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1998 BF40 twins surging, rough idle and one carb flooding

J

JamesSShelby

New member
I have spent much time reading applicable threads. Thank you all for the time you spend. Boat and motors are always fresh water, bought new 26 years ago. Low hours, live in way north climate, 2 1/2 month season. Both ran great for 24 years. Port engine was worst surging, cleaned and rebuilt all 6 carbs. Checked everything I could think of on fuel system, checked coils and spark.Idles worse and did not solve the surging problem. Trying again to solve the problem this beginning season. Rebuilt carefully all carbs, synced etc, still poor idle, can see #1 carb on starboard engine flooding.
In reading many of the blogs with similar problems I discern that the carbs are terribly finically and almost always the problem. I notice a number of members with 20+ year old motors having carb problems. I only saw one thread asking about “heavy” floats. I do not see in either the Honda service manual or carb manual a weight spec. Any thoughts? I am getting ready to take the intakes off again and look at all 6 carbs again.
 
Hi,

Could you elaborate about "seeing the #1 carb on starboard engine flooding"?

Is fuel exiting the air vents at the top of the main body? Or, are you seeing it leaking out from someplace else?

You are right about these being very finicky to get properly cleaned. They require specific knowledge, procedures and much trial and error to clear once clogged or varnished.

I had rebuilt carbs for years but still had problems with these until I purchased and read the "Honda Marine Carburetion Manual". It has helped me help others here get these Keihin brand carbs working again.

To my knowledge there's no "float weight" specified for these. I have used a small scale to weigh floats and compare them before but that's all I know to try.

If you have a flooding condition it could be a sinking float but that's pretty rare in my experience. It's much more likely that it's not sealing at the needle valve for some reason.
 
jgmo said:
Hi,

Could you elaborate about "seeing the #1 carb on starboard engine flooding"?

Is fuel exiting the air vents at the top of the main body? Or, are you seeing it leaking out from someplace else?

You are right about these being very finicky to get properly cleaned. They require specific knowledge, procedures and much trial and error to clear once clogged or varnished.

I had rebuilt carbs for years but still had problems with these until I purchased and read the "Honda Marine Carburetion Manual". It has helped me help others here get these Keihin brand carbs working again.

To my knowledge there's no "float weight" specified for these. I have used a small scale to weigh floats and compare them before but that's all I know to try.

If you have a flooding condition it could be a sinking float but that's pretty rare in my experience. It's much more likely that it's not sealing at the needle valve for some reason.
Click to expand...
While syncing the carbs and trying to get the engine to idle better starboard # 1 is dripping fuel, seems to be the vent but the “freeze” plug is also wet:
 
Ok.

Well, one of the vent covers does look like an expansion or "freeze plug" so it's definitely flooding. You need to figure out why that's happening before anything else.

Remove and shake the float to see if it might be holding fluid. If so, it's done for.

You can also use a postage type scale to compare it's weight to the other ones. I once asked the lady at the post office to weigh some floats for me and she did.
I lived in a small town at the time.

Look down into the needle valve seat to see if there's anything stuck to it that might not let the valve tip seal. If so VERY CAREFULLY clean the seat.

The needle valve tip should be "pliable" and not hard. They get hard over time and won't seal.
Luckily, the needle valve and float are both still available.....
....but not for much longer I'm thinking.

If the valve seat is damaged or deformed and not allowing the valve to seal, that's bad because I don't know how to fix that. But I've never seen one like that.

I'm betting that the needle valve is no good.

Good luck.
 
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