Weber help?

arringto · 08-30-2003, 11:18 AM

Hi,

I have installed webers on my (73.5) 2.4t motor which is now in my 68 911 Targa. The problem I am having is. . I have synchronized the carbs the best I can (side by side balanced at 1200 and 3000 rpm). When I drive the car it seems to cut out and start spitting and popping around 3000 rpms and has little power. It runs fine in the lower rpms and idles like a champ. I have timed the car, set the dwell and adjusted the valves as well prior to synching the webers.

Questions:

1) the distributor on the engine has a vacuum advance, do I need to use this?

2) there seems to be a vacuum port on the left weber is this a vacuum port or an overflow of some sort? There is one on the right carb that has been pinched to be sealed.

3) Could this be a jetting problem?

Any help would be greatly appreciated.

Thanks,
Alan

arringto
1968 911 Targa

911pcars · 08-30-2003, 11:44 AM

How are things at higher speeds? If it's crappola after 3000 k,

Two things to check:
1. Fuel pressure and volume - Should be around 3-4 psi. Volume should be min. 1 pint in 30 seconds or so.

2. Float level - Could be too low (maybe). Easy to check with the PMO float tool. This screws into the side of the float bowl and allows you to see the fuel level. Should be between the two upper lines.

Do you have any fuel filters between the pump and carbs? If so, check for clogging.

1) the distributor on the engine has a vacuum advance, do I need to use this? No. Just set total advance (about 35º, check specs) w/timing light at around 6000 rpm.

2) there seems to be a vacuum port on the left weber is this a vacuum port or an overflow of some sort? There is one on the right carb that has been pinched to be sealed. Don't need vacuum. These can be sealed.

3) Could this be a jetting problem?
Clogged jets perhaps, but shouldn't affect all cylinders. Your idle/low speed running seems fine so I would tend to discount overall crud invading just the main jets.

If you don't know, you should find out what the jetting is, just for your reference (main venturi size, idle jet, main jet, air correction jet, emulsion tube).

Hope this helps,
Sherwood Lee
http://members.rennlist.org/911pcars

john walker's workshop · 08-30-2003, 12:54 PM

be sure that all the primary venturis (the small plug in ones) are facing the right direction. if the side with the port is not facing toward the emulsion tube well, no fuel will enter that cylinder beyond the idle circuit. a common problem when the carbs have been disassembled.

Randy Webb · 08-30-2003, 01:26 PM

I'd also check the ignition system.

Raynald · 08-30-2003, 01:51 PM

Hello,
What is the size of your main jets ?
this carb is from a 2.0L engine ?

arringto · 08-30-2003, 05:40 PM

The webers are from the 68 911 (130hp). The idle jets have 50 on them, not sure what the size of the mains are. The venturies are 32mm. Current motor is a 73.5 2.4t.

When I was trying to equalize volume on the right bank, there were two barrels that were not responsive unless I opened up the idle screw almost all the way. . Just didn't seem right at all. Would this be a symptom of what John was saying regarding the primary venturis?

Also, could this be an issue with the CDI box? Remeber the car runs fine at low revs (idle circuit).

Thank you all for the help, many of good suggestions.

-Alan

Arringto
1968 911 targa

911pcars · 08-31-2003, 12:29 AM

"When I was trying to equalize volume on the right bank, there were two barrels that were not responsive unless I opened up the idle screw almost all the way. . Just didn't seem right at all. Would this be a symptom of what John was saying regarding the primary venturis?"

Would that be the idle mixture screws or the idle air adj. screw?

Would those unresponsive cylinders be numbers 4 and 5?
3 6
2 5
1 4

The throttle shaft that controls all three throttle valves on each carb are of a two-piece construction locked together with a coupler. If the shafts are not "in synch" the throttle openings will be different. It sounds like number 6 throttle valve is opening sooner than 4 and 5 throttle valves (these two share one shaft). If so, remove the offending carb, back off on the throttle speed screw, loosen the coupler, then verify all throttles valves are closed (no daylight sighting through the air passage). After installation, start w/all adjustments identical on both sides with the linkage disconnected. Use a synchrometer or equivalent to balance the carbs.

The "primary venturis" you refer to are more accurately called "secondary venturis". These are the ones that can be install 180º, preventing fuel flow into the air passage from the main jet circuit. Did you have these out?

I think there's a fuel delivery problem. Check the pump pressure, then let us know. That should take less time than the above adjustments.

Sherwood

arringto · 08-31-2003, 11:00 AM

"Would that be the idle mixture screws or the idle air adj. screw?"

Idle air adj.

I placed the synchrometer on 4,5,6. Number 4 was pulling the most volume by far. The directions I was following stated to open the idle adj screw until each barrel pulled the same as the reference barrel. I ended almost opening them all the way up on 5 and 6 and really never was able to bring vacuum to the same as the reference barrel. That just didnt' seem right at all.

"Would those unresponsive cylinders be numbers 4 and 5?"

5 and 6 as number 4 was pulling the most volume.

"The throttle shaft that controls all three throttle valves on each carb are of a two-piece construction locked together with a coupler. If the shafts are not "in synch" the throttle openings will be different. It sounds like number 6 throttle valve is opening sooner than 4 and 5 throttle valves (these two share one shaft). If so, remove the offending carb, back off on the throttle speed screw, loosen the coupler, then verify all throttles valves are closed (no daylight sighting through the air passage). After installation, start w/all adjustments identical on both sides with the linkage disconnected. Use a synchrometer or equivalent to balance the carbs. "

I would think it would be #4 opening before the others if it is pulling more volume? Good advice I will pull it off today and check these clearances.

