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Webber DGAV3D

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Blueghost

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1978, 1500 w/ Webber DGAV3D, has run "normal" (some days good, some days OK) for 4 years, 10,000 miles plus. Seemed to be running less than good the last couple of months but still acceptable, and just failed Oregon DEQ. No big deal, I know how to adjust and got through DEQ in 3 attempts. They only check at 1000 rpm. All pollution crap removed by previous owner. Only thing remaing is PCV valve installed by me a few months ago. Installed new inline fuel filter. Decided to open carb, and cleaned, installed new gaskets, new needel and seat, set per Redline and Haynes data to 41 mm. Adjusted valves to .010 (only two out slightly at .012) Checked other items at same time. Compression 150-155 (9:1 pistons and mild cam installed 3 years ago). Fuel PSI 5.5 dropping off to about 4.5 PSI at 5000RPM. Runs fine at low end, low speed. Hard acceleration 1-2 shift at 5000 RPM, 2-3 shift 4500 rpm, starting to "feel" weak at shift, 3-4 shift at 4500 rpm and it goes in the toilet, no power, feels like starving for gas. Back off on accelerator and gets better, but rough for 3 to 5 seconds, and when accelerating easy will not run above 50 MPH.

Initially felt heat related; swapped out coils and seemed to help, but not really and probably just me wanting it to be better. Finally installed new Petronix Flame thrower distributor and coil. Absolutely increased RPM and performance, but still can't go over 50 MPH. Re-set float to about 35 mm to allow extra fuel in bowl. Seemed to help but not really. Reset float to 31mm. Once again semed to help but not really. Installed new power valve in carb; no change. Now have carb off and re-soaking in cleaner. Considering changing jets to larger number and emulsion tube air bleeds smaller number to enrichen.

Nagging question; this thing ran OK until about a month ago. Nothing else change; WHAT AM I MISSING?????? Elimited fuel tank restriction by running fuel direct from 1 quart bottle under hood. Same story.

With air cleaner off I have used cardboard strips slipped through holes in float bowl cover to measure gas in bowl. At Idle fuel level is about 1". At 2000 RPM no load same. At 4000 RPM fuel level drops to about 3/4". 5000 RPM same. When "starving for gas" under load at 5000 RPM load I have pulled over and checked level still about 3/4" in bowl.

How is it that I can hold 6000 RPM w/ no load, yet I can't hold 55 MPH.

Really looking for tip on best settings for float, best jet sizes, etc from someone that really knows what sizes work.
 
If it ran right a month ago then it's not a jet size problem. More likely there is a restriction somewhere or a weak fuel pump. I'm no Webber expert since the only ones I ever had were on Fiats and never had to work on them. But I'm a little suspicious of your 1/4 inch drop in float bowl level at rpm. I think it should stay right at the level you set the float at all rpm. Have you checked or replaced all the filters? If so then maybe it's time for a flow rate test on the pump. I would certainly do all that before trying to compensate by messing about with the jets.
 
I had similar symptoms once with a Weber 38/38, found one of the venturi tubes, (the things that stick out over the throat where the gas mist gets introduced into the stream) had come loose and had pivoted around until it was pointing up out of the carb instead of down into it. Drop of loc-tite and all was well. Probably not your issue, then again easy to check.
 
Thanks for replys. I agree that since it ran resonably well for a long time that changing jets won't fix the root cause of this recent problem. Since it started running "less well", and I put a carb kit in it (gaskets, needle and seat, general soak cleaning) and messed with timing to get thru DEQ, I'm suspicious there may be a small piece of crud in a galley. That is why I have it off and soaking again.

Yes I installed new filter. I mentioned fuel PSI is 5.5 at low RPM and drops off to about 4.5 PSI at 5000 RPM. I believe this should be plenty, even at 4.5 PSI. Can't find a pump psi specification in Medget 1500 manual, but even if it was there, it would not be for Webber.

Seems logical for psi to drop slightly during high useage. At low rpm pump is supplying more than needed, and as gas gets used quickly, pump should still deliver more than being used, but maybe not as much excess as at low rpm???? <span style="color: #FFFF33">Does anyone know desired (or minimum) psi for this Webber?</span>

Similarly, for the 1/4" float bowl drop at failure rpm, this is a product of float setting. That is why I set float level higher to possibly compensate for high rpm.

<span style="color: #FFFF33">Finally, does anyone have specific numbers for jets (all) that work best with this engine/carb combination?????????? </span>If I had a base line to start with I could eliminate a few other items, and maybe have things better in balance.
 
When I had my 38/38 issue I suspected fuel deliver issues too, checked flow and had about 15 gph as I recall, I suspected that wasn't enough and I moved the pump back to the tank, changed the fuel lines and ended up with 23gph (memory is fuzzy on actual numbers) did no good, this was with psi regulater at 4ish which is what Webers like as I recall. It was that upside down venturi tube the whole time for me, totally obvious, still can't believe I missed that. Did you see if your tubes are loose at all?
 
