50 hp high speed misfire

[kalebsheridan]

So I'm trying to get my 1988 50hp running right. I recently had to replace the stator and trigger and the motor is still new to me. I'm currently attempting to do a tune up according to the clymer manuel. It starts up fine and seems to idle okay. At high rpms it seems to misfire pretty bad though. Misfires even worse when I back off the throttle, then it evens out. Am I just doing something wrong? Still out of tune? Any help would be awesome.

 

[jerryjerry05]

Do the starting fluid test.
Start motor, spray SF around the intake side of the motor, that includes under the coils and pack, around the port covers(2) a the base of the carb.
The port covers have a gasket that can fail with a misfire, cough and stutter allowing the motor to run crappy.

 

[cdavy000]

It sounds like your distributor is having mechanical advance or timing problems, if you can open up the distributor and look at the springs underneath the plate that is under the distributor cap. Look for stretched or rusty springs, also clean out gunk inside if you find any. You also need to check your engine timing.

 

[kalebsheridan]

Okay Jerry, I did spray around the motor but did not spray under the ignition coils. I will try that. My carb was a bit loose which caused a reaction with the spray but I fixed that and this condition still persists. Also, I did notice the spark plugs were wet, not 2-stroke wet but flooded wet. This is even after performing the carburetor adjustment. My manual references that as a symptom of a clogged or faulty recirculation system. Could that be the case? Cdavy, I will look into that. I suppose timing could be a problem. I did just replace the stator and trigger. Is that what you are referring to? I was considering timing but that is a bit out of my capabilities at the moment, and if nothing else solved this, I know a mechanic would could do that for $100 or less.

 

[kalebsheridan]

Also, I had taken my boat out two weeks ago, and excluding needing some obvious throttle adjustments, the motor seemed to be running quite well. Smooth idle, decent throttle response, and only a slight miss at 3/4 throttle. At that time, I had only attempted to tune the carb by ear since I didn't have a tach to use. This is after replacing the stator and trigger. However, after each subsequent start, it seemed to have a harder time starting. More backfiring and rougher idle. This weekend I had planned to use a tach (not a good one) to properly tune the motor but the longer I went on tuning and going into a decarb, it started to run worse and worse.

 

[cdavy000]

The distributor I’m referring to is the device that all spark plug wires are attached to, you need to open that up to look at the springs/weights underneath (This is assuming you don’t have an HEI distributor) I would find the factory idle speed and fuel mixture settings for your engine online and reset them back to what they should be. Messing with them to compensate for the backfiring problem is just putting a bandage on the issue instead of solving it, it won’t fully fix it. I would definitely suggest checking timing and going from there, because the next steps would be getting into the nitty-gritty such as potential vacuum leaks or worn points.

 

[kalebsheridan]

Hey Cdavy I'm not sure I have a distributor like you are describing, unless you are referring to the ignition coils. Correct me if I am wrong though. I just don't see that in the diagrams for my motor. I will check timing for sure, I just need to have a mechanic do that as I don't have the tools or experience for that. I get I'm working backwards by your standard, but I don't want to get a hold of the mechanic just so he can tell me something else is the cause, especially if it's something I can fix you know? I did develop a bad water leak at the gasket between the power head and motor leg so that needs to be replaced first as well.

 

[kalebsheridan]

Oh and as far as the factory setting, I did set the carb to factory setting and tune from there. This worked pretty well early on but as the idle began to worsen despite this, I was certain the carberator was probably not the issue. I did service the carb this year as well, except for the float valve which looked pretty good at the time, but I will order one anyway. As I addressed earlier as well, I did inspect for vacuum leaks using starting fluid but found no leaks, except for under the ignition coils as jerryjerry recommended. Oh and when I tested the compression I got 120 psi on both cylinders. Idk how accurate my tester is since it's a cheap one but I think the fact that the values were the same is what is important.

 

[Nordin]

If you have change trigger you have to set the timing.
You adjust by the rod that move the trigger connected to the timing tower.
Use a timing light to adjust, set it 28dgr BTDC at WOT at cranking speed (starter speed).

 

[topgun3690]

I'm not sure I have a distributor

Get a factory manual......will answer that question and a lot more....
Btw....your engine does not have a distributor, points, or a vacuum system....many folks try to apply automotive knowledge to these old 2-stroke motors.....they are nothing like your car/truck.

