Timing Questions

[BillyRok]

I currently have 2 XJs, my daily rider and another that I picked up cheap last fall and have rehabbed over the past months. Mine doesn't seem to have the same acceleration as the other one when I crack open the throttle. It is completely stock in terms of exhaust, air box, and carbs (which were broken down completely, run through the ultra sonic, butterfly shaft seals replaced, stock jetting, float heights correct at 23mm and verified with clear tube), then bench synched / vacuum synched, and valves are shimmed properly. Bike #2 has a Mac 4-2 with turn outs, stock air box, and the carbs got the same treatment as bike #1, valves shimmed properly. I'm not sure if the jetting in #2 is stock as I stupidly never bothered to look at them closely when I had them apart.

The one major difference is my bike has the 850 FD while #2 has the stock FD...but here is how I compared the acceleration between the 2 bikes. Bike #2 runs 3500 rpms @ 55 mph in 5th gear and pulls pretty well when I hit the throttle. I compared that to my bike at 3500 rpms in 4th gear to compensate for the taller gearing in the FD, and it makes more noise when I open it up but it doesn't have the acceleration that #2 has.

So now I'm wondering if maybe my timing isn't advancing properly on my bike? Here is what the service manual says, 5 degrees BTDC @ 1100 rpm and 36 degrees BTDC @ 5500 rpm --

[IMG][/IMG]

This shows how to check the timing and where it is supposed to be at idle --

[IMG][/IMG]

My timing plate --[IMG][/IMG]

So how do I verify that the timing is really advancing to 36 degrees BTDC at 5500 rpm? The vacuum advance is controlled by a small sensor under the tank, has a vacuum line that connects to #2 carb body and wiring connector that goes into the harness to the TCI. The change in vacuum at varying rpm must alter the electrical signal sent to the TCI?

Anybody know how to verify proper advance? Or think that something else might be causing the sluggish acceleration?

On a side note, when I removed the timing cover I found a small amount of oil inside the cover --

[IMG][/IMG]

Does this mean the crank seal under the timing plate is going bad? Thanks for your thoughts.

[3Phase]

Billy,

Yep, the oil seal is bad and should be replaced.


Do you have a timing light, a vacuum pump, and a multimeter?

Checking the timing would be simple if you have an adjustable timing light. If you're feeling adventurous, you can take the wheel off of the engine and use a protractor to mark it at 36 degrees and 50 degrees.

If you're not up for pulling the wheel, I made a quick and dirty degree wheel with your picture so you can guesstimate the timing:-



Look at the picture and mark the Timing Wheel at 36 degrees.

Start the engine and check the base ignition timing at idle.

Watch the timing light while you run the engine up to 5,500 RPM, the ignition should advance to the mark you made at ~36 degrees.


Use the vacuum pump and the multimeter to check the Vacuum Sensor:-




This part isn't in the manual so it may not work!

If you want to see how much advance the TCI will add all by itself without the Vacuum Sensor, disconnect the vacuum line and plug it, then run the engine at 5,500 RPM.

To see how much advance the Vacuum Sensor and the TCI add together, put the vacuum pump on the sensor and bring the sensor to 200 mmHg (~8 inHg), then run the engine at 5,500 RPM.

If the XJ1100 all-electric ignition timing is similar to the XS1100 electrical/analog system, the sensor should have the TCI add 15 to 18 degrees of advance when it's all-in and the total advance will be between 50 and 55 degrees at 5,500 RPM.

Have fun!

.

[CaptonZap]

Geeze Scott,
Is your math right? 50 to 55 sounds like a lot. The compression would only be around 40-60 PSI on the compresion stroke when the thing fired.
Most of the things I have played with don't do well above 35-40 deg.

Hers something I picked up off the net;

http://www.hotrod.com/how-to/engine/...m-performance/





"Here is a basic set of curves showing what ignition timing does to combustion-chamber pressure. The pressure curve is critical to getting the most power from each combustion cycle. Curve 1 shows a smooth, deep curve while Curve 2 represents too much ignition-timing advance showing pressure spikes, probably caused by uneven combustion, which could lead to parts failure. Curve 3 represents ignition timing that has too much retard in it and is relatively flat, resulting in lost power. Ideal timing results in good power."

Scroll down and there is a chart/ graph with some interesting numbers.

Ping me if I'm wrong, pun intended.

