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Weber 38 Tuning on My Jeep -

7K views 67 replies 7 participants last post by  dirtdudeaz 
#1 ·
Starting a new thread to get out of the longer "Weber Setup and Tuning" one. Here's my last post to describe what I have done recently.




Originally Posted by dirtdudeaz

Ok I'm back!

I was able to get a wideband installed and have been driving around a couple times now with it watching what the gauge does in different driving conditions. Jetting conditions are as follows btw (145 main, F7 Etube, 190 airs, and 55 idles). If I remember, I was about 1ish turns out on the mixture screws, and idle is set to about 650-700, and I have about 930 miles on the new engine build. For the most part, I am not smoking once warm, so the rings could still be settling in.

When I get the jeep to lean best idle per the weber instructions, I am showing a bit rich. When I shoot for 13.9-14.1 on the AFR, it seems to sound a little rough (slight "misfire" sound). One thing I noticed is when I take out the PCV, I am going lean, and I can see the crank case fumes (about a difference of 1-2). I am assuming I should set the lean best idle and 14.1 with the PCV sucking in the fumes? The other thing I noticed is I seem to be rich from off idle to about 1800-2000 (is this close to the transition?). When I am cruising under 2000 I seem to go rich (10-11), and then once I get above 2000, with increasing speed and RPM I go pretty lean (going as high as 17-18); This is also true for full throttle.

What I am thinking is I need to possibly increase my air bleeds to the next size or two up (195 or 200), and then possibly another step on the mains as well to a 150. Does this sound about right?




"Consider starting a new thread. This one is so long in the tooth, I think a lot of guys ignore it.

Now to your questions. Yes, you should have the PCV and all other vac systems hooked up when you tune the carb.

I would drop your idle jets to 50, or possibly to 45. You should be able to achieve a 14-ish A/F ratio with the mix screws around 2 turns out.

Once you get the idle circuit dialed in, we can move on to the main circuit.

Matt "
 
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#2 ·
So I have some 50's that I had in it, and I was more than the recommended 1.5 turns out. I also had a pair of 50's that I tried drilling out to 60 (close to 59 or 61's if I remember), and I was less than a turn out on the needles.


If my air bleeds are too small, wouldn't this affect my off-idle acceleration and cruise up to the transition into the other circuits?

I agree on the advice of not messing with the mains until I get the idle and off-idle stuff figured out. The circuit curves appear to be 75% affected by the idle and air corrector jets.
 
#4 ·
If my air bleeds are too small, wouldn't this affect my off-idle acceleration and cruise up to the transition into the other circuits?
190 air correctors should be more than big enough for your elevation. I believe the factory ACs are 185s, and they are calibrated for a sea-level to 2000 feet application.

Factory idle set size is 50, which also should be about right for your rig. Remember, any mix screw setting between 1-1/2 and 2-1/2 is acceptable.

Idle speed screw should be no more than about 1/2 turn in.

Matt
 
#3 ·
Per the Weber tuning instructions....

If the mixture screw is more than 2 1/2 turns out turns then the Idle jet is too lean (too Small). When the mixture screw is less than 11/2 then the Idle jet is too rich (too large).
Where did your mix screw end up when you achieved the 14 A/F ratio?

Matt
 
#5 ·
Per the Weber tuning instructions....

Where did your mix screw end up when you achieved the 14 A/F ratio?

Matt
Interesting! I was using the Redline instructions
http://www.redlineweber.com/html/Tech/38_dgas_tunning.htm

I think I am about 1 turn on either of them plus/minus 1/4-1/2 turn; I say "I think" because that's the last number I remember in all this messing around I have been doing.

190 air correctors should be more than big enough for your elevation. I believe the factory ACs are 185s, and they are calibrated for a sea-level to 2000 feet application.

Factory idle set size is 50, which also should be about right for your rig. Remember, any mix screw setting between 1-1/2 and 2-1/2 is acceptable.

