Anyone know about motorcycle carbs? Solved mostly

"DarrenMR" (darrenmr) 10/23/2015 at 13:24 • Filed to: None

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This is literally the first time I have ever touched a carb. I have no idea what Im doing.

Its a Mikuni TM40-6 and I basically have 3 questions.

1. Is the choke on when its pushed in or pulled out?
in off, out on

2. Is the plastic knob the idle adjuster?
Yes

3. What is the brass like screw on the outside of the bottom?

Air/fuel screw

http://www.mikuni.com/pdf/hs4 0_manual.pdf

Edit: thanks guys

Now I just need to figure out why it starts to die in 4th and 5th. 1st, 2nd, and 3rd all pull up to speed pretty good. Then 4th bogs and I lose a few MPH.

TheHondaBro > DarrenMR 10/23/2015 at 13:27

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Scooters typically have less carbs, so you can have a scooter, or a motorcycle following a light salad.

DarrenMR > TheHondaBro 10/23/2015 at 13:28

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I dont think that fits your honda, so it doesnt help me.

bob and john > DarrenMR 10/23/2015 at 13:28

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“carbs”
*runs away*

i HATED the carb on my Buell. but it have an auto choke, so thanks buell

to help you: choke is usually on (richer) with the thing pulled out
2: probably idle adjust.
3: could be a Air/Fuel adjustment screw

Shour, Aloof and Obnoxious > TheHondaBro 10/23/2015 at 13:31

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Well, motorcycles that use carbon fiber in their frames and various parts DO have a higher carb count than scooters, but because it's carbon fiber, you subtract them from the overall carb count. Generally, the net carbs on carbon fiber-bodied bikes actually end up lower than the carbs on scooters!

Future next gen S2000 owner > DarrenMR 10/23/2015 at 13:31

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1: Pull to set the choke. Says on the knob.

2: Yes

3: I don’t know which screw you are referring to in the picture. One likes like a fuel line almost and the other looks like it holds the bowl on.

The last time I dealt with a carb I just bought a new one and bolted it on. Good luck!

DarrenMR > Future next gen S2000 owner 10/23/2015 at 13:32

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In the pic the bowl is unscrewed and Im holding it on. The nipple in the center on the bottom is the bowl overflow. Im taking about the screw directly left of the plastic knob.

MontegoMan562 is a Capri RS Owner > DarrenMR 10/23/2015 at 13:39

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I would guess the brass screw is your float adjustment. I’ve never worked on motorcycles, but it seems right giving what I see. That should be where the float is just inside the metal part (bowl) to the right of the screw in this picture

Lumpy44, Proprietor Of Fine Gif > DarrenMR 10/23/2015 at 13:40

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1. The choke is on when it is pulled out. Off when it is in. You want it out to start it likely and once its running push it back in.

2. The plastic part is an idle adjust.

3. Is probably a jet adjust, not to sure what this is for.

Klaus Schmoll > DarrenMR 10/23/2015 at 13:41

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On my vintage scooter the choke had to be pulled out (as everywhere else that I’ve seen so far.) One screw adjusted idle, the other screw adjusted the throttle cable response (also messing with idle as it can result in an always slightly open throttle.)

Master Cylinder > DarrenMR 10/23/2015 at 13:45

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Pull to activate “choke.” (I believe on these it’s actually an enrichment circuit and not a choke, but the end result is the same and the distinction is meaningless from moat users’ standpoints)

The big knob is for idle adjustment. Tighten to increase idle speed; loosen to decrease.

The small screw is for adjusting the idle mixture. Sometimes they’re “air screws,” which add air as they’re turned out, leaning out the idle. Some times they’re “fuel screws,” which add fuel as they’re turned out, richening the idle mixture.

Sir Halffast > DarrenMR 10/23/2015 at 13:46

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I presume you’re coming off of Atkins or Paleo or something? I guess I’d recommend starting slowly, maybe with a bit of bread at meals or some well-cooked pasta.

SidewaysOnDirt still misses Bowie > DarrenMR 10/23/2015 at 13:47

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I’m fairly certain that carbs are black magic.

Birddog > DarrenMR 10/23/2015 at 13:48

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That brass screw underneath is your Pilot Fuel adjustment.

Tohru > DarrenMR 10/23/2015 at 13:49

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Pull choke to turn it on.

White knob is an external idle adjuster.

I don’t know what the brass does.

Ross Kraz > DarrenMR 10/23/2015 at 13:55

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How I deal with carbs...

Step 1: set tools down

Step 2: walk away

Step 3: get new hobby

Or just buy a new carb.

I kid. Just open her up, replace seals/diaphragms as necessary, clean everything really well. Be very careful to not lose parts; I usually do it in a plastic bin so things can’t roll away. Then use the Googles to find factory settings to start from.

By the way, that pdf has a diagram that confirms the idle screw. And the other screw looks like the pilot fuel screw...? But the diagram shows it inside the bowl, not outside.

Andrew P. Collins > DarrenMR 10/23/2015 at 14:58

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Carbs are not that bad!

-guy who burned his eyeball last time he worked on one and now has an EFI bike