CZ

[3Phase]

It isn't a load test, it's an ignition system function check!

The ported vacuum will consistently give you max advance during light, part throttle and at deceleration right when the throttle plate closes. The ported vacuum signal drops on hard acceleration so the engine won't ping. The signal comes up again after you've made the jump to lightspeed and your cruising so, yes, I'm sure about my math!

I'm not sure about the timing specs for the '81H/SH or the '82XJJ.

The '78 is 10 degrees base + 26 degrees mechanical @ 4,750 RPM + 16 degrees of vacuum advance for a possible 52 degrees of advance.

The '79 is 5 degrees base + 31 degrees mechanical @ 5,400 RPM + 16 degrees of vacuum advance for a possible 52 degrees of advance.

The '80G/SG is 5 degrees base + 30 degrees at 3,900 (plus or minus 300) RPM + 15 to 17 degrees of vacuum advance for a possible 50 to 52 degrees of advance.

I don't have the specs for the '81H/SH but it's 5 degrees base and it should be close to 30 degrees (?) of advance with the 4RO TCI instead of the mechanical advance + ~15 to 17 degrees (?) of vacuum advance for another possible 50 to 53 degrees of advance.

The timing chart for the '82 XJJ shows 5 degrees base and 36 degrees at 5,500 RPM. I think the vacuum solenoid is left connected but I'm not 100% positive. There is very little ported vacuum signal for the advance even at 5,500 RPM so it doesn't really matter, you have 36 degrees + ?? degrees of vacuum advance from the vacuum solenoid and the 10M TCI. If it's even close to the XS1100 ignition timing numbers, it should be another possible 50 to 55 degrees of advance.

.

[mack]

timing plate

That is the most useless timing plate I've ever seen. Glad I don't own an xj. But didn't I see someone using a generic degree wheel about five years ago after a rebuilt. Or, was that just to find TDC after putting the cases back together?
Scott & Cap: what you guys are talking about is well above my knowledge base. I think thats why I would rather have an old pre-electronic car where you can recognize whats under the hood, and fix most things with a crescent wrench, screwdriver and a hammer. Now the mechanic's only know how to plug them into a card reader and follow the computer instructions.
Good luck Billy, your clutch has been serviced on that dude right?

[3Phase]

Even though there's not much ported vacuum signal at 5,500 RPM when the bike is sitting on the centerstand, I wonder if the XJ's 10M TCI ignores the vacuum sensor above ~5,000 RPM. The fine manual has a voltage test for the vacuum sensor and checking the ignition timing at 1,100 and 5,500 RPM would let you verify TCI's base and RPM-based advance without unplugging the vacuum sensor. Or I could be full of malarky and TCI technology wasn't that smart back in the '80s.

I agree, that timing wheel is horrible but the reluctor is part of the wheel. You can't take it off and use a degree wheel because the ignition won't work.

'78 to '80 is just like a car or light truck with transistorized ignition. You could work up something to replace the reliable reluctor and TCI with points and condenser so it would be 100% analog, then you can hit with a hammer and screw with it with a screwdriver -- every other day or every 500 to 1,000 miles as the points wear and get funky above 5,000 RPM.

.

[crazy steve]

Scott's math is right on.... Vacuum advance contributes almost nothing to 'performance' but is basically there to improve part-throttle fuel economy/emissions. At higher speeds/small throttle openings the fuel mixture is lean so running more advance give the lean mixture time to fully burn. You could disconnect the vacuum advance and probably never notice the difference except for how often you need to stop for fuel... LOL.

Seeing how the XJ ignition is fully non-adjustable, you might want to look at the cam timing. A tooth off on one or both cams will affect performance. Check your valve lash while you're in there too, you may have some tight valves...

[trbig]

As was said, you have no mechanical advance on the XJ. Mack says it's the most useless timing plate he's ever seen and glad he doesn't have an XJ. Made me laugh. It's idiot proof and that's why it's awesome. No fussing or messing or bearings moving mechanical timing plates with wires to flex and break.

You have a boost sensor that sits under your tank on the left side of the frame hooked to your #2 carb body with a small vacuum line. This changes your vacuum from a mechanical thing to an electrical thing and is what tells your TCI to advance/retard the timing. Nothing moves on your timing plate. It's all done electronically. You can unplug that line from the sensor to the carb, cover the hole the line was connected to with some electrical tape or something, then ride the bike and see if that changes anything. These boost sensors sometimes go bad. Sometimes it's just a leaky rubber vacuum line.

