Cam Timing Woes... Maybe?

[GoldenEye]

Morning all!

I’ve been using the advice on this forum for the past 3 years while putting back together/building my ’73 that I bought in pieces, but I’m stuck now (have been for ~2 weeks) so I’m hoping someone has a word of advice and the patience to read this novel I seem to have written.

Bike:

’73 frame
’72 motor
’74-‘75 BS38 Carbs (4N8 needle, unlinked, choke on left side only) with floats set at 24mm and mix screws at ¾ turn, bench synced with sighting to a light and then thin strip of paper.
K&N pods with cut down stock headers that reach the foot pegs and have homebrewed baffles

New:
All gaskets and O-rings
Cam chain
Valve stem seals (valves were lapped before reassembly)
Wiring (strung it myself)
PMA conversion with Banshee rotor
JBM Industries carb mounts and diaphragms

Updates:
Pamco ignition, mechanical advance
Dual output coil from Mikes (17-6903 High Output)
Upped pilot jets from 45 to 47.5 (1 size and genuine jets from local dealer)
Upped mains from 127.5 to 132.5 (2 sizes and genuine jets from local dealer)

Engine specs:
Compression is 170/165 on the right/left respectively
Capacitors charge at 14.4 volts when the bike is running
Fuel is 93 octane running through an inline filter off a newer and freshly coated alien tank

Where I am stuck:
Rebuilt the engine, got it back in the frame, set cam chain tension to flush, buttoned up with valve lash set to .006 intake and .012 exhaust, set Pamco to center of adjustment area, then fired it up and put a timing light on it. It ran long enough to time it (had to move almost all the way advanced, CW) but it didn’t WANT to run. I pulled the carbs, cleaned them from top to bottom (except the throttle shaft which I am doing when I get a chance in the next few days to get some JIS screwdrivers for the plate screws) using the almighty carb guide (HUGE thanks to all who contributed) and put it back together and still no dice. It sounds okay for maybe 10-15 seconds and then does what I can only describe as “woofing” through the carbs with a nice cloud of fuel vapor coming out of the throat before it dies. It also coats the carb throat in what looks to me like a mix of carbon and fuel since I can wipe it out with a shop towel and the residue is dark and smells like gas.

Now, I took quite a bit of time to read through the forum and try to make sure my cam is positioned correctly in relation to my crank and I have found the following.

Started by finding TDC with my homemade piston stop, “precisely” super glued a printed degree wheel to my rotor which you will see in a hot minute, and determined that my handiwork had fetched me a TDC at about 1° on the degree wheel (can’t adjust, super glue…) at which time I also took a picture of the cam pin position on the ATU side of the bike.

At TDC

• GoldenEye
• Apr 25, 2017

ATU at TDC

• GoldenEye
• Apr 25, 2017

From here you can see it is NOT at 12 O’clock, marked out with my nifty earplug string and some duct tape setup, so I proceeded to move the crank in 5° increments (2.5° at the cam) to see where it became vertical.

So here is the picture at 5° ATDC

5 Degrees

• GoldenEye
• Apr 25, 2017

ATU at 5 Degrees

• GoldenEye
• Apr 25, 2017

10° ATDC

10 Degrees

• GoldenEye
• Apr 25, 2017

ATU at 10 Degrees

• GoldenEye
• Apr 25, 2017

15° ATDC

15 Degrees

• GoldenEye
• Apr 25, 2017

ATU at 15 degrees

• GoldenEye
• Apr 25, 2017

And finally 20° ATDC which is where, if I understand correctly, one tooth forward would be if I moved the cam

20 Degrees

• GoldenEye
• Apr 25, 2017

ATU at 20 Degrees

• GoldenEye
• Apr 25, 2017

To me, the 5° ATDC seemed like the closest to vertical I could get but being that that is ~2.5 degrees at the cam I would think this would be okay right?

But after seeing this, and reading some more, I went out and bought a dial indicator and decided I was going to find out once and for all if that cam was in the right position. With the new tool, a harbor freight special, I took measurements and this is what I got for the intake lobe center.

Lobe Centers

• GoldenEye
• Apr 25, 2017

While they aren’t perfect, 5/6 come out within a standard deviation and the only one that does not is the 104 measurement. The spec for the 256 cam intake as far as I can tell is 100°, so I am about 2° retarded at the crank or 1° at the cam right? This seems to tell me that I am in the right tooth position on the cam, but the only explanation I can convince myself of is that the “woofing” of the fuel vapor through the carb throat is from being a tooth off and having my intakes open/close late which keeps the valve open during compression.

