1972 cb/cl 100

Didn't get anything done on the 100 last night. Enjoyed a movie night with my wife. I rode my daily to work this morning. I leave work at 1. Hoping it passes first. Otherwise it's my first ride home in the rain gear for this season.
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#110 is in. Waiting for the rain to stop to test her out. No fenders front of rear, so I'm not going to ride in the rain today.
 
Keep em crossed. Didn't dry enough to ride. Kicked it started, had to have the choke wide open. Before messing with fuel mix, my neighbors dad came out to talk to me. Nice guy knows a lot about bikes he has a couple Yamaha singles and a few 650twins at his shop. I told him to get on this forum. Anyway, while talking he said it sounds rich now. I chatted with him for a while, then had to leave for dinner. Now family time then kids in bed. Hoping for tomorrow, if not I won't get time to work on it until Wednesday or Friday. Thank God for my daily fuel injected ride.
 
main jet wont become operational until you physically lift needle out via throttle.

If it dont require some choke to start cold, need to tweak on the A/F mix needle after shes warmed up to operating temps. 5-10 minutes of riding...atleast.
 
See, I still have so much to learn. Thanks man. My neighbors dad was insisting on getting the air fuel mix proper as well. I didn't think about the full mechanics behind the main jet and needle. Wish it wasn't raining out.
 
Just dont waste your time making the adjustment until that engine is fully warmed up.

The hot insulator and intake passage is what really helps to atomize the fuel for optimal burn.

Thats the reason it has a manual adjustable choke. It needs more gas= less air when cold.

The atomized fuel from carb will condense back to liquid state as it passes through the cold insulator and intake passage. Liquid fuel doesnt burn near as efficiently as atomized fuel.
 
And another thing....lol

the reason the A/F mix is adjustable...I know your just dieing to know.

Outside air temps.

Even though you ALWAYS adjust A/F mix w engine fully warmed.

If you adjust A/F and its 45 degrees (springtime) outside it will run poorly once temps reach 85 (4th of July) (cause the engine can only warm the air so much). So, it will need re-adjusted.

Thats why the carb maker gave you an easy to adjust needle...rather than a difficult to change fixed jet.

And thats the rest of the story. ;)
 
https://vimeo.com/130927323 #110, and #100 are too rich. Got some blueish smoke from it now. Smells rich too. Got it to temp in the driveway, I Couldn't ride it. Maybe I've been going the wrong way with jets. Maybe I need to go leaner. Out of time for today. I'll try the #92.5 again. Later in the week and see what happens. then maybe keep going smaller.
 
It's still idling fine. The sputtering is when I try to put any throttle on it. I could turn the fuel/air mix screw all the way in and it kept running. If turned out too far it would start smoking and idling down. It was good and hot before I messed with the fuel/air screw. Carbs are not my friend.
 
turning A/F mix all the way in should kill the bike right now...your basically shutting off ALL FUEL at idle circuit.

That carb is junk...dont waste any more $ or effort on it.

Sorry dude. Previous owner must f-ed up the needle seat on A/F mix by turning it in too hard.

UNLESS, on that model carb it controls AIR only...then I know nothing about all that kind of stuff or that carb.
 
Im sorry bubba, you really did give the old college try. And yet smart enough to know when to say when...Kudos for that!

Im sure you will have a better chance w a fresh and correct carb. Who knows what that thing was intended for?
 
If you are after a cheap half decent carb check out Oko, they are a rip off of mikuni but aren't horrible quality.
 
Thanks Brodie, I looked at those Oko's but didn't see a direct bolt on for my bike. I ordered the same one Trek bought. It should be in Friday, so I'll get back to tuning it then. In the meantime I might start fabricating a different seat for it.
 
DohcBikes said:
Welcome to my sarcastic way of helping and adding information. Try not to get too butthurt about it, its just the way I roll.

I only read a few pages back on this single carb saga but you guys are all over the place with your tuning info. For christ sake, how can you give advice if you dont even know whether he has a fuel mix or air mix screw? Too many changes at once....only jetting but no tuning...many assumptions. This is why it is so hard to fix things over the internet.

Believe it or not, your symptoms are not always soley cause by improper jetting.

Whats your compression?

Are your valves in spec? These valves on these motors get tight in a hurry.

Any exhaust obstructions?

The easiest way to tell whether you have an air mix screw or a fuel mix screw (any professional tech should know this) is to determine whether it is on the INLET side of the carb, where the AIR enters, or on the OUTLET side of the carb, where FUEL is mixed with air to make that scooter go. Some have both...OH MY!!

Checked for air leaks?

Carb bolted on too tight? These carbs have a tendency to run funny when that is the case because the carb body distorts.

You are not running the stock airbox, therefore regarding hiw the air moves, everything changes.

Are you positve that your air bleeds are clear?

Have you tried a different needle jet or jet needle? Foe the record, my feeble mind thinks this could be one of your issues. You may also have a bent jet needle. If you never try other needles (which is always a step in the jetting process) we will never know.

Tried different slides with different cutouts?

The suggestion that your mix screw seat may have been damaged is a good one, although it simply would not cause an engine to bog from 1/2 to 3/4 throttle. That is jet needles time to shine.... Not the idle circuit OR the main jet, unless light years off, will cause this. More likely, the issue with it staying running when seated is either a broken tip on the mix screw, a missing oring, or a pilot jet that is too large.

Ahhh screw it. Just order a new carb, throw this one in the trash, and start all over. Maybe you'll get lucky.

Pics are neat. I'll include one of a cb100 that got a full engine rebuild and TUNING at with 714 miles on the clock. The owner that has had the bike since new left it idling outside his shop with a full tank and forgot about it. Got a little warm. Then he tried to rebuild it himself. And then he brought it to me.
Click to expand...

Hey thanks for the education. I learned a little just reading what you typed.

Once I get battery and spark plug, and carb ...I'll be trying to start my little puppy up.

Tell your customer, thats a good looking little bike.

Sorry for the thread jack JB.

Back at ya JB.
 
Dohcb, so does that carb have an air mix or a fuel mix ?

Also, no a bad mix needle seat wouldn't cause the mid throttle problem. The question at hand was. Turning mix needle into bottom the bike continued to run at idle. I found that pretty curious? From my experience w carbs on my 360, would kill her long before bottoming.
 
The current non oem carb is a fuel mix, screw is on outlet. Redliner and I discussed that a while back. I bought a new oem replacement because it will be a lot easier to work with. The PO went through two shot carbs before buying this eBay one. I don't think he tried to clean the originals. I'm not sure what this carb goes to, but it's not right for this 100. I've read that different size carbs cause many different issues as well. I know I will still have to tune the new one due to the fact that the PO did not have the airbox when I bought the bike. It was cosmetically pretty, but not running when I got it.
I have not checked compression, but the valves and timing are set correct.
As for the current carb, it idles fine, it just is not cutting out with screw all the way in. Could be a missing o ring.
As for all the jets, it bogs at 30% throttle with no smoke which makes me feel it's lean.
Either way the new one should be in the end of this week, so we shall see.
Thanks for all the info.
 
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