Determining which carb is leaking

[tom203]

Yeah - I figured there'd be some interpretations of my little Rorschach test.


So basically, even a little spitting back into the airbox is indicative of a problem?


That sounds like something would impact all the carbs which seems to match the symptoms. What can create back pressure?

I'm going to go way out on a limb here. IF ( and this is big IF ), the intake cam was off by one tooth, then the intake valves would not be closed soon enough as spark ignited. This would result in back pressure thru carbs, especially at lower speeds; it would be less a problem as rpm's went up as the carbs are moving air/fuel mixture quicker and it's harder for the flow to reverse due to momentum. Now , I will get another beer!

 

[scott]

I'm going to go way out on a limb here. IF ( and this is big IF ), the intake cam was off by one tooth, then the intake valves would not be closed soon enough as spark ignited. This would result in back pressure thru carbs, especially at lower speeds; it would be less a problem as rpm's went up as the carbs are moving air/fuel mixture quicker and it's harder for the flow to reverse due to momentum.

Hmm - that doesn't sound good. Is that something I could have messed up doing the valve adjustment?

Not sure if this is useful or related but on a ride today, it started getting a very low idle / stalling at idle. This happened a few weeks ago on a very hot day (I wasn't sure if the temperature was a factor). It wasn't hot today but I was riding at 50+ MPH for a bit. I pulled over and tried to adjust the idle screw but it didn't seem to make a difference. I basically had to hold the throttle on slightly while waiting for lights to change to keep it from stalling but I made it home at least. I tried starting it up to see about tweaking the idle screw and it wouldn't stay idling so I just let it sit. Several hours later it did start with the choke. I'll have to revisit the idle screw adjustment the next time I get the bike warmed up.

Since people always mention the petcock (even though mine is a practically new OEM model), I took off the tank and tested it to rule that out. No fuel by default, fuel when the prime screw is loosened, fuel when I suck on the vacuum hose. I tried blowing on the vacuum hose at first but that didn't do anything. So, the petcock seems fine.

I also tried checking the voltage drop between the battery and the coil connectors (taking stabs at things to test). With the key on, the drop was ~1.5V at one connector, and ~0.5 V at the other. I wasn't sure how to test it with the connectors attached to the coil. I was kind of surprised it was different at the 2 coils though. From what I've read, this voltage drop could get worse when hot which may relate to my low idle / stalling issue. I should have measured this right when I got home I guess. Since the fuel in the airbox isn't dependent on the engine being very warm, I'm guessing it's not related.

Now , I will get another beer!

Enjoy - thanks for all your help!

 

[cowboyup3371]

How many turns out are your mixture screws?

 

[scott]

How many turns out are your mixture screws?

I started at 3 turns out and tweaked from there. I didn't note how much I turned each mixture screw from 3 though. I wasn't able to get a noticeable change on some of the carbs so I wasn't positive I got it right.

I'll try resetting them today when I do the idle adjustment after I get the bike warmed up on a short ride. Are you thinking I have a rich condition? Other than smelling gas (like when the choke is on), I'm not sure how a rich vs lean condition behaves.

Maybe I should bite the bullet and get a Colortune. At this point, I'm not sure if I have serious problems with the bike though (see possible intake cam issue mentioned above) so I'm hesitant to spend a lot of money.

 

[cowboyup3371]

Yours sounds more lean than anything much like what mine did.

 

[scott]

Yours sounds more lean than anything much like what mine did.

Oh! I guess I'll try them at more than 3 turns out. I would think making it richer would cause more fuel to go to the airbox but I wouldn't know.

I tried to re-do the vacuum synch (homemade manometer with bottles of water, tubes, etc.). It never seems to work quite like it's supposed to - I wind up having to tweak all the adjusters. When I try to do the Carb 2/3 adjuster, then 1/2, then 3/4, it never seems to work. It always seems to throw the Carb 2/3 out of synch and I have to go back and forth to all of them (as opposed to setting Carb 2/3 and leaving it).

I got them close - to the point where water wasn't being pulled by any carb. I wouldn't say it was idling super-smooth. I couldn't really drop the RPM to 900 to do the Highest RPM mixture setting. Also, revving the engine would show the carbs were not in synch at higher RPMs but I assume that's not unusual. And of course, it was dripping fuel out the airbox during this.

I'll take another stab at the vacuum synch / mixture screw setting.

 

[scott]

And of course, it was dripping fuel out the airbox during this.

Correction, I assumed it was fuel because that's what has been dripping out of the airbox after rides. It actually seems more like dirty water is dripping out of the airbox during the vacuum synch. Huh? Water isn't being sucked into the vacuum ports, but maybe condensation from the bottles is? Is this hurting anything or indicative of something?

 

[tom203]

Correction, I assumed it was fuel because that's what has been dripping out of the airbox after rides. It actually seems more like dirty water is dripping out of the airbox during the vacuum synch. Huh? Water isn't being sucked into the vacuum ports, but maybe condensation from the bottles is? Is this hurting anything or indicative of something?

