750 big pin seizure !!!!

[SUPERTUNE]

they don't call them seize-co's for nothing!

That's not fair! Just somebody using a over aggressive squish and chamber design can cause detonation even at lower compression ratio's. Wiseco pistons don't like a lot of piston crown heat...You should look at the headpipe size and make sure it's not too small as this will cause these problems.

 

[madscientist]

hey chuck, i am setting up my 750 now and i could use some jetting help.

SMALL PIN 750 :
1. EXHAUST PORTS CLEANED UP not a lot of material removed, and polished
2. TWIN 40 MM KEIHIN FROM AN XIR
3. BLASTER FPP LIMITED CHAMBER
4. MSD T/L SINGLE CH. ANALOG
5. WESTCOAST HEAD W/ 29 CC DOMES ( 190PSI)

HAVE 68 LOWS AND 130 HIGHS NOW AND LOOKING TO ORDER NEW JETS AS DIRECTED

 

[SUPERTUNE]

Maybe with 44 or 46 Mikuni's...I never thought in a million years that I should have kept more jetting notes for the past 30 years!, with the last 20 with PWC (jetski's).
Duh! Never thought that I wouldn't remember...

 

[tor*p*do]

That's not fair!.

maybe not,
but if not set up just right (and I do not doubt that you know how)
they are not very forgiving and
you can have problems

 

[x2fatkid]

What about water leaks in the casting ,of an almost brand new jetsport exhaust manifold.With only 3 rides....blew the motor each ride.Thats what the latest news is on my motor.tested under water all sealed up and filled with air..would that continue to blow the motor every ride?

 

[X2guy]

Blew another motor today in the water tank!!!!:crazy:!He called to let me know..I've called wiseco and they recomend 6+ on piston clearence.He just won't here that, he says thats not the problem.He wants me to run aviation fuel atleast 50/50 ,he still believes it's detonating..He says the exhaust is way to hot.

He better start hearing that or he's going to keep scuffing your pistons. That's just the way wisecos are. you cant run OEM clearances. I've been there. Post pics of the pistons.

 

[X2guy]

What about water leaks in the casting ,of an almost brand new jetsport exhaust manifold.With only 3 rides....blew the motor each ride.Thats what the latest news is on my motor.tested under water all sealed up and filled with air..would that continue to blow the motor every ride?

Yes. First if the exhaust manifold leaked it would only blow the water into the pipe. If it was running low piston clearance it would seize even if the engine didnt leak air. Wisecos suck if you ask me. Run Pro X. I run 83mm wisecos in my small pin as there are no others and I run .008" clearance.

 

[x2fatkid]

750 big pin motor bored to an 800 cc,44 carb, ADA head 180 psi, modified stock exhaust manifold, factory head pipe, blaster limited chamber westcoast waterbox,notsure of the timing advance but am checking that soon,dual cooling lines all routed . Any advice on where my jetting should be? Right now needle and seat is a 2.0 low is at 125 not sure of the high jet..my guy water tested my ski on tue and he said that thejetting was close on the bottom but way to lean on top . and he thinks he will have to hone and put in new rings before he rejets. Anyone running a similar setup? looking for some jetting advice...Thanks:beerchug:

 

[2XLR8]

I would start with at least a 155 main and I would make sure I did not have the 115 gram spring and maybe not even the 95 gram spring. I don't understand why you have to hone and replace the rings again?

 

[X2guy]

Can you post pictures of the pistons? Is it a lean seize or a cold seize. Cold seizures usually have the 4 corners of the pistons scuffed.

 

[x2fatkid]

Sorry but i live about 60 minutes from my buddies shop and i have not seen the pistons.From what he has told me it sounds like it is a 4 corner seizure.I don't think that there has been any real piston damage,mostly cylinder scuffing.Again i have not seen any of the 3 sets of pistons that have come out of my ski yet.my ski has been in sac since 3 weeks before memorial day,hoping to have it back before 4th of july:dunno:

 

[shawn_NJ]

I hope this guy isnt charging you anything.... Get a mechanic who will set the motor up to with the clearances Wiseco told you. Nuking a motor 3 times is rediculious.