Has anyone seen this before or have any thoughts on the matter? I am about at my wits end with this bike, but I love it too much to give up and buy anything else so I’m hoping someone/anyone was willing to read through all of that and hopefully tell me what I am missing?

Big thanks in advance,
GoldenEye

 

[retiredgentleman]

When you installed the camshaft, there are 3 reference marks that must be lined up. A slot on one side of the cam that is at approximately 12:00. A punch mark on the other side of the camshaft, that must aline exactly with the top surface of the head.
The TDC mark lined up on the alternator. Did you use all 3 marks?

 

[B Burdine97]

Being 1 degree off at the cam should not affect your motor that much, expecially if your running points because you are able to advance or retard the timing to compensate for that. I recently was reading a post where 2M showed that one of his older bikes had stretched the cam chain enough to through off timing 15 degrees I believe! (could be wrong, but I remember it was a lot) And he said it was still running... Decently.. I hope I can find that thread again. You cannot be off a tooth on the cam because that would cause you to be 20 degrees off at the crank, not two. The 2 degrees that your off would normally be from a stretched cam chain, but you said you have replaced the chain. Also you said you have the cam chain tensioned correctly so I'm kind of stumped. I would think your points could compensate for this..

 

[5twins]

Yes, I think you've got the cam "clocked" right, or at least the best it can be. Moving the cam one tooth either way would throw the pin off much more than it is in your 1st pic. These were mass produced so I suppose it's possible your cam sprocket isn't in the exact best position. Pressing it off and moving it a little may be your only solution if you wanted to get the valve timing closer. But, I don't think the small amount it's off should be giving you the problems you're having.

 

[grizld1]

First off, congratulations on taking the right kind of measurements in the right kind of way.

Yamaha specifies .012" lash as the inspection setting for all valves when checking valve timing. At that setting, with a stock XS2 cam, the intake valves should begin to open at 47* BTDC and should close completely at 67* ABDC. The later 447 cam (1974 and later) is also inspected at the very start of the opening event and the very end of closing, with lash at .012" with spec timing as IO=36* and IC=68*.

I don't know how to interpret your numbers. Your opening event looks very close to 447 spec. with the sprocket 1 tooth off. Taking a reading on final closure is very tricky, especially on a slow ramp cam, which is why most cam manufacturers specify reading the valve events at a defined lift, usually .040" or .050". I suggest that you take a reading on exhaust valve openings. You may have a 447 cam with an early sprocket mounted on it. For the early cams, EO=60*BBDC, EC=41*ATDC. For the later cams, EO=68*BBDC, EC=36*ATDC.

 

[xjwmx]

Cam Timing Woes... Maybe?

We will find out. On one end of the camshaft there's a hole. With the crank tdc the hole should be practically vertical. If you were off one tooth the distance from vertical would be something like 360/no. of teeth on cam sprocket = a lot. If it's not off anywhere close to that amount the timing is right. With the head cover off my suggestion is tdc the crank so that the mark on the cam sprocket is vertical-ish. Then ask yourself if you were to move the sprocket by one or more teeth in either direction would the mark be more vertical? If not then it's timed as well as is practical.

 

[GoldenEye]

Sorry for the long wait, posted this on lunch at work and just got home and went out and took a few more measurements to double/triple check.

RetiredGentleman - In my almighty wisdom, and as a slow learner, I set the notch in the side of the sprocket at its nearest point to vertical without checking the dimple in the other side and am now just realizing this mistake might've been made because of how remarkably awful the bike runs.

Burdine97 - I'll have to see if I can find that thread since my main worry is that if I am already past the theoretical 100° perfect position/12 o'clock mark that cam stretch will pull me even farther and I will not be able to time the bike since I'm almost already out of CW rotation on my pamco plate!

5twins - I'm thinking its right too, but man I was actually secretly hoping it wasn't so I would have a reason that I could point at as to why the bike is running like this!

grizld1 - went out and redid the cam lobe centers because I wasn't checking them last night to a specific lift (pure laziness honestly), just the same lift on open and close to find the center. I set the lash to .012 and got an IVO of 49° and a IVC of 73° which seem to say that I am in the right spot for a 256 cam. Then I checked them at .050 lift and got IVO at 17° and IVC at 38°, but the screenshot I have saved from the Bob Bertaut article only has numbers for the 447 cam so I'm not sure if those are appropriate (although they do say my lobe center is 100.5 which pretty well matches what I got yesterday).

