More Q and A…with Patrick James

//More Q and A…with Patrick James

More Q and A…with Patrick James

From time to time I stop into Yellowbullet.com to help the folks out.

Here are a couple of excerpts from those conversations:

I have changed my jetting beyond what most of my friends say is safe for my carburetor.  What is the problem?

Tips on Jetting.  If your carb designer has known combinations that they build from and have wet flow technology to verify their work, be concerned any time that you move more than a few numbers from where they have baselined it. Not really with the carb so much as the combinations variance from a known requirement.

As we all know, there are intake to exhaust percentage ranges that engines typically prefer to operate properly.

If, for example, your intake side is flowing a much larger percentage than is preferred as compared to the exhaust side, the combination will typically be rich (to prove this: add a typical restrictive type muffler to a combination and notice the engine runs richer…remove a typical restrictive type muffler and notice the engine will get leaner).

If your supplied information from your build requires a jetting change that goes outside of the parameters that we’ve selected, contact our shop as we want to talk to you a bit more about your combination (as compared to thousands we have seen and documented) so we can get an idea of what circuit actually needs changed.  Or even a possible change to the vehicle combination in case after further questioning, we discover a bottleneck.

Many times, if a carb is rich at an idle, the owner will jet the carb down as it shows rich going down the race track when in reality it has simply loaded the plugs up and they are cleaning out as it goes down the track. This gives the impression of too rich of a main jetting selection but in reality its a rich idle. Or even both.

But you have to get the idle set before you even go to wide open throttle.

A simple idle mixture screw or idle air bleed or intermediate change will properly correct the idling air to fuel ratio.

A clean idle is very important so excessive fuel hanging around in your intake area and on your plugs doesn’t skew your down track air to fuel ratios. A clean idle ensures proper ratios and fuel curves as your plugs are clean and ready to go for a good starting line launch.

Then you can move on to main jetting and review of the program for jetting changes.

I am running into a problem with my engine since I changed to a new high octane fuel. The engine now backfires when its cold out and burns piston and raises ringlands easily when I spray it with nitrous.  My engine builder says I have too high of an octane fuel.  Can too high of an octane fuel cause these conditions?

Remember octane is “resistance to ignition”. If you run too high of an octane the engine will interpret it as being lean as it has an unburnable mixture displacing a location where burnable fuel should be and there are left over available oxygen molecules looking for a companion.

This problem will also compound as it gets cooler out as you go further away from the “auto ignition” that you were trying to escape with the high octane. Making it even leaner and more of a problem (cooler fuel..harder to light..cooler air more available oxygen).

SO YES, too high of an octane can cause a lean condition and puddling etc…

Hope this helps.

By |2008-10-20T23:52:19+00:00October 20th, 2008|Uncategorized|Comments Off on More Q and A…with Patrick James