19.8 mpg? - Page 2

GotaT · 12-03-2007, 10:19 AM

Im getting about 15.5 IN TOWN driving with of course spurts of power! on my 2.4 w/ Webers

Still have yet to check it on the HWY.. but I know I need some throttle shaft repair.. = not tuned the best right now.

BlueSideUp · 12-07-2007, 10:47 AM

I did a little checking on my Webers this week but the batteries were dead so I couldn't fire it up. I removed the idle mixture screws and the air correction screws to spray some carb cleaner in the holes and clean things up a bit. There wasn't much build up at all but I did notice the air correction screws are all nearly bottomed out. Is that a normal setting? Last time I checked with my synchrometer the throats are all balanced very well.

The idle mixture screws are also nearly all the way out, maybe one turn in on each cylinder.

911pcars · 12-07-2007, 11:02 AM

Quote:

Originally Posted by BlueSideUp

I did a little checking on my Webers this week but the batteries were dead so I couldn't fire it up. I removed the idle mixture screws and the air correction screws to spray some carb cleaner in the holes and clean things up a bit. There wasn't much build up at all but I did notice the air correction screws are all nearly bottomed out. Is that a normal setting? Last time I checked with my synchrometer the throats are all balanced very well.

The idle mixture screws are also nearly all the way out, maybe one turn in on each cylinder.

That's the normal position of the air correction screws. They're used to balance the airflow into each cylinder at idle since it isn't possible to have all three throttle plates in perfect unison (at least for idle purposes).

As for the idle mixture screws, they have more travel and adjustment range than one turn out from seated, which, btw, seems about right.

Sherwood

BlueSideUp · 12-07-2007, 11:20 AM

Thank you for the help Sherwood. My idle mixture screws are actually one turn in, the spring seats on the carb body and then they are about one/half to one full turn in from that. I assume that is nearly full rich.

I am planning on making sure the idle and main jets are clean when I get back home this week. The intake gaskets need to be checked as well so I'll be picking up either ether or carb cleaner for that.

Hopefully I can get a video up soon so you guys can see how she runs.

911pcars · 12-07-2007, 11:40 AM

Quote:

Originally Posted by BlueSideUp

Thank you for the help Sherwood. My idle mixture screws are actually one turn in, the spring seats on the carb body and then they are about one/half to one full turn in from that. I assume that is nearly full rich.

I am planning on making sure the idle and main jets are clean when I get back home this week. The intake gaskets need to be checked as well so I'll be picking up either ether or carb cleaner for that.

Hopefully I can get a video up soon so you guys can see how she runs.

The idle mixture is leanest when the mixture screw is screwed in to the stop (internally). The spring merely provides tension to maintain the desired adjustment setting and thus has no effect on the mixture.

Sounds like you have a fairly rich idle mixture if you're using the spring as a reference.

The correct reference point is to start with all the mixture screws lightly seated, then back them off approx. 1 - 1 1/2 turns. I would also recommend a Synchrometer and a CO meter to monitor the settings while adjusting.

Idle mixture settings are fairly sensitive to small changes, and since the idle circuit is still active into the cruising range, a rich idle setting will affect overall fuel mileage more than one would expect.

Sherwood

gigem75 · 03:33 PM

Well since my speedo reads 85 @ 3800 upm in 5th and I know it's not 85 because the wheels are 14's and I'm assuming it's calibrated for 15's I'd probably break 20 going 3300? @70. With 15's, 19.8 @ 85 and 3800 would be pretty good? I'm not taking into account the exta aero drag so we could call it maybe 19, 18.5?

This is a great thread for webers

71 T still backfires

BlueSideUp · 01-10-2008, 08:19 PM

I followed the suggestions on the thread suggested by gigem75 and was able to tune my carbs.

Then I filled it up and did some driving. The improvement in gas mileage was actually really nice! I think I was getting around 14 or 15 miles per gallon before tuning the carbs. My last gas tank which was admittedly 70% highway 30% city averaged 23mpg!

I am going to run this next tank with more of a 50/50 split so we'll see how that one goes.

gigem75 · 06:44 AM

It was 31 degrees this morning and with a couple of squirts with the pedal she fired right up. Took a little finesse with the throttle to keep it running, it did die once or twice but all things considered espeically no cold start aids other than pumping the gas pedal it went fine. My original 18 mpg was on a very fresh complete engine rebuild and I've since refined the carb adjustments I would expect it to be better now. Having 14 inch wheels doesn't help though.

BlueSideUp · 01-11-2008, 07:33 AM

My car is the same way on startup, it's a little fussy at first and then calms down.

