Club 80-90 Forums

I have a slight flat spot just as I press the accelerator pedal. This is most noticeable when pulling away. I have looked at the carb for anything obvious (timing and mixture are set up). The only thing I can see is that the lever of the accelerator pump is not touching the cam at the end of the spindle. The gap is probably about 1.5mm ( I can't get an electricians screw driver in the gap).

If this is the cause of the flat spot what should I adjust? If it just the cam screw or is there any other adjustments that need to be made first?

Could be timing lagging a little through being incorrectly adjusted or leaky vacuum advance too. If it is the accelerator pump/diaphram, its usually better to just fit a new one.

Thanks for the reply Covkid. I set the timing last week and checked it two days ago - it's bang on. The accelerator pump is operating healthily (admittedly I can't find a none intrusive way of measuring the quantity). I'll check the advance pipe although it's def affecting the timing as soon I connect it to the dizzy.

Might also be worth checking the base plate in the dizzy as it can get stuck. If you take the dizzy out and spray the plate with WD and the flat spot goes, next thing would be to strip the dizzy down for a clean:

https://club8090.co.uk/forum/viewtopic.php?f=39&t=138696" onclick="window.open(this.href);return false;

That could explain the flat spot as the vacuum advance may not actually moving the dizzy. Will the gap of the accelerator pump give a similar effect as, momentarily, the mixture is leaned?

Remove vac advance pipe from carb and with dizzy cap off and rotor removed, check for smooth and consistent movement of dizzy base plate when sucking on pipe before assuming its carb. When the plate moves, if you put your tongue on end of pipe when plate moves, plate should stay there.

I'll give that a try and get back to you all

I had a look at my dizzy, it has a part number ending in C which is plausible as the engine is an early DG. My spare engine has a dizzy, part no ending in Q (late DG).
could I use this spare dizzy on my fitted engine? That would buy me some time to strip and fettle the spare dizzy.

What happened on the suction test. Don't tempt providence by fitting something that may/may not work. If plate is stuck, a squirt of WD40 should free it. Bear in mind, it does run but if you move too far away by fitting something else, you could give yourself a right headache. Do the diagnosis then consider other solutions.

I didn't get round to the suction test today. I'm pretty sure I've tried before and couldn't get it to move. My plan tomorrow is to overhaul the carb tomorrow. I'm now thinking that I'll overhaul the spare carb first as a trial. That'll boost confidence for the main event. Both dizzys are around 30 years old so a bit of TLC can't hurt.

Update: I stripped the spare dizzy as a practice - just as well: i lost the tiny dowel that locates the vane. It eventually fell out of the dizzy body after I'd searched the floor for 20mins!
I operated the vacuum advance by sucking but it wouldn't work. I then attached it to the hoover - it still didn't work.

I rebuilt the unit and swopped it with the van's dizzy (it'll do for a while). I stripped the van's dizzy and again the vacuum advance doesn't work. I think I know why I have a flat spot!

I'll order a vacuum advance now. Any recommendations, both heritage and brickwerks do a unit although brickwerks is almost twice the price. (It's an early DG with a suffix C dizzy part number)

In the mean time I'll diy zinc plate the screws and the clamp. It should look and operate a lot better in a few days!

yay!

Bubble Meister wrote:Any recommendations, both heritage and brickwerks do a unit although brickwerks is almost twice the price. (It's an early DG with a suffix C dizzy part number)

Back in April I bought a vacuum unit for my DG's dizzy from VW Heritage - £27, special order, part number C025-905-271/C.

Since then I picked up another unit as a spare at Busfest. This one, for £16.50. The chap on the Powerspark stall said the advance curve was slightly different, but only a couple of degrees, and that it should work fine. I don't know how true that is, as I haven't fitted it, but I can't believe that a few degrees will make very much difference.

Bubble Meister wrote:Update: I stripped the spare dizzy as a practice - just as well: i lost the tiny dowel that locates the vane. It eventually fell out of the dizzy body after I'd searched the floor for 20mins!
I operated the vacuum advance by sucking but it wouldn't work. I then attached it to the hoover - it still didn't work.

I rebuilt the unit and swopped it with the van's dizzy (it'll do for a while). I stripped the van's dizzy and again the vacuum advance doesn't work. I think I know why I have a flat spot!

I'll order a vacuum advance now. Any recommendations, both heritage and brickwerks do a unit although brickwerks is almost twice the price. (It's an early DG with a suffix C dizzy part number)

In the mean time I'll diy zinc plate the screws and the clamp. It should look and operate a lot better in a few days!

Sorry to jump in, but is the zinc plating easy enough to do?

The vacuum unit arrived from Brickwerks today - a bosch unit with the same identification stamped on it as the vacuum unit I removed. I rebuilt the dizzy, plonked it on the van and turned her over. Nothing - she just cranked. It turns out that the fuel pump I'd fitted on Saturday was duff! (https://club8090.co.uk/forum/viewtopic.php?f=37&t=147178" onclick="window.open(this.href);return false;)

New (budget) pump on order from BW so standby.

Zinc plating: whilst I was waiting for the new vacuum unit to arrive I zinc plated all the various removed bits. I got the Gateros kit early on this year but this is the first time I've properly used it. The plating activity is a little time consuming (probably about 2hrs to do) but you could do simultaneous activities as sometimes your waiting for certain processes.
Yes it's easy to do but I think practice is needed (I touched a part and so the zinc wouldn't take in that area).
To set up you need to consider some storage space for the various tanks / buckets that will be full of fluids. I have: oxalic acid (rust remover), alkaline cleaner (removes greases), acid pickle, zinc plating, passivate (for yellow finish) and a water (for rinse and safety). That's over 50ltrs!
Setting the kit up was consuming as you have to mix all the chemicals (wear ppe as the acids are very strong before mixing - I created a splash that caught my face. Luckily I had the bucket of water to flush with).
To prep the kit you need to have some chemicals pre warmed, I use 2 fish tank heaters. The alkaline cleaner, zinc plating and passivate all need heating (I use the heater that was in the alkaline to then heat the passivate whilst the components are being plated).
I don't think the plating is as strong as a professional plater, the passivate certainly isnt. But then thats what you pay a professional for. I think the diy kit is best for rejuvenating old parts and giving back a nice surface finish (and prep to paint). My dizzy base clamp went in looking it's 30 years bit emerged looking baby fresh! I don't think the kit can be considered ideal as a industrial strength chemical coating.
Separate to all of this I like the experimentation aspect - garage chemist! Using electrolysis for rust removal started me off - took a vectra brake caliper covered in 8 years of gunk. After 24hrs we could clearly see all of ATE's identification stamps! It looked good after it was painted as the surface was so smooth.