No Start

[manicmechanic]

Video....

Yeah Dennis, I went to the link too and saw the simple video explanation on the way the stroke works. It does only show one cylinder, but the easy way to understand it is by looking at a crankshaft. If the two sparked at the same time, then the part of the crank where you attach the connecting rods to the crank, would be equal. They aren't. When you take off the heads to any engine, including the 4-TEC, then you'll notice pistion position is different on every cylinder. Except a V-8 engine. In the V-8, two pistons are up TDC at the same time. But being a 4 stroke, that means, one is at the power stroke, the other is at the end of the exhaust stroke.
Look at a crankshaft you have around your garage. Notice the stager in the area where the pistons connect. By theory, it would be impossible to balance a motor if both cylinders sparked at the same time.

 

[Dennis]

Engines And Ignitions

MANICMECHANIC,
So you know, DAWG is not new to the world of the internal cumbustion engine. I've got over 35+ years experience working on 2 and 4 stroke engines for a living and I'm well aware of how they work internally. Like you, I also owned my own shop and have spent countless hours repairing motorcycles and jet skis'. Having said that, here's what I found out this morning about the subject we have on SeaDoo 2 cyl. 2 stroke non- fuel injected ignition.
A customer of mine gave me access to his 1999 SeaDoo Speedster. It has twin 787 carb engines. I removed the spark plugs from both engines, brought #1 (front) piston to TDC and marked the PTO at the rear of the engines. I then reinstalled the spark plugs and put the plug wires back on in the factory position. I ran both engines a little bit and was satisfied with their performance. I then reversed the plug wires on both engines. I restarted both engines and again they ran just fine. I then reinstalled the plug wires back to the factory position and hooked up my timing lite with the pick up on #1(front) cylinder and pickup arrow pointing towards the plug. Restarted the engines and was able to see the timing mark I made on the PTO. I then installed the pickup on the #2 ( rear) cylinder plug wire with the arrow on the pickup pointing towards the spark plug and proceeded to look for the mark on the PTO but the timing lite would not blink. I connected the pickup to the rear cylinder plug wire so that the arrow was facing away from the spark plug (pointing towards the coil) and then the lite would blink and I could see the mark on the PTO. The results were the same for both engines.
All of this has led me to these conclusions:
Reversing the plug wires will not cause the engine not to run because the spark plugs fire at the same time. That is why I could see the #1 TDC timing mark on the PTO with the pickup on #2 plug wire.

The post by ROBIN about waste spark is probably correct.
Current flowing out of the coil, thru one plug wire, across the plug gap, thru the cylinder head, across the other plug gap, thru the wire and back to the coil. This would explain how both spark plugs fire at the same time and why I had to reverse the arrow direction on the timing lite pickup in order for the timing lite to work on #2(rear) cylinder. This method of firing spark plugs in engines that have 2 spark plugs per cylinder has been used by the auto makers for years.

DAWG

 

[robin savell lloyd]

that is unbelievable but I will take your word on it

wowwwwww. you go dawg. great post. from what i understand there are many other engines that use this idea. I hear that it is less costly to make.

 

[robin savell lloyd]

MANICMECHANIC,
So you know, DAWG is not new to the world of the internal cumbustion engine. I've got over 35+ years experience working on 2 and 4 stroke engines for a living and I'm well aware of how they work internally. Like you, I also owned my own shop and have spent countless hours repairing motorcycles and jet skis'. Having said that, here's what I found out this morning about the subject we have on SeaDoo 2 cyl. 2 stroke non- fuel injected ignition.
A customer of mine gave me access to his 1999 SeaDoo Speedster. It has twin 787 carb engines. I removed the spark plugs from both engines, brought #1 (front) piston to TDC and marked the PTO at the rear of the engines. I then reinstalled the spark plugs and put the plug wires back on in the factory position. I ran both engines a little bit and was satisfied with their performance. I then reversed the plug wires on both engines. I restarted both engines and again they ran just fine. I then reinstalled the plug wires back to the factory position and hooked up my timing lite with the pick up on #1(front) cylinder and pickup arrow pointing towards the plug. Restarted the engines and was able to see the timing mark I made on the PTO. I then installed the pickup on the #2 ( rear) cylinder plug wire with the arrow on the pickup pointing towards the spark plug and proceeded to look for the mark on the PTO but the timing lite would not blink. I connected the pickup to the rear cylinder plug wire so that the arrow was facing away from the spark plug (pointing towards the coil) and then the lite would blink and I could see the mark on the PTO. The results were the same for both engines.
All of this has led me to these conclusions:
Reversing the plug wires will not cause the engine not to run because the spark plugs fire at the same time. That is why I could see the #1 TDC timing mark on the PTO with the pickup on #2 plug wire.

