Carb woes

Discussion in 'Mech Tech' started by Adam W, May 10, 2019.

  1. Hello everyone. Hopefully someone with a little more experience in this issue will be able to help me with this one!

    Basically, my bus (1600 type 1 engine) is running OK generally. Starts fine, idles nicely and nips along nicely when on open roads. The problem is a massive flat spot in the power delivery, most noticeably when pulling away from a slow corner in say 2nd gear. It happens more when the engine has warmed up rather than when it is cold.

    I've done a fair bit of reading around this, and most articles point to the 34 PICT-3 and 009 distributor combo, but I've got a vac advance pertronix dissy and I still have this issue...

    So far, the following have been checked:
    • Timing
    • Valve clearances
    • All manner of carb adjustments
    • Fresh fuel
    • Carb was cleaned and rebuilt with gasket set and diaphragms etc
    The carb is an original Solex 34 PICT-3, ignition is now pertronix with flamethrower coil and leads. Exhaust is the JK stainless silent pack. Air intake is a aftermarket filter as I haven't been able to get my hands on an original one yet, but as it happens more when warm, i'm not sure this is the issue.

    Does anyone have any more ideas on what to check before I shell out on a new carb (or set of twin Webers :) )

    Thanks in advance!

    Adam
     
  2. Dubs

    Dubs Sponsor

    If it's a pancake type filter, bung it in the bin. Even when warm, a standard air filter will give better acceleration. In fact, you will probably find it will run better with no air filter at all. Though I wouldn't advise it..

    You can actually get a pancake to run better by raising it off the top of the carb with a 50mm ish spacer, but it's much better just to stamp on it and fit a proper filter.
     
    snotty and Adam W like this.
  3. have you set the carb up with a Co² meter up the exhaust ?

    I've got the same set up as you and don't have a flat spot....
     
  4. ^this. Ditch the chromy filter. If there’s no preheat, you can get manifold chilling even when the engine’s hot - feels like a big flat spot. I’d also ditch the Pertronix coil - they don’t have a great reputation. Keep the original Solex - it’s better than anything “new” you can buy.
     
  5. I would get in touch with either Megabug or FBI VW and try for a stock air cleaner.

    If not, go to swapmeets like Slough, where such things are often hiding under tables surrounded by dusty bits of tin off Beetles and old VW magazines.

    They are £60-80 on eBay, maybe £20 under tables.


    You still have the accelerator pump to tweak on a 34 PICT-3.

    This effect is probably the carburettor cooling down as a result of driving near idle.

    Also check your exhaust heat risers are unblocked on that exhaust.. they were not on my JK single quiet pack. Needed Dremel and patience.
     
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  6. In addition to the above it'd also be worth checking your vac advance in the dizzy is actually advancing. Pull the hose off it and give it a suck, you should see the plate in the dizzy move.
     
  7. Thanks everyone for your comments so far. Keep them coming!

    Yes carb was set up with a probe up the exhaust, as mentioned it runs sweetly and goes really well once past this flat spot and idles well too.

    We've ruled out air leaks with a vac gauge and pulls a good vacuum so dont think it's that.

    Also tried to rule out the air filter by removing it and taking it for a run, but no improvement there. I will get a proper one once I can find one though. If it was manifold chilling, would this not present itself at higher speeds when the airflow is greatest, rather than lower down in the rev range?

    Pertronix coil was swapped for a high output coil and it did make a bit off difference but not the solution.

    Accelerator pump provides a good dump of fuel (which is a possible fix for the 34PICT3/009 issue). Increased it another notch for good measure!

    Distributor seems to be working fine and will hold a vacuum (does leak down over time, which i think is normal/OK). All advances correctly when revving hard.

    I haven't checked the heat risers - good shout on that one.
     
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  8. Another poss is that the Pertronics module is playing up. Swap it temporarily with breakers? One step at a time...
     
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  9. Thanks Snotty, sadly I thought the old dissy (009) was the original cause of this problem so fitted the pertronix to fix it! No such luck
     
  10. Did you get just the Pert module, or the whole dissy?
     
  11. Adam W likes this.
  12. I'm another for carb iceing...Mine did do it in the past with a twin quiet pack...
    Do you get any condensation on the manifold up to the carb.. maybe heat risers are blocked with crap or exhaust not been drilled correctly.
     
    Dubs likes this.
  13. Thanks again everyone.

    @snotty the whole dissy, brand new with vac advance on it

    Yep, think it needs to come apart and check the exhaust to see if it was drilled out - I doubt it as I believe they leave them undrilled for those running twin carbs?
     
  14. Unlikely to be drilled out, as it’s difficult to do. Useful to just bolt the exhaust risers to the manifold stubs - at least you’ll get some heat by conduction. With a 4-into-1, you’ll get little gas flow through the preheat tube anyway (unlike a stock exhaust). Worth having the hot air feed into the carb that’s part of the stock air filter.
     
    Dubs likes this.
  15. Dubs

    Dubs Sponsor

    The heat risers are a good shout. Ideally you need both the hot air feed to the top of the carb, and decent heat risers, to keep a single carb up to temp.

    When the engine is at normal operating temp, both heat risers should be too hot to touch. If they are not, or just the left one is, then they are not doing their job.

    Or just use it all as an excuse to justify a pair of Dells.. :D
     
    Valveandy, Adam W and snotty like this.
  16. Hello again,

    I've started my search in earnest for the proper air cleaner... but which one? My bus seems a bit of an odd-ball, so can someone identify the cleaner bracket as being for an oil or paper filter?

    Thanks!
     

    Attached Files:

  17. Early oilbath type
     
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  18. Andy76 likes this.
  19. So, little update, the heat risers are connected and working fine. Get nice and hot when running. The problem definitely only happens when the engine has warmed up, and still can’t put my finger on it.

    I know the intake system isn’t ideal, but I would have thought that would make most difference when cold, and you need that dose of warm air. Doesn’t feel like that is it. Can only think the carb is playing up when warm, maybe one of the spindles is getting stuck or something.

    But, time presses on and so I’ve taken the plunge and gone for twin 34 icts! Bit pricey once everything required is included but it should hopefully return more than just a smooth running engine. Also don’t need to source a working air filter unit. Robert at Eurocarb was great, and is jetting them to suit WayOutWesty’s setup which I hope will help them run sweetly over the ‘as delivered’ stock setup.

    Coming tomorrow so hopefully fit next week!
     
  20. Hurrah! The flat spot is no longer.

    The heat pipes were pretty crusty once I got them off, and that coupled with the Jk stainless exhaust may have contributed to the low end issues.

    The carb seems absolutely fine, cleaned out either carb cleaner and an airline, jets all checked and removed so I’m not sure what the issue was in the end, but twin 34s has fixed it!

    Just need to get the linkages set up nicely and put that one to bed hopefully.

    Thanks for everyone’s help and advice, got there in the end

    Adam
     
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