![]() |
![]() |
#1 |
Registered User
Join Date: Mar 2013
Location: Waukesha, WI
Posts: 15
|
Sgl or dbl brl carb?
Getting 10mpg; would love 15mpg; which way do I go? straight 6 / 250.
|
![]() |
![]() |
![]() |
#2 |
Senior Member
![]() Join Date: Oct 2009
Location: Godley, TX
Posts: 17,964
|
Re: Sgl or dbl brl carb?
Welcome to the board Poppa. Could you provide a little driveline info? Trans/ratios - rear end ratio, tire size, etc? That might help. Personally, I would use a 2 barrel on a 6. 1 probably not enough, 4 too much.
|
![]() |
![]() |
![]() |
#3 |
Registered User
Join Date: Oct 2005
Location: Overland Park, Ks.
Posts: 5,217
|
Re: Sgl or dbl brl carb?
If the Monojet carb & ign. are all tuned good it should get better MPG then that. Like Jocko says , a lot depends on the gear ratio.
|
![]() |
![]() |
![]() |
#4 |
Registered User
Join Date: Dec 2009
Location: Glendale, AZ
Posts: 337
|
Re: Sgl or dbl brl carb?
I have the 250 as well, and a 3 speed M/T. I'm not positive on the rear end gear ratio, but I think it is 4.11. With HEI and a rebuilt monojet, I have never gotten more than 11mpg on good day.
|
![]() |
![]() |
![]() |
#5 | |
Active Member
![]() Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
|
Re: Sgl or dbl brl carb?
Quote:
It could be one or several things involved. What I would do is to start with the simplest thing first. Replace all the ignition components like distributor cap and rotor, points, condenser, plug wires and plugs themselves. Maybe even the coil. After that get a kit and rebuild the carb. They're very easy to work on. If that doesn't help, you're looking at engine rebuild or rear axle swap. I get about 15-16 mpg on my GMC 250 with single barrel and 3.54 rear axle.
__________________
68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... |
|
![]() |
![]() |
![]() |
#6 |
Registered User
Join Date: Mar 2004
Location: Hoytsville, Utah
Posts: 3,365
|
Re: Sgl or dbl brl carb?
Yeah, that's about right where I am. 250/4 speed. Not real sure about my gears, either, I used to think 3.73, but I think maybe 3.54 seems more realistic with my mileage and the fact that I can do 70+ all day long on the flat.
__________________
'68 Panel Project Boogie Chillin' '68 C-10 Ol' Green |
![]() |
![]() |
![]() |
#7 |
Registered User
Join Date: Mar 2013
Location: Waukesha, WI
Posts: 15
|
Re: Sgl or dbl brl carb?
12 Bolt 373 gears 235 75r15 tires brand new
|
![]() |
![]() |
![]() |
#8 |
Senior Member
![]() Join Date: Oct 2009
Location: Godley, TX
Posts: 17,964
|
Re: Sgl or dbl brl carb?
I'm assuming you have a grann4 or 3 ott? If that's the case, the one thing I would focus on, rather than the carb, is the trans. 1:1 final trans ratio will kill highway mileage. If you drive it above 55 mph much at all, you'd probably see more gains by swapping in an o/d trans, such as a T5 if you prefer manual or 2004R or 700R4 if you prefer autos. Might be more than you want to spend - but since you're looking for a fairly BIG improvement in gas mileage, I'm afraid you won't get it just by changing to a 2 bbl (or from a 2bbl to a 1 bbl, vice versa).
Only other realistic option (but it would cost you bottom end acceleration (I'm not talking drag racing here, but basic bottom end torque "feel") would be to swap out the 3.73's for something lower numerically. 50% mileage increase is a lofty goal - and, as you've seen, you're getting roughly what everyone else is getting with your combo, so it would take a major change to get what you're looking for. Great question - I'd still like to hear from others that may have swapped 1bbl vs 2 bbl on a similar setup just to learn. |
![]() |
![]() |
![]() |
#9 |
Registered User
Join Date: Oct 2005
Location: Overland Park, Ks.
Posts: 5,217
|
Re: Sgl or dbl brl carb?
Its obvious you need a higher gear but some tuning & adjustments might help. Make sure the vacuum advance is working. It is good for 2-3 MPG. You could try hooking it up to full manifold vacuum as generally they are hooked to ported vacuum. Check the metering rod adjustment. You might lower it a little if it is at the factory spec or higher. Make sure the float level is correct & the float is not heavy. Try setting the initial timing a little more advanced then specs. If it pings after that you will need to set it back.
|
![]() |
![]() |
![]() |
#10 |
Registered User
Join Date: Mar 2013
Location: Waukesha, WI
Posts: 15
|
Re: Sgl or dbl brl carb?
Pritch thanks for your input.
|
![]() |
![]() |
![]() |
Bookmarks |
|
|