37 replies to this topic

[EunUCh]

Bit of a continuation from another thread!

Seems like a few people use or like them for whatever reason and have had a  bit of practice with various combo's..so if any one is happy to share a few things...put in here.

 

They are probably one of the least understood carb.,  which might account for why so many end up getting sold or mothballed.

Bit of an intro.  ... have never had much to do with them other than on a 4 with IR,the main jetting as recommended as roughly 4 times (IR only) the choke size is ball park and is usually a bit on the rich side (for safety sake),i know that a 130 main on a 32 choke is a bit rich at operating temp. but niceish on "warm up" then turns to shit when hot,so much so that you can feel it, a 112 seems pretty good.

 

The other point,not all of us have access to dyno's and the good gear to set them up, so getting a bit of "feel" and looking at plugs and gaining a bit of an understanding on symptoms and cures might just help some one out later on should they decide to use weber or have them now.

 

Go for it...anything about webers will do...pictures...descriptions of operation...faults..good points...experiences .....anything.

 

 

 

[kiwi-lilj]

Webers are great with forced induction.

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[EunUCh]

Another classic example of why people can pick up a set of quads (cheap) with manifold for a 308 is because some people don't understand that the "stock"  settings are a "safe zone" .

Prime example,me ol mate put a set on his brok o door,after an "initial warm up" the thing would get out of the shed in reverse no problems with 38 chokes/150 mains,

after a small spin,park in same place and the stupid thing would just bog down and "choke", pig of a thing....he borrowed a set of 120's just for shits and giggles...amazing difference...not only getting out the of shed but much cleaner across the range...don't be afraid to lean(or richen) the things out a bit...just don't take too big a step in one direction or the other and leave the "adjustment" in there too long without observing the results on what happened ?

[EunUCh]

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most will be familiar with the idle/transfer ports as most carbs. will have these and weber is no different in the principle operation.

As per the illustration on the left of the picture,the carb. is "throttled",or in an idle state,the picture shows what is happening and the fuel/air is controlled by the idle jet/s.

The idle jets come in a few sizes marked #F#,the first number denotes the size of the hole in the jet that meters fuel,the F# seems to have no set pattern in the size of the hole on the side of the idle jet and is the size of the air bleed.

 

The idle mixture of course (like most) is controlled by the mixture screw,usually not many dramatic problems happen in the idle circuit and going on what most of the weber manuals say the idle screw needs to have about 1&1/4 - 1&1/2 turns out to have any reasonable 

control over the idle adjustment.Going on what i played around on IR manifold with any less than this it is a bit of pain to get any sort of "range" of fine fine adjustment as it denotes that the idle circuit is a bit rich which is either too large an idle jet or too small an idle air bleed.

One home remedy is to sneak up the idle air bleed size with "index" drills  and see if that helps,if it does and the idle screw now has a bit more range then we are on the right track,if it gets to a point where the air bleed needs to too big,then drop a size on the idle jet and start again.

Most people would not recommend drilling the jet itself whereas the air bleed is not so bad but still needs to done with some precision.

The transfer is the next,and same as most carbs. the same principles apply.

As can be seen in the illustration to the right in the picture the transfer starts to operate when the plate exposes the transfer holes and that the idle circuit is still in operation.Now we have two circuits both working off the idle jet,the idle systems flow is controlled by the mixture screw,but the transfer system is controlled entirely by the idle jet and the transfer holes (which are usually larger than the idle jet hole so the transfer holes are doing nothing?) and there is a good chance that the idle circuit is starting to "drop off" due to lack of signal at the idle feed hole?

 

Problems in this area also relate to the idle jet.The main noticeable problems can take a bit to "sort out" but having said that i found that by getting the idle "nice" it seemed to fix the transfer fault as well.

Too lean on the idle jets and you might get a backfire when slowly opening the plates on a light load,or it will feel "draggy".

