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HONDA BF20D power loss

M

Marcuseric

New member
I have a 2004 Honda BF20D4 that has been a wonderful engine did routine maintenance, but after it had an episode of overheating I have just finished replacing impeller, thermostat, spark plugs, oil/fuel filters and all fluids. I replaced the carburetor and have adjusted the mix & idle so it runs great...until I put the cowling back over the engine and after about 5-10 secs the power drops, it start to idle rough to the point it stalls. I have good water coming out the pee hole and engine exhaust out the back and it runs great without the cowling, but slows noticeable\y when I put the cowling back on? The air intake through the cowling is clear. I can't find an air filter on the engine itself and would appear to be an "air intake"problem, but I don't see a leak, so I'm befuddled...
 
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Hi,
This symptom favors an exhaust leak starving the engine for oxygen when the hood is on. It was a fairly common occurrence on the old, original Honda twins although I've never seen this before on a later model twin like a 15 or 20D.

The intake and exhaust "manifolds" (for lack of a better term) are integral to the cylinder head and the exhaust exits downward through the port side of the casting. The head gasket has a portion that juts out from the main section to seal the gasses. See item 3 in the link


Just a guess but see if you can detect a leak from that area.

The gasses continue down to the "exhaust chamber" (see items 1 and 2 in link below) where they are mixed with exiting cooling water and out the extension case.

I suppose there could be a problem there but I'm not sure how the fumes would work back up into the upper engine compartment. But, like I said, I've never seen this before on a 20D and anything might be a possibility.

Sorry I don't have a sure fire solution for you.
 
Thanks to all above. It turned out to be a small leak on the thermostat cover! I presume water and fumes leaking into the engine compartment with cover on
 
Wow! Never seen that one before but glad you figured it out!

Thanks for posting your findings. It might just help someone else in the future...
....like me!
 
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