Jetting a Weber 38 on a 2.0/2.2

[thescifiguy]

I haven't found a thread that specifically addresses the jetting of my carb on my present engine setup: Weber 38 on a factory 2.0
The only other alterations are:
Elec. ignition and electric fuel pump with regulator
Sprint manifold and a somewhat less restricting exhaust than stock.

I have incredibly strong and even torque throughout all speed ranges, but I have the chronic Opel stall tendency when I accelerate from a stop while idling and I seem to be running kinda rich(a fair amount of gas smell to the exhaust and not very good gas mileage). At Carlisle, everyone remarked about how smooth the engine ran and I keep the idle at about 1000-1100rpm. An old post by Gary mentions a RallyBob suggested change to F-66 emulsion tubes to fix the hesitation/stall problem. Here's 4 questions:

1) What do you guys suggest for jetting of this engine(for economical daily driving)?

2) F-66 tubes to fix the hesitation/stall problem?

3) If I put a manifold with a flow divider and medium flowing and porting, would this change my jetting? If so, what would be some likely suggested changes?

4) I'm under the impression that I can pop a 2.2 crankshaft in this factory 2.0 with no other alterations. What would the suggested jetting be for that setup?

[RallyBob]

Originally Posted by thescifiguy I haven't found a thread that specifically addresses the jetting of my carb on my present engine setup: Weber 38 on a factory 2.0 1) What do you guys suggest for jetting of this engine(for economical daily driving)?

You won't find specifics posted here unless someone else has the exact same engine combo. Every change can affect the jetting, even your local fuel.

2) F-66 tubes to fix the hesitation/stall problem?

It certainly helps on any 4-cylinder Opel I've tuned.

3) If I put a manifold with a flow divider and medium flowing and porting, would this change my jetting? If so, what would be some likely suggested changes?

Yes, it likely will affect the jetting...but only you can determine which direction to go in by reading plugs or fitting a wideband O2 sensor.

4) I'm under the impression that I can pop a 2.2 crankshaft in this factory 2.0 with no other alterations. What would the suggested jetting be for that setup?

You can pop in a 2.2 crankshaft and 2.2 pistons and you've have a 2.2. With the 2.0 pistons and a 2.2 crank, the pistons would stick up above the deck of the block .151"!

Once again, the jetting cannot be determined over the internet, it's decidedly a hands-on tuning procedure. Either trial-and-error, or tuning via wideband.

Bob

[thescifiguy]

Thanks Bob! Are O2 sensor gizmos commonly available at an auto parts store? What do they cost? What range of oxygen levels would be typical of a well-tuned engine like ours?

[hrcollinsjr]

Originally Posted by thescifiguy Thanks Bob! Are O2 sensor gizmos commonly available at an auto parts store? What do they cost? What range of oxygen levels would be typical of a well-tuned engine like ours?

Gordon,
I believe Rallybob was referring to O2 sensors that you weld in a bung to accommodate a sensor, similar to what more modern computerized cars have. Check out this O2 sensor for custom applications. I'm sure there are other brands, I just knew K&N had one.

HTH,
Harold

[wrench459]

There's two different O2 sensors out there. The narrow band and the wide band. For tuning a wide band is a must! After it's tuned your can plug off the bung. Since you're running a 38 without feedback fuel control theres no reason for an 02 sensor at all unless you want to be geeky.
BTW I know of one certain 38 carb that has a known A/F ratio that you could calibrate the sensor to.

[thescifiguy]

This particular Weber 38 used to be owned by one of our members who had it "tuned just about right" for his 2.0, which got totalled, so he sold off the parts and moved on to an MG(How could you go from a GT to an MG? It boggles the mind.) I bought his sweet wheels and carb.

I'm gonna investigate acquiring an O2 sensor. I haven't pulled the jets to see what it's got, but that's my next day's off project(Tues/Wed). I'll get back to you guys with what I'm set up with.

[wrench459]

Originally Posted by thescifiguy I'm gonna investigate acquiring an O2 sensor. I haven't pulled the jets to see what it's got, but that's my next day's off project(Tues/Wed). I'll get back to you guys with what I'm set up with.

One other thing to think about.
Where are you going to place the 02 sensor in the exhaust stream?
I see you've got a sprint with a two to one pipe I'm guessing.
My thought would be around 4-6 inches after the common....ophs now where into tuning again and how even the simple differences can make a huge gain or loss in power.

[opellane]

I have a Weber 38 DGES and been using it ever since Rallybob installed it back in 1995 at C&R Small Cars. "THANKS BOB" It runs GREAT with "Lots of POWER". He base line jetted it and I just played around with some jets to get it tuned better. I tuned mine the old fashion way. Start with new Spark Plugs (NGK-BP6HS) Make jet changes,adjustments - get the jets in pairs (2)

DRIVE (20 to 30 miles) and check engine performance, then check the spark plugs. should be clean and not fouled. May have to do this many times, or do it with the O2 sensor way.
My engine is bored .030 with ported intake and stock exhuast
I think the jetting is: 130 mains (2) 170 air correctors F66 emolision tubes (2)
55 idle (2) The carb. has been jetted like that for years with no problems, maybe a choke adjustment here and there.
Hope that can help, but as they say "Every Engine is Different"

[opelbits]

I found the jetting for my 38 on the site somewhere, but haven't been able to find it again.

