Burbling and Popping on over-run.

[wasserleaker]

Fitted my new VW Speedshop stainless exhaust today, four hours of sweating and swearing, mainly getting the old buggr off, and on the whole, very pleased with it, a bit 'frutier' sounding, but not too loud or chavvy.
been getting some burbling and popping noises tho, on over run/coasting off the throttle, which it never used to do before, re-checked all bolts are good and tight, and gaskets sealing properly, will it be an air leak, or incorrect fuelling now the exhaust is letting the engine breathe more freely?
i know some people like the sound, but to me it just suggests that there's a problem, any help would be great!

[ricicles]

poss fueling if popping. mine was doing it after being put away for the winter, had the carbs set up again and improved things then checked the plugs and replaced and all is great again.

[armyphil]

i'd leave it love hat sound. But it does usually mean a fuelling problem

[VWCamperfan]

If you have less backpressure and you run an engine with a carb then you will have a leaner mixture if your exhaust system is now more free flowing.
Don't ask me to explain this one... It'll take up a whole page... It's just how it is!

Richen mixture slightly and you should be ok.

[toomanytoys]

Even a small air leak on the zorst will cause popping.. it wont show as a leak for a bit until a bit of carbon has "stained" the area... but also if the mixyure is a little weak and worth checking ignition timing is set correctly..

[wasserleaker]

thanks for the replies.
have retightened all exhaust nuts/bolts today a couple had loosened very slightly since fitting, no early signs of sooty deposits to 'telltale' of an air leak yet, pretty sure its all good and airtight. checked the sparkplug colour though, and they're white, which indicates a weak mixture. they were always a nice light brown before the exhaust swap, as you say, Camperfan the free-er flowing exhaust/less back pressure must have caused this, it a DJ, Digijet inj. engine, am i right in thinking the CO level screw only adjusts the mixture levels at idle, and not throughout the rev range, or have i got that wrong, and this will richen the mixture at all speeds?? if so i can get the friendly MOT man to tweak it while hooked up to the CO meter hopefully, just worried about driving it with a weak mixture incase it damages anything. will also change the temp sensor when i can find a vw van centre to get one from near me that hasn't closed down like the derby and nottm ones have!
oh... checked timing as well and its still spot on

[toomanytoys]

Plug colour on petrol or LPG?
prob want to open the "power valve" a 1/4 to 1/2 turn to richen it up a bit...

Digijet adjusts fuel to air flow.. so less back pressure should = more airflow thus more fuel...

Temp sensor? is it one for the Fi??? was this faulty and the plugs checked before the exhaust change?? Brickwerks has temp sensors in stock now...

[wasserleaker]

Cheers, Toomanytoys.........
the plug colour is when running on petrol, ( after a run and not after sitting at idle,) as the gas system is out of action for now (filler relocation and other work planned)
and yes, the coolant temp sensor for the ECU signal is the one i have had doubts about, (blue one on the side of 'stat housing) before the exhaust change i had occasional starting and rough running probs- timing, plugs, throttle pos. switch adjustment, and dist cap, rotor all tested and fine, so would like to change the temp sensor, if only to elliminate it as a poss cause of the occasional reluctant start/rough running warm up.
will get one ordered from Brickwerks, had a thought regarding poss air leaks.... all the plugs are the same white colour, if an air leak was present, would it only affect the plug/plugs at the cyl, or cyls with the airleak on its port?
its unlikely all the ports have an air leak which makes me think the mixture is a more likely culprit. if the engine is revved to say 4k while stationary and left to slow again to idle, the popping and burbling happens as well as when decellarating. still not sure wether the CO adj. screw only affects idle richness levels, or the whole rev range?
think i may replace the sensor and see if that cures things, and go from there.

[Fritz]

Dear Wasser, we have been running one of these VW Speedshop/LA Performance systems for just over a year and so far so good. I did take quite a bit if time making sure every joint was secure and have only recently stopped checking it on a weekly basis.......

As peeps have suggested check your mixture and make sure flange faces are square with the heads, and the back box gasket is adequate.....

Good Luck,


Regards,


Fritz,,,,,,,,,,,,,,,,,,,,