Mysterious Weber issue on 67S. HELP!!

RetroSC · 04-18-2009, 01:14 PM

I've got an autoX tomorrow and have ran into a large stumbling block with some new Webers.

Some history:
My 67S had some worn out (loose shafts) Weber IDT's. They worked great at full throttle but didn't idle too well. I've been looking for some nice IDS' for years and finally found an excellent pair off a vintage race car. They are nearly perfect with absolutly no shaft play.

This week I swapped all my jets, venturies, and such to these new IDS's and fitted them today. 125 mains, 55 idles, 32 venturies, 180 airs, F3 emulsion's. Did the baseline settings I always do on a new set of Webers. Air screws 1 turn out, Idle mix 2.5 turns out, basic linkage adjustment and fired it up.

Ran terrible and smoked black like crazy!! Fouled all the plugs in 1 minute and wouldn't run anymore. OK.... Checked the floats to make sure they were not flowing over. All were nicely in the middle of the gauge. Checked accelerator pump volume, which looked normal at .4 -.5 ml.

Tried several different settings of idle mixture and air, but it made absolutly no difference. It doesn't pop or spit, but smokes a lot and starts missing after 10 seconds or so and then gets progressivly worse. I've removed and cleaned the plugs of 3 times now and same result on each startup. It is fouling all plugs equally after 30 seconds or so. They are all sooted up and a bit wet with gas. Something's seriously wrong and I'm scratching my head here.

The car has no ignition or timing issue's whatsoever. Valves are all good and it ran great with the old carbs, other than the crappy idle. I know I could just put the old ones back on, but it's a major pain to swap everything back and not know what is wrong with these carbs.

Any ideas??

Thanks, Bill

Tooth911 · 04-18-2009, 01:55 PM

I wonder if turning the fuel mix screws in so far its as lean as it will run on to see if theres any change also turn the airs out some as well.This is only to check if the fuel mix can be changed any.Good luck!

red67 · 04-18-2009, 02:01 PM

just a thought - did you clean the new housings before you swapped all the parts over?
if not, then crud + dirt could play havoc

RetroSC · 04-18-2009, 02:59 PM

Cleaned them pretty good, but I need to go over them once more because something is seriously wrong here.

I've tried all extremes on idle air and mix screws. Tried to lean it out totally like you said and it made absolutly no difference. Lots a smoke still.

Totally stumped, but I guess I need to start over and thoroughly clean these again.

snbush67 · snbush67's Garage

Does your car start and run with the mix screws all the way in? If so then your idle jets are the wrong size.

Maybe you have too much fuel pressure? Do you have a pressure gauge and can you adjust the pressure? If so it should be between 3.5-4.5 lbs.

dvkk · 04-18-2009, 06:28 PM

Excessive fuel pressure, or your inlet valves are leaking.
If you have an electric pump, turn it on with the engine off and have a look down the throats. If you see fuel dribbling down and pooling on the throttle plates, there's your problem.

RetroSC · 04-19-2009, 04:40 AM

Yep, got a PMO gauge on the system and it shows 3.5. I even changed the floats and ball valves to my old ones that I know worked and still no luck. The idle jets were moved from my old carbs and are a standard size known to be correct on the 2.0S motors, and worked fine before. But yes, I suppose it did run with the idle mix screws all the way in. What's strange is no matter how far I had them turned in or out it ran the same, lots a smoke.

When I turn the ignition on the pump runs and I didn't notice any fuel running down the carbs, probably need to check that again though. Even tested all the float levels and they don't creep up like a leaking ball valve would let them do, so I'm doubtful that's the problem.. but who knows at this point.

1QuickS · 04-19-2009, 07:49 AM

Perhaps the interface between the aux venturis and the main throttle body are passing fuel. These may be flattened to assure good fuel sealing.

Also, check that the air correction jets on the transition circuit (the little pressed-in brass jets on the top of the lower throttle body) are not blocked. I think this is the most probable item to check, the gasket between the carb bodies is probably blocking these little holes.

Air correction screws are typically set all the way in and then adjusted to equalize air flows at idle. Your jetting for IDS sounds right for a stock 2.0S so there shouldn't be any issues there. When I rebuild carbs I find that the new float valves require a bit of settling before they establish a happy working position with the floats. I've also found that the floats NEVER are correct in their geometry, I ALWAYS adjust them to be correctly aligned. You may want to check for freedom of float movement in their wells.

Are all cylinders suffering the same plug fouling problem? Very unusual to have all cylinders suffering a problem simultaneously. Sound's like fuel pressure is high but 3.5 is a good (upper) pressure to use.

When the butterflies are closed do they close all the way and seal the first progression hole with their edges? The transition circuit holes should not be exposed when the engine is idling, only the idle mixture screw should supply fuel and the air passing the closed butterfly should provide air to run the engine.

Paul Abbott
www.PerformanceOriented.com

snbush67 · snbush67's Garage

Quote:

Originally Posted by 1QuickS

Also, check that the air correction jets on the transition circuit (the little pressed-in brass jets on the top of the lower throttle body) are not blocked. I think this is the most probable item to check, the gasket between the carb bodies is probably blocking these little holes. www.PerformanceOriented.com

Great advice! That is probably it.

RetroSC · 04-19-2009, 12:23 PM

Thanks Paul! That really gives me some ideas to work from. As for the pressed in idle jets they are not covered by the gasket, but I do need to spray some cleaner in them to verify they are not clogged.

What's so strange though is all cylinders are suffereing the same fouling issue. Every plug will be black within 30 seconds or so of running.

I'll dig into them this week and check some of the items you mentioned.

