Weber jets??All who live for their triples please read this

[eds240z]

mixture screw is turned out just a tad under 2

[2eighTZ4me]

With the 200 mains and 180 airs, it shot up to about 19:1, so yeah - even given the "rule of thumb" the car is still out of wack. The 220's brought it down to about 16:1 at that rpm range. Going leaner is not an option. There's something causing a spike at 4k-5.5k that has us baffled. 180s would burn a piston, so I can't take your advice there. The car is like nothing you've ever seen on a street setup before, the car is a full GT-3 car and has parts in it that even I scratch my head at. Idle jets have absolutely nothing to do with the scenario at the RPM range I'm working with. We're talking WOT at 4000rpm. Idle jets are LONG out of the picture at that point. Not even worth addressing. Car idles fine at 12:1 and drops to about 8:1 to 10:1 at about 2k and slightly increases to about 13:1 until it hits 4k - then it shoots through the ceiling. Then strangely enough, starts coming back down about 5500rpm.

 

We're dealing with an anomaly here, not the norm, and I'm trying to find something in the main circuit that could cause it to do this. I have 44 Mikuni's on my 240 and have it dialed in right on the money across the rpm range. Something is wrong here with his car and I can't quite figure out what. I DO appreciate the input though - keep thinking and throwing ideas our way - every little bit of knowledge helps!

[Lazeum]

Idle jets are LONG out of the picture at that point. Not even worth addressing.

You've written "At base and up to about 3500RPM, the car is so rich". This is idle jet range. So yes, it was worth addressing (relevant? it is up to you but since it is for a race car, I understand what you meant)

 

Afterward, you might be right. I'm just shooting ideas as stated I'm nowhere an expert.

 

It might not be an issue with the carbs then... I'm interested thou to know how you could fix the issue.

[2eighTZ4me]

You are correct - as stated earlier - I don't have the graph and was going on what he said. Regardless, on a dyno pull or any straight line acceleration, your idle jets are gone by 2000rpm at WOT, so that really doesn't come into play. The problem we're facing is truly focused on the main circuit. Why would it be fine from 2500-4k - take a dump in the "lean" pot, and then start evening back out?

 

I've got my 240 dialed in such that (after tip-in leanness) it starts at about 12.2 at around 2k and works it's way up to about 13.6 at about 7k. Perhaps still a bit lean - but linear nonetheless across the rpm range. Something's amiss with these carbs - starving for fuel? I have got to get him to check the float level on the second carb. That is the ONLY thing I can think of that would cause that type of lean condition. Jets just wouldn't "clog then release" - on a consistent basis of 6 dyno pulls. Even with the larger jets in there - it did the same thing. It' CAN'T be jets if you follow the logic there...dont you think?

 

DO appreciate the input - keep it coming - I'm a Mikuni guy - these Webers are screwing with me! Thanks Lazeum!

[locodrftr]

Hello all i am fairly new to the whole weber scene as well but like everyone here i got my own problems.....anyway so far here goes my setup

 

L24 up to 2.5 and some sort of regrind on the cam e88 head, 6-2-1 msa header

 

40 dcoe 151

40 pump jet, air corrector 180, f11 emulsion tube, main jet 120, idle jet 50f9

30 mm main venturi and 4.5 auxilliary venturi, 50 bleed valve basically a stock setup,

the carbs originally had 110 mains and was crap above 4000rpm now the 120 mains are much better however im thinking of going to 32mm main venturis car still feels like it has more in it....dont know for sure but only changes will tell. Like everyone else here the car has a slight stumble from idle to about 3000rpm dont know if its the throttle plate setup or idle jets or what.....when i setup the throttle plates to just cover the first progression holes the car will idle but seem a bit too lean as i will get some poping in the exhaust at idle and mixture screws are about 1 full turn out from the seat to idle about 1000rpm. trying to drive the car like that is horrible however if i barely set the throttle plates to just before the first progression hole and have the mixture screws 1 1/2 turns out the car is pretty good but still a slight stumble from light pedal to wot to 3000rpm but its the best setting the car likes so far. any inputs?

im thinking maybe bigger idle jets or a bigger pump jet, maybe a longer stroke on the pump jet rod? Any input is appreciated, and im gonna wait a couple of days before i start ordering jets and venturis online....

 

2eighTZ4me

more info on all the jets and emulsion tubes and engine specs would help everyone give you some more advice.....from what i know the main jets affect the entire main circuit (2000rpm) and up while the air corrector jets are mainly for higher rpm range..

anyway have u thought about changing the accelerator bleed valve to one that doesnt bleed back as much or any fuel? It could maybe be the needle valve that isn't keeping up with the demand of fuel.... hard to say but maybe even changing float heights to hold more fuel might help.... i wouldn't think keeping stock specs of certain things would apply to an all out race car....just some food for thought maybe it will spark some idea's for you or anyone else here, good luck and keep us updated on the progress...