I'm running a stock 2.0E (not a bored 1.9, which will be different, mainly because of the head) with sprint manifold, slight porting of the intake to match the carb, electric fuel pump, and a 75 distributor. Exhaust is pretty stock (small!).

The jets:

140 mains
45 idles
170 air correctors
F66 tubes

I have no problem getting an 850rpm idle. When I switched to this carb and jetting from my 32/36, my mpg went up to around 30 from 20-25-ish. I attribute the increase more to the greater torque of the 38 than to my jetting. Just don't need to rev it as much as with the 32/36.

[thescifiguy]

Many thanks to Opellane and Opelbits, your info was just what I was looking for. I just needed some kind of jetting reference point from folks with similar engine setups to go by. It sounds like Opelbits has my same setup 'cept for the 75 distributor. Mine's got the old '68 distributor from the previous owner's engine rebuild/replacement.

I'm guessing a 75 dist. omits the vacuum retard aspect? I reconfigured the intake manifold "tree" with brass plumbing/air fittings to make for a smoother flow of the brake booster hose and modulator vac for the auto tranny I converted the car to. I don't have anything attached to the vacuum retard outlet on the '68 distributor. Is there anything else particularly special about a 75 distributor?

[Paul]

The 75 Distributor eliminates the vacuum ADVANCE and retains the vacuum retard. Also, it has less total advance, about 25 degrees. This way you can give some intital advance, up to 10*, and still not have more than 35 total.

[opelbits]

Glad to hear we helped, at least a little bit.

As Paul said, the 75 has no vacuum advance. Initial timing is set at about 10 degrees adv. (but you have to take into account the fact that the 2.0E block has the timing pointer 5 degrees from where it is on a 1.9 when using the 1.9 flywheel on a 2.0E, or some such nonsense) and it keeps total advance to less than 35 or so. Makes a big difference in how the car feels and there is no detonation or pinging from too much advance.

I think Opel GT Source is listing rebuilt 75 distributors. If so, it is a lot easier to just get a 75 than try to modify an earlier one. By the time you figure in your time and effort (unless you have a good distrubutor and a really good idea of what you are doing before you even start), the money spent is not too bad. You can find the info for eliminating the advance here on the site.

Hopefully, I'll soon get around to building a decent exhaust and get more out of the carb and engine, then I'll probably be rejetting.

[thescifiguy]

I just investigated my jets and here's what I've got:

F-66 e-tubes
155 mains
180 airs
50 idles

I don't know how the interplay of these jets works, but since my complaint is a rich running condition, it looks like I should reduce my mains. Would you think that the 180 airs or the richness might be contributing to the stalling when first touching the pedal from a stop? Opinions please....

[RallyBob]

Originally Posted by thescifiguy I just investigated my jets and here's what I've got: F-66 e-tubes 155 mains 180 airs 50 idles I don't know how the interplay of these jets works, but since my complaint is a rich running condition, it looks like I should reduce my mains. Would you think that the 180 airs or the richness might be contributing to the stalling when first touching the pedal from a stop? Opinions please....

At first glance it looks like the idle jet may be too small (try a 55), and the main jet is too big. Drop down to 145 at least.

[opelbits]

I'd say it could be a combination of things. If the mains are too big, you'd be running rich at cruising speed and if the idles are too big you'd have to open the throttle speed screw to get enough air for the fuel which means the throttle plates may be uncovering the progression holes (which could explain the high idle speed) all of which may contribute to the stumble as you open the throttle more and the accelerator pump squirts in even more fuel. And I'm not sure how the 180 air correctors would affect it all.

Your idles aren't too far from mine (1 step larger), but the mains are quite a bit different (3 steps).

It might help to know how many turns your idle mixture screws are from 'bottom' and how many turns the idle speed screw is from the point of contact with the throttle lever with the engine hot (no choke)

Also, you might check to make sure your vacuum advance is working correctly and does not have a leaking diaphragm. A sluggish/inoperative advance will cause a stumble too. If you have a 68 distributor it will be a dual vacuum unit with separate vacuum cans for advance and retard, if I remember correctly. Do some searching on the distributors, I think the least recommended distributors were the early ones (68-70, with 73-74 being most prefered next to the 75. Use the name Calvin in the search, he posted a bunch of advance info and I think there is other info in that thread.

Edit:I see Bob posted while I was writing....listen to Bob before listening to me.....

[thescifiguy]

I had some 140 mains, so I put them in, baselined my idle speed and mixture screws, adjusted them for smooth running, and the "first touch of the pedal stalling" went away, as did the gassy exhaust smell.

Now I get a stumble or bogging down as the accelerator pump kicks in. I tried some 45 idles, but that just seemed too lean to get a smooth idle and I put the 50's back in. I'll try RallyBob's suggestion and order some 55's to see what that does.

