Webers and Low idle inconsistant
 

Hi all still trying to sort it out, somedays she runs strong and smooth .Other days in the morning on the way to work she starts up coughing with miled smoke and backfire. wont holed steady idle ,drops to 500 or so at a stop light and preforms ruff or even like its running on 5 cylinders.then on the way home outsidetemp is up to 50 or so runs great idles at 1000 and has strong responce. Ok hers the background on the car 77 911s recent 2.8 E cam 9.5 cr intake ports 37mm. backdated exhaust dual in dual out muff. weber jets 155 mains F3s 60 idle 180 airs. fuel pressure 3.5 psi on the in line gage.36mm venturis. I know webers run rich and even more so when its cold out here in the seattle area but the inconsistant extrems make it hard to figure out. engine temps normally at 170 but when its running crappy the temp wont go up to 150. some times it will smoothout while driving like the power comes back to normal after a few studders.I hope the weber guys that have been there have some answers thankks in advance Chuck!

Have you checked the condition of the throttle shafts?

I don't think that worn throttle shafts alone will cause the misfiring you are describing when cold but will result in varying idle speeds if the throttle plates do not "seat" the same every time the throttle is closed.

My 2.4L "E" engine (about 9.8:1 CR) with Webers has recently developed the same cold running problem you are describing. In my case it seems to have developed after I reworked the chains and cam timing. The cam timing is set near max advance (3.3mm) but no changes were made to distributor timing or carb settings. I don't know if there is a correllation but I suppose someone on this board will know.

Oh yeah, spark plugs are new and the car runs extremely well when warmed up.

BTW, sorry for hijacking your thread! ;)

I have experienced icing in my Webers on cold damp days here in the NW. You bust your a$$ to keep em' cool on hot days......... :confused:

I had an old Ford pickup (straight 6)that was really bad with this.
A freeway drive for bout 45 minutes in the 40 deg damp weather and it would just quit.....the carb looked like a snow ball. I cobbled up some intake heat for that.....no solution for the Pcar....other than shut it off & let it get nice & toasty in the engine room.:D

are the plugs staying light colored enough to fire properly? what plugs are you running? 155 mains may be a tad too big. try 150s. dirt of any sort in the idle jets comes from the float bowl, so cleanliness is important. 3.5# may be a tad high, try 3#. fresh needle and seats? float levels correct? what's the timing set at for total advance?

Also make sure the distributor/points/etc are working correctly. I was having a lot of trouble with my 6 and it was more dist than carb.

Thanks JW total advance I think is correct I thought fuel pressure was an issue I have another set of carbs to rebuild Ill make sure of the float settings I will also lower fuel psi to 3#. Red beard dizzy was redone by Barry Hershon and recurved for E cams also protronics is in for ignition.thanks guys !I will keep you posted .oh yah plugs are bosh copper core #8s but ther probibly fouled I check it out thanks again Chuck

bosch copper core plugs don't like carbs. either do the platinums for that matter. try some denso irridium plugs. expensive, but they pay for themselves soon enough because you don't have to change them all the time.

Interesting. I was once told that copper was the best and not to bother with platinum. But, I just end up changing them every 6,000 miles.

Last I recall I am using the Bosch copper W8DC. Any idea what the Denso equivalent should be? (The auto parts jockeys can't always figure this out right!).

Thanks!

the coppers do work on stock engines (2.0) with stock jetting, but when the engine is cammed and the jetting is enlarged to feed it properly, or the 2.0 liter carbs are jetted for a larger engine, they tend to be right at the edge of fouling. then there's the MFI rich runners.
the denso equivilent to W8DC is IW16 (5305). i highly recommend them.

I'm loath to suggest buying stuff to mask symptoms, but early 911s (especially at idle) usually benefit from an improved ignition system.

I'd look at the throttle shafts and make sure they aren't worn, a common occurrence. However, no ignition system will cure the symptoms of worn throttle shafts.

Sherwood
http://members.rennlist.org/911pcars

Thanks JW its monday nite and I cleaned out idles and lowered fuel pressure to 3#. I would like to try those denso plugs who sells them ? thanks Chuck.

I'd also add you might try backing all the idle screws out 1.0-1.5 turns and see what happens. At worst it will run richer at best it will smooth out even in the midrange. I had to do this with my Zenith's on a 3.0. I'm running 1.65 idles. Now the car starts up nicely when cold, let it idle for a couple of minutes and it drives fantastic. Idle rpm is around 500-600 and a tad rich but it is WAY smoother at idle and part throttle.