Runs on only one cylinder

Hey everyone. This thread has been great in helping me come up with a plan, as this sounds very very similar to whats happening with my bike right now. So I thought I'd tack on another question.

I noticed its been running on one cylinder but, runs. So thats something.

I havent actually done any of the work mentioned above yet, and today I went to start the bike up. With full choke on, it barely idled then died.

It wouldnt turn over, on any choke level, and when I finally got it to turn, it came on, idled around 5500 for a few seconds, then dropped, and shut off. Couldnt get her going again.

I also noticed the left side (weak cylinder side) when it was running, there was a touch of grey smoke coming out the exhaust (no smoke on good side) and it sounded hollow and high pitched.

Does this sounds like more symptoms of a dirty carb, and un synced carb floats?

If I read this threads history correctly, what solved your problem jscgdunn, was:

Adjust the float level to perfection.
Cleaned the carb, and most importantly the float bowls (using heat)
Had the valve clearances checked and carbs sync'd.

Ive read that the 81's carb sync screws are inset by factory default, and should not be tampered with. And also that I can remove the float bowls without taking off the whole carb. Does that mean I can clean the float bowls, and adjust the floats without taking the whole carb off?

Im fairly new to moto maintenance and carbs frighten me! haha.

Can anyone confirm any of this?

Thanks.
 
Most likely you will need to pull carbs. They are pretty simple

Here are the steps:

1) Get a manual: you can find one oneline; there are also some really good drawings on this forum
2) Read a bunch of the posts on this forum; there are some real experts here on these carbs
3) Pull the carbs off the bike and disassemble carefully. I would reccomend you get a JIS philips screwdriver or you will ruin quite a few of the screws.
4) Once you see where all the air and fuel passges you need to get them really clean; other wise you will be pulling them again
5) The hard starting is probably related to float level and the enrichener circuit. On mine the passages in the float bowls were plugged. I need heat and compressed air to clean them.

It will be worth it; my son ened up in Tofino and got back ok (no troubles) and is still commuting on it. On July long weekend he loaded it up and went skiing on a glacier.

See pic:thumbsup:
 

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OK- where to start....

The "inset" carb sync screws you are talking about, are not the carb sync screws. You are talking about the idle mixture screws. On an '81, they are covered by an aluminum plug.

The screw used to sync the carbs is on the shaft that connects the 2 carb butterflies together.

To me, it sounds like the carbs are dirty, and I mean the little passages inside the carb. Here is how I clean them.

http://www.xs400.com/forum/showpost.php?p=64401&postcount=17

These carbs are not easy to get clean.

Yes- to adjust the floats properly, the carbs need to come off.

Once the carbs are all clean, try it again. The carb mixture will probably need to be adjusted (which means removal of the aforementioned plugs), but ensure the carbs are clean first. The symptoms you have are classic for a gummed up idle circuit.
 
Thanks for the replies, I appreciate the help.

I would reccomend you get a JIS philips screwdriver or you will ruin quite a few of the screws. Great tip, thanks it's on my shopping list.

I have the Haynes manual, and I came across a post that has the factory, and shop manuals. The problem I have with them, is that they're written for someone with a bit more working knowledge of bikes. Which is fine, I'm learning every day. They just leave out some details. Or a lot of the photos. I have a Clymer manual for my DRZ thats about 3 times as thick and covers everything in written and photographic detail.

The symptoms you have are classic for a gummed up idle circuit.
That is awesome to hear! A diagnosis, while its an educated guess, points me in the right direction! Thank you! I'll look over how to clean them.

While I can figure out how to remove the carbs using my Manuals, its small things that might seem obvious to someone with more experience that discourage me.

Is there anything I need to know about removing the carb that might not be in the manual? Like, draining the fuel so it doesnt pour all over the place when I remove the fuel line, etc. Or, making sure the bike is level. I only have the side stand, no center stand.

I've never attempted anything this involved mechanically before.
 
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Sounds like you have the right ideas. Make sure your petcock isn't on prime. Detach all the cables first, and make sure all the boots are completely loose. Keep the carbs level until they're out, and then drain them using the drain screws on the bottoms of the carbs. I find the boots at the back (the intake boots) are easiest to remove first. Then sit on the bike, grab hold with both hands, and yank and twist until the carbs pop out of the front boots.

Like I said, keep it level, and drain the gas into a clean container (I use a glass measuring cup I stole from the kitchen) so you can pour it back into the tank later (gas is too expensive to just throw away.)

