Weber jetting and overall settings (Any suggestions Jake)

914fan · Post by **914fan** » Thu Mar 03, 2005 1:33 pm

Perhaps Jake could provide some insight as to what I'm asking. Also Jake have you found that there is a trend on what settings (idle speed and idle jet volume screws) you see on your DYNOmite engines. Do you try to get the idle jet volume screws to a certain range.\I am willing to bet that when these carbs were designed, they had some specifications to what settings made the carb the most efficient. I wonder if the shop manual for the cars these originaly came on said "... the proper adjustment for XYZ is to set the idle speed screw to 1.25 turns to 1.75 turns in. If idle can not be set to whatever then check that the idle jet volume screw is turned to within "A" and "B". If the engine still Bla Bla Bla then use this size of jet etc....."
I feel that the settings I have are close. The car runs good, but I bet it could be better.

My goal is to get the butterflies more closed. At this time adjusting the air by-pass screws does little or nothing to the airflow of that cylinder. For instance the front throat is at 6 on the Snycrometer. The rear is at just below 6. The Air by-pass screws do not change the flow number on either throat. I think that by butterflies are not closed enough to allow the adjustment.

Thank you all again

Post by **Piledriver** » Fri Mar 04, 2005 12:03 am

You should be able to get the motor to idle ONLY on the bypasses, with CLOSED throttle plates, using the bypasses if you wish.
...At least both sets I have are like that.

Most folks recommend running with them CLOSED.
(The bypasses that is. I use them to get perfect balance on the individual runners. Yes, I should buy some new throttle shafts...)

I have heard some carbs have plugs.. Might have a peek.

And a bit of Ultra Copper Permatex RTV works WONDERS at the head, as do those copper 12mm "exhaust" lock nuts...
(Remember to sand/lap flat your manifolds...)

I have tried it both ways, either works "ok", but as I said, the "authorities" all seem to say bypasses CLOSED.

If you set the timing as has been suggested, the throttle plates will be barely cracked open at idle.

I have found the best drivabilty & fuel economy with "too big" idle fuels and the screws cranked in to <1/4 turn. Right now, all 4 of mine are ~1/16th turn (cracked, and a hair more)

Cold, it needs some "help" staying running for a minute or so... No chokes, and no plans. If I want cold enrichment, it'll come from an EFI system, and not something that washes all the oil from my cylinder walls on startup and loads up my oil with raw fuel.

Opening up the idle air drillings (the holes on the sides of the idle fuel jets) MAY be the ultimate tuning fix in this circuit, but I haven't jacked with it yet.

Some later Webers supposedly have proper idle air jets, unless I read into what I have read.

914fan · Post by **914fan** » Fri Mar 04, 2005 9:04 am

thanks for the update. I will get some larger jets and close up my buterflies. I do feel that having them open as I do is helping to cover up a lean problem.

Is there anybody else that has an opinion on the buterflies position at idle?

I found a site for Ingleese (sp) he does V8s with webers and his site basically said no more that 3/4 turn out on idle jets, (get them bigger to bring it down) and the buterflies almost closed. Also after reading the CB book for the umteenth time I found a side note that was simular.

Perhaps with larger jets I will not need the cold start enrichment. Right now it is only needed for less than 30 seconds.
Is the only problem with them that they dump in too much fuel? or are there more concerns?

Thanks again to all

BajaPorsche · Post by **BajaPorsche** » Fri Mar 04, 2005 9:44 am

Here's something that may or may not help......
when i'm getting a engine running, especially from a car thats been sitting awhile......
if it's popping through the carb.... I find what cylinder is popping (take off air cleaners, and watch)
Then i adjust outwards the Idle jet volume screw for that cylinder..... that is, if the idle jet volume screw are the two screws with the springs on em, on the carb, for each cylinder ......
and alot of times it will stop the popping through the carb..... not always though..... but if it doesn't, then I check compression to see if it might be a leaky intake valve, on that cylinder........ but usually it stops the popping by richening the screw, cuz it might be running too lean on that cylinder.

Any other comments on that?

914fan · Post by **914fan** » Fri Mar 04, 2005 10:04 am

I do believe that I may be running a hair lean overall. Hense my butterflies are not as closed as they should be at idle. When warm it is great. Smooth idle, no popping or stumbling. At this point the only time it pops is when starting cold. It may simply be that when starting cold it is too lean. Cold starts require some sort of enrichment. When I use the cold staer enrichment AKA chokes it does not pop. What you are saying does make sense. By the way how close to closed are your butterflies at idle?

Lots of stuff to check and play with this weekend.....

BajaPorsche · Post by **BajaPorsche** » Fri Mar 04, 2005 10:33 am

Nah... just my opinion, it pops just cuz it's cold........ the choke has something to do with that....but myself, I don't like chokes, and when it's cold, it can pop.......
also, my experience shows alot of engines have different personalities...some adjust different then others, and finding where they run best is part of the adjusting process...... if you think your running lean (whiter plugs) then fatten up the enrichment screws a bit (outwards)....
if your plugs are black.... then lean it inwards.......
if they look cocobrown then that's where I like to run em..... but then again, people might have different preferences.

When setting my carbs.... first i disconnect the linkage... turn down the idle screw on each carb til the butterflies are closed, and then try to fire it up.... sometimes they start, sometimes they don't, then twist the screws in, get it started, then sync em at idle, with the idle set screws......
if you have dual carbs, your carbs might just be way out of whack, and one is running alot while the other is running little.....
but the way I do it, is sync em, with the linkage disconnected, and at idle...... then set/re-connect the linkage, and retest em.....
but once again, I am NO EXPERT IN HERE..... alot of other people have WAY MORE EXPERIENCE then me.

914fan · Post by **914fan** » Fri Mar 04, 2005 12:45 pm

Both carbs are syncronised ans pulling at 6 on the snail o meter. Your procedure is prety much what I do. I also am no expert.
I think that adjusting the carbs can be viewed from a technical standpoint in adition to as an art form. The enginers must have had parameters in mind when they designed and re-designed these carbs. They worked hard to perfect these and I am just trying to follow thier footsteps. Before installing these IDFs I have never used a carb. They intimadated me. I have now found out that they are basic in a very complex way. So much can be done to tune them. You could set up the carbs with jets A and have it run great. Then you may switch to jets B and it still runs great. One of them is going to be more correct, and the difference may not be felt in the seat or seen at the pump. It may only show up on a dyno. However I believe that the carbs will give you clues (popping, throtle settings, etc) to what it needs. I hope to be able to learn the language of the carburator to be able to tune mine and help others.
Again thank you all for sharing in my learning expierence.