The post by ROBIN about waste spark is probably correct.
Current flowing out of the coil, thru one plug wire, across the plug gap, thru the cylinder head, across the other plug gap, thru the wire and back to the coil. This would explain how both spark plugs fire at the same time and why I had to reverse the arrow direction on the timing lite pickup in order for the timing lite to work on #2(rear) cylinder. This method of firing spark plugs in engines that have 2 spark plugs per cylinder has been used by the auto makers for years.

DAWG

this method of firing spark plugs in engines that have a wasted spark has been used by the auto makers for years, is what I think you mean. please correct me if I am wrong

 

[Dennis]

Hi Robin,
You are correct. Thanks, DAWG

 

[seadoosnipe]

I'm just in awe here

I'm just in awe here............If both plugs could fire at the same time, then why have a trigger coil or a response from the mpem to give the necessary signal? Why have a timing system? And lastly, if the plug was to fire when the piston was in the down stroke to suck in fuel (where the vacuum is being created) before the power stroke, it would cause pre-ignition. This is also the instant that the rotary valve is in the open position, using that vacuum to deliver fuel. That "wasted spark" would cause a backfire through the carbs.
I wish you well in learning more about the theory of operation of the 2-cycle engine. This is my last response on the subject. I can't find any other way to help point this out...........:cheers:

 

[kustomkarl]

Good Post Dawg...and a proven point! The concept of timing is so important in a 2 stroke engine. The rotary valve playes an important part in the correct timing and fireing of the engine in our seadoo's, to allow the power and rpms of the engine. I love discussions like this...it makes ya think.
Karl

 

[seadoosnipe]

Can't let this go!

I can't seem to let this go because of how important it is to understand the basic application of the firing order of the 2-cycle engine. During the compression stroke, the fuel and air that was picked up at the bottom of the exhaust and intake cycle cannot have an ignition spark. There would be no power or fuel left for combustion when the piston reaches the top of the chamber.
Once again, I've found another link that further explains this. Please keep an open mind and read the article. You'll also note the animated engine only shows spark when the piston reaches the top of the stroke.
http://en.wikipedia.org/wiki/Two-stroke_engine

 

[kustomkarl]

So now that this thread got hi jacked, Jeff did you ever get spark from your seadoo, and get it to pop at all...uh, this was your thread to begin with ... Let us know how your problem is doing. I think we all still want to help, I know I do.
Karl

 

[kustomkarl]

I'm re-hi jacking this thread!!! I have checked like 9 manuals and can't find any info about the firing of the ignition coil on any seadoo 2 times! Nowhere does it say that the coil fires on TDC and BDC! The only recollection to firing as stated from seadoo manuals is it fires close to TDC and that's it. I can't find it anywhere that the plug caps are specific either. My eyes are red from all that reading. The manuals only tell about the flywheel, the coils, the ignition timing, both static and running. I understand the point Dawg stated in a earlier post, and I agreed with him as it could have been sound... but I need proof that what he states is 100% correct. A lot of theories fly and if this was some mechanical miracle than seadoo would have mentioned it in there manuals. A spark plug that fires at TDC,(top dead center) and BDC, (bottom dead center) would cause a misfire of unused gases in the combustion chamber while firing at BDC...

I'm still looking into this as maybe it is a maricle...but I doubt it.


Now back to the original thread...Jeff is your seadoo firing yet?
Karl

 

[manicmechanic]

Engines?

I honestly don't mean to sound critical of someones opinion, but this isn't opinion, it's science. I learned the cycles of the 4 stroke and 2 stroke back in high school.
There is no way a cylinder can fire as the same time another one is. Not even in a V-8......if you look on the intake manifold of any V-8, you will see the firing order stamped in it. For example: the old chevy 350 was 1-8-4-3-6-5-7-2...........An engine only sparks during the compression stroke, just before TDC. And in theory, you can not take any plug wire from the one it is on and have it fire correctly else where.............