I have 15x7s and 8s with RS flares on the rear and a '74 915. My order for just went through Pelican to repack my CVs with new boots, put Swepco 201 in the trans, and I might pick up some Brad Penn for the oil change. We'll see if any of that effects the mileage.

gigem75 · 01-11-2008, 07:55 AM

my dreamometer says I'm doing 85 at 3800rpm so I'm sure it came with 15's

GotaT · 05-27-2008, 01:48 PM

I wanted to refresh this post a bit. I just got my Webers back and have tuned them. I am only getting about 13 in town, whereas before I was getting around 16. They were bored from 40 to 41's.. I know this will have some effect but I think I should get at least 16 still IN TOWN..

I will be taking a trip from Laf to Houston this weekend and am wondering If I should make any changes to my MIX screws before I hit the road.. Sounds like some of you have been able to make changes AND havent complained about any extra POPPING OR SPITTING than before..

What did you do.. I think we would agree to get bettter economy you would need to lean them out a bit

BlueSideUp · 05-27-2008, 01:57 PM

I leaned out the idle circuit on mine according to instructions posted by Steve at Rennsport. I seem to be getting much better gas mileage than before and the exhaust is less eye watering. My understanding is that at cruising load on the highway you are still running on the idle circuit so that would have a big effect on the fuel economy.

I have Weber 40s on what I think is a 2.2.

GotaT · 05-27-2008, 07:02 PM

Where are the instructions by Rennsport, or do you have them, id be interested in seeing if they are the same or similar to what I have.
Thanks

BlueSideUp · 05-27-2008, 08:28 PM

I can't find Steve's post but here is a good one.

Quote:

Originally Posted by T Bird

Cerbin
See below. I had to post in two replies due to the length. Hope it helps.
John

Weber Set-up
Part I

STEP 1- Accelerator Pump Volume
Measure the accelerator pump volume at each of the 6 nozzles. Before starting the car, turn the key “on” and energize the fuel pump. Let the pump run a minute or so to fill up the float bowls. The air cleaners are off. Now, lower the vial down the throat of barrel No. 1 and park it directly under the nozzle. Have the assistant in the car depress the gas pedal all the way, nice and easy. Withdraw the vial, record the results on a piece of paper, and dump the contents of the vial. Repeat at each nozzle. (You may have to remove the velocity stacks for cylinders 2, 3 and 6 to gain proper access to the nozzles for those barrels.) Adjust the nut on the accelerator pump rod as necessary. Turning the adjuster nut out will increase the amount injected, and vica versa. You want .6 to .8cc (ml) (.75cc works great). Get them all even.

This procedure can also be done on the bench. Just fill the float bowl that has the brass valve in the bottom that feeds fuel to the accelerator pump. Then activate the pump and measure. The advantage of measuring at this stage, as opposed to when the carburetors are attached to the intake manifolds, is that if there is a blockage, it is easy to get at the check valves, nozzles, pumps, and float bowl valves and clean them out.

This procedure also provides a good opportunity to check that the throttle plates are opening all the way (vertical) with the gas pedal floored. If they are not, turn the plastic adjuster under the gas pedal in to give more travel, or out (less travel) if the throttle plates rotate beyond the vertical position.

STEP 2- Float Level Adjustment
Remove one of the two float bowl plugs on one of the carbs. There are two plugs per carb since there are two float bowls and two floats per carb. Careful- all the fuel in the float bowl will dump out so catch it with a little jar. Now insert the tool and tighten it to prevent leaking, since any leaking at the washer will give false readings. You need to focus on the upper two lines scribed on the vial portion of the tool. The lower two lines are for the Zenith carbs that some 911T's used (70-71). Have the assistant turn on the key to energize the pump but don't try to start the car. Now the float bowl will fill and you'll see gas fill the vial. After the vial is through filling, carefully examine where the meniscus is. You want it right between the top two lines. Turn off the key. Remove the needle valve plug, back out the needle valve and seat and add or subtract washers as necessary to raise or lower the fuel level, respectively. (ADD SHIMS= INCREASE FUEL LEVEL; REMOVE SHIMS= DECREASE FUEL LEVEL). Replace the needle valve and seat and the plug and have the assistant turn on the key. Note the fuel level. Continue to adjust until the meniscus is spot-on. The washers that come with the tool differ in thickness. After you do one, you will develop a sense for how many washers you need to raise/lower the fuel level. Then remove the other float bowl plug on the same carb and repeat the process. Keep at it until you've got them all perfect.

A couple of things- some books say to measure the fuel level with the car running. I've tried it that way and believe me, it's pretty hard to do since the engine is vibrating when it’s running. This vibration makes the fuel is slosh around in the vial and thus it becomes difficult to determine if the level is correct. This is exacerbated by the fact that the two lines scribed on the vial are near the very top of the vial. Second point-- the washers under the float bowl plugs are crush washers that are good for one shot. After you replace the plugs, if you re-use the washers, they are likely to leak. If you have some extra ones, use them. If you don't, don't overtighten the little bastards. Just snug them and move on. You can always order more from PMO and then go back and replace them at your convenience.

