jetting help for a 1438 OHV with Weber 32/36 DFEV

[JimD]

Hi Guys,

I replaced the stock DHSA carb in my 124 Special with a new Weber 32/36 DFEV last spring. The DFEV I bought was in a Redline kit K518 intended for a 124 Spider with DOHC, not the OHV in my sedan. The car runs much better with the new carb, but I know nothing about jetting and the performance doesn't seem quite right. So I was looking at the old vs new carb jets. Here is what I see.

The DHSA carb has jets stamped 160 and 210 in this orientation:

The DFEV has jets stamped 160 and 165 in this orientation:

In the pictured orientation, is it primary on the right and secondary on the left? Can I swap jets from the old to new carb? Or are jets specific to one carb? Like I said, I know very little about this topic.

 

[kmead]

I assume you have a factory manual for the car, if so, I would first verify that the original carb was set up per the factory intent, there have been a lot of years and a few owners between the factory and where you are now.

There are many other factors deeper in the carb. Emulsion tubes, idle jets and the accelerator pump jet to name a few.

Fiddling with a second carb willy nilly on the basis of how your old one was set up is unlikely to be a path to happiness. Before setting off on this do you have data points for what isn’t “right” about it? Flatsposts, failure to accellerate properly when dipping into the throttle and so on. Is it running reall rich, too lean? Knowing what needs fixing will help someone (not me) to assist you with choosing more appropriate parts.

Even better would be to do some analysis with a wide band 02 sensor or a classic exhaust gas analyzer given that your car doesn’t have a catalyst so what comes out the end is pretty indicative of the balance of the combustion process.

Not much help, sorry. Just some breadcrumbs along the path...

 

[JimD]

Well Karl, you are no help at all. I tried searching the "Karl's Best of Xweb", but I couldn't find the "Karl's Best of Xweb". Muahahahahahaha!!! (I miss the little devil emoji the most)

I got out the 124's shop manual and did find a page for the stock settings. I am not sure which items to look at, but in general there isn't anything listed with a measurement of 210. It could be that the new carb is closer to the mark than the old carb.

Obviously I will need to learn this stuff or find a competent shop... or just sell the car. It is actually running OK. I have driven it around town a few times this week. (We had a really heavy rain for 2 days last weekend, salt be gone!) The car started up really easily after sitting.

 

[NM850]

The jets from many Weber’s interchange. If they screw in just check them for length.
Those jets you show are the air correctors, below those will be the emulsion tube and below that will be the main jet. Can you tell me what size the main jets are?
An air/fuel reading is what’s used these days but an engine can still be tuned by the old school method of reading the spark plugs .
Basically the Weber has three circuits. Idle, transition, and running. Idle is self explanatory, running is usually above 2000 rpm and transition is between. What part are you unhappy with?

 

[JimD]

Hi NM850,

I have a couple issues. One is that the car runs like crap under load (ie going uphill) until it is well warmed up. I don't think the automatic transmission's kick down thingy is working, but if I move the stick from "D" down to "2" manually it does better. The second issue that had me thinking about jetting is my engine running hot. I read that a lean mixture can cause the engine to run hot, so I was wondering about the new carb and if it needs adjustment.

I think my problem is I really have no idea what I am doing with this car or with the carb. I keep flailing away and really need to attack it systematically. I just have real world issues right now that prevent me from dedicating a lot of time to the cars. I will try to find time to look at the jets, but for now I think I will park the car and work on one of my Xs.

Thanks for offering to help. If I can get some organized info and questions together I will seek you out.