Just prior to starting this thread I had put a pressure regulator in and added a clear fuel filter just before the metal filter that the electric fuel pump had(I wanted to visually verify that my cleaned relined fuel tank didn't have any loose bits floating around). I had the reg originally set at 3.5 and took a test ride and had a catastrophic stalling and sputtering problem, which I'm pretty sure was due to the float bowl running dry. I opened the regulator all the way up to 5 or 6 and had the same problem(after I did the rejetting today). The filter has stepped inlet/outlets of 1/4" to 5/16". I guess you're supposed to trim off the 1/4" part for our cars.......but I didn't.

Is it likely that the 1/4" filter outlets are restricting the fuel flow and starving the carb? I'm going to either remove it or try nipping off the 1/4" reducers. When rejetting I also took out the 180 airs and put in 170's - the car test drove fine, when I tried the 180's I got the starved for gas condition.
What part in this process do the air correctors play?

[wrench459]

Originally Posted by thescifiguy I had some 140 mains, so I put them in, baselined my idle speed and mixture screws, adjusted them for smooth running, and the "first touch of the pedal stalling" went away, as did the gassy exhaust smell. Now I get a stumble or bogging down as the accelerator pump kicks in. I tried some 45 idles, but that just seemed too lean to get a smooth idle and I put the 50's back in. I'll try RallyBob's suggestion and order some 55's to see what that does

What's the a/f ratio when it stumbles?
As you found out the air bleeds or correction jets works backwards from the main jets.

[opellane]

Originally Posted by thescifiguy I had some 140 mains, so I put them in, baselined my idle speed and mixture screws, adjusted them for smooth running, and the "first touch of the pedal stalling" went away, as did the gassy exhaust smell. Now I get a stumble or bogging down as the accelerator pump kicks in. I tried some 45 idles, but that just seemed too lean to get a smooth idle and I put the 50's back in. I'll try RallyBob's suggestion and order some 55's to see what that does. Just prior to starting this thread I had put a pressure regulator in and added a clear fuel filter just before the metal filter that the electric fuel pump had(I wanted to visually verify that my cleaned relined fuel tank didn't have any loose bits floating around). I had the reg originally set at 3.5 and took a test ride and had a catastrophic stalling and sputtering problem, which I'm pretty sure was due to the float bowl running dry. I opened the regulator all the way up to 5 or 6 and had the same problem(after I did the rejetting today). The filter has stepped inlet/outlets of 1/4" to 5/16". I guess you're supposed to trim off the 1/4" part for our cars.......but I didn't. Is it likely that the 1/4" filter outlets are restricting the fuel flow and starving the carb? I'm going to either remove it or try nipping off the 1/4" reducers. When rejetting I also took out the 180 airs and put in 170's - the car test drove fine, when I tried the 180's I got the starved for gas condition. What part in this process do the air correctors play?

1st: Did you check the float level measurement. I think it's 30mm from carb base to bottom of float. See weber instruction sheet. This could screw things up.

2nd: Make certain there are NO Vacuum leaks. Quick test. When engine is idling, spray Carb cleaner spray at the base of carb and around. Any change at all in RPM's or stumbles, you have a Vac Leak.

When you step down on the gas you run on the mains Jets, when your foot is off the gas you're on the Idle Jets.

I ran into this problem between when you're on the gas then off, stumbles and I just had to change the idle jets a few times. Try going larger idles, 55, and maybe smaller mains ?? trial and error system

How hard do you like to punch the gas too.

After you think it's running right. Change the spark plugs and re-check, re-road test.
Sounds close to my setup.

[thescifiguy]

I removed both fuel filters and replaced them with a see-through replaceable cartridge one that screwed into the electric fuel pump. Ditched the pressure regulator, too. Float level and function perfect. The engine has only run about 8 hours since it's rebuild and has all new hoses and gaskets, but checked with carb cleaner for leaks anyway. None detected. Mixture screws out 1 1/4 turns, idle set at my prefered 950rpm. The "catastrophic stalling" while driving went away. Probably had a clogged filter.

Still stumbles pretty severely at the idle to acceleration transition. If I "flutter" the gas pedal as it's happening I seem to get through it much better than if I just slowly ease down on the pedal from a stop. None of this is new to me, all four of my GT's, modified and stock, acted this way and I was never able to cure it.

Got to wait for payday to buy some jets and a few other things. I'll order the 55 idles and some other sizes of mains. I'll get back to y'all next week.

And YES, I DO enjoy squashing my gas pedal! It's a sports car - it's what you're [I]supposed[I] to do! Yee-ha!

[thescifiguy]

I decided to mess around with the timing and, lo and behold, all my issues went away! The jets remain in the last configuration I quoted and the idles are 1 1/4 turns out. I can maintain a 750rpm idle with no trouble(even with the added resistance of the automatic) and there's no hesitation or hickups.

Holy cow, that timing adjustment can be fussy! A microscopic movement counterclockwise and the engine knock and bogging down were unbelievable. A fractional movement the other way and I had the symptoms previously described in this thread. And the engine at idle basically sounded the same in each configuration! I couldn't tell any difference until I was over 40mph.

Thanks to all of you for helping for helping this non-motorhead fellow to understand this stuff!