Mercury 40hp 3cyl no power

[doc_cody_blue]

Hello people,
I bought a 144 Glastron with a 40hp Mercury yesterday. The engine is a 40hp 3cyl. Dont have it close to me so I dont have the serial.
The motor starts up ok but has no or bad idle. If I put wot right after start, it runs really good for lets say one minute, then only the top cyl runs, the lower 2 are like flooded. The engine runs if I stay in wot. But 1000rpm, no power. Under this bad condition we have a spark on all 3. The first thing I did was cleaning the carbs, they were in a really bad condition, lots of green dirt. The old owner told me, the engine wasnt in use for 3 years. The carbs were extremely dirty. So what I did now: exchanged the old fuel, cleaned carbs, change the hose that connects the checkvalve (what is that good for? it goes somewhere from the 1st to the 3rd cyl) because it had hole in it and gas or oil was spraying out. Checked spark and plugs. spark on all 3 even if the motor runs bad.
What can i do now? I dont any longer think that dirt causes the problem.
Should I check the reed valves next?
Please help, guys, its incredible hot here this weekend

Take care,
Andy

 

[Toddboat]

Re: Mercury 40hp 3cyl no power

You are describing the classic symptoms of clogged low speed and idle carb jets. The flooding is also due to the carbs.
Take the carbs apart, remove all plastic and rubber parts and soak them in Techron for 2 days.
Then clean out all jets and passages with spray carb cleaner. Then reassemble them and blow into the fuel inlet. When right side up, air should go through. When upside down, no air should blow through. If it does, the needle isn't seating in the seat and your motor will flood. Work on the needle and seat until it seals. You may need to buy a new needle/seat, which can be bought separately or as part of a carb repair kit. Replace any worn gaskets.
Then put the reassembled carbs back on the motor and link and sync them.
The only other thing to check is the fuel pump. You can diagnose this easily by priming the bulb when the motor starts to bog down. If it helps, then your fuel pump could be going. You can replace the membrane in the pump, or just replace the whole fuel pump assembly. A faulty fuel pump will not cause the motor to flood, though, so I think your problem is still in the carbs, even though you think you cleaned them thoroughly already.
Clean the spark plugs after the motor floods. Oil residue could be on them.

 

[doc_cody_blue]

Re: Mercury 40hp 3cyl no power

Hm, yes, possible. But I cleaned all jets with breakcleaner and air and they look good and air flows as supposed. I will check if the needle closes as supposed. To be honest, I didn?t do that yet.

I made a test run today. If cold, engine runs ok. after 3 minutes the 2nd cyl dies, 5 seconds later, the 1st cyl dies. Engine still runs on 3rd cyl. This is repoduceable everytime. Just let it cool down like 30 seconds, start again, run for a minute. The again, 1 cyl dies, then the other one.

Since it is like that every time (tried at least 10 times ) it may be an electrical issue also?

You guys may have a look at this youtube video I took, since my english is too bad to describe this problem in detail.
Mercury 40hp - YouTube

 

[doc_cody_blue]

Re: Mercury 40hp 3cyl no power

ahh and btw the engine does not flood if i just continue pumping the primer ball. for me this indicates that the needle must been closed, doesnt it?

it is a 1999 modell, serial op047549

 

[doc_cody_blue]

Re: Mercury 40hp 3cyl no power

hey people,
I want to order the gaskets and needle valves for the 2 carbs that dont work. can broken reed valves also lead to the same symptoms? in that case i would order them also and change them since that seems relatively easy

 

[doc_cody_blue]

Re: Mercury 40hp 3cyl no power

hey again
I am really stuck now.

This is what I have done until now:
Rebuilt the carbs with the Mercury kits. The needles are closing fine. Did check that like todd recommended. Float level on all 3 carbs is equal and adjusted according to the service manual.

I changed the sparkplugs. I cross-changed the coils.
I also checked ignition spark on all 3 while engine was running bad. Cant tell about the timing though, except for the 1st cyl. There is no mark for the others.

I ran the engine without the oil mixing stuff to see if there is too much oil coming in. just another idea without result.

Symptoms are still the same. Starting with a cold engine at WOT, its running fine, I would say it delivers the 40hp. After a minute, cyl 1 dies, then cyl 2 dies. During the whole run, gas spraying on all carbs look equal, as far as I can tell. Even if the 2 cyl die. Then, after turning of the engine and let cool it down for a minute, it runs again with full power for about 30sec. This happens over and over again.