[Daeron]

I have a question.

 

 

We've got alcohol in our fuel now.

 

Are the vaporization/misting/venturi effects of the fuel in any way altered by the addition of alcohol?

 

I am no carb person either, but with regards to the 200SX I almost wonder if there isn't something happening that is causing an air bubble to form in the float bowl somehow at that point.. Maybe there is a range there where the floats open up, fuel starts flowing in and there is a "slosh" air pocket formed that the emulsion tubes snort up some atmosphere instead of petrol. Is he by any chance running a slightly high fuel pressure (or low fuel pressure) for any reason? Could the fuel pressure be higher than it "should be" (ie, malfunctioning pressure regulator?) Overly high fuel pressure might just cause a splish situation or a tiny pressure hammer or something along those lines...

 

I am trying to approach this from a point of view like so: The carb is working right, but something unanticipated is causing the E-tubes to starve. Any chance that incorrect floats are in there, or float arms? Maybe the floats are too light for some reason? (don't open up quickly enough)

 

You know how I work by now.. I throw ideas out there, you feel freee to shoot them down.

[Lazeum]

I was thinking about your AFR level. 19:1 is super lean (16:1 also). there's almost all the oxygen going through the system. It seems oxygen does not burn at all.

If I check AFR in my exhaust pipe after shutting down the car, this is the kind of AFR I've got.

 

You either have: no gas as Dearon stated, no explosion or bad explosion (detonation, knock?).

 

A lean condition like this should create something obvious you should be able to feel or to hear. How does this lean peak translate from a driver stand point?

 

Could it be an issue with the distributor?

I haven't heard anything like this but could it be a resonance in the system (with springs/cam for instance) since you have something "nobody has ever seen" ?

 

For my own knowledge, what is the impact of cam advance? Why do we do that?

[Daeron]

For my own knowledge, what is the impact of cam advance? Why do we do that?

 

Go to the L series sub forum and read Braap's sticky on how to degree your L-series camshaft. Even if the details of the procedure and how its done just get glazed over, the post will explain better than anything else the answer to your question.

 

Its a longish post, but like I said you can more or less skim the process he is going over and not worry about walking away knowing how to degree in your cam.. just worry about understanding the what and the why of it.

[2eighTZ4me]

Matt and Daeron - he hasn't "driven" the car yet. He's bopped up and down the street a few times, but wanted to do the dyno tune before hitting the track. The car is far from street legal. I too had suspicions about his float levels. He has a front strut bar that prevents removing the top of the front carb. Told him he's gonna have to pull that and check.

 

He had the carbs professionally redone with new floats. I don't know HOW - but the new bronze floats that were put in the carbs were getting hung on the float bowl walls and not allowing ANY fuel into the bowl. They were just too big. We replaced them with the original floats (which were a black rubber/plastic looking composite instead of bronze) and we had fuel. Checked float levels at THAT time - but nothing further. He ended up putting on the strut bar and therefore no access to the front carb. I'm with you - he's starving for fuel somewhere. He's running 112 race gas, so I doubt there's any alcohol in that formulation. If so - probably negligable to the very furthest extent.

 

Oxygen doesn't burn at all?? Tell that to the folks that drive the medical trucks carrying oxygen - they'll tell you to the contrary. It is extremely flammable in its' molecular form.

 

He's running DIS - Electramotive HPV-1 crank trigger ignition. No dizzy to speak of.

 

I finally got a hold of his dyno run. Red and Blue are with 220 main and 200 air. The blue is where he backed off the 3000rpm timing by 2 degrees.

[Daeron]

Fuel pressure/flow rate of pump? Regardless what those figures are, I would be SORELY tempted to try running the car with a different pump, and also running the car DISabling the FPR and then greatly DECREASING the fuel pressure.. Just for purposes of data collection.

 

Like I said, I keep seeing bubbles in the float bowl, and I really am picturing bubbles from a stream (like the classic surge tank issue on locating your high pressure pickup point somewhere where the inflow from the low pressure pump will not give you a negative effect.)

 

 

These kinds of problems are simultaneously the biggest stupidest PITA of working on cars, but also the most stimulating and DEFINITELY the most satisfying once you FINALLY figure the @%^$ thing out!

