Honda B100 misfire under load

[flexnuts02]

Picked up the typical looking B100 for $80 with very low hours, it did not run.

Pulled carb and took it down entirely, including the main bowl pickup tube and found some residues.

Verified all needle passages in the throat of the carb are clean when spraying carb cleaner through different ports. Float needle works properly, clean fuel, bowls fills up and the motor fires right up and idles fine.

Took it to the water and had trouble getting it to keep running. At first I was playing with the choke and a richer choke would keep it running. But could not get the RPM much off of an idle without lean pops and stuutering/hickupping/misfiring.

At first playing with the choke under WOT would give it small bursts of quality combustion. And then by the time I finally got the 7' boat on plane the choke was fully off, but it took awhile until I was able to get it to combust properly just enough to get it on plane.

When on plane it will stay on plane and run what seems O.K. but likely not perfect. It was scary on that little boat but I did plane for a solid 5 minutes until I hit chop and dropped plane.

Tried a few more times and could not get the bow out of the sky, misfiring and backfiring.

As a fulltime mechanic I think it seems spark related as if your flipping a switch on and off, the symptoms seem too "sharp" to be carb related. More electronic feeling. Feels like spark misfire to me.

**I checked the plug wires just now with a gap jumper and one wire does not spark, the other jumps nice and long. Need some info on the ignition/wiring system so I can diagnose this!**

**Also, under WOT I tried to slowly cover the intake screen with one finger, then two fingers and IF anything it would start to choke it out, as if it were NOT starving for fuel.

 

[Sea Rider]

Re: Honda B100 misfire under load

Sometimes you need to dip and soak carb in real cleaning products for some hours, not just blasting carb spray alone. Are fuel pump diaphragms in opt condition ? check if dried, cracked, ballooned, replace if so. Check spark plug cond or replace and test with new ones, check plug cap cond, replace if craked, rusted inside.

Happy Boating

 

[flexnuts02]

Re: Honda B100 misfire under load

Thanks buddy, I have heard of this but in my doings I have NEVER soaked a small engine carb (2-4 stroke) and the results were just brilliant.

I find it interesting that the 3 needle hole jets in the throat spray nice and thick streams when using a carb cleaner straw.

I also find it interesting that there seems to be either no spark or week spark on on of the 2 wires.

It is interesting that under load the issue seems to irradically electronically related. In other words it goes from pure bogg on a misfire to a quick spark of full life and then immediately misses again. Would fuel be able to do that??

I wonder if its week spark on one cylinder and it can idle fine, then as you add mixture it simply cannot combust properly. Like I said as it got hotter it did not need choke at all, and suphocating the intake would choke it out as if the week spark was better burning as the cylinder got hot enough.


**Just for the heck of it what do I soak the carb in? And must I remove ALL components before soaking it??**

 

[Sea Rider]

Re: Honda B100 misfire under load

Some issues,

If boating constantly all year round probably carb will remain in inmaculate clean condition, if boating not that often and sitting engine for long extended time periods, when fuel evaporates could leave unwanted dregs narrowing thin fuel passages and engine not performing at it's opt when giving gas. Check car shops for carb cleaning products. All carb plastic, rubber components must be removed before soaking, soak at least 3-4 hours. Blast dip left overs with carb generic spray, dry well.

Will need a plug gap tester to check if ignition coils are doing their homework, if sparks jumps shorter than specified, must replace that ignition coil if happen to have one for each pulg, worst scenario the costly whole unit. You can also have a bad, cracked, corroded plug caps too, expect poor low spark and engine performance too.

Happy Boating

 

[flexnuts02]

Re: Honda B100 misfire under load

UPDATE:

The Autolite plugs were removed for the proper NGK number plugs. I Did not know that to test a dual terminal coil you must also keep a spark plug in the second wire when testing the other.

I have blue spark jumping a nice gap, on both wires for sure. I tested a wire at a time, with the other one connected to a spark plug installed in the motor.

Seems to start and idle just fine, revving it in a bucket I cannot tell if it is 100% or not. I will take it out on water to see if it is cured.

To verify, this motor has NO mechanical timing advance of any kind linked to throttle. It has two small coils under the flywheel and one main dual terminal coil pack bolted to the exterior of the block, one of the two is for charging the other is for the main coil pack.

I will be bringing a timing light with me to the water this time to see if I can tell if it is a spark misfire if the issue still exists.