If this is your first time, then sit back, have a beer, and call all your friends to tell them that you're now a motorcycle mechanic.
 
Someone I know (me) changed a tire and forgot to button down all the bolts before riding up a mountain.

brake rod came loose and wrapped AROUND the axle. That was an interesting day. Had to engine brake for a week before the replacement arrived.

So don't feel bad. We all forget to bolt stuff back up! It's part of the zen.
 
Hey everyone, back again.

So, I spent an entire day taking apart the carbs cleaning them in an oxidizing tank blowing all the holes out with a 125lb compressed air gun and putting them all back together. Checked the floats, which seemed strange. The manual, and Yamaha website both show ROUND floats in the carb. Like two little hockey pucks. Mine are not like this, they are both round, but have a flat side. So, I can't exactly match it to the manual specs as it causes the floats to be HUGE. So, since the right side seemed fine, I just matched the Left to it.

I also checked, and adjusted my valves, they were open a little wide. Easy fix there.
And changed my spark plug caps. I put in new plugs a couple weeks ago, so I left those, although the left one was telling me previously, that my fuel mix was too rich. I should try a new one in there again to see if, after cleaning the carb, it's still doing it.

I also re-routed my throttle cable, as it was getting caught on the headlight and accelerating in right turns...sketchy.

The bike runs great. Better than before! It no longer hangs on idles, it comes right back down every time and idles like a dream....

However. It still seems to be running weak on the left cylinder. I think its getting flooded, which points to float I would imagine. Even though, they are matched up.

Whats happening is, randomly and rarely, it'll backfire in 1st or 2nd. LOUD. It rarely does it when I shut it off, but it usually "gurgles" a couple quiet pops when I shut down. More often than not it does this.

It also feels like its not getting enough power in 1st and 2nd, almost like theres...too much air in there, and I can feel it skipping on power, almost, jerking me down the street. Its subtle, and Im sure no one notices but me. But it just doesnt ride smooth in those lower gears.

Based on what Ive done, checked, and mentioned....Any new ideas?

I might go order the OEM floats, or look into what exactly is different about mine. Until then, she rides fine, just not 100%
 
did you change float valve?

carbs upside down the middle of your floats should be 1mm higher than middle of carb body (without touching them).

if needle and float hight are ok and still flooding on that side.. change oring on float needle seat
 
Hey duder,

You won't really need new floats, just floats that a. Float, and b. Allow the valve to open when it's got the float tang the right height from the lip of the bowl, often quoted as 26mm or whatever but it's essentially got to be parallel from what I've seen.

As long as your floats aren't leaking, then the issues are no longer your carbs.

you'll now need to look at ignition, head gasket, and vaccuum or exhaust leak.

Or you, like me, can learn to live with an imperfect bike.
 
I have not checked the compression yet. I'll check that on Saturday, if the shops got room for me.

You think the weak cylinder and backfires/gurgling on shut off are a sign of "bad" compression?

I don't have my Haynes manual with me, but Im assuming it goes over how to actually do this? I've been going to a rad little DIY shop in Vancouver here, Motomethod. They have all the tools, I just need to know what I want to do when I get there. Pay by the hour and all ;)

Think it could also be my float valves? I have to pop the carb off again anyways to peek to install a couple new jets.

Also, this is going to sound dumb, but, at the shop and at some dealers, they mention an online parts feuge (not sure what the spelling is, or if this is even the right word) I should probably try to find that.
 
I have not checked the compression yet. I'll check that on Saturday, if the shops got room for me.

You think the weak cylinder and backfires/gurgling on shut off are a sign of "bad" compression?

I don't have my Haynes manual with me, but Im assuming it goes over how to actually do this? I've been going to a rad little DIY shop in Vancouver here, Motomethod. They have all the tools, I just need to know what I want to do when I get there. Pay by the hour and all ;)

Think it could also be my float valves? I have to pop the carb off again anyways to peek to install a couple new jets.

Also, this is going to sound dumb, but, at the shop and at some dealers, they mention an online parts feuge (not sure what the spelling is, or if this is even the right word) I should probably try to find that.


Soe hints from the web...and a littel editing:
There are some general guidelines to follow when running a compression test on a four-stroke gasoline engine. Rotary, two stroke, diesel, and other types of engines require a different procedure. It's always a good bet to follow testing steps recommended in a service manual before drawing any conclusions based on test results. The service manual will also have compression service limit numbers.