STEP 3- Initial Start-up Adjustments
Make the initial adjustments to the screws as per PMO and fire it up.

Initial adjustments (PMO) are as follows:
Idle air correction: 1/8 turn out*
idle screws: ½ turn in after touching throttle arm on each carb
idle mixture screws: 2 turns out

(*I suggest turning all the idle air correction screws in (gently!) until they hit their seats, and lock them down for the initial start up. You want a nice rich mixture for starters to avoid excessive popping which is really distracting, and then work from there.)

Here is where it gets tricky- while your assistant in the car keeps the motor running by judicious applications of throttle so that the engine warms, you have to diagnose in a grossly rough way, what is going on and what you need to do to smooth out the idle so that you can get the car running tolerably well enough to begin the real work of balance, synchronization, mixture adjustment and idle speed adjustment.

If the engine idles (regardless of speed) with the initial settings, do the following: if any barrel is spitting, slowly open the mixture screw- like 1/8 of a turn at a time. This should reduce the incidence of popping/spitting. Once the popping is reduced, quickly measure vacuum on each barrel with your STE. Are the barrels of each carb pulling roughly the same vacuum? If not, and vacuum is all over the place, determine which carb is pulling, on average, more vacuum than the other. Then open up the idle stop screw on the carb that pulls less vacuum, or turn in the idle stop screw on the carb that pulls more vacuum, or both, so as to get both sides roughly equal. Keep engine speed close to idle speed (900 rpm).

If the engine won’t idle, have the assistant hold it at a faster speed and adjust the mixture screws to avoid excessive popping. Once the engine runs smoothly, release the gas pedal and see if it idles. Check vacuum and make any adjustments to the idle stop screws that are necessary to get the car to run at idle. Once the car is warm (140 degrees or better) and holding an idle, it is ready for accurately setting balance, sync, mix and idle speed.

END PART I

BlueSideUp · 05-27-2008, 08:30 PM

Great write up by John

Quote:

Originally Posted by T Bird

Cerbin
Part II below.
John

Weber Set-up
Part II

STEP 4- Vacuum Adjustment- (balance)
Disconnect the right and left carbs from the crossbar by undoing the short press rods on each carb. Use an 8-mm wrench to pop the ball cups free of the throttle arms. You don't want the linkage affecting this adjustment. Pick a carb. At 900 rpm, measure vacuum at each barrel and record results. Determine which barrel pulls the most vacuum (“reference barrel”). Lock down the jam nut on that barrel’s idle air correction screw. Now, carefully and slowly turn out the idle air correction screw on one of the two barrels that doesn't pull as much vacuum as the reference barrel. Get the vacuum exactly equal to the reference barrel. As you open the idle air screw to equalize vacuum, you are going to experience popping, since you are leaning out the mixture by introducing more air into that barrel's idle mixture. DON"T PANIC! Just open the mixture screw up a hair to compensate so that the popping doesn't distract you, or if it's just occasional popping, you can leave it alone for the moment. When vacuum is equal to the reference barrel, lock down the jam nut. Equalize vacuum in the remaining barrel the same way.

Now, you have all three barrels on the one carb pulling equal vacuum. Repeat the process for the other carb.

Step 5- Side-to-Side Balance @ Idle (synchronization)
Using the STE synchrometer, determine which side is pulling more vacuum. Turn the idle stop screws out or in a hair until both sides are pulling equal vacuum and you have 900 rpm idle. Turn the idle stop screws in to speed or out to slow, keeping each side balanced with the other. Now, the engine should be running at 900 rpm with each barrel pulling exactly equal vacuum. You are probably getting an occasional pop since your mixtures are all off.

Step 6- Side-to-Side Balance @ 3000 RPM (synchronization)
Reattach the press rods. Check the side-to-side balance at idle to make sure that the linkage isn't off at idle. If the press rods disturb the idle balance, adjust them so that they exert no preload on the carb throttles. Now you are ready for balance at 3000 rpm. Have the assistant hold the engine at 3000 rpm. Quickly run the STE over each barrel and record the results. Each barrel of each carb will match. But, your linkage could be off, causing the right carb to be out of sync with the left—that is, one carb may be pulling more vacuum than the other at 3000 rpm. If one carb is pulling more vacuum than the other @ 3000 rpm, lengthen or shorten the right/left press rods to compensate. When you get vacuum to balance at 3000 rpm, check that the linkage adjustment hasn’t screwed up idle balance. When vacuum balances at idle and at 3000 rpm, you are synchronized and ready for the "artful" part of this process, where it helps to have the ear of a musician.