Until you get a handle on the problem. You should be 100% sure you are not running ANY timing advance. My big pin motor with 205 compression did deto with the 650 stator 5deg advanced, and 93 oct. You could hear it "pinging". Solved with running 50/50 race gas/93 and backing advance down to 3deg. I personally would also throw a stock head on the motor. And start with a 160main and work back.

 

[X2guy]

Sorry but i live about 60 minutes from my buddies shop and i have not seen the pistons.From what he has told me it sounds like it is a 4 corner seizure.I don't think that there has been any real piston damage,mostly cylinder scuffing.Again i have not seen any of the 3 sets of pistons that have come out of my ski yet.my ski has been in sac since 3 weeks before memorial day,hoping to have it back before 4th of july:dunno:

Tell him to use at least .006" clearance. I set mine up with 8 as I had so much trouble. Now that I bore my own cylinders I have found it very suprising when setting up a cylinder using oem pistons. I have a hard time using only .0025" in some cases. Has he had not much experience with wisecos?

 

[kevbo]

You can stick an OEM piston just as fast as a Wiseco if the setup is not correct.

 

[x2fatkid]

He is not using weiscos this time i believe they are WSM,and he said that he set them up at 5 thousands .I think he should have it dialed this week,all he has to do is put new rings and hone it again,he thinks that there was some light scuffing due to the lean carb..sounds like 160 is a good starting point.Thanks for checking my post,i just wish i could give you all better feedback and picks for you're trouble.

 

[x2fatkid]

Ok got the ski back still need jetting advice..how about 120 low 180 high jet, 2.0 needle and seat? 1 1/4 out top and bottom screw..I tried 110 low 215 high 2.0 needle and seat bogging real hard when i turn right and left!! plugs look good though,any help would be nice.. I know 215 seams really big but the plugs looked lean last night in the dark!! O -yeah pistons are clearanced at 7 thousands

 

[BlueBreadTruck]

ive had great luck with wisecos...I have 2 seasons on my 800 and still has 180 psi.

Now, what head are you running? For me, with the 800 cc bore, i use the stock head to get 180 psi....about the max i would want to run. I hold mine WOT for long periods with no issues, but im also running 750 electronics with NO advance

 

[shawn_NJ]

Ok got the ski back still need jetting advice..how about 120 low 180 high jet, 2.0 needle and seat? 1 1/4 out top and bottom screw..I tried 110 low 215 high 2.0 needle and seat bogging real hard when i turn right and left!! plugs look good though,any help would be nice.. I know 215 seams really big but the plugs looked lean last night in the dark!! O -yeah pistons are clearanced at 7 thousands

If you want 46SBN specs....I have (3) 750 X2's, all piped with 46sbns. Been running for 2 years with this jetting. Also know a bunch of other 750 x2s running these specs.

120L
150H
2.3n/s 95g
Stock SuperJet FA

 

[x2fatkid]

If you want 46SBN specs....I have (3) 750 X2's, all piped with 46sbns. Been running for 2 years with this jetting. Also know a bunch of other 750 x2s running these specs.

120L
150H
2.3n/s 95g
Stock SuperJet FA

Are you running a blaster limited chamber on any of them?Also my head pipe says mariner/factory pipe..it only has 2 water screws,any advice on where they should be set at?I think i will try a 46sbn on my ski this week with those settings.Thanks ..what are you're high low srews set at?

 

[shawn_NJ]

Are you running a blaster limited chamber on any of them?Also my head pipe says mariner/factory pipe..it only has 2 water screws,any advice on where they should be set at?I think i will try a 46sbn on my ski this week with those settings.Thanks ..what are you're high low srews set at?

I am running the SJ mod chamber on one and a coffman on the other. Jetted the same within a 1/6th of a turn. You have a very very old headpipe made for 650's. I had one of those years back, it needed to be bored out to atleast 47mm!! If its the stock 40 or 42mm opening this is not sufficient for your setup, and could be one possible reason you are burning pistons. (As Chucky mentioned in post #21) What is the diameter of the opening in the headpipe and ex manifold?