Engine - minor popping backfire - video

[Elliott99]

Hi Guys,
Hoping someone can suggest what to do next?
I have a 1970 T2 with a just run in 1776 engine, twin IDF 40s,and Vintage Speed exhaust.
Symptoms: continuous sporadic low popping noises from the exhaust, just audible between the firings. A really loud backfire one or two seconds after I turn her off. The exhaust smells as if its running rich, and is coloured black. However, the colour of the plugs says the mixture is exactly right.
I suspect that unburnt fuel is getting through to the exhaust, and today did a leak down test which gave 1 and 3 showing 20% leakage, and 2 and 4 showing 10%, which I believe is a pretty good result.
You can just hear the popping noises in the video if you listen hard.
Any ideas on what to do next please?

Elliott.
[photobucket] [/photobucket]

 

[K@rlos]

Check the timing.

 

[Matt_B]

Worth investing in a rolling road session too to get it really well tuned.

 

[ozziedog]

Second that,, ^^^^ timing, check the timing, sounds like he`s getting hot as well, that nasty backfire is funny on the movies or someone elses car but can cause a hell of a lot of damage, I`d also check the float levels are spot on.

Ozziedog,,,,,,,,,,,,,,,,, Bang :mrgreen:

 

[Trikky2]

Sounds to me like its running a bit lean on one of the carbs. Try adjusting the mixture screws slightly for max rpm. If the tickover speeds up then you have found the problem.

If adjusting the mixture does not speed up the tickover eg. they are already at optimum, then it sounds like the carbs are not correctly synced or you have a minor air leak.

 

[Trikky2]

Oops double post

 

[Elliott99]

Thanks for all the suggestions, much appreciated.
I have checked the timing, it is sitting at 30 degrees advance at 3000 revs with the vac advance disconnected and blanked. It has an Accuspark electronic ignition fitted, but the symptons did not change when I fitted it. Haven't checked the float settings yet, although looking down the tops of the carbs with a mirror, whilst it is running, there is no sign of any fuel landing on the top faces of the butterflies. I will try the WD40 leak check next, and then Trikky2's mixture screw experiment. Next stop the rolling road!
Thanks again to all of you,

Elliott.

 

[Elliott99]

Trikky2, you were spot on! The mixture screw on cylinder 1 was too lean, tweaked it and the misfire went away!

I will get it on a rolling road asap, and get things set up properly.

Thanks again!

Elliott.

 

[Trikky2]

Trikky2, you were spot on! The mixture screw on cylinder 1 was too lean, tweaked it and the misfire went away!

I will get it on a rolling road asap, and get things set up properly.

Thanks again!

Elliott.

Glad you got it sorted :mrgreen: