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Weber Carb Help.

Discussion in '"Stock" Alpine' started by Mike O'D, May 22, 2019.

  1. Mike O'D

    Mike O'D Gold Level Sponsor

    I'm looking for some help from the experts.

    Freshly rebuilt 1725. Weber carb from Sunbeam Specialties - about 10 years old, but also freshly rebuilt. Set carb according to Weber instructions - 1.5 turns in on speed screw and 2 turns out on mixture. Starts and runs poorly at about 500 rpms. Turn mixture in - no real change until 1 full turn in, where rpm increases a bit and idle improves. Turn in another 1/2 turn and rpm increases further with better idle. Turn mixture screw all the way in and have really smooth idle at about 1000 rpms (speed screw not touched). Also note: prior to carb rebuild on old worn out engine, the carb pretty much reacted the same way.

    What do you guys think?


  2. 65beam

    65beam Donation Time

    Sounds like my cars that have been converted to a Weber 32/36. All were jetted by Tiger Auto. None of my cars have ever idled at 500 RPM's. My cars idle at around 900 to 1000 RPM's.
  3. RootesRacer

    RootesRacer Donation Time

    3 things I can think of.
    1) Your idle jet could be too large.
    2) You are possible leaking fuel from the bowl onto the throttles.
    3) Somewhere along the line someone turned the mixture screw all way in and damaged its seat.

    On #1, Idle jets are selected based on transition, quality not idle speed or quality.

    On #2, uncontrolled fuel from other sources will cause you to have to trim the idle mixture to a leaner position to compensate for the richness.

    On #3, I have experienced this with a carb I bought that the PO had decided to screw the mixture adjustment screw in so hard that
    it cracked the casting and you could see the crack on the throttle side of the case. The usable adjustment range was the last 1/4 turn due to the
    large amount of fuel leak-by.
    Finger tight, never more.
  4. jumpinjan

    jumpinjan Bronze Level Sponsor

    The Alpine idle speed is 1000 rpm
  5. johnd

    johnd Donation Time

    Mike - Is the engine hard to start?
  6. Mike O'D

    Mike O'D Gold Level Sponsor

    Thanks for all of the input guys.

    RootesRacer - Carb originally came from SS, so the assumption is that it has the correct jet. What size are you guys using? I will double check the size.
    I bought the carb from a fellow forum member. It looked to be in very good shape, and the indication was it was never messed with and was working fine. Needle valve looked good with no signs of abuse. The rebuild kit came with a new needle valve, so I used that along with all of the gaskets, seals, etc. I looked things over pretty carefully when I had it apart, and didn't see anything suspicious.

    John - super impressed with how quick/easy it starts. From cold - 1 pump on the throttle, pull the choke and almost as soon as the starter gear hits the ring gear, it's running. Not a lot of hot starts yet, but same thing except no choke - starts very quickly.

    The problem is that it idles so smoothly with the mixture screw all the way in, but doesn't drive right - surging at low speed but fine accelerating or running higher rpm. With the mixture screw turned out 1/2 turn or more, the idle is pretty rough but it drives a lot better.

    Any additional input is greatly appreciated.

  7. johnd

    johnd Donation Time

    Mike - Ha - I have the opposite problem. Tried to address idle problem many times - changing jets, etc - to no avail. Hard to hold a steady idle and very hard to start (its almost like a vacuum leak exists). However, once the engine warms up the car runs great, so I no longer mess with it.
  8. RootesRacer

    RootesRacer Donation Time

    The correct idle jet is a tuning thing, has to do with what the engine wants. No guarantee that it wasnt changed by PO, no guarantee the jet provided would have been right for your engine. I seem to recall that Rick had a rather large idle jet installed to proactively remedy lean progression complaints.
    I would think a 45 or 50 jet would be right for a stocker, what size is yours?

    Having the idle mixture screw need to be all the way in indicates an over rich condition, either due to very large idle jet or mangled mixture adj seat like I already mentioned.

    While running, inspect to be sure that you see no drips going into the carb at idle (like from the accel jet nozzle or from the booster venturi).
  9. alpine_64

    alpine_64 Donation Time

    Jan, when you say idle speed is 1000rpm on the Alpine, are you saying with a dgv or in general. I thought SI/II on the Zeniths was 850?

    I know i used to have my Zeniths down at 800 and stable... After i changed cam and went 2x dcoe i went to 950, but means the idle is a little touchy tilm warm (im not running a choke setup)
  10. 65beam

    65beam Donation Time

    The shop manuals tell of different idle speeds for different series and various conditions. The later manual concerning series 5 shows a hot idle speed of 950 RPM. Cars using the Solex 32 PAIA show an idle of 850. I have a manual for series 1 Alpines and Rapiers of that time that show a hot idle of 650 RPM. The figures are probably based on engines and carbs with no wear . It's all up to the owner.
  11. spmdr

    spmdr Donation Time

    It's been a REAL long time, but there was a time when SS sold carbs with the wrong idle jet.

    Fought that SOB (carb) ASSUMING it had the correct jets, ...it WAS NEW.

    I VERY quick change of the idle jet made ALL the difference in the world!!

  12. Mike O'D

    Mike O'D Gold Level Sponsor

    Thanks guys.

    John - I know we talked, and it seems like you have tried just about everything.

    Rootes Racer - I need to re-check what size is in there. I thought I wrote it down when I had the carb apart, but can't find it. Good suggestion about looking down the carb when it's running to see if anything is dripping. Honestly, that's sort of what it feels like when it is idling. I'll check that out too.

  13. Mike O'D

    Mike O'D Gold Level Sponsor

    DW - do you know what size you ended up with?


  14. pruyter

    pruyter Donation Time

  15. pruyter

    pruyter Donation Time

    Hi Mike,

    I myself have installed the Webcon conversion which is developped in a cooperation between Webcon and SAOC in the UK.
    This conversion exists out of a Weber 32/36 DGV 5A and a special designed inlet manifold. In spite of the fact that you have only installed the Weber 32/36 and not the special inlet manifold it may be of some help if you know the jet setting of the Weber 32/36 as used in the Webcon conversion. So I will give this information to you in the hope that it could function as a guide line for you:
    Well, her it is:

    Primary main jet: 140. Secondary main jet: 135
    Primary air correction: 165, Secondary air correction: 160
    Primary idle jet: 52, Secondary idle jet: 50
    Primary emulsion tube F6, Secondary emulsion tube F6.

    Maybe this setting could be something to start with.


  16. Mike O'D

    Mike O'D Gold Level Sponsor

    Thanks for the information Peter. I'm finding out there sure are a lot of different combinations that people are using. So, I pulled the idle jets and found a 60 in the primary and 50 in the secondary. I can't say if it came this way or I mixed them up when I did the re-build. The numbers are tiny and the 50 looks like a 60 (or vice versa). Anyway, I switched the 50 to primary and the idle is now very smooth and the adjustment falls in line with the Weber instructions. I'd say I'm about 1 1/2 turns out on the mixture and less than 1.5 turns in on the speed screw for 1000 rpm. Unfortunately, I started hearing some rocker noise and upon investigation found that oil wasn't getting up top. I haven't had a chance to investigate the cause or the extent of the damage yet.


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