Need to run a compression test, Check to see if firing on all cylinders, probably need to remove and clean carbs and ckeck for fuel restrictions ion fuel supply to motor.

Well, did discover no fire on 2 of the 3 cylinders. removed and replaced the two coils that were not firing. Ran easily on the 3 with wot of 4800, again. no idea why the coils failed, but they did fail in a pair for some reason.

BUT, my joy was short lived, as in less than an hour at wot or just under wot, one of the coils, plugs or wires failed, and i was down to 3600 at wot. So got something killing the coils i guess, have not yet taken it apart yet, due to a vaca and some family issues that took 1st place in our lives.

At $105 per coil, i cannot keep replacing them, so must find out why they are blowing. The 4800 is also low for this motor as 5500 is pretty much normal, but I believe this problem is cause by a mismatched prop. The motor came off a river fishing boat with a 13x21 prop with a half something???, ported and tuned, hardly suitable for a long 22' - 25' 2500 pound [empty] pontoon boat, so ordered a 14x15 prop which should perk that rpm up to around 5500,

But there still remains the failure of 2 spark coils for no apparent reason. Again, it ran fine on the sellers boat the day before at 47 mph, scaring me half to death. I am praying that its not a stator failure or worse, but how can it work one day and fail 6 wks later for no apparent reason.

I am stumped but will replace the latest coil and see if its one of the new or remaining original coil. Might have a short somewhere causing it, but nothing is obvious to the naked eye. Guess we will start doing some voltage readings and see what we get. Again, why good one day and on new boat, issues??? Thanks for reading and your help. ed

Definately seems like you have a short. Start with the stator and trigger assy.

problem solved for now

the mechanic suggested using third party CDM calls because they were cheaper. after cha nging out 6 CDM Carls under warranty it was determined in those were probably not going to work with this boat .

the number 1 cOILnever failed never. it was always 2 or 3 or 2&3 that failed. we took some old CDM coils off of the mercury motor that was on the lot and reinstall them on the 2007 and it's worked just fine ever since . sometimes cheaper doesn't mean better .

we are now experimenting with propellers to get the right pitch and size on to get it 2 up to 5500 it's running around 5000 . our next size will b of 14 by 15 and were hoping that'll do the trick should bring up about 3 or 400 a RP M's .
thanks for your help I appreciate it, ed

cdms failing on 2007 90hp merc 2 stroke.

Well, not sure anyone will get this since its been a while since I posted, but maybe it will help someone else w same problem. After blowing numerous cdms at a hundred each, never #1, always 2 or 3 or 2 and 3 I went for a year w/o a failure just keeping motor below 3500 rpm, so I figured I simply got screwed when I bought the used motor.

In 2015 I put the boat in the water expecting yet another yr of going slow but saving money by not blowing cdms. As feared, when I tested it by going to 4000 rpm, the boat lurched forward and I was back to 3000 rpm wot. So i drove around for a bit and put the pontoon on my lift, and cursed a bit.

The following trip, I decided for some reason to change the bad cdm and while turned around on the lift, the 3 spark plugs at $10 each. There is nothing cheap on this motor, so avoid mercs with serials starting with 1b nnnnnnn in your future, I was told by an 80 yr old mech that they experimented w something on the 1b nnnnnn engines and they were unstable for some reason, thus the cdm failures, 6 in total, almost $700 out of my pocket. I think the b stands for beta or bad or something not good.

Anyway, I changed the plugs and #1 was oily and so I assumed it was failing. I took all 3 home and put in the 3 new ones on the motor. #2 and #3 were clean and dry. #1 was wet and oily. I cleaned it up with a rag and checked all 3 plugs with a volt/ohm meters. 2 and 3 were fine, 0 ohms, however, #1 plug, the oily one, the ohms meter jumped around like crazy from 0 to hundreds of ohms and higher and back and forth. Again, these plugs were OUT of the motor and on my workbench. So #1 plug HAD A SHORT in it and I guess that it was sending 2x the voltage to #2 and or #3 cdms and blowing them out.

Since then, for 3 yrs, knock on wood. the motor has run at 5500, its wot, and not blown a cdm in 3 yrs. So we live and learn I suppose. And so of course last Sunday, I hit a log on the lake going 3500 [I go slow to conserve gas since I don't have money to burn, but can do 5500 if I want to for hours w/o blowing anything, like if a 50' cruiser is trying to swamp me, great fun at lake of the ozarks for them]. I had wood shards in the cowel, the pee hose was gone, and some part was busted off that connects the big water line to send the water/exhaust out of the prop. Water was coming out the bottom where the lower unit goes into the power head but got back to the lift [5 miles] with no problem since the water pressure was ok on the meter, it was just the water was not leaving the engine thru the prop, it was running out above the lower unit???????????????????????.

Got that fixed by a retired mech, and all seems to be fine now, so I await my next clamity. And to make it all worse, my best friend and boating partner had a fatal heart attack a couple months ago, so now I am on my own. . Getting old is not for the weak, that's for sure.

ed