Hi everyone.
First boat for me.
I have a 1998 tidecraft wildfire with a 2stroke 1998 C150TLRW yamaha, it was sold to me with a 14x28p SS yamaha propeller. The engine would not get anywhere near the recommended rpm range of 4500 to 5500. Wot run tests resulted in less than 4000 rpms. Looked at yamaha's website and could not find anything up to 300hp that reccomended a 28 pitch prop. So first stab at a replacement prop was a generic prop, alum 3 blade, at a 14x23pitch, and wow, its made so much difference, its like a new boat. With the new prop, 5000 rpms at full throttle. Middle of the reccomended rpm range for this engine. This generic prop is uncupped and probably not of the best quality of the props that are available.
But I noticed this and want some input if possible. With new prop had to hold back on throttle for first 10 minutes or rpms would go over 5500 max range, easily. After the warming up, we could not get rpms over 5000 regardless of trim or throttle.
My question is: is this normal for a 2s engine? Or does the lowered rpm after warmup indicate the carbs may be to rich at WOT? Timing issue? Boat really launches onto plane very quickly, no spitting back through carbs at all, Engine seems to run ok, starts within 3 five second attempts when its cold, when warm starts on first cranking. The idle after warmup is a little flakey at times, all the slow speed adjustment screws on all six carbs are exactly 1 turn out, *I find this odd because all the bikes I have had and carbs that I rebuilt as a GM technician, there was always a slight difference in adjustment from barrel to barrel.* Adjusting them is on the to do list. Plugs are new and correct for engine. The Carb plugs covering main jets have been pulled and there was zero debris or buildup inside bowl. Compression testing during initial bringing the boat back to life (stored 2 yrs by PO) showed 60 psi on all cyl. I have run engine for approx 2 hours during a recent boat ride with good yamalube oil and Ringfree plus, the compression raised to approx. 80 psi on all but the two lower cyls which were 75psi. Used a bore scope on engine twice, first time on initial compression test showed heavy carbon buildup on piston tops, no hideous scaring noticed on cylinder walls. but after the 2 hour run, the piston tops are almost completely clean, only small flakes remain, all piston numbers and up symbols can now be seen. Small loose flakes of carbon could be wiped from shell of spark plug easily. Have not performed the shock treatment with ringfree plus yet, but think I will do it soon. Also I have not found a spec on compression for this engine yet, buying a service manual is also on the list. What do you all think? Not asking for a fix, I just want some opinions on 2s engines and how they operate at wot. Relating to engine temperature based on your experience with boat motors.
Thanks to steelespike for recommending I post this question here, was hung up on prop issue,
oops posted in prop section.
and to craze1cars for his saying this is not normal.
Thanks for any opinions on this question.
Bill
First boat for me.
I have a 1998 tidecraft wildfire with a 2stroke 1998 C150TLRW yamaha, it was sold to me with a 14x28p SS yamaha propeller. The engine would not get anywhere near the recommended rpm range of 4500 to 5500. Wot run tests resulted in less than 4000 rpms. Looked at yamaha's website and could not find anything up to 300hp that reccomended a 28 pitch prop. So first stab at a replacement prop was a generic prop, alum 3 blade, at a 14x23pitch, and wow, its made so much difference, its like a new boat. With the new prop, 5000 rpms at full throttle. Middle of the reccomended rpm range for this engine. This generic prop is uncupped and probably not of the best quality of the props that are available.
But I noticed this and want some input if possible. With new prop had to hold back on throttle for first 10 minutes or rpms would go over 5500 max range, easily. After the warming up, we could not get rpms over 5000 regardless of trim or throttle.
My question is: is this normal for a 2s engine? Or does the lowered rpm after warmup indicate the carbs may be to rich at WOT? Timing issue? Boat really launches onto plane very quickly, no spitting back through carbs at all, Engine seems to run ok, starts within 3 five second attempts when its cold, when warm starts on first cranking. The idle after warmup is a little flakey at times, all the slow speed adjustment screws on all six carbs are exactly 1 turn out, *I find this odd because all the bikes I have had and carbs that I rebuilt as a GM technician, there was always a slight difference in adjustment from barrel to barrel.* Adjusting them is on the to do list. Plugs are new and correct for engine. The Carb plugs covering main jets have been pulled and there was zero debris or buildup inside bowl. Compression testing during initial bringing the boat back to life (stored 2 yrs by PO) showed 60 psi on all cyl. I have run engine for approx 2 hours during a recent boat ride with good yamalube oil and Ringfree plus, the compression raised to approx. 80 psi on all but the two lower cyls which were 75psi. Used a bore scope on engine twice, first time on initial compression test showed heavy carbon buildup on piston tops, no hideous scaring noticed on cylinder walls. but after the 2 hour run, the piston tops are almost completely clean, only small flakes remain, all piston numbers and up symbols can now be seen. Small loose flakes of carbon could be wiped from shell of spark plug easily. Have not performed the shock treatment with ringfree plus yet, but think I will do it soon. Also I have not found a spec on compression for this engine yet, buying a service manual is also on the list. What do you all think? Not asking for a fix, I just want some opinions on 2s engines and how they operate at wot. Relating to engine temperature based on your experience with boat motors.
Thanks to steelespike for recommending I post this question here, was hung up on prop issue,
oops posted in prop section.and to craze1cars for his saying this is not normal.
Thanks for any opinions on this question.
Bill