 

[Nordin]

As topgun3690 says no distributor with vacuum advancing at these OBs.
The older 3 and 4 cylinder engines had distributor but the time advancing was made by turning the plate in the distributer where the points is mounted to.
Your engine advance the timing by turning the trigger ring to make the spark from the coils to fire earlier.

 

[cdavy000]

Get a factory manual......will answer that question and a lot more....
Btw....your engine does not have a distributor, points, or a vacuum system....many folks try to apply automotive knowledge to these old 2-stroke motors.....they are nothing like your car/truck.

You are correct no distributor on this engine my mistake.

 

[cdavy000]

As topgun3690 says no distributor with vacuum advancing at these OBs.
The older 3 and 4 cylinder engines had distributor but the time advancing was made by turning the plate in the distributer where the points is mounted to.
Your engine advance the timing by turning the trigger ring to make the spark from the coils to fire earlier.

If you have change trigger you have to set the timing.
You adjust by the rod that move the trigger connected to the timing tower.
Use a timing light to adjust, set it 28dgr BTDC at WOT at cranking speed (starter speed).

I second Nordin on setting the timing after changing trigger.

 

[kalebsheridan]

Wow lots of replies! Topgun, would the clymer manual suffice? Nordin, yup that's what I kinda thought. When I replaced the trigger, the new one came with the little arm. I just adjusted the new arm so that it was identical in length to the old one. Would a very minute difference result in this miss? Plus the motor ran pretty dang well right after I replaced the trigger. This current problem developed after two trips out and some idling in a barrel. If the timing was that off, wouldn't it have been bad the whole time? I will still absolutely check timing though as I want to be sure that it is set up properly after my trigger replacement. Also I should mention that this thing smokes like crazy when running at high rpms. I did put a double dose of seafoam in the gas while on its first runs to help clean the motor after the trigger replacement so I'm sure that accounts for some, but this is like I did a seafoam shock treatment and it only occurs when I run the motor at high rpms. When I back off the smoke stops. Just massive clouds of smoke.

 

[cdavy000]

Wow lots of replies! Topgun, would the clymer manual suffice? Nordin, yup that's what I kinda thought. When I replaced the trigger, the new one came with the little arm. I just adjusted the new arm so that it was identical in length to the old one. Would a very minute difference result in this miss? Plus the motor ran pretty dang well right after I replaced the trigger. This current problem developed after two trips out and some idling in a barrel. If the timing was that off, wouldn't it have been bad the whole time? I will still absolutely check timing though as I want to be sure that it is set up properly after my trigger replacement. Also I should mention that this thing smokes like crazy when running at high rpms. I did put a double dose of seafoam in the gas while on its first runs to help clean the motor after the trigger replacement so I'm sure that accounts for some, but this is like I did a seafoam shock treatment and it only occurs when I run the motor at high rpms. When I back off the smoke stops. Just massive clouds of smoke.

What color is the smoke? (White, Black, Slightly Blueish)

 

[kalebsheridan]

Ahh maybe a whitish blue. Like when you do a seafoam shock treatment.

 

[cdavy000]

Ahh maybe a whitish blue. Like when you do a seafoam shock treatment.

Blue or white smoke are “uh oh” smoke so hopefully that’s just from the sea foam. Was it happening before you used sea foam?

 

[kalebsheridan]

Blue smoke is uh oh? This is a two stroke so shouldnt blue smoke be expected? Before the seafoam there was very little smoke. The fuel I was using did have some seafoam that I added just as a light cleaner and fuel stabilizer. The motor ran as if all it needed was some very slight adjustments. Since then, it sat for two weeks, then this last weekend I was running it in a barrel to do these adjustments as per the clymer manual. It didn't smoke right away, I warmed up the motor to so I could start tuning. Eventually, on high revs it started smoking as if I was doing a shock treatment. Only at high rpms though. The smoke would stop at idle speeds. At first I thought it was due to the sea foam basically having been hot soaked for two weeks and then burning off, but it wouldn't clear up as one would expect.

 

[cdavy000]

Blue/white smoke is normal out of a 2 stroke but if it’s excessive like the entire engine is engulfed in it then no.

 

[kalebsheridan]

Oh okay yeah that's what I thought. I figured the color was normal but the volume was excessive.