Honda BF20D5LHTA

I bought a new accl. plunger kit, new supply hose. and drained fuel system so I would be sure and have fresh clean fuel. The engine will start and idle fine. I can reave engine up about 1/3 throttle and all works well. What is not right is when I open throttle all the way up the engine will buck and back fire and not smooth out. Any ideals? Thanks

You should not rev the motor up in neutral and not under load. The bucking is normal. Once you have a prop on it, in the water and under load, it should not buck unless the rpm is too high.

Mike

Why did you replace the accelerator pump plunger? Was it stuck? As Mike warns, don't "free rev" the engine up against the limiter....not healthy.

The backfiring might be because of a "lean" condition or because you are revving it and the limiter is taking away spark and then re-introducing it and firing "leftover fumes" in the "waste spark" cylinder while the valves are partially open.

If you are not doing this then we have misinterpreted what you wrote.

I replaced the accl. pump because a couple of years back I tore it apart because the accl. pump was stuck. I just cleaned it up at that time. I said if I ever toke it apart again I would replace it. The carburetor had ssome water in it this fall when I took boat out and seen opportunity to tear carb. down and replace accl. pump. Thanks to both of you on the advice of not rev. engine up not under a load. Didn't know that, but I think it was doing that when I wen across the lake to take out of water for winter. Thanks again to all.

If you continue to have problems with hesitation and backfiring under load, it has been my experience that if the accelerator pump piston is stuck, then it is very likely that the fuel delivery nozzle for that circuit is, at least, partially clogged. If it is, the carburetor won't work properly and you will experience these symptoms until the nozzle has been cleared. The nozzle is a small, brass tube with a very small orifice that juts out into the caburetor throat at the air inlet side of the carb.

jgmo said:

If you continue to have problems with hesitation and backfiring under load, it has been my experience that if the accelerator pump piston is stuck, then it is very likely that the fuel delivery nozzle for that circuit is, at least, partially clogged. If it is, the carburetor won't work properly and you will experience these symptoms until the nozzle has been cleared. The nozzle is a small, brass tube with a very small orifice that juts out into the caburetor throat at the air inlet side of the carb.

Click to expand...

OK I'm going to have to put it back in the water to be able to determine if engine is running right now? Or can I put on ear muffs and put in gear, will that put a load on it to test for backfire? You talking about this brass tube being clogged, I sprayed carb. cleaner in every crives I could find and used high pressure air to blow through all possible holes. Thanks

It us never a good practice to run the outboard on muffs and put it in gear. Horrible accidents can happen. Besides, that won't load the prop at all. The use of a "test tank" will work for that purpose although most home made tanks, usually a trashcan, will not retain water as the prop powers up. You only get a few seconds of mid to high throttle before all the water pushes out on to your legs and feet. Butc that may work for your purposes in this case.

If you did not identify and specifically power flush the accelerator pump nozzle passage, I suspect that you probably didn't get it cleaned out thoroughly. It usually takes flushing from the main body inlet to the nozzle and then from the nozzle orifice back through the inlet several tries to free it up properly. This is a sort of back and forth backflush of the passage to loosen and clear the scale out. This can only be done with the float chamber off and the throttle plate propped all the way open.

I always have my "students" perform this flush until they can get a 6 to 10 foot stream to shoot from the pump nozzle out the back of the carb throat when they use a can of brake kleen and the plastic sraw inserted into the pump passage inlet of the main body. A 5 foot stream WILL NOT work and indicates that the passageway is still dirty.

If this is confusing to you, I understand. Most guys that don't own the carb manual don't get it the first time around. I will be happy to answer any questions you may have about this.

The bottom line is not to get so frustrated that you give up. We'll keep at it till it purrs like a kitty again.

Put in water and ran before I read this last message. All seems OK though. Running in lake it runs good at full throttle.Will sure remember I can't reve up engine while out of water. Thanks to all.

That's GOOD news! Glad I was wrong about the carb being dirty. Looks like you did a good job of blowing it out after all.

One other thing to keep in mind is that ALL gasoline....no matter how clean it looks or where you buy it....has SOME small amount of WATER in it. AND, that FACT gets a bit worse the longer it SITS and CONDENSATION is allowed to take place.

Frequent draining of the carburetor float chamber, when the outboard is going to sit for more than a few days, is CRUCIAL for keeping the scale deposits from forming and then "sluffing off" and clogging internal passages. Do that and burn FRESH gas and your outboard's reliability will improve greatly.

Happy boating.