Weber ICT - jetting, fuel pump pressure

Discussion in 'Mech Tech' started by rob.e, Jun 7, 2018.

  1. When i bought my bus back in 2014 i knew it had just been fitted with some new Weber 34 ICT carbs and being a newbie i didn't really know much about how these worked or what the potential issues might be if they weren't set up right. I mean, the kit was sold for a type 4 engine so it must be right, right?

    Er. maybe not.

    I'd had the first problems with these after a year or so, with fuel leaking/ syphoning through when parked up leading to hydro locking of the cylinder at one point. I solved this (or so i thought) with a fuel cut off valve - only allows fuel to flow when the ignition is on. At the time this was fitted my local chap said my needle valves were worn so he'd replaced them. I was a little confused by this at the time as the carbs were'nt that old, and i hadn't done that many miles?

    Thanks to the great info that's available on this forum and across the internet i then did some proper research and found that there is a widely held opinion that these carbs are shipped with jetting that does not suit the vw. In addition i read that the electric fuel pump that's fitted to a bus like mine (originally fuel injected) would be giving significantly more fuel pressure than was good for the carbs.

    Armed with this knowledge i then proceeded to ignore the situation :) .. focusing instead on my starting issues, exhaust, suspension, breathers, filler pipe etc as the bus was running ok it never really got to the top of the list to address. Occasional pop and backfire, sometimes through the exhaust sometimes through the carb but nothing so bad you couldn't ignore it or put it down to "character". :) It did seem to use a hell of a lot of fuel though..

    March this year though i was heading off to Volksworld early morning with the kids on board and the bus was running like a pig, much worse than before, lots of backfires, way more than normal, lack of power, struggling to climb any gradient. I gave up on the trip and stopped in the services - lots of fuely smells at the tailpipe and looked like there was fuel in the oil too. Oh dear. I nursed it back home and decided to properly look at what was going on.

    Oil change (yes it was thin/ fuelly) and i put in some new plugs - old ones were very black / coked so indicative of overfuelling as i thought.

    I was a bit wary of attempting to re-jet my carbs on my own so i did some searching and came up with this guy, Mike Leather

    Mike has a lot of experience with ICTs and ran them on his own bus which he's taken on some mega adventures including a trip across the states.

    I asked the guy at eurocarb what would have been fitted in my kit and he said 145 mains and 55 idles, with 160 airs. Mike's recommendation for the type 4 on ICTs is: 165 mains, 185 airs, 55 idles, 150 needle jets and F6 emulsions. However if the fuel pressure is above 2.5 psi then it doesn't matter what jets you have it will still overfuel as the high pressure wears out the needle (float shut off) jets. Based on Mike's advice i got new pump at the same time; the Huco low pressure pump gives a true 2.1 psi which is ideal for these carbs apparently :

    Mike's a great guy, very knowledgable, helpful and honest - spent a day fettling in my garage; he removed and stripped both carbs, cleaned, adjusted and rebuilt with the new parts, refitted, balanced and setup the linkage and installed the Huco pump.

    The difference with the re-jetting and setup is really noticable. It starts easier, idles smoother, way more responsive at low speed manoevering, a lot more flexible n general driving. The bus is SO much nicer to drive now.

    So, in summary, problems were:
    - i had a pump that was giving way too much fuel pressure, so way too much fuel going into the carb
    - the carbs were incorrectly jetted so were allowing too much fuel to flow
    - the high pressure was wearing out the needle vales, so the carb was not able to regulate the flow properly
    - the overfuelling was coking up my plugs so making them less sparky, so less able to ignite the fuel potentially

    re-jetting, low pressure fuel pump, professional balance and linkage setup.
    vinnyboy, paul2590, paradox and 9 others like this.
  2. It might be a good idea to put a version of this posting in the how to section because it is good advice.
  3. Merlin Cat

    Merlin Cat Moderator

    Maybe that’s the problem with mine? It revs high and always backfires when I turn off. Uses lots of petrol too :)
    rob.e likes this.
  4. I think its very common.

    Along with dieselling on as the fuel is ignited on all the red hot carbon coke buildup in the cylinder head and on the piston.
  5. Merlin Cat

    Merlin Cat Moderator

    What’s dieselling on please?
  6. It’s where the engine runs after they ignition has been turned off, sometimes when there’s lots of fuel still in the engine and an ignition source like something really hot
  7. If yours was FI originally and now runs carbs and you’ve still got the original pump it’s likely to have similar issues to mine. The fi fuel pump is too strong for the carbs. I expect the high pressure has worn the needle valves so they can’t stop the flow of fuel.
    Merlin Cat likes this.
  8. Merlin Cat

    Merlin Cat Moderator

    Hi @rob.e
    Yes, mine was f.i the previous owner converted it.
  9. Similar issues a few years ago. 2.0 type 4 and 34 ICT's

    This is what worked for me.

    Posiflow electric fuel pump (low pressure and not the cheap brass coloured one, get the black proper one) Fuel regulator set to about 3 1/2. Rolling road and re-jetting.
    All good for 4 years now.
    rob.e likes this.

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