This is a weird one...

[dbeardslee]

So a bunch of us have been working on Varnae's bike (81 SH) over the past several months. We swapped the engine, reworked the head on the new one, cleaned, adjusted, and synced the carbs, and straightened out some mismatched ignition parts (mechanical advance vs. rotor). Primary and secondary resistance on the ignition coils are in spec and the high tension wires have been replaced (stock 3 ohm coils), and Randy Rago's TCI quick test says it's OK. Pickup coils are in spec, and the wires look good. The problem we're having is that, under load, the engine refuses to go past 4.5k, except for one brief interlude when it took off almost like it's supposed to. We checked the timing (which was of the fixed variety) and it was advanced by 15-20 degrees. We drilled out the tamper proof bolts, and made it adjustable. With a timing light on it, no matter how far we moved the ATU, we could not get the pointer to align with the T mark on the timing plate. We checked the cylinder for TDC to insure that the pointer is properly adjusted, and it looked OK using a long screwdriver in the #1 plug hole as a gauge. Cam chain is properly installed and aligns with the marks properly. All four header pipes are showing about the same temp (checked with an IR thermometer). Compression is good. Even though it tests out OK on the quick test, I'm still wondering if the problem is in the TCI. I'm also wondering if the cam chain could be a tooth off at the crank (I don't trust the pointer 100%), or would that bend valves? Any ideas?

[Silent]

Just a thought, but I've had small engines run in a similar fassion. Turned out to be a clogged exhaust systems. Cleaned out the exhaust, and they ran like new.

[randy]

dbeardslee,

When setting ignition timing with a timing light, you're looking to line up the 'F' (for firing) mark, not the 'T'. And the vac advance hose must be disconnected from the vac canister and plugged.

Just to double-check what you wrote, you have a 4RO TCI with no mech advance, just the plain rotor, right?

On the pickups, make sure the gap is correct. a wider than spec gap can cause missing at high rpm's. The closer the rotor is to the pickups the stronger the signal it generates. POINT 7 mm is the spec (.7). POINT 5 is better. DAMHIKIJK

[Steptoe]

timing

JMHO, if the chain is out the cam marks won't line up with crank.
One tooth out won,t bend valves I've found but it won't run great either though.
Can you work it thru the 4500 to go better or is that as far as it will go?

[dbeardslee]

Randy - This 4R0 timing plate doesn't have an 'F' mark - just a T and something that looks like a musical note to the left of it. Maybe the musical thing is a substitute for the 'F' mark. At any rate, I can't adjust the timing far enough to get on either one of them. It actually sounds like it runs better where the original non-adjustable ATU was set. Timing was set with the vacuum advance disconnected and plugged.

Thanks for the heads up on the T though. I had Betsy set on the F mark, and read somewhere (at least I think I did ) to set it on the T, so I changed it. I checked the manual again, and there it was as big as life, just like you said. Looks like I've got another one to set the timing on.

On the pickup coil gap, I took the pickups off a 2H7 ATU, and put them on the 4R0 unit, as that one had a bad wire. I set the gap at .61 MM. On mine I have them set to .56 MM, but with the wide pointer on the 4R0 rotor I thought I would leave it slightly wider than mine, but still closer than .7 MM.

The reason he had it over here was because it had had the mechanical advance where it shouldn't be, and the first thing we did was replace it with a plain rotor. Funny thing is, it ran about the same with the mechanical advance as it does with the rotor.

Silent - Judging from the billows of smoke that were coming out of the exhaust, I'm relatively certain it isn't restricted . The exhaust system is much newer than the bike, and it appears to be a mac 4/2. IIRC Varnae just bought it not long ago. I stuck some wires down into the tubes to feel for restrictions when we swapped the motors, and it doesn't leave any debris behind the exhaust, so hopefully that's OK.

Steptoe - When we put the head back on all the marks were properly aligned. The chain had been replaced somewhere down the p.o. line, and it was actually in pretty good shape. It had stretched a little, so the dots weren't perfectly on the arrows - very slightly to the outside on both, but not enough for it to be one tooth off. Compression was checked afterwards and it was 155 150 145 150 IIRC, and that was after it ran for a while, so I'm pretty confident about the upper marks.

On the lower mark, it was on the T, which has me wondering if the pointer is located properly. It still has paint on the bolt head, and you can tell it's never been out, and it doesn't appear to be bent, so maybe I'm all wet on that thought. The other thing that's kind of strange is it doesn't draw as much vacuum on a sync gauge as other XS's I've done. Most of the time they're right around 22 CM of vacuum at 1k rpms. This one only draws about 16 CM.

[DGXSER]

another voice in the crowd

I happened to be over helping Doug with this demon spawn of an XS.

To add to his input, I ran the compression check on it a few weeks back after the head work was completed. and the numbers he posted are what I recall taking. Darn close for sure.

We did note some black almost oily liquid coming out of the exhaust on the 1-2 side. I checked both plugs and neither shows any sign of oil in the cylinder. Perhpas it is loadin gup with gas enough to run into the exhaust and loosen the carbon that may be in there to make the black stuff that runs out the joint sin the exhaust system??

