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Popping exhaust, lost power


samtope
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Hi forum, I am having a problem with a very loud popping and burbling from my series 2/3 exhaust. Its a 2 1/4 petrol and the noise is on deacceleration and engine braking, i.e hill decents etc. It also has even less power than normal. At first I suspected the obvious, a blowing exhaust, but on inspection the pipe seems fairly air tight although old. However blocking the end of the pipe with my hand and a rag does not slow or stall the engine at all. I've done some internet searching and many blame timing and fuel mix, but this engine has run very sweetly for 2 years and there is no smell of fuel at the tail pipe to suggest a petrol biased mix. It sounds very 'blowy' and I would like to just buy a new silencer and fix the problem (if the baffles are shot) but before I spend, perhaps there is a more conclusive test I could try?

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Hi forum, I am having a problem with a very loud popping and burbling from my series 2/3 exhaust. Its a 2 1/4 petrol and the noise is on deacceleration and engine braking, i.e hill decents etc. It also has even less power than normal. At first I suspected the obvious, a blowing exhaust, but on inspection the pipe seems fairly air tight although old. However blocking the end of the pipe with my hand and a rag does not slow or stall the engine at all. I've done some internet searching and many blame timing and fuel mix, but this engine has run very sweetly for 2 years and there is no smell of fuel at the tail pipe to suggest a petrol biased mix. It sounds very 'blowy' and I would like to just buy a new silencer and fix the problem (if the baffles are shot) but before I spend, perhaps there is a more conclusive test I could try?

Have you done a compression test? could be a burned valve seat or a sticking valve, but the engine would run lumpy if this was the case.

Try disconnecting the silencer at the flange next to the gearbox x member, now run the engine (you may have to remove the bolts and replace them with new ones before getting away from the neighbours to do this in a field.)

If the silencer is blocking up the engine will run better without the box attached.

My SIII engine always gently burbles and pops on the over run, been doing it since I built it 6 years ago.

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Just a follow up to thank you for your excellent advice. I tightened all clips and nuts and bolts from the air filter to the inlet manifold and around the carb. Some were loose and some were fine. The best results began when I started on the timing, I loosened the collar and twisted the distributor to the right. The tickover revs shot up, It must have been miles out. I gave it a few degrees back to the left as per some instructions read elsewhere, and the difference is amazing. Much faster, hills taken easily in higher gears than before and no more popping and backfiring, just a natural sounding burble. Also much more positive out of junctions, without that heart stopping lag that might leave you stalled across 2 lanes of fast moving traffic! Looks like the '09 D90 can wait a few more years yet.. :)

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