Step 7- Mixture Adjustment
Speed the car to 1200 rpm using the hand throttle in the car to hold it there. (This is the BA method- put rock on gas pedal. PMO advises to disconnect the right press rod and speed the engine with the idle stop screws. I use the BA method.) Now start with barrel 1. Slowly turn the mixture screw in until you hear slight popping in the muffler- a little more and the idle speed drops. You may get an occasional BIG POP while doing this- this is normal. As soon as the idle speed drops, slowly turn out the screw until idle speed comes back up- this should take about 1/8 of a turn. You may hear that faint popping in the muffler at this point. If you do, turn the screw out a bit more until the popping disappears and the engine runs smoothly. (NOTE: Slow turns on the screw are warranted. Reaction to changes in the screw’s position is not immediate.) Now, note the position of the screw and slowly give it 1/2 a turn more. This is the initial setting. If it continues to pop or spit up before moving on to the next barrel, turn out the mixture screw an additional 1/8 turn. All should be well with that barrel for the moment. Proceed to barrel 2- same process- then 3, 4, 5 and 6. If it took ½ plus 1/8 of a turn to get barrel 1 to behave, then turn out the mixture adjustment screws for all of the other barrels the exact same amount.

After you run through them once, you will have some doubts as to whether you got the mixture on the first few barrels equal, since as you move through this process, you will begin to develop the "ear" and the "feel." Start over with barrel 1. Make sure that each screw is turned out the same amount from that point where the idle speed returns without faint exhaust popping after it has dropped as a result of turning it in. The point here is to get them all equal. Run through them as many times as it takes to smooth out all popping and spit ups and to get satisfied that you have them all open the same.

Step 8- Idle Speed Adjustment
Release the hand throttle and let the engine return to idle speed. If idle speed is off, disconnect the right and left press rods. Adjust the idle speed to 900 rpm with the idle stop screws. Make sure that side-to-side vacuum remains equal. The engine should be running smooth- no popping and holding a nice idle. Reconnect the press rods and check balance at idle and at 3000 rpm again just to be sure!

Step 9- Test Drive
Take the car for a test ride. Is there any surging between 2000 and 3000 rpm? Is it popping on deceleration? Is it transitioning seamlessly between idle and main circuits? That is, no flat spots, right?

Return to home base. Make any final adjustments that you feel are necessary to the mixture screws. In other words, if it popped occasionally or surged, turn all mixture screws out an extra 1/8. Repeat test ride. Make any further adjustments that are necessary.

If the mixture screws are turned out more than 3 ½ turns from full in, the idle jets are too small. If the engine stumbles on acceleration or is slow to return to idle, the idle jets are too small.

End Part II

gigem75 · 05-29-2008, 10:40 AM

double check your ignition timing, I was chasing some spitting and popping with the carbs and it ended up being the timing. Don't ask how it got that far out overnight because unless I changed it while sleepwalking I have no clue.

GotaT · 05-29-2008, 10:43 AM

Really!? ... What did you set your timing to? I think mine is about 15 ATDC per instruction given to me.

What engine are you running?

BlueSideUp · 05-29-2008, 11:25 AM

I think that sounds like a severely retarded setting, you might try running it more advanced. I think the spec is 5BTDC but you have a 2.4 in there so it may be a little different.

edit: It looks like a 2.2 should be 0-2 degrees ATDC according to the fan strap sticker on a 2.2 911E. A 2.4 T E or S should be 5 degrees ATDC

Is your exhaust really hot with a 15ATDC setting?

gigem75 · 05-29-2008, 12:59 PM

2.2 and if I remember correctly I think it's 5 before. I've got the marks lined with white paint to see it better under the light. Everything was great and then one morining she was spitting and coughing, really weird, even took one apart completly and checked everything. Then checked the timiing and it was way off, at least 10 degrees, weird. Set it back to 5 before or whatever the mark next to tdc is and life is good.
If it is 5 after that is probably to meet emissions and 5 before might work better?

2.7RACER · 08:46 PM

GotaT,
You asked if leaning out the idle fuel mixture screws would help your mileage on your trip from Laf to Houston.
Remember with Webers the engine runs on the secondary venturi at rpm's above 2500/3000 rpm's.
Any adjustment of the idle mixture will not affect your mileage at hiway speeds.
For better mileage at hiway speeds you'll want a smaller venturi and corresponding smaller main jets.
You want better mileage around town? Smaller venturi and smaller idle jets; then retune.
The Webers get fuel from the idle passageways to the idle and transition jets at rpm's below 2500/3000 rpm's.
You end up trading better mileage for less performance.