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honda bf-225 low rpm at full throttle

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This is my first post and I welcome any help available. I built a splashwell with a 6 inch bracket on the transom of a 24Ft. harbor security boat. The boat has an agressive vee with hard chines and one lifting strake per side. The transom angle is estimated at 18 degrees. I mounted a 30 inch counter rotating engine with a 15 by 17 three blade prop. First sea trial only showed 3000 rpm at wot. I then ran a seperate fuel system to eliminate fuel issues. Same result. Both eng. filters/water seperators are new and the engine tested good on the eng analysier prior to a 500nm shipment here. I then put a 15by15 prop on and rpm increased to 3400 rpm. My tach idles at 700rpm and at neutral I can achieve highrpm (4500rpm plus) The vessel is estimated at 4800lbs. It feels as though the engine is "up against a wall" as it just cant penetrate past 3400 rpm. I am beyon perplexed.....any helpfull ideas/thoughts?
thanks jim
 
My boat is similar to yours in terms of weight and size, so that engine should push your boat at approximately 40 mph at WOT (6000 RPM) with the 15 X 15 prop, so you do have a problem. Attaining WOT at around 6000 rpm is very important for the health of these engines. Idle speed should be 650 RPM +/-50, so you are okay on that front.

Is this a replacement motor? If so, what did you have mounted before and how did it perform?

Simple things first. Try to eliminate items external to the engine before digging into that as the problem.

Are you sure your engine is mounted properly? If mounted too low, that could be your problem, especially with the 30 inch shaft. As a starting point, with the boat level and the cavitation plate level (trimmed approximately half way) the center line of your prop hub should be approximately even with the lowest point on your transom. If you have a motor extension off the back of your transom, then it should be above the lowest point of the transom by one inch for every foot of extension off the transom. These are all approximates and can be fine tuned once everything else is operating properly.

Given your aggressive transom angle, are you sure you are able to trim up the engine properly? When you are on plane, the cavitation plate should be just skimming the top of the water coming off the bottom of the transom.

You said "engine tested good on the eng analysier prior to a 500nm shipment here." Was that with the Honda Diagnostic System (HDS)?

Any alarms going off - I assume not, since you did not mention.

Do you know how to pull the fault codes off the MIL? If not, order the SCS service connector (part number 070PZ-ZY30100 - under $20.00) and use that to plug into the 4 prong red service check connector and short it across the proper terminals to pull any fault codes off the MIL.

Finally, do yourself a big favor and spend the $115 for the Helm shop manual for this engine.

http://www.helminc.com/helm/search_service_owner.asp?session=48A505189F43457A8F10AC7E6420EDCE&Style=helm&class%5F2=MAR
 
Everything he said...plus make sure that the motor is actually getting full throttle.

Page 3-19 of the manual shows the steps to take to check and adjust for full throttle. Many of the 200/225 seem to have an issue with this. It should always be checked when the motor is installed.

Mike
 
Thank you both for the great insight. I was able to borrow a Honda HDS diagnostic and connect it to the engine at all power settings. The idle check showed all systems ok: yet at full throttle I was only able to get 3300 rpm with a TP sensor reading of 51 degrees. In addition the ect sensor1 stayed at 162 degrees and the IAC valve command was at 79%,,,All other readings were in limits. The TP sensor in the book says full throttle should be 80 degrees. Any thoughts from any one why I can only get 51? In addition the cavitation plate is approx. 1 inch up from the bottom of the lowest point of the vessel: yet it appears as though it could be raised further up based on the spray from the engine. Any help greatly appreciated. thanks again Jim
 
Cavitation Plate - What is the distance from the bottom of the transom to the back of the prop hub when the cavitation plate is level? That will tell you the rise you should have. For each foot of offset, raise the center of the prop hub 1 inch. Also, make sure your exhaust tubes are at least 5.9 inches above the standing water line.

ECT sensor at 162 degrees is on the high end of normal. When you get the throttle part straightened out, you may want to peer inside the thermostats.

Don't know enough to comment on the IAC.

TP sensor at 51 degrees???? Hmmmm- check to see if your throttle cable isn't binding or totally out of adjustment. Disconnect the throttle cable at the engine and work it by hand. If it is still 51 degrees, inspect the throttle cables as they go from the throttle are up over the top of the engine to the throttle cam. It is not unusual for those cables to get messed up over that run. Then re-check the throttle linkage adjustment.

If that doesn't solve the problem, we'll address the throttle cam adjustment, which can be a minor pain.
 
I will repeat...page 3-19 of the Honda Manual shows how to adjust throttle linkages on the engine to assure full throttle and full TP sensor reading.

Mike
 
Hondadude has not been active on this forum for a while. And I cannot answer your question since I'm not that familiar with the later model 225's.
 
I have a similar issue on my BF9.9. Won't go to full RPM when in gear. When idling, I can rev engine all the way up. Try something easy. Change your spark plugs. That solved my problem.
 
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