Idle speed screw should be no more than about 1/2 turn in.

Matt
It wouldn't hurt me to throw the 50's back in and try setting it all back up with those and confirm mixture screw turns.

Speed screw is definitely not in a whole lot. I also took the air filter off and confirmed I am not dripping any fuel into the chamber from the secondary because of a high idle or too many turns on the speed screw.

Also, a side note, I am running a stock 1-in 2 out fuel filter with the center going to the carb and the side outlet at the 12 O'clock position going to the return line. I also have the Viton needle set, and the float as been set to 18mm (bottom of lobe). Engine timing has been set to 9(ish)-degrees (somewhere in between the 8-10 marks on the cover).
 
#7 ·
The Weber 32/36 DGEV settings are the speed screw 1 1/2 turns in MAXIMUM, with the mixture screws out at 2 turns for a 6 cyl (1 1/2 for a 4 cyl)


The Weber 38 DGES setting are the speed screw 1/2 turn in MAXIMUM, with the mixtures screws out around 1 1/2 turns.


I am looking forward to your final settings at 14:1 on the A/F meter.


UPTILLNOW
 
#10 ·
I would go the opposite direction with the air correctors; smaller. I did a lot of testing and went the larger this and larger that deal and you just end up with a fuel mixture that burps out like a perking coffee pot rather than an well-atomized fuel stream.

I would try 145 mains and 170 air correctors along with the 50 idle jets. As long as the mixture screws don't fall out, you'll be fine. Mine were just over 2 turns out.

Hope it helps.


Shawn
 
#11 ·
I would go the opposite direction with the air correctors; smaller. I did a lot of testing and went the larger this and larger that deal and you just end up with a fuel mixture that burps out like a perking coffee pot rather than an well-atomized fuel stream.

I would try 145 mains and 170 air correctors along with the 50 idle jets. As long as the mixture screws don't fall out, you'll be fine. Mine were just over 2 turns out.

Hope it helps.

Shawn
I was just wondering this while looking at the air/control jetting curves for the weber. It appears the air correctors are a big part of the circuits, but my question is, are the ones you can change in the Weber's the main air correctors or the idle air correctors? I was thinking originally they were idle, but now that I have looked at pictures more, it looks like they are the main. For grins before I read this, I swapped in the 170's that came with the carb and test drove.

So for this last round of test drive conditions I had 170's AC's, F7 E tubes, 50 idles, and 145 mains. Idle AFR readings set with engine warmed up (180/190-210) to 650/700 rpms.

At idle where it was, I am at 1 turn on each screw (1 full 360* turn) to get to 13.9-14.1 on the AFR.

Immediately off-idle throttle input and cruising, I am running 12.9-13.7. If I get a little more throttle input I can get mid 13's and up to 13.9. Zero throttle to 1/2 throttle I can stay around high 13's and low 14's. Anything above 1/2 throttle I stay low 14's until I hit 3/4 to full throttle. Once I go 3/4-full throttle I see the gauge go to about 15.5-17.

When I am warm (over 185) I will get some spark knock or pinging like I am lugging the engine at the 3/4-full throttle.

RPM's don't seem to affect the numbers as much as how much throttle I am putting in.

So with this, it seems the lower idle jet helped, although maybe I could drop down another size? Maybe up on the mains a size as well?
 
#12 ·
That lean hole you're seeing is why I drilled out and replaced my idle air correctors with a smaller one (can't remember which one- should be in the first 20 pages of the Weber thread).

That will help keep the idle jets from leaning out too quickly up top before the mains activate. I still had a bit of a hole so my next test was going to be F5 emulsion tubes.

Too bad they don't have various accelerator pump cams like Holleys do.


Shawn
 
#14 ·
I think you're fine on jets at the moment. I'd like to see you close the gap on that lean hole and that'll likely require an extension of the usable idle/low-speed circuit and reducing the draw required to pull the mains in.

