Weird fault - what could it be?

[andrew882]

Hi all

We've just been over to the east coast in Duff (our 84 1.9 petrol bus), all good all the way over there, but around 20 miles from home he started playing up and I'm not sure what it could be.

The engine refuses to tick over, it doesn't like part throttle, but will rev on a full throttle (although it didn't like pulling a load, which made getting going from stationary at traffic lights a nightmare). Have replaced dizzy, rotor arm, leads, plugs, fuel pump and filter (have cleaned filter in carb too). I didn't replace the fuel pump push rod as I didn't know it was replaceable when I did the pump, but wouldn't that reduce fuel at the top end more, which doesn't seem to be what's happening?

Any advice would be greatly reduced, I'm at a bit of a loss at the moment!

Cheers, Andrew

[937carrera]

Have you checked ignition timing - don't adjust it, but see where it is, could the dizzy have moved ?

Any induction air leaks, inlet gasket blown out ?

[tobydog]

Blocked idle jet?

[andrew882]

Thanks for the advcie so far, I'm going to go through the fuel side of the problem tonight and see if anything obvious leaps out. Starting with filters, then will give the carb a blow out with compressed air (only have a can, any advice on where to aim it??) and carb cleaner.

I thought I'd read somewhere about putting your hand over the carb somehow to try to draw any crap out that way too, but can't find the post...any pointers here?

Any advice on how to check vacuum lines for leaks? Mine look in good nick, but are just pushed on to the spigots - should they have clips?

I've also got a carb rebuild kit on order if the first round of stuff above doesn't produce a result.

Sorry for all the Qs, but the knowledge here is such a great resource!

[Mocki]

The little Vac pipes are easy to check , take them off and seal your fingertip on one end and suck the other end , if you can pull air through they are leaking .
The big one from the inlet manifold for the brake servo is harder , but with engine running spray brake cleaner or engine degreaser on the pipe and if the revs change it’s sucking the brake cleaner in and changing the mixture .

Don’t forget to check the fuel filter in the carb inlet spigot if it’s a DG engine with correct carb .

[diabolov]

I think this is the post you were looking for http://forum.club8090.co.uk/viewtopic.php?f=37&t=168328

Kevtherev wrote:

If you remove the duct off the carb and put your hand over it (creating a seal) get an operative to crank it a few times, does it try to start, or try when your hand is removed?
Alternatively tried the neat fuel tipped in the carb trick.
If it tries to start then it's the idle circuit thats the issue.
Pierburg has two circuits idle and main.
Even though it's new something is blocking fuel for the idle

And to add to Tobydog from earlier, I wrote:

Take the pancake cover off the top of the carbatooter and unscrew the idle jet, I'm sure it's the only one you can unscrew
from the top (on a pierburg) you haave to split the carb for the other. Make sure you have a good fitting flat blade screwdriver so you don't break the jet.

Once out blow through and look up the middle to make sure you can see light through the centre, replace and then try.

symptoms sounds like a blocked idle jet, as it will run once off idle and main kicks in but won't start without your foot
on the accelerator.

My symptoms started on a run where it would cut out at junctions or when I slowed down to stop ( come of main or main/idle onto idle).
I could restart but had to keep the revs up to keep it running.

Also take a look at the videos linked in this post http://forum.club8090.co.uk/viewtopic.php?f=37&t=168422

Regards

M

[andrew882]

Thanks all for your help, I'm hoping I have found the issue...

The culprit seemed to be the idle jet - I gave the carb a good whack of cleaner and blew everything I could out with the compressed air, tried again,but symptoms still persisted. I removed the idle jet to see if I could sees blockage, blew it out again (including the holes in the side) and also gave the aperture in the carb a good blow out too. Refittted and......success!!!

I took duff out for about 2 miles and all seems ok...fingers crossed for the next longer run.

Appreciate the help guys, it's always good to get additional brainpower on the problem

[tobydog]

Would be worth checking the condition of your fuel hoses in case they're breaking down internally and some of the debris is getting through

[harris121163]

i would unbolt your fuel pump with the hoses connected then pump it manually. if no fuel is pumped replace the fuel pump as the diaphrams cold be perferated.
i had a simalar problem and it was the fuel pump. the new bio fuel attacks the rubber in the fuel pumps.
when having starting issues always check fuel then spark.