"The "primary venturis" you refer to are more accurately called "secondary venturis". These are the ones that can be install 180º, preventing fuel flow into the air passage from the main jet circuit. Did you have these out?"

I did have them out and I guess it is possible though I thought I was careful to place them back the same way they were removed.

"I think there's a fuel delivery problem. Check the pump pressure, then let us know. That should take less time than the above adjustments. "

I concur but I have replaced the fuel pump and fuel filter but still the same result. Is there any way this could be related to a flakey ground in the engine compartment? Or would that be more apparent at lower speeds?

Thanks for the good advice and time Sherwood. This is the last piece of a long installation and I am eager to get this thing running and out of the road

Thanks,
Alan

arringto
1968 911 Targa 2.4T

john walker's workshop · 08-31-2003, 12:38 PM

so check the "secondary" venturis for proper position. THAT'S a fuel delivery issue.

206aa · 08-31-2003, 03:33 PM

John, You were right. Two of the secondaries were in the wrong position. I removed both carbs and inspected all of them. Everything is correct now. I am going to try and re-tune them and hopefully get some better results. Thanks for the help, as usual your advice was very helpful and accurate.

-Alan

Arringto
1968 911 Targa 2.4

rlane · 08-31-2003, 04:39 PM

Arringto..hope your carbs are set up..I do not mean to hijack the thread but wonder if the experts on here can give me some advice?
I just bought a nice RS clone with a 2.7/2.8 and PMO's. The PO is going to help me set up the carbs later but was wondering if there are recommended books..reference..instructions on setting up these carbs...I haven't fiddled with a carb since this 1973 was brand new! (course the carbs I fooled with were Holleys on a 72 Camaro!
Thanks in advance

lateapex911 · 08-31-2003, 05:36 PM

As a guy who will dive into his rich running popping Webers as soon as he gets his ignition finalized, this is a great thread. keep us informed on your progress!

arringto · 08-31-2003, 09:48 PM

Success!

What I had to do:

* Removed both carbs for inspection
* Took John Walker's good advice and found:

"secondary" venturis- - 2 (one per carb) were in the wrong positions. Flipped them around to the correct position (ported side facing the emulsion tubes).

* Took Sherwood's good advice and realigned my throttle valves making sure I could see no daylight at the closed position.

Started the car up and measured volume with the synchrometer on 4 5 6 and they were fairly close, close enough to easily adjust to pull the same volume.

Went through the whole process of tuning the carbs with a much better feeling about it. . . Time for the moment of truth.

Started out the same as usual, running well in the low revs in the residential ares. . then I had to do it, stomped on it and it actually started behaving like a 911. No hesitation, the fuel was making it there and I had some fun. . The car finally has some power and runs well!

There is still some popping going on because I ran out of daylight but they are definetly close. It's minor and I should be able to work it out tomorrow.

Thanks for the good advice guys!

This whole carb project has pretty much been a Pelican project. I followed the directions from Wayne's 101 book to rebuild the carbs, I am fairly sure the rebuild kits came from Pelican, I followed advice from numerous posts and folks like John Walker and Sherwood. The tuning directions came from a Pelican post as well. . Good stuff!

Anyway thanks again to all who helped.

-Alan

Arringto
1968 911 Targa, 2.4t

911pcars · 08-31-2003, 09:55 PM

Alan,
Hooray! Diagnosing stuff over the phone or the internet is often a hit and miss proposition. I'm glad the info was of some value. John hit paydirt with the secondary venturis, though.

Are you sure the fuel pump is okay?

Sherwood

Trust Me · Trust Me's Garage

ok. I'll say it! Webers Suck! Leaking Bastards!

RMartin · 09-14-2003, 05:42 PM

I have a 68S that I bought 2 months ago with the exact same problem. I put on a new fuel pump, set the valves, and had the dizzty checked. Still the same thing the car will not run over 3000 rpm. Today I rebuilt one of the carbs but it did not help. I am going to take the carbs off and check the secondary venturies, but the exploded view of the carb on this website does not list "secondary venturi". Also are the emulsion tubes the brass tubes that stick up on top of the carbs?

Rich911E · Rich911E's Garage

Go back through the archives. There is a great weber tuning article that was written by another board member. He and I were going to collaborate to update it with pictures and all but that sort of fell apart. I still have it if you want to e-mail me and I will send it along.

Rich

RMartin · 09-15-2003, 05:23 PM

Thanks Rich I found the article. Took the top off the carbs and checked the secondary venturies today. Unfortunately they were all correct. I know that sounds bad but I was really hoping that was the problem. I've ordered the PMO float gauge to make sure the float level is correct. Anybody else have any ideas as to why the car wont go over 3000-3500 rpms?
One other thing, the car will rev fine in the garage, its under a load that it will start to backfire and sputter.

RoninLB · 09-15-2003, 05:35 PM

Quote:

Originally posted by RMartin
One other thing, the car will rev fine in the garage, its under a load that it will start to backfire and sputter.

sounds like a fuel flow problem

911pcars · 09-15-2003, 06:12 PM

From my previous post in this thread:

Two things to check:
1. Fuel pressure and volume - Should be around 3-4 psi. Volume should be min. 1 pint in 30 seconds or so.

2. Float level - Could be too low (maybe). Easy to check with the PMO float tool. This screws into the side of the float bowl and allows you to see the fuel level. Should be between the two upper lines.

Do you have any fuel filters between the pump and carbs? If so, check for clogging.

Sherwood