That will most-likely be done with your idle air correctors and emulsion tubes. My F7s cleared most of that up so I'm a little miffed at why yours is still that bad.

What does it do at WOT?


Shawn
 
#15 ·
So 3/4 (ish maybe a little less like just above half) to WOT I immediately go lean. About 15-18 consistently. I can accelerate at less than the 3/4 (or 1/2) throttle and I stay pretty close to ideal

It's concerning because I am chasing that spark knock/detonation at WOT and it acts like I am lugging, even if I stretch the gears out and shift at 3200-4000 from 2nd to 3rd and 3rd to 4th. As soon as I hit 3rd to 4th, it really gets bad. Ive been using 92 octane, and just replaced plugs gapped to .045; the old ones looked a little lean and coated in white (probably from some of the blowby as I have been breaking everything in). It's more noticeable when I get to the high end of my running temp range. If I am driving normal I stay around 190; if not and/or there's a bunch of stop and go or idling, I will run up to 210 and stay there until I get moving fast again. On the stock gauge, it's always in the green, but the difference of being in the 3/4 area to the edge of the high end of the green.
 
#16 ·
That doesn't sound right at all. Now I'm thinking something's up with your power valve, blocked jets, terribly low float level... something.

That's just crazy lean for the jet/e-tube combo you have. Maybe we can prod uptillnow to chime in. I still have my fire suit ;)


Shawn
 
#18 ·
That doesn't sound right at all. Now I'm thinking something's up with your power valve, blocked jets, terribly low float level... something.

That's just crazy lean for the jet/e-tube combo you have. Maybe we can prod uptillnow to chime in. I still have my fire suit ;)

Shawn
Ya I'm curious too. I did give a good spray of carb spray into the various passages when I had it all apart changing the jets to make sure passages were all clear. I also checked my float level to 18mm from cover face to bottom edge of lobe; I also am getting the 2mm or whatever of needle travel

Dirt,

Forgive me if you covered this, but have you ever checked the fuel pressure, or for leaks in the fuel lines, or are you using a FPR?

Recently, I had a hose clamp become loose at the inlet side of the fuel pump. In this condition, my fuel pressure would drop to around 2 psi, and would fluctuate, when the engine got warm. in this condition, the engine ran normally up to about 1/2 throttle. AFRs at idle and light throttle cruise were the same as always, but as soon I put a load on it beyond half throttle, it would stumble badly and the AFRs would go extremely lean. I tightened the clamp, and the problem went away. Sometimes it's the easy stuff.

And I agree with Shawn, I'd double check your float settings.

Matt
No FPR, but am using the Viton needle as well as the stock style 1in-2out filter (which using both those I understood a regulator would not be needed). I have one mounted on the fender, and was using it, but it didn't seem to change anything whether it was being used or not.

One thing I may check is the fuel pump and fuel lines up to the filter. I have an extra new pump, so it may be worth slapping it on.

The clamps I have are all tight as I just changed the filter.

One thing I may try is disconnect or clamp the tubes to the evap canister. I had installed a new xj style and believe the lines are correctly routed (per the thread that showed it with pictures).
 
#17 ·
Dirt,

Forgive me if you covered this, but have you ever checked the fuel pressure, or for leaks in the fuel lines, or are you using a FPR?

Recently, I had a hose clamp become loose at the inlet side of the fuel pump. In this condition, my fuel pressure would drop to around 2 psi, and would fluctuate, when the engine got warm. in this condition, the engine ran normally up to about 1/2 throttle. AFRs at idle and light throttle cruise were the same as always, but as soon I put a load on it beyond half throttle, it would stumble badly and the AFRs would go extremely lean. I tightened the clamp, and the problem went away. Sometimes it's the easy stuff.

And I agree with Shawn, I'd double check your float settings.

Matt
 
#20 ·
So, I take that as a "no" on checking fuel pressure and/or fuel line leaks. It may be worth doing before you go to the trouble of replacing the pump. You might get lucky, like I did.

