Horrible Mileage - FIXED! 100%

[Amskeptic]

also...Adjusting the spring in the injection pump for tension or length can give 'short,sharp burst of fuel' or 'long,smooth'.....if you think that might help your scenario

I think he wants the longer interval, sounds like a little lean.
Colin

[Sluggo]

Got my new pistons & cylinders in. Fixed my head leaks. Fixed my vacuum leak. Carbs are damn close to perfectly jetted. Engine runs smooth and strong. Except.....There is a flat spot. Regardless of RPM.

What happens is when I accelerate slightly I'm good. But give it a little more and I get a big bog. The Air/Fuel Ratio meter shows that when I hit the gas I totally lean out. If I go wide open throttle it's good. But if I give the pedal any more than a slight touch it leans out. Cruising is great. But when I try to accelerate more than slightly, I get the big lean bog.

Jetting is currently:
55 idle
115 main
160 A/C
30 Vent
33 pump jet (springs cranked down all the way)
Aux vents have no markings.

All the jets including the pump jets have been cleaned and flow freely.

If my Vents are too big, could that cause this problem? It just seems like they get to much air at partial throttle.

[Amskeptic]

33 pump jet (springs cranked down all the way)

I think you might have your accelerator pumps shut off.
You crank down on the springs and lose interval.
The more spring, the longer the squirt interval.
Colin

[Sluggo]

33 pump jet (springs cranked down all the way)

I think you might have your accelerator pumps shut off.
You crank down on the springs and lose interval.
The more spring, the longer the squirt interval.
Colin

I need clarification. When people say "crank down on the springs", do they mean the spring that is on the arm or the spring that is in the diaphragm. I tightened up the spring on the arm. It is compressed all the way in.

[Amskeptic]

I need clarification. When people say "crank down on the springs", do they mean the spring that is on the arm or the spring that is in the diaphragm. I tightened up the spring on the arm. It is compressed all the way in.

(the spring inside the diaphragm is out of sight out of mind)
You need to see which position makes the longer interval versus the shorter interval. Longer interval makes it "richer." That spring is just the way all carburetors allow the accelerator injection period to extend past your stomp-the-throttle. You should see the actuating link move immediately with the throttle lever while the accelerator pump diaphragm sort of lags while the spring extends at its own rate. The longer it takes to extend, the more accelerator pump volume you have introduced to the engine. Remember, a rich bog can be mis-interpreted as a lean hesitation. Experiment scientifically.
Colin
Colin

[Sluggo]

(the spring inside the diaphragm is out of sight out of mind)

Thanks. I'll make a note.

You need to see which position makes the longer interval versus the shorter interval. Longer interval makes it "richer." That spring is just the way all carburetors allow the accelerator injection period to extend past your stomp-the-throttle. You should see the actuating link move immediately with the throttle lever while the accelerator pump diaphragm sort of lags while the spring extends at its own rate. The longer it takes to extend, the more accelerator pump volume you have introduced to the engine. Remember, a rich bog can be mis-interpreted as a lean hesitation. Experiment scientifically.
Colin
Colin

I did note and observe the way the pump operates. Pretty much as you described it. It seems to be best all the way in. Bringing it all the way out made the bog way worse. It has to be lean because as soon as I hit that pedal more than slightly the monitor shoots to off the meter lean (much more than 15.1).

[Sluggo]

I put in 70 idles. The flat spot is almost gone. Someone over at Samba explained how I should picture the transitions. Makes sense now. I'll probably still have questions though while I hammer it all out.

[Sluggo]

I just took it on a freeway run. Head temps were good. Between 325 & 375 (if I'm passing cars or going uphill). Oil temps were 210-230. A little higher than usual. Best the Bus has ever run.

I think I'll bump the main up to 120 with a 200 A/C. It's still running a little rich But the performance is better than ever.

[Amskeptic]

Best the Bus has ever run.
But the performance is better than ever.

I look forward to driving it just before we tackle the 411/412.
Colin

[Sluggo]

Best the Bus has ever run.
But the performance is better than ever.

I look forward to driving it just before we tackle the 411/412.
Colin

Definitely want your opinion. With the increase in compression and vacuum even the brakes are better.

[Sluggo]

Oh Man! It's so damn close to perfect now. Everyone was right about the accelerator pump adjustment. 21 half turns out (so 10 & 1/2 turns but I count em in halves) seems to be the spot. I didn't realize the adjustment increments were so small. And using F-7 e-tubes seems key too. Now there is just the slightest flat spot. I wouldn't even call it a flat spot. I still accelerate just not as quickly and if I pull back or forward even in the slightest it goes right through it. Before it bogged and lost power.

The set up is now:
Weber 36's
55 idles
200 A/Cs
115 mains
F-7 e-tubes
33 pumps (10 & 1/2 turns out)
30 vents
??? Aux vents (no markings)

Mileage seems good. I'll be going on a road trip to SF this weekend. I'll do thorough charting to see exactly what speed works best for my mileage and head temps.

[DurocShark]

We best be seeing pics!!!

[chitwnvw]

Everyone was right about the accelerator pump adjustment.

How do you adjust this? Or maybe I don't want to know since mine is driving pretty well now...naw, tell me!

[Sluggo]

Everyone was right about the accelerator pump adjustment.

How do you adjust this? Or maybe I don't want to know since mine is driving pretty well now...naw, tell me!

Do you have Weber IDFs?

[chitwnvw]

Do you have Weber IDFs?

Yes. Dual 40's.