[Lazeum]

Oxygen doesn't burn at all?? Tell that to the folks that drive the medical trucks carrying oxygen - they'll tell you to the contrary. It is extremely flammable in its' molecular form.

 

Of course it burns! but to get an AFR of 19:1, I meant the oxygen went thru the engine without any reaction, it went it and out without any major explosion...

[Lazeum]

I went back to business this past weekend Weather was awesome (70°F, sunny, dry) I've seen many nice cars in the forest where I test drive my Z (Ferrari 330 GTC, Lotus 7, MGs, Triumph)

Anyway, I was there to tune the Z. ( Colors on curves are chosen - Yellow Curve on 1 picture is the same as other yellow curve)

 

* Timing Adjustment *

I first started by adjusting the timing where it should be: I went first at 16btdc at idle and 32 total (previous setup was 10@idle / 28 total). The engine was pinging at 2.5k rpm under heavy load. I had to back up timing to 14btdc and 30 total. Pinging was still barely there. So I've changed the springs inside the dist. to avoid issue at mid rpm with 2 orange ones from the Mallory tuning kit. Pinging is gone!

 

I've the checked AFR to see where I stood; mixture was way richer than before (can weather be responsible as well for such a difference?) so I've changed main jet to 135.

 

 

 

* Accelerator Pump Jet *

I've changed accelerator pump afterwards (40 to 45). Car has a bog when I hit the throttle, I wanted to eliminate it.

It did not change anything as far as feeling inside the car but when you look at the following curves you could see the difference. It affects mixture up to 4k rpm. I do not know how the bleed valves at the bottom of my bowl look like. I've heard some have hole, some don't. Unused gas can go back to the bowl depending on the bleed valve setup.

I guess this is the next item to touch if I want to get rid of the bog (if I can, since everybody seems to have this issue anyway with webers and L engine)

 

 

* Needle Valve *

Last item on the list was the needle valve. I've switched 1.75mm ones vs. 2.00mm.

First of all, my 1.75mm were not in good shape:

- 1 was ok (the one I've checked to control their size)

- 1 was very loose (0.5-1mm of radial play for the needle inside the housing)

- 1 was destroyed. the needle was damaged. There was no spring action anymore, the ball housing was crushed to make sure the ball was not going away.

 

So it means to me: 1 carb was ok, 1 was probably so-so and the last one was out of tune as far as fuel level. I did not check bowl height, I should but I didn't

Difficult then to conclude anything as far as needle valve effect.

Anyhow it was a good operation, I've spotted broken parts inside my carb, it should improve tunability in the future.

 

 

Check out the results.

 

* Next Steps *

The mixture get rich at max rpm, I would like to try bigger air corrector (195 or 200 instead of 180) (not smaller as I said earlier) but I would need to order some.

Depending on how air jet affect AFR I may have to go down a bit with main jet as well to lean out 3k-4k range.

 

To conclude the rich spot is still there, I could not remove it. I start to believe it is part of the setup, I may have to live with it. A good trial may be to switch choke (venturis) and see how the rich spot behaves. Bigger chokes might also help me targetting 12.5 AFR at max rpm since I've read max rpm AFR would not be affected too much with air jet.

 

Car feels really good today. Throttle response at every rpm above 2500rpm is very good. I can hammer the throttle at 4k, engine reacts immediately. I would call it a good tune but I can do better

 

More to come but I need to order more parts....

[locodrftr]

Looks pretty good, a bit of a lean spike though at the 2500rpm though....Be as accurate as possible setting the floats, i recently checked mine and they were off a bit......setting the float heights alone had a tremendous effect on the off idle to 2500rpm range. It definately takes some time to do it right and get them all the same but it absolutely payed off...... I set mine at 12mm fuel shut off and 26mm droop but yeah check the float height for sure since you removed the needle valves and see if it helps...

keep up the good work Matt

[didier]

salut

Mathieu

Je ne comprends pas ce creux de pauvreté à 2500 t/mn.

Et toujours cette richesse entre 4500 et 5500,je pense que c'est un accord qui se situe là, un résonance, et qui remplit mieux, donc plus d'air ?

[zredbaron]

FANTASTIC presentation of data, matt. thank you. nice to see exactly what each change is doing.

 

alas, the rich spot remains. you know my thoughts on that.

