Another Weber Tuning Thread!

[Fishcop]

Before the Search Natzis' pipe in... yes I've searched!

I am having a lot of difficulty dialing in my webers on the new engine: 2.7 RS replica

I have set the rebuilt webers up as per PMO spec for this engine including F3 emulsions. The one thing that is not quite right is the use of a set of .65 idle jets rather than a recommended .60

I've tuned both sides in relation to air correction and synchronised them, and I believe that linkages are correct. Accelerator pumps are set at .65cc. Following an excellent thread from T Bird, I've tuned them until they just pop and then back them out a half turn. I've also tried this at Bruce Anderson's recommended 1200 rpm.

Plain fact is that they still fart and burp and the transition from idle to mains is attrocious. I have the musical ear of a deaf moose and just can't seem to get a "feel" for them. I'm sure all passages are clean and although I don't yet have a regulator from the pump, it was previously all fine when the 2.0 was in there.

Given I live in a place that I don't have access to "everything" like those of you in SoCal... should I be buying myself an A/F meter or similar? Does anyone have some suggestions for where I'm going wrong?

Frustrated....

[dhoward]

What happens in the transition, John? Any popping? Your floats are pretty close, right? Too much fuel presure can be a problem too....
You don't have any of the secondary venturies in the wrong way?
Just thinkin' out loud...

[Fishcop]

During the transition it just goes flat with lots of popping. I must admit I have not fine tuned the floats since I set them as per "101 Projects", I have the PMO float gauge. I don't think fuel pressure is an issue as it wasn't when the pump and webers were on my 2.0

Secondaries are definitely in the right way (but now you've made me paranoid and I'll have to have a look )

[dhoward]

Flat with popping sounds lean.....
How 'bout them transition ports under the flat screw above the mixture needles? Might want to check the float levels...I know it's a gas dribblin' mess but?

[lateapex911]

John you and me both buddy! I have the exact same issue. Just cruising down the highway, all is sweet, but tip in just a little and it goes "..brgrgwbbrgwgwbrgw"..sounds like it's trying to clear its throat.

I've swapped jets up, down, meesed with a Unisyn, followed the "Easy 94 steps to Weber Heaven Program" ,and still the sme thing.

Rick Deman (of Deman Motorsports, a firm with a fabulous rep) built the motor and HE spent over an hour swapping jets and got the same result.

I mentioned this to a fellow SCCA racer who runs sidedrafts, and he said "emulsion tubes". OK...not sure what about them though as we were doing some other things at teh time.

I took my car on a fun run the other day, and after about two hours of driving, suddenly, for some strange reason, it ran fine. No popping, burping or gurggling. For a whole 5 minutes until we stopped. Upon start up the devil had returned.

Which makes me think....
1- throttle shafts? could mine have heated enuf to seal a leak? My issue *seems* to be right bank only.

2- A gasket leak or such, and the heat expansion sorta sealed it? (the temp was 100C)

3- sounds crazy, but would valves too tight cause such a thing? naaa...right?

I need to set the floats, but I have no guage and don't know the proper setting. I do think they look reasonable, (I know, thats the kiss of death!) and I did adjust one to match the left ones, but it made no difference. I do need to get a regulator and guage.

I hope we get some ideas here so I can learn as well!

[Fishcop]

I completely stripped these webers and rebuilt them adding the correct venturis/jets/correctors and emulsion tubes as recommended by both Anderson and PMO.

However both PMO and Anderson recommend .60 idlers and I have added .65's... could this be critical?

I pulled off the exhausts over the weekend and added some sealant to prevent leaks, I've sprayed carb cleaner around the shafts and ports but there didn't seem to be a leak. I just can't seem to dial out the burbling with the odd pop. I originally began with .55 idlers but felt I was running out of adjustment so I'm using the .65 I had from a previous project. Someone's going to tell me to use .60's aren't they?

[Tyson Schmidt]

Sounds like low float levels, since that affects how early the mains come in. It explains why you needed larger idles.

With higher (proper) float levels, the mains will kick in earlier, and richen up that lean spot. Setting float levels can be a pain. Make sure you have lots of varying shims, and run the car a bit to settle the float level to make sure it's accurate.

After changing shims, drain the float bowl a little, as removing the needle/seat usually floods the float chamber a bit, giving a false high reading. I think this is the very reason that I find so many people give up and bring their cars to me . I almost always find the float levels too low.

[dhoward]

...and too high, makes idle adjustments impossible. That's a pretty thin space between the two lines on the gauge! Pressure needs to be rght also. Too low and the bowls won't fill fast enough, too high and the pressure pushes the needles off the seat. Ask me, no really, go ahead and ask me how I know...

[al lkosmal]

This is exactly what caused me to wrench my newly rebuilt Zeniths off my motor and humbly go back to CIS, whimpering like a whipped rodent. It's winter, I'm ready to try again. Fishcop, somebody check their floats and let us know how it works.

P.S. My 2.7 CIS setup is 34 chokes, 140 mains, 180 air,55 idle. Decent Idle, atrocious tip in, bat out of hell 3KRPMS and above. Basically an on/off switch. Occasionally exciting though.

[Fishcop]

Thanks Tyson, you were about to get a PM!

I will very carefully set my floats (I have plenty of shims), and thanks for the tip on draining the bowls a little.

Thanks for the input everybody... standby.

[lateapex911]

Tyson..I have a question...

on the float level setting., I have Grosse jets as installed by the PO of the (used) Webers.

