1.8 8v EX engine with Weber 32/34 DMTL

Discussion in 'Carburettor' started by Brenjacques, Nov 26, 2020.

  1. Brenjacques New Member

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    Hi all

    First Post here after joining, hoping I'll be welcomed being the owner of a Mk2 Scirocco. I'm hoping to find some advice with (presumably) the carb which is causing some trouble.

    I've got a problem where the revs are dropping off during warm up with the choke on. I can start the car fine, drive it for 10 minutes or so but as the temperature reaches the point between cold and half way the idle revs start dropping back down requiring more choke or keeping my foot on the accelerator.

    I initially thought it may be a poorly adjusted choke ie not enough throttle and the choke flap too far closed so I adjusted it this afternoon for more throttle so the choke flap can be open more but I'm still having the same problem. Also noted that if I pump on the brake pedal during this it pulls the revs back up- possibly too rich during this short period?

    Once the engine is warm I have no problem, it idles nicely and pumping on the pedal makes virtually no difference to the idle revs.

    The carb is a weber 32/34 Dmtl which is only a few months old.

    Anyone got any ideas on what could be causing it?
     
  2. rubjonny

    rubjonny Administrator Staff Member Admin

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    did you check/replace the rubber flange under the carb? if using the original airbox is the rubber mount still there at the front which holds it steady as well
     
  3. Brenjacques New Member

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    Yep, the carb flange is all fine, I fitted a new one last year when it was still running the pierburg and I checked it again yesterday to be sure it is okay. The airbox is held correctly at all points and it is a good fit.

    I noticed the garage that fitted the weber didn't fit the carb heater so I fitted that this weekend and the warm/cold air flap was seized in the down position so I've also freed that off and it is working okay.

    I took it for a drive after all of this yesterday afternoon (the car was up to temp by the time I had it off the drive) and it was fine, ran okay with no problems at all. Starts it this morning and drove to work and it is having the same problem again.

    Also noticed if I remove the vacuum hose from the rear of the carb the idle speed picks up and it runs much smoother (when it is idling poor). Idle mixture has been set with the engine warm and the car runs fine if it gets up to temp before driving.
     
  4. rubjonny

    rubjonny Administrator Staff Member Admin

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    might be worth checking idle/co again, since if it runs better with an air leak this would suggest the engine is running too rich at that moment like you say. if you check my signature link theres a couple of weber pdf, may be worth looming at the jets perhaps
     
  5. Brenjacques New Member

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    Thanks, I'm thinking it's too rich also, but strange that once warm and at idle I've set it a couple of times and it still does it. I'm having someone come and look at it on Friday to sort it out and tune it up.

    Also been thinking that I have filled up recently with Esso supreme 99, wonder if that has anything to do with it? This cars never been too happy on any esso petrol for some reason and I usually use shell but reading that Esso's new 99 has no ethanol in I thought it would be worth a try. Might give it a few good runs to drain the tank down and fill it back up with the usual shell stuff and see if that makes any difference.
     
  6. rubjonny

    rubjonny Administrator Staff Member Admin

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    if anything I'd expect it to run a bit better, though you would need to advance the timing a bit to get the best out of it. I only use sainsburys premium in mine just because its cheap and never had an issue. run my old 1.6 carb on it (well, mostly sainsburies 95 really but now and again I had to put premium in) and all of the different 1.8/2.0 8v, 16v, kjet, abf engines I've put in my GTI :lol:
     
  7. rubjonny

    rubjonny Administrator Staff Member Admin

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    on that note have you checked the ignition timing? assuming original dizzy just done at idle with vac line on to 18 degrees BTDC, line up the diamond in the gearbox hole for basic setting then you can tweak a little more advance with good fuel. if you have a kjet gti dizzy its done with vac line disconnected, to 6 degrees BTDC. the carb flywheel mark is wrong if you change to the gti dizzy though so have to make your own marker or use a timing light with advance dial
     
  8. Brenjacques New Member

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    That's what I thought when filling it up haha! I recall a similar problem on the pierburg where it would splutter a bit at idle when using esso fuel, really haven't a clue why but I've never had a problem with shell or BP, same with this weber, it's been fine for months but now I've clocked on that I filled it up at esso using their premium 99 the past 2 times... Not saying its definitely that but it's worth some thought.

    I sorted the timing the other week on it, it was quite a bit off. Used the 18° mark on the flywheel and a timing gun at idle with hose connected, so that is all as it should be.
     
  9. Brenjacques New Member

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    Just had a look on my lunch break, leaned it off until removing the vac pipe made virtually no difference, the revs dropped off quite a bit but I've adjusted them back up, will see how it drives on the way home tonight and if that's sorted it out.
     
  10. Brenjacques New Member

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    Thought I'd update this thread, I had someone out to tune the carb and check the engine over, ignition timing was fine but it was running slightly rich, this was soon corrected and he was very pleased with the results from the emissions tester, which he advised was really good for the age of the car.

    Dispite all of this it has still been running awful when cold, so I've been waiting for the tank to drop nice and low so I can fill up and switch back to my usual choice of shell premium. I did this last night and filled the tank, gave it a good run and parked it up for the night.

    This morning I've driven to work and it's been perfect, hasn't had any trouble with lumpy idle or idle drop and I managed to put the choke full in as soon as it the temperature needle was out of the cold.

    So there we have it, looks like it was the Esso petrol all along, not the first of my older cars to do this with esso fuel but this one really didn't like it at all. Back to shell or BP from now on... I wonder why Esso in particular?
     

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