1994 99 Mariner problems at higher rpm

"1994 9.9 Mariner has 90psi on

"1994 9.9 Mariner has 90psi on both cyliners, starts easy and idles fine but falls on its face intermittently when revved up at medium to high rpm. I decarbonized it big time. She seems to be getting fuel just fine between sputters. Further suggestions much appreciated, thanks."

"Mark, you have probably one o

"Mark, you have probably one of the best 9.9's ever produced ever.

You need to determine whether your hesitation is ignition or fuel related.

If you can get ahold of a timing light you will be able to quickly determine if you are losing spark intermittently causing the "hitch".

If both plugs confirm to be getting spark then it is back to troubleshooting the fuel system.

How old are the plugs? that may be a 5 buck fix just to rule them out..."

"Hi Graham, thanks for the hel

"Hi Graham, thanks for the help. I agree with your hunch of an intermittent spark problem (under the flywheel perhaps?). Spark plugs are new. Coils are throwing spark because the rpm drops when I pull each wire. Will try the timing light and check back in with you. What makes this year one of the best 9.9's? Heard some of these Mariners were Asian built, is this true? I need a tiller kit for her as well. Thanks, Mark."

"Mark, Mercury started produci

"Mark, Mercury started producing the 9.9's for the 1986 model year.

The line continued with one major change coming in the 95 models up until the they were discontinued in 2005 (when Merc stopped producing "conventional" 2 strokes, save the 50, 90 and EFI 150's).

Earlier Mariner 9.9's (78 thru 86) were Japanese built, 100% Yamaha engines.

The 86-94 9.9's (whether Merc or Mariner) were built using a 12.8 cu in Yamaha powerhead and Yamaha 2.08:1 gears. That combined with Walbro carbs and Merc's Thunderbolt 4 ignition made them the most reliable and durable outboards ever built. You have to really neglect and mistreat them before they will break. The 6, 8 and 9.9 motors of that year range were identical save the carb and exhaust.

In late 94 they switched powerheads on the 9.9 and replaced the 12.8 with the 16.0 cubic inch power head that was being used on the 15 horse (since it's rebirth in 1988). The rest remained the same.

99% of all parts for any 6/8/9.9/15 produced from 1986 on is interchangeable (save the carb, exhaust and powerhead itself) and there was thousands of the motors produced.

I personally own 3 motors from that series. An 86 9.9, 87 9.9 and 91 15 horse. Both of the 9.9's have well over 1500 hours each and the 15 is just approaching the 1000 hour mark. Aside from spark plugs and impellers, not a single component has been changed or needed repair (of course with proper winterization and lower unit oil changes thrown in as required).

Additionally, I have never worked on one that required more than regular maintenance. So either all those owners have been lucky or maybe it's just an exceptionally built motor (I would lean towards the latter). It is difficult to find a 20 year old OMC that hasn't replaced a powerpack or other ignition component. I have heard of 1 or 2 Mercs that required a switchbox, but never seen it myself..."

"It's good to have knowleg

"It's good to have knowlegeable friends. Your help is much appreciated. Sounds like a bullet proof little motor. Keep your fingers crossed for good news from this end. Thanks, Mark -"

"graham , i had one of the 15h

"graham , i had one of the 15hp you are speaking of and had the same intermittant problem that drove me crazy till i decided to take things apart.i found in the carb there was no hook between the float arm and the needle valve and the viton tip was jamming in the port i fabricated a hook and that solved all my problems.as for my experience i've been working on mercs since my racing days in the 50's"

Good point Mr. Pops. It sounds

Good point Mr. Pops. It sounds like an engineering defect in that the manufacturer installed no "hook." Am I reading your recommendations right or was your hook just missing? I'll have a look. Thanks -

"another person at the marina

"another person at the marina had the same problem and asked me to check his motor i found the same condition.mfg. defect ,cost cutting who know?"

"Hello Gentlemen, long time no

"Hello Gentlemen, long time no talk. Mainly because we went rounds with this lil 9.9. After comp check, a new damn stator and trigger, reed valves check, guess what? The exhaust tube was 70% restricted from lack of decarbonization maintenance. Cleaned it out and the high rpm hiccups are el' gondee. Sure appreciate the help from all of you. Check those exhaust tubes for restrictions!"