Horrible Mileage - FIXED! 100%

Post by **Sluggo** » Mon Mar 05, 2007 12:59 pm

I'm getting disgusting mileage. 11.68 Street and 13.65 Highway. New professionally rebuilt Weber 36 IDFs jetted at:

F11
75 idles
135 Mains
200 airs
30mm vents
Mixture screws 3/4 out.

New Redline Weber fuel pump at 3.5 PSI. No leaks. All fuel lines and breather lines are new and leak free. SVDA with a Hot-Spark. C-Grind Cam & lifter set (don't know if it matters).

I'm at a loss here. Could a vacuum leak cause that kind of crappy mileage without drastically overheating the heads? I do hear a slight hissing in the carbs. Maybe brake drag? I hear a slight grind from the right front tire but the brakes work fine and are not overheating.

hambone · Post by **hambone** » Mon Mar 05, 2007 4:35 pm

Have you checked your plugs yet? They can tell many tales...
If you have a vacuum leak, it could affect things. Try spraying carb cleaner around the manifolds etc. where they mate and see if it affects the idle.
I'd bet it's the carbs somehow..

Post by **Sluggo** » Mon Mar 05, 2007 6:45 pm

Pulled out the 70 idles (I mis-spoke when I said 75) and put in the 55s. Also traded the 135 mains for 130s. Reset the floats to 9mm. They were at 11 & 12. Had to put mixture screws out to 1 1/2 turns out again. Had to come inside to take the brat while my wife goes to work so I'll try it out tomorrow. Started her up and she seemed okay at idle.

Post by **Sluggo** » Mon Mar 05, 2007 6:53 pm

hambone wrote:Have you checked your plugs yet? They can tell many tales...
If you have a vacuum leak, it could affect things. Try spraying carb cleaner around the manifolds etc. where they mate and see if it affects the idle.
I'd bet it's the carbs somehow..

Plugs are sooty on the metal rim and whiteish/tannish on the ceramic.

I'll try the carb cleaner deal.

chitwnvw · Post by **chitwnvw** » Mon Mar 05, 2007 11:18 pm

Isn't this your second set of carbs, with the same bad mileage? Might be time to think outside the box...now if only I can find my way out...

vdubyah73 · Post by **vdubyah73** » Tue Mar 06, 2007 5:00 am

chitwnvw wrote:Isn't this your second set of carbs, with the same bad mileage? Might be time to think outside the box...now if only I can find my way out...

Thats what I'm thinking. Either you're making the same basic mistake over and over or there's something wrong with the build. How many miles on it? Mileage goes up as it breaks in. Don't know if it would go up that much though. Maybe some one else should take a look at it, someone not involved with it at all.

Bill

covelo · Post by **covelo** » Tue Mar 06, 2007 10:56 am

vdubyah73 wrote:Mileage goes up as it breaks in.

That's a good point. My mileage went from about 13mpg to about 17mpg (all highway/freeway) from when we first installed the AVP rebuild to our latest trip to Death Valley.

Post by **Sluggo** » Tue Mar 06, 2007 12:15 pm

I'm at 1600 miles right now. Absolutely everything has bee replaced except the Pistons & Cylinders and the manifolds. I had this problem before the rebuild.

Rebuilt the engine.
Restored the fuel tank.
All new fuel breather & delivery lines.
New fill hose.
New fuel pump.
New Carbs.
New Heads.
New Exhaust.

But the mileage is still the same.
The only remaining parts are Pistons & Cylinders which are being replaced in a few weeks (could that cause these problems). And the Intake Manifolds which I suspect could be leaking where the vacuum ports thread into the manifold. Could mileage be this far off because of a vacuum leak?

Post by **Sluggo** » Tue Mar 06, 2007 1:23 pm

Yesterday I swapped the 70 idles for 55s (I mis-spoke when I said 75) and the 135 mains for 130s. We'll see what happens.

vwlover77 · Post by **vwlover77** » Tue Mar 06, 2007 1:58 pm

Is your odometer accurate???

(How's that for outside the box?

)

Post by **Sluggo** » Tue Mar 06, 2007 4:25 pm

With the 55 idles I put back in yesterday I have the same heavy bogging I got last time I used them. All of a sudden it loses power but gets it back with more throttle. It gradually goes away as I increase the idle jets to 70.

vdubyah73 · Post by **vdubyah73** » Tue Mar 06, 2007 4:49 pm

You're not using a stock cam, are you? Is your compression ratio compatible with the cam duration?
I wouldn't know how to calculate it but some of the hp guru's over at thesamba would.

Bill

Post by **Sluggo** » Tue Mar 06, 2007 4:56 pm

vdubyah73 wrote:You're not using a stock cam, are you? Is your compression ratio compatible with the cam duration?
I wouldn't know how to calculate it but some of the hp guru's over at thesamba would.

Bill

C-Grind cam from European Motorworks. 7.8 CR. They said the cam should be fine.

fido · Post by **fido** » Wed Mar 07, 2007 4:04 pm

try a slightly higher float height - say 7mm. Emulsion tubes can change that flatspot too. You might find that your pump jets are too big too - smaller ones squirt the fuel slower, and cover a wider range before the extra fuel runs out. A distributor with quicker advance can help too (you got that vac can hooked up? - try being positive with teh flatspot rather than tentative on the gas pedal.)

I am with Vwlover77 - double check your odometer. Mine is about 8% out using GPS.

vdubyah73 · Post by **vdubyah73** » Thu Mar 08, 2007 4:49 am

Front tire size?

Bill

Itinerant Air-Cooled

Itinerant Air-Cooled

Horrible Mileage - FIXED! 100%

Horrible Mileage - FIXED! 100%