So during this homemade vacuum synch, water is finding it's way to airbox? This can only be from your synch setup and still means that some pressure is forcing air/gas/water back thru carbs throats- wrong direction! When you did your valves, did you have to go change shim thicknesses by a large margin on intake side? I don't think this is an electrical problem and an idle stop screw that appears to do nothing still points to a mixture problem. Is this a new-to-you bike or an old friend?

 

[scott]

So during this homemade vacuum synch, water is finding it's way to airbox? This can only be from your synch setup and still means that some pressure is forcing air/gas/water back thru carbs throats- wrong direction!

Yes - condensation seems like the only possibility (water boiling in the bottles I guess). I definitely didn't see water going up the vacuum hoses - it really shouldn't be possible unless all the water went into 1 bottle which I didn't let happen.

When you did your valves, did you have to go change shim thicknesses by a large margin on intake side?

Here's my shim changes on the intake side (my exhaust valves had larger shim changes).

Position      Original (Shim; Clearance)    Current (Shim; Clearance)
IN #1         2.64mm; < 0.04mm              2.59mm; 0.08mm
IN #2         2.67mm; 0.05mm                2.61mm; 0.10mm
IN #3         2.70mm; 0.05mm                2.67mm; 0.08mm
IN #4         2.58mm; 0.05mm                2.56mm; 0.08mm

I don't think this is an electrical problem and an idle stop screw that appears to do nothing still points to a mixture problem.

Just to clarify, my idle adjustment screw normally has an effect. It was just when I had the low idle/stalling at idle problem the other day, adjusting the screw had no effect / didn't prevent it from stalling. Today when trying to do the synch, the idle screw definitely did something.

Is this a new-to-you bike or an old friend?

New-to-me in Feb/March (my first bike). Obviously I am very inexperienced with this stuff so I really appreciate the help. The bike has < 8K miles but I don't know much about its history.

 

[tom203]

Yes - condensation seems like the only possibility (water boiling in the bottles I guess). I definitely didn't see water going up the vacuum hoses - it really shouldn't be possible unless all the water went into 1 bottle which I didn't let happen.



Here's my shim changes on the intake side (my exhaust valves had larger shim changes).

Position      Original (Shim; Clearance)    Current (Shim; Clearance)
IN #1         2.64mm; < 0.04mm              2.59mm; 0.08mm
IN #2         2.67mm; 0.05mm                2.61mm; 0.10mm
IN #3         2.70mm; 0.05mm                2.67mm; 0.08mm
IN #4         2.58mm; 0.05mm                2.56mm; 0.08mm

Just to clarify, my idle adjustment screw normally has an effect. It was just when I had the low idle/stalling at idle problem the other day, adjusting the screw had no effect / didn't prevent it from stalling. Today when trying to do the synch, the idle screw definitely did something.

New-to-me in Feb/March (my first bike). Obviously I am very inexperienced with this stuff so I really appreciate the help. The bike has < 8K miles but I don't know much about its history.

You're gaining experience ! You did the valve adjustment (and kept a record!), so you're doing fine. However, with an unknown bike history, there's new stuff to explore. This spitting into airbox is strange- you've correctly ruled out petcock-, so I think you have to check the camshaft to crankshaft timing, just in case someone screwed up. I recall seeing info maybe on a link from Basscliffs, but I haven't done this myself yet. It involves putting the crankshaft on TDC and making sure both camshafts are in correct position- this likely means counting chain links between intake and exhaust camshafts. Hopefully someone with experience will chime in and explain. It would be nice to rule this out as a problem.

 

[cowboyup3371]

Honestly, set your screws at 3 turns out and get rid of that homemade manometer. Get a decent one and test your settings again. Afterwards, set your idle at 1500 or 2000 and adjust your screws by the highest idle method listening and watching for that needle to move.

 

[scott]

I think I'm missing something. First of all, the Clymer manual says for 82 models and earlier to line up the mark to the left of the T for the TDC mark. Mine has a mark to the right of the T (and no mark to the left).

My pics didn't come out great for some reason:

My pic doesn't look exactly like the the Clymer manual so maybe I don't have a stock unit? It does look newer than 30+ years.

Also, with the marks lined up as above, my chain doesn't seem to be lined up anything like the manual. It's definitely not in a position for me to count the pins between 2 and 3.

I must have screwed up somewhere so I'll do some more reading. Anyone have any tips? Or is this indicating something is wrong and is causing my back pressure issue?

 

[scott]

Reading the Clymer manual and the service manual from BassCliff, I didn't see anything obvious (other than my TDC markings don't seem to match). The service manual does say "While holding down the timing chain, rotate the crankshaft" which I'm not sure what they mean but it is in the re-assembly section so I was assuming it's because the crank sprockets aren't installed yet.

A side note, this is what my spark plugs looked like while I have them out checking the cam chain. If this is only showing the last state of the engine, it was doing the vacuum synch so it's showing the idle state (unless they're so badly charred that my recent mixture changes are not showing). The plugs are only a month or two old if that's relevant. If I'm reading this right, Carb #1 is lean, Carb #2 is ok, Carb #3 is ok, Carb #4 is rich.

