Thirsty and sluggish bus - retune 101 please!

Post by **Globbits** » 27 Aug 2008, 14:23

Hi all

My 1.9DG engine'd Caravelle's not been right since we fitted a recon engine to it. Bearing in mind that, since the recon engine's gone in, she's had a replacement dizzy, vacuum unit, the carb's been stripped, cleaned and reassembled, lots of valve-lifter tweaking (don't get me started on that one!) and various other meddling, it's not entirely surprising she's not that happy.

Don't get me wrong - she'll still do 80ish if pushed, but she's really sluggish to pull away, isn't fond of gentle hills, let alone steep ones and is drinking fuel. (Let me clarify this - she has pulled up hills better than she does now and has used less fuel in the process)

The dizzy is the right one for the bus and the vacuum unit's a brand new proper one (yes, I know it's different to the Solex-carb'd unit)
The valves are now adjusted properly - no tappety noises, yet still maintaining contact
Timing is spot on 5 degrees BTDC at 900rpm, vacuum plugged (no idle stabiliser fitted)
Plugs are gapped nicely and are in good condition

I have no reason to doubt the engine, just how it's set up. So firstly, is the above right? Second, how the hell do I reset my Pierburg? I'm assuming the only thing I should consider touching is the mixture screw, but how do I tune it please?

Thanks as always!
Richard

Post by **Titus A Duxass** » 27 Aug 2008, 14:54

Hi.
How are the brakes?
Are the wheels turning freely?

Post by **Globbits** » 27 Aug 2008, 14:59

Brakes are fine and wheels turn freely. The engine temperature stays pretty constant - even at high speed - which would imply the issue isn't drag-related

Good thought though

Post by **HarryMann** » 27 Aug 2008, 15:03

I'm assuming the only thing I should consider touching is the mixture screw, but how do I tune it please?

This will make not a jot of difference to how it pulls, it only sets the idel mixture AFAIK

Take it to a small local garage with a well experienced mechanic and have it analysed for ignition and mxiture and compressions as well.
What mpg are you actually getting long term?

Using too much fuel: trust the air filter is new, no air leaks in inlet or exhaust.
is it near the pinking threshold in hot weather, full boot when heavy in 2nd or 3rd?

Post by **Rozzo** » 27 Aug 2008, 15:24

does it pull away better when it's stone cold? sounds to me like the choke might be sticking on.

Post by **Globbits** » 27 Aug 2008, 15:24

HarryMann wrote: This will make not a jot of difference to how it pulls, it only sets the idel mixture AFAIK

Damnit

That's what I thought

Air filter's 5 days old and the inlet/outlet side of things is nice and tight. I fitted a new exhaust system when the engine went in and there's no signs of backfiring or anything

Actual mileage is about 250miles on a tank, which is about 18-19mpg. But that's on a run - go around town and it drops like a stone. Ok, it's an auto, but I'm not being heavy-footed while I'm trying to work out what's going on.

As for taking it to a garage, that's my problem - our friendly VW garage are tearing their hair out too. Maybe I'm expecting the world, but I can't keep up with my g/f's 1200 beetle when she pulls away from a junction and it just doesn't seem right

HarryMann wrote: is it near the pinking threshold in hot weather, full boot when heavy in 2nd or 3rd?

Not that I know of. I've tried advancing the timing by a couple of degrees and it just made the bus even more sluggish!

Any advice?

Post by **dugcati** » 27 Aug 2008, 17:52

could be worth verifying the following are correct....

Spark plug type
plug gap
are the coil/s OK
Are the carbs overfuelling?
tyre pressures
gearbox ratios

Post by **Globbits** » 27 Aug 2008, 20:27

Thanks for the pointers - will investigate tomorrow

Richard

Post by **HarryMann** » 27 Aug 2008, 21:34

Not that I know of. I've tried advancing the timing by a couple of degrees and it just made the bus even more sluggish!

Yes, while not ignoring other's ideas, I'd say that was good to do that, you obviously know a bit then

Tried backing it off 2 degrees as well? That might be my next step, and if didn't noticeably go worse, I'd go another 2 until it did, just to see like - you obviously have your timing datum well setup and marked, so go for it... watching the heat buildup though so if it doesn't go better, don't thrash it for long.

Post by **Adrian244** » 29 Aug 2008, 20:19

I'm no expert on T25's but I would suspect and swap the carb out. That seems the most likely thing to me. I had a pierburg on a mk2 golf driver last year. When it was working it was fab when it was playing up argh

.
I picked up a cheap Weber on ebay and instantly got much more power and better mpg.

Post by **HarryMann** » 29 Aug 2008, 21:01

I had a pierburg on a mk2 golf driver last year. When it was working it was fab when it was playing up argh Twisted Evil .

there ya go, another idea...

Also had a Pierburg on a SEAT Ibiza, the auto-choke was the devil's own invention, but you could get kits to change to a manual choke, which we did and it transformed it from a fuel guzzling beast that still had its choke on after 5 miles..

Post by **Mocki** » 29 Aug 2008, 21:28

when you timed it, you plugged the vac pipes.......... try setting it with the vac pipes open to atmosphere.............

Post by **AngeloEvs** » 29 Aug 2008, 22:22

You said that you replaced the dizzy, was it new or S/H? I would check the centrifugal advance mechanism. Not sure about the VW dizzy, but the ones I am familiar with utilise spring loaded weights and I have known the springs to become detached or the movement of the weights is hindered.

Post by **HarryMann** » 29 Aug 2008, 23:02

e.g Cent Adv. curves DG/DJ

Post by **HarryMann** » 29 Aug 2008, 23:19

Recent question on Syncro forum about Pierburg carb refurb