Setting/Tuning Carburetors

Hey all,

On my '74 Honda CL 200, I've disassembled and cleaned the carburetors thoroughly. I'll be putting them back together soon.

I've never adjusted the carburetors on one of these and thought I might ask for some pointers here.

I did a search or two on some more specific sites, but didn't come up with what I was looking for.

I don't even know what adjustments there are. I'm guessing two...maybe an Idle and something else.

It's an aircooled 200cc parallel twin. So...two carburetors.

Any help?

Thanks, Clem

Make and model number of carburetor?

I'll see what I can find...

Thanks, Clem

You have slide carbs on this little beasty, right?

There will be idle speed and an air/fuel mixture screw. Generally speaking, if the mixture screw is on the airbox side of the carb, turning it out will lean the mixture.

For this application, ear tuning is more than close enough. You can pull the plug wires (insulate yourself or your pliers, obviously) to isolate one cylinder, and tune by ear to get them setup about the same. Basically, to get started you just want to have both carbs set the same, and make adjustments from there. I like to set my mixture screws at 1.5 turns out, and just set the idle screws about as low as you can while still keeping the bike running. At that point, use the mixture screws to smooth/raise the idle, and drop it back down to the right range with the idle screws. (You should idle anywhere between 1000-1500 rpm on this thing.) The mixture screws are pretty sensitive on these little carbs, so operate about a 1/4 turn at a time, and give it a second to catch up to your changes before you go turning some more.

Isolate the cylinders by pulling a plug wire again, and rev it to about 3k rpm to see if your cables are lifting the slides about the same. Honestly, they'll have to be way off to cause a problem, so I wouldn't spend too much time worrying about that.

That's about the best you can do on these things, since I don't think they even have a place to hook up a vacuum gauge.

Keep in mind that you want to do this with the engine reasonably warm, but don't let it sit there running too long without a break to cool off. A fan will help, but it still needs a break occasionally. And I'd have a jump box handy, 'cause you'll be starting this thing over and over and over and over.

racinginc215 wrote: set the plates to a set of bread or garbage bag ties. new ones preferred. Lay them in the bottoms of the bores and screw the idle plate until both touch the bread ties evenly.

I learned a lot of old timer tricks at my old shop, but I never heard this one. I like it.

(Do it with the engine off, of course.)

Don't forget to remove and "read" your plugs after you've ridden it a few days, to check if your running lean or rich.

COol folks...thanks a bunch. This is exactly what I needed to know.

Looking at the squeaky clean (as clean as I'm going to get it anyway ) carb body I see KEIHIN and on the flange "027B" on one side and "[A]LEE" on the other.

Thanks, Clem

Ah, the bread tie trick pertains to butterflies, but Clem has slide carbs, I think. In that case, I'm not so sure it will work - I think he'll need a little more room under the slides. But, Clem's a sharp fellow, I'll bet he understands the principle behind the trick, and can translate it to suit his needs.

Yes, Slide type carburetors I have.

Again, I appreciate all the info folks!

So, which is the idle and which is the mixture screw. I'm guessing the idle screw is the knurled one that sticks out so you can adjust it by hand while you're cruising down the road .

When I got the bike, it just wouldn't idle. And then sometimes it would idle at 2,000 rpm for a few minutes, and then it wouldn't idle again. I don't know what could have caused this, but I'm certain it was the carburetors. So, I'm hoping the cleaning will take care of whatever was gummed up and caused the running problem. Now if I can get them tuned right, I'll be set!

Thanks again, Clem

ClemSparks wrote: So, which is the idle and which is the mixture screw. I'm guessing the idle screw is the knurled one that sticks out so you can adjust it by hand while you're cruising down the road .

That's usually the case, yes.

ClemSparks wrote: When I got the bike, it just wouldn't idle. And then sometimes it would idle at 2,000 rpm for a few minutes, and then it wouldn't idle again. I don't know what could have caused this, but I'm certain it was the carburetors. So, I'm hoping the cleaning will take care of whatever was gummed up and caused the running problem. Now if I can get them tuned right, I'll be set!

Check the float level, and check if there is any blockage in the tank vent (does it do that if you run the engine with the filler cap off?)

BoxheadTim wrote:

Check the float level, and check if there is any blockage in the tank vent (does it do that if you run the engine with the filler cap off?)

Well...considering that the tank latch was broken when I got it...I'm guessing it's not the tank vent (though that COULD be a problem still). That is to say, it ran like this when I got it and there was effectively no tank cap because it wouldn't latch (I've since fixed that).

Anyone know what to set the float level at? And where to measure from? I assume turn the carb body upside down and measure from top of float to base of carb body...but I'm not really in tune with that...

Thanks,
Clem

If you're working with floats that seem to be in good shape and relatively unmolested, I may not mess with the fine-tuning the float level, unless something is obviously wrong. On this bike, all they really need to do is open when the bowl needs gas, and close when the bowl is full. You're not going to be too worried about the intricacies of fuel levels or high-end starvation.

