CKRC Forums

Hi All,

Today we had a new VLR motor that would idle but wasn't able to rev under higher throttle application. After diagnosing everything from the reeds to rebuilding the carb, changing plugs and checking the wiring harness the culprit was the Carburetor Intake Manifold(item 30). The hole by the red arrow (in photo) feeds crankcase pressure to the carburetor pumper with each stroke of the crankshaft. The carburetor was getting enough pulse pressure to run at idle but under higher RPMS the motor would starve for fuel. In this case there was a manufacturing defect that did not have the tunnel machined out completely. Once this defect was identified and the tunnel was cleared the motor ran as normal. Red arrows above and below show pathway of case pressure pulses.

How long did it run without sufficient fuel? I would be concerned about the bottom end not having been lubricated enough, and may lead to pre-mature bearing failure.

It didn't ! Because it wouldn't clear itself it loaded up the bottom end and when we took the exhaust off it was swimming in oil ! I have sent a message to ROK Canada and ROK USA to make sure they know of the problem in case we have a Warranty issue.

The same thing will happen if you get the gasket installed upside down. In other words, if the hole in the gasket isn't aligned with the hole in the intake, it will do the same thing - it will start and run but won't rev up. I found this out when I had to remove my carburetor and reeds for inspection after a heat race and then before the main race, my engine wouldn't run right. Fortunately, the engine builder knew exactly what I did wrong and helped me rotate it 180 degrees.