Matt
Leaks yes, pressure not necessarily. I suppose I could hook the regulator back up (has the pressure gauge mounted on it) and open it all the way, and watch it.

I am not dripping fuel anywhere, and clamps are all tight from the filter to the carb.

Just a somewhat related question, what's the stock line size from the pump to the filter? And any idea on the flare type/number?
 
#21 ·
There are a lot of potential leak points in the system beyond those from the filter to the carb. A leak in the fuel lines between the tank and pump won't necessarily drip fuel, since they are under suction. So don't think a lack of visible fuel dripping is a sign of no leaks.

IIRC, the supply lines on a 258 are 3/8" and the return are 5/16". Not sure what you mean by "flare".

Matt
 
#22 ·
on the fuel outlet, it is flared where the hard line connects to it. But if it's similar to brake line sizes, then the flare is standard for whatever diameter the tubing size is? I suppose I can take the extra pump into the auto parts store and see if they have some universal pieces of 3/8" tubing already flared and see how it fit against the pump.
 
#24 ·
If you're in a rush, or just impatient like me, you should be able to make your own out of brake line. I've been running my Scout that way for years because parts for that are hard to come by.

I believe the fitting is 1/2"-20. I'm not sure of the flare type but you should be able to match it to something.
 
#27 ·
OK! Here's what I've done and what I've observed.....

  • I dropped the tank and tightened the clamps
  • I made sure all clamps from the tank to the pump were tight
  • I changed the pump to carb hard line using a 5/16" brake line with flare on it
  • Tightened all clamps from that hard line to the carb
  • Connected the regulator that has my gauge on it and opened it up all the way

So I started it and used a soap solution and sprayed it all over the fuel lines to observe any bubbles or air movement; didn't see any.

Upon startup, I was in the choke mode (1000-1300 rpm) and was getting 4psi. When it was warm and I took it off choke, the pressure went to 3-3.5 psi. When I steadily increased throttle, the needle climbs to 3.5-4, and then a little more drops it to 2, and then full throttle lets it go back to 2.5 and then 3.0 psi.

The other important thing I noticed, was when I blip the throttle a few times and then go to heavy throttle or WOT, the accelerator pump armature is dripping gas. It's not a stream, but it is 3-4 big drops. I checked the cover, and the screws are tight.

So....

1st thing is the fuel leaking. I suppose if it's coming out of the arm, the AP membrane/gasket needs to be replaced, and I should check the cover to make sure it's flat? Could the gas be coming from anywhere else? If it is leaking, could these few drops be enough to starve fuel and cause that lean condition?

2nd thing is fuel pressure. Shouldn't I be close to 6 or 7? I feel like it was at some point because it was a new pump. If I tightened all my clamps, could this mean it is the pump? I have that extra one and can change it?
 
#28 ·
2nd thing is fuel pressure. Shouldn't I be close to 6 or 7? I feel like it was at some point because it was a new pump. If I tightened all my clamps, could this mean it is the pump? I have that extra one and can change it?
With return line, 4-5 psi is normal. It should be 7-8 psi without return line.

Matt
 
#30 ·
Replaced the fuel pump last night, so I will fire up today.

I ran it the other day with the return line clamped and noticed the fuel pressure was at 5 most the time, and then when everything was warmed up, it went down to 3.5-4psi. I think this is partly due to the higher RPM's when the choke is on and the engine is warming up, but we'll see if the new pump changes anything.

After that test and results, I will check the float
 
#31 ·
I'm looking at my float now.... I understand to hold the cover so that the pivot is on top and measure with the gasket on.

I need some help clarifying again the 18mm and 2mm movement.

Is the 18mm to the float edge closer to the pivot or lower edge further away from the pivot? Should the needle be closed? When my needle is closed and I measure to that top edge to 18mm, my float is hitting the top of the power valve when it drops. So much so that it's not even letting the needle drop until it hits the adjustment stop


I can't rotate the picture from the phone, but it's vertical like the example above
 

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#34 ·
So I got the float adjusted and drove it to work today.