 

[Dennis]

Suggestion From Dawg

Karl is absolutely correct about ol' DUSTHAWKS' ski not running. All this debating over ignition and 2 stroke engine operation isn't fixing his ski and after all that is how this all got started. Suggestion......................
Start a new thread about this subject. Please keep some things in mind here: I have PERSONALLY reversed the plug wires on purpose to see what the outcome would be and that action had no ill effect on engine operation. This was not a "freak", "only happened once", "can't duplicate it again" situation.
I'm not drunk.LOL
There is absolutely, positively no doubt in my mind that if your were to reverse the plug wires on your Challenger you would come up with the same running results. I totally agree that having the spark plug fire when the piston of a 2 stroke engine is at BDC theoretically will only cause problems but I can't ignore the fact that reversing the plug wires does not cause problems. The use of the term "waste spark" may not be the correct terminology for this situation (assuming my ignition theory is correct) but it is the term the auto makers use for describing the spark that happens (purposely) when the piston of a 4 stroke car engine is at TDC of the exhaust stroke and therefore the only thing I could compare to. The auto makers use this type of ignition depending on application. Some vehicals have it, some do not. This, MANICMECHANIC, is a fact and I'm sure I can provide proof of that if necessary. I"m hoping we can open a thread on this subject. I'm also hoping that anybody out there that has first hand knowledge on the subject and/or literature will post it.
Thanks, DAWG

 

[dieselman]

You are correct I think some are talking about a waste spark that still only fires on TDC but sends the spark to a pairing cyl. on its exhaust stroke.Now not trying to step on anyones toes but older two strokes could not have waste spark but newer injected ones it could be possible but I have not seen one. Now I think Dusthawk is wondering what all this has to do with his no start trouble let us know if you got any more info on getting it to fire or not.

 

[robin savell lloyd]

1 mans wasted spark is another mans treasure spark

seadoosnipe that is the best working illustration of that type of 2 cycle I have ever seen. super job thank you. A wasted spark is just what it says it is. a total waste, a total loss. it has no value, except to machanical knowledge junky's like us, that are always trying to stay on the cutting edge of technology so that we can have a beter understanding of what we are repairing. why should seadoo say any thing about something that has no value, it is a wasted spark. it has no great repair value so there is not a need to go into detail about some thing that is a total waste. try and find other pwc, auto or motorcycle manufacturers that say anything about their wasted spark ignitions. do a web search, good luck. now just type in wasted spark, if you look hard enough you might find a ignition manufacturer that will talk about theirs. or find one of those companys that sell those fancy performance ignitions for pwc's and call them and ask if seadoo has this wasted spark on some of their rotax engines. if someone will do this please post it, as i allready have way to much time in this. ps. I may be wrong please correct if i am, I am still learning so what I say may not be fact so please research your self. thank you all and good luck

 

[dieselman]

Just getting back to the waste spark for a second my Hemi has the waste spark and how thay made it work was having 2 spark plugs per cyl. The coil plugs on to one plug with a high tension wire going to the pairing cyl for the waste spark so it fires 2 plugs at the same time but from the same coil one on the cyl. at TDC the other on exhaust of the pairing cyl.

 

[manicmechanic]

Motorcycles?

And you may remember the old Suzuki dirt bikes that had two plugs per cylinder. For the same reason. To make sure they made use of the capable horsepower by leaving no fuel to waste.
I don't think they use that application on dirt bikes anymore.
I do remember them in the hemi........

 

[ScubaDoo]

Hey guy's what ever happened to Dusthawks thread and the problem he is having. I think another thread is already going on the hi jacked subject.

ScubaDoo

 

[manicmechanic]

Hi jacked!

I don't know that his thread was actually hi-jacked, since this debate is in direct response to a problem that may be what is causing him not to get any spark (pop) to his engine. I've read back into his post and he's tried just about everything else and I see where someone has made the request as to whether or not he may have his plug wires crossed. This is where the debate took off as to that shoudn't be his problem. So while some think it isn't, some think it is. So if we solve the problem of the possibility of whether or not he has his plug wires crossed, the thread hasn't been hi-jacked. It's just been expanded to include the idea that he may have his ignition connected wrong.........

