Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

[itchyfeet]

The exhaust on the legs is the higher compression ratio, very noticeable difference, I think with experience you could tell a DJ from a DG by this.

[CJH]

Ah yes, of course, blowing the gas out under higher pressure. At idle it almost sounds like my exhaust is blowing, but the noise only comes from the tailpipe.

[CJH]

I took my son out in the van this evening, expecting to wow him with my engine building prowess, but the damn thing ran like a dog - way down on power, kept stalling until it warmed up. It turned out to be an easy fix - the timing had shifted to almost 10 degrees AFTER TDC - but I think that's it, I blew my big chance to impress him

I suspect I hadn't tightened the pinch bolt enough, and must have moved the distributor when I lifted the cap to put the dust cover under the rotor arm. But it made me wonder about timing. I've read the wiki about using 5 degrees BTDC for 95 RON and 10 degrees for 98 RON. I only have 95 in the tank at the moment (the demise of the DG came sooner than I expected) so I've set it to 5 degrees, but longer term I intend to use 98. I've also read on here about VW reducing the power of the 2.1 by changing from 10 degrees to 5 degrees, so as to prevent the 2.1 engines throwing a rod - I don't know whether any of that is true.

But I'm not going to be squeamish about getting the most from the engine - firstly it's on a carb so probably won't be quite as powerful as an injected engine. Secondly, when I take it to the rolling road to have it jetted properly they're going to want to set the timing to its optimal value for maximum power. When I reset the timing this evening, it seemed to want more advance than 5 degrees - I felt as though it ran better if I advanced it further. So I'd like to know what the risk to the engine is if I set it to 10 degrees but can't get 98 RON for the occasional tankful. The wiki suggests this could damage the engine - is that right?

[itchyfeet]

You should set to 5 deg for 95, easy enough to change it later when you swap to 98, no point risking pinking it causes damage
when setting timing you have vac off so how it feels is not representative of reality.

I did exactly the same, forgot to tighten bolt but I was lucky it didn't move

[kevtherev]

I believe reducing the power this way also extends the life or even negates the 2.1 rod bolt failure syndrome.

[CJH]

Seems a shame to build a bigger engine and then have to limit it artificially like this. Was (is) the bolt failure problem widespread? Wear I can live with - I don't do enough miles for it to be an issue. Then again, leaving the timing slightly retarded like this would allow me to continue using the cheaper petrol I suppose.

[itchyfeet]

Chris, Marco mansi took a stock 1.9 and tutbo charged way beyond anything the DJ makes 300 hp Iirc, drove it hard and could not break it, eventually he boosted it so hard he broke a piston ring but not a big end, he is still turbocharging WBX for racing beetles he has has 500hp and somebody else has had higher.
chances are you don't do a high mileage, you don't thrash the nuts off and you will do regular oil changes.... 98 ron will be fine

[CJH]

chances are you don't do a high mileage, you don't thrash the nuts off and you will do regular oil changes....

Yep, that's me. It's a camper - it doesn't take corners well, I'm never in a hurry to get anywhere in it, and it feels most stable at 65mph on the motorway. I do have a small caravan* to tow with it, so some extra torque is mostly what I'm looking forward to.

*tsk - why does the forum insist on adding spelling errors.....

[CJH]

Took the van out for a bank holiday drive to the Peak District today. It was great on the way there - smooth, powerful, temps under control. On the way back it got progressively harder to drive - stalling whenever I came to a halt, underpowered, temperatures going up. I need advice.

I pulled over to take a look, and discovered a split in the distributor vacuum line where it meets the carb. "Great", I thought, "little or no vacuum advance - that explains the higher temperatures and the lack of power". So I snipped off the split bit, checked the rest, connected it back up and drove off. It was better. A bit. Still stalling at idle though, and still a bit underpowered. When I got home I figured it was either some catastrophic problem with a valve (poor adjustment leading to a burnt valve or seat?), distributor related, or carb related.

I checked compression, albeit after about 20 minutes when everything (including me) had cooled off a bit. 183 psi to 200 psi - all good I think, so the valves and rings seem to be sealing ok. So it must be something simpler. The distributor pinch bolt was still locked solid where I left it the last time I set the timing to 5 degrees BTDC. And I can see the vacuum advance moving, and staying moved, when I suck on the vacuum pipe.