 

[Fiataccompli]

I am no carb wizard by any stretch but I seem to step into that world frequently. That said, I know it sounds very basic but being certain there is not a cooling system issue and a transmission issue (I think the kickdown cable being broken somewhere on these is almost universal, but it could be a torque converter issue) would be a good way to rule out some outside variables. If the driving/temp issues only appeared after changing carbs, then yeah. So if it's the carb here are some thoughts in no particular order:

1. Are you sure the base gasket/spacer is sealing correctly? Could you have an air leak that more or less closes once all of the metal is up to full temperature? I think the DFEV had a thinner base flange than the one you removed, yes? If so, warp/seal issues could be a factor (think...lean, behavior changes with temperature).
2. I do NOT have the answers, but going from both DHSAs & DMSAs to DFEVs. (Why?) I found that the right feeling (did not use a wide band O2) set up was philosophically different than the DH/DM carbs. Remembering the basic philosophy of balancing throats size, fuel jet & air corrector (how many steps in air equate to a single step in fuel?) helps. I believe I have a full scan of a wonderful (and readable) Weber tuning book I could email you if you'd like. I'm still in a phase of remembering (and sometimes learning from past mistakes) stuff that I knew & forgot, so I reach for references when I start scratching my head.

3 . Have you reached out to any other 1438 pushrod owners? I believe Andy Truscott has this in a 238 van and has likely done some thinking there, but I know there are others.

4. Yes, in that family of carbs, all of the jets are interchangeable. The think - I think - that makes the DFxV carbs different to set up is the power valve...I suppose ultimately it makes for a bit more of a civilized feel, and that's probably the exact reason that after toiling over two of these on 1608s (with similar lack of others to consult) I got them right and decided I liked the 34 DMSA more.

5. Do not discount the idle circuit. What you describe makes it sound like the idle (which is really more like 800-2500 rpm) is OK but the enrichment is off...it could be that your idle is failing at the high range before the enrichment can take over. That's fun to think about, right?


Hey, you could just decomplicate things and unload that Sedan by sending it to me!

Seriously, good luck with it.

 

[JimD]

Thanks Chris,

The car has run "hot" since I purchased it. It never gets into the red, just closer than I would like compared to an X1/9. I have slowly made progress on the issue and perhaps I have done enough. The shop manual doesn't seem too concerned with engine temps, it says that if the gauge gets into the red, pull over and let it cool off.

I have had the radiator check out and repaired by a local shop, replaced the external thermostat and all the hoses. Converted from points/condenser to a Pertronix electronic ignition device and bumped the timing a bit over 10 degrees. All off these changes had a small or tiny positive effect on temps.

I chose the DFEV because I was told it was a compatible carb and I was able find a brand new one. The DFEV changed the car for the better, the original DHSA on the car was worn out. I took the DHSA apart and cleaned it and all its jets, then "rebuilt" it to the best of my abilities. It ran better, but still not well. The DFEV ran pretty well from the first start up with it, I did the basic adjustments for idle speed and idle mixture that were part of the carb install process. I have added a fuel pressure regulator and gauge since I did those original adjustments, I don't recall redoing the basics afterwards, so probably should redo the basics.

Regarding the kick down cable. To me it looks like that mechanism is out of adjustment. If I manually cycle the throttle cable it just barely puts any pressure on the kick down. I mean the movement is tiny. he jam nuts are jammed and I have been soaking them with PB blaster so hopefully I can get some better pull on that cable.

Jon at Midwest124 mentioned that I should look into getting a different intake manifold. I think he said the 1438 stock intake is single plane and I should get a dual plane.... maybe I have that backwards. So I will talk to him about that again and get the specifics.

I don't know any other 1438 OHV owners. I thought I was the only one. Good to know I am not alone.

Thanks guys for all the ideas to think over. I really appreciate it.

If nothing else, watch the FS&W section!

 

[bruakeman]

I have a 1438 pushrod (124b) in my 57 1200TV. It has a 36dcd on it. Runs fantastic, but I've never checked the jets, never needed to. I have a hot rod 124b in my 73 850 spyder. It has a 1608 crank, 124b stock rods, and 128 1100 1mm oversize pistons (I think, if memory serves). PBS built the short block for me, had to clearance the block a bit. It runs in reverse rotation via Abarth timing gears. I have a SEAT head on (sourced from Greg Schmidt just before he disappeared) it with a side draft 32 DCOF carb. The original 32 DCOE carb (off of an Abarth 1300/124) was junk so I bought the 32 DCOF new. Strangely it does not have interchangeable jets like the DCOE. But it was luckily good to go, that engine also runs great. Not that any of this is really any help, sorry, but others do run these engines.