Topic: Weber carb set-up

[scottly]

No doubt, Mick! I'm very curious about when these changes came about. I'm guessing they were due to meeting emissions for import into the states?

[Tintop]

[What is the difference in the idle screw? Is it a very slight taper compared to the standard ones? Any idea what year Lambo or Maserati it was used on?

No idea what year scotty, but I'm going to do some checking to find out for interest.   

The screw has a long thin taper.

[scottly]

Interesting. I would still try the 50 idles with maybe 1.5 turns out? As far as the pump spring, do you have any idea of what you have now? Extended (free) length, wire diameter, and number of turns. I'll measure a spring or two tomorrow.

[Tintop]

When I was speaking with Pierce and said it was a '149', he immediately said were it was used.  In talking about the accel pump valve difference (ie a ball under and over the demand weight, and hole in cover) he explained the reason.  They didn't want high speed richening.  From there we talked about the pump it's self.  Given my application he said to stay with the 10 rod, but change the spring to a 47600.055 (strongest).  Reasoning being that the current stock spring (soft) is creating too long an overlap, causing it to go over rich as the mains come in (the stumble when I crack the throttle).  I've also ordered regular pump jet valve covers (no hole) so I can convert it later if I find I need high speed richening.

Interestingly he also confirmed that the 34 chokes are OK (though at the top end) for the cylinder capacity, and application.  Seems I'm dealing with a relatively rare carb, in an application with no background history.  Like the saying goes - the good thing about Weber's is they are infinitely variable / the bad thing is they are infinitely variable.

[scottly]

I wouldn't mess with the pump spring until you see how the motor reacts to the other changes. You'll know you need a stronger spring if the motor sneezes back through the carb when you whack the throttle open.

[Tintop]

Generally I would agree scotty, however with the changes already made I'm basically back at square one.

Last year there was a big 'stumble' coming out of low speed turns when I whacked the throttle open.  That was why the suggestion to go to the stiffer spring.  There is no doubt when looking at the motor / exhaust etc that it was running very rich.

I also got a Syncometer, so that will help getting things balanced at idle to start with.  If there is time, and availability I'd like to get it on a dyno before the test & tune weekend.  With what I know now, and the parts at hand it should be much easier to get the A/F right.

[Tintop]

Re the 40DCOE 149 carb scotty.  Looks like it was meant for a Lamborghini Espada or Urraco.

[scottly]

I think the stumble was due to the volume, rather than the duration, of the accelerator pump. With those huge 50 squirters, the duration would be very short, even with the weakest spring. A 50 jet has close to the same area as two 35 jets combined. 
The spring I measured today came from a "16", that was attached to an HD manifold.
free length: 54.3 mm
coils: 15
wire dia. .4 mm

BTW, the overall length of a 10mm stroke rod is about 60 mm.
Here is a pic of the earlier idle screw:
 

[Tintop]

Big difference in the amount of taper in the two idle screws.  I've re-set mine to the recommended 2 1/2 turns.  I got 50 idles, but will start with the 45's, as I now know the setting was way off last year.  It also has the plastic floats so those have been set to 12.5 closed (end of float), and 25 open (middle of float).  The closed is slightly more than factory (12), but is what I used for my 2TG Solo motor.  Also went back to the 175 needle, as there is a likelyhood that the 200 could be causing the bowl to over fill with high fuel pressure.  I'm going to add a fuel pressure gauge.  Would like to keep it at no more than 3 1/2lbs.  If it's higher than that I'll add a regulator, probably a Holley as their compact, easy to source, and I've used them before.

Besides the 35 pump jets I also have 40's.  I'm also not sure that the 50's were original, as this carb had been used as a parts bin before I got it (cheap ).  Figure with the 2 springs, and ability to change it back to high speed richening I'll find a combination that works.  Good thing is the rest of the rig is sorted from last year.  I'd have to make some carb changes anyway with the new cam, so I'll just create a new baseline setting, and go from there. 

The spring and some other bits should be here mid next week.  I'll measure both then.

[Tintop]

measurements for the spring -
free - 44mm / coils - 24 / wire - .74

Question - how does everyone else remove the accel pump?  have always just pulled it out by grabbing the exposed flat part of the pump rod.  this one doesn't want to come out.

[scottly]

I made a tool from a small flat-bladed screwdriver that hooks onto the underside of the brass retainer, through the exposed part of the slot, with a nut welded halfway up the shank to pry against for really stubborn ones.
Don't pull too hard on the rod, as you can bend the hook that attaches to the piston.

[Tintop]

.......as you can bend the hook that attaches to the piston.

That's what I don't want to do.  Thanks scotty, will make something up tomorrow.

[scottly]

I learned that one the hard way.
I had thoughts of taking a picture of the tool at the same time I was measuring the spring, but didn't. Basically, I heated the tip of the screwdriver up, bent it 90 degrees, then ground it and filed it until it would fit into the slot. I sort of roll it into the slot, then pull straight up. Sometimes it's necessary to alternate the side of the plate you are hooking the tool on.

[Tintop]

scotty comparison of the two pump springs -



New issue to deal with however.   When I install the new stiffer spring, when you roll the throttle closed it is stronger than the throttle spring, and the butterflies don't close all the way.  If you let it snap shut, it's OK.  I do have a secondary spring installed, but don't want to rely on it to finish closing.  Got a call in as there should be stronger throttle springs for this issue.  Thought it might be binding, but when I re-installed the old spring everything works OK again.

