Tip for finding exhaust leaks. Exhaust popping.

[MotoBug]

I was shown a great little trick today for finding air leaks in your exhaust system. My bike has decel popping with both the stock and aftermarket mufflers.

To find the leaks get a length of plastic tube ~12mm diameter, I used one from an old Camelbak water bag but home brew types are sure to have something similar lying around.

Start the bike and put one end of the hose near your ear and the other end you use like a stethoscope near/around all the joins in your exhaust system starting at the header. If it's leaking you can hear it chuffing away plain as day. I suspected my muffler clamp area was leaking but was surprised to find my 5 month old V7 had leaks at the balance pipe joins as well.

I got this tip from an 83 y.o relative who before retiring used to make manifolds and exhaust systems for sports and racing cars.

[pete roper]

And while it may have a minor contributory effect on your bike it is generally an irrelevance.

The reason why modern Guzzis pop on the over-run is because Marrelli keep the idle fuel turned on at minimum TPS value at all rpm. At certain points as it slows down the engine will start 8, 12 and 16 stroking and when it does ignite a charge in the cylinder the exiting gasses from that cycle will ignite the previously unburnt charge in the exhaust causing the backfires.

The parameters and effects of FI and Carburetted engines on various phenomena are entirely different. Your relative's advice is fine for a carbureted motor but you can't apply the same logic to a MM fuel injected one.

Having said that air leaks are never good, especially on a bike using an O2 sensor to trim fuel but don't expect a miracle cure to backfiring on the over-run by sealing your exhaust perfectly. Also make sure you use a sealant that is O2 sensor safe.

Pete

[MotoBug]

Points taken Pete. I'll suck it and see And report if any change after tightening and sealing.

[rodekyll]

I'm chasing a popping on overrun too -- up to 2800 rpm, when I roll off or am riding 'easy' in a 25mph zone, it's embarrassing and damaging to the engine.  I've even shortened the life of my ATF drivepiece (that nasty hex shaft they cursed Convert pumps with) by those tiny, intermittent chugs.  After triple-checking the engine baseline (valves, etc), tps baseline, the tb synch, re-positioning the ambient air temp sensor, and "exhaustively" checking for leaks at the pipes, the popping continues.  Having eliminated all else, it must be map-related.  I'm working with Beetle on converting a 15M ecu and attendant subsystem from 1100 Hydro specs to fuel a1200 Breva.  It's a little out-of-the-box (which is why it's fun!), so we expect a few false runs at it before getting it right. 

One thing that Beetle and I agree on is that you can't really develop a good map if the other pertinent systems aren't completely Skookum.  Ok.  Beetle doesn't know what Skookum means, but he knows what it is.  So I've suspended his effort until I KNOW the rest of the specs are correct.  Otherwise I feel that I'm wasting his time and talents.  I wonder how many folks who aren't getting the results they expect from his maps are trying to use them more like Power Commander band-aids to mask unrelated problems.

My point is, that even if there is no significant effect from any one little detail being out-of-spec, the accumulated effect of a bunch of things being a tiny bit off can have a big impact on the overall performance and drivability of the machine.  I don't think time checking and tweaking the little things is wasted.

$0.02