Red Pepper Racing

Alright guys. By now I am probably being a pain. I did a Si head swap and devac. Now the gas mileage went from around 40 mpg all the way down to 18 mpg! I have read a lot of people getting more miles to the gallon after the devac but, I prepared my self to get a little worse cause that's how things go for me most of the time. The car seems to run just fine. What do you think would cause this? Carb needing to be tuned or what?

How is your timing? Did you set it to the DX spec or the FI spec? Check the service manuals for the specific numbers, but the FI timing spec is about 4 degrees more (probably due to the different combustion chambers/pistons) and you might want to go closer to that for better fuel consumption.

Just a thought.
Cheers,
Mark

have you checked your spark plugs to see how its burning. i just did the same swap i have a weber 32 34 dgv and im getting around 28 or so. sounds to me like it is running way rich

Lean out your mix, and advance the timing with the distributor slightly. This should correct the issues you are seeing now.


One question, How is your idle? Is it high? Like 1200 to 2000 or is it low 700-1000?

It might be an idle issue, this is corrected through a couple of ways, the screw at the base of teh throttle cable on the carb, and the throttlecable itself.

You have a little gas hog in yur tank....get the 30/30 out....bang...lol

I have an Si motor running on 32/34 DMTR. I get 27 city, 32 hwy. Check your cam and ignition timing.

Which carb are you using and what did you do with the CVCC barrel?

I'm going to check the distributor timing tomorrow as well as plugs. The crank and cam are lined up perfect. I just have to borrow my bros timing light. It idles high like 1200 but, when you turn it down it acts like it wants to die and a lot of the times it does when it is below 1200. Would this be caused from a rich mixture? The cvcc port is sealed off. Going from 40 mpg to 18 mpg is like a kick in the gut. Thanks again guys for helping me out.

I had the same issues (well still to a point do to a bad carb) when I devac'd the Dx mani and swapped out the EW1 head (that was cracked) for my EW3 head. I played aroung w/ some vaccum line routing, and that fixed the idle issue. Now it either runs way TOO rich or TOO lean. I'm only getting about 20mpg. Hopefully my bike carbs will help me out a little the the whole A/F ratio BS! Seeing that gauge go LEAN scares the shit out of me!

my gas milage is prolly like 5 mpg

5mpg would suck for a daily driver like mine.

Okay I leaned out the carb a little and advanced the timing. I have only gotten to drive it around the block so no difference I could see yet. I am out of town and will get back in a day and a half and test it a little more. I adjusted the gas in the carb just below the middle of the window. Do I need to go more or do you think that should do it? Thanks again.

Your adjustments should be fine, maybe a little lower on the carb window. Mine(before I cracked the head) was just at the lower needle in that window. 32-38mpg.

Looks like you received some good advice above. One more thing - the thermostat. You swapped the head, so you probably have a different thermostat now. What is the opening temp of the thermostat? Honda's get best mileage with a hot engine. Maybe you need a different thermostat? LOL So many things to check.

Okay, I got the ignition timed and the gas turned down a bit and let me tell you there was a huge difference. There is no more slow bogging 2nd gear and is pulling pretty solid in all the gears now. Now to check the gas mileage. Thanks guys for the help. I do have one more question though. It wont idle below about 1100 rpm without dieing. I can get it below but then is starts looping going up and down then it dies. When it's set at 1100 it stays put and doesn't move. What do you think?

when mine did that i had a small vacum leak