BLOWN 26cc CY!

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voo2doo

voo2doo

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After putting my billet inlet anifold on I took my MT out for a spin.On starting it up which took ages I opened the throttle and it instantly bogged down.I tried various carb setting but it was thew same.
I bought it back to my workshop and 7 screws later it was clamped in the vice with the tank attached and the pipe on.I pulled it so many times the started bust! So I opened it yp and stripped it down.On closer inspection the inside of the mill was full of fine sand( I run in a sandy area with the standard filter on).There was a slight score on the cylinder liner and a very small hole in the center of the piston( Is that meant to be there ???)I cleaned everything and reassembled it (using the same gaskets) I tried to start it with a drill but it wouldn't even pop!!!
I've injected fuel directly into the barrel.
I have put another carb on (WT-668)
The coil has been off but have put it back with a credit card clearance.
The needle are back to standard setting although I've tried different settings
There is compression and a real healthy spark.
Any ideas fellas? as this might just turn into a door stop!
Thanks
James.
 
Should be no hole in piston....Buy a piston kit...rebuild the lower case..new engine bearings
that sand will chew up stuff....slawhammer
 
benckie said:
you could have the pulse port blocked also fine sand inside the mill ill say shes just worn out and lost enough compression not to run
Click to expand...
I know what you mean Benk but I've put teflon gaskets on the intake and checked 4 times to see if it was right. There is good compression in the bore and I have tried direct petrol injection into the cylinder but it still wont fire?
Cheers J
 
even though she feels like good compression ill bet my left nut shes had it, sand will do that, ive had plenty of motors that have felt like great compresion but they hare just to worn and lost just enought not the start.

i hear but its got lots of compression, but wont start all the time, a new piston and ring or a new head kit with the same carb and and carb settings and they fire right up.

also i forgot to mention befor there is ment to be a hole in the top of the piston, its more like a mill dot the hole will not go all the way thru the piston but its there on all psitons normaly, most of the times it gets full of carbon so most people will not see them
 
Yeah I knew what you were talking about so I snapped a quick shot to show that this hole is ok... But if the hole is big enough to use as an ashtray, well you MAY have a problem :lol:
 
yeah I thought he ment like a hole made from the spark plug..running to hot and melted a hole....not the one from machine work to hold the piston...Slawhammer
 
hole to me meant it went right through. lol. that would surely kill compression.

I have noticed on a few heads lately that the plating has been wearing off of the heads. we were looking at a number of heads and it seems there was a run of heads with a weak plating? these heads were fairly new. a friend I run with mentioned ddm just got a huge batch of new heads with the better plating, but I can't confirm or deny the statement. they have a dealer account with ddm and order a ton of stuff.

I just know we have looked at a lot of heads recently and I have seen premature wear. one head had shown wear just from trying to start from new and never did start.
 
i would if soome where built dry

try zen heads the seam to fair better

here is a picture i found of a 36mm piston from a gp290 28.5cc head i found in my photo bucket account from an engine that cracked after 3 tanks

S8002635.gif
 
Trip said:
Yeah I knew what you were talking about so I snapped a quick shot to show that this hole is ok... But if the hole is big enough to use as an ashtray, well you MAY have a problem :lol:
Click to expand...


That was funny buddy:) I took it apart again and,yes,it is a machined hole Thanks for your help fellas I think I will go with he 28.5cc head with a 2mm stroker in.Can you advise me what to get and where to buy as mentioned there are weak plating on some heads.
Thanks
again folks.
J.
 
voo2doo said:
That was funny buddy:) I took it apart again and,yes,it is a machined hole Thanks for your help fellas I think I will go with he 28.5cc head with a 2mm stroker in.Can you advise me what to get and where to buy as mentioned there are weak plating on some heads.
Thanks
again folks.
J.
Click to expand...

A 28.5 head with a stroker crank will give you a 30.5... I believe.

I have never heard of plating problems with the gp 290 (28.5cc or 36mm) the cy 29cc (29cc 35mm) were the ones with problems, but I believe that was years ago. The plating problems are now SUPPOSED to be gone.
 
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