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Exhaust popping

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

Exhaust popping

Postby St George » Wed Aug 05, 2015 5:23 pm

We all know the sound of a Lammy exhaust popping when the throttle is closed. Mine is popping much more and faster than all the other scoots I hear. Does anyone know why. I am running Stage 4, 48 mm Rayspeed and a 30 mm carb.
Many thanks Colin
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Re: Exhaust popping

Postby Rich Oswald » Wed Aug 05, 2015 10:06 pm

Either your tickover is set too fast or you have an air leak,

Rich'
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Re: Exhaust popping

Postby coaster » Wed Aug 05, 2015 11:48 pm

St George wrote:We all know the sound of a Lammy exhaust popping when the throttle is closed. Mine is popping much more and faster than all the other scoots I hear. Does anyone know why. I am running Stage 4, 48 mm Rayspeed and a 30 mm carb.
Many thanks Colin


Do you mean sounding like a machine gun? if so that is called 4 stroking and all 2 strokes do it to a greater or lesser extent. It's due to running slightly rich at that particular spot on the throttle travel. Tuning the carb might help.
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Re: Exhaust popping

Postby St George » Thu Aug 06, 2015 5:08 pm

Thanks Coaster, must admit I thought that it was a bit rich on the pilot, bit hesitant low down ( Farty ). Otherwise it is flying along and starting well. Cheers lads.
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Re: Exhaust popping

Postby Scooterlam » Thu Aug 06, 2015 6:18 pm

If you down jet the pilot do a couple of plug chops in the area where it goes from pot to the non tapered part of the needle.
a rich pilot can mask a lean spot in this area.

Just don't ask me how I know.
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Re: Exhaust popping

Postby CHRIS in MARGATE » Fri Aug 07, 2015 9:00 am

I keep mine a little richer at that point and the 4 stroking helps when coming down hills off throttle with a few quick blips to ensure that a nice rich mixture is cooling the engine.
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Re: Exhaust popping

Postby St George » Sat Aug 08, 2015 5:50 pm

Thanks Chris. How are you keeping.
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Re: Exhaust popping

Postby CHRIS in MARGATE » Sat Aug 08, 2015 8:35 pm

I'm well mate. Went to the Worthing Music Mania rally fortnight ago, my 4th year running. Got soaked going and soaked riding home. Slept in damp clothes in a sleeping bag and now have bad chest !!! Scooter ran brilliantly for nearly 250 miles.
Went our last Thursday and was racing a couple of the other guys down the Thanet Way at a true 70+; up the hill a mile from home doing 30 and rear shocker snapped clean in half. Terrifying!!
Apart from that very well. Lots of scootering but camping at 60 is getting more and more uncomfortable.
Very little sympathy from my wife though.
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