Stumped!

[Mac]

After farting around all last year with my '96 ZXI 1100 that i bought in parts and put back together (ski had a blown motor) I took it to a dealer. I could never get the ski to run over 40 mph on the speedo and it wouldnt rev past about 4500 in the water. Starts fine and revs fine out of the water. I rebuilt the carbs and checked compression. 5 weeks after i dropped it of I called the dealer and they too are stumped. He checked compression , took carbs apart and checked that the right jets were in, checked the reeds, checked the stator,fresh gas and said he is going to check the jet pump to see if maybe it has a bad bearing. Here is the thing every once in a while it would start to rev high for a second and then go back to only 4500 rpms. Today the tech said that when he took it out the other day it still ran the same and then all of a sudden it ran at 7200 rpms and 70 mph on the spedo ( I know thats not acurate) He stoped shut it off and the when he restarted it it was right back to running crapy. Could this be a CDI going bad? It does have spark at all 3 cylinders. Also what does CDI stand for? Sorry it so long but It's almost 2 years and I still havent been able to get it to run right. Any help would be greatly appreciated.Thanks

[dowkk]

Re: Stumped!

CDI is capacitive discharge ignition. That's most likely all you wanted to know but if anyone is iterested in a little more fun reading the info below is from a VW site.

Introduction/Description

A conventional induction ignition creates a spark by applying electric potential (12 volts) to the primary side of the coil. The coil steps the primary potential up to as much as 10,000 volts and delivers this high voltage to the spark plugs. However, this "step up" process is relatively slow, and as crank speed (rpm) increases, the secondary voltage declines dramatically.

This limitation was partially solved by the development of capacitive-discharge ignition (CDI) systems. Instead of applying 12 volts to the coil, a CD ignition increases the primary current by storing it in a kind of miniature battery called a capacitor. When this higher primary current is applied to the coil, the secondary voltage is dramatically increased.

The principal advantage of a CDI system is the ability to present a superior spark to the air/fuel mixture inside the combustion chamber, thus maximizing burn efficiency. The easiest way to get a bigger spark is to increase the spark plug gap size. However, increasing the gap distance also increases the voltage necessary to ionize the air/fuel mixture. And the resistance of the air/fuel mixture increases as the mixture is pressurized in the cylinder, requiring even higher voltage to spark across a plug. A CDI system provides the higher voltage required by the increased spark plug gap size, thus providing very intense spark.

A CDI ignition system can create spark potential as high as 37,000 volts. Most engines only need about 20,000 volts for reliable ignition. The stock system begins to 'droop' as the rpm goes up. At highway speeds, the spark voltage becomes more and more marginal, averaging about 18,000 volts. With a CDI system, the step up process is very fast compared to a conventional 12-volt induction. This assures a more consistent spark delivery across the plug gap, even at very high crank speeds (rpm).

Note: The consistently higher voltage will cause neoprene-type insulation to break down rather rapidly. You need sparkplug wires with better insulation, such as silicone or non-metallic.

[Mac]

Re: Stumped!

Interesting, is this just a fancy version of points and condesor style ignition? What happens when a CDI starts to go bad? Could it cause a problem like mine?

[tom21]

Re: Stumped!

I recently rebuilt a 99 stx1100 and I think I had the same problem. It ended up being the needle and seat were leaking in all three carbs. couldn't go faster than 15 to 18 miles an hour and it would not rev higher than about 4500rpm.

[Antwon]

Re: Stumped!

Interesting, is this just a fancy version of points and condesor style ignition? What happens when a CDI starts to go bad?

Mac, no. CDI "Usually" works or it doesn't. There is nothing to adjust. I say usually because heat, moisture and vibration can make some interesting intermitent problems.

[Mac]

Re: Stumped!

Thats what I thought but what ever it is its intermiitent. The tech checked the carbs and couldnt find anything wrong. Stopped in today and he had pulled the jet pump and all was fine. What else should I or he be checking?

[Antwon]

Re: Stumped!

I guess if your sure that it has the correct fuel and compression, I would stay on the ignition. Maybe swap out parts if you can get your hands on them. I assume that the dealer tested the ignition following the shop manual and since it's an intermitent problem, it's not showing up..yes? Are all the electronics bone dry and have a good connection? It could be something as simple as a plug wire shorting or not making a good contact with one of your plugs. I just had a ski that had a male/female connection rotted but wasn't visible until I pulled it appart to grease everything with dielectric grease. It would sometimes make a poor contact and half *** work.

[Mac]

Re: Stumped!

Ok 6 weeks later the mechanic says the crank is "twisted" How do you check this with out pulling the crank and why would it run ok one minute when he is test ridding it and run like crap the next? Would it even run if this were the case? What symptoms would it have it the crank was twisted? The ski start fine but will only rev about 4500 rpms in the water and only about 45mph. I'm currently looking for a tall building to throw this thing off of!

[Technical Support]

Re: Stumped!

Put the front piston to TDC, the other two should be even with each other. Symtoms can vary, depending on the degree of twist.

[Mac]

Re: Stumped!

Does this sound like the symptoms of a twisted crank?

[Technical Support]

Re: Stumped!

Some of it does - it's very unlikely though.

[Mac]

Re: Stumped!

Is there a tolerance for how much difference there can be? What would cause it? Thanks I dont want to buy another SBT motor already!

[K6jet]

Re: Stumped!

Hey, just as something you can try, take your spark boots off and look at the plug wires, if they're corroded, trim them until you get a nice contact, and you can always try replacing the spark boots also.

[Mac]

Re: Stumped!

I went to look at it today and the tech put the #2 cylinder @ TDC and then measured the distance between the spark plug seat and the top of the piston. Then he measured the #1 cylinder and said there is a big differance. I told him I thought you were supposed to put #1 @ TDC and measure # 2 & #3 cylinders and check for a difference. He said it didnt matter they'd be the same. Is it time for a second opinion? He wants to put a SBT rebuild in it.

[Bill O'Neal2]

Re: Stumped!

With #2 at TDC, numbers 3 and 1 should be exactly the same distance down from the sparkplug hole surface.