750sxi pro will not run properly

[Magyar68]

that is over Jetted on top, unless your low jet is too low AND the high Jet is too High. thinking your low jet needs to be 88 or more. BOOG to much fuel, DIES not enough. Did the same thing happen when you had the 155 in it, Doing the Same test?
PO may have attempted a Reverse Jetting. Also Breaking up, could be the Rev limiter kicking to soon n the CDI.
that looks to be a Small pin Head. the second water mount has been drilled, so the Casting mark is gone. But if its a 11001-3717 A casing, the chamber is bigger than the other 750 Heads, could explain your low Compression, even if its been milled.
FYI the stator Cable mount going into the ebox is backwards, you'll want to turn it around before the wires break.

 

[Magyar68]

Also check your Plug ends, the Blue boot just pulls off and you should see the copper core in the Pulg winding. if there is any corrosion, or discolor to the Copper, you may just need to trim them a little pop the Boot back on and see if that helps.

 

[johnmx854]

Yea the ski ran the same with the 165 and 155 main jets in it.. And if it is the head u think it is does that mean i should jet a different one? And the kid I got it from said it had an aftermarket ignition and I haven't taken it apart yet to see but it does have the vilder flywheel in it which would lead me to belive that it might have the ignition too. Do ignitions go bad or malfunction in that way?

 

[Magyar68]

On the ignition seen several posts about Stock ones doing that, not real sure about the aftermarket CDI's. I have an MSD, and no problems yet. the head is tricky, guess it depends on the accuracy of your Gauge.

 

[veedubs]

You need an actual head gasket for that stock head. Also the pulse line is too long.


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[johnmx854]

The stock head was decked and milled out for o rings. Do you need both orings and head gasket?

 

[johnmx854]

And what do you mean by pulse line? The one from the crankcase to the carb?

 

[veedubs]

Ahh got it. If its o-ringed then no stock head gasket.


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[johnmx854]

Well I just checked the compression again and only have 125psi in both cylinders. Is that not enough to run to its full potential and give me the problems that it has? Is it a good idea to leave that milled head on or should I get a legit aftermarket head or just stay with a stocker

 

[veedubs]

Seems low to me. Should be higher. Yes pulse line is the hose from the crankcase to the carb.


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[johnmx854]

Yes I does seem low to me esp with a decked head but wondering if that was my problem all along.. Def seems plausible

 

[Little_Franny]

ski has NJ reg numbers, you in NJ. I just helped a buddy tune a similar setup and we ended up with 117.5 low speed jet and 150 high speed jet. I think it was a 2.3 N/S and an 80g spring. Ran good.

Your compression numbers are def low and performance will suffer because of it.

As for the pipe screws, I have found the best combo to be 3/4 open on top, mid and bottom closed, and add a FCV inline to the stinger.

 

[johnmx854]

I purchased the ski from jersey but am from ct..a few things u stated I am not familiar with like 2.3 n/s and fcv in the stinger line.. I have had a few slightly modded 650sxs but this thing threw me for a loop Tryin to get it to run right

 

[Little_Franny]

2.3 n/s refers to the size of the needle and seat in the carb, it is used in conjunction with the spring weight to tune pop off pressure.

FCV is a flow control valve, it is installed in the cooling line that goes to the pipe that attached to the bottom of your chamber. A fcv is a spring valve that stops water flow into the waterbox at low rpms to keep it dry and help throttle reponce. you need not worry about this until you get it running right.

 

[johnmx854]

Oh gotcha. Thanks for the advice.. I've read a buncha of things on tuning and was unsure but everything you have said makes sense and I have to get some carb parts before it starts snowing

 

[johnmx854]

Well one more thing about the flow control valve. Is this something that is made for jet skis or a house plumbing part made to work because I just did a quick search for a valve and haven't seen anything that pertain directly to pecs. Thanks

 

[Magyar68]

http://www.speedsupplies.com/accessorylistingdetailpurch.asp?item=103576