 

[scott]

I found a post in another thread that seems relevant:

Remember - 4 cycle motor, so the cams CAN be 180 out, give it another rotation (I assuming you did this) to see if something lines up

So I rotated it until the 2 was near vertical and noticed that there was a different notch on the ignition plate so I lined those notches up. It seems closer at least. Here is the ignition plate position (it looks slightly misaligned in the pic but maybe that's the camera angle):

And here is how the sprockets look:

I count roughly 23 pins, not 20. Could it be this far off and still run?

 

[tom203]

I think I'm missing something. First of all, the Clymer manual says for 82 models and earlier to line up the mark to the left of the T for the TDC mark. Mine has a mark to the right of the T (and no mark to the left).

My pics didn't come out great for some reason:

My pic doesn't look exactly like the the Clymer manual so maybe I don't have a stock unit? It does look newer than 30+ years.

Also, with the marks lined up as above, my chain doesn't seem to be lined up anything like the manual. It's definitely not in a position for me to count the pins between 2 and 3.

I must have screwed up somewhere so I'll do some more reading. Anyone have any tips? Or is this indicating something is wrong and is causing my back pressure issue?

Your signal generator looks like the ones on the 80 550 (later models had hole cutout, instead of big slot) "T" mark is TDC for #1 and #4 unless the japs are out to confuse me (very likely!). My clymer manual for chain drive 650 indicates 19 pins ( between mark 2 and 3 ) but 20 pins for shafty 650- I will take a wild guess and say that the 550 and chain drive 650 are identical.-but I often leap to conclusions so beware. That pic you show of chain with mark 1 facing forward and mark 2 vertical, is that with crankshaft on "T" mark ? Looking at that pic it seems to me that mark #3 should be about vertical and 19 pins from #2, not 23 pins. Would it run? apparently yes! Intake camshaft appears to running behind. What does this mean? At bottom of piston travel after intake stroke, piston reverses and starts to compress mixture, but intake valve has to be closed or the mixture can shoot back thru intake valve and then thru carbs.
Are we having fun yet???

 

[scott]

Your signal generator looks like the ones on the 80 550 (later models had hole cutout, instead of big slot) "T" mark is TDC for #1 and #4 unless the japs are out to confuse me (very likely!). My clymer manual for chain drive 650 indicates 19 pins ( between mark 2 and 3 ) but 20 pins for shafty 650- I will take a wild guess and say that the 550 and chain drive 650 are identical.-but I often leap to conclusions so beware.

The manual seems to indicate it should be 20 pins.

That pic you show of chain with mark 1 facing forward and mark 2 vertical, is that with crankshaft on "T" mark ?

No, that's with the crankshaft on the "F" mark. I assume that's 180 degrees off but according to Big T's post in the other thread, that may not be a problem (could be wrong).

Looking at that pic it seems to me that mark #3 should be about vertical and 19 pins from #2, not 23 pins. Would it run? apparently yes! Intake camshaft appears to running behind. What does this mean? At bottom of piston travel after intake stroke, piston reverses and starts to compress mixture, but intake valve has to be closed or the mixture can shoot back thru intake valve and then thru carbs.
Are we having fun yet???

Hehe - well it's looking like you were right about the cause of the problem! Pretty impressive! I have to wonder how it would have gotten so far out of alignment though. It's not clear to me how to get it into alignment either. The stuff in the manual seems to be coming from the perspective of having everything disassembled. Is that what I'm going to have to do? I hope not.

I'm wondering if I should post a new thread in the Engine/Drivetrain/Clutch - while I thought I had a carb overflowing problem it seems to be something else entirely.

 

[tom203]

The manual seems to indicate it should be 20 pins.


No, that's with the crankshaft on the "F" mark. I assume that's 180 degrees off but according to Big T's post in the other thread, that may not be a problem (could be wrong).


Hehe - well it's looking like you were right about the cause of the problem! Pretty impressive! I have to wonder how it would have gotten so far out of alignment though. It's not clear to me how to get it into alignment either. The stuff in the manual seems to be coming from the perspective of having everything disassembled. Is that what I'm going to have to do? I hope not.

I'm wondering if I should post a new thread in the Engine/Drivetrain/Clutch - while I thought I had a carb overflowing problem it seems to be something else entirely.

If manual says 20 pins, so be it- it that's wrong, one of the gs members should have dove in by now and said otherwise. So, your intake camshaft is running behind. Someone probably fiddled with it years ago, and left you to fix it. The cam chain tensioner is an odd device- if not installed correctly (with lock screw released ). the chain would be too loose and could skip on the gear, but who knows. Low mileage, so chances are good that this is an old problem causing poor running.
If you removed the cam chain tensioner, I don't know if there is enough slop in chain to let you relocate chain on gear. Remove all spark plugs, and turning the 19mm nut on crankshaft, you might be able to do it. Usually, you should only rotate crankshaft clockwise, but with tensioner removed, you maybe could rock it back and forth to get more slack. And you got valve spring tension to add to fun!

First bike, keep up the good work! next bike will be alot easier!