1.9 Watercooled misfiring

[acornishpirate]

Hi guys. Really hope someone can help me with this one as I'm running out of ideas.

Van is a 1991 water cooled 1.9 petrol camper van. 51k on clock. Pierburg 2e3 carb.

The van starts OK and idles fine. While stationary and not under load it will rev up and down smoothly.....but only to a certain point. At about {and I'm guessing here} 3500 or above revs, it starts with an irregular misfire. If I try to increase the revs any more the engine will start to 'pop'. Any more than that and it backfires! It also 'fluffs' as the revs fall back to normal when I back off the throttle.

Whilst driving, the van has an irregular misfire on acceleration. On the overrun it also misfires or if I am going downhill, say in 4th/5th gear.

Things I have tried already;

New fuel pump and pushrod.
Complete new fuel line from tank to pump and carb.
New in-line fuel filter
Checked filter on inlet spigot of carb
Split top half of carb, blown out jets with compressed air. All clear.
Carb cleaner
Fresh fuel

I inherited the van from my father in law a few weeks ago, it's probably only done 50 miles in the last 3 years. It has mostly been stood for the last couple of years, except for its annual trip for MOT when it's run fine. It also ran fine when I drove it over here. I was initially thinking blocked carb jets or fuel starvation due to petrol 'gumming up' but am unsure what to check next?

New HT leads?

Any help/suggestions/ideas would be greatly appreciated.

Many thanks, Howard

[CovKid]

Checked timing? vaccum pipes to dizzy? Does vac unit on dizzy actually work? I'd start there. Remove pipe from dizzy to carb at carb end and suck on pipe with dizzy cap removed. Does plate in dizzy move and will it stay there if you put your tongue over end of pipe when sucking? If it moves back even with pipe sealed, unit is knackered. If plate doesn't move its rusted up or again vac unit knackered. If vac checks out ok, check timing. Either would definately cause that problem.

[acornishpirate]

Checked timing? vaccum pipes to dizzy? Does vac unit on dizzy actually work? I'd start there Remove pipe from dizzy to carb at carb end and suck on pipe with dizzy cap removed. Does plate in dizzy move and will it stay there if you put your tongue over end of pipe when sucking?

Hi CovKid.

Thanks for your reply. Sorry, forgot to mention I replaced the the vacuum advance pipe and checked mechanism. I've not checked timing though as can't find my strobe light {had diesels for years} but I'll go and sort that now.
Cheers, Howard

[acornishpirate]

Checked timing? vaccum pipes to dizzy? Does vac unit on dizzy actually work? I'd start there. Remove pipe from dizzy to carb at carb end and suck on pipe with dizzy cap removed. Does plate in dizzy move and will it stay there if you put your tongue over end of pipe when sucking? If it moves back even with pipe sealed, unit is knackered. If plate doesn't move its rusted up or again vac unit knackered. If vac checks out ok, check timing. Either would definately cause that problem.

CovKid. Think you moght be on to something here. I've just remembered. A couple of days ago I disconnected that pipe whilst the engine was running....and it stalled. If I recall correctly this pipe needs to be disconnected plugged when setting timing dynamically....so it shouldn't stall?
Going to have another look now.

Cheers, Howard

[acornishpirate]

Timing was slightly out when I eventually found strobe light, but not by much and it's made no difference. Clutching at straws now so going to try a new set of HT leads.

[CovKid]

Compression check always good too as you will have a better idea of the state of the engine. Yep, could be leads, they can break down and perform poorly.

[kevtherev]

Has your distributor got a rev limiting rotor arm fitted?

[acornishpirate]

Has your distributor got a rev limiting rotor arm fitted?

Yes, I believe it has. You think I should replace it?

[kevtherev]

It would cause a power loss/misfire at the higher rev range.
I fitted one to my van and it has a tacho, the dang thing sarted limiting the revs at 3700 rpm.
use a non limiting one to eliminate it

[Highroller]

Maybe a bit of a long shot, Is the fuel fresh? If the van has only done 50 miles in the last 3 years it could be contamimated fuel.