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Message started by Mattdw on 09/09/08 at 08:28:25

Title: Rejetting and MPG change.
Post by Mattdw on 09/09/08 at 08:28:25

All,

I have a non-calif '96 and I'm trying to figure a few things out with my jetting changes. Looking in Clymer's, there is a table that shows the stock carb's main jet size. I can't figure out my carb model to determine if it is the 145 or 155 main jet.

I have added a screenshot of the table in this posting.

http://www.wheatoncs.com/CarbSpecs.jpg

For the moment, I am going to assume I have a 145 main jet as people seem to 'jet up' to get more power.

Based on average driving 60-70 MPH, and using the Lancer jetkit with 150, 152.5, and 155 main jets, and rough idea what the MPG change should be from one to the next, all the way down to the 145 I presumably have?

Title: Re: Rejetting and MPG change.
Post by verslagen1 on 09/09/08 at 08:54:34

How are you going to chart mild smile to buhaha?

Title: Re: Rejetting and MPG change.
Post by serowbot on 09/09/08 at 09:49:29

Far as I know,

125# is Cal. and some foreign countries
155# is the 80's 4 speed model
145# is non-Cal US 5 speed

Pilot jet will affect mileage most, unless you tend to jackrabbit. The main and slide work mostly under low vacuum open throttle conditions.

Title: Re: Rejetting and MPG change.
Post by Mattdw on 09/09/08 at 10:01:17

2E382F322A3F32295D0 wrote:

Pilot jet will affect mileage most, unless you tend to jackrabbit. The main and slide work mostly under low vacuum open throttle conditions.

So, is it reasonable to put back my original pilot jet and still run with a 150, or a 152.5 main?
I have done the spacer mod to about 1/2 original spacer (using washers from the Lancer jetkit)

I did the original rejetting to get rid of the BIG BANG backfire. I like the additional power of the larger jets, but I still want to get rid of the backfire and retain fuel economy.

I would like to avoid taking the whole carb out again (ugh). I can mess with combinations of the pilot and main jets without removing the whole carb. Does the slide (spacer mod) affect mileage, do I need to revert that change to work on this?

Title: Re: Rejetting and MPG change.
Post by serowbot on 09/09/08 at 10:23:10

Depends on elevation and humidity, but generally staying with the stock pilot jet will help maintain good cruising mileage,.. best reduction of bang is with idle mix and higher idle speed. Bigger main and slide mod will help acceleration up to a point,...To test the main, Accelerate from 30 or 40 mph, in 4th or 5th gear at full throttle for several seconds, then reduce throttle by about 1/8,...if power increases for a second, you are lean on the main jet. Go up one jet size and test again.
Best of luck and ride safe,
Serowbot

Title: Re: Rejetting and MPG change.
Post by verslagen1 on 09/09/08 at 22:06:45

5A4C5B465E4B465D290 wrote:

Pilot jet is for up to 1/8 throttle or thereabouts. I'd don't know how you ride but I give 1/2 throttle more or less up thru the gears and hold it there till I have to stop. So pilot has the least effect on my gas mileage.

Title: Re: Rejetting and MPG change.
Post by serowbot on 09/10/08 at 11:23:49

564552534C4147454E11200 wrote:

Taking off, you're sucking gas,.. but while cruising, the engine is at high vacuum, pulling the slide needle down into the jet passage,...so most of the gas is coming from the pilot circuit. Spacing the needle increases that some, but the engine requires little gas to cruise at a steady 60mph.
70+ for me, seems to start opening up the needle and then you're right,... it's on to the needle/main curcuit.

Here's a quote from Mikuni,
"Normal highway cruising speeds (65 mph/ 100 kph) require rather low throttle openings, generally less than º throttle. Air/fuel ratios in this throttle range are controlled by the pilot circuit together with the jet needle and needle jet. Thus, poor fuel economy at normal cruising speeds should be addressed by altering or adjusting these parts."

Title: Re: Rejetting and MPG change.
Post by T Mack 1 on 09/11/08 at 11:50:33

283E29342C39342F5B0 wrote:

..........

Here's a quote from Mikuni,
"Normal highway cruising speeds (65 mph/ 100 kph) require rather low throttle openings, generally less than º throttle. Air/fuel ratios in this throttle range are controlled by the pilot circuit together with the jet needle and needle jet. Thus, poor fuel economy at normal cruising speeds should be addressed by altering or adjusting these parts."

thanks...... this is helpful...