Jeff asked about misting fuel at the carb throat. This is a problem caused by a number of factors. Igntion timing isn't one of them!! Aaron correctly mentioned one of them: cam overlap. The other major factor is the design of the exhaust system you are using.
Many people mistakenly refer to "back pressure" in the exhaust system as a good thing. It isn't. The unimpeded flow of exhaust gasses is a always a good thing. The problem with modified exhaust system is that they can cause reversion waves. This causes a pulse effect back up the exhasut system. If you are running a cam with a lot of overlap you can end up with this pulse running right through the combustion chamber and having the effect of pushing some vaporized fuel out of the carb. Then it's sucked back into the carb causing an over rich mixture. Typically this will only happen over a small amount of the rpm range. There are many cures for this including exhaust crossovers (used on current Mustangs for example, often referred to as H pipes or X pipes); exhaust venturi "cones" which sit in the exhaust header next to the port and prevent the reversion wave getting into the combustion chamber. Another technique is a "brooklands" style (aka collector) exhaust system. By using these techniques racers can optimize reversion characteristics to suit their needs. A great example are Harley drag bikes. Unbaffled drag pipes are a potential reversion nightmare. By cutting the pipes incrementally shorter you can tune the reversion out of the rpm ranged used. In fact one can tune the reversion wave to help scavenge the combustion chamber. The typical street bike is probably giving up as much as 10hp by running those loud pipes.... HTH Neil Jeff wrote: Another lister mentioned something that I've noticed with my carbs -- the slight pushing out of air with some fuel misting from the carb throat. I started with a MkIV engine, but it's been highly modified from the head on down, including a fast road cam from Ted Schumacher (.425 lift). Is this just a very fine tuning timing issue? Or should I be concerned about something else? __________________________________________________ Yahoo! Tax Center - File online, calculators, forms, and more http://platinum.yahoo.com /// [EMAIL PROTECTED] mailing list /// Send admin requests to [EMAIL PROTECTED] /// or try http://www.team.net/cgi-bin/majorcool /// Archives at http://www.team.net/archive /// Send list postings to [EMAIL PROTECTED] /// Edit your replies! If they include this trailer, they will NOT be sent.
