I just finished my first full tank of gas following the repairs on my R* Silverado. I like the increase in power the new Hard Chrome 3" sideburners seem to have given me, but the miles per gallon seem to be very low. No backfire problems and I need a little choke to get it going on cool mornings. AIS is gone. The carb was adjusted by the shop to get rid of the backfire in the old moded OEM pipes (Biker Brackets modification) and I don't think it was adjusted by the shop when they put on the new pipes. What I am wondering is: if I increase the air flow by drilling out the air box sides, will that lean it out a bit? I am thinking that it is running rich because of the lower miles per gallon and I get a puff of black when rapping out the throttle if the bike has been sitting for a hour or so.

"but the miles per gallon seem to be very low" .... how low?

40-50 is OK.

"I get a puff of black when rapping out the throttle if the bike has been
sitting for a hour or so" .... when you first start it? That would be normal as you have the choke on.

Drilling does not increase the flow rate a lot as you still have the OEM filter in it but it may be sufficient for your setup.

Try re-adjusting your PMS. Make sure it idles at about 8000 rpm. Warm the bike up, slowly turn the PMS in until the bike stumbles, turn it out until it stumbles, halfway between these two points is about where you want to be. If you have a tach then set the PMS to where the revs max out.

Doc<br><br>Post edited by: DocShadow, at: 2006/05/04 10:50

DocShadow wrote:


Try re-adjusting your PMS. Make sure it idles at about 8000 rpm.

i take it you&acute;ve disconnected your rev limiter then?

I'll bet ol' Doc lays rubber every time he lets off the clutch with an idle like that!

I'm sure he meant 800!

It's colder up North so we need to keep the idle up

Now I know you guys are reading the posts.

Doc

Doc, I figure that I'm getting close to 30 mpg. I used to get 40 to 45 with the modified pipes. The HC sideburners have fixed mufflers in them and I don't want to mess with them. I was thinking about cutting holes in the air filter cover like some have done. My questions is, will having more air lean out the air/fuel mixture? I'll give the PMS some twists to see where it is at as well.

Doc. Will changing the filter in the OEM box help? Any suggestions for a replacement?<br><br>Post edited by: JMayton, at: 2006/05/04 12:23

I'm surprised your mileage is so bad after adding only pipes.

My recommendation is that one should change pipes and aircleaner as a unit. That will give one the most bang for the buck and the least hassle.

I recognize that it's not always possible to do so, in that case pipes first and aircleaner second. Pipes first 'cause you don't need to mess with the jetting .... and it looks and sounds better than the aircleaner

Yes, drilling holes (especially in the front) will allow more air to get in. How much? Don't know as you're still dealing with a restrictive paper filter vs the K&amp;N. Certainly will not cost you anything to try it.

I would not buy a K&amp;N filter for the OEM unless you like the OEM airbox. Even with the holes I don't think it's as efficient as aftermarket ones.

Try the PMS. If that does not work then you will need to rejet and I would buy the complete kit (needle + jets) rather than individual jets. Most crusing is at 1/4 or less throttle so I suspect the needle may be contributing to the poor mileage. If you turn the PMS in and you cannot stall the engine then you are too rich.

My recommendation is Baron (good needle) but the final decision is yours.

Sorry I can't give you firm answers. Most of the carb tuning is 'get it in the ballpark' and then 'trial and error' to refine it.

Doc

Doc. Which direction is in; clock or counter clock?

Same as screwing

Lefty loosey, righty tightey. But don't forget it's upside down.

Tighten carefully; seat it lightly not hard.

Doc