Verifying Ignition Timing Marks

Short of removing the outer primary cover and setting up a degree wheel, is there any way to verify the accuracy of the timing marks on the outer cover?

Although my MK II starts easily and seems to have good low and midrange power, it falls off above 5000 RPM and falls on it's face at 6500 in 3rd gear.

With 260 main jets and peashooters it should be jetted properly, but on a 200 mile ride last weekend the guy I was riding with observed black smoke when I pushed it hard.

I purchased a timing light at Harbor Freight yesterday and confirmed that it does work with my ignition setup.

Unless your bike is modified, why would you expect it not to fall on its face at 6500rpm? That’s way past peak power.

Taking the primary cover off is very easy. Finding TDC through the plug hole is quite accurate if you’ve a steady hand and take your time. Then using a protractor, you can mark the stator at the required degrees of advance, then rotate your engine accordingly so the rotor mark aligns with your stator mark, then re-fit the cover and see if the marker plate lines up.

Of course, this is not guaranteed to be as accurate as a dead stop and degree disc, but if you‘re careful you’ll be close, and certainly close enough for what matters for these engines.

Fast Eddie said:

Unless your bike is modified, why would you expect it not to fall on its face at 6500rpm? That’s way past peak power.

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By "falls on its face" I mean it's like it hit a rev limiter. I would expect it to fall off but not just quit pulling all together.

Dan1950 said:

By "falls on its face" I mean it's like it hit a rev limiter. I would expect it to fall off but not just quit pulling all together.

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Try it in second gear. It'll rev. But the torque monster is at it's best below that. It's why I run a 22 cog, using the mid range torque.
I held my 850 WFO for twenty miles Friday.
270 mains

Dan1950 said:

By "falls on its face" I mean it's like it hit a rev limiter. I would expect it to fall off but not just quit pulling all together.

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A stock 850 does tend to feel a bit like that

concours, do you normally get deposits like that on the electrode? its hard for me to tell but some of those little balls look a lot like aluminum in that picture.

Dan1950 said:

By "falls on its face" I mean it's like it hit a rev limiter. I would expect it to fall off but not just quit pulling all together.

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If yer got tired valve springs, could be valve float and / or bounce.

But I wouldn’t worry about it, there just no advantage to being up at those revs… but plenty of disadvantages…!

Fast Eddie said:

If yer got tired valve springs, could be valve float and / or bounce.

But I wouldn’t worry about it, there just no advantage to being up at those revs… but plenty of disadvantages…!

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Well. I neglected to share the fact that the bike will barely break 90 MPH in 4th gear.

My 250 Sprint would do that.

Dan1950 said:

Well. I neglected to share the fact that the bike will barely break 90 MPH in 4th gear.

My 250 Sprint would do that.

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Thats a slightly different issues isn’t it as the bike will be no where near 6500rpm at that point!

Your bike sounds very similar to mine before I rebuilt it, but mine had a single Mikuni, which I blamed.

You have twin Amal’s right?

So sumthins not quite right IMHO. Could be fine tuning of timing, carbs, etc, could be sumthin serious like shot bores or cam or etc…

Dan1950 said:

Well. I neglected to share the fact that the bike will barely break 90 MPH in 4th gear.

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What front sprocket?

My stock 850 use to run out of puff at 6500 rpms wouldn't rev any higher in any gear it was more like valve bounce, but after rebuilding the motor for the Featherbed frame, balanced crank, cam build up and grind to Combat specs, major head porting (still run original valves) and a shaved head, 40 oversized pistons and a tight final hone bore to piston, carbs jetted up, running a Joe Hunt maggie that produces a big spark and open pipes with just a little baffle to give it that back pressure it needs, my HOT motor will rev freely way past 7000 rpms, infact it would keep reving till it went bang so got to watch it but I don't let it rev that hard these days, was good when I was young and silly, but no need to pull to 7000 rpms these days, but it gets up there really quick and with a super light bike its a lot of fun and surprises a lot of modern bikes and riders.
Best way to do timing is with a degree wheel as timing marks can be out as the keyway bush could be out with wear even new rotor's could be out with the marks, I only use the timing marks for satic timing and I don't use a timing light as well the JH runs full advance from kick, low revs to full revs and retard it till no kick back when kicking it, my Norton starts first kick every time even after sitting for some time and once fired up first time for the day will fire up on 1/2 swing on the kicker, I also did this when running EIs over the years and my last Boya EI for 32 years.

Ashley

dorset said:

concours, do you normally get deposits like that on the electrode? its hard for me to tell but some of those little balls look a lot like aluminum in that picture.

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No I don't.

Dan1950 said:

Well. I neglected to share the fact that the bike will barely break 90 MPH in 4th gear.

My 250 Sprint would do that.

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GPS? Or Bermuda Triangle brand clocks indicated?

The only way a Sprint (and I use that term loosely) 250 would do 90 mph is if it was pushed out the back of a C130.

At one point I was running a Dunstall 2-1-2 exhaust with a 19 tooth sprocket on my '73 850 and in fourth gear I would have to roll off the throttle around 110 mph to avoid revving past 7000 rpm so something is not right. Black smoke usually indicates a too rich mixture.

Agree - my stock 850 will easily rev to 7k though I realize there is no useful reason to go there...but I do anyway once in a while...remembering my old, original 19 tooth, '71 750!

Over rich main jet or blocked air filter will do exactly what you describe. Over advanced ignition will do the same but can heat up the plug to make it look lean and give it little spots of aluminium.
Dave.

Are those 260's really 260's, a lot of knock off Amal parts were made in the past, main jets included, and the number stamped on them was just a wild guess. Also if your needle and needle jets are worn the rich mixture from 1/4 to 3/4 throttle will impact acceleration so by the time you get to full throttle its too late to gain speed.

cash said:

Over rich main jet or blocked air filter will do exactly what you describe. Over advanced ignition will do the same but can heat up the plug to make it look lean and give it little spots of aluminium.
Dave.

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We have a winner.

The initial reading with the strobe light showed ignition retarded off the scale. A static check with the Tri-Spark indicated 20* BTDC.

Setting the static timing at 29* BTDC yielded adout 22* with the strobe light.. That would suggest that the initial timing was running at around 13* BTDC.

After setting the timing at 29* BTDC with the strobe, the bike now runs much quieter. Energy that was going out the exhaust is now being used as rotational force. Starts just as good or better than before and the idle is less choppy, less shake in the Isolastics below 2800 RPM. At 65 MPH I can barely hear the exhaust while cruising.

Overall a great improvement.

As far as the A/F ratio? That will be the next step. The Amals are in like new condition, no wear or scoring on the slides. I'm hoping to see if the additional spark advance will improve fuel economy. I was hovering around 42 MPG but the bike seems to pull so much easier now.