Running out of ideas?

[Ginder75]

1990 Evinrude 50 hp.

If you read my half dozen other posts, you will remember that this motor has been a labor of love. Too date, I have replaced the waterpump and reassembled the lower unit. I replaced the plugs, switched from the VRO to a fuel pump and premix. I rebuilt the tilt and trim and the carbs, and checked the linkage and sync.

Every time I swap a part the motor runs a little better, but it is still not perfect. Yesterday, I took the boat out after swaping the fuel pump and rebuilding the carbs.

She idled fine, I pulled off the trailer and pulled up to the dock waiting on my wife. As we cleared the no wake zone I accelerated to full throttle and trimed the motor up. FINALLY (first time since I assembled the package), the boat was on plane and running like a dream. I thought I had finally worked all the bugs out of my "Bargain" motor.

Well, the feeling lasted for 10 minutes as we soared up the river. Then I instantly lost 1300 rpms. I pulled the throttle back and started looking for the problem (tank was vented, fuel bulb was firm, both plug wires were connected). I started the engine and began to pick up speed, when I hit 4000 rpm the motor seemed to drop a cylinder (3000 rpm) and the it reved back up.

It goes back and forth between 3000 and 4200 rpm. We tried squeezinng the fuel bulb while running and no help. I pulled the plugs and the top was normal, while the bottom was wet and oily.

Am I loosing a coil, carbs not in sync, ... Where should I start looking. We took the boat out again today, and the same problem was evident from the start. No matter what we did, the boat was going to osicallate back and forth between 3000 and 4200 rpms.

I feel so close to having this motor finished, but I am missing something.

Ginder75

 

[tashasdaddy]

Re: Running out of ideas?

the bottom plug was wet. completely swap the coils, take care to note where the wires go. should take about 15 minutes to do. then run the boat again. if the top plugs wet, you know you have a bad coil. the oem manual has the step by step instruction for the link n sinc. it must be done in the order in the manual.

 

[Ginder75]

Re: Running out of ideas?

The motor has a dual coil on it, the two coils are moulded into one casing. Can I swap the two trigger wires and the two spark plug wires on this style coil?

I thought about that, but when I say they were one unit. I hesitated. I have a new one on the way to my local parts dealer (don't have to pay until I pick it up).

Is there anyway to do these tests at home? I thought I would ask, but since my problems don't become obvious until 3000 rpms with a load on the motor. I figure I will be on the water tomorrow.

 

[reeldutch]

Re: Running out of ideas?

Run moter on the water until problem is duplicated and hook up a inductive timing light to the suspectet cylinder secondairy wire.
run motor and check for spark with timing light.
compair this to the other cylinder.
if its not the same you have intermitted spark.

see what you got.
i dont think the motor wil rev up till 3000 rpm on only 1 cylinder but i could be wrong.
i think you might have intermitted spark.
check all the grounds and wires.

if you have no spark on 1 cylinder i would check the output of the stator and the output of the trigger.
(check service manual for spec, i believe stator output is around 230v and the trigger around 1.5 v. at 3000 rpm it could be more)
if that is all good you have a bad pack.
good luck

 

[ezeke]

Re: Running out of ideas?

Are you using a tachometer or estimating the RPM?

 

[Ginder75]

Re: Running out of ideas?

I have a new tach installed, so the numbers are real not guesses.

My plan of attack will consist of four new spark plugs and a new coil. I am going to install new plugs and run the motor on a hose for some time at idle. I am then going to check the condition of the new plugs. If they both appear normal, I am off to the lake. If one (bottom) is fouled and damp, I will install new plugs and swap the leads on the coil to see if the problem follows.

If the problem follows, then I know I have a faulty coil and I can go from there. If the problem does not follow then I have a carb situation and I can clean the carbs a second time.

I have checked compression, it was 130 on both. So that made me feel a little better about the work I have put into the motor so far.

 

[Ginder75]

Re: Running out of ideas?

Well, I ran the motor two more hours on the muffs and I am no closer to a solution.

According to the timing light and the new plugs, I do not have a coil problem.

What if the carbs were WAY out of sync? Is it possible for one cylinder to run too rich and wet foul a spark plug causing the hit or miss condition?

I have followed my Clymer manual four times over, but my linkage and carbs still seem out of whack.

Are there any tips or a link to a better set of instructions?

Second question, the motor has an unknown past. I am not sure how many wrenches have ever laid hands on the motor. If the two mixture screws are out of adjustment, how do you reset them? My manual says to carefully count the number of turns it takes to seat the needle, then when you rebuild the carb. Just seat the needle and back it out the same number of turns. BUT WHAT IT, the original setting to me was incorrect.

I feel like a dog chasing his tail on this one. I am so close to taking it to a mechanic it is not funny. I hate it, but I need to get the motor finished.

Everyone has been so helpful in the past, any thoughts where I need to direct my attention now?

 

[iwombat]

Re: Running out of ideas?

You really owe it to yourself to get the factory manual specific to your year. It's head and shoulders above the clymer for fine-tuning procedures.

And yes, it is possible for a carb that out of whack to cause wet fouling.

 

[mikesjohnson]

Re: Running out of ideas?

just an half-educated comment, but if your running at WOT, or close, carb synch shouldent matter all that much. there should be enough velocity in the combustion chamber, ports etc. to make up for a out of synch condition (to an extent). it sounds to me like one of your coil windings is going bad, building heat/resistance and dropping out. you wont find this porblem at idle on the muffs, it will need to be under a load to genrate the necessary heat for the problem to show itself. i can run my evinrude 70 at idle for over an hour, and can still put my hand on the "pee stream" comming out of the motor. not enough load to generate heat

i like you idea of switching the trigger wires and plug wires to see if it moves, just do it on a day when there isnt much wave action. falling of the back into the drink sucks!

 

[ezeke]

Re: Running out of ideas?

You might want to revisit your carburetor floats.