Weber problem ( I think)

[cegerer]

My Weber 40IDA 2.5L has developed the following problem:

1. The problem is somewhat intermittent.
2. At steady speed (any RPM, any gear), the motor runs slightly rough and occasionally backfires.
3. A slight press of the throttle and it clears itself and runs fine. Until you go back to a steady speed. As long as I am accelerating, the motor runs perfectly (if there were no speed limits, this would be acceptable to me!).
4. Haven't pinned this part down yet, but seems to stumble a bit during hard cornering as well.

Sounds like carbs to me. I've run some carb cleaner thru it and that seemed to help a bit but the problem always comes back. Any suggestions?



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1971 911T - 2.5L Big Bore

[BRAINIAC]

Check your float levels first. That's also the same symptom as having too lean of idle jets or clogged idle jets.

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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[cegerer]

OK, will do. Thanks.

[Joeaksa]

Braniac is correct. I had the same problems with the webers on my 2.2/2.4 cars. Never did find the problem (car was stolen) but what did help was a very good fuel filter inline to the carbs. I assume it was either rust in the fuel tank or metal lines.

What it sounds like you have is that one or more throats is running lean and when you push on the throttle the acc pump is squirting a jet of gas into the mixture and the motor runs fine for this time period.

I ended up pulling the air/idle jets and blowing compressed air at low pressure through the passages and cleaning out the float bowls.

Fuel level is very important for your idle and must be consistant. I was too cheap to order the "float level gauge" from weber and made my own, drilling a bolt out that fit the float drain hole and rigging up a plastic "T" fitting with plastic tubing that showed the fuel level in each bowl.

Good luck!

JA

[dhaines]

I have to clean the idle jets a couple times a year on my '67 911. Pull them out and blow through them. Takes a screw driver and 10 minutes. Clears it right up. Also make sure no paint is peeling on the inside of your air cleaner housing. This also caused me headaches! Good luck

[cegerer]

Cool! Thanks for the tips. I picked up a Weber handbook today. I've never torn into Webers before, but it is time to learn.

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1971 911T - 2.5L Big Bore

[David McLaughlin]

Is there anything that one should look for when doing this proceduer. I have teh same problem with my 2.0L and was just about to post that question. Also, what would cause the idle to sit at 1200 rpm just as you come to a stop, then after a minute drop to <500 rpm? Any thoughts? I hope to pick up a weber book soon and the Haynes is for the birds. What I need is a Porsche Engines for Dummies book.



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Dave
1970 914/6
1995 Golf GTI-VR6
1996 Passat TDI
djm914-6@mediaone.net
http://www.pelicanparts.com/cgi-bin/pmpre/pm.cgi?action=display&login=DJM914-6

[cegerer]

dhaines: it actually took me a screwdriver and 12 minutes, but I'm just a beginner Amazingly, blowing out the idle jets seems to have taken care of at least 80% of the problem. Thanks!!

Checking the float levels appears to be a much more involved process. The Weber manual I bought doesn't do a good job explaining this procedure. Can someone explain it better than my $19 book?

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1971 911T - 2.5L Big Bore

[dhaines]

floats are a bit trickier. There is a plug at the bottom of the float chamber, actually 2 per carb as there are 2 chambers. Remove one of these plugs. Be careful, cause gas comes out as the bowel empties! I use a small can to catch it. Then screw in you float level tool (you gotta have one to do this, I think!) Turn on your ignition and the float bowl fills up, as does the tool. Look and see the level of the gas in your tool. If it different that your book says, open the top of the carbs (bunch of little nuts, also nuts in center) and bend the metal that attaches the float to the pivot. The book says to use shims under the needle valve, I think. Too much work for me! Then reassemble with a few screws and try the level again, Keep doing it until you get it right. Sorry, best job I could do in short written form! Also, while the floats are out, shake them to make sure there is no gas in them. Look them over for holes. Either will not make it float correctly, obviously. Good luck. It is a pain, but you usually only have to do it once. One more thing, make sure the car is on flat surface....

