Honda BF50 bogs down, expert mechanic perplexed. What say you masters of mechanics?

[Walleyehunter4]

Greetings,

I have a Honda BF50 that I purchased mid last season from a dealership. It is missing it’s serial number plate, but the dealership thought it was a 2000 year model. When it was fired up at the dealership, it ran nicely. Compression test was perfect. However, once I got it on the water, it was perpetually disappointing. Hard starting (sometimes VERY hard to start), sometimes runs rough, other times runs nicely. But, it has always bogged down when accelerating rapidly.

So, I took it to a highly respected mechanic shop. Amazing reviews, great reputation. Local guides choose this guy, etc. I told the mechanic I was hoping this would be a motor I’d keep for a long time, so that I wasn’t concerned about the cost to get it in tip-top shape. The mechanic has been great. Kept me up to date on progress. Replaced some gaskets, got the carbs spotless, valves adjusted, carbs synchronized, and more. It now runs like a Honda should run (starts immediately, runs silky smooth) except for one thing—it still bogs down under rapid acceleration. He has some tool that allows him to run it under load in the tank.

He still has the motor, and hasn’t cried uncle, but he’s close. He just can’t even come up with a hypothesis about what’s causing the bogging down. He’s had it in the shop off to the side while working on other outboards, and every once in a while an idea pops into his head, but the idea never comes to fruition.

I asked him to not give up yet, and that while he’s noodling on it, I’d post to a few forums to see if any Michael Jordan of Honda Outboards mechanics had any ideas. I’m not sufficiently mechanically skilled to try to re-state all he’s tried. But, assuming he’s a very competent mechanic (which I’m confident that he is), here is my question: Do any of you Jordans out there have any advice? Anything he should consider that is decidedly non-obvious, even to an expert mechanic who has spent hours troubleshooting? Anything specific to that vintage Honda?

Thanks ahead of time for any ideas!

 

[MattFL]

Does it bog momentarily then come up to full power, or does it just never make power when you open the throttle?

 

[ahicks]

The hard starting is often a sign that it's lean - especially when cold. They can be a bugger to keep running til warmed. A bog when accelerated is the same - a sign it's lean. This leaves me wondering about a few things. Like where are the idle mixture screws set, exactly (the "factory" suggested settings often leave the motor lean)?

Have all 3 of the tiny O-rings that come with the carb kits been replaced on all 3 carbs? If one of these is cracked or hardened, they can easily cause a lean condition.

If this engine is still equipped with the "tamper proof" caps on the idle mixture screws, that's a good sign one of these tiny o-rings have NOT been replaced on each carb where the caps are still installed.....

Has the motor been checked for vacuum leaks by spraying something flammable in the area where the intake manifold bolts to the block with the engine running, where the carbs bolt to the manifold, and also the condition of the vacuum lines. Is there a possibility one of those is cracked or improperly plumbed?

Have the carbs been synchronized so each is pulling the same load/amount of air?

 

[MattFL]

If the carbs still have the original EPA locked fuel screws, you definitely need to get those things out of there and replace with truly adjustable fuel screws. That will make a big improvement in overall running and only takes a few minutes to do. If it only bogs momentarily when opening the throttle, but eventually picks up and runs correctly then the fuel screws will likely help with that. If it bogs indefinitely and never makes power then you've got a different issue.

 

[Walleyehunter4]

Thanks everyone! I gave the mechanic these links. We'll see how it goes. Really appreciate your help!