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BF 225 with fuel mixture issues

R

Reel Steel

Member
I have twin BF 225's and am in the process of adjusting the valves and performing other maintenance. The starboard engine has been burning about 12 percent more fuel than the port engine throughout the rpm range. The starboard bank of spark plugs look very rich while the port bank on the same engine seems to be burning fine. Since the fuel mixture should be the same for both sides I don't know what could be causing this.
 
Thanks for that. The different color plugs are on the SAME engine. I did find that one of the thermostats was messed up so I am wondering if there was an operating temperature difference between the left bank of cylinders from the right bank. Otherwise the fuel and air mixture should be the same for all cylinders. I did find some tight exhaust valves as well.
 
What you described is a typical problem with a thermostat that is stuck open. On the 225 the t-stat should start to open at 140 F and be fully open at 160 F. Full open should be at least 3 mm.
 
CHawk man, The rubber seal on the tstat was torn. That was the side with the rich looking plugs. I'm waiting for some gaskets then I can put the boat back in the water and see what happens.
 
That was likely your problem with the rich mixture. Depending on the age of the t-stats, you may want to change them out, especially if you are running in saltwater. I change mine annually.

I have also installed heat sensors on each bank of cylinders on the block. That lets me know the operating temps of the engine and signals if I may have a t-stat or water pump problem. Normal operating temps for the 225 are 160 F to 170 F. If one of the heat gauges does not hit that temp, then I know I likely have a t-stat stuck open. If one gauge kicks up much above 170 F, then I know I have eather a t-stat not opening far enough or a blockage in the water jacket. If both start kicking up over 170 F, I know I likely have a water pump problem. If you want details on installing the heat sensors, then send me a private message.
 
chawk man, thanks for the offer on the heat sensor. I think that I just need to be more aware of the thermostats since that seemed to be my problem. The exhaust valves were also very tight, running from .015 to 0 clearance.
 
Don't have my manual with me, so cannot comment on proper clearance on exhaust valves. Perhaps HondaDude or one of the other techs can jump in with that info. Alternatively, call a dealer that has an onsite maintenance shop. They can tell you in a minute.
 
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