lean
i read this article
so factory pipe gave me new larger jets but since i run 35 ada dome head do i need to install anything else anyone have this happen to them and had to go up in needle and seat sizes???
Seizure by running out of gas - as many people already know, a larger size needle and seat must often be installed into a carburetor to contend with the increased fuel demands of a moderately modified engine. If a modified engine is operated at full throttle with a stock size needle and seat, it will usually carry full rpm for about 2 or 3 seconds and then shut off as if someone hit the kill button. When the machine comes to a stop, the rider touches the start button to see what the problem is. The engine, no longer in fuel deficit caused by the undersized needle and seat, unexpectedly starts right up.
This instant high speed shut off is caused by the carburetor literally running out of gas. It is sometimes implied that during this shut down moment of fuel starvation, the engine is also starved of the oil that is pre mixed in. This perceived oil starvation is then blamed for any subsequent piston scoring or seizure. Watercraft pistons do not seize in this way...ever.
At the moment that the fuel starved engine shuts down, combustion and all the heat associated with it "ceases". Unlike a motorcycle whose rear wheel traction continues to move the pistons in the bores at a very high "friction causing" speed, the propeller and pistons in a fuel starved watercraft stop turning almost instantly. The heat and movement friction that can cause seizure are virtually non existent in a fuel starved watercraft shut down. This same concept applies to any machine that simply runs it's main tank dry before having to switch to reserve.
It is possible for a rider, whose carb has an under sized needle and seat, to induce a piston seizure. However this would require a great deal of combined skill and stupidity. Once the rider has established that extended full throttle operation causes his engine to quit, he might make the very poor choice of only applying enough high speed throttle to avoid starving the engine. When he does this, he will be capable of maintaining about 90% throttle which will hold the engine endlessly on the lean thresh hold of fuel starvation. As this rider eventually masters this throttle position, he will be able to maintain a very high rpm with the carb feeding a horrifically lean mixture. Ultimately his finesse will be rewarded by one of the most abrupt and destructive lean mixture seizures that his mechanic has ever seen.
