Is this normal MPG?

[crvc]

Thanks, I knew it's physically manageable to unscrew the main jet but there's no room to reach in to grab it unless the top is removed. Working in my dim garage or with the garage doors open working in the cold, I worry about losing the jet somewhere in the bowels of the engine. It's a bit of a pain but dismounting the carb seems safer, as long as I don't damage the manifold mounting studs. Again.

kevin

[crvc]

I put the carb back together with the 120 jet. It won't idle and when pulling on the throttle lever to keep it running there's a loud screech. At first I thought it was fan belt noise but now I think the screeching was coming from the carb???? I don't know why but now the battery won't turn the starter. So it's on a trickle charger til tomorrow.

My wife says give it up and to back to the 18mpg jet. But I have parts from three carbs, one an Empi that I quit using because of leaking gas.

kevin

[aussiebug]

Kevin,

Is the screeching sound an air leak? If it is that might also explain the poor idling. The only thing(s) electrical about the carb which might affect the battery are the choke and solenoid cut-off connections from the + side of the coil. But I don't see how these could have affected the battery without burning out the wires (as in - causing a short) so that one is a puzzle.

[crvc]

I wondered about the noise being a vacuum leak. If that were the case spraying the carb with starting fluid might restore the idling momentarily. I've collected a half dozen main jets from old carbs but none of them have visible numbers. I read your treatise on jets. A 110 is 1.1mm wide, 125 is 1.25mm wide, etc. The whole problem has been poor mileage with black exhaust tips. Two signs of a too-rich mixture needing a smaller jet?

kevin

[aussiebug]

Kevin,

Poor mileage and a black exhaust are certainly good indicator of running rich, particularly if the exhaust is sooty, rather than sticky/oily, which would be more likely to indicate worm pistons rings (oil burning).

Si jetting an a good tuneup might improve things for you.

Yes - if there is an air leak, spraying with WD40 etc (NOT carb cleaner, many of them have no "fuel" in the ingredients) at the leak area should make the engine run better - confirm the leak.

[Jim Ed]

i read somewhere that a stock 1600 cc dual port Type 1 engine is supposed to get 26 MPG city. I usually get about 17 MPG city but, I got it set a little on the rich side so it is more fun to drive. Setting it too lean causes big problems.

[Piledriver]

Sooty exhaust and poor mileage can also be a weak coil.

[mountainkowboy]

I get a combined of around 23 mpg in the vert. Stock 1600DP with a 34 pict 3.

[crvc]

So from one problem to another. I got it running using a 127.5 main jet and 55 idle jet. But there's a "flat spot". It idles fine, maybe a bit fast, but I have to push in the clutch and race the engine to get it moving from every stoplight. Granted, it was minus 25 (F) this morning but I've had the problem even when the air temp is above zero (slightly). The VW shop I use in Salt Lake City doesn't have any more jets to try. I use a newish 34pict 3 carb. I moved the small adjustment from 2.5 turns to 3.5 and moved the large adjustment one turn to increase the idle. It starts right away and races until I tap the accelerator pedal. It then idles steadily but I haven't measured the rpm. The car only seems to run well at high RPMs. I wonder about the automatic choke. This carb doesn't have the three marks on the electric choke. My next thought, unfortunately, is to turn the choke clockwise to see whether that helps.

Rob&Daves website suggested the altering the carb adjustments and higher octane gas. In the past I've always bought the cheapest.

Any suggestions?


TIA,

kevin

[Max Welton]

Unless I missed it, everything in this thread has been fuel related. Tell us about your ignition setup. Which distributor and how is it timed.

Max

[Marc]

Unless the engine was built with a significantly higher-than-stock compression ratio it shouldn't require higher octane at that altitude (it wouldn't surprise me to find that the norm for Regular in your locale is even slightly lower than the 87 (R+M)/2 sold in the flatlands.)

Set the choke when the ignition's been off for a while and the heating element is at ambient temperature. Remove the aircleaner so you can observe the position of the plate; in more moderate climes it's typically set so that it doesn't quite go fully shut when cold. You're going to want it set "richer" than that, but avoid setting it so that it snaps shut so smartly that it gets stuck. There's a vacuum-actuated "choke break" that pulls it open at high throttle openings so you can get out of your own way with a cold engine, but it may not be able to unstick a plate that's jammed closed. As a general rule, the plate should be fully open within about three minutes with the key on...it may take a bit longer at -25°, but I'd draw the line at 5 minutes.

