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

[T-Bone028]

lazeum, I had a similar issue when I went from 33's to 36 mm main venturis.  To get good throttle response, I had to go up to a 55F9 idle, but I was running rich at cruising speed.  Switched to a 50F9, and my cruising AFR was acceptable (in the 13's) but my transition to WOT had a huge stumble.  

 

I ended up changing my exhaust bleed valve from a 50 to a "0" exhaust bleed to get a longer pump shot and help bridge the transition from idle to main circuit.  It helped dramatically.  Currently, my pump jet is a 40, but I think a 50 or 55 would serve me better to get a bigger pump shot.

 

The pump jet circuit exhaust bleed valves are only like $5 from piercemanifolds, and you only need 3 of them!  If it helps, then you can consider changing pump jets accordingly.  Definitely worth a "shot" (pardon the pun).  

[Lazeum]

This is what I have on my setup also, some bleed valve shut with solder. car is very driveable with no majot stumble issue.

 

Since my last message some hours ago, I've been working on my Z (not the s130 from my previous message - if you still follow ) to swap 32mm chokes with 34mm units.

I did not have to change anything at all on idle jets to make the car runs perfect.

So I came to the conclusion that choke size should not make any change on idle jets. Something is going on my friend's car we need to find out. I think we need to get to the basics (fuel level, jet inspection air leak, etc.)

 

Regarding my Z:

Low rpm stumble is more noticeable now. With 32's & an agressive way of driving (WOT after each corner :/ ), I could not get any stumble. With 34's, if I'm a little bit too low, like 2500rpm in 3rd gear, I've got some.

I'll try to play with timing and see if that could help, timing map is conservative around that engine state.

 

I've recorded some AFR logs, I still have the AFR going lean as it was with 32mm so choke size did not help...

I'll try next emulation tube modification and see if that would solve my problem then.

 

Anyway, car with 34mm is really really nice to drive. AFR are a little rich so lean spot is at the leanest around 13.5:1 while richest point is at 11.5:1.

Cruising AFR are between 13.5:1 & 15:1, O2 sensor came up clean after a 45 minutes session.

 

If weather is ok, I'll play around with parts tomorrow.

Edited October 19, 2013 by Lazeum

[AZGhost623]

Whats your pump jet size? When you mash the pedal, the pump jet kicks on to give an extra burst of fuel, it may not be doing enough with the bigger choke. The pump jet is specifically related to a very sudden change in vacuum. You may need to look at this part in helping your transition, but other than that it sounds like your on the right track. I run a 36 choke on my DCOE 152, and I have very large idles to help in my transition, I run a 70F9 in addition to a larger pump jet (55)

Edited October 19, 2013 by AZGhost623

[Lazeum]

70f9 is huge!!!

How is your fuel economy with such idle jets?

 

I'm running 45 accel jet. I've also got 40 in my jet box. Looking at my AFR shows that, lean spot starts by being too rich & not long enough so trying again 40 now might make sense & bring good results. I'll see that tomorrow. My o'ring for accel pump jet are pretty bad, that might not help either even if I did not see any leakage from the outside.

[madkaw]

It's funny I just happen to pop on this page to see you guys are discussing my same issue on the Mikunis!!

Transition- transition- transition

I have exhausted all angles to fix my lean issue in the 3500rpm range- sometimes a bit higher. It is only a problem during moderate acc under load. I have been up and down the scale of main air and main jet. I have increased float levels and have changed acc pumps and settings- nothing seems to eliminate this. I can watch my wideband gauge as AFRS climb 16+ or more during this lean- stumble area.

 

The only thing I haven't tried is changing emulsion tubes, but not many options for that. So I am intrigued about this conversation of plugging some of the holes in the bleed pipe. Not sure if Webers are the same, but probably similar enough.

I was thinking of modifying the bleed pipe, but wasn't sure of the theory of how it works. So shutting off some of the holes at the top of the bleed pipe should help draw more fuel in sooner???

 

I couldn't be happier with the way the carbs run everywhere else . Cruise is 14.5-15 and WOT is 13ish

Idle I set at 13ish because the car starts best there.

[AZGhost623]

70f9 is huge!!!

How is your fuel economy with such idle jets?

