Wanted...2 Stroke Ignition Timing Lesson

[Jason2tpa]

Either the Yam service manual procedure for checking timing is missing steps or not exact, or I'm missing the required brain cells to understand this procedure. See attachments.

I'm getting stumped on the very 1st-3rd steps..."turn flywheel clockwise and align timing plate and specified mark". If the specified mark refers to the manufacturers straight line mark on the underside of the flywheel....when this mark is align with the timing plate arrow, it's impossible for this mark to also align with the base assembly mark when the magneto control lever is fully advanced. What the heck?...this makes no sense.

Timing lesson 101...who's up for teaching?

[panasonic]

Jason turn the flywheel until the 25 degree BTDC mark on the outside surface of the flywheel lines up with the timing mark, which is a little metal tab shaped like an arrow held on the block with a single screw.

Then push the magneto control arm all the way until it hits the full advance stop. Look up underneath the edge of the flywheel and see if mark "a" on the flywheel is lined up with mark "b" on the timing plate base. That is full advanced.

I don't see how your timing could be off if you never touched it.

[Jason2tpa]

Aahh, so "specified" mark refers to the 25° BTDC mark. Thank you sir. Having some what I redkon to be fuel related issue after pulling carbs dor new kit install. After reinstall and sync i lost power. So just wanted to also check timing before I load test.

[Jason2tpa]

....and at full retard with the arrow at 5° ATDC the notch under flywheel should align with mark on timing base. Correct?

[99yam40]

If you are doing this because I mentioned checking timing,
I meant to put a timing light on the motor and see where the light indicates the cylinders are firing at .

If the timing is off according to the light then do some adjusting.

I did not realize this old motor was mechanical linkage.

but either way when you are done checking this all I would still put a timing light on it to make sure you know where it is sparking.
you can fine tune as needed

[panasonic]

....and at full retard with the arrow at 5° ATDC the notch under flywheel should align with mark on timing base. Correct?

Yes correct. Do you have a timing light? Nothing wrong with doing a static timing test but a live one would be much better.

Is the timing plate moving smoothly back and forth, no sticky spots or wires binding it up.

I really don't think timing is your trouble Jason.

The engine worked fine BEFORE you took the carbs off and rebuild them. So it is only logical to think that this problem was self induced. In aviation we call this a " self induced snag" it happens all the time because we are pulling stuff apart that is working perfectly fine to do required inspections and tests...sometimes mistakes are made and stuff goes back together wrong. Thats why we test the crap out of everything.

I would go back over everything you did, with a fine tooth comb, with your carbs...I believe the answer lays there. Look at your new parts as well..are they correct for your engine...ect.

Let us know how you make out with it.
.

[boscoe99]

Yes correct. Do you have a timing light? Nothing wrong with doing a static timing test but a live one would be much better.

Is the timing plate moving smoothly back and forth, no sticky spots or wires binding it up.

I really don't think timing is your trouble Jason.

The engine worked fine BEFORE you took the carbs off and rebuild them. So it is only logical to think that this problem was self induced. In aviation we call this a " self induced snag" it happens all the time because we are pulling stuff apart that is working perfectly fine to do required inspections and tests...sometimes mistakes are made and stuff goes back together wrong. Thats why we test the crap out of everything.

I would go back over everything you did, with a fine tooth comb, with your carbs...I believe the answer lays there. Look at your new parts as well..are they correct for your engine...ect.

Let us know how you make out with it.
.

Does the "bathtub" curve come to mind?

There are several Yamaha manuals wherein they say something to the effect of "if it ain't broke don't go trying to fix it or big troubles will happen". Carburetor adjustments being one of them.

[Jason2tpa]

Panasonic...I couldn't agree more. After installing new kit and experienced the issue, i pulled carbs and jets again, reassembled, still had issue. Def not the kit causing the issue. Human error is possible, of course. However, I've done this PM in particular numerous times w/o issue.

Replaced plugs last nite (2 yrs old). Top 2 plugs looked good. Bottom port had what looked like wet brown rust at base of plug. Bottom starboard plug pictured. Tip of electrode shortened and thinned. Possible spark wasn't jumping the widened gap. Ran out of time after installing new plugs...didn't load test.

[99yam40]

Panasonic...I couldn't agree more. After installing new kit and experienced the issue, i pulled carbs and jets again, reassembled, still had issue. Def not the kit causing the issue. Human error is possible, of course. However, I've done this PM in particular numerous times w/o issue.

Replaced plugs last nite (2 yrs old). Top 2 plugs looked good. Bottom port had what looked like wet brown rust at base of plug. Bottom starboard plug pictured. Tip of electrode shortened and thinned. Possible spark wasn't jumping the widened gap. Ran out of time after installing new plugs...didn't load test.

I would like to see this wet brown rust on the plug.
could mean water in cylinder

[zenoahphobic]

Panasonic...I couldn't agree more. After installing new kit and experienced the issue, i pulled carbs and jets again, reassembled, still had issue. Def not the kit causing the issue. Human error is possible, of course. However, I've done this PM in particular numerous times w/o issue.

Replaced plugs last nite (2 yrs old). Top 2 plugs looked good. Bottom port had what looked like wet brown rust at base of plug. Bottom starboard plug pictured. Tip of electrode shortened and thinned. Possible spark wasn't jumping the widened gap. Ran out of time after installing new plugs...didn't load test.

Woh, plug gap huge, how would that motor run to get it to that stage? High voltage (obviously was able to jump) will now find another path.

I don't know what the phyc term is, but humans cannot perform any task EXACTLY the same again and again; we get bored and become creative consciously and subconsciously. Women specifically suffer from this inability! We also get frustrated by our subsequent strong belief that we either are positive that we didn't do anything wrong, OR we believe we are complete idiots.

I use camera on everything, before, during and after to relieve the pressure on memory. Changing the speed at which you check things and laterally think helps; eg. so I would not check pulling the carbs the same way (expecting a different result this time).

[Jason2tpa]

Bad plugs was the issue. Back to running like a champ. Appreciate all the support.

[panasonic]

Glad to see you found your problem. That plug is in hard shape. Funny how we lead on along a path from past experience, you had some acceleration trouble and went straight for the carbs as being the culprit...probably from past experience. If you pulled the plugs first, the easiest thing to do, you would have found the trouble right away. Lesson learned...always check the easy things first. I have been lead down that path many times!!

Now what has caused that plug to be eaten away like that would be my next question. I would keep a close eye on that cylinder and check the plug every few hours and monitor it's condition....compare it to the others as time goes by.Something is different about that cylinder.

I take it your static timing check was OK?

[Jason2tpa]

You're spot on Pano. Should of checked the plugs. And I will keep an eye on that cylinder for sure.

Re: timing
Btw, my flywheel marks TDC1 and TDC2 w/numerical knotchs and DC3 and DC4 w/out knotchs. TDC1 was like -6 at full retard. TDC2 was 20/22 at full advance. Soo that needs adjusting. At least I figured out the fuel issue, which wasn't a fuel issue. I'll need to tackle the timing next. Appreciate ur support.