lumpy idle

Post by **Frostbus** » 16 Apr 2006, 19:09

hi all
another problem 84 dg velle
have very lumpy idle have replaced igni leads plugs cap rotor checked valve clearence and rebuilt carb, no leaks on vacum pull down etc.
checked timing miles out!! reset but still lumpy on idle fine while driving pulling etc.
what have i missed
cheers

Post by **HarryMann** » 16 Apr 2006, 22:12

If by lumpy you mean a rhythmic diesel like idle, then try weakening the pilot idle a bit...

Excessive weak idle = hunts (revs increase then decay over several seconds; unstable)
Excessive rich idle = throbs (strong but rhythmic idle; stable)

Post by **Frostbus** » 17 Apr 2006, 08:26

hi
have tried but still rough
it's rocking alot when idleing but if you rev it, it runs smoothe.
all the jets are clear advancing or retarding makes no difference to idle.
checked the plugs... not wet light grey in colour all gapped ok.
sparking at each plug.
it runs as if i have the leads the wrong way round,checked all ok.

any idea's
thought i had done a good thing selling my bug to get bus!!

cheers

Post by **HarryMann** » 17 Apr 2006, 09:30

Doesn't mean the plugs are all firing nicely when its idling - necessarily.

What are all 4 compression pressures?

Post by **Frostbus** » 17 Apr 2006, 15:52

hi harrymann

compression as follows

1=145
4=155
3=145
2=150

would the difference make that much difference in idle it's shaking the bus!!
rev it it's fine!! not smoking plenty of power pulls well just turns us to jelly when we stop in traffic
exagerating a bit but never had engine this rough on idle

any idea's
cheers

Post by **HarryMann** » 17 Apr 2006, 19:37

Well those pressures are fine, 5 psi between them is nothing at all...

Ideas....

Yes, the leads.

Either have all 5 leads checked for resistance;
Change them for a new set
OR get it on an engine analyser and look at the spark traces on idle..

Something's wrong, as it can't be firing evenly/properly on all 4 when idling.
IS it burning any oil, maybe a plug's oiling up at idle.
I might try yet another set of new plugs, or even a set of old ones, as from what you say, one or two just isn't firing at low rpm... engine analyser should easily troubleshoot this.

Also, lever the engine support bar about with a jemmy whilst inspecting all the metalistic engine mountings for delamination.

Post by **kevtherev** » 17 Apr 2006, 21:12

Has the idle speed screw been touched

Post by **Ivor Brownun** » 18 Apr 2006, 12:30

I know you said you had changed the leads but a mate had a similar problem and it was the leads, have a look in the dark and see if they are arcing. On my 2.1 I think there is a idling valve you can hear it buzzing when the ignition is on perhaps someopne who is technically minded can tell you how to check this. (if you have one)

Post by **Frostbus** » 22 Apr 2006, 16:05

hi all me again

have changed the plugs again!! for bosh triple electrode.
rebuilt the carb again!!! changed all the gaskets etc blown out jets.
checked the timing
checked the valve timing
checked the vacqume for the brake servo
compression all checked all within approx 5 psi of each other (150) and built up quick on each cylinder.
changed leads over for old ones no difference.
checked electro mag cut off on carb.
new rotor and cap.

engine mounts not delaminated.
and it still idles rough!!!!!!!!!!!!!!!!!!!!
only thing i havent tried is the coil and the electronic module.
any idea's
new module is expensive
do coils break down...or just fail.

please help

Post by **HarryMann** » 22 Apr 2006, 17:34

do coils break down...or just fail.

Nearly all electrical/electronic parts do both - unfortunately

Sound like you ened someone alongside with similar motor for subst of lecy bits. Certianly don't want to going out buying exepnsive lecy bits on guesswork (what some VW garages do, so I hear!)

Post by **kevtherev** » 22 Apr 2006, 20:45

Checked mixture on gas anyliser? at idle and 3000 rpm

Post by **HarryMann** » 22 Apr 2006, 22:04

Exactly! As said a long way above...
Lumpy, rhythmic idle - weaken it off
Hunting - richen it a bit

But get it on an engine analyser - and look at the traces of those sparks at idle and if all OK?? then check the absolute advance figure

Theres few other ways of moving forward with this now....

Post by **diviy** » 22 Apr 2006, 22:30

pull off the main fuel supply going to carb in the brass end there is a filter
have a look cured my mates problem same as you had

Post by **Frostbus** » 23 Apr 2006, 11:55

hi all

have had a analyser on it set co2 etc (fatherinlaw is a mechanic) it was still rough
it's a diferent sound to hunting weak rich etc.

been out this morning and checked all again found the following:

rev limiting rotor (interpart) has been fouling the centre pick up on the cap!!!) this has worn a groove on the cap.

replaced rotor

also have removed the vacqume and blocked off

it now runs perfect .......

sorry for all the posts guys
and thanks for all your help especially harrymann

just need to replace little bit of vacume pipe and hopefully thats it!!

thanks again

Post by **kevtherev** » 23 Apr 2006, 12:08

HOORAY! well spotted..and well done