Bore seize why?

[bakaracer]

Greetings:

Jetting and apparent temps aren't the only things that can kill a bore.

A bad tank of fuel - either too-low Octane or shrapnel blocking a jet - will cause sudden failure. Chunks-O Hot Metal can cause pre-ignition and the Detonation Death Spiral faster than any gauge could register. Often the Temp That Really Matters happens off-throttle - if the Pilot jet is too small. Bad or insufficient oil can do it too. So can sufficient oil, if it's not where it needs to be.

I'm surprised Baka hasn't mentioned chamfering the edges of the ports and piston skirts - he has many times. The more affordable bore kits have knife-edges that scrape too much of the oil off the cylinder walls and basically the piston/bore interface runs dry of lubricant. It's a short time indeed at 200 strokes/second before the piston goes red-hot. Poof!

I think I said that more than enough for the regulars that come on here to see.if they still not doing what i recommend then thats their fault if it seizes

[Limp1144]

Thanks wheelman poor design runs the piston dry. That sounds like what happened

[tru72]

Greetings:

Jetting and apparent temps aren't the only things that can kill a bore.

A bad tank of fuel - either too-low Octane or shrapnel blocking a jet - will cause sudden failure. Chunks-O Hot Metal can cause pre-ignition and the Detonation Death Spiral faster than any gauge could register. Often the Temp That Really Matters happens off-throttle - if the Pilot jet is too small. Bad or insufficient oil can do it too. So can sufficient oil, if it's not where it needs to be.

I'm surprised Baka hasn't mentioned chamfering the edges of the ports and piston skirts - he has many times. The more affordable bore kits have knife-edges that scrape too much of the oil off the cylinder walls and basically the piston/bore interface runs dry of lubricant. It's a short time indeed at 200 strokes/second before the piston goes red-hot. Poof!

I think I said that more than enough for the regulars that come on here to see.if they still not doing what i recommend then thats their fault if it seizes

[Limp1144]

Someone send me baka write up on knifing the skirts and bore thanks. Reporting back another 30 miles and temps are very low 200f. My next question the bore had a little surface rust in it. When I stop the scooter will heat up about 30 to 40 f but I am not seeing a pilot on this carb.

[atomicareprise]

under jettings...u'll be lucky if ur piston don't melt...

but i'm guessing it does...

78 mj is too small especially when you have a 48mm bore..

[Limp1144]

On my vino it would hit 66mph only had a 70main. I did not modify my airbox so I could use small jets and still get 68 mpg. As far as the temps go I could use a smaller jet really. The bore and exhaust are not restricted like the factory setup so it is more efficient. Went on a wot run 10 miles 268f on the temps. I would like to see it near 350f

[Bear45-70]

Someone send me baka write up on knifing the skirts and bore thanks. Reporting back another 30 miles and temps are very low 200f. My next question the bore had a little surface rust in it. When I stop the scooter will heat up about 30 to 40 f but I am not seeing a pilot on this carb.

Rust on the bore means there is not enough oil or the oil isn't doing it's job by stay adhered to the surfaces of the engine.

OMC (Johnson and Evinrude outboards back then) found that the TCW-II oil worked fine at 100 to 1 ratio. The problem turned out to be that the bore, rings bearings, etc. rusted because of insuffiecent oil to protect the parts from rust if they sat for several weeks. So they recalled all the 100 to 1 self oiling tanks and changed the premix spec back to 50 to 1.

What carb are you using?

[Limp1144]

The bore was old and had surface rust before I installed it. Stock carb

[Limp1144]

Plug looks great nice coco brown color.

[bakaracer]

thats not where you read a plug for 2 strokes. that read is for 4 strokes. you need to use a new plug after the engine is warmed up and do a wot hold for 3-4sec then shut the engine off with the throttle wide open and come to a stop as quick as possible so that you dont foul the plug read. you then are looking at the base of the porcelain for a smoke ring. should be a dark grayish brown ring. the top of the plug will be white or off white. if no ring then up the main.

[tru72]

very good ,, Baka knows.. I try to tell that to alot of people that the way they read plugs are wrong for 2 strokes, but it just goes thru one ear thru the other..
Bum Bai they learn...then hard way!

[bakaracer]

very good ,, Baka knows.. I try to tell that to alot of people that the way they read plugs are wrong for 2 strokes, but it just goes thru one ear thru the other..
Bum Bai they learn...then hard way!

they surf the internet to much thats why. i havent seen a plug read chart for 2 strokes yet. mostly 4 stroke plug reads i see posted

[Limp1144]

So found out what the problem is. I feel dumb. The cht ring was binded under the spark plug a little bit and the plug felt tight but it was not. After fixing the cht ring properly around the spark plug went down the road about 45mph. Temp read 402F wow. 78 main right now what size main would take it down to 350 ish. I dont wont to kill my gas mileage. Everyone says a 90 but sounds like it will destroy mpg. Any suggestions does anyone have this jet too. thanks guys

[Bear45-70]

I would thing 90 to be very safe but an 85 would be more reasonable choice, IMHO.

I have an 82, 85 and 88 in my PA carb jet box.