Re: Honda BF40 on Pontoon Boat
You could try running a double dose of Sea Foam or Stabil Marine but if there is a major blockage, it probably will not help.
Runability problems generally are either a compression, spark/timing, or fuel problem.
In one of my previous posts, I suggested a compression test. So we still do not know if compression is where it should be. Can you do a compression test?
Not having a compression test is like a doctor trying to figure out why you are having chest pains without at least taking your blood pressure.
Before we go to check spark...might as well finish up testing each carb for lack of fuel. It probably will not tell us anythiing, but we might as well do it to complete the fuel test. As you could probably see when you disconnected the choke linkage, you can now operate the choke on each carbuator individually. Again, just a quick flip or two of each choke lever and see if there is pickup. If no pickup, do they all react the same?
In case the yields us nothing...
Go back to pulling the spark plugs wires one at a time. This time, keep the connector close to the spark plug and listen for the ticking of the spark jumping onto the spark plug. At idle, the ticking should be fairly slow. Listen first for ticking at each spark plug. Pay close attention to the speed of the ticking compared to the other cylinders. They should all be the same. If one (possibly the bottom cylinder) is faster (like another 1/3 faster) than the others, then we definitely have a spark issue. If there is no ticking at any cylinder, that is not good. If they are all the same, the spark is probably ok, although this is not an absolute since we are not using a spark checker.
If one cylinder had no ticking, swap that spark plug with another one and see if the problem follows the spark plug.
One repeat of a question in an above post...did you change the spark plugs before or after you started having the problem? If it was before or you can not remember, change them again. NGK DR7EA
One other major item can cause it to run like this....timing. If the timing belt has jumped just one notch, it can run like it is a carburator issue.
Have you ever purchased a repair manual yet? The manual explains how to check the timing. It is quite difficult to explain how to find the marks without pictures.