My current primary fuel jet is a .072, I ordered 3 sets of jets from .069 to .071, .069 was the smallest available for the Quadrajet.

The jets should be here next week, going to install the .069 first. Try the smallest first hope for the best fuel mileage, with0ut running to lean.

This is just my opinion, If it is running good I would not change a thing. A Q-jet is already best self adjusting metered carb built. I will take a well running engine over fuel economy any day. You most likely paid more for jets than you will ever get back in g savings. The best way to save on fuel cost is to slow down. Proper tire pressure will gain some saving. Just accept you got an 8 mpg hog and enjoy it.Overdrive might help, but you will never get a return for the investment. If you drive East and down hill will help. My best mpg increase came from driving the class C over the Class A. 7.8 mpg average to over 10 mpg.

Doorman you are probably so right it is scary!!!

Actually the jets were the cheapest part of this whole experiment, got them on Ebay, $18 for the lot.. having an oxygen sensor bung welded in and my Cadillac sensor had six pins, would have been impossible to use in this application so a new sensor was needed, those were the expensive parts.

But what would I do with my time during this covid issue if Nose did not fill my schedule and empty my wallet.

Just one comment, since the overheat issue on the trip to Elkhart last year, you folks have put up with my rants and raves, given me excellent advise and just made this adventure a fun and learning experience for me. I hope y'all have had a good time too!! Lets get on the road! Thanks all.

After years of hoping to have someone come up with the magical gas mileage improvement, Have not seen the miracle yet. Running speeds seam to be the biggest improvement. As far as changing the primary main jets. They only control fuel flow when the primary are wide open and you are runnig off the secondary system. At part throttle fuel is controled by the rods. Both size and height of rods. Changing rod sizes and lift cams will change this fuel circuit. Set up right the Q-jet is one of the better fuel economy carbs. Electronic FI is the way to go for the best fuel contol. Even with FI iI have not seen the improvment to justify the investment. I understand the obsesion with trying to improve miliage.But at what cost. All of P-30 owners want the same thing. More power and better gas mileage. Steve VW Improved his But at what cost. In my younger days driving a motorhome was the cheaper way to vacation. now it has become a luxury. With this covid it may be the safest way. Duane, good luck my friend with your venture. Like you said it gives you something to spend your time on. Hopefully things get back to normal One of these days and we can hook back up at some gtg. This social distanting sucks!!!!

These old carburetors are pretty highly engineered devices for sure. The recommended diameter change is .030 rod to jet hole.

Doing some math, jet hole area minus rod diameter area, should give me fuel flow area. I will start out with my current set up .072 jet and .042 rods this is fuel flow at idle, before the taper on the rod begins to engage. This gives me an area of .0027..the new area using a .069 jet and no changes to the rod is .0023. making a net change in fuel flow area at idle of .0004. as a percent about 15%. this is of course is with no changes to rods or springs, and I am not sure what effect this will have on the flow as the rod taper comes into play. Assuming all works the same should see a similar (perhaps a small decrease) percent change at any point in rod movement operation. with the rod tips out of the holes ( do not think this ever happens) the change in area is about 8%. Thus less fuel flow should occur all the way thru the travel of the rods or to the secondary's open. Maybe!!!! lmao

My fancy new gage will tell the story after the change in jets!!!!

I thought I would just cacluate the cost of doing a similar experiment to this,

1) a gage to measure mixture ( would get the expanded range gage) $125
2) Oxygen sensor, and bung kit $125
3) weld in bung $80
4) jets $8 each (discounted if you buy 3-$6 each)

So $350 m/l Oh well it is only money!! So if one can save save .5 mile per gallon (go from 8 to 8.5 mpg @$2.50 per gallon) thats about $.15 per gallon. Payback about 2500 gallons or 21000 miles, what a deal!!!!

quote:

s

So $350 m/l Oh well it is only money!! So if one can save save .5 mile per gallon (go from 8 to 8.5 mph @$2.50 per gallon) thats about $.15 per gallon. Payback about 2500 gallons or 21000 miles, what a deal!!!!

If you can get them to raise the price of gas you will save even more $.

quote:

Originally posted by Doorman:

quote:

s

So $350 m/l Oh well it is only money!! So if one can save save .5 mile per gallon (go from 8 to 8.5 mph @$2.50 per gallon) thats about $.15 per gallon. Payback about 2500 gallons or 21000 miles, what a deal!!!!

If you can get them to raise the price of gas you will save even more $.

I am going to try and get that going right away!!!

Back in the 1970's I bought a bunch of stuff from J.C. Whitney to improve gas mileage . I ended up having to carry empty gas cans around and drain a few gallons off every weekend.

Could alway swap in a 6.5T diesel. Add sometype of overdrive unit and at least double your mpg. The engine is still in production and used in the Armys Hummer. Have fun.

Or a nice little 4bt Cummins

You'd be cranking out 20 mpg in no time

That little 4bt can be turned into a workhorse

Ok Diesel is nice but talk never living out the payback!!!

Well I changed out the jets, chickened out on going the smallest .069 and went with .070.

Now here is the weird part, under acceleration and deceleration the fuel/air mixture is right very close to 14.7 to 1. However at cruise it is off the map lean, to lean for the gage to give a readout. At idle the reading is a bit rich but not bad according to the gage. Seems like if it gets anywhere over 2500rpm it goes to lean.

Thinking maybe the .071 would be a better choice, have to do the math to determine the change as a percent. Certainly did not anticipate a change this large. Remember I started with .072.

Did the math. Using the .071 there would be a 4% change in fuel flow area rather than the 15% using the .069 jet. a little less than 3% with the rods out of the jet. Make the change tomorrow!!!

You are having entirely too much fun

Hum (aka Jim)

Here we go again, while changing to the .071 jets, took a look at the fuel filter in the Rochester, the thing was completely fouled. Looks like rust, was pretty sure the tanks were clean by now..Wrong!!! Very few miles or run time on this filter.

Anyway, put the carb back together, fired it up. Seems to run well the fuel/mixture gauge during acceleration and deceleration is right on, at idle it is a bit rich, in the driveway at a constant speed anywhere above 2500 RPM until about maybe 4000rpm it is very lean. Before making any judgement, it needs to be road tested...Tomorrows job.

Going to get a vacuum gauge might have a leak, curious where it is running.

Thinking out loud again, might go back to the .072 jets and check if things have changed, one would think there are better things to do with ones life!!!

Has anyone glued the lead plugs, they say they are prone to leakage and maybe my reserve bowl is draining over night. Internet says JB weld is the best, but how much does one put in or do you just cover the lead plugs periphery as best possible can't find a picture of one that has been sealed.

Have sealed many Q-jet well plugs. I have used a 2-part epoxy. JB weld should work fine. Turn the carb upsiide down and clean the plug area good and just pour a good cap on top of them and let i dry. I found if i let the fuel settle for a few min. after filling up that my filters did not clog near as often. I did end up dropping the tank and cleaning it.