 

 

 

95% of the time you drive on the idles, even when your on the highway cruising, your still on the idle jets. The only time you get onto the main jets is when your giving it some heavy pedal. Sudden WOT the pump jet also plays a role by doing a bit of an extra squirt of gas. This is covered in some early posts in this thread too. It took a long time of testing to find out where the best transition was going from idles to mains. Make sure to document everything you change/try along the way.. Every engine is setup differently and this is what my engine liked. The other thing is that the idle jets are somewhat tunable too, since you have the screw that directly affects the idle which I found to be helpful. From previous posts anything more than a 1/4 turn and your idles are too small. Etubes also play a very important role in how your main jets come on. In my opinion your etube should be either a F11 or F3 (almost identical tubes, with the exception of F3's are .5mm smaller diameter, all holes are same diameter and in same spots)

 

As far as gas milage goes... as long as I am not heavy footed its not bad

[Leon]

95% of the time you drive on the idles, even when your on the highway cruising, your still on the idle jets. The only time you get onto the main jets is when your giving it some heavy pedal. Sudden WOT the pump jet also plays a role by doing a bit of an extra squirt of gas. This is covered in some early posts in this thread too. It took a long time of testing to find out where the best transition was going from idles to mains. Make sure to document everything you change/try along the way.. Every engine is setup differently and this is what my engine liked. The other thing is that the idle jets are somewhat tunable too, since you have the screw that directly affects the idle which I found to be helpful. From previous posts anything more than a 1/4 turn and your idles are too small. Etubes also play a very important role in how your main jets come on. In my opinion your etube should be either a F11 or F3 (almost identical tubes, with the exception of F3's are .5mm smaller diameter, all holes are same diameter and in same spots)

 

As far as gas milage goes... as long as I am not heavy footed its not bad

 

Franckly (LOL), F11 e-tubes are just about the worst in DCOE applications. They have bleed holes ABOVE the fuel level, which only serves to delay tip-in (read: flat spot). This is why you're running such a fat idle. Keith documented this on sidedraft central, the F7 e-tube is the one to go for if you're staying with Weber e-tubes. The one caveat is that it won't deliver great mileage because it's impedance is too low (small OD).

 

Most (if not all) of the Weber e-tubes were designed for downdraft applications and work really poorly in the sidedrafts. This is because the height of the auxiliary venturi passageway is lower on sidedrafts.

 

Transition has everything to do with the e-tube, this is what most don't realize. The e-tube/air jet combo controls WHEN the main circuit is able to kick in, and how strong that kick is. Most people just use a fat ass idle jet and/or accel pump shot to cover that issue up. This obviously causes problems elsewhere.

Again, I recommend people register with the Sidedraft Central Yahoo Group, if not just for the sake of taking a look in the Files section. In there you'll find Keith's White Paper on tuning these carbs. While some of the info can use some updating, the majority of it is very much true. It's a thoroughly scientific way of setting up the carbs, skipping the typical guess-and-check and he-said, she-said methods.

[Lazeum]

AZGhost623, I know how DCOE works sort of... I'm missing some details here & there such as why AFR curve shapes are very different with different heads. With N42 head, AFR were almost even accross the entire rpm range, with p79, it is a totally different animal, why is the question I'm wondering about.

As far as time I spend on idles, I can guarantee you that I'm spending less time that this but don't tell the police

 

With full programmable DIS ignition with load control, you decrease a lot your gas mileage too with proper timing. Some downfalls coming from carbs could be outweighed with proper ignition now versus old dizzy setup. It helps to burn the mixture when it needs to be

 

Last comment, I'm running F11 so it should be quite acceptable but it is not (but close, once more car is very nice to drive) Somehow Leon & Keith might be right but why was it working before and not now anymore is over my head for now.

 

So I'm trying to see what could have gone wrong in my setup to give me unnacceptable/unsteady AFR.

- etube could be tweaked somehow. I can try to plug some holes and see how it goes. I can try to plug top holes to affect low end which would require to get richer main jets (which I've got, up to 145)

- Intake manifold has been ported a little, I left a step between head and manifold (manifold smaller than intake head port) to keep some anti-reversion feature for driveablity. Could that cause some turbulence at high speed (=high rpm) lowering flow (= less fuel mixture going to the engine, hence the lean spot)

- I strongly believe fuel supply is out of the picture and works quite well (pressure ok, lean spot at every gear, new filters, new hoses, fuel tank fully restored - cut opened, sanded, welded back & seal with resin)

- Carbs still to small, venturi change was not big enough?

 

Last question, how would you plug holes on etube? Some solder (how to remove it afterwards?), some wooden toothpicks?

My friend with his 280zx is using F7 etube, I should try to borrow them and make some trials with them.

[AZGhost623]

I tried f-7's, were great up top but I had to run 205main and 180 a/c to get 13:1 afr's at WOT and it was 10:5 at cruise causing rich stumble on cruise. A guy in my neighborhood who drives a 911 suggested a F3's which is what I worked around, and it seems to work great for mysetup. I didnt play with F7's for very long tho... I later found out from TJ, F11's were recommended by Rebello which is what he is running. When comparing the two thats when I found out they are near identical except for the .5 smaller diameter. F11 does seem to be the goto tube if you look at the majority on here with their setup.

