Topic: K0 4 Cable Sync Question - Low pressure Cyl #1

[jakec]

Today I was doing a carb sync on a K0. I rebuilt the carbs and then rode this bike around a bit and it was fine except for a high idle when hot. So before doing a carb sync I did a full tuneup (timing, valves, tensioner). All the plugs were showing the same and looking good.

I was following the sync procedure from the manual word for word. I did the idle sync with the 4 separate screws and that went alright. I got them all pulling at 21 (spec 20-22). It took a while to bring the cyl 1 pressure up but I got it there.  I ran into my problem at the next step.

The manual says slowly rev to 1/4 throttle and hold. Adjust the cable of whichever carbs don’t come up in pressure or are slower to come up. In my case the #1 is way lower. I adjusted it where I f I blip the throttle quickly they all come up in unison and it looks great. But if I go slow like the manual says I get nothing from #1.

I tried swapping fittings and hoses and well as putting the blank off screw back in but it’s still the same and the engine is hesitating like if I had a clogged jet or the needle was in the wrong position or something like that. Also checked and the piston is not in backward.

I would normally think I need to check my jets and stuff but this problem really only seemed to come up during the sync process. So if no one can think of something I could be doing wrong, I will get into that #1 carb and look at jets and needle position. I attached a pic of the meter when I sustain 1/4 throttle like the manual says.

[Don R]

 I recently bought a previously owned but not used carbtune, haven't tried it yet.
  Since yours works on a blip but not in a slow rev, I can't help wonder if in yours the #1 gauge is a bit sticky. Have you tried swapping the hoses from 1 and 2 to see if the issue stays with the gauge or carb? If the low reading stayed the same, it could be the gauge, if it moves with the hose then it's a carb issue.

[PeWe]

The Carbtune has been working before on other carbs?
If not, check that hoses have the restrictors mounted as delivered with it.
I cut my hoses ca 100mm from the ends, put the plastic restrictors as adaptors keeping the hoses together.

I had to add extra hose into the end to fit my carbs smaller connections, 4mm ID hose, ca 200mm long.

[Scootch]

Make sure you don't have a vacuum leak at that #1 port.

[newday777]

Make sure you don't have a vacuum leak at that #1 port.

Plus 1 check for vacuum leaks.

[jakec]

So it’s not just thag the reading is low but the bike is actually struggling too when I maintain 1/4 throttle. It’s stumbling just like it has a carb problem. So unless it’s the port/hose/meter being hooked up introducing an air leak I don’t think it’s meter related. I thought it was adjustment related.

The carbtune works because I used it on my 400 which is running perfectly now. I also did swap everything except for running the #1 cyl on the #2 gauge. When I switched everything over to cyl #2 it still behaved the same (so hose and fitting are ok).

I also put the blank off screw back in and ran it with only 3 cyls on the meter. It was hard to tell if it was better because I’m only going by ear. Finally, when I pull up on the cables they all have about the same free play, about 2.5mm.

[jakec]

I just checked the #1 needle position and it is in the middle position. I won't be able to try the sync again until after work today.

[Don R]

 Slides can be dropped in backwards on a K0. I'm sure you would have noticed by now but it happened to me once.

[Ujeni]

After going through the obvious stuff like jets, float height, mixture and choke, my first thought is that you have a vacuum leak. Can you check for that before proceeding?

Next, would be to check the cable play at the carbs. This is not scientific, but it gives you a clue to where the problem could be. When the throttle is at zero and the bike is off, there should be about the same about of play in each cable at each carb (a few mm). Lift the cable of each carb inside the brass adjuster and stop before you begin to raise the slide. If you find that all of the have about the same amount of play except for #1, the you have a issue with your brass cable adjuster on the #1 carb. Your idle sounds ok, but thats at zero throttle. As you advance the throttle and the slides move up, they need to move at the exact same rate (assume all else is equal). If one of them is off because of cable play, then the slide would raise later or earlier than the others. A common problem is to switch cables on the 1&2 or 3&4 carbs after remounting them. This can cause cable adjustment to be way off. Make sure the two slightly longer of the four ends are going to 1 and 4.

After years wrestling with K0 and K1-6 carbs, I much prefer the K0 carbs. Perhaps I'm nuts

[Scootch]

On my bike k0 I have found that the play adjustment at the top of the carbs is critical to syncing them. This spec is 1 to 2 mm. And they all need to be pretty much exactly equal. With the bike off and a quiet ambient you should be able to twist the throttle open and closed and listen for the slides to click on the idle screws. Make sure they are all in sync. Also watch and feel the cables at the top of the carbs to make sure that they are all pulling the same. In addition on a k0 on the one and four carbs the cable is supposed to go over the top of the frame rail.

[jakec]

Well looks like we have 3 blue K0's in here, let me see if I can find a pic of mine.

When I synced my 175 carbs back in the day, I would go by the sound of the pistons seating in unison. I will try this today before starting the bike again. The other stuff has been checked and is OK. Cables are in correct order, cable play is OK and visually the same. Pistons are in correct way.

