Merc90 2stroke symtoms for weak/damaged coils ??

jpn · 29 August 2010, 14:54

What are the symptoms/signs of damage of the ignition coils? I believe my coils fire well whencold but after sustained running they get weak...

uncle al · 29 August 2010, 18:56

remove clean and make sure that all earths and electrical connections are clean and tight,
what is your seraial number? you could have the cdm ign system it is a bit more complicated it might be easier for you to get a service manual email me at alan.surman@barrus.co.uk
with a serial number and i will give you the p/n for the correct manual for your engine which you can purchase from any merc/mar dealer

jpn · 30 August 2010, 02:22

Thanks for the reply uncle al....if its a cdm malfuntion meaning it could be the rev limiter kicking in even ifitdoesnt have to??? I was told it was a possibiity?

uncle al · 30 August 2010, 15:50

your problem sounds more like either a trigger or stator problem or a bad connection some where

jpn · 31 August 2010, 01:47

I just found out my merc 90 is the CDM type ingition system...could it be one of the CDM that is damaged?

uncle al · 31 August 2010, 08:07

yes it could be a cdm

jpn · 31 August 2010, 11:33

thanks for the reply uncle al....all cdm replaced (i borrowed) and still same problem....runs good first 3 minutes...even up to WOT and reaches correct rpms....but misses after 3 min., throttle back to idle for a couple seconds...back to WOT it will be ok for a couple seconds then misses...the longer I let it idle, the longer it can sustain WOT....and the misses...if I just just below 3K rpms all cylinders seem to function alright....

well anyway i will be going to the stator and trigger as you suggested Uncle Al....I know ideally I should try replacing both at same time, but if I had to make a choice, which should I try first...stator or trigger?

uncle al · 31 August 2010, 15:09

before you spend lots of money i stongly advice that you do an electrical test of the trigger and stator, if it is a black stator it could be a bobbin in the stator breaking down the new stators are now red more powerfull

jpn · 01 September 2010, 12:48

I am getting really frustrated...the stator is red one....I borrowed stator and trigger from good engine..still the same...good power out of the hole...everything seems normal for a couple minutes, then I loose power...now I will be checking the fuel lines...but the prime bulb seems fine...its hard...I throttle back...idle a couple seconds, give WOT ok again for a short time and I don't even have to pump the bulb...

One thing I noticed, after engine starts to lose power, if I go back to idle for long period, It can sustain WOT longer, as compared to if I just throttle back to idle and back to WOT it will lose power right after it tops out....and the fuel pump is new.....seems like the carbs or at least one carb is not getting enough fuel to get in the bowl...

Downhilldai · 01 September 2010, 12:59

Sounds like a fuel pump problem. Is the new pump sealing well to the block?
Have you tried a different primer bulb?

jpn · 01 September 2010, 13:19

thanks for reply...I will check if pump is sealing well...does the primer bulb affect fuel flow? It is still hard even when the engine seems to be starving/losing power?

Downhilldai · 01 September 2010, 13:26

You could try running the engine at WOT with someone squeezing the primer bulb. If it runs ok when they do this, then you have a problem with the fuel supply to the carbs.

Fuel supply problems could be:

1. blocked tank vent - unlikely in your case
2. blocked fuel filter or water in the filter housing.
3. bad fuel hose connection, which draws air.
4. Faulty fuel connector on the tank or outboard.
5. Fuel pump failure. Diaphragm stretched/holed, or badly sealing O ring to the block
6. Faulty primer bulb - could be a sticky valve inside.
7. Carb float settings

Good luck

jpn · 01 September 2010, 15:30

Thanks a lot for the list....

1. blocked tank vent - unlikely in your case (I ran without fuel cap already)
2. blocked fuel filter or water in the filter housing. (new filters installed)
3. bad fuel hose connection, which draws air. (I believe I checked this correctly)
4. Faulty fuel connector on the tank or outboard. (I yet have to check pick-up tube)
5. Fuel pump failure. Diaphragm stretched/holed, or badly sealing O ring to the block (new)
6. Faulty primer bulb - could be a sticky valve inside. (not yet checked)
7. Carb float settings (a very likely suspect since carb has been opened by previous owner)

jpn · 03 September 2010, 15:24

Problem still exists....aaarrrgghhh!!!!!

Well I got the fuel system sorted out, no leaks, new pump and it still has the problem.....after further investigation I just found out we havent tried replacing the trigger, we only tried replacing the stator....

Uncle Al I have a question....Is there a way of bench checking a trigger...tocheckit before installation?? I did get hold of a trigger a good running motor, but I just want to make sure if it is really ok by testing it with a tester before intalling it???

Another question...the motor is fine for several minutes before the misfiring, and I am sure I do have no rev limiter installed.....could the trigger still be the likely culprit...is there any logical explaination, from my understanding the trigger only signals when to fire a cylinder...and if doesnt miss giving a signal the 1st few minutes how can it starting giving bad signal after a couple minutes running?

jpn · 05 September 2010, 11:18

On the day I decide to trash my merc 90, it seems it is now working fine, I replaced the ignition wires (seemed ok though) and then "viola" the motor seems ok....

For those of you interested on my problem....it was several problems that caused all my frustration...here is the list...

1. Main jets were clogged, that was fixed but there was still a problem in sustained cruising and WOT...
2. Whole ignition system was replaced and still had problems after a couple minutes running
3. Fuel inlet of the carbs were clogged (inlet volume ws restricted) and then resolved but I still had a missig cylinder afer sustained cruising/WOT operation..no missing cylinder idle high rpm without load...
4. Changed ignition wires, now seems ok....

ssdvc · 12 September 2010, 13:24

I have the same problem with my 85/86 Merc 50hp 2 stroke. Red Stator and some other new parts. After a few minutes of idle, I can go WOT for about 30 sec to a minute and then it bogs down. The motor will slowly (takes about 5 sec) loose power. Idle is still smooth and even after that and if I go WOT, the engine won't rev up much, but it runs even.

Compression is 120-130psi in all holes. Just had carbs cleaned.

I will try to replace my plug wires this week. What else could it be?

Thanks

uncle al · 12 September 2010, 19:35

hi i am glad to read that the problem is sorted,the only way to bench test a trigger is to do a resistance test (i dont know them of the top of my head and i am on vacation now for a fortnight so the figures are not available to me) but we prefure to check by voltage with the obm either running or on the starter motor, it is a known problem that either a high speed bobbin or a low speed bobbin to fail after a short time running usually black stators .
regrds
alan (uncle al)

lifeboatman3 · 20 September 2010, 18:06

I had the very same problem on my 90 merc, its as if you have lost to gear!!
I checked and changed most things to find out it was a sticking stator and it wasnt advancing! I got a new stator cleaned and greased everything else and she ran fine