Bad running after new exhuast fitment

[Josh NZ]

Hey folks.

I recently fitted a new exhaust to my landy because my old one was holy and seriously noisy, and i now have a bad running engine

Its recently had a big dollar rebuild in the engine department and is running approx 9:1 ratio with oversize bore, reground crank, unleaded head etc and was running sweet as a nut until i replaced the exhaust last week.

It starts on the button and settles into a rather lumpy idle and if i blip the throttle or hold it approx 1200rpm it will chug a bit of black smoke out. I feel that its overfuelling badly..

How can i fix the issue (Its stopping me from driving the truck).. is it a job for the mixture screw or is it my timing or something worse?

And what would have caused the issue in the first place? I would like to find this out as its a good thing to know for future landy excursions

Josh

[Tanuki]

What engine are we talking about? I'm guessing the standard 4-pot 2286 LR petrol lump rather than a six or V8.

Changing the exhaust shouldn't have caused your problem - unless someone has done something stupid. Did the intake/exhaust-manifold have to come off? (I'm thinking here about needing to drill-out old manifold-to-downpipe studs).

One really odd problem I did experience a while back was where the heat-riser plate (sandwiched between the intake and exhaust manifolds) had a hole rust in it. At low RPM exhaust-gas was being fed back into the intake-manifold - which caused all sorts of lumpy/smoky/backfirey-types of problems.

[Bowie69]

carb o-ring if still running the old zenith?

[Josh NZ]

Sorry haha 2.25p!

Yes it's running the old zenith, I'm loathed to take the carb apart as its never played up before.

It could be just a coincidence but it seems such a wired time for something else to just go

[Gassed'58]

If you have the engine set up to suit the clapped out exhaust then it stands to reason that it will need tuning to suit the new exhaust. You need to double check all of the settings and especially that of the mixture. Simple stuff before stripping carbs and such like.

[Bowie69]

I doubt very much that the exhaust change from old and clapped out to new would make it belch black smoke... The zenith is so simple, you only set the idle mixture anyways, running is fixed.

Could also be that whilst trying to get to exhaust in you snagged the choke cable....?

[Josh NZ]

I didn't think to look at the choke cable, but It doesn't really have stuck choke characteristics.

Does the exhaust affect anything to do with the running?

Could It be that the exhaust is restricting the engine in some way? It seems to be way too much of a coincidence that the carb would suddenly decide to play up. I don't think the fuels dirty.. Might top it up anyway. Carb cleaner didn't have any effect so I might go get some wd40 and start lathering the engine in it and see if there's a leak

[secondjeremy]

Did you use exhaust paste/sealant? If so its possible surplus has blocked the pipe. Land Rover exhausts shouldn't need it - generally joints are dry - and SWB silencers use a gasket. Possible this has been omitted and paste used instead.

[Josh NZ]

I haven't used any exhaust paste on the joins, it sealed up nicely without it.

I'm having a go at the carb tuning later today, I'll see if I can get a sneaky video if what's going on

[Josh NZ]

Problem solved!!

Turns out the carby tried to make an escape and unbolt itself. The bolt under the vacuum line was nearly off!

Thanks very much for all your replies!