Eyeball it: oriented in the position in which they'll be installed on the bike, check (a) the float doesn't rest so low that will contact the bottom of the bowl, (b) the float needle is open when the bowl is at rest, (c) pressing the float up a few millimeteres closes the float needle. If you haven't replaced the float needles I'd also inspect them for wear around the point where they seat. If they have a rubber (actually viton) tip, they can wear a ring around the seating point, which will contribute to leaking gas with a full bowl.

When you're satisfied you have things back together, regardless of screw settings and such, I'd recommend hooking the carbs up to a fuel source and resting them on a bench in an operation position, to make sure you're not leaking gas anywhere. Much less frustrating to find that out before you've reinstalled them.

For the real, actual, proper float level, you're probably going to need a manual. The factory manuals for '70s Hondas are actually pretty good.

The idle speed will be somewhere around the vertical barrels of the slides. All that screw does is act on a little wedge/ramp shape built into the side of the slide, and prevents the slide from dropping past the point at which you set it. Very simple machinery.

The mixture screw will be a little more hidden, maybe even on the bottom of the carb body, or in another place that's hard to access once the carbs are back on the bike. It will be on the airbox side of the carb.

Your prior running problem sounds like a classic case of the carbs being way out of sync.

FYI- I learned more about carbs in this thread than in 10 books. I love this board. (Yes, I have a motorcycle or two that I will someday have to adjust carbs on)

Oh! Don't forget to check that your floats float. Take 'em off and shake 'em next to your ear. You don't want to hear any liquid sloshing. If you do, that means you've got a hole in the float, and if it lets liquid inside, it won't float. Therefore worthless; if it won't do what it's called, you know?

I attempted to remember the advice in this thread and tune the carburetors yesterday...but I didn't get very far. Between a spotty memory (ha) and a a few distractions, it just didn't work out for me.

Before doing this, I attempted to purchase some plastic pliers or something from Harbor Frieght. I couldn't find what I wanted, but maybe someone here has a pointer.

I want to feel confident that I won't shock the excrement out of myself when pulling and replacing plugwires while the bike is running (as suggested by Alex, thanks). I've shocked myself enough times in my life that the "oh, that was neat" factor has long since worn off.

What do you guys use to touch plug wires and manipulate them while an engine is running? And, way more importantly, what do you use that WORKS? Welding gloves? The metal pliers with platic dip coated handles?

Harbor frieght had a little t-handle plastic plug boot puller...but that only solves half of my dilema (I still need to put them back on).

So, turning the mixture screws OUT leans the mixture, eh? I just caught that again today while rereading the post. That's counterintuitive to me and was probably the main cause of my failure yesterday. I'll print the thread and bring it with me for my next tuning session.

thanks again!
Clem

The idle mixture screws on that old of a bike OUT is Richer. its a real mixture screw. Newer carbs the screw is realy an air bleed so out leans out the mixture.

Regular plastic diped you should be fine. if your not possitive use rubber gloves too.

Haha,

I'm "positive" that I could be come the quickest route to negative...ground.

Sorry...just a bad pun I had to use.

Yeah, the rubber dipped handles will work for you. You don't have to get the plug wires really securely connected while you're tuning, just basically resting on the sparker, close enough to make contact. So, I'd start with them sitting loosely on the plug, just to minimize the time you have futzing with 'em.

Yeah...I'm with you.

I pulled them loose and put them back just resting on the plug. My idea was plastic clamps, but I forgot to bring them. And my clothes pins weren't quite big enough to hold the wire, but too big to let it fit into it's spot.

Thanks again for the tips!

Clem

The idle sync issue is why I sold my CB360. One minute it was high idle, the next it was low. I decided that as a beginner a single modern carb was my best bet.

Now I've got a buddy who's got a 80 XS400 with dual carbs with the same problems...so looks like I'll be able to learn carb adjustment on his bike.

What exactly is "syncing" the carbs mean? Adjust them to similar mixtures? floats?

Sync is syncronization of the vacuum levels on the engine side. If one cyl has higher level of vacuum at idle when you crack the throttle the motor can stumble or vibrate due to the cyl making un-even power. On a two stroke twin cyl motor (like RD's etc) you open the throttle all the way open then feel inside the carb at the top and fell the slides are evenly open at the top by adjusting the cable slack adjusters then you unscrew the idle screws (big brass screws in the side) they hit a ramp cut in to the slide. You then start the bike pull one plug wire and adjust the firing cyl untill it just dies. then swap sides and adjust the other cyl idle screw now plug both plug wires on and re-fire Rev it to clear the unfired mix and your idle should be just right. Now you play with mixture screws and reset the idle as above.

BTW, synching carbs is a lot easier on more modern carbs that have a vacuum port for the express purpose of synching. That way, you can hook them up to a gauge (usually mercury) and eliminate the guesswork involved with doing them by ear. Although, again, getting it right by ear is close enough for 9/10 of street bikes.

So there's definitely something screwy with my left cylinder.

I'm thinking I need to set the valves. It looks like they're spec'd for 0.05mm clearance/lash. I assume this is a hot measurement...and also assume the adjustment method will be pretty apparent when I get the round access covers off. Let me know if I'm off base here.

the engine will run pretty smooth and even on the right cylinder alone. But the left cylinder is erratic.

Thanks, Clem