Bill

DanielDudley · 04-19-2009, 05:44 PM

How's the gap on your points ?

DanielDudley · 04-19-2009, 05:46 PM

Condenser or coil can also be suspect. Stranger things have happened.

RetroSC · 04-19-2009, 06:05 PM

Yes, those need to be checked as well. No points though, it's a petronix unit, but maybe it's acting up. I was wondering if something crazy might have happened with the the ignition.. everything needs to be checked though because I'm running out of ideas on the carbs.

1QuickS · 04-22-2009, 07:27 PM

Had another thought, if you set floats recently after carbs were apart then they may need some settling-in. When I set floats (after blueprinting them for geometry - they're NEVER right) I check them a couple of times. They seem to take a little vibration to let them get happy with their adjustments. I like to watch the fuel level with the engine running. The fuel will vary as the fuel is used and the valve opens to resupply the fuel in the wells. I also use a rod to deflect the floats down and allow the fuel to rush in a bit to check that the valves are closing properly. (I insert the rod down the vent tube that sticks up between the air horns.)

If the tabs on the floats have divots from the fuel valves then you may consider filing these tabs to provide a new flat surface for the valves to operate against. Relocated floats can stick if the divots don't correspond to the tip on the valves. Float geometry has the tab aligned with the horizontal plane that contains the float fulcrum when the fuel is at the correct level. Also the top of the float is 13mm (I think) above this horizontal plane. I typically find the tabs are not horizontal and this can cause a side loading of the float valves...leading to a sticking condition.

One more thing to check. If the accelerator jet screws (the screws with the ball valves that secure the jets to the top carb body) are stuck (the balls are stuck open) then it is possible to draw fuel through these, although this would only be realized during larger vacuums and not at idle. Check them out by blowing and sucking through them to see if their is positive sealing action. Also, stroke the throttle lever to check for squirting action, wait a few seconds and do it again. If the balls are not closing properly then fuel will drain back into the bowl and now provide a full shot of fuel when demanded.

Tech Tip: I find that a 0.010" thick shim under the float valves correspondes approximately to a change in fuel level in the bowls of the distance between the two lines on the fuel level gauge. The meniscus is what you want to use as the fuel level.

Best of luck!

Paul Abbott
www.PerformanceOriented.com

911pcars · 04-22-2009, 10:24 PM

"When I turn the ignition on the pump runs and I didn't notice any fuel running down the carbs, probably need to check that again though. Even tested all the float levels and they don't creep up like a leaking ball valve would let them do, so I'm doubtful that's the problem.. but who knows at this point."

Did you mention with the Ignition ON and Engine OFF, the pump eventually stops running? If so, that's normal. If the pump runs continuously, fuel is going somewhere - not normal. You have an early dead-head fuel supply system to the carbs, not a closed-loop recirculation fuel pump circuit.

Can you confirm?

Sherwood

RetroSC · 04-24-2009, 04:10 PM

Thanks Paul, more stuff to check... when I can get back in the garage. My 8 month old takes up a lot of time right now.

Sherwood, yes I was referring to Ignition On and engien off. My car has the old Bendix pump with no return. These pump up pressure and then slow down to a tick, tick, tick when pressure is up and stop pumping fuel. I know the pump is fine and my pressure is good. Has always worked normal with my other carbs as well, so I don't think there is a problem there.

911pcars · 04-24-2009, 04:40 PM

Quote:

Originally Posted by RetroSC

Thanks Paul, more stuff to check... when I can get back in the garage. My 8 month old takes up a lot of time right now.

Sherwood, yes I was referring to Ignition On and engien off. My car has the old Bendix pump with no return. These pump up pressure and then slow down to a tick, tick, tick when pressure is up and stop pumping fuel. I know the pump is fine and my pressure is good. Has always worked normal with my other carbs as well, so I don't think there is a problem there.

I wasn't too much worried about adequate fuel pressure. I wanted you to confirm the fuel pump doesn't continuously pump fuel through the carbs and into the engine through some heretofore unknown path. If the fuel pump stops "ticking", that indicates the float needle valves are indeed shutting off flow at the fuel inlet.

Just to confirm; there is no raw fuel spilling into the throat(s) when ignition is ON, engine OFF, correct?

Sherwood

RetroSC · 04-24-2009, 07:36 PM

Sherwood, no raw fuel spilling over and the float needles look to be holding pressure fine. I even checked the float levels with the PMO gauge with the engine off but pump on to make sure the levels were not creeping up when under pressure, and all looks good, nice steady fuel level on all floats.

The more I think about it I'm starting to suspect the ignition maybe. It's just so strange that all plugs foul so quick. My next plan is to move all the jets and such back to my old (and known working carbs) to verify nothing else is wrong with the engine.

I know it would be a crazy coincidence for something else to go awry with the engine at the same time I swap carbs, but I just can't find anything wrong with these carbs that would casue such a severe problem.

RetroSC · 04-25-2009, 02:30 PM

Update.... I moved everything back to the worn out IDT bodies, this includes floats, needles, jets, venturies, everything really. Car runs fine again with these on, no smoke issues or plug fouling, so it's definitly the new carbs that are the problem. Can't imagine what's so wrong with them, but I'm going to spray out all passages and double check a lot of Paul's suggestions.

Thanks for all the good input so far.

Bill

1QuickS · 04-26-2009, 07:48 PM

FYI:

IDT's have a drasticly lean transition circuit compared to that of IDA or IDTP carbs. They can be helped by changing the air correction jet for the transition circuit for that of the IDA carbs or a smaller size; not a screw in jet but replaceable just the same.

Paul Abbott
www.PerformanceOriented.com