Too rich and it will feel "soggy",again on light opening/light load ...all with engine at operating temp...and worse on a warm day.

The other thing is that if the idles are bit on the rich side is that if you just open the plates just a tad to make transfer begin is that it will not come back to a clean idle...sort of like a bit of choke "stumble" if you like.

 

Some times it can help on finding out which way to go by simply taking another set of jets that are quite a bit larger or smaller to try and see what the result is,you will soon know which way to go...i think even on very light openings that the pump adds a bit as well,might not be much.

 

I have only found this out with a bit of reading an stuffing around and don't claim to be some expert,it's just from personal experience and a bit of help from around the place.

 

 

 

 

 

[EunUCh]

fast forward to choke size.

On an IR setup the basic guidelines from weber seem to be close,although a bit of "tuning" may be needed..who knows what is is needed on a 9 port other than a big choke will kill the low end,not a problem on an all out race engine where the bottom end only needs to keep the thing  running to some degree until things are happy?

 

Does a too big a choke on a 9 port with triples kill the bottom end a bit considering that one pot is drawing off 2 chokes as compared to an IR?

Do we need to pull down the choke size a bit within reason to suit cam characteristics on the 9 port considering induction pulses and robbing due to induction phases?

If just for a good street/driver do we to come down on choke sizes on the 9 port to make the thing driveable?

 

Do we take a guess and pick a choke size of about 90% of valve throat Diam. and work out that a 9 port might need a bit less after working out a CSA of throat considering that one carb. with 2 big holes is basically feeding a cylinder of the same size as if it was on an IR setup?

dunno...i just find this stuff interisting

 

 

 

 

[A9X]

 

 

i don't mind them.

[EunUCh]

Borrowed from another thread!

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pictures do tell a thousand words,the sensor shows where the problem lies,not only the initial major problem,but looks like a bit of "clean up" up the top could help a bit as well?

Bolt them carbs on another engine and the problem i am guessing will still be there?

 

drove an 8 once with quads,bit of a 'weird" sound from under the bonnet

[EunUCh]

The weber can offer some "good" gains if set up right,they are still used by many people on various applications from daily drivers to race applications,that is the beauty about IR induction,but i think if we take the time to get at least a basic understanding of how they or any carb/manifold setup  works that we play with along with some sensors that are relatively cheap then they can be sorted out to be not too bad considering their age of conception...i would hate to even contemplate the mathematics that went into designing one...or any other carb for that matter?

 

They have no "power valve" system and in that area i would hazard a guess at saying that is why there are so many emulsion tubes available to address that issue?

Just a tad off topic....as already said...3 holes on a 9 port work better...if weber made a singe side draft then it would be a gain...but they don't,but  that is an entirely different topic.

 

 

 

[jd lj]

On the dyno graph above you can clearly see the lean spike in the high 2000's rpm, this is where the transition circuit is dwindling off and the emulsion tubes aren't supplying enough fuel for the initial stage of the main circuit. After that it appears that the main jets are to big.

When you talk about how many turns out the idle mixture screws are you should specify if you're talking about the older style screws which were in use when all the books were written about webers or the newer style screws with a sharper taper.

Set your mixture for a warm engine, it sounds like you're getting caught up in what it's doing while cold.

[EunUCh]

That's a good point,they did change a few little things along the way and quite honestly they were given too me and just worked with what was there.

The idle was set on warm/half warm/cool just to get an 'idea" of what was going on to "find out".

 

One bit of an "oddity" is the idle strength over those ranges is that  on the slightly 'rich" side as set coolish results in a bit of a stumble after a "short drive" but when left to "hot soak" for a bit would 'clean up'

When idle set on fully warmed through engine  no problems,also on certain days where the temp and humidity were "just right" you could pull up,lift bonnet and condensation droplets could be seen,even after a 30k drive...weird...a story i heard was that some Fords used to suffer from ignition problems when fitted with triple webers?

