Gen1Pat
Well-Known Member
Besides, the only way for the air and fuel to enter one of these engines is by the vaccuum created when the piston moves down on the intake stroke. That vaccuum is what pulls the air and fuel into the combustion chamber. You can sit there all day long with the engine off and hold the throttle wide open and fuel isn't just going to pour into the intake, sure the accel pump will spray the first time you hit the throttle. But it's not going to pour in like on an automotive carb that has a pressurized system (because these atv systems are gravity feed, not pressurised by a fuel pump). Any of use that have worked on a carbed car will know that with the engine off you can open the throttle and fuel with spray into the intake until all the residual pressure has been depleated from the system (and yeah I know that carbed or tbi automotive engines still need engine vacuum to pull the air and fuel into the intake/individual cylinders as well). Especially that of an older auto with a mechanical fuel pump.
Sooo, when the intake valve is closed the vaccuum has stopped for that VERY brief period, so very little fuel can even build up in the intake. How long is that intake really closed for, a mirco 2nd? And that's just at idle. No way for fuel to really "build up" in the intake before the valve opens again.
A good way to understand how fast the valves are opening and closing (for those that have never done this), would be to put your palm over the carb inlet (with the engine running) and it'll suck your hand right to it and will shut the engine down. And that's at idle, too. So the valves open and close fast enough just at IDLE to have very continuous vaccuum. And any quad that has ever had a fuel pump (old honda 350 foremans, suzuki quadrunner 250s) have them because they don't have gravitly feed fuel tanks. The tanks are mounted below the level of the carb and the pumps are used to circulate fuel into the float bowl. The air and fuel still need engine vaccuum to be drawn into the intake. Just my .02 Always love a healthy debate. lol
Oh, and ksowin87. Checking your valve timing isn't hard or long and is only good practice, especially since you sound as though you have doubts about it. Your there, we're not, only you know what the bike is doing first hand. And adjusting your valves is good maintenance as well. Good luck to ya.
Sooo, when the intake valve is closed the vaccuum has stopped for that VERY brief period, so very little fuel can even build up in the intake. How long is that intake really closed for, a mirco 2nd? And that's just at idle. No way for fuel to really "build up" in the intake before the valve opens again.
A good way to understand how fast the valves are opening and closing (for those that have never done this), would be to put your palm over the carb inlet (with the engine running) and it'll suck your hand right to it and will shut the engine down. And that's at idle, too. So the valves open and close fast enough just at IDLE to have very continuous vaccuum. And any quad that has ever had a fuel pump (old honda 350 foremans, suzuki quadrunner 250s) have them because they don't have gravitly feed fuel tanks. The tanks are mounted below the level of the carb and the pumps are used to circulate fuel into the float bowl. The air and fuel still need engine vaccuum to be drawn into the intake. Just my .02 Always love a healthy debate. lol
Oh, and ksowin87. Checking your valve timing isn't hard or long and is only good practice, especially since you sound as though you have doubts about it. Your there, we're not, only you know what the bike is doing first hand. And adjusting your valves is good maintenance as well. Good luck to ya.
