Another two-stroke carby tuning thread

**motorbyclist** · 10th November 2009, 17:06

1986 Honda H100S with racing pipe, rode her two-up from nelson to auckland via the east cape without problem, then holed piston riding to uni on motorway.

.25mm bore (1cc!), new piston/rings and some racing reeds later she's running frighteningly lean (grey plug).

The air mix screw seems inneffective, so open the carby and the pilot jet is blocked. holed-piston mystery solved. Unblock, check the needle is on the top clip, and now she's running somewhat rich.

Attached photo is after fiddling with the air mix as best I can but changes are hard to judge. It's currently at 2.25 turns out from bottom. Don't know if the jets are standard or not but she was mint if not slightly rich prior to the pilot blocking.

I'm hoping to ride to/from wellington next week, so any advice would be appreciated:

Can I get away with this? I'll be thrashing her so it might lean out a bit, but the plug is wet.

What more can I do to get this right?

Anyone who has the elusive manual would be my hero.

edit: missus reckons it's a "dark chocolate". I'm evidently too colour blind to tell anything other than tan.

**avgas** · 10th November 2009, 17:16

What oil you running - the last thing you want is for it to clog up while running lean.
Sounds like you have got most of it sussed.
Check the float though - as I had a TS185 of same period with a possessed float.
You should totally polish the internals of the carb though - make her suck more air!

**speedpro** · 10th November 2009, 17:36

Originally Posted by avgas

You should totally polish the internals of the carb though - make her suck more air!

Hmmmm . . . . .

**motorbyclist** · 10th November 2009, 17:37

Originally Posted by avgas

What oil you running
You should totally polish the internals of the carb though - make her suck more air!

I've been running her on fully synthetic castrol stuff since nelson - the seller had always been running that too. allegedly being runnier means it pumps that little bit extra, preventing bottom end issues.

I'm very tempted to do some more serious bucket-performance work beyond the current mods, such as a larger carb, but might save it until the eventual seizure and subsequent 16cc boreout i hear these things can handle

- currently she's the booze/bakery run and backup bike and those reeds have her running like a cut cat

**speedpro** · 10th November 2009, 17:47

Mine's out to 52mm bore. I've heard rumours of getting into alloy at 53mm.

**I GS 1** · 10th November 2009, 17:57

Originally Posted by motorbyclist

1986 Honda H100S with racing pipe, rode her two-up from nelson to auckland via the east cape without problem, then holed piston riding to uni on motorway.

.25mm bore (1cc!), new piston/rings and some racing reeds later she's running frighteningly lean (grey plug).

The air mix screw seems inneffective, so open the carby and the pilot jet is blocked. holed-piston mystery solved. Unblock, check the needle is on the top clip, and now she's running somewhat rich.

Attached photo is after fiddling with the air mix as best I can but changes are hard to judge. It's currently at 2.25 turns out from bottom. Don't know if the jets are standard or not but she was mint if not slightly rich prior to the pilot blocking.

I'm hoping to ride to/from wellington next week, so any advice would be appreciated:

Can I get away with this? I'll be thrashing her so it might lean out a bit, but the plug is wet.

What more can I do to get this right?

Anyone who has the elusive manual would be my hero.

edit: missus reckons it's a "dark chocolate". I'm evidently too colour blind to tell anything other than tan.

When you start going the route of fitting of racing, pipes reeds etc. the tuning starts having to be more precise. Jetting that could be mint one day could be too rich or lean on another. Temp, barometric pressure and to a lesser degree rel. humidity all effect it. In karting you may change jetting three of four times during a day's racing. You would be better off running on the rich side as optimal performance isn't all that important on the road.

Be careful with what you read about plug colours, particularly in older books, because leaded fuel burns different colours to unleaded. Some of the pictures may only apply if you are running avgas or 100 octane raceing fuel.

For what it's worth. Can't be of more help as I don't know the particular carby