[LC-GTR-1969]

Just for the point of conversation, I think I will chime in…

 

My set-up is currently using 40mm chokes on a 9 port head- street driven.

 

The max power is produced at about 6000rpm (it holds the peak between about 5800-6200rpm). Power holds well until 6800, where it then starts to drop off. The power band really starts to come to life at about 4500rpm (with 40 chokes).

 

However, I would like to drop choke size down to 36mm… I have an old dyno read out (from before I owned the engine), where it was running 36mm chokes. The power curve, with 36mm chokes, had the max power at 5200rpm, and the power band was noticeably better at lower rpm- basically the torque curve was stronger down low, as expected).

 

But the interesting thing is that there is only about 10hp difference in the peaks. But I think it would be better to sacrifice 10hp at the top end, to gain  more usable torque down low.

 

In all honesty, the car does drive quite good with 40mm chokes, even considering the gearing is quite tall- all things considered…

 

With shorter gearing, I would actually stick with the 40mm chokes, as the gearing helps to get the car on the cam.

[gtrboyy]

Mine with the old 202 was sorted out very well so I went to shorter 3.90 gears instead which transformed the car into something much nicer to drive on the street.

[jd lj]

Is anyone using anything other than f2 emulsion tubes?

I'm interested in testing some F7's or F8's if anyone has some spare.

I'm currently trialling some modifications to my f2's, if it goes well I'll fill you in.

[LC-GTR-1969]

Mine with the old 202 was sorted out very well so I went to shorter 3.90 gears instead which transformed the car into something much nicer to drive on the street.

What size tyres? 

 

I have 3.9 gears, but 26 inch tyres… I fitted some 22 inch tyres to see what the gearing effect would be like, and it really did make the car more comfortable on the street- the cam and the 40mm chokes seemed to find their sweet spot quicker and with less nonsense. From memory, I worked out that I would need 4.4s to have the same effect as going from 26inch to 22 inch tyres…

[EunUCh]

Here is a bit of a list and some numbers about the tubes.

They don't seem to be  just an ordinary bit of work when closely looked at?,i suspect all the depths/sizes of holes/positions etc play some part in not only the main (or normal phase as weber put it),but also have something to with "power valve" operation which they do not have? Note the "fat section" more or less in the center of the tube.

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[EunUCh]

the "normal phase"...obviously at WOT...who drives like this "normally"?

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I figure that somewhere between transfer and this phase that there is a bit of stuff going on that is related to MAP.

Again ,just another guess,but because of the lack of a "power valve" circuit that some one with a pencil and paper worked out how

to somehow combine both 'power valve" circuits within the main ("normal") and figure out that one does this under certain conditions given that this and that are happening and end up with a variety of tubes to suit every condition?..bit of a head spin but interisting.

 

one thing i did notice when a mate and i were stuffing around with tubes is that going from a F16 to a F2 on the sort of equivalent of a 12 port that when the F2 was used...black smoke from pipe at lowish rpm under normal drive off condition...obviously getting too much fuel in the early stages...but that might be different on a 9 port?

I think Weber Performance have a bit of a chart for 9 port stuff,and it seems that F2 is popular for this application.

 

[gtrboyy]

Back then it was m20/3.90 with 205 tyres on sprintmasters...drove super nice for something so lumpy.Could handle 60 km/h in 4th no pig-rooting.

Was a bit tedious with wheelspun but was lightyears improved over 3.5 & 3.36 gears trialed.Absolutely hated it with 3.08 gears.

 

Later put on 225/65 things that filled wheel arch for better traction...60km/h 4th had to be light throttle or it slightly bogged down,fine at 65-70 km/h

 

Decent comp with 'good' headwork + short gearing goes a long way in making them streetable.

 

 

Is yours nice & revvy or is it moreso about taming it for speed limits?

[LC-GTR-1969]

Back then it was m20/3.90 with 205 tyres on sprintmasters...drove super nice for something so lumpy.Could handle 60 km/h in 4th no pig-rooting.