Finally xjwmx - those first two pics sure lead me to believe I am in the right spot as far as the hole for the pin is concerned, I just don't like that I am already setting the pamco towards the full CW position when, in the long run, this new chain will stretch and retard the timing so sooner rather than later I will run out of rotation and be SOL.

To ALL of you, first off thank you for taking the time to help the new guy who is probably doing something stupid which is making his bike run like a turd. Second, anyone have any ideas as to what might be causing the bike to run so poorly if it isn't the cam position?! I forgot to mention that I am also in the second spot on my needle, per what I think I need with my open headers and pods, and just as a shoutout for the wealth of knowledge here I also just did the "elephant's foot" mod with the feet from CB Performance and hopefully I will really notice the difference when I actually get to ride this thing again!

 

[xjwmx]

just don't like that I am already setting the pamco towards the full CW position when, in the long run, this new chain will stretch and retard the timing so sooner rather than later I will run out of rotation and be SOL.

If the bike cam timing looks good, but you're about to run out of adjustment on the Pamco then the Pamco or its installation is wrong. I don't know what that could be though. Don't know Pamcos.

 

[grizld1]

GE, I don't know what to tell you re. the Pamco. Right, your timing plate is at full advance, and if you were installing a Boyer or Probe ignition I'd tell you to move the rotor in the camshaft and reset the plate. I've never used a Pamco and don't know if you can adjust it that way.

Re. the bad running, have you put a strobe to the ignition at idle? If the motor won't idle long enough for you to take a look, here's a bit of treachery you can try if the electric foot will spin the motor. Remove the plugs, put the caps on them, and ground them firmly to the motor, with the inductive pickup attached. Then have someone push the starter button while you observe. You can also turn the crank with a wrench and look for the flash of the timing light. The mechanical timing unit may have stretched the advance curve, and the ignition may be firing too close to TDC at idle. If you find that issue there's plenty available on fixes; search and you'll find.

Don't apologize! You're working with tools and procedures that are new to you and you're doing a fine job of thinking things out. Continue the march!

 

[B Burdine97]

I agree with grizld1.
I just went back and re-read your first post. You say it will run fine for 10-15 seconds before it starts "woofing". I would hook up the timing light and look at your timing at idle before it starts "woofing", if your able to do so quick enough. And then right as it begins to start woofing see if the timing changes or stays the same. Is this woofing something that would be able to be heard in a video?
Please keep us updated!

 

[GoldenEye]

Unfortunately there isn't an electric foot on this old beast of burden, just a kicker and my boot! I will try to have someone (read: unwilling girlfriend ) roll it over while I watch the spark and strobe, hopefully that'll work... Also, I will grab a video of it tomorrow afternoon and see if I can't get the sound. If I had to try and explain it further, its like the motor is spinning backwards and kicking the vaporized fuel out of the carb throat like the firing is happening at a point where it can kick the piston back down and reverse the engine rotation? I might just buy new springs and cogs for the ATU since I shortened the springs last summer and they might just not be up to par anymore.

I will report back tomorrow with a video of the noise/bike actions and hopefully we can get this resolved so the ol' lady can get back on the streets!

 

[hmusket]

Just throwing out as a question, l don't know the answer, could a 447 cam chain work on a 256 engine? If it could then maybe you were sent the wrong replacement.

 

[grizld1]

No, hmusket, the pitch is different, so you can't play mix-'n'-match with the chains.

GE, just use a socket and extension on a ratchet and turn the beast over by hand with plugs in the caps and firmly grounded (not in the holes, you don't want to risk the beast starting while you're holding a wrench on the crank!) Wrench in left hand, light in right hand, turn CCW. You don't have to spin the crank fast, just turn slow and look for the position of the marks when the light flashes.

 

[TwoManyXS1Bs]

I love the degree wheel on the rotor.
But, this requires a bit of reverse logic regarding ignition timing.
You'll want idle fire when -345° aligns with the TDC arrow.
And, full advance fire when -320° aligns with the TDC arrow.