 

 

2eighTZ4me,

 

i have electromotive ignition as well. my hpv-1 took a dump a few years back and i've since upgraded to the hpv-x. some cool features but more or less the same performance. i'm running a very high end 109 octane VP fuel, so i'm with you there as well. to the discussion about alcohol, yes, there is alcohol in these fuels. there is also alcohol in pump gas. depending on manufacturer and geographic location (ie state laws), both pump and race gas will contain varying degrees of both alcohols and ethers: ethanol, toluene, xylene, etc. whats different in more extreme fuels is the concentrations of the ingredients used to produce the required octane. there are disadvantages of each type and mixture of fuel. i'm by no means a chemist so i won't go further than that. the point of all this is that the suggestion that weird things might be happening when the fuel is emulsified is a very valid theory. the specific gravity of fuel has a significant effect on the emulsification and eventual atomization of the air/fuel mixture.

 

if anyone wants to read more about fuel, go here:

http://www.offroaders.com/tech/octane.htm

http://www.idavette.net/hib/fuel/

just don't listen to the making your own brew with xylene advice. bad idea. bad on your cars plastic's (ie fuel lines and tank parts) and doesn't perform well or consistently.

 

that said, in my own experience, my car was much smoother when i went to the race gas. i assume this is because it is *engineered* to have a fast flame front and burn well, not to mention the fact that a >= 12.0 compression ratio demands ~104 octane at a minimum. it smells nothing like pump gas, not even a resemblance as it smells very pure and pleasant. my theory is that even with the A/F ratio off significantly, this fuel is going to burn and burn fast in an engine that calls for it.

 

side note, what is so *extreme* about your engine that you need 112 octane fuel? no offense, but your power output is consistent with a street performance motor, not a race motor. (is this your friend's 200sx or a Z?) you may find better results with pump gas in the 91-93 octane range. also, tell us more about the engine. displacement? cam specs? venturi size?

 

since you are going lean, i would start down the fuel delivery investigative path. re-check your floats, inspect your needle valves (like the one's in matt's pics). if those are good, then i agree with the suggestion to toss the fuel pressure regulator and instead invest ~$100 in a good electric pump. you want a high-flow capacity, low pressure centrifugal fuel pump. webers like 3.5-4 psi. don't send any more pressure than that.

[Lazeum]

Thanks guys for your comments

 

locodrftr, I haven't reply back to your post but for sure I will play with bowl height to make sure they are all the same. I've done it once but with my old crappy valves, I know I'm off now.

I'm going to review the whole idle adjustment too. There are some improvements to do as well.

[Lazeum]

salut

Mathieu

Je ne comprends pas ce creux de pauvreté à 2500 t/mn. I don't understand the lean spot at 2500rpm

Et toujours cette richesse entre 4500 et 5500,je pense que c'est un accord qui se situe là, un résonance, et qui remplit mieux, donc plus d'air ? Regarding the rich spot, would it be a resonance that helps to feed the engine better?

 

=> The lean spot is when I hammer the gas pedal, it is fuel starvation from carbs not able to inject mixture fast enough

 

=> The rich spot; you might be right it could be related to resonance. What to do then? Increase the lengh of the intake manifold? change the air horns? change the chokes? We might have to live with it as Mark (and I, now) said.

[akumazeto]

I am running a holley blue fuel pump. I set the PSI level at 3 and its running good. I tried the 3 1/2 and I'm dumping alittle fuel so when I set it at 3 its running perfect. I have tripple webers 151 and all I have is

180 air

f11 tubes

130 main

50f9 idles

needles are 2.0

55 pump valve

28 chokes.

When I'm driving from 1st and second it stumbles cause I think I need to go bigger chokes. As soon as I can I'll try the 32 chokes and see how that pans out.

I'm not an expert but all I can say is its also the elevation people live in. Cant realy determine what people use due to this factor. some go bigger some smaller.

I studied and studied alot on this and it draws down to where people live.

Like Lazeum said some flat spots you might just ahve to live with it.

All things people do to tune it up gets really expensive!!! but its how much you live for the car.

Who knows really? everyone jsut needs to test, try and do all they can.

I might just try 200 air just for kicks. The only thing I can say is its never going to be perfect so just live with some issues.

[yetterben]

all 19 pages are great. i just picked up a set of 40's for my l28 240. hope it goes well.

[Lazeum]

Good luck with the tune, bring us back some feedback

 

Since my last post, I haven't done too much to my car (home improvement project on going taking precedence )

I've just spotted a Weber carbs retailler with jets available 3 miles away from home I have to visit them!

 

Otherwise, I've ordered a new head to Braap (P79) with port/polish/unshrouding work + a new rebello cam. I might be soon the time to maximize ventiru/choke size and especially to get timing the way it should!

 

I'm wondering also if the lean spot at 4.5k rpm is not the results of acoustic resonance into our intake (Helmholtz principle?) To check that we might have to decrease or increase length on the runners, not sure I want to proceed in this direction...