Was a bit tedious with wheelspun but was lightyears improved over 3.5 & 3.36 gears trialed.Absolutely hated it with 3.08 gears.

 

Later put on 225/65 things that filled wheel arch for better traction...60km/h 4th had to be light throttle or it slightly bogged down,fine at 65-70 km/h

 

Decent comp with 'good' headwork + short gearing goes a long way in making them streetable.

 

 

Is yours nice & revvy or is it moreso about taming it for speed limits?

 

Thanks for feedback!

 

Mine is quite revvy- revs to 7500 no dramas, but I am not up there much, I generally shift about 6800)...

 

My gearing is quite tall, as even though I have 3.9s, the wheels are 15 inch with tall profile (so diameter is 26inch). It does 90km/h in first, which is just silly by my reckoning... The car feels much better with 13 inch wheels- but obviously revs higher on express ways etc...

[gtrboyy]

The 225/65or70 tyres were on 14 inch widened monaro rims...guess they were 25 or tad under 26 inch tyre,either way barely fit in wheelarch so they were huge compared to 205 wide sprntmasters.

 

Spent 90% of time suburban driving so short gears suited it for quick blasts & skids.Also I'd come off a long suspension & for 5yrs had less than 3 points..needed the car to be tamed down.

 

Mine could buzz over 7000rpm too but felt like  6-6500rpm was sweetspot.

 

I remember previous owner of mine had an m21/3.08 combo,1st & 2nd gears were all you needed....spastically long.

Must have some tall gears in that gearbox of yours lol

[LC-GTR-1969]

The 225/65or70 tyres were on 14 inch widened monaro rims...guess they were 25 or tad under 26 inch tyre,either way barely fit in wheelarch so they were huge compared to 205 wide sprntmasters.

 

Spent 90% of time suburban driving so short gears suited it for quick blasts & skids.Also I'd come off a long suspension & for 5yrs had less than 3 points..needed the car to be tamed down.

 

Mine could buzz over 7000rpm too but felt like  6-6500rpm was sweetspot.

 

I remember previous owner of mine had an m21/3.08 combo,1st & 2nd gears were all you needed....spastically long.

Must have some tall gears in that gearbox of yours lol

 

My wheels are 235/60 on 15 inch rims... This equates to about 26.1 inch diameter... The tubs are modified to suit and the diff has been shortened... First gear is 2.54, so relatively tall... basically at 7200rpm I am doing 90km/h. 4.4 gearing would bring the shift point down to 80km/h

[jd lj]

Here's a little job for the webers.
Quite often the cold start circuit gradually leaks fuel even with having made a gasket for the blank off plates.

The solution is to stop the fuel entering the circuit all together.

To do this you can plug the 2 holes in the bottom rear corners of the float bowl or remove the starter jets and tap a thread into the orifice in the bottom of the well and use a grub screw and thread sealant to seal it from that end.

Another way around it is what I plan on doing this weekend and remove the starter jets and fill the hole in the bottom by soldering it up and use a bit of thread sealant on the bottom of the jet just to make sure the seating surfaces are sealed. I figure this way I'm not altering the actual carbs at all and could be reversed in the future.

Obviously I don't use the cold start mechanisms, but instead use the pump jets to start my car when cold.

JD

[jd lj]

If you want to plug any holes in jets this can also be done by using high strength loctite and heating it for around half an hour.

I used a heat gun to heat up my emulsion tubes recently to fill the holes 2nd from the top of my f2's. I also removed 2mm from the bottom of the emulsion tubes which then brings the 8 X 1mm holes just down to the fuel level and richens the beginning of the main circuit to reduce the classic flat spot. Note, you'll also need to remove 2mm from the part of the main jets that goes inside the emulsion tube.

I've still got some more testing and tuning to do with this modification and will report back with results another time, but so far there's been an improvement.

JD