Yamaha 225 surging proplem

[9989]

I have a yamaha 1989 225 excel with micro computer ing. system. lately i've noticed a problem when i pull back the throttle to reduce crusing speed from 4000 rpm to 3000 rpm. the rpm will continue to slowley drop to about 2300 rpm on its own and stay there. When i just touch the throttle to bring rpm back up the engine and rpm surge noticibly back to 3000 rpm. The engine is new to me this season so i have no service history. I have replaced the fuel water seperator- engine mounted fuel filter-both fuel pumps-and spark plugs. Aside from this problem engine starts, idles, and runs smooth. Any help would be appreciated

 

[rodbolt]

Re: Yamaha 225 surging proplem

how big a boat is this? you may be overshooting the 3K mark. as more hull drags it has to have more power but there were also some TPS issues from the old style TPS.<br /> and see if a dealer can recreate it with a test wheel to isolate engine and hull.

 

[9989]

Re: Yamaha 225 surging proplem

Rodbolt-thanks for the reply. Boat is a 1984 Wellcraft 22'. This is a new problem that just came up. Did not exist for the first four months of the season. Last year same boat ran perfect with a 200 yamaha. I,ve also noticed on a few occasions engine dropping maybe 300 rpms and than picking back up while cruising without me touching the throttle.

 

[9989]

Re: Yamaha 225 surging proplem

would tps cause this type of surging and is it expensive or difficult to replace.

 

[rodbolt]

Re: Yamaha 225 surging proplem

it will and can but its easy to find. keep a timing light on it. if the TPS is bad the timing will flutter. you can also monitor the voltage with a DVM and the test harness. also monitor the reference voltage. it should stay steady at about 5 V. but it still sounds like fuel.