T1 engine won’t idle. Help!’

Discussion in 'Mech Tech' started by JamesLey, Feb 20, 2019.

  1. Perfect. Wasn't sure of the default setting for bypass screw, that's very helpful.
    When you say "actually moving"?
    Choke is all good; once engine is warm the throttle is on the bottom of cam and butterfly valve is upright.
    Sounding likely that I've done a pokey job of setting the static timing. Wasn't aware that the lightbulb method would work with pertronix, so set it roughly using mark on dizzy lip to get engine running and used strobe light.
    snotty likes this.
  2. davidoft

    davidoft Sponsor

    Have you got an svda dizzy? The timing to the mark should be good enough but which crank mark are you using ?

    So with the idle cam, the idea is the butterfly stays in idle part of the carb throat, the idle control valve controls the idle circuit as it’s been isolated by the butterfly, so turn until it’s touchimg then a midges winkle more , but make sure the butterfly is free and moving, it’s possible to let the butterfly go far enough to stick. When setting the idle can screw just make sure the butterfly is starting or sort of just before starting to move if you know what I mean, not stuck :) . My guess is blocked idle jet, did you fit a new float valve ?
    snotty likes this.
  3. Bosch SVDA dizzy yes. To the 7.5btc mark.
    New float valve fitted yes.Will take another look at idle jet. Which air hole in the carb bowl supplies the idle jet? Just so I can check it's not blocked too.
  4. Give it another go. If the timing’s out, you’ll have problems. The Pertronix 1 can be statically timed with a bulb just the same as breakers. Use the 7.5 mark on the crank pulley - ignore the mark on the dissy. Put your timing gun away!
    JamesLey likes this.
  5. But it's so shiny!
    Lasty, Valveandy and Dubs like this.
  6. Put the gun down and keep your hands where we can see them, James.
    JamesLey likes this.
  7. davidoft

    davidoft Sponsor

    Some/ all of the after market float valves can be trouble some.

    Make sure all 4 cylinders are actually firing ;)
    JamesLey likes this.
  8. Dubs likes this.
  9. Been reading that religiously! Is very useful.

    Sent from my iPhone using Tapatalk
    Dubs likes this.
  10. Ok tonight’s progress.

    Checked timing and it was off but to rule out the new (to me) dizzy being the issue I’ve refitted the 009 one and static timed with a lamp to 7.5btc.

    Took the carb off again. Fuel bowl was nice and full, no leaks so float valve seems fine. Blew out the idle jet. Realised there is another aux jet just underneath it which I hadn’t removed (Bentley manual didn’t mention it but Haynes did), so blew that out to.

    Double checked that all cylinders are firing. While I was there did a compression test and all up around 115psi so good.

    It now idles ok with the choke fully on, but once it steps down one or two pegs on the cam it starts cutting out again.

    I’d noticed that after running for a few minutes that cylinders 3/4 felt noticeably cooler than 1/2 (I could touch the exhaust flanges on the 3/4 side). So I fired it up again and sprayed some WD-40 on the flange between inlet manifold and head. The rpms picked up considerably! As the engine tried to stall again I sprayed some more and that picked it up again so it would appear I have an air leak on that side. Presumably that side feels cooler as it’s sucking air in and weakening the mixture considerably?

    I fitted all new gaskets so hopefully it’s just a case of nipping it up a bit tighter?

    Sent from my iPhone using Tapatalk
    snotty likes this.
  11. davidoft

    davidoft Sponsor

    It’s cooler because it’s not firing effectively, fix air leak, the engines now running to lean, try nipping up the inlet but usually once the gasket has a leak path they need. It’s not a carb or timing issue, told ya check it’s runnimg on 4 ;), it obviously only running on 2 and 2 halves
    Poptop2, snotty and JamesLey like this.
  12. Check that the tinware wasn't trapped under the manifold when you tighten'd it down
  13. One way of messing up the inlet manifold is if you tighten it down unevenly - one nut goes tight and the other end is still up in the air- the ridge on the metal gasket holds it up.
    Did that once ..as well as trapping tinware, pinching the manifold boot instead of tightening it up.. splits in the vacuum hose from the air cleaner hot air flap to the carb...
    JamesLey likes this.
  14. Great progress today. When I took the manifold out it was clear it was leaking, you can see the wd40 I’d sprayed pooling in the base:
    And this is the culprit. The crush part of the gasket is completely off centre:
    Compared to the new one:
    Engine now runs great and I even drove the van round the yard and into the workshop. Happy days!!
    Thanks all.

    Sent from my iPhone using Tapatalk
  15. Poptop2

    Poptop2 Moderator

    This not idling malarkey is usually air leaks in my experience. I began reading this and thought it would turn out to be an exhaust leak, but alas I was too late. Glad you’re sorted James.
    JamesLey likes this.
  16. For future reference, the EMPI -- yes, EMPI! - fibre gaskets are pretty good. Better than the metal squish types, I'd say.
  17. Hi James,
    Thanks for reply on Iris thread, my rebuilt T1 is also reluctant to run smoothly on lowest cam with all things adjusted to correct settings. I am very grateful for this thread and will be following some of your tricks especially the WD40 on manifold joints and manifold stud removal.
    JamesLey likes this.
  18. There are so many threads covering rough running but I thought it best to add my experience to this relatively fresh one by James in the hope that others may find it. Restoring Lottie (separate thread) I have been plagued by rough idling at various stages. I rebuilt the twin port single carb 1600 engine completely and it ran well on a test bed for 2 years whilst I fettled the body. But idle was not great and deferred until I had fitted it to body with air filter and all plumbing in place. Various ignition issues were tackled and things improved. But there were 2 underlying problems; there was a manifold leak from of the rubber boots connecting the steel manifold to the twin port alloy casting because the new shiny stainless pipe clips, supplied with the new boots were a bad design. Basically the ends secured by the clamp screw were too far apart when tightened and encouraged a ruck to form in the rubber. I reused the old VW clips and the leak was sealed. The second issue was float level. I rebuilt the carb twice following differing references form Bentley and Haynes manuals but when I still had rough idle, sooty plugs and eye stinging exhaust fumes I decided to lower the float level using a repro float valve with slightly longer body and also a 1mm alloy crush washer. Finally I have the engine running well at idle, allowing final tweaks to dynamic ignition timing by strobe light and responding properly to adjustments of air bypass and idle mixture screws. Doubtless some more tweaking when road running at speed.
    Valveandy and JamesLey like this.

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