 

[Dennis]

2 Stroke Ignition

I went back to the 1999 S.D.Speedster w/twin 787 carb engines and checked the ignition operation again. I removed the spark plugs, grounded each plug with a seperate ground strap to the engine block, installed the plug wires and then spun the engine over. Both plugs sparked at the same time. Not one before the other or one after the other but at the same time. CAUTION: To check for ignition spark using this method may cause a fire if fuel vapers are present.....always be careful! NOW........................
There are two basic methods a person can use in order to learn how something works: OPERATION IN THEORY( how something is supposed to work) and OPERATION IN PRACTICE( how something actually works when being used). The tests I have used to come to a conclusion about this ignition issue are "operation in practice" which I have always found to be
"the bottom line" and the mechanic in me will always trust this method especially when I'm completely baffled about a issue. My conclusion is that both spark plugs fire at the same time on a rotax 2 cylinder, 2 stroke, SINGLE coil ignition engine that we have in alot of our jet skis' and here is why:
1. reversed plug wires and engine still ran correctly.
2. can check #1 piston timing using #2 spark plug wire.
3. seen both spark plugs fire at the same time with my own eyes.(SOBER!)
I have always agreed with MANICMECHANIC and SEADOOSNIPE that a spark plug firing in a 2 stroke engine when the piston is at BDC should (in THEORY) cause havoc so I decided to make some phone calls to some people that I know to be a reliable source of jet ski knowledge. One person is a lead tech at a SeaDoo dealer here in FL. Another is a lead tech in a SeaDoo dealer in Ohio and the other source is a employee at a major jet ski reman engine company. Here is what I found out:
All three sources said the S.D. 2 cyl., 2 stroke, single coil engines fire the spark plugs at the same time. I was told by the reman engine source that Yamaha and Kaw 2 cyl., 2 stroke, single coil engines also use this method.
The reman engine source told me that this is NOT true with the S.D.951 carb engine because it has 2 coils (1 for each cyl.) and that the plugs fire independant of each other. (I checked a wiring diagram for a 2001 GTX and he is correct...2 coils). ROBIN and I have been using the term "WASTE SPARK" to describe the spark that occurs when the piston is at BDC. The reman engine source referred to that spark as "LOST SPARK".
I asked all three sources how it was possible to have the "LOST SPARK" occur when the piston was at BDC without having a real bad effect on engine performance and all 3 sources came up with these same basic THEORIES. (None of the sources were absolutely sure).
Because the spark for the piston that is coming to TDC happens at approx 10 deg before TDC it means that the "lost spark" is happening 10 deg before the other piston is reaching BDC.
The intake port in the block of the S.D. is closed off by the rotary valve when the piston is at BDC therefore no backfire thru the carb.
The air, fuel, oil charge is not under compression when this "lost spark" occurs and therefore there is no cumbustion.
This concludes my report. I'm still not sure I buy into their reasons for no ill effect on engine performance but it"s all I got! Oh yeah, there are a couple of more things I know to be a fact based on "theory in practice".
1. Like KUSTOMKARL, all of this researching has given DAWG a headache.
2. DAWG hates headaches.
3. There are numerous beers in DAWGs' garage fridge.
4. DAWGS' current status of "sober" is going to change to a status of "less than sober" this evening at approx. 7:30 P.M. E.S.T.
THANKS, DAWG

 

[robin savell lloyd]

You go dawg, great post. that is the same info that I have been recieving my self, it has been explained to me the same way from another seadoo dealer today I was just curious if this mechanic ever heard of this wasted spark he did and comfirmed but he did not know that the coil completed the circuit back up the other coil wire but I still think this is correct as dennis comfirmed that he had to change arrow direction on his timing light facing coil insted of spark plug. dennis I am still not sure if this will convence anyone though.

 

[kustomkarl]

DAWG, I'm impressed with your research of whats going on inside the 2 stroke twin model's with a single coil. So to sum up all the problems Jeff (Dusthawk)is having with his seadoo...who can answer the $10,000.00 question?
What is the problem, and what is his next direction of attack?

I still say it's the flywheel out of time.

 

[robin savell lloyd]

if dusthawk can get rid of that wasted spark i think it will run

 

[kustomkarl]

I think he should save it till he needs it...:ack:

 

[Dennis]

I've lost track of where everythings at with his ski. I'm still curious about whether or not DUSTHAWK feels air huffing back thru the carb when he cranks it.
I'm thinking that if he emptied out the garbage can full of waste spark and then went around and found all of the lost spark that it just might start.
Just a less than sober thought.
DAWG

 

[kustomkarl]

Hey Dawg, are you Miller-ing over the problem with you friend Buddy Weiser, or is this just a Forster-ing idea of you contemplating Bush on Ice skating over the Bass on the Black and Tan pond? :ack: