32 replies to this topic

[Kevybmini]

 

No 1 spark plug is very white if that makes any sense. No 2 normal

Possibly running excessively lean at full throttle, causing the exhaust valves to overheat and bind in the guides, preventing them closing and engine dies. Lack of compression so won't restart. Valves cool sufficiently after 20-30 seconds and free off adequately in guides allowing them to close again. This would account for vacuum gauge readings too.
If the above should be the cause, the valves and guides will need replacing and the cam and followers will likely be wrecked as well.
Have you had it set up on a rolling road since modifications have been carried out?

 

No, but an interesting theory 

[Kevybmini]

 

 

No 1 spark plug is very white if that makes any sense. No 2 normal

Possibly running excessively lean at full throttle, causing the exhaust valves to overheat and bind in the guides, preventing them closing and engine dies. Lack of compression so won't restart. Valves cool sufficiently after 20-30 seconds and free off adequately in guides allowing them to close again. This would account for vacuum gauge readings too.
If the above should be the cause, the valves and guides will need replacing and the cam and followers will likely be wrecked as well.
Have you had it set up on a rolling road since modifications have been carried out?

 

No, but an interesting theory 

 

I drove it today from cold and kept the choke on - still did the same. 

[johnR]

I had similar symptoms with my re-built 1293 on twin HS2s - it would rev fine at idle, pull strongly until about 60mph then it felt as though it was being starved of fuel, stopped for a few minutes then off it would go again. After upgrading all the fuel system it turned out to be the big ends binding when warmed up and they failed at @100miles. Still don't know why unfortunately as the clearances were all checked as part of the build as usual.