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Hello
Just wondering if anyone had experience or ideas with this problem. I have a 1998 Yamaha two stroke 40 owned since new. Compression is perfect on all three cylinders at 115. Carbs were just cleaned by a mechanic with the ultra-sonic. The issue is that it runs rough (like a stutter or slight miss) all the way up to WOT, and once you get on WOT for about 6-8 seconds it sorts itself out and runs perfectly. Trouble is it does it every time you throttle down around idle or shut it off and start up again. Also, if you run for a bit at half throttle it gets choppy.
I tried another CDI off another engine and same thing. Also, changed all three ignition coils and same things. Also, tried unhooking the oil level sensor and the two temp senders and no difference. Also, took the fuel pump apart to see if the diaphragms had holes but they looked good, and ran the same after checking.
The engine starts perfectly every morning even after sitting a few days, and starts perfectly all day. Tried some STP carb cleaner and fuel treatment and ATF in the fuel but no difference. Fuel is clean and new.
I can't really tell if it is a fuel/carb problem or electrical at this point, but really seems like a carb problem. I am not sure how to sync the carbs if that were the problem.
Thanks for any and all help.
Graham
Just wondering if anyone had experience or ideas with this problem. I have a 1998 Yamaha two stroke 40 owned since new. Compression is perfect on all three cylinders at 115. Carbs were just cleaned by a mechanic with the ultra-sonic. The issue is that it runs rough (like a stutter or slight miss) all the way up to WOT, and once you get on WOT for about 6-8 seconds it sorts itself out and runs perfectly. Trouble is it does it every time you throttle down around idle or shut it off and start up again. Also, if you run for a bit at half throttle it gets choppy.
I tried another CDI off another engine and same thing. Also, changed all three ignition coils and same things. Also, tried unhooking the oil level sensor and the two temp senders and no difference. Also, took the fuel pump apart to see if the diaphragms had holes but they looked good, and ran the same after checking.
The engine starts perfectly every morning even after sitting a few days, and starts perfectly all day. Tried some STP carb cleaner and fuel treatment and ATF in the fuel but no difference. Fuel is clean and new.
I can't really tell if it is a fuel/carb problem or electrical at this point, but really seems like a carb problem. I am not sure how to sync the carbs if that were the problem.
Thanks for any and all help.
Graham