honda bf100 problem

[grayspi]

hello new to the forum treat me gentle<br />my honda 100 has a curious problem if i fit new plugs it runs full power for about 3 hours but then the top cylinder dies when plug is removed it is clean,wet and smells of fuel.<br />the engine still runs but only low power.<br />can the engine flood on one cylinder?and if so what do i do any help greatly appreciated thanks

 

[45_red]

Re: honda bf100 problem

CDI or points?I'm guessing weak spark.

 

[hondon]

Re: honda bf100 problem

Do a valve adjustment ,then a compression test , and get back to us in the morning.Any overheats we need to know about?How is that fuel quality?These engines seldom foul the top cylinder so let's find out what's up.

 

[grayspi]

Re: honda bf100 problem

thanks for the replys i will be going at the weekend to try your solutions. fuel is new in new tank no over heating and engine starts easily

 

[cp]

Re: honda bf100 problem

From reading posts on this forum, Hondon is a Honda tech and knows what he's talking about, but maybe he mis-read your question? You don't say that the top cylinder is fouled as Hondon recommends troubleshooting for, but rather that the plug "is clean, wet and smells of fuel." You also say that the the engine runs well with new plugs for a while, and it would seem that valve and compression problems should not be related to the newness of the plugs. Before you tear into the engine, may I suggest you rule out the simpler possibility of a spark problem similar to what 45_red guesses? You must be getting good spark to the lower cylinder, and since the common ignition coil on a BF100 fires both plugs simultaneously, the question then becomes why might you not get good spark to the top cylinder? If the lengths of the spark plug wires from the coil to the plugs will allow, swap the wires (both ends), i.e. mark which went where, then take both wires off and use the top one on the lower and vice versa. Run the engine as before, and if the problem moves to the lower cylinder, you've discovered that the wire that was on top has high resistance; replace it. If there's not a simple solution, then have at it and go deeper into the engine. Good luck.

 

[grayspi]

Re: honda bf100 problem

tried swapping leads over no difference timing correct, new points and correct gap

 

[grayspi]

Re: honda bf100 problem

ok next episode. brand new plugs start engine whoosh were away full power great slowing down to moor up hit reverse bit sticky engine revs high in neutral b4 selecting reverse gear back in to forward top cylinder gone.seem to remember this was the senario last time as well.can one of the plugs go because of the high revs? any more ideas?

 

[45_red]

Re: honda bf100 problem

What is the condition and gap of the top plug after this happens?Are you using the right plugs?

 

[grayspi]

Re: honda bf100 problem

plug looks ok but gap has increased by 0.30 mm checked this twice on two plugs from top cylinder plugs are NGK DR5HS and are correct according to manual

 

[45_red]

Re: honda bf100 problem

Have you done the valve adjustment and compression Check(ce;Hondon)? Sounds like a mechanical malfunction.

 

[grayspi]

Re: honda bf100 problem

valve clearances within specified perameters.have had a compression test done and its good

 

[cp]

Re: honda bf100 problem

I think we've reached the point where you need to provide more specific info for the good Honda techs on this forum to help you. Doing that using separate sentences would be easier to decipher too .<br /><br />How are you determining that the top cylinder "dies" and the bottom does not? This is key since both cylinders share the same ignition source and the same fuel source.<br /><br />When your engine loses power, is replacing the plugs the only way to restore full power, i.e. the old plugs are totally unuseable?<br /><br />Or does full power return using the old plugs if you wait a while, i.e. let the engine cool?<br /><br />Since the problem seems intermittent, but related to some duration of running the engine, has your troubleshooting of the spark, etc. been done right after loss of power (in the failed mode) or some time later (when the engine may have cooled or otherwise reverted to the good mode)? Maybe you've not found the problem because you've been looking at the engine in the good mode when the problem was not evident?<br /><br />If ignition is good, fuel is good, and valves/compression are good the engine should run just fine, which you say it does do for a while. Something's changing after you run a while, and you just have to find it.<br /><br />Long distance troubleshooting is always difficult, but the more specifics you provide, the more likely someone like Hondon can help you.

 

[grayspi]

Re: honda bf100 problem

will try to be as clear and specific as possible <br /><br />when the engine is running rough and top plug cap is removed engine runs exactly the same.<br />when engine is running rough and the bottom plug cap is removed engine immediately dies. <br /><br />replacing the top plug is the only way to restore power.<br /><br />it does not matter how long i leave the engine or if it is cool.<br /><br />new top plug must be used each time as the old one becomes unusable<br /><br />problem is not occuring intermittently.as i said on previos post i have realised problem occurs when the engine is put in to reverse and over revs <br /><br />have checked for spark on top cylinder when engine is bad NO SPARK <br /><br />today i have changed the plugs NGK DR5HS for ones of a hotter grade NGK DR4HS and so far they seem to be working well the engine is running fine. this is the first time the engine has lasted an entire journey without losing power.<br /><br />however if anyone has any other ideas i would be glad to hear them .

 

[cp]

Re: honda bf100 problem

I was hoping the clear specifics you've provided would stimulate the memory of someone on this forum who might have had and resolved a similar experience. Since none has responded, my own thought in view of the symptoms and troubleshooting results you've described, is that the root cause of your difficulty may be that your carburetor is running rich, but I am at a loss as to how that might affect only your top cylinder. Perhaps there is more than one contributing factor. At any rate, you've found one solution in the hotter plugs. Happy boating!