Doug

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Doug '67 911

[dhaines]

Dave, sounds like you need to go through the proceedure to adjust your carbs to me. Sounds like the idle mix/volume is off to me, IMHO...

Doug


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Doug '67 911

[cegerer]

OK, thanks Doug. I'll give that a try but will have to get the test tube first.

[dhaines]

One other thought, you might as well order a new gasket for the top of the carbs also as the old one usually gets torn up. Good luck



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Doug '67 911

[cegerer]

The saga continues. The steady-speed studdering returned today. Took the idle jets out again for cleaning (haven't been able to take it for a test drive yet due to rain). But did notice that 4 of them are 60's and 2 of them are 57's??? The rebuild specs on my motor call for 55's. Bruce Anderson recommends 60-65's for the 2.5L big bore.

The 2 different idle jet sizes makes me think that either somebody randomly installed whatever they had on hand (unlikely) or that somebody spent a lot of time experimenting with different sizes in order to get this thing to run smoothly on the idle circuit. Is it common to install varying size idle jets?

Also, should the jets fit tightly into the holders or should they be free to rotate within the holders? Thanks!

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1971 911T - 2.5L Big Bore

[This message has been edited by cegerer (edited 06-10-2001).]

[Joeaksa]

Cegerer,

The jets should be all the same size. Would not think that this would cause your problem though, just a bit of an uneven mixture. Do the plugs all look the same when you pull them? Would wonder if the cylinders with the larger jets would be a bit richer looking...

Been ten years since I last worked on Webers but seem to remember that they were tight in the holder, but would still rotate a bit when turned.

One thing that I did not know until I was "educated" about Webers by an old German guy is that the motor runs on the "idle" circuit while idling and up to around 2500-3000 rpm. Past idle speed the "main" circuit starts flowing fuel and provides more and more fuel until the idle circuit is finally bypassed as the rpm increases. This is one reason why the idle jets are important even at the lower motor speeds. When they are clogged they effect much more than just the idle.

JoeA

[cegerer]

Haven't pulled the plugs yet. But I plan to do that as well. I'm going to order some 65's and see what those do.

[dhaines]

maybe a lot of crud in your carbs and need to be taken apart and cleaned. It does not take much to plug these jets up. All should be the same size. Sometimes I have also shot carb cleaner through them to make sure there is no build up. Wear your safety glasses as the stuff goes everywhere! Mine fit tight in the holders, but also doubt that is the problem.

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Doug '67 911

[dhaines]

Forgive me if you get this twice, didn't seem to go through first time. .. I would suggest that your carb has gunk in it, maybe stuff in the float bowls and passage ways. I would take them apart, partially anyway, and blow it out. Note settings of idle mix and air comp screws and such when you take it apart. Return to those settings. It takes so little to plug up the idle jets, so any contamination in there will continue to plug them up. Maybe a good time while setting your float levels, the top is off and you can see how dirty the float bowels are....


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Doug '67 911

[cegerer]

Doug - I suspect you are right. I went through the receipts of the previous owner and the last time the carbs were disassembled and cleaned was 1988. Last year the PO had it in for similar problems to what I'm having now and the mechanic cleared it up with some carb cleaner but wrote that he suspected varnish buildup and recommended more thorough cleaning in the future. On the bright side, the car went from 1988 to 2000 without a single carb problem. The PO was only driving about 2000 miles per year during this period.

[cegerer]

Could Techron have possibly cured my problem?! I tried some Gumout Extra or something like that several days ago but didn't do much. So I blew out the jets once more then added a bottle of Techron 2 days ago. Drove it for 1/2 hour or so. Running pretty good but still stumbling at steady speed on occasion. Didn't drive yesterday. Took it out for about a 1 hour drive this evening and it ran absolutely perfectly! Knock on wood.

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1971 911T - 2.5L Big Bore

[dhaines]

Don't know! I'll give it a try next time. It seems once I got everything clean the problem crops up less and less now. Keep me posted on how that works

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Doug '67 911