siezed my 70cc topend!!!

[zuma2003]

I dont know what i did wrong if anyone can help that would be great! I got 160 miles and then it was over. I am running a 19mm carb,zx pipe,cdi,and perf clutch. I also am running the stock oil inj. I put the bigger main jet that came with the carb. The siez is on the exhaust side of the piston and cyl. Could it have siezed because the cdi? Or the stock oil inj? Or what? I put the 70 kit on when the bike had no miles (brand new) This is my 2nd zuma with the same set up and I have over 1500 miles with no problems. Any Ideas?

[Lennox]

what brand carb? Are you sure the oil/vac lines are not reversed?

Can you post a pic of the scoring on the piston?

[Zuma_II]

Dumb question - is the oil injector like the one's on old DS7/YDS5/R5/RD/RZ's where you can adjust the oil flow? And if so - did you crank it up some for this 40% larger engine?

[XPS1210]

the zuma oil injector can't be adjusted for the larger set up... it's set at the factory and can't be adjusted.

[zuma2003]

I am running a Arreche 19mm carb. The lines are hooked up correct. I havent tested the oil pump yet. I will take a picture of the piston and post it asap. The strange part is I see lots of people running the same set up with no problems heck my other zuma has the same set up with more miles and no problems. The only diff is the one that siez has the better cdi box. Has anyone else had any problems with there 70 kit, like siezing?

[Lennox]

I am running a Arreche 19mm carb. The lines are hooked up correct. I havent tested the oil pump yet. I will take a picture of the piston and post it asap. The strange part is I see lots of people running the same set up with no problems heck my other zuma has the same set up with more miles and no problems. The only diff is the one that siez has the better cdi box. Has anyone else had any problems with there 70 kit, like siezing?

yes, I seized one..... do the hoses going to the carb match up with the same size fittings on the caarb?? if so, this may be your problem.......

[zuma2003]

would a cracked exhaust header cause the topend to siez?

[rydah]

that could happen if the cold air got into the cylinder. its kinda rare but it does happen once in a great while.

[Zuma_II]

A cracked exhaust header could definately cause a motor to sieze (as could an air leak at the carb manifold). Is your piston also burnt/siezed near to the exhaust manifold?

[hybridrazz]

i would say ditch the oil injection ,and go to premix to be on the safe side.

[zuma2003]

It siezed on the exhaust side.

[hybridrazz]

yeah the exhaust did that for sure i was just saying go to premix after you fix it so you dont have problems with the mix later.

[Zuma_II]

Personally I'd stick with the oil pump. When I used to race motorcycles I'd remove the pump to save the weight of the pump and oil tank, and to remove the little bit of drag that it creates on the engine. But for street use I'd keep the pump and resevoir for ease of refueling.

[Lennox]

It siezed on the exhaust side.

how about that pic? of the burnt piston....

[zuma2003]

Here is the picture....

[zuma2003]

Sorry...let's try again

[XPS1210]

ouch... that blows...


Mine's no where near that! Thank god... at least it still works but is scared up...

Gesh....

[florida derbi rocket]

Ok...Shut me up... and Throw old 50cc parts at me if I'm Wrong......But How does a Seizure occur on the Exhaust side......if the gasses are Exiting.?.......Does some kind of Re-Circulation of the Exhaust gasses happen?........I did notice some Black Carbon-Type Scrapes in the Photo of the Piston........ if He was Pre-Mixing kinda Rich ..without the Oil Pump......Could the added lube have Prevented this??............I really wanna know these things..John

[Lennox]

on a 2 stroke, backpressure is key. when there isnt any (in the case of a cracked pipe) cold air can take the place of the hot exhaust gasses and seize a piston.........

[florida derbi rocket]

So...Is there Re-circulation Happening??...Like half Exaust/ Half new Air?..(In a working 2-Stroke)?? John

[Lennox]

with a stock pipe only a little.... an expansion chamber pipe will add more....

[zuma2003]

The bike never ran better right before it siezed. :p Now the the exhaust is welded and fixed and I cant get the new topend to siez.(and i put 100 miles on it since) I guess it was the exhaust leak. NOTE TO EVERYONE...... check your exhaust for leaks at the header I didnt think it would siez a topend.........but it can!

[Zuma_II]

An air leak in the exhaust or intake side will make the engine run lean (it's not moving as much fuel in the mix as it is air). This is true for 2 strokes and 4 strokes. A leak on the exhaust side also creates a hot spot - the hot spot is what took your cylinder out - if it was just the running lean then you could have done a lot more damage before noticing it. Running a little bit lean is often accompanied by a little boost in power. That's why when you're rejetting carbs you can't just go by the seat of your pants, you need to look at the plug(s). I used to always lean the mix until I found the most power - and then richen it back up a jet size or two until the plug(s) looked good. I'll bet the plug was very light. Actually the damage didn't look that bad - I've seen lean running bikes eat holes in the tops of the pistons (yeah - I've even seen one of my own do it). :(

[thc70]

i had a big loss of power and after trying everything it was also a cracked pipe at the jug. im glad i didnt run it much!