[Lazeum]

For information I've overlaid AFR curves with 32 & 34mm chokes. Lean AFR at high rpm did not change at all; neither "intensity" nor within rpm range.

It means to me this issue is not air flow dependent since I would have expected something to change with different choke size. Even if 34mm chokes are still too small, it would have made the change less "dramatic" but it isn't.

 

Regarding white pages from Sidedrafts central, I found this:

Let me emphasize: The target AFR is adjusted via the float bowl fuel level and the main jet hole size and not by diluting the vacuum signal by installing an oversized air corrector jet. This is why the emulsion tube only impacts the AFR at partial throttle and has little affect at WOT. At WOT and high air induction velocity there is enough vacuum signal strength to pull even unmixed raw liquid fuel into the engine.

 

I have the feeling Keith (Sidedrafts central Admin for those who did not subscribe - yet!) has changed his mind about it with Gravity etube. However with regular Weber etube it seems etube are not the key to my lean issue at WOT.

 

I've always considered air jets as tuning tool for AFR in high rpm which isn't what Keith thinks about them:

 The size of the air corrector jet is crucial for two reasons.

- First, it determines the onset of flow from the main jet circuit in conjunction with the chosen auxiliary venturi and main choke. (...)

- Second, it introduces an air leak and reduces by diluting the highest attainable vacuum signal from the auxiliary venturi.

 

I've experienced some stumbles at WOT at 3000rpm in 4th gear (very minor), trying different air jets might be something to do. I'm using 165 jets, I've got 180 & 195 in my jet box. What would happen if my air jet is way too small resulting in maximizing out the vacuum signal in the aux venturi?

I would have expected AFR to be way too rich at high rpm but I might be thinking the wrong way...

Edited October 20, 2013 by Lazeum

[AZGhost623]

I've always considered air jets as tuning tool for AFR in high rpm 

 

Thats exactly how I have always looked at it, and used to my advantage on tuning my setup, not just at AFR for high rpm, but in general on the main jet itself.

 

After some serious head work today on fixing some spring problems, my AFR's are now slightly off and Ill need to play with it a bit. But while I had my sparkplugs out, for the first time in months, they were all perfect a very nice light tan color on the insulator!

After the fix on my springs (new Schneider high lift double springs, retainers, and keepers), my cruise home on freeway at 3500 rpm/80mph Im now low to mid 14's AFR now. Previously, as I was dead center in 13's before the fix. My WOT is now way to rich into the low 12's, and I need to use an air corrector, and it will fix that right up IMO. I guess what Im trying to say is that even the smallest change, changes a lot of other things. 

 

 

 

I have the feeling Keith (Sidedrafts central Admin for those who did not subscribe - yet!) has changed his mind about it with Gravity etube.

 

Wait what? Can you elaborate on this a bit on why he feels all his work has him now second guessing?

Edited October 21, 2013 by AZGhost623

[madkaw]

Franckly (LOL), F11 e-tubes are just about the worst in DCOE applications. They have bleed holes ABOVE the fuel level, which only serves to delay tip-in (read: flat spot). This is why you're running such a fat idle. Keith documented this on sidedraft central, the F7 e-tube is the one to go for if you're staying with Weber e-tubes. The one caveat is that it won't deliver great mileage because it's impedance is too low (small OD).

 

Most (if not all) of the Weber e-tubes were designed for downdraft applications and work really poorly in the sidedrafts. This is because the height of the auxiliary venturi passageway is lower on sidedrafts.

 

Transition has everything to do with the e-tube, this is what most don't realize. The e-tube/air jet combo controls WHEN the main circuit is able to kick in, and how strong that kick is. Most people just use a fat ass idle jet and/or accel pump shot to cover that issue up. This obviously causes problems elsewhere.

Again, I recommend people register with the Sidedraft Central Yahoo Group, if not just for the sake of taking a look in the Files section. In there you'll find Keith's White Paper on tuning these carbs. While some of the info can use some updating, the majority of it is very much true. It's a thoroughly scientific way of setting up the carbs, skipping the typical guess-and-check and he-said, she-said methods.

 

leon,

 

you seem to be saying here what I have seen myself with the Mikuni's.I've been trying fix a problem with transition by oversizing all around the issue.

 

I tried many times to register on the Yahoo group, but never had any luck. I finally just got frustrated and gave up, but it sounds like some good info on there.

