rough, started stumbling (or i guess you could say coughing or bucking). I backed it down and let it idle for a couple minutes and it seemed to sort itself out.

Got the boat back on plane for about 5 minutes then it started doing the same thing again. This time it didnt sort itself out and kept and still is running rough.

So far I've ran through all the fuel lines. They're all pretty new replaced them 2-3 months ago also rebuilt the fuel pump then to. Have been using the boat a couple times a week with no issues till now.


Here's a video of the motor and how it sounds (that deep-dull constant pop/knock sound there at idle or at speed):

http://www.youtube.com/watch?v=g1d1Li9Jw3I

So far in troubleshooting:
1. Check all hose fittings from tank to carbs all look good and even re-did a couple, bulb stays firm.
2. Check plugs bottom two cyclinder plugs seemed pretty fouled. I cleaned them but haven't had a chance to start it up again. Pic of one below:


Not sure where to go from here. Any advice on where to start troubleshooting would be appreciated. Not sure if its' a fuel or spark issue. Maybe both. I guess i'm hoping someone's heard that sound before and can point me in the right direction.

 

[jerryjerry05]

Re: 1998 Force 120 - Running Rough / Stumbling

Start with a compression/spark test.
Water in the fuel?Check the pump diaphram.

 

[buzzbomber]

Re: 1998 Force 120 - Running Rough / Stumbling

Just pulled apart the fuel pump, check valves & Diaphram all look good.

Spark on top two cylinders look good as well.

Ran out of juice so charging batteries. Will test compression and spark on bottom cylinders in a few hours.

 

[buzzbomber]

Re: 1998 Force 120 - Running Rough / Stumbling

compression numbers (top -> down)
140
150
145
141.

For water in the fuel, I check the racor water/fuel seperator and didnt see any water pooled at the bottom (one of those clear bowl ones). Filter in it is pretty new and fuel maybe 3-4 weeks old. tried to by pass it to to see if it made any difference and motor still ran the same.

Still need to check spark.

 

[buzzbomber]

Re: 1998 Force 120 - Running Rough / Stumbling

ok, just checked and have spark on all four cylinders.

Spent a lot of time trying to figure this out today on whats causing the coughing/bucking. To add more description this dull knocking/popping noise is constant wether at idle or at speed. When under way engine will jerk or vibrate. When checking spark I noticed that the pop/knock noise seems to be coming from the top carburetor. Does that make sense to anyone?

Jerry will try your suggestion and hook up an external gas tank to make sure water didnt some how get into the fuel. Just want to make sure I check everything out first before I spend the 50 bucks on the external tank.

Appreciate any and all advice want to get out fishin

 

[buzzbomber]

Re: 1998 Force 120 - Running Rough / Stumbling

Also one last piece of information, when removing the plugs all plugs seemed pretty gummed up other than the plug in cyclinder #1 (top). That plugged looked almost new.

Still trying to figure out wether it's electrical, carbs, or fuel.

 

[bentle]

Re: 1998 Force 120 - Running Rough / Stumbling

Kinda sounds like reed pedals. Popping back through the carbs is a sure sign of bent or even broken reeds. Your compression is well within proper range so that tells me none are broken, but possibly bent. I say that because a broken reed could end up along the piston wall and piston causing some ring and piston wall damage. Other than that it could be air or even water in the fuel. One other issue you could be having is the timing might be out a bit.
I have a 125 force outboard that had two bent reeds and had the same symptoms your having. Other than the time to replace them it was a pretty easy fix and the reeds were only around 10 bucks a piece. I purchased mine through boats. net.

 

[buzzbomber]

Re: 1998 Force 120 - Running Rough / Stumbling

Thanks Bentle,

Looked up the reed cost and its $65, http://www.boats.net/parts/detail/merc/M-11645 2.html, this looks like the whole assembly can't find just the reeds.

Also what's a good way to test if the timings off? havent done that before.

 

[buzzbomber]

Re: 1998 Force 120 - Running Rough / Stumbling

Bentle you da man! Thanks to all who replied.

Had time to dig into the motor again and pulled the carbs and got to the reeds. Discovered one pretty badly broken reed pedal View attachment 110400.

That one was on the upper carb, explains that popping noise coming through the upper carb.

Also the bottom reed assembly has two chipped reeds so gonna order a replacement for that one as well. Wish they'd sell these reeds individually, pretty pricey. Also have to order a retaining ring, sent one flying like a frisbee when taking off the carbs and couldnt find it.

Pretty cool learning how all this stuff works. Thanks again. I'll post results after replacement.

 

[buzzbomber]

Re: 1998 Force 120 - Running Rough / Stumbling

edited - was looking for retaining ring (found some on ebay)

 

[bentle]

Re: 1998 Force 120 - Running Rough / Stumbling

Glad to help. Those retaining rings can also be bought at your local hardware store. Might be a good idea to pull your head and exhaust plate and make sure that little broken reed pedal isn't still hanging out in there somewhere. Hate to read one day you lost compression on here on one or more cylinders. But its your call man. If it was me I would do the extra work just to be sure. Have you gotten a manual for your motor yet?

 

[buzzbomber]

Re: 1998 Force 120 - Running Rough / Stumbling

Yea, i've got a clymers. I got all next friday to put the new parts in and get the fuel intake system back together. Makes sense to check for the steel shards in the engine. If you think it's worth it i'll give it a go. I want to keep this motor running.

Can the exhaust plate and head be pulled off with the motor mounted?

 

[buzzbomber]

Re: 1998 Force 120 - Running Rough / Stumbling

Alright just want to post back results. If anyone else comes across the same issue. Not a Mechanic so its the only thing I can do to give back for the help I've got.

Since I had 2 of the 4 reed assemblies with chipped reeds I decided to replace them all. At 69 bucks each that's about 280.00 (plus gaskets around 300.00) just for parts, you can't buy just the reed pedals unless you ebay (clymers says the assemblies non-servicable). Found boyesen after market reeds for about 100.00 for all the 8 sets of reed pedals a lot cheaper and you can replace all the reeds.

Installed the reeds and after adjusting idle and adjusting carb screws screws glad to say i'm back on the water. Actually have a lot more pick up than I did when I got the boat. Never did the link and sync but with clymers, a couple hours, and a patient girl friend got it tuned to spec.

Haven't ever done much mechnical stuff before... didn't know what a carbereutor was before I started this project.

Also if you reed through the thread I mentioned popping out of the top carb it because reed on the top carb was pretty much broken in half and had to go almost full throttle to get the engine to start.

Parts I ordered to get the job done:

Boyesen reed kit (B244)... also if you go this route dont use the stock reed stops use the plate that comes with the kit, had to call to find this out.
Carb Gasket kit x2 (FK10023)
Reed Deflector Plate x 2(F406406)
Gasket Carberator Intake adapter x 2 (828316)

Also a clymers manual. Only advice I can give other than what the manual says is that I think the torque specs in the book are iffy. I ended up snapping one of the bolts putting back on the reed plate housing trying to meet their torque specs for 3/8 bolts for the instake system so I went by feel after that.

Gotta say thanks to all who help and just the forum in general, pretty cool to work learn how it all works and save some money.

 

[bentle]

Re: 1998 Force 120 - Running Rough / Stumbling

Posting your fix and parts numbers will help someone else that searching for that fix for there motor or at least get them in the direction. I believe just about any one can work on and fix their own force motors but together we can do anything. Good luck.