Shims? Where? How? And this guage..where can I get one? Can yu point me to a thread that describes the process perhaps?

[John Rogers]

I finally broke down and bought two of those float gauges so I could do one side complete at a time which I found was much easier. I would recommend a fuel pressure gauge as too much pressure will cause a too rich look to things. I had approx 4.5 PSI when I put my new pump on and several BMW vintage racers said that was way to much as they run 3PSI max so I put on a regulator, droped the press to 3PSI and all the stumbling and other strange things disappeared. I also set the float level at the bottom line on the PMO gauges which is the norm for racing I guess. Finally I found the cams in the engine had a large effect on things as they are the "906" cams and with the amount of overlap they have the idle tuning is pretty hard to do. Good luck.

[Fishcop]

Thanks John, interesting point in regards to the high-lift cams.

[Early_S_Man]

John,

It probably is the float levels as Tyson mentioned.

But, to get to a perfectly running engine you probably want a fuel pressure regulator and a dash-mounted fuel pressure gauge to monitor things accurately!

Do you have the phenolic 914/6 heat isolator-spacers [901.108.131.00] installed under the manifolds? An isolator made from 1 mm Titanium sheet wouldn't hurt, either ... right next to the cylinder heads [gaskets on both sides] ... wouldn't hurt under the phenolic spacers, either!

Starting to get pretty warm down under, these days , right?

[jwetering]

FWIW - - I've been twiddling my 40 IDA for a while now and I 've found that the mixture adjustment is pretty subtle. I was at the point you describe earlier this year, except that my transition fromidles to mains was never a problem. Lot's of popping and fartingthough. You mention this:

Following an excellent thread from T Bird, I've tuned them until they just pop and then back them out a half turn. I've also tried this at Bruce Anderson's recommended 1200 rpm.

It sounds as though you are may still be too lean. My experience is that if you dial the screws in until the engine starts to pop, then you've gone too far already. I've found it better to stop when I just hear the idle start to waver a bit. Then I give the screws a good half turn out, maybe 3/4 turn.

Provided the float levels are good (you did measure the needle valve drop when you rebuilt the carbs right) then I would start by giving all the screws another full turn out, then drive around. If the popping through the carbs goes away, then I (you) are on the right track. You gotta be patient, and you gotta remember that there are six throats and each one has to be tuned and that it won't run right until they all are right. Close you eyes when you are turning thos escrews in and only move an 1/8th of a turn at a time. Use the force you know. Popping through the carbs is lean, popping through the exhaust is rich.

A last word of caution - early on I figured rich was better than lean so I turned the screws al the way out and went for a drive. It wasn't long until the engine was misfiring all over the place. This was real scary until I figured out I'd foulled one or more plugs. It sounded at first like I had a blocked idle passage.

Part of the joy of weber carbs is getting the tune right and then bragging to anyone who'll listen about how you were able to dial in the dual triple carbs on your Porsche. This is best done in a nonchalant "it was easy" kind of way.

DON'T GIVE UP!

[Fishcop]

Thanks Jasper, you've got me inspired to give it more work over the weekend!

Tyson and Warren, you guys were right, my float levels were WAY out (even though I set them according to the 101 Project specs...) I've begun setting them more accurately with shims. Warren, I've always wanted to add the insulating spacers you're refering to, but by my reckoning the Sportomatic system won't work as the plunger cam is attached to the manifold yet plunger switch is attached to the carburetta... ergo the vacuum switch won't work with spacers. Do you have a thought on this?

And yes... the heat begins!

[RoninLB]

fwiw, I'm running 60 idles@ 2 1/2 turns. A 1/2 turn is worth about 50-75deg in confirmed EGT in each cylnder.. The difference between the max and low cylinder EGT will decrease as you get closer to a more stable induction. In my case I would say it sounds slightly rich in exhaust tone. In a small garage with the door open the exhaust has that good ole quick eye burn and stink. All my mix settings are the same, except the air. Initial timing will slightly affect the poping unless your way off. A bad dizzy curve is another story. I'm new to 911 carbs so fwiw.

[Fishcop]

Peter, that makes sense to me now... I'll have a look at those isolator blocks again.

Ronin, I sure got the eye burn last weekend! I was trying to do the right thing by the neighbours with the noise... but I'll be doing out on the drive this time. Does anyone think I should bring the .65 back to .60?

Cheers

[911pcars]

Idle mixtures (CO levels anyway) are sensitive at idle. I managed to get mine down to 4% with a CO meter. Doesn't take much to go to 6 or 8%.

Sherwood

[RoninLB]

Originally posted by Fishcop
Ronin, I sure got the eye burn last weekend!

... but I'll be doing out on the drive this time.

Does anyone think I should bring the .65 back to .60?

Not a 911 carb expert so only fwiw.
I'll assume floats are set and you don't have a clogged idle jet.
I'll also assume your dizzy initial & curve is carb ok.

Try the 60s at a mix setting of 2 1/2 turns on each cyl. ie: keep all settings =

Repeat at 3 turns. all being =

A quick run around the block is ng imo. I wait for a full 10mi street warm up. An idling engine never really warms up.

I think you gotta try 60s for more info

once I got the carbs ok I was able to tweak the accelration flow for more zoom without affecting the accelerator pump mechanical geometry. I can almost bog the engine it's so rich on acceleration. I gotta control the pedal 'cause it comes on almost like a mechanical secondary Holley.