havoc_squad
Senior Chief Petty Officer
- Joined
- Mar 5, 2011
- Messages
- 739
Model is VJ90TLASB.
I have a mysterious misfire situation that I can't seem to narrow down the issue to. At this current time, I'm leaning towards electrical or something mechanical that isn't cylinder compression (Maybe crankcase sealing rings or some 2 stroke specific issue I'm not thinking of).
Once it gets warmed up to operating temperature, a random misfire/stumble happens every 3 to 10 seconds. The motor does not appear to struggle under load at low idle, but the misfires do drop the RPMs down briefly. It does not behave like a lean sneeze, more like a dead cylinder at that given misfire moment.
At around 1500 to 1800 RPM under load in water, the same issue would roughly happen, it would go for a while then the motor would appear to randomly misfire somewhat every 5 to about 15 seconds.
Of all situations I have checked with IR temp gun, the engine is getting proper cooling and the replaced thermostats are doing their jobs. The engine hovering around 135 to 153 degrees F on the top of the heads and no overheat alarm. I tested those sensors before I put the motor back together to make sure they function at overheat temp.
At this moment, my compression tester has a bad or worn out o-ring on the quick-disconnect and I'm waiting on the replacement part on order.
Not wanting to mess around, I wanted to know what the results were on a leak down test.
Today, I bought a mid grade level quality leak down tester and did a leak down test on all cylinders at 80 PSI, all cylinders had no more than 5 PSI of leakage at close to top dead center.
Spark gap tester at 1/2 inch shows full strong spark on all cylinders when testing spark.
Put a timing gun light on all spark plug wires at idle , could not notice any timing gap in spark.
At idle (900 rpms) while this stumbling issue was going on, if I hit the primer solenoid/choke in, the engine slightly stumbles and recovers. Since the motor didn't smooth out, that to me lead me to suspect it wasn't fuel being the issue.
The gas oil mix is at 32:1 for break in period.
Here is the background of steps in case something might shed some clues. Bear with me.
First, did my best to keep the motor at or below 1500 rpms for the first hour of running.
Initial setup about a month ago of setting max timing and idle timing using Joe Reeves method after getting rebuilt powerhead installed with correct re-circulation hose routing.
After that, I couldn't get it started and I knee-jerked pre-maturely and pulled the carbs and thourghly check them. Found nothing wrong and put them back with new applicable parts per OEM service manual and current parts diagram. Draining the fuel when the motor was tore down worked just fine.
Figured out mistake, got the engine running well enough, if there was a misfire I didn't see or remember it. This is where I noticed issue with Recifier/Regulator due to tach. (Missing grounding washers cooked it.). Was running at 4 BTDC at idle supposedly smoothly.
Next, I re-adjusted the carb throttle arm in the attempt to get it better situated in being centered on the arrow. I didn't disconnect the throttle cable to test first. It created a mismatch where the carb throttle didn't pick up when it was supposed to.
I started it up and didn't notice anything wrong until the primer solenoid fuel burned off, then it begin varying from 1100 to 1800 RPM for about 25 to 40 seconds. I was trying to figure out the situation, then I pulled back on the throttle (I think) and it died.
I checked the service manual and it identified it as possibly incorrect linkage. Then I looked at the throttle linkage and identified the issue and fixed it, then checked my work.
I took a compression test reading at that time afterwards out of caution and it seemed all was fine 115 115 on starboard, 110 110 on the port).
Replaced rectifier/regulator after bench test identified it as failed and ensured grounding washers properly installed to fix my installation screw up.
Re-installed stator and flywheel, then checked max timing via Joe Reeves method. Still the same timing. Started it up and verified charging system and tach worked as expected.
After this, it was a lake test where under load I noticed that the motor kept misfiring randomly after it was fully warmed up.
I have a mysterious misfire situation that I can't seem to narrow down the issue to. At this current time, I'm leaning towards electrical or something mechanical that isn't cylinder compression (Maybe crankcase sealing rings or some 2 stroke specific issue I'm not thinking of).
Once it gets warmed up to operating temperature, a random misfire/stumble happens every 3 to 10 seconds. The motor does not appear to struggle under load at low idle, but the misfires do drop the RPMs down briefly. It does not behave like a lean sneeze, more like a dead cylinder at that given misfire moment.
At around 1500 to 1800 RPM under load in water, the same issue would roughly happen, it would go for a while then the motor would appear to randomly misfire somewhat every 5 to about 15 seconds.
Of all situations I have checked with IR temp gun, the engine is getting proper cooling and the replaced thermostats are doing their jobs. The engine hovering around 135 to 153 degrees F on the top of the heads and no overheat alarm. I tested those sensors before I put the motor back together to make sure they function at overheat temp.
At this moment, my compression tester has a bad or worn out o-ring on the quick-disconnect and I'm waiting on the replacement part on order.
Not wanting to mess around, I wanted to know what the results were on a leak down test.
Today, I bought a mid grade level quality leak down tester and did a leak down test on all cylinders at 80 PSI, all cylinders had no more than 5 PSI of leakage at close to top dead center.
Spark gap tester at 1/2 inch shows full strong spark on all cylinders when testing spark.
Put a timing gun light on all spark plug wires at idle , could not notice any timing gap in spark.
At idle (900 rpms) while this stumbling issue was going on, if I hit the primer solenoid/choke in, the engine slightly stumbles and recovers. Since the motor didn't smooth out, that to me lead me to suspect it wasn't fuel being the issue.
The gas oil mix is at 32:1 for break in period.
Here is the background of steps in case something might shed some clues. Bear with me.
First, did my best to keep the motor at or below 1500 rpms for the first hour of running.
Initial setup about a month ago of setting max timing and idle timing using Joe Reeves method after getting rebuilt powerhead installed with correct re-circulation hose routing.
After that, I couldn't get it started and I knee-jerked pre-maturely and pulled the carbs and thourghly check them. Found nothing wrong and put them back with new applicable parts per OEM service manual and current parts diagram. Draining the fuel when the motor was tore down worked just fine.
Figured out mistake, got the engine running well enough, if there was a misfire I didn't see or remember it. This is where I noticed issue with Recifier/Regulator due to tach. (Missing grounding washers cooked it.). Was running at 4 BTDC at idle supposedly smoothly.
Next, I re-adjusted the carb throttle arm in the attempt to get it better situated in being centered on the arrow. I didn't disconnect the throttle cable to test first. It created a mismatch where the carb throttle didn't pick up when it was supposed to.
I started it up and didn't notice anything wrong until the primer solenoid fuel burned off, then it begin varying from 1100 to 1800 RPM for about 25 to 40 seconds. I was trying to figure out the situation, then I pulled back on the throttle (I think) and it died.
I checked the service manual and it identified it as possibly incorrect linkage. Then I looked at the throttle linkage and identified the issue and fixed it, then checked my work.
I took a compression test reading at that time afterwards out of caution and it seemed all was fine 115 115 on starboard, 110 110 on the port).
Replaced rectifier/regulator after bench test identified it as failed and ensured grounding washers properly installed to fix my installation screw up.
Re-installed stator and flywheel, then checked max timing via Joe Reeves method. Still the same timing. Started it up and verified charging system and tach worked as expected.
After this, it was a lake test where under load I noticed that the motor kept misfiring randomly after it was fully warmed up.