What I noticed:
-It's still lean when I give it moderate to full throttle (15-17 on the AFR).
-when I am sitting still and stab the throttle or try to recreate the lean condition not moving, I can't do it; it only happens under load.
-When I am moving, in gear, let off the throttle and coast I notice it goes lean to 15-16, and then just the smallest throttle input brings it to high 13's or 12's.
-It seems like I am very close to being as good as I can get, but it's just the moderate to full throttle where it falls apart.


My question now is what's the next thing to replace? Power valve; Main jets?
 
#35 ·
One thing I really wish Weber's had was various accelerator pump discharge rate options like the various pump cam options on a Holley. In my opinion, they discharge too much early on and leave very little from a half-throttle stab.

It's also possible that your power valve is screwed.

Maybe uptillnow can give you some options to deal with that or another opinion.


Shawn
 
#36 ·
One thing I really wish Weber's had was various accelerator pump discharge rate options like the various pump cam options on a Holley. In my opinion, they discharge too much early on and leave very little from a half-throttle stab.

It's also possible that your power valve is screwed.

Maybe uptillnow can give you some options to deal with that or another opinion.

Shawn
I did find that interesting too that they aren't adjustable for either timing or volume of discharge.

The power valve or diaphgragm could be damaged; it's the only thing left I could think of from all the reading I have been doing. I should have looked at it when I did the float adjustment....
 
#38 ·
Dirt,

Did the new pump cure the inadequate and variable fuel pressure issues you were seeing?

Matt
It seemed to help a little, but not completely. It looks like it helped with the variable part, but I am at 3-3.5 psi while running, and it never dips below 2 at all. For grins I clamped the return line to see what it would do, and I am getting about .5-1 psi improvement on pressure, and the line remains pressurized after I turn the engine off (as you would expect).

The only thing I can think of for this "issue" is to replace fuel lines, or cut the ends off and reattach one by one again and check after each one if there is improvement. All the hardlines along the frame rails were new, and at this point I have replaced all the soft lines as well. Every clamp has been checked and tightened more.

I am also wondering if the hardline that comes off the pump needs to be flared at all at the filter side where it connects with the short piece of flex line. otherwise, all the other joints have flares, so maybe it's required.

Could I still be sucking air in on the pressure side of the pump, or is it only the suction side?
 
#39 ·
Hmm, it still sounds like inadequate fuel pressure to me. Mine reads 5 psi with the return and 7-8 psi with the return pinched.

I can tell you that a loose hose clamp at the inlet side of my fuel pump caused the same symptoms you are experiencing...variable fuel pressure depending on how warm the engine was, and a bad lean stumble at 3/4 to WOT under load.

Matt
 
#40 ·
Hmm, it still sounds like inadequate fuel pressure to me. Mine reads 5 psi with the return and 7-8 psi with the return pinched.

I can tell you that a loose hose clamp at the inlet side of my fuel pump caused the same symptoms you are experiencing...variable fuel pressure depending on how warm the engine was, and a bad lean stumble at 3/4 to WOT under load.

Matt
So it sounds like I need to keep looking on the inlet side for leaks. I guess the new hard fuel line could fail too...

I called Redline and they suggested a smaller air corrector and/or bigger main; and probably not a power valve with the symptoms I am having. So, I may hold off with any of the new parts though until the fuel pressure gets figure out. I imagine I could fix my issues with bigger mains or smaller airs, but then I would be masking the real root cause of my problem if it is in fact an air leak in the suction side of the pump.

I have tightened all the clamps, replaced soft lines, and replaced the pump, so maybe now I'll pull the lines off and disconnect at the sender and pump ends, and then pressurize while holding it all under water to look for air bubbles. If I see some, the line/clamp will get replaced/tightened, and if I don't see any, then maybe I look at the sender? I'm assuming a leak on the pressure side of the pump would show as a leak.
 
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