[scottly]

I ran into the same issue with the heavy pump springs on the V-8 set-up. I had to use external springs to get the throttles to close at all. Like I stated earlier, I would try the original spring first, and see how the motor responds to the new squirters and discharge.

[Tintop]

I ran into the same issue with the heavy pump springs on the V-8 set-up. I had to use external springs to get the throttles to close at all. Like I stated earlier, I would try the original spring first, and see how the motor responds to the new squirters and discharge.

That's what I decided to do scotty.  I don't want to have to depend on my external spring to finish the closing.  It's only there for safety.  If I still get too much overlap I'll look again at changing the spring.

New baseline configuration (will set idle mixture & sync starting from this) -
4.5 auxiliary venturi / 34 chokes / mains - 135 / airs - 185 / tubes - F11 / 50F9 idles / 10mm pump rod / 50 discharge / 135 pump jets / idle mixture screws (long taper) 2 1/2 turns / idle screw 1/2 turn / air correctors closed.  The pump valve has been changed to standard config (no hole in cap), so pump jet will now give high speed richening.

[scottly]

New baseline configuration (will set idle mixture & sync starting from this) -
4.5 auxiliary venturi / 34 chokes / mains - 135 / airs - 185 / tubes - F11 / 50F9 idles / 10mm pump rod / 50 discharge / 135 pump jets / idle mixture screws (long taper) 2 1/2 turns / idle screw 1/2 turn / air correctors closed.  The pump valve has been changed to standard config (no hole in cap), so pump jet will now give high speed richening.

Sounds good to me.
This whole discussion has revealed the possible solution to a problem on my bike: when in stop-and-go traffic, my bike tends to get loaded up. I'm now thinking it's due to too much pump. I'm currently running 55 discharges, and I'm going to try larger ones to see if it helps.

[Tintop]

Agreed, this thread has really brought some interesting details to light.  One of the main problems seems to be that the vast majority of Weber books were written in the 60's.  As I've found out when your dealing with a later carb the info (like mixture screw setting) can really lead you down the wrong path. 

One other interesting thing that came to light is that there is a wide variety of progression hole configurations.  Both in the number and the size(s).  Adds another twist to buying used ones when your trying to put together a set.

[scottly]

You will now be running the same pump set-up as I, other than the slight difference in the discharge. If you find no need to increase the total output with your larger (per cylinder) motor, that will be confirmation that I may indeed have too much pump...

[Tintop]

The other thing I'm interested in seeing how it plays out is the idle mixture.  Given the very different settings for the two styles of mixture screws, I was set quite lean.  If I have to turn it in less than 2 (lean it out), I'll put the 45 back in.

[Tintop]

Follow-up regarding progression holes.  Tried to get this picture before...finally got a good one. 

Progression holes in my 40DCOE 149's.  Notice that they are different sizes and pattern is staggered.  The first (big one) is uncovered with with hardly any shaft movement (1 1/2 turns of idle screw), last one when lever is about 1/8 to 3/16 off idle screw.  Figure that means my range of idle adjustment is only from 1/4 turn to 3/4 turn before the progression hole(s) start to effect the idle mixture.

[scottly]

I'll check the location of the progression holes with regard to the throttle plates on one of my carbs to see how it compares. This reminds me of Solex carbs used on late '60s VWs, which also had a bypass idle screw; it was really a pain to get the idle right until I figured out that it was a completely different procedure. What you may need to do is set the "normal" idle speed screw just barely open, then adjust the speed with the air by-pass screws?

[Tintop]

Figure this thread is becoming a Weber FAQ scotty so bare with me (know you know this ) but maybe others following this don't.......

Weber never made a 'universal' carb, they were all for specific manufacturer applications.  Hence the differences, eg Lotus Elan carbs only have two progression holes, Alfa's (?) four, and mine (off Lambo V12) three.  So getting progression spot on could be a bit hit and miss, when using a carb in an application it wasn't built by Weber for (like me ).  Their purpose is the fill the initial lean condition that results when the butterflies just start to move, before the accel pump can cover/fill in the overlap to the mains.  However, you should always be able to get the idle correct without the progression holes being involved.  Hence knowing how many turns on the idle adjust screw before they start to be uncovered on the particular carb(s) being used.

Because the butterflies are not 'air tight' even when fully closed (idle screw not touching lever) the engine should idle if the idle jets are sized dead on, and the idle mixture screws set middle of their range.  According to Pierce Manifold you only use the air corrector to do the final fine tune sync.  Up to that point they're closed, and you shouldn't be touching the idle screw.  Using my idle mixture screws as an example.  Their range is 2 turns to 3 1/2.  So if your less than 2 the idle jet is to rich, more than 3 1/2 to lean.  I'll use my Syncometer to determine which is the 'strong' side then adjust the idle mixture to get the best balance.  As it's highly unlikely that the 50F9's are too lean, if I have to go less than 2 turns I'll change to 45F9, and start again.  Once I get the best result possible doing that, then I use the air correctors to fine tune the sync between barrels.  I know that going past 1+ turns on the idle adjust screw starts to bring the progression holes into the mix.  So if I have to do that, again the idle jets are wrong.  Should be able to set the final idle speed within a 1/4 turn in, or out at that point.

[lwahples]

My Webers have 4 progression holes,and yes.This thread has/is a very good read for any one looking into running Webers.

[Retro Rocket]

I don't even have webers and its a good read....