Help on backfiring exhaust...

gwamba · Full Member Joined: Jul 10, 2008 Posts: 29

I just purchased a 1978 XS 650SE and got it up and running, with the help of a cycle buddy.
The bike is running well but the 2 into 1 aftermarket exhaust system (looks like the one Mike's sells) is fairly loud and backfires while backing off the throttle...not sure what, if any baffles are still there?

any suggestions out there? I'm coming back into biking after a 25 year absence...my last bike was a 1978 GS 1000 Suzuki, which I sold in 1984.

Retiredgentleman · Posted: July 13, 2008, 8:19 pm Post subject: Re: Help on backfiring exhaust...

The carbs may be running too lean. You could try opening the air/fuel mixture screw 1/4 turn.

gwamba · Full Member Joined: Jul 10, 2008 Posts: 29

Retiredgentleman wrote:

The carbs may be running too lean. You could try opening the air/fuel mixture screw 1/4 turn.

Thanks, I will try that tomorrow! Smile

gwamba · Full Member Joined: Jul 10, 2008 Posts: 29

Retiredgentleman wrote:

The carbs may be running too lean. You could try opening the air/fuel mixture screw 1/4 turn.

Is that what the service manual calls the "pilot screw"?

Retiredgentleman · Posted: July 13, 2008, 11:49 pm Post subject: Re: Help on backfiring exhaust...

Yes, also called Idle Mixture or Pilot Screw.

gwamba · Full Member Joined: Jul 10, 2008 Posts: 29

Tried 1/4 turn richer, then 1/2 turn richer... no change in backfire, just higher idle speed... almost 2,000 rpm...

The headers have a $49 universal muffler on them but there IS a baflle installed...

Timing maybe???
It runs strong though? Just POPS a lot when backing off the throttle...

dpmphoto · Posted: July 17, 2008, 12:05 am Post subject: Re: Help on backfiring exhaust...

check for leakage

Cooltouch · Posted: July 17, 2008, 12:32 am Post subject: Re: Help on backfiring exhaust...

Yeah, usually the popping on trailing throttle is caused by one of two things: too lean of a mixture, or a leak somewhere in the exhaust system. My '81 has the Mac 2-1s on it, and it does the same thing, although not so bad. I'm pretty sure it's the muffler/header joint, cuz no matter what I've tried, I can't get that connection tight. I have an '80 with the same exhaust system on it, and the joint is very secure. Go figure. Guess my '81's system was made on a Monday.

Best,

Michael

bsquared

Can I jump in? I've got the same problem, except I'm using MIkes Commando style pipes on my xs2. I've got some leaking where the pipes join the downpipes, where the clamp is. I ordered exhaust gaskets but, for the life of me, I can't fit them in. The fit between ID and OD of the pipes is so good, the gasket won't fit, and yet, it does leak. Is there some kind of sealant that won't permanently glue the pipes together?
I can live with it, but it is irritating.
Have a great Labor Day!
Peace,
Bsquared.

Mikesxs · Full Member Joined: Feb 06, 2007 Posts: 134 Location: FL

Check the cylinder head pipe gaskets. If leak at muffler/headpipe joint persists apply a bit of high temp silicone seal and clamp it together (let it set up a while before firing up the engine. Retighten after it's got hot once.

Mike Lalonde Mikes XS

.

artie · Full Member Joined: Jul 22, 2006 Posts: 14

after 3 sets of rebuilt carbs I still have this popping problem I run a 2 into 1 mack I'm down to thinking that exhaust restricters maybe the trick thoughts thanks

xsjohn

Mix screws have to be dead on with straight pipes........(BS34) 45 pilot....I use a custom 46...and the mix screws are seldom exactly the same on both sides...when decelerating the mix has to be perfect to feed each stroke correctly.......rich can cause unsteady decel and of course lean will for sure cause it.....set each side independently...........think the stock 42.5 may idol ok but not enough fuel for heavier decelerations.....think 2-1 exhaust causes a lot of backpressure already...?.....not the expert on that but have solved the decel problem for others with a bit bigger pilot....and careful setting of the mix screws.........also they will run leaner when the weather gets cooler.....another catch 22 for sure......and just the smallest movement of the mix screw with larger pilots does a lot once they are close.......

xsjohn

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