Topic: Yet another carb jetting post

[AirCanuck]

Gents,

Here are the before and afters of the carbs.

The total rebuild is complete and the carbs are back on the bike, synced with the 1/8” drill method for now. Floats we just set to factory 14.5mm... gents helping me had limited time so we didn’t have time to clear tube it.

My question is this: how long would you say these carbs went without being cleaned? Given that I just replaced all o rings, floats, needles, jets (except main which were fairly new) etc ie a complete rebuild when would I next have to take these apart?

Link to album before and after:

https://imgur.com/gallery/Yp8iq

[brewsky]

FWIW, here is a spreadsheet of my 78 k model carb settings with stock engine.

The values in the table are measured A/F readings from an onboard O2 sensor at various throttle settings under on road conditions.

There is a typo in the chart....the carbs are actually PD46C

[Deltarider]

Curious to know where exactly you have that sensor.

[brewsky]

In between clutch and points covers in outside exhaust.

[AirCanuck]

FWIW, here is a spreadsheet of my 78 k model carb settings with stock engine.

The values in the table are measured A/F readings from an onboard O2 sensor at various throttle settings under on road conditions.

There is a typo in the chart....the carbs are actually PD46C

I'm afraid you are well beyond my level of expertise there, friend.  I don't even know how to interpret that data. 

Everything is all rebuilt now anyhow, plus with non-stock filters and pipes, it's moot.  But I do appreciate you sharing.

What do you think of my question above wrt how long those carbs probably sat and when they'll need love again?

[DaveBarbier]

I would drop the bowls at least every year anyway to clean out inevitable debris. Have a look up in there and if you like what you see, ride on.

Proper storage will keep them looking like what you posted above. Ethanol free gas is best but if you have to use ethanol laced fuel like the most of us in the US then just ride often to keep replenishing the fuel. And store with a fuel stabilizer and you’ll be good to go.

[brewsky]

FWIW, here is a spreadsheet of my 78 k model carb settings with stock engine.

The values in the table are measured A/F readings from an onboard O2 sensor at various throttle settings under on road conditions.

There is a typo in the chart....the carbs are actually PD46C

I'm afraid you are well beyond my level of expertise there, friend.  I don't even know how to interpret that data. 

Everything is all rebuilt now anyhow, plus with non-stock filters and pipes, it's moot.  But I do appreciate you sharing.

What do you think of my question above wrt how long those carbs probably sat and when they'll need love again?

Hard to say how long they sat before you opened them up, but Dave's advice is good.
I would add that it is easy to drain the bowls for long storage on these carbs i.e. over the winter by just opening the bowl screw.

As for the chart, the table just shows actual air/fuel mixture the engine is using at given throttle positions (idle, 1/4 turn of the hand grip etc. up to WOT ((wide open throttle))). The carbs meter the air/fuel mix from different jets depending on how high the slide is opened. With 14.7/1 being the "ideal" for complete combustion, a number smaller is richer and larger is leaner.

I'm guessing planes, especially piston engine types, have A/F (mixture) adjustments for altitude? Motorcycle carbs, unfortunately, do not.

[AirCanuck]

FWIW, here is a spreadsheet of my 78 k model carb settings with stock engine.

The values in the table are measured A/F readings from an onboard O2 sensor at various throttle settings under on road conditions.


There is a typo in the chart....the carbs are actually PD46C

I'm afraid you are well beyond my level of expertise there, friend.  I don't even know how to interpret that data. 

Everything is all rebuilt now anyhow, plus with non-stock filters and pipes, it's moot.  But I do appreciate you sharing.

What do you think of my question above wrt how long those carbs probably sat and when they'll need love again?

Hard to say how long they sat before you opened them up, but Dave's advice is good.
I would add that it is easy to drain the bowls for long storage on these carbs i.e. over the winter by just opening the bowl screw.

As for the chart, the table just shows actual air/fuel mixture the engine is using at given throttle positions (idle, 1/4 turn of the hand grip etc. up to WOT ((wide open throttle))). The carbs meter the air/fuel mix from different jets depending on how high the slide is opened. With 14.7/1 being the "ideal" for complete combustion, a number smaller is richer and larger is leaner.

I'm guessing planes, especially piston engine types, have A/F (mixture) adjustments for altitude? Motorcycle carbs, unfortunately, do not.

Most pistons are fuel injected now although there is a mixture knob to lean it out properly.

I fly turboprops however so it’s a whole different ballgame with a turbine engine

[Joao_f3rr3ira]

Hi guys!

Thanks for the tips on the initial post AirCanuck! I'm rebuilding a set of Keihin PD41B's, my bike will run on a 4 into 2 exhaust, oversize pistons, ported head and velocity stacks. Following the tips on the first post they will give me a main jet size of 110. My question now is, does anyone think I should only change my main jet from 105 to 110 and leave the slow jet and needle untouched, or should I also mess with them to?

Thanks!