Make certain the battery is in good shape, as it will have to spin the engine quite a few times. Warm up the engine. The reason for this is that heat makes all the metal parts inside the cylinder expand and seal up better. Having things warmed up will give a more accurate compression reading. A cold engine will give inaccurate compression readings. Stop the engine, and remove all the spark plugs. This way the starter can spin the engine freely. Disable the ignition system by either pulling the coil wire, or disabling the ignition coil. To perform the actual test, insert the compression tester into one of the spark plug holes and crank the starter to rotate the engine in order to build compression in that cylinder. There may also be other required steps, such as disabling the fuel system or holding the throttle open. (You should hold the throttle open). Record the compression number for that cylinder. Move onto the next cylinder until numbers have been recorded for each cylinder. Once all the numbers have been recorded they can be compared, and an overall conclusion can be drawn.

Even Burning

In a perfect world, the parts inside an engine all wear out together at the same rate. In every other world, this rarely happens. If your car or truck or bike is using or burning a great deal of oil, has lost power, or is just plain running poorly despite a tune-up or other mechanical measures, a compression test is a good way to check what's going on inside the engine without taking it apart. Keep in mind that the numbers will mean nothing unless they are referenced against manufacturer recommendations found in a service manual. The thing to look for in a compression check is even numbers. If all the cylinders check out within 10 or so PSI of each other, and those numbers sync up with the factory specifications, then you're good to go.

If one or more of the cylinders show a difference of 15 or more PSI, then there are problems inside. If one cylinder shows a low reading, remove the compression tester and squirt a small amount of motor oil inside and test again. If the second test reveals a higher reading, then worn piston rings or cylinder walls may be the culprits. If the reading stays the same then suspect worn valves or valve seats. If the gauge shows a very low or no reading on any one or more of the cylinders, then serious internal damage has occurred. Any time a low compression reading is indicated on one or more cylinders, the time is right for engine work. There are a few tips to determining what these problems are, but keep in mind these are very general guidelines. The key point here is that an engine with low sealing compression in one or more cylinders will never run right—no matter how many new parts are connected to it.

Hope this helps.....:thumbsup:
 
I seen a question about backfire ing. I had the right side backfire on throttle up, and again on returning to idle. super loud. I took my carbs apart, and since It had been recently clean, I didn't dig too deep. just by spraying carb cleaner, I seen something come out of a hole. it was a piece of paper towel. I put it back together, and it was working much better immediately no back firing. Note: I did notice some pitting, which has caused me to run to the Motor cycle salvage yard. to find a pair of floats. Goodluck
 
Hey guys,

Now that I've officially taken over this thread, I'll give an update.

Spent the day in the shop. Installed new AIR jets. Seperate from the main jet, these went in a little hole right on the side of the rim on the air intake for the carb.

I cleaned the carbs, and checked the floats again. Still good. This time I got right into the float valve, which I hadnt looked at before. They were pristine. So I reassembled the carbs, and put them back on.

I put on all new hose clamps on all the air hoses, in and out.

Checked the timing, which was great.
Check the compression, which was perfect.

Then we started looking closer at electrical. Turns out, there was a horribly loose connection on my Left side ignition coil ( I think its the ignition coil. Hooked right onto the spark plug) So I cut out the connection and soldered the wires together directly. Worked great.

The battery was fairly low, so we charged that up too.

It fired right up, and idled well. But its still kind of weak on that left cylinder.

Now there s a new problem. It seems to idle low now, then come back up after a moment.

Any ideas?
 
Okay, Im going to try to eliminate some possibilities.

So, I had the carb running well, for the most part the other day. But it was still weak on that Left Cylinder. The idle was alright, it went up when I accelerated, and came back down when I stopped. Makes sense.

But it still ran kind of, poppy, or chuggy, for lack of a better description. What it felt like, was as if there were air bubbles coming into the fuel, and it was skipping on power. That's just how it felt under me. Almost, stuttery in power.

Why I think its not electrical is, because it only happens on accelerations, or when I crack the throttle, its like, sometimes, nothing is there, or it caps at a certain amount of power, unless I decelerate, and try again, then its back. Its happening in direct response to what Im doing with my throttle.

It comes to life when I just crank it! Unfortunately I live in the city, and just cranking it doesnt happen as often as I'd like, except for midnight rides, or weekend warrior rides, which Im skeptical of going on until its running a little more reliably.