But your test should be pretty accurate. The 850 FD in 4th is almost exactly the same gear ratio as the stock FD in 5th. That being said, you can have two of these bikes side by side, same everything, and one will just be faster than the other.

[BillyRok]

I hooked up a timing light today, got 5 degrees at idle and 36 degrees at 5500 rpms (close guesstimate using Scott's degree wheel, thanks!), couldn't check it with the sensor unplugged 'cause the motor was too hot to reach in and disconnect it. I knew there was no way to adjust the timing but am wondering if the total advance is supposed to be higher than 36 degrees, like it sounds may be the case with a '78-'80 XS? Tod do you know what the total amount of advance is on the XJ?

Mack the clutch plates were all within spec and I put Barnett springs in it.

Steve the valve clearances were checked and shimmed about 3,000 miles ago. Not to reopen this can of worms but when I did the valves and the ACCT, I discovered the cam gears appeared to be bolted to the cams a half turn off...when the dots on the cam were up the cam gear bolt holes with the pointers were down. I posted my findings and quite a discussion followed. I can't remember for sure but I may have put it back together the way I found it so my timing could be off a bit. And I could be off a tooth maybe. Only way to know is pull the valve cover...man I hate doing that! It will be middle of next week probably before I can get to it.

[mack]

Idiot proof?

I still think they could have put the appropriate timing marks on it. If it wasn't for guys like Scott, no one would know how to check them.

[TopCatGr58]

Little Thread Hijack

Seeing how the XJ ignition is fully non-adjustable, you might want to look at the cam timing. A tooth off on one or both cams will affect performance. Check your valve lash while you're in there too, you may have some tight valves...

Hey Steve,

Little Hijack here. I had a new member writing to me in the ADMIN email.

1979 XS110 Special 7700 miles.(yeah, they never rode it)
ignition timing is off, idles advanced at 20degrees, and no more adjustment. :/
cleanish plugs- correct gap 28-31, no cracks in the wires, clean connectors, pick up coil gap good, pick up wire mod done.
coil ohms reading were:
primary 1.5 and 1.5
secondary 28K and 26K with the caps on. 15.9K and 16.1K with the caps off.
(getting green dynatek 3ohm coils)
cap ohms ranges were 4.8, 4.89, 4.9, 4.4
(getting all new 5ohm caps)
mechanical advance taken apart, cleaned and lubed to try and remedy the problem. no change.

A friend who has one with 46,000 miles on his keeps telling me i skipped a tooth on the cam chain.
it sounds fine, no blow back, no sputtering, no back fires, no misfires.
Since the cam and cam chain do not run the ignition(it runs off the crank) how could that possibly cause a 10 degree advance???

Thanks for your help.
Mike

Now, I didn't ask him about any carb work....I know if they aren't properly synched, that can cause them have a high idle...and that could cause the cent. adv. to adv. a little.

My question is that IF the valve timing is off a tooth, can this cause an unadjustable high idle/timing advance of 20 degrees as stated above??

T.C.

[trbig]

Will keep my mouth shut.. lol..

Not for sure, but I thought the 36 deg was max.. but don't quote me. Apparently your boost sensor is working or it wouldn't be moving at all.

[crazy steve]

Hey Steve,

Little Hijack here. I had a new member writing to me in the ADMIN email.

Now, I didn't ask him about any carb work....I know if they aren't properly synched, that can cause them have a high idle...and that could cause the cent. adv. to adv. a little.

My question is that IF the valve timing is off a tooth, can this cause an unadjustable high idle/timing advance of 20 degrees as stated above??

T.C.

No, the valve timing won't affect the actual setting of the ignition timing. A high enough idle will start to bring in the mechanical advance though. And having the intake cam off by a tooth or two would affect how the motor runs, maybe enough to cause the problem. Other possibilities are the 'key' on the mechanical advance that indexes the timing plate is damaged so that the timing plate isn't indexed right or damaged/defective springs on the mechanical advance.

[TopCatGr58]

Thanks for the info Steve,

Apparently the fellow saw this post, but replied to me via the Admin email again, he solved it. Apparently he had been PO'd....the PO had cross wired a few wires at the TCI....once he fixed that it runs right now.

T.C.