The primary reason for the "flat spot" on acceleration is that when the throttle is opened and manifold vacuum decreases, the fuel/air mixture reaches its dew point and fuel condenses on the walls of the intake manifold causing a lean condition. The accelerator pump is there to inject some extra fuel in to compensate, but it can only do so much (and if maximized, it'll make for truly shitty fuel economy in all but steady-state cruising). That condensed fuel does eventually dribble down the manifold and make it to the cylinders, but at that point it's in the form of large droplets that won't have time to fully burn before being swept out the exhaust. This can lead to soot formation in the tailpipes that misleads you into thinking the jetting is too rich (or the ignition's weak) when the root of the problem is just that the intake manifold is too cool.

Enter the preheat system, which pipes some exhaust up along the bottom of the intake manifold to warm it. A stock muffler has the heatriser pipes plumbed so that one end is at a low-pressure point in the muffler to induce a net flow of gasses through them, but 99.9% of aftermarket exhaust systems merely tap each side into an exhaust port - there're are pulsations, but no significant difference in pressure, so most of the heat transfer ends up being from convection only...not nearly as effective as the stock setup.
The heatriser passages in the intake manifold notoriously can "coke up" with carbon which restricts the flow of exhaust gasses and reduces heat transfer. With everything in good order with a stock muffler it may take decades for this to become a problem, but once the buildup starts things worsen fairly rapidly - the worse it gets, the more soot forms in the exhaust and the worse it gets ;(

The thermostatic aircleaner also helps by directing warm(er) air that's just come off a cylinder head into the carburetor - when it's not working correctly in warmer environs it's not usually missed, but you definitely need one in sub-freezing temperatures. Because of the chilling effect of the latent heat of vaporization, it's possible for frost to form in the intake tract even at ~40° ambient when the humidity is high.

[crvc]

It's a two year old vacuum dizzy with Petronix module and matching coil. Timed to 7.5 BTDC. Valves are at 0.006. I found the three marks on the electric choke and rotated it about 10 degrees CCW (to the left). It was minus 15 on the drive home. I pulled the oil bath and the butterfly valve was wide open. I had noticed on the morning drive to work that acceleration was good for the first five minutes, but then I needed to play with the clutch and accelerator pedal at every stop light. That's what got me thinking it's a choke problem.

Yes, the thread started with me whining about poor MPG. But since then we've gone from fall to arctic winter. Right now I'm more worried about having to race the engine at every stop light to get it moving. That won't help the mileage but I'm resigned to live with 18MPG since I'm out of options.

kevin

[FJCamper]

Hi CRVC,

Listen to Marc. A plugged-up heat riser will do exactly what's happening you you. The car starts, runs, the manifold freezes, and the car runs badly.

The only fix short of a new manifold is to pull your manifold and ram heavy wires through the heat riser to Roto-Rooter out the carbon. Then make sure your muffler connections to the heat riser are clean.

FJC

[Piledriver]

If you have a header and any way to fab it, one side of the heat riser can be plumbed to the collector like a case evac setup.

I guess the first thing to check would be in the heat riser is plugged, I agree that would produce all discussed symptoms.

[aussiebug]

Kevin,

As Marc mentioned above, do you know if your heat riser under the carb is getting warm or hot? The stock uni-directional versions usually gets VERY hot at one end (depending one which way the gas flows - different manufacturers make the flow one way or the other), quite hot under the carb and still warm at the other end. The aftermarket "pulsing" type (header connection at both ends, direct to No2 and 4 exhaust connections) should be very hot at both ends and still warm/hot under the carb. For info, if you have an aftermarket muffler, these are often delivered with the heat riser fittings undrilled, so the muffler can be used with twin carb setups which don't need heat risers. So check that the heat riser connections are drilled through into the exhaust pipe - about 1/4" drill bit will usually do it. The heat should be quite noticeable within a minute of so of the engine starting.

On a cold engine, set the choke to JUST shut, and see how it runs with those two features working. As Marc says sometimes the choke need tweeking, but setting it JUST shut on a cold morning should get it about right for the ambient temps in whatever area you life in...until you get to a warm climate like mine, where (as Marc says) it usually works best when set cold when cracked open a mm or two. You also need to make sure that the choke is actually opening up too. It starts to open the moment you turn on the ignition and should be standing upright (or almost upright) within about 2 minutes. That matches the engine warming up so long as you drive off immediately as VW recommend in the Owner's Manuals (the engine should NOT be idled to warm it - it will still be 1/2 cold when the choke has opened up and there will be less heat in the heat risers too, so you get a poor fuel mixture and a stumbling engine for the first mile or two).

The combination of enough choke to get the engine started, and a good working heat riser to keep the fuel suspended in the airstream along that long induction manifold, make a huge difference in the way the engine drives.