I feel like if it was electrical, it would be a lot more random, and not specific to acceleration, or deceleration. Like, maybe on a bumpy section of road Id be loosing power due to faulty electrical jiggling around.

Aside from that, we tested all the electrical and it seemed fine.
Compression tested flawlessly
As did timing, and valve clearance.

This still feels like a fuel/air mix problem. Maybe Im wrong, because I know next to nothing about engines.
 
I've been scouring the site looking for issues with my DOHC '82 and I found this post.

My '82 is lacking power across all RPMs. It used to be awesome, and then one ride it started acting up after I had just started out... lack of power like it wasn't firing right. I took off the spark plugs and LH was the pasty while color and the RH was black. I figured the RH wasn't right, so I switched the caps and plugs. It ran more consistently, but still terrible. (by terrible I mean: can only do 75MPH downhill. 6th gear is worthless and 5th is barely sustainable, MPG dropped too)

Since reversing the plugs and caps meant an improvement, should I just give her a minor tuneup or pull the carbs too?

Thanks guys!
 
well i have another question for you guys, im pretty positive is a carb issue, but before i dig into them guessing id like to go into it knowing what to fix. so, question, it starts up fine (its kick only), it idles fine, compression is fine.....but! after a little while of riding and it warming up a good bit, and i park and start it back up to go back riding i notice that when i start going up in gears and let off the throttle it will just stay at those rpms and when i go to down shift it has trouble coming back down when i engage the clutch. scenscenario being: ill get going, get up in 4th or 5th and a red light comes so i start to slow down and go through the gears going down. when i engage the clutch and shift down the rpms are up there and dont come down until i release the clutch a little, just to where it barely catches. so if i have to stop in a hurry and go all the way down to 2nd quickly all while the clutch is engaged the rpms will be really high until i release it and then it slows down and starts going. this is very hard to explain. it does almost the opposite or what its supposed to. like i have to shift down and engage each gear on the way down for it to not do that, which is fine... but not for immediate stops for instance a car pulling out in front of me. i will engage the clutch and brake hard and shift down to be able to take back off and the rpms are really high then i let go of the clutch and they drop down and i can gas it hard and go. but whats making the rpms so high and not go down when the clutch is egaged and its stopped??
 
Uhhh.....

There are a few things that can be going wrong with that...

Before we start, are you comfortable servicing your own carbs?

Because I'd first recommend that you clean you idle circuits out, which is why you're idling mixture is jacked up probably. If it were lean, it would be stalling at lights, instead, its running rich and causing high revs. This means your idle circuit is clogged, and you or someone else has dialed out the carb screw to compensate, which causes the high revving once the engine is heated up.

Starting on a day when you can do this without needing to ride the bike, you need to wake up with it fully cold,

Clean the carb with cleaner and compressed air. You can't really do it wrong but the idle circuit, which is a tiny hole just in front of the butterfly, is usually glued shut, carb cleaner and a skinny guitar string will help you here.

adjust the valves next. You can get set of tappet valve feelers at autozone. The .005 is the same width as a soda/beer can , so you can just make that one. Rarely are they included in the sets you buy.

Then the timing, make sure its perfect with a timing light. All of this is covered in the manual and the garage section of the forum. Get the timing perfect after that checking it with an auto timing light.

last, using the tach feature on a timing light, set the idle to 1200 and balance the carbs with a tube manometer. Find the link using google search.

carbs, valves, timing, ignition, balance. In that order.

You are asking about a multi problem symptom. Its not solved with one answer, sadly.

Sometimes you can have a vacuum leak as well, and the procedure to find that is on the forum too.

Good luck, keep notes, solve one problem at a time, and don't rush. Zen is in doing, not solving. otherwise you just have to do it all twice.

Drewcifer

PS Matt, you want to start your own thread, not out of cruelty, but the responses here going to domo, and if they're going to you, it can get very confusing.
 
I mostly agree with Drewcifer, although I also think it is running lean, not rich. I had the same issue with the same symptoms on my bike and this all sounds very familiar.

Start with a vacuum leak test (forum search or youtube for tips). Then check your exhaust for holes (does it hurt your ears?). Make sure your choke pushes all the way back in (or did you forget?).

Then go ahead and clean those carbs. Here's a thread with some help

good luck and let us know if it works out :)
 
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