Weber - gas coming out of 1 throat

Elan Discussions
21

I went to O’Reily’s and rented their fuel pressure kit. Pretty neat - it comes with lots of fittings, one of which fits the fuel inlet banjo on the Weber - so easily done. In any event, my replacement mechanical pump (no glass bowl) seems to be ok - the gauge goes to 200 psi or so, and the first tickmark is either 2 or 4, and that’s where the needle stuck very solidly. So I don’t think fuel pressure is the issue.

My EZ Turn Lubricant (the ONLY sealant that Keith recommends - all others will do HORRIBLE things to your jets or whatever - so you’ve been warned) is coming from SkySupplyUSA - all the vendors I could find for this were in the aircraft biz - no Amazon vendor even carried it. $20 for a 5 ounce tube, and $10 for shipping. So I hope it lasts a long time.

My current plan is to go ahead and pull the head and get the plug thread issue addressed, take that opportunity to inspect the carbs closely. If problems persist - i.e., the rough running - once the head goes back on, seek professional help.

Keith wants me to run much smalller air correctors. They’re currently 200’s, he wants me to try 120’s. Every book I have, and the Weber/Redline warranty guy, says this will enrich the mixture at higher revs. Keith says it will lean the mixture. We’ll see what my O2 sensor says.

Again, thank you everybody for your input.

22

Steve,

Don’t dismiss fuel pressure issues quite yet. A bit more digging on the net suggests 2psi to 3psi fuel pressure is the optimum range for Weber DCOE carbs, and that they will start to flood at pressures over 4.5 psi.

The pressure gauge you borrowed is aimed at fuel injection systems which have much higher pressure than normally aspirated carbs like the DCOE. If you are lucky and the gauge you borrowed is of decent manufacture and hasn’t been dropped too often, a 200 psi borden tube gauge should have an accuracy of somewhere between plus/minus 1% and 3% of full scale - so plus/minus 2psi to 6psi. Mechanical gauges are notoriously inaccurate as they come off the zero stop, it is common to pre-load the gauge slightly so that needle rests against the zero stop at rest. It takes a few % of full scale to get it moving. The chances of you getting an accurate enough reading from the gauge you are using of the fuel pressure and being able to distinguish between 2psi (fine) and 4.5psi (flooding) are very low.

Ideally, you want to choose a gauge so the pressure you are trying to measure is somewhere near the middle of the range, so a gauge with a full scale of between 5psi and 10psi would be ideal.

Andy.

23

I’ll jump in here with just a few random ideas to consider (in addition to the good ideas above):

  • are the Weber floats made from plastic (not compatible with modern fuel…) as some suppliers of “genuine” parts are proposing these?
  • why not swap over some parts (chokes etc) from one carb to another to audit/see if there are undetected sizing issues (on either the parts or the carb bodies)

As mentioned above, it is best not to drive too far (perhaps bag up the distributor / coil if you must).

Andrew

24

Sorry Steve but the all metal Pump is not “stock”. I had exactly the same problem on a +2S130 when someone sold me an all metal pump made in India.
I suggest you get a real “stock” pump with “glass bowl”.
When i fitted the “all metal” pump there was fuel being pumped everywhere and a very big “fire risk” please be careful.
Alan

25

I went back and looked at the gauge - it’s actually reads to 100 psi. But I get your point.

Instead of running around trying to find an appropriate gauge, and figuring out how to plumb it into the system, we instead look at the fuel level in the bowls. High pressure should mean high fuel level, right? Even if the fuel pressure is a bit high, adjusting the float higher should put more more pressure on the valve and shut off the flow sooner, right? Which should still give the correct fuel level of 25 mm below the mating surface of the cover plate.

