I have a brand new Parsun 15hp two stroke outboard I purchased here in Venezuela. It was an inexpensive motor especially so because the local government subsidizes products from China.
The engine is a copy of a discontinued Yamaha engine and can use Yamaha parts.
The issue I'm having is the motor wanted to make a coughing sound, like a muffled backfire. It was not backfiring out the carb. The noise sounds like it's down in the motor's leg. I was able to vary the throttle position and find places where it happened less or not at all, as long as I stayed under about one third throttle.
I pulled the cover and tried making the mixture richer and leaner (covering the carb's intake and using a thin flat object to cover the main jet) and that made no difference.
This motor has a mechanical timing advance and I eventually tried varying the advance and found if I retarded the spark the coughing went away. What I find is that the coughing begins right at the point where at full throttle it produces the most power. So I have to adjust the spark advance to the point just below where it coughs to get the best power.
I'm assuming that what's happening is if the spark is too far advanced the ignition is occurring when the exhaust port is still open and it's firing down into the exhaust, which I'm assuming is going to do unpleasant things like flame etch the rings. So I've adjusted it so it doesn't "cough".
The timing adjustment in the mechanical linkage wasn't enough and I had to bend a little metal tab that is the timing advance mechanical stop which the timing advance linkage hits at full advance. That I wasn't able to get the timing right through the normal adjustment makes me wonder what's up.
I'm out in the jungle and have no access to a timing light, compression tester or other gear like that. The engine passes the old thumb-over-the-spark-plug-hole compression test with flying colors. That's my main test down here with outboards. If I can't hold back the compression and it comes out hard that's a passing grade.
Does anyone have any ideas other than "don't buy Chinese made outboards"? I do like the motor and it seems like a good motor. I like that it can use Yamaha parts. I figure over time it will become a Yamaha motor as I replace parts. : - )
Thanks for your comments!
Greg
The engine is a copy of a discontinued Yamaha engine and can use Yamaha parts.
The issue I'm having is the motor wanted to make a coughing sound, like a muffled backfire. It was not backfiring out the carb. The noise sounds like it's down in the motor's leg. I was able to vary the throttle position and find places where it happened less or not at all, as long as I stayed under about one third throttle.
I pulled the cover and tried making the mixture richer and leaner (covering the carb's intake and using a thin flat object to cover the main jet) and that made no difference.
This motor has a mechanical timing advance and I eventually tried varying the advance and found if I retarded the spark the coughing went away. What I find is that the coughing begins right at the point where at full throttle it produces the most power. So I have to adjust the spark advance to the point just below where it coughs to get the best power.
I'm assuming that what's happening is if the spark is too far advanced the ignition is occurring when the exhaust port is still open and it's firing down into the exhaust, which I'm assuming is going to do unpleasant things like flame etch the rings. So I've adjusted it so it doesn't "cough".
The timing adjustment in the mechanical linkage wasn't enough and I had to bend a little metal tab that is the timing advance mechanical stop which the timing advance linkage hits at full advance. That I wasn't able to get the timing right through the normal adjustment makes me wonder what's up.
I'm out in the jungle and have no access to a timing light, compression tester or other gear like that. The engine passes the old thumb-over-the-spark-plug-hole compression test with flying colors. That's my main test down here with outboards. If I can't hold back the compression and it comes out hard that's a passing grade.
Does anyone have any ideas other than "don't buy Chinese made outboards"? I do like the motor and it seems like a good motor. I like that it can use Yamaha parts. I figure over time it will become a Yamaha motor as I replace parts. : - )
Thanks for your comments!
Greg
and you can't sue the little buggers or even send them a nasty e-mail.