Conteniously piston brake down (for the experts)

[Sonic-speed]

Although i have been in the scene for 8 years, this one is very tricky to me. A friend of mine have this minarelli SD horizontal engine with the following setup:

MHR team 70 CC Pro Flow Tuned
C21
RT 28 mm. Carburatour
VL14 membrane
MHR Team Crankshaft
Malossi MHR digitronic ignition
OR Kit

(HP 21-22-23 - when it runs)

After around one hour of driving the piston brake down. Has happen 6 times now:

Settings:

Mainjet: 162. I do know it sound very high, but anything under that is way to little for the engine, and it has NO leaks. With this mainjet the sparkplug looks just fine, and the engine sound very good in the whole range. Squise is 0.55. Fuel 99 octaine with 3% oil = so rich in that way.



The same thing has happen now 5 times. We have tested bigger jets, but only result in a bike that run very very rich - we don't want that. Ignition is set to 2.25 as it shall be.

What can it possible be?

One problem i am thinking of is that the bike vibrate quite a bit at the 90-110 km/h range - where the bike always fuck up. Maybe the carburatour have problems dealing with those vibrations causing the fuel not to run very good. This is just my theory, i have never experienced it, even on hard vibrating aluminum sprinters.



Come up with what you think it can be, anything helps. 6 pistons don't come cheap.

 

[tragerdantraag]

empty float chamber?

sometimes caused bij heavy vibrating carburator or a empty feul tank or same level of feul in carb as in the tank.

 

[Sonic-speed]

empty float chamber?

sometimes caused bij heavy vibrating carburator or a empty feul tank or same level of feul in carb as in the tank.

That's the question i am asking myself. What to do about it, vibrations cannot be romoved due to the subframe is stuff (trackbike).

 

[tragerdantraag]

try another carb first. or rise up the feul level in the carb by resetting the float.

 

[Cruz_e_Silva]

Check/change the CDI also...maybe it's advancing the ignition too much at some revs

 

[Pronk]

Set the ignition on 2.15mm before TDC. I had the same problem i few years ago, killed two pistons with it and the ignition was set on 2.25 according to the malossi specs. It won't change your power output that much, probably little less aggressive on the throttle and somewhat more peak power.

Like cruz is saying, maybe there's something wrong with the ignition curve inside the CDI. If you have a dyno you can check the ignition point with a strobo?

 

[Barry.]

Ground cable proper set?

 

[Sonic-speed]

We will try another ignition and carb. this weekend. One at a time.