I'm thinking that the 'woofing' may be "wasted spark" backfire on the overlap cylinder, an ignition timing issue.

To bypass this potential "wasted spark" interference, you could pull a plug, ground it to the engine, leave that cylinder open. Try to start/run on the other cylinder...

 

[5twins]

..... which would put the zero at the "Fire" or "Advance" marks.

 

[grizld1]

That would be my guess too, 2M. GE, after you've checked marks at idle, clip a bob weight to its tab to hold the ATU at full advance and check the marks again in that mode. My guess is that you'll find a wider interval between retard and advance than the spec. 25* (full retard=15* BTDC, full advance =40* BTDC). You won't get a very accurate reading off the brief flash of the strobe light, but you'll get close enough to tell if the advance curve has stretched significantly.

 

[pamcopete]

I'm thinking that the 'woofing' may be "wasted spark" backfire on the overlap cylinder, an ignition timing issue.

To bypass this potential "wasted spark" interference, you could pull a plug, ground it to the engine, leave that cylinder open. Try to start/run on the other cylinder...

The wasted spark is per cylinder. There are two sets of magnets on the PAMCO rotor spaced 180 degrees apart so a spark is created twice for every rotation of the cam, or once per revolution of the crank so a spark occurs on each cylinder 15 degrees BTDC at idle every revolution of the crank including both the compression and exhaust stroke. The spark on the exhaust stroke is the wasted spark. You can try loosening the nut holding both the PAMCO rotor and the slotted disk on the advance side and then hold the rotor clockwise as you tighten the nuts. This will take out the free play and provide you with a tad more advance if that is what you need. Do the opposite to get a little more retard if needed.

Also, don't forget to check for the presence of all three locating pins on the cam. The one that many people miss is the pin that locates the advancer itself.

Although I see from your pics that you used this pin for a reference when checking the timing.

 

[GoldenEye]

Alright folks, the video is here!

The bike does the fuel push through the carbs ("woof") fairly regularly, as can be seen, but it also kicks fuel back when the ignition is not on, so is the intake valve somehow open when it should not be?! I should also add that I do not touch the throttle through this entire video, the bike is changing RPM's all on its own at this point.

And as far as checking the timing by spinning the engine over, figured out I can't do that with a capacitor setup so I guess I will have to find a battery somewhere and hook that into the system before I can try that

 

[pamcopete]

Alright folks, the video is here!

The bike does the fuel push through the carbs ("woof") fairly regularly, as can be seen, but it also kicks fuel back when the ignition is not on, so is the intake valve somehow open when it should not be?! I should also add that I do not touch the throttle through this entire video, the bike is changing RPM's all on its own at this point.

And as far as checking the timing by spinning the engine over, figured out I can't do that with a capacitor setup so I guess I will have to find a battery somewhere and hook that into the system before I can try that

Well, somehow I missed the fact that you are using a capacitor. I would recommend that you use a fully charged battery with the PMA and regulator disconnected. I think you will find that it works correctly that way indicating a problem with the PMA and /or regulator. We could spend several days and a dozen or more posts about why that is, but it's just simpler to do it that way and then trouble shoot the PMA regulator.

 

[B Burdine97]

GoldenEye I can honestly say that i have never seen something like that before.. Im really trying to think out of the box and am thinking out loud here so please no judgement. Could a restriction in the exhaust causing extremely high back pressure cause this? I noticed you said you have "homebrewed baffles" in your pipes that are cut off at the foot pegs. I would then think that the stuff coming out of the carbs would be mostly exhaust fumes, but Im not sure exactly what is coming out of the carbs to start with. I noticed that every time it shot whatever it is shooting out of the carbs, the idle speed would slow down, and immediately afterwards it shoots stuff out pf the carbs, the idle speed seems to return to a more normal idle speed. These observations lead me to a conclusion of, could there be an exhaust restriction in your baffles that restrict enough exhaust fumes which then begins to choke the engine out, shooting fumes out of the carbs, until there is so much back pressure it finds a way through that exhaust restriction for a split second, thus then reducing exhaust back pressure allowing the engine to return to a normal idle speed. This being a quick reoccurring process of course explaining why it seems that the idle speed reduction and spitting fumes out of the carbs almost seems to have a sort of rythm to it.
Are the baffles fiberglass packed?
Once again, thinking out loud here and out of the box..