Bf50

[dahornietoad]

I have a 50hp honda. I have gone thru the fuel system twice. New fuel, carbs are clean. Spark on all 3 cyl.
Problem is when you put it in gear and fast full throttle it will die. Put it in gear and ease into the throttle to full throttle position the boat will run. Any ideas?

 

[jgmo]

Hi
My guess is that you have a leak in the dashpot system or possibly the check valve is plugged or installed backwards.

Simply stated, the dashpot diaphragm gives a burst of air pressure to the accel/decel check valve when the throttle is opened quickly. That air is delivered through the check valve and pressurizes the delivery tubes for each carb. That in turn briefly pressurizes the main fuel wells to provide a quick burst of fuel to aid acceleration and prevent stalling.

Hopefully you replaced the accel/decel vacuum lines in their respective positions when you reassembled.

Make sure that you have the correct check valve installed. Yours should be black on the Inlet side and gray on the outlet side. The arrow that indicates air flow should be pointing toward the carbs.

With the engine not running, take the line from the outlet side of the check valve and quickly open the throttle. Note that a quick burst of air comes out of the check valve.

Remove the Inlet line from the check valve and quickly open the throttle again and compare the burst of air from the diaphragm to the first test. The air pressure should be very close for both tests. If the air coming from the diaphragm is much greater with the check valve removed, then the check valve is likely bad. It has a piston and spring inside that can stick. You could try hosing it out with carb spray to see if it's plugged with dirt.

If the diaphragm and check valve test ok, then it's likely that there's a leak downstream of the check valve that not allowing a full pressurizing of the carb bowls.

Good luck.

 

[dahornietoad]

Hi
My guess is that you have a leak in the dashpot system or possibly the check valve is plugged or installed backwards.

Simply stated, the dashpot diaphragm gives a burst of air pressure to the accel/decel check valve when the throttle is opened quickly. That air is delivered through the check valve and pressurizes the delivery tubes for each carb. That in turn briefly pressurizes the main fuel wells to provide a quick burst of fuel to aid acceleration and prevent stalling.

Hopefully you replaced the accel/decel vacuum lines in their respective positions when you reassembled.

Make sure that you have the correct check valve installed. Yours should be black on the Inlet side and gray on the outlet side. The arrow that indicates air flow should be pointing toward the carbs.

With the engine not running, take the line from the outlet side of the check valve and quickly open the throttle. Note that a quick burst of air comes out of the check valve.

Remove the Inlet line from the check valve and quickly open the throttle again and compare the burst of air from the diaphragm to the first test. The air pressure should be very close for both tests. If the air coming from the diaphragm is much greater with the check valve removed, then the check valve is likely bad. It has a piston and spring inside that can stick. You could try hosing it out with carb spray to see if it's plugged with dirt.

If the diaphragm and check valve test ok, then it's likely that there's a leak downstream of the check valve that not allowing a full pressurizing of the carb bowls.

Good luck.

Thank you
I was wondering if that might be it. I had already gone thru everything else

 

[jgmo]

Well, I said "my GUESS is" for very good reason.

I was giving you the benefit of the doubt as to if you did a good job getting all of the transition ports clear during cleaning.

However, if you can't find any leakage in the dashpot plumbing, then the transition circuits will be suspect for this symptom.

The transition ports in the BG model KEIHIN carbs are especially critical in the operation of the "acceleration pump" action and ALL the transition ports (3 per carb) must be clean to prevent stumbling and stalling during hard accel.

I always recommend multiple "backflushes" of delivery ports when cleaning Keihin carburetors and that is doubly true for BG model transition ports because of their role in anti-stall.

So, again, if you can't find an issue in the dashpot air system, you may be looking at going back and revisiting your treatment of the transition ports.

Please let us know what you find.

Good luck.