 

I would also say cam selection and engine purpose have a lot to do with this. I almost think that the more radical the cam, the easier it would be to tune these 'racing carb' set-ups. My stage 2 cam puts big demands in the mid range which causes a big draw in this transition area, making it tought to tune out. Developing a tune with this carbs for everyday driving situations is a challenge. 

[Leon]

leon,

 

you seem to be saying here what I have seen myself with the Mikuni's.I've been trying fix a problem with transition by oversizing all around the issue.

 

I tried many times to register on the Yahoo group, but never had any luck. I finally just got frustrated and gave up, but it sounds like some good info on there.

 

I would also say cam selection and engine purpose have a lot to do with this. I almost think that the more radical the cam, the easier it would be to tune these 'racing carb' set-ups. My stage 2 cam puts big demands in the mid range which causes a big draw in this transition area, making it tought to tune out. Developing a tune with this carbs for everyday driving situations is a challenge. 

 

Hell yeah it is! Although I would argue that the less radical the cam, the easier to tune. Long duration cams cause a lot of reversion in the low and mid range (if radical enough) which requires more fuel in order to have enough fresh mixture within the cylinder. My stock-cammed L24 took well to leaning out my idles and progression circuit.

 

I know that Keith has done some work with the Mikuni PHH, but unsure of how far that was taken. Strange that you had issues joining.

[Lazeum]

Wait what? Can you elaborate on this a bit on why he feels all his work has him now second guessing?

I have the feeling gravity etube are made to tune AFR right at WOT also. 

I believe he's trying to get rock steady AFR with gravity etube while he's asjusting AFR level at WOT with wet jets. Am I missing something here?

Edited October 21, 2013 by Lazeum

[bradyzq]

Lazeum,

 

I have a theory that if you can't feel AFRs that go as lean as into the low 20's at WOT high RPM, then, well, they aren't really going that lean. Your car should hardly even run at those AFRs, let alone pull hard!

 

Where is your wideband located?

If it's in the tailpipe for testing, do you have a dual outlet? I've seen one pipe on a dual tip outlet read free air while the other one right next to it read the correct afr. And you couldn't tell from puting your hand in front of each outlet. They felt like they had the same flow!

Might there be an exhaust leak ahead of the sensor that somehow manifests itself at that point due to some wacky harmonics?

Or something of the sort.....

[Lazeum]

That's a very valid point about my exhaust.

Such observation on AFR has been made roughly when I've redone my exhaust.

I've kept the msa 6-2-1 exhaust manifold, the dynamax muffler but I've redone the pipes + an intermediate resonator. We've made sure with my friend to avoid any leak but we might have missed one...

 

To check AFR, I've got an Innovate Mototorsports exhaust clamp at exhaust tip (single exit)

Edited October 22, 2013 by Lazeum

[steve260z]

Question, I'm currently running a 280zx distributor on my stroker.

I've got the timing set at around 34 all in. (no vacuum)

 

The below link has an excel spread sheet at the bottom of the 1st post.

Most of the distributors would appear to work fine. 17 degree centrifugal and set the initial timing

at 17 degrees and there you go. 34 degrees.

 

Am I missing anything here by assuming any of the 17 degree units would work fine?

The column titled "static" simply referrers to the factory spec'd timing for that particular car, correct? Does not have anything to do with that particular distributor???

 

 

http://www.classiczcars.com/forums/electrical-s30/34192-280zx-distributor-advance-curve-reference.html

Edited October 26, 2013 by steve260z

[Lazeum]

I don't think you're missing anything. Not sure though to understand your concern.

Anyway, if I would have built a stroker with the budget involved, I would get an ignition up to the task to deliver most of the torque/power of the combo.

 

To go the simple route, I would lock the centrifugal advance in the dizzy & get an CDI box with timing management such as MSD AL2-programmable (if it is still available since MSD is in chapter 11)

Once more (I'm alway repeating  ), I've ditched the dizzy and went with Megajolt/EDIS ignition, difference is night & day. I love my ignition setup but it cost more (~$800 total)

Edited October 26, 2013 by Lazeum

[steve260z]

Really, night and day??? I'll check that out..

 

But, in reference to my original post: Is the "static" timing built into the distributor?

If my distributor has 17 degrees centrifugal and I'm running 17 at idle is that 34 degrees all in

OR

should the calculation also include 10 degree "initial" from the spreadsheet column 1?

If so I'd be running 44 degrees.....

 

Does that help?

[T-Bone028]

Steve, I think another method could be to buy some timing tape or make some additional markings, and get a friend to help measure timing at all in. Set the timing for max, and let idle timing fall wherever it may be.