Keith recommends an acrylic rod and nylon sleeve to measure that. After removing a main jet assembly, I took a dial micrometer and first measured the distance from the lip that that the jet cover sits on to the top cover mating surface. Then I cranked the engine about 5 revolutions to ensure the bowl was full, and dropped the depth rod of the micrometer down the jet well with a light shining on it, stopping when the tip of the rod disturbed the surface of the pool. Subtracting dist A from B and converting to mm gave me 26.21mm for one, 26.49 for the other. So my fuel level is actually a bit low - it can come up 1.21 mm on one carb, 1.49 on the other to get to the spec Keith, and presumably Weber, calls for. Which means when the mains are functioning, I’m a bit lean. Presumably the idles as well.

Make sense? I’ll rerun the measurements, but I think this may clear the pump of any part of the problem. I’ll run this by Keith and see if he concurs as well, and if it’s worth it to tweak the floats to raise the level a bit.

26

If you don’t trust an aftermarket pump without a glass bowl, why would you trust one with a glass bowl? What’s so significant about a glass bowl?

I appreciate the thought about the pump concern, but keep in mind that this pump worked great feeding a pair of Strombergs for the 15k miles or so I’ve put on the car, and who knows how many miles before that. Are Webers and Strombergs so different in their presssure tolerance?

In any event, the post just above this one has my initial results looking at the actual fuel depth in the bowl, which I think is the whole point of this area of concern.

27

Yes, they’re plastic. Obviously, Weber thinks they can handle modern fuel. I’ve had them out multiple times setting and checking the float levels, and haven’t noticed any degradation.

Interesting thought on the swaps. But since gas is coming out of the throats of both at times, I’m not sure what that will tell me. The gas is seeping out, not flowing out, so at this point I’m thinking the EZ Turn will likely take care of it. That will still leave me with the driveability issue.

No, I’m not driving far, if I drive it at all.

28

Hi Steve,
I’ve never had a “glass bowl” pump produce too much pressure in 50 years tinkering on Twinks.
But the only "all metal " pump i have bought was producing too much pressure.
Maybe if you prefer to keep an “all metal” pump you could fit a Pressure Regulator inline.
Alan

29

Lol, You just can’t accept the evidence that this pump is working fine, because you once had one pump that didn’t have a glass bowl that was faulty?

In any event, thank you for the suggestion, I do sincerely appreciate your concern.

30

it appeas your later 40DCOE have the screw to clamp in the aux venturi rather than the spring clip used on the earlier ones. This clamps the opposite side of the venturi to seal the main jet fuel passage into the venturi. Leakage here is why you need some sort of seal on the trumpets. I have never needed it if the spring clamp or clamp screw is tight and the aux ventrui properly seated.

leakage due to high fuel level / high fuel pressure will occour at all revs but if itonly occurs when then engine is under load its due to a loose aux venturi

cheers
Rohan

31

Could a faulty spark plug be causing unburnt fuel to be pushed back out of the trumpet? There’s plenty of fake fake plugs out there. I’ve had a few NGK - first issue is that the gasket ring doesn’t last two torqueing events. Didn’t run them in the engine even though they were untested. That was enough for me.
Getting a decent spark on the faulty plug? Plug lead / igntion system etc?

If you are confident it isn’t the pump delivering too much pressure and that the auxiliary venturis (ie chokes) are sealing correctly, other than fuel height and the seating of the needle valve, there isn’t much else it can be except for machining tolerances on aux vents and trumpets etc. What do you think it could be?

32

The fuel pressure according to the LTC workshop manual for Weber carbs is supposed to be 1.25 to 2.5 lb2. Given the decimal places in the figure you will need a sensitive guage. Not all glass bowl fuel pumps are the same so don’t just assume because it has a glass bowl that it is the correct one. The delivery pressure is determined by the diaphragm spring according to the application. Also carefully check the needle and seat - is it worn? Is it genuine? Is the sealing washer OK and has it been torqued correctly in the cover? You won’t know if the float is good or not unless you throw it in some hot water and watch for bubbles indicating a leak.