So surely, it must be a carb problem. I figured that since I'd not got around to putting the new LT carb through the standard adjustment procedures before I fitted it, I'd swap it out for the DG carb (which was running very sweetly before I took the engine out), and fit a service kit to the LT carb and make sure all the adjustments are OK. I removed the LT carb, and immediately realised that the four screws holding the two halves of the carb body together were positively loose. "Bingo! An air leak - that explains the stalling and the lack of power". I'm still going to fit the service kit, but I bet that'll fix it.

But I put the DG carb on so that I can use the van while I'm servicing the LT carb, and I can't get it to run, and this is where I need advice. The van will run for a moment if I keep my foot on the gas (not just on the gas, but pumping it), but then it will 'pop' and stall. I folded down the rear seat so that I could watch it while I'm in the driver's seat, and I left the pancake off the carb, and I can see that the 'pop' is accompanied by a blow back through the carb. I could do with some advice on what can cause this blow back. If the timing is wrong, I can't set it any better than it is unless I can get it to idle (I'm pretty sure it hasn't moved since it was set to 5ºBTDC) and I know it's mostly right because I can get it to run for a second or two before the 'pop'. I've been very careful with the carb assembly, and I don't think there's a leak anywhere, including the vacuum pipes. Apart from the change of carb, the only other change is that I've now filled up with Shell V-Power - I was going to set the timing to 10 degrees BTDC, but hadn't done so yet (incidentally, I thought it would be easy to get 98 RON fuel, but my nearest garage doesn't do any 'super' unleaded, the next nearest (BP) has 97 RON, and then the next nearest (Shell) has V-power, which is 99 RON)

So what can cause blow back through the carb? Could it be the (very slightly) greater valve overlap in my cam causing exhaust gasses to blow back and cause this ignition in the manifold? And if so, why didn't it do it for the first couple of hundred miles, with the LT carb?

[CJH]

I've googled a bit, and an overly lean mixture seems to be favourite, given that I think I've ruled out a stuck inlet valve with the compression test. And I know that the DG carb works well on a 2.1 because lots of people run them, so I think it points to an air leak somewhere. Time for some new gaskets I think.

When I mounted the LT carb on the manifold I made sure there were no leaks by using Hylomar AF on the gaskets, but I noticed today that they had gone quite dry already in only a couple of hundred miles (doesn't fill me with confidence that the Hylomar AF is doing much around the cylinder compression seal ). I also used it on the gaskets between the inlet manifold and the heads - I wonder if that's also dried up. A leak there could cause a lean mixture, so I'll check those bolts too.

[itchyfeet]

Just because the piergurg was working does not mean its good now.

pumping it will inject lots of fuel, its not designed for that who knows what will happen, yes a backfire is possible from too much fuel.

[CJH]

Pumping the throttle was the only way to get it to run for a couple of seconds - I was trying to build the revs up. Without pumping it would simply pop and stall immediately - so since pumping it has added fuel, which extended the run time, it does point to a lean mixture I think, which suggests a leak. I agree that it may not still be good, although it was only about three weeks ago that it came off.

I think the solution is to just be methodical with the LT carb. I've cut new manifold gaskets, and I have a service kit for it, and this evening I'll strip it, check it, adjust it and refit it. I'll also check the manifold to head gaskets, and also the hedgehog seal and gasket (which were both new).

[itchyfeet]

lean could also be lack of fuel, are you sure its pumped through?

[CJH]

Yeah, pretty sure. I have an electric pump, supplied by a tachometric relay, which means the pump runs for a moment whenever I turn on the ignition. I only have to do that a few times to fill the carb. And I get a healthy squirt of fuel when I operate the throttle pump.

[itchyfeet]

I can't help thinking it would have to be a very bad air leak to do this.
Are you sure vac unit on dizzy works? ( suck test)
air bypass valve on carb works?
try setting timing to 10 degrees.

both carbs displaying similar fault suggests problem is not carb.