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10hp (B100S) Full Throttle Miss

H

Hockeyguyjohn

Member
Hi,

My original 10hp (B100S) is missing under load at full throttle.

Pretty green on experience, what should I check or try?

I had this motor serviced in the spring by a mechanic before I bought my other motors ( still checking these out, waiting for parts). The mechanic put another carb on this motor, he found that the guy I bought the motor off had taken some of the motor apart and did not properly re-assemble it. It idles okay.

It has fresh hi test fuel in the tank.

Thank you

John
 
CDI or breaker point ignition?
Sometimes this can be as simple as a bad spark plug. That's probably where I would start.
 
Hi jgmo,

The motor is a CDI model. The motor started doing this last weekend and it cleared up but started again.

I will check the valve clearance and look at the valve springs. Do I need a special tool to adjust the valve clearance? Can I reuse the gasket on the valve cover?

I replaced the spark plugs in June but I will buy some more. I was going to try the alternative plug listed in the manual, the DR4HS plug. Will this be okay?

I will try another coil from my parts motor as well.

It is difficult as my tools and my other motors are at my house and this motor and boat is at my in-laws cottage (about 3 hours away), no place to work on it at the cottage either. My lack of experience is also a factor!

Thank you for your help!!!

John
 
Sorry mate I presumed you were running Denso plugs as you listed NGK as the alternative. But yep I see what you mean. Your lucky to have a 'parts motor' trying that coil with a new plug will narrow things down a lot.
 
Hockeyguyjohn said:
Hi Deanmck,

That is an NGK spark plug number, the Honda repair manual lists two different plugs.

Standard: DR-5HS
Alternative: DR-4HS (hotter plug I think?)

Thank you

John
Click to expand...

Yes. With NGK the lower the number the hotter the plug.

From the NGK site

Misfires

A misfire occurs when the spark travels the path of least resistance instead of jumping across the gap. Misfires can be caused by the following:

Carbon fouling

Worn or deteriorated ignition system components

Too large of gap size

Spark timing excessively advanced or retarded

Damaged spark plugs (cracked insulator, melted electrodes, etc.)

Mismatched ignition system components (plug resistance/wire resistance, ignition coils/igniter modules, etc.)

Insufficient coil primary and/or secondary voltage – voltage required to jump the spark plug gap higher than coil output
Click to expand...

Neil
 
Last edited:
Update.

I had a few minutes last night to look at the motor. I found the ignition coil was no fastened properly. It had only one screw barely holding the top, the screw and spacer at the bottom were never there (a bought this motor last year from a guy whom was less then honest as it turns out and I was lacking some knowledge and experience).

I checked the Ohms reading as per the manual and I am getting a much higher reading between the spark plug wires. I am getting 28K instead of 8K. On the other test point I am getting 0.7O instead of 0.56.





Before going any further I decided to check the compression, it was not great. I took both plugs out, put the motor into forward so I could open the throttle fully and pulled the cord 3 times on each cylinder test. On the top cylinder I got just over 90PSI and on the lower cylinder I got about 85PSI.

I am going to test my parts motor tonight for compression and see if it is worth swapping the power heads.
 
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