Thanks Jvandyke,

Secondary venturi (size 4.5) is snug. Primary venturi bar (size 3.5) is slightly loose. I tried to wedge a strip of .004" aluminum tape on the non-ported end. Wouldn't fit. With the new gasket fitted it won't move unless I grip it with a needle nose and try to move. And it definately is not upsidedown. :smile:

In the middle of all this troubleshooting I got rid of the always noisy electric klicker pump. Using an AC Delco that makes no noise. I believe you are correct that Webber should work fine with 4 PSI. I did those checks with a hose "t'd" in to the carb inlet and a temporary wet line with reasonably accurate gague held in my hand at all speeds. I only know PSI is 4.5 at hi rpm (5000). With an electric pump it is easy to hook to 12 volts and run for 6 minutes and multply by 10 for gallons per hour. Not sure how to get GPH with a mechanical diaphram pump.

I have also thought about hooking old electric pump in series with mechanical. probably wouldn't bee too hard, and couldn't hurt.

Still looking for anyone with good recomendation for all jets, and settings for good street perfoemance with 1500cc and webber DGAV3D.
 
Blueghost said:
Secondary venturi (size 4.5) is snug. Primary venturi bar (size 3.5) is slightly loose. I tried to wedge a strip of .004" aluminum tape on the non-ported end. Wouldn't fit. With the new gasket fitted it won't move unless I grip it with a needle nose and try to move. And it definately is not upsidedown. :smile:
Click to expand...

That's not your problem then I'm sure. Mine was so loose it would spin around from vibration. I'd recommend rigging up the old pump if you still have it just to see what effect it has. I tend to agree that jetting shouldn't be an issue now, if it wasn't before. You have filters before the carb I trust? Just reread your post, you do. Sure sounds like fuel starvation under heavy load, exactly what my 38/38 did with the loose tube. You could run it hard to the point of loosing power, shut it down immediately (to stop the pump) coast over and take the carb top off to see where the fuel level is at that moment. I did that a couple times when trouble shooting mine.
 
Thanks Jvandyke,

Update, reassembled carb, reinstalled, hooked up the electric pump in series (in fornt of) the mechanical pump. To my surprize with electrical pump on and car off, I still had good fuel delivery to carb. I had already removed remote fuel PSI hose and hand held gague. Took out for standard test drive. Very good performance, acceleration, smooth running to about 40 mph for first 4 miles. Then I get to the stretch of road where I can open it up adn not wory too much about "the Man." And once again, at very close to 50 it just starts to die. Back off, takes several seconds (8 or 10) and I can again drive 40 / 45 MPH no problem. Kick it up to 50, and dies again.

Next thought is possible clogged catalitic converter, or muffler. Tonight disconnected exhaust pipe at flange in front of Cat. Ran in garage. RPM climbs VERY QUICK. Could not run at night as neighbors would scream. Tomorrow will sneak out a quietly as possible and let you know how it went. Also, on reassembly of carb, I recorded every jet/orifice/setting. Still looking for that extra smart guy that has best jet/venturi/settings for DGAV w/ 1500. Don't care much about economy, but also don't have a race machine. Just want a quick 65 mph midget.
 
Thanks texas bugeye,

Update, as stated above I removed exhaust from cat back. Without any back pressure it ran much worse starting at about 40 MPH. Next tried primitive method of using a small syringe with 4 feet of vacuum tubing to inject gas directly in to throat of secondary at about 50 MPH when failing. Syringe was too small to get good test. Couldn't control well enough to make an accurate statement, but addition of gas might have helped.

Bottom line, runs very good up to 45 MPH, and it still dies at 50 MPH under hard acceleration. No matter how I play with the accelerator pedal I can't get it past 50. Also hard acceleration 2nd to 3rd gear at 5000 rpm (35/40 mph) has same effect. If I back off and add gas slowly, I can continue to accelerate to about 50.
 
I had a similar problem with my SU - it would idle but "run out of gas" if I accelerated. turned out to be timing.

I'd also check vacuum advance.

my strong hunch is that one of the two above may be the issue
 
90% of all carb problems are in the ignition circuitry...
 
Does it rev happily sitting in the driveway?
 
Thanks DrEntropy. Well stated. My first "feelings" were that it was ignition related as in breakdown of coil/ignition/brain box due to heat/vibration. To that end installed new Petronix Flame Thrower distributor and coil. Plugs wern't very old but put in a new set of NKG platinum (cheat trouble shoot).

Thanks JPSmit. Timing set and double verified at 10 BTDC at 750 rpm. The Petronix distributor has about 4 degrees more mechaical advance than stock. Current numbers are +8 (18 total) @ 1400 rpm; +14 (24 total)@ 2000; +18 (28 total) at 3200. Regarding vacuum at distributor port; currently 0 Hg @ 750 rpm; 2 Hg @ 1250; 21 Hg @ 3500. Spraying carb cleaner around carb/induction system does not indicate a leak. I have not checked actual vacuum advance/retard with new distributor, but on old distributor it was right in book spec.

Thanks Jvandyke. Yes it revs very happily in driveway.

The saga continues. Open for any suggestions as to what I am missing.
 
Clogged air correctors e tubes that would make it go rich on progression to secondary.?
Vacume advance leak?
 
Wouldn't it seem more fuel related if it happens under load but not in the driveway? Put a can of SeaFoam in your gas tank.
 
I vote for fuel related but darn if I can think what it might be except for float levels.
 
Is the Gas tank vented to the atmosphere?

m
 
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