1985 Honda B100 Races when Choke Pushed IN:

[OldVintageOutboardMan]

My B100 (B100S-1700XXX) will absolutely race with rpm's when I start closing the choke lever after starting. I've performed the following maintenance tasks:
New impeller
All new lower water seals
New spark plugs
Disassembled and cleaned carburetor
Functioned checked throttle, choke plates & linkage
Fresh 10W30
Fresh 90W gear oil
New reinforced fuel lines and clamps
Engine starts easy, runs really well as long as the choke knob is out. As the choke is depressed the rpm's increase as if the choke was a throttle.
Strangest thing. Hmm...
I'm old, retired and collect and use old outboards, this one is the newest one. The others are running 1960's-80's models. Where I live in Northern Colorado no one will even attempt to service these fine old outboards.
Your thoughts and suggestions are greatly appreciated. Thank you

 

[Scott Danforth]

welcome aboard.

go back to the carb

 

[OldVintageOutboardMan]

[h=2][/h]

Eureka! Engine getting too much air...why? If there is no gasket between the carburetor and the intake manifold you could encounter a "Run away choke". Pushing in the choke knob opens the choke, yes it acted like a throttle. The closed choke was compensating for the air coming in at carburetor/intake juncture. Sometimes you can over complicate a situation when the issue is right in front of your nose! I'm ordering the gasket but since I have a good supply of gasket material I may fabricate one today.​

 

[OldVintageOutboardMan]

Lets postpone the Eureka for now. So much for euphoria. I installed my fabricated a gasket, started up the old girl and my disappointment returned. I've still got a combination choke lever/throttle. However I was able to run it for a while in foreword gear with the choke pushed in. Some encouragement there. I double checked the spark plug gap, both .026mm. I really felt with the addition of the carburetor/intake manifold gasket it would take care of the issue. The plugs aren't pleased with the choked condition, basically black and sooty but dry. I'm going to figure this out.

 

[OldVintageOutboardMan]

The problem was that the gasket under the inlet manifold was compromised. With the engine running I sprayed carburetor cleaner around the inlet manifold and the motor immediately sputtered and wanted to stall. I honestly believe the motor will run like a Swiss watch when the two gaskets are replaced. Yes, there are two gaskets, one on each side of the manifold plate. The carburetor was my first suspicion though it needed a good cleaning anyway, the racing issue with the choke off is caused by unregulated air entering the cylinders. Happy boating!