With regards to spark plug thread repair I recommend locknstitch. Quality stuff that won’t come loose again in that difficult application. See link below.

castingrepair.locknstitch.com/c … ad-inserts

33

On a very good YouTube channel Mike’s Restorations concerning a 67 911 (worth watching as the fellow is a first class car restorer), Mike (Las Vegas) had quite a few problems of the same type with IDFs.

I suggest you watch this.

34

You need to rule out #1, & #2, above.
Colourtune, or a laser thermometer and measure each exhaust runner @ head (less precise)
Pressure, verify

35

Steve,

Keith’s VP (Venturi Pump) conversion works on a different principle. My understanding of this is that the larger the dry jet (air jet or air corrector jet) the more fuel your engine will inhale. Keith is a physicist I am a mere engineer, but what Keith has come up with appears to work on the same principle as an ejector. I have only come across ejectors using steam, the flow of steam through the small hole (dry jet) induces a flow around that jet, the bigger the jet the more flow. In my case the purpose is to suck the air out of a chemical process vessel.

Hope this helps

Richard Hawkins

36

Could one of you who keep putting the fuel pump on the suspects list please explain to me why the fuel level test doesn’t clear it? I would think if the pressure was too high, the fuel level would be way too high in the bowls, not 1.2 - 1.5 mm low. What am I missing here?

37

Thanks, it does. I need to ask Keith about that. I would have hoped that if switching to his tubes meant that the standard rule of thumb for air correctors doesn’t apply, he would have mentioned that on the website or in the doc sent with the tubes. But maybe physicists don’t think like that.

38

Darn good question.

There are two problems here that may or may not be connected.

  1. Fuel seeping out of the throats.
  2. Rough running, most clearly felt during acceleration, but always there to some extent.

For 1, it sounds like based on several replies in this thread, and Keith’s view, that it’s the nature of the beast. Run a bead of EZ Turn around the base of the trumpets and call it a day. If fuel still seeps out, go back to the drawing board.

That leaves problem #2. I’ve got to believe that the soot on plug #4 is a clue. I have checked the temps of the header runners, and #4 is as hot as the others, but I’ll recheck. The head is newly rebuilt, so maybe it’s involved here, although the compression #'s seem to say it’s ok. But I’ll take a closer look when I pull it. Rough running indicates that 1 or more cylinders aren’t pulling their weight, so what’s different between the cylinders? Well, the thread insert on #2 came out, so that plug is different than the others, both in type and length of service. So get that fixed and it will remove one difference.

On to the carbs. What’s different about throat #4? No idea, but one test would be to swap the carbs, front to back, and see if now #2 looks like #4. That would definitely (?) point to something in that carb being the culprit.

I’m not sure if this is significant, but when I run with my O2 sensor stuck in the exhaust pipe (bung not yet installed), the numbers vary pretty wildly, particularly at higher revs. That seems to indicate that there’s significant mixture differences between throats. Since all have the same jets, the fuel levels are almost identical, etc., it’s either how the jets were assembled, part variation, or I don’t know (tried to follow the rule of 3, but…).

So tomorrow I’ll get back to what I know, and pull the head to get it fixed. That will give me some more time to think this through.

39

With all due respect you are not doing things in a logical manner. Sort out your fuel pressure and report back what it is. I don’t know what Keith Frank is about but it’s normally the sort of stuff I steer clear of because it sounds too much like black magic. I could be right or wrong on that but just sharing my approach for you to take it or leave it. If Weber got it to work with their standard range of jets and calibrated components there’s no reason why anybody else shouldn’t be able to do the same. Get it to the point where it isn’t a fire hazard and drive it to the nearest rolling road dyno to have the jetting and maybe other issues sorted out.

40

I would, if someone could explain how I can have correct, or slightly low, fuel levels and high fuel pressure. Barring that explanation, fuel pressure is a red herring and pursuing it a waste of time. Which seems logical to me.