Normally I would think it would be the cable binding up somewhere or popped out of the housing at the 4 into 1 connector. But that would give a higher pressure reading, not lower. I will check for a vacuum leak, I'll put the blank off screw back in and use wd40 on the boots. Then if that's all good I will try switching the hose to the #2 gauge.

[Ujeni]

Nice looking bike you have there!!

[jakec]

Thanks! So what carb casting should I have? I just looked at them and couldn't find a number anywhere. I see in this image found on the forum here, the "JN" (jet needle?) setting is "4." Would that mean 4 from the bottom? The #1 needle I took out is in position 3. Being too high though would produce more vacuum, not less..

I also took these pics of the #1 and #2 idle adjustment screws, showing they are basically the same. So the idle sync being good on the gauge and showing visually the same here is a good sign to me (confirming that adjustment is done correctly).

So a fauly #1 gauge.. or a leaky carb boot? Could cause the low pressure? The carb boot because it is after the gauge's intake?

[jakec]

I see now that I don’t have the top gasket in any of my carbs.

[Don R]

 Me neither, I don't think they all had the top gaskets new. If you do add the top gaskets, be careful of the threads they are fine and cross easily.

[jakec]

Haven’t gotten anywhere yet, when I got everything set up I noticed the oil light wasn’t working. Just spent an hour chasing that down and it seems the sensor is broken. It’s not creating a ground anymore. I tested my other 750’s sensor and it does create a ground.

I did change the #1 carb cable stop setting, now they are all in unison (by ear). Gona start it up briefly and see if there’s a difference. Also going to test switching the hose so it is displaying on gauge 2.

[jakec]

I ran it for a bit again, #1 is up but #2 is way up and can’t seem to get it down. The adjustment is bottomed out for #2, and bringing all the others up doesn’t seem to work.

I also have some light backfiring (puff puff) out of one of the left exhausts. And I saw a bit of fuel come out of the #2 overflow hose.

The pic is with the gauges connected in order.

[jakec]

Oh I also tried the carb boots for leaks and did not find any. I’m wondering if I should open the carbs back up again due to the backfire. Or buy a set of K1 carbs lol.

[Scootch]

The pic indicates that #2 cyl is not contributing much. You need to adjust it's cable and or slide. Is #2 cyl firing? Check the #2 exhaust pipe to see if it's hot.

[newday777]

I ran it for a bit again, #1 is up but #2 is way up and can’t seem to get it down. The adjustment is bottomed out for #2, and bringing all the others up doesn’t seem to work.

I also have some light backfiring (puff puff) out of one of the left exhausts. And I saw a bit of fuel come out of the #2 overflow hose.

The pic is with the gauges connected in order.

Your puff puff is more likely valves too tight. Go back through the adjustment procedure when cold engine(overnight cold). Too tight, especially exhaust and as the motor heats up, the exhaust valve stays open.

Your overflowing gas needs to be addressed. Either overflow tubes have cracks or float adjustment height is wrong. Did you put in aftermarket carb brass parts?

[jakec]

So at idle all 4 cylinders are matching and it idles nicely. All pipes were equally hot. To bring down the pressure reading on #2 I want to screw the adjuster IN correct? For more cable play? That's what I did, until the adjustment was maxed out.

I never ever let the valve adjustment be too tight. I always err on the side of too loose. I measure with an .003" gauge (spec) and then confirm with a .004" to make sure I am not too loose. Sometimes the .004" if it just barely fits, I will leave it as is.

I don't have any aftermarket parts aside from floats which are the solid plastic type. And it's not a constant leak but a burp kind of leak, where suddenly a bit of gas will come out the hose, and then nothing for the next 10 minutes.

[jakec]

The pic indicates that #2 cyl is not contributing much. You need to adjust it's cable and or slide. Is #2 cyl firing? Check the #2 exhaust pipe to see if it's hot.

Can you explain what you mean by not contributing? I thought the high reading means throttle is wide open. Is that not the case? It seems counter to what's happening which is backfiring (rich mixture, throttle too closed)?

This is so funny because I rode the bike about 100 miles prior to this process, and the only problem was a high idle and slow to warm up. So I've probably just been doing something wrong with the cable adjustments.

[Scootch]

In this case high vacuum means that a cylinder needs to be made to "contribute" more by increasing it's throttle command. You do that by adjusting the cable at the top of the carb. When the throttle is completely closed there is supposed to be 1mm slack with the cable at the top of the carb and the thing that determines idle vacuum is the idle mixture and speed screws. As you roll on throttle other elements start to take effect. However each throttle cable has to be adjusted such that each slide opens the same amount and at the same time. You have to get the cable adjustments at the top of each carb set such that as you actuate the throttle each slide moves in sync and the same amount. The cable adjustment at the top of the carb and the idle speed interact so you have to have patience and develop a feel for it.

[jakec]

The vacuum port is behind the throttle. And the piston is moving up and down making vacuum. So a high vacuum is due to the throttle being closed? Be opening the throttle allows ambient air into the vacuum port, lowering the overall pressure reading?

So to lower the vacuum reading, I need to reduce cable slack in this instance? Am I understanding correctly?

[Ujeni]

The fuel coming out of the overflow tube for the 2nd carb seems like a clue to me. I would double check your float heights and mixture settings.