As to the timing and setup, as Doug mentioned, I took a long screwdriver and put it into the no 1 plug hole sitting on top of the piston and found the top of stroke and noted that location on the timing plate as about 3/16" before the T mark, then noted the start of the piston dropping and it was likewise about 3/16" AFTER the T mark. So the T mark is within a 1/16" or less of center of the top of stroke on no 1 piston. (Checked it twice at least).

Like Doug stated, we tried rorating the timing plate and it never got to where the T mark lined up. And as stated, it seemd to run better throughout the RPM range wiht the timing closer to original setting.

I think we need the exorcist to stop by!!!

[DGXSER]

Additional Info

Ok, I went to the mancave and did soem investigation on my 4RO SH.

The timing plate had only the C mark and the T mark, next to the T mark is a U shaped mark open end pointing outward from the center.

Attached timing light (Just realized as I am typing this I forgot to remove vac advance ). Anyway, at idle speed of about 11-1200 RPM the timing is right at the far end of the U away from the T mark. As it advances, it moves counter clockwise away from the T or further from the T.

When we had the demon spawn SH hooked up, it was idleing at about twice the advance (with the vacuum removed) as mine gets to at 4-5K RPM! Like we stated, we feel confident the T is lined up for TDC of no 1 piston.

[dbeardslee]

I'd like to take the valve cover off and verify that the chain is still lined up with all the marks. I don't see how it could have changed, but who knows. I'll feel better if I look at it again . Assuming that everything is where it's supposed to be, I'm wondering if a faulty TCI could cause these symptoms, but still pass the quick test. Randy?

Carl wasn't sure if he'd be able to bring it back down next weekend. He's got some tests coming up, and he's got that newlywed thing going on, so it might be a week or three.

[DGXSER]

Thinking out loud

Yeah I know, Thinking, got to get me in trouble doesn't it.

Anyway, the way I see it is this, The rotor is attached to the end of the crank by the key way. No way to get it in wrong, correct?? And the plate goes on with no way to get it wrong or offset. And the timing plate goes on and cannot be on wrong, save maybe 180 off.

Now the pickup coil sends voltage to the TCI which sends voltage to the coils, as the pickup coil opens when the rotor hits it, it breaks and no longer sends voltage to the TCI. So the TCI signals the coils by dropping voltage and that causes the high side to send the spark to the plugs, both at one time for the coil.

So, the engine may run like crap if the cams are off from the crank by one tooth, but the timing will not change. Only options I can come up with so far is the TCI is signaling the coils crazy, the plate we have is off another bike.

I did notice the vac advance on my bike seems to have a longer arm on it than the one I think I saw today.

[DiverRay]

Take a CLOSE look at the pickup coils!!!! The 4R0 units MAY have the metal pickup bit located in a DIFFERENT PLACE than the 2H7 units! I am NOT sure about this, but with what you are saying the symptoms are, that would be my #1 guess.
Do I win the free beer if I'm correct???

[DGXSER]

Ray,

I watched Doug set the pickup clearance and I am certain I saw him measure where the metal piece is at. It was the left side fo the pick up coil on these. But anything is worth checking again, and even again at this point.

And if you guess correctly and help get this fighter to comply and run correctly, I'll but you a pitcher or two!!

[dbeardslee]

Ray - According to the fiche the pulsar coil assemblies are all the same, 78-81. I wound up using the coils and the housing that were on the bike and the bearing assembly from the 4R0 since it had the larger slot for the rotor pointer. I tried two different timing plates - the 4R0 and a 2H7. Although the markings are different, the T is in the same place, and the timing light showed the same thing with both. Funny thing is, it runs about the same as it did with the mechanical advance and the other bearing assembly. I was almost hoping you were right about the pickups as I would gladly send a beer to the guy who figures this one out. Of course I'd charge it to Varnae, though .

I've got to learn to type faster . When I set the pickup gaps I did it with the pointer on the pickups centered on the rotor pointer. The pointer on the rotor is rounded and about four times wider than it is on the earlier models, and it looked like the point that passes closest to the pickups was in the center, so that looked like the place to set it.

[thewiz]

Might have missed it, but are the carb slides lifting all the way? Diaphrams and jet needles correct for the carbs?

[dbeardslee]

We had the carbs apart a couple months ago when we swapped motors. All the parts were checked when we cleaned them, and everything looked OK. I initially had the same thought, but throttle inputs seem to have no affect on the 4.5k barrier. I even tried messing with the choke while riding it and could get no change in the problem. Kind of makes me doubt that fuel is the problem, particularly with what we're seeing in the timing. Everything keeps pointing to something in the ignition.

One thing that bears mention is the fact that somewhere, sometime, somebody rewired this bike. It looked to be a pretty good job, but who knows. All the tests we've run on the ignition components looked good. I did notice that we were only getting about 11.5V at the TCI, but that should be enough. Didn't check the regulator/rectifier though, and another post suggested that as a potential culpret for this type of problem. Might be worth a look. The only way I know to test it is to check the voltage at the battery at idle, and again when it's over 2200 rpms. Should show 12.5V at idle and somewhere around 14.2V when it's over 2200. Anybody know a better test?

[The Lorax]

Doug, you mentioned that it doesn't pull as much vacuum as others on the sync gauges. is it possible that there is not enough vacuum being pulled to lift the slides sufficiently or at all? just a thought, maybe there is a vacuum leak somewhere or something of that sort that is causing this odd issue. that's all I got, have a nice day and ride safe