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

[jakec]

I was switching the hose around to all of the different input spots on the meter and the problem would follow it around. so I'm pretty sure it is the hose. Also I have the brand new/NOS valves and seats just installed. And floats are also new and recently verified at 26mm.

[69cb750]

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?

Yes

Opening the throttle allows ambient air into the vacuum port, lowering the overall pressure reading?

Yes

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

It is important all four cables have the same amount of slack at idle so all four slide move up and down in unison.

[Ujeni]

I was switching the hose around to all of the different input spots on the meter and the problem would follow it around. so I'm pretty sure it is the hose. Also I have the brand new/NOS valves and seats just installed. And floats are also new and recently verified at 26mm.

Great!

If your float valves and seats are new, then the spitting is likely due to dirt in your carbs not allowing them to seal closed.

[jakec]

I was wondering if it could be due to some combination of the vent orifices or hoses, and the fact that it's on the 2 line petcock. because the burps are coming from the 3 & 4 carbs which are on the same fuel line. So maybe it could be that air in lines or vapor lock could be holding fuel back, and then pressure is equalizing suddenly and allowing some gas to come through before floats react?

Dirt in carb is certainly possible but I've been in there a few times recently and I don't think it's the case, unless it's inside one of the internal passages (has happened to be before on a 350).

[jakec]

The fuel comes out of the drain tubes (usually one or the other) very suddenly about a teaspoon or less (more than a few drops, it's a stream). Then it stops just as fast. And happened every few minutes while doing the sync.

[Scootch]

My K0 has a tendency to pee a little bit out of the carbs sometimes. I think it happens bcz of change in baro pressure and or temperature. It seems to happen whether it's on the center or side stand. But seems to be more so when it's on the side stand. I also put a block of wood under the side stand so it doesn't lean over so far.

[jakec]

I received the new vacuum hose but it was too loose for the restrictor. Even tho it’s supposedly the same ID as the Morgan tubing, 5mm. I ended up just eyeballing it by swapping hoses around. Revving up and down and maintaining 1/4 throttle feels fine.

So then I went for a ride and adjusted the idle mixture screws to 1.5 out to bring the idle back down to around 1k. Rode around a bit more and got the highway. I can rev it all the way up and went about 80mph before I realized my speed (was looking at the tach lol). However the power felt a bit laggy and soft, not throwing me off the bike when I grabbed the throttle. Also there was noticeable backfire on decel constantly.

So I figured it must be overly rich, but checked my plugs (very old ND plugs) but they are looking more on the lean side. I got some new plugs so I can diagnose it better later. Not sure what to think for now tho.

[jakec]

Better pic. Who knows how old these plugs are, but #2 actually was a little wet with fuel.

[RAFster122s]

Backfiring is generally always a lean condition

[jakec]

I had never heard of backfire being from lean condition. It is mild/quiet “bub bub bub” on decel. But it’s consistent. And got worse when I leaned out the idle to bring it down.

I had previously got the idle set right at 1k with the spec’d pressure on the sync gauge. But on the stand with the fan running it never got “truly” hot like after a ride. Then I had to bring the idle down with mixture screws.

Should I have left the mixture at 1 turn out and turned out all the idle screws (the ones that move the pistons up)?

These carbs are so annoying. I set my k1 carbs in 10 minutes and have been putting 1000s of miles on them. Lol

[jakec]

I just got the idle dialed in. It’s still running lean in the upper range though. Above 4-5k rpm the power is lacking.

I’ve seen the chart of the 3 carb models that they put on these bikes and the different jetting they did, ranging from 100-120 I think? I have 110s. And I have all stock parts. I also confirmed all my needles are in the middle position. But im definitely lean. Im wondering if there’s anything else I should consider before I look into the carbs and consider jetting?

[PeWe]

Lean from 4-5k rpm on 5th gear?
Sounds like needles for me.
1 step higher, 4th from top should fix it.

Richer mains too, but probably too rich at higher speeds then.

[jakec]

Not in 5th gear, I was only in first and second gear due to the area I'm riding in. I would agree about the needles. I have moved the needles on my chopper which has K1 carbs and it made a great difference moving only one notch.

[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?

Looking back at this post I have the needles in the 3 position. So I will go to position 4.

[jakec]

I want to say it’s all figured out. The bike is running well. I haven’t checked the plugs yet but it feels good. I will check them after a few more miles. Here’s a pic of the bike. Wish that seat foam was available… oh well

Oh yeah, I also installed new genuine fuel lines and hose clamps. Not sure how that would have any effect, but there was no more gas leaks on the ride yesterday.

[jakec]

Fourth ride on the bike since last week. When the bike has been started in the last 24 hours it's great. When it sits for a few days it's hard to warm up. It doesn't want to move under load but it also won't warm up until I start riding it. So I just take off with it chug chugging, after about 30 seconds it's good go. I wonder if I need to be riding it a few blocks with choke on. I've never done that on a bike (I have another 750 with K1 carbs and it doesn't need this).