Exhaust Popping On Over-run

[Guest Mike G]

Hi guys

My Exmo (1600cc Pinto) seems to be making an increasing amount of noise from the silencer. No problem with that you might say! However, I thought I had better check it out, in case there might be penalties elsewhere. The noise is 'popping' when slowing down, and my foot is off the accelerator - usually called the 'over-run' I think.

 

I believe the usual faults are leaks at the exhaust or inlet manifolds, or poor seal between exhaust pipe and silencer, maybe even ignition timing. The silencer is a fairly modern Custom Chrome job. I don't think the problem is with any of these, but could it be with the carburettor settings? This is a Weber 28/32, which I had reconned a few years ago.

 

I was thinking that maybe I have tweaked the pilot jet screw too far, and the engine is getting a weak petrol/air mixture. From Haynes, it is difficult to decide which way to turn the screw to richen it up - clockwise or anti-clockwise? I've got the engine to tickover quite happily, and it pulls away OK, so what else?

 

Anybody got some ideas, please?

Cheers

Mike G

[niduncan]

I had the same problem on a 2.0l pinto which was caused by valve seat regression. It was a leaded head and I was using unleaded petrol with the magic tin pellets in the tank (which don't work). The exhaust valve seats had worn, the valve clearances on a couple of valves was zero so the valves were not closing completely. Lots of popping from the exhaust and the odd backfire as well.

 

Cured by fitting an unleaded head.

[Guest docter fox]

mines always popped, suspect a leak on the exhaust downpipe to be causing it but I kinda like it

[Guest crwoodford]

The 2Ltr Pinto in my Sub K does the same? I thought is was normal? Changing down from 4th to 3rd and then to 2nd, the engine/exhaust pop's on overrun?

 

To be honest it sounds quite nice I also occasionally get a small backfire when I turn off the ignition?

 

I know the timing is correct because I recently checked it courtesy of Trevor2B's timing light.

 

I was told by the guy I bought it from that it was an unleaded engine and therefore uses unleaded fuel, the doner was a 1988 Sierra. Is there an easy way (externally) to tell if the engine really is unleaded?

 

Col (Taunton)

[Guest paul091085]

Can it not be caused by the mixture being to rich and the popping is the unburnt fuel in the exhaust?

 

My brother used to have a nova and the only way to get the car running well was to run it rich, which in turn meant a lot of exhuast popping.

 

Must admit i also like the noise, so wont be doing anything to change mine

[peter_m7uk]

Col, check this: Pinto ID,

if you want to tell whether your engine is unleaded.

 

Pete

[Snapperpaul]

Could it be simply that your silencer has got a bit light on its stuffing?

[Guest hypermick]

Mike,. have the mixture checked properly, ( spark plugs should be a nice mid beige colour - if theyre whiteish theyre either wrong grade or youve very weak mixture) the result of which could ultimately be burned out valves. The worst scenario is melted pistons !

Check all inlet and exhaust joints and gaskets thoroughly especially the flange gasket on the cast manifold(if youre still using it ? )

 

 

Mick

[Guest charlyfarly]

My 1600 Pinto EXMO has always done that since we got her when she's in tune.

 

And thats a rebuilt engine and tuned by a mechanic most times.

 

Its also a non-unleaded vintage running now on unleaded with the Castrol valve seat protector (when I remember)

 

To be honest I thought it was normal of a decently tuned carb engine losing a little excess fuel throught the exhaust as you come off the throttle and the carb takes a moment to catch up and settle, especially with a short single silencer exhaust as apposed to the longer 2 or 3 box systems on tin tops.

 

And it sounds great...

[Guest Mike G]

Thanks guys

On reflection, I am wondering whether it is the stuffing (or lack of it) in the silencer. Although I have fiddled with the carb pilot screw a number of times, for this problem to gradually get worse (or better -depends on your point of view!) the silencer could be the obvious culprit. It makes a nice noise, which if I am honest has been getting louder. I'll check out the other points just in case.

 

Thanks for your ideas

Cheers

Mike G

[Guest vacinc]

same here, has always did it, i thought it was normal ? does run a bit rich, and the box does need repacking, and it is an leaded head, but it does sound good ?

[Swan Jnr]

its a lovely sound.

Ifit ever went away i'd miss it!

 

paul

[Guest chris brown]

I am wondering whether it is the stuffing (or lack of it) in the silencer.

I think you are probably right Mike. Mine with the RHE box got so it did it every time I lifted off until I repacked it. Then it only did it occasionally but now with the wonoff fitted it only does it if I don’t take my foot right off the pedal.

[Guest Bob Green]

If all is well with carbs setting, gasket joints and the like, you may still experience popping from the exhaust. I had this with a 172 bhp Pinto in a Westfield,

 

I fitted a wasted spark MegaJolt 3D ignition system and the popping went away. This is due to the “double” spark burning all the fuel which in turn stops the hot exhaust system igniting any unburnt fuel coming through.

[Guest Battery Bill]

Paul

its a lovely sound.

Ifit ever went away i'd miss it!

 

I agree, whats the problem