Super Jet this is strange!

[incorp01]

this ones got me stumped. Any ideas guys??????

generally, ski runs great, heaps of power everywhere.

but, if i slow down to a speed where i can just balance the ski and not tip over, i hear all these random deep pops from the engine, its not a smooth bbbrrrrrrrrr its more like bbbrrrr pop brrrr pop pop bbbrrrr pop brrr.

if i do this for a minute and grab the throttle it jumps out of the water and takes off, no hesitation or bog.

if i slowly up the revs, it "pops and brrrss" all the way up to the mid range and then clears up.

i can ride it round all day working the throttle flawlessly, but everytime i try to hold a constant speed, it sounds like crap.

its basically a new engine.
62t ported epoxied case.
61x cyl @ 82mm.
new B limited, screws: top 3/4, middle closed, bottom closed.
v force reeds.
lightened stock flywheel
stock ign.
ada head 180psi even.
stock 38s 72.5p 135m 115g springs.



so far, my trouble shooting has been:
different carbs: 38s, 44s, single riva PB, back to 38s all jetting / pop off combinations on all carb configurations.
checked reeds at each carb change always good.
new charge coil and lighting coil on stator.
changed cdi 3 times: stock to a mates msd back to different stock one.
3 coils.
countless compression tests.
countless plug changes always perfect dark tan colour br8es-11 Gapped to .70
countless pipe header screw changes (brand new full pipe today as well)
fuel mix is 40-1 castrol power tts full synthetic, 98 RON.

forgot to mention, sounds crisp and smoothe on the trailer when reving.

thanks in advance!

 

[eeerieski]

The engineer in me says your water box is filling up with water and gurgling, similar to how a sailboat exhaust acts like a geyser every few seconds.

Edit: But of course I could be wrong

 

[Waternut]

Do you mean 0.7mm or 0.070" on the plug gap?

 

[incorp01]

sorry 0.7mm same as BR8ES (THE BR8ES-11 NEEDS TO BE RE GAPPED)

something i forgot to mention, the motor shakes and vibrates the whole hull, pole and bars at low speed, i can feel the "pops" vibrating through the tray area- all engine mounts are perfect, shaft and pump alignment is perfect.

 

[Waternut]

2 strokes normally shake pretty bad around idle but it should clean up above 2k rpms. I wonder if your crank is unbalanced or if someone replaced only one piston and it's a different weight from the original.

How long have you owned this ski? Is it a new issue or always been there?

 

[incorp01]

its a new jetmaniac trued and welded crank, new paired wisecos, the builder actually rejected the first set of wisecos because of a 30gm difference, this delayed the build, but his dilegence during the build assures me its done correctly.

took posession in january, the motor was built from scratch with all new parts, the ski has always been like this, hey thanks heaps for helping so far waternut.

 

[munki63]

As for the shaking your motor probably isn't aligned properly, Do you have a Jet Works valve going in to the end of your B-Pipe?

 

[incorp01]

it is aligned properly, the shake, is in time with the "pop", its like a constant random backfire in the chamber, or an extra spark detonating at 90', i dont have a Flow control valve jet, but i do have a 4mm restrictor in the stinger and my chamber sizzles in the right spot.

 

[FlightPlanDan]

any backfire is not good.
maybe running too hot?
It's amazing to hear that somebody got the chamber to sizzle at all!
One screw less than 1/2 open....and I can't sizzle! I know the paperwork that comes with the pipe says it should....
Just a thought.

 

[munki63]

Test your stator and ecu, the specs are in the owners manual I'll post them when I get home if you want

 

[Tyler Zane]

my chamber sizzles. bottom 1/4, middle closed, top 3/4.

i would get a fcv, it will only benefit you

 

[Big Kahuna]

the Rattle is most likely your chamber hitting the top of the bedplate.

The bad shaking overall I would say your alignment is out... Or your carbs are not sync'd well causing a rich/lean condition between cylinders

 

[Proformance1]

Bingo! Dent your new chamber and or grind your bed plates

 

[munki63]

Bingo! Dent your new chamber and or grind your bed plates

you should be able to fix the problem with out denting or grinding...imo
ive never had too

 

[Big Kahuna]

you should be able to fix the problem with out denting or grinding...imo
ive never had too

In many cases you can, but if you have reinforced your hull the space changes, where you could rotate the camber to clear the bedplate, not will cause you to be hitting the side of the hull. Hence the reason to tent the camber, this way you are clearanced at the hull and bedplate.

 

[incorp01]

thanks for your help guys, but there are no alignment issues. if i took it out and sat in on the workbench it would still run the same.

the chamber does not touch anywhere. im tyring to explain that the motor runs like crap at constant throttle, if i take off the hood and watch the motor with a bit of throttle it shakes like i have pulled one of the plugs and has random explosions in the chamber. misfires/backfires
if i increase throttle it cleans up smooth and crisp until it settles and runs like crap again.

if i ride it for a while (5 minutes) at constant throttle when its running like this and pull the plugs they are wet.
if i put new plugs in and ride for 5 minutes working the throttle constantly and pull the plugs they are dark tan not wet.

if i ride for 5 minutes at constant throttle and pull the throttle (you would expect a bog or hesitation) it rips and goes like nothing was wrong.

it cant be the carbs out of sync or a carb issue, i have tried a set of aftermarket 44s, 2 different sets of oem 38s and a single riva powerbomb 48 and had the same issue with all these carbs.

im guessing its electrical, but everything is in spec when i test it with a multi in reference to service manual.

i have disconected the start stop switch with no improvement.

 

[Proformance1]

did you check for a cracked or chipped reed?

 

[incorp01]

hi mate, i have checked yeah.

can the ramps built in the case intakes and the epoxy/port work cause this?
im thinking like when you alter the intake/exhaust timing with an agressive cams on a 4 stroke, you lose idle and smoothness.

someone chime in if thats stupid.

are x scream cased motors with cylinder porting smooth? do they idle ok?

 

[Big Kahuna]

check for a twisted crank. Make sure your crank has not gotten out of index, this would make your motor run bad.

Just because your chamber is not touching right now, it can when the motor is running, at different RPM's the harmonics change, you can watch your pipe and actually see it moving differently at different RPM's It may move alot a 0-1500, settle down from 1500-3000, move more at 3000-4500, get worse at 4500-5500, smooth back up above 5500. All this moving around can cause it to hit when you think it is clear. and they changes could give you the rattle tat pow tat tat pow tat tat tat tat pow..........

 

[Proformance1]

BK thats exactly what mine does. all i did was change from MOD to Limited pipe and wow it was insane! Thought the motor was blown