I dont have any idea what to check next. Since i am on vacation I would really like to have the boat running

Would it help to make timing marks for the other 2 cyl to see if the fire wrong time?

Please, if one of you guys has another idea, I will try everything.

Kind regards,
Andy

 

[steviethev]

Re: Mercury 40hp 3cyl no power

Could be something to do with the ignition system - sometimes if a trigger / stator / switch box is bad when they heat up they can cause problems that they won't when they're cold.

Test the ignition system using the troubleshooting guide from CDI

Technical Support | CDI Electronics

Also, I'm pretty sure that on that motor there isn't a way to adjust the timing. If the 1 cylinder shows TDC at the timing mark, then the rest are OK too. You can adjust spark advance, but that's still for all three, not independently.

You stated you checked ignition spark - how? If you have an adjustable tester, make sure you have thick, fat, bright blue spark jumping at least 7/16 of an inch. Inline testers can be had at any auto parts stores for around $5.

I recently had a problem on my motor where an inline tester would show spark, but on an adjustable, it wouldn't jump 7/16 of an inch, and if it did, it was a really thin line, not thick like it should be.

 

[steviethev]

Re: Mercury 40hp 3cyl no power

Just watched the video - sounds like it's losing spark. I would think if it were a carb problem, it would start to bog down, not just sound like it's completely cut off.

If it were a timing problem, it wouldn't run that well.

How does it run at half throttle? Will it run longer on all three cylinders at half?

Test the ignition system. Make sure all the grounds are OK.

 

[doc_cody_blue]

Re: Mercury 40hp 3cyl no power

I am reading the cdi troubleshooting guide right now. Interesting, that the rev limiter has 3 seperate circuits to switch of each cyl. So a faulty rev limiter could lead to the same symtoms. To be honest, I didnt use an inline spark tester but I ordered one today - adjustable . I used the timing gun to check.

I agree with you, it feels like ignition because its kicking in really hard.

At half throttle it acts the same. Runs for like 60secs, then the 2 cyl die.

I have to get a DVA adapter now.

Will constantly update, have to wait for the spark tester though.

Thank you very much.

Andy

 

[doc_cody_blue]

Re: Mercury 40hp 3cyl no power (CDM / Stator internals

Re: Mercury 40hp 3cyl no power (CDM / Stator internals

Hey people,

this is just a quick update.

Regarding to the CDI Troubleshooting-manual it may happen, that if one CDM is broken, the return path for the current for the other 2 CDM may be interrupted. This may happen, if the diode in the CDM (thay one on the working cyl) is broken.

I had no access to the engine but really wanted to do something, so I bought a new CDM. Last weekend changed the CDM -> without success Super-Andy

I then swapped the 2 stator wires (green-white and white-green) and the other 2 cyls came on, while the first (that one that worked before) now doesnt run. According to the CDI Trouble-shooting guide that means, that the stator is broken.

I now ordered a new stator, that will arrive this weekend. We will see if that fixes the problem.

Could anyone with knowledge please give me a hint, how changing the wires helps out? In my opinion (and thats what the service manual says) the wires are the 2 ends of the stator coil. That means, that the magnet passes by the coil, it pushes a current through the coil and I then have voltage between the both wires. First positive, then negative. Simply: AC. This voltage charges the CDMs. The positive drives the 1st CDM, the negative the 2nd and 3rd CDM. So, if this coil is broken, how can it be, that changing the wires then charges the other CMDs? In my opinion, broken means, that there will be no current at all?

I trust the manual, but generally I would like to understand these things.

Kind regards,
Andy

 

[doc_cody_blue]

Re: Mercury 40hp 3cyl no power (CDM / Stator internals

Re: Mercury 40hp 3cyl no power (CDM / Stator internals

Finally

New stator kit arrived yesterday and the engine runs fine now.

For the one who cares: The 2 CDMs could run with a broken stator coil, because the old stator has a seperate ground wire. The new red stator kit hasn't. So the trick to swap the both wires may probably not work on new stator kits.

Thank you all for your help. I have to fix the powertrim now and check why strange noise coming from the gearbox but thats a whole different story.

Take care,

Andy