Strange noise from exhaust.

Dixie6789 · Post by **Dixie6789** » Sun Mar 01, 2015 4:48 pm

This is a strange one.

My engine at tick over, through the rev range and full chat is silky smooth. No rattles, not tapping, no ticking nothing. Just that fabulous roar.

But when I rev it and then let it fall back to tick over I get a funny noise. Not a metallic noise, but I kind of fluttering or chattering/puffing noise. Almost like air being drawn back up the exhaust on the last throws of the rev up just before it goes to tick over.

Doesn't do it on the rev up, doesn't do it at any other time, other than when it goes to tick over from being revved, then goes quiet and is silky smooth.

Very odd.

Has anyone else had this?

Mark

Ian Anderson · Post by **Ian Anderson** » Sun Mar 01, 2015 5:55 pm

Sounds to me like unburnt fuel getting int the exhaust and then catching on fire

Add a spark and you would get a backfire of note

Presuming here that u are running carbs

Ian

ChrisJC · Post by **ChrisJC** » Sun Mar 01, 2015 5:57 pm

Carb going too lean on overrun? (is it carb?, I forget)

Chris.

Dixie6789 · Post by **Dixie6789** » Sun Mar 01, 2015 7:16 pm

Yep, its a Eddie 500 carb.

Runs perfectly, doesn't bog, doesn't miss fire. Sounds lovely and goes like a stabbed rat.

Should I try and richen up the idle?

Mark

Have a look at my video. 3 minutes in, small burn out at the Bath and West. limiter coming in at 4000 rpm.

8 mins in. Another run up the straight at Bath and West.

mgbv8 · Post by **mgbv8** » Sun Mar 01, 2015 10:45 pm

Mark !
Why is your limiter set to 4000 rpm ?

If its on stock hydraulic lifters I would set the ign cut to 5500rpm ?

If you have the limiter set that low and rev the engine you will no doubt be chucking unburnt fuel into the exhaust system.

Perry

Dixie6789 · Post by **Dixie6789** » Mon Mar 02, 2015 10:41 am

Hi Perry.

Only set that low due to new engine. Its only done 156 miles, so put a "Acuspark" rev limiter on it. Will slowly increase it to 5500 when I have a few more miles on it.

Using standard lifters, on a "Stump Puller" cam.

Mark

ChrisJC · Post by **ChrisJC** » Mon Mar 02, 2015 6:25 pm

SU's used to sound like a farting weasel on overrun. I associate it with Morris Minors.

Have you a lambda sensor or anything that will tell you what's going on?

Chris.

Dixie6789 · Post by **Dixie6789** » Mon Mar 02, 2015 7:20 pm

No Chris. Nothing, only ears.

I used a 82 jet and a 65/47 rod. Was going to get a exhaust analyser on it to see what it is doing.

Car runs well, doesn't smell rich, and runs well at all revs, so motor cant be far out.
M

Baracus · Post by **Baracus** » Mon Mar 02, 2015 8:30 pm

I had something that sounded similar when i had 4 or so broken inner valve springs on my double valve spring setup. The lifters on the affected cylinders were pumping up when revved, which gave that sort of odd sound on tickover for a brief second until the lifters bled back down again.