Low power & pinking after carb overhaul

[Jokerbetty]

Message for the oracles. I recently had moments of power loss on a 1.9 dg then all would be fine again, so I overhauled the carb (pierburg) & this has got rid of that problem. However now she seems down on power and I noticed just now on a long run (20mile) that there is like a pinking when I give it some pedal. Could my new clean carb and new fuel and vacuum pipes have altered the timing? I don't want to start fiddling with it till I am sure it's not a carb issue.

Whaddyathink?

She goes in for a gas conversion soon so I wanted her to be right before he starts.

Thanks in advance.

Jez

[CovKid]

Well, you could stick a timing gun on it and see if its at least close to what it should be. Checking won't alter anything. Not had it so much with these lumps as they have better controls (and electronic ignition) but certainly on Beetle engines I'd often come across situations on other folks engines where the carb had been tweaked to get around timing that was actually way off, or timing set to get round a carb prob. One can mask a fault in the other put it that way. What you need is a dead certainty in one or the other.

You don't by any chance have conventional points do you? ie a 009 or similar dizzy? When warm and off choke, does it idle at around 950rpm and if so, whats the timing mark say?

[bigherb]

Did you fit the vacuum pipes to the correct ports on the carburettor?

[itchyfeet]

^^^ whs possibly second choke vac unit not operating whould give you lean mixture, or if its just when you accelerate accelerator pump faulty
if it worked well befre except for the intermittant fault then less likely to be timing but always worth checking as said, you cant fault find with too many unknowns.

[bigherb]

less likely to be timing but always worth checking as said,

It would be if the vac advance and pre heater pipes are transposed.

[itchyfeet]

I didnt know that
appart from being 15mm appart the both connect through directly below the second barrel throttle, why does it matter which way you connect them?

or did i miss the point?

[Jokerbetty]

Hi all. Thanks for all the ideas. I dropped it at the garage and it struggled to restart when warm. The timing is well advanced according to the garage. He is going to strobe it before he starts o n it. It does point to my carb clean, new seals, and all new vacuum pipes changed the vacuum and advanced the timing. The carb was an oily mess (never been cleaned in 30yrs I think) and the vacuum pipes were loose fitting and in need of replacement.

When I get the van back I will report back about the power/timing issue.

Thanks all

[Jokerbetty]

Oh and itchyfeet, your idea was exactly my first thought. I tested by sucking on the pipe with the throttle open (not running) and it worked fine.

[bigherb]

I didnt know that
appart from being 15mm appart the both connect through directly below the second barrel throttle, why does it matter which way you connect them?

or did i miss the point?

They work the opposite way round the distributor port has no vacuum at idle the air cleaner has full vacuum at idle. If they are connected the wrong way round the timing will be advanced by the vacuum at idle.

[itchyfeet]

You learn something new every day
i just dont understand how its done when both connections look the same to me
And if dizzy has no vac at idle why disconnect it for timing measurement?

I'm going to have to experiment i think

[Smosh]

what's the (sorry silly question) purpose of the vacuum?

[Smosh]

what's the (sorry silly question) purpose of the vacuum?

[ghost123uk]

I have just checked on a spare carb I have and those 2 pipes do both go to the same place, ie below the throttle butterfly. This means that they are both subject to the same vacuum as each other regardless of throttle opening etc. One of them however has a pin hole restriction in the pipe. Without going and looking at the van I am not sure which is which, but I bet the pinhole one goes to the pulldown unit to make it's operation somewhat "damped" ?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Smosh, the vacuum varies with throttle opening. At low openings the engine is trying to suck air in faster than the small opening will allow, so a larger vacuum exists. At say "pedal to the floor" the opening of the throttle is large so more air can get in, so the vacuum ("sucking effect") is lower. This variation in vacuum is used to move the base plate in the dizzy (via the dizzies vacuum diaphragm on the side) to adjust the timing according to the revs and engine demand. The timing needs to be more advanced (ie spark happening earlier) at higher revs (due to the relative delay in the explosion happening in the combustion chamber compared to the speed of the piston). Hope that helps a bit.

[bigherb]

The vacuum advances the ignition timing at part throttle loads when the mixture is weak as it takes longer to completely burn a weak mixture. The vacuum is taken from a port just above the throttle butterfly where the vacuum is most at part throttle.
The other vacuum is used to work the air cleaner pre heater flap and is taken from a port just below the throttle butterfly where there is the most vacuum not effected so much by throttle position until near full throttle.

[ghost123uk]

The vacuum is taken from a port just above the throttle butterfly where the vacuum is most at part throttle

Ah, of course, the dizzy vac isn't connected to either of those on the base is it. I had only looked at a bare carb, not at the van