Can't find the leak

[Guest]

1982 GS450L

running really well for years when sudden onset of popping / backfiring from exhaust on deceleration a few weeks ago.

Done so far:

-carbs dipped for full 24 hours & new o-rings throughout.
-intake boots are newer (<3 years) as well as the intake O-rings (checked them & they are still soft/pliable).
-valves are all in spec (checked 2 months ago).
-air filter is oiled & seated correctly.

-bike starts easy, idles well, revs all the way up.
-plugs show it is running lean.
-mixture screw settings did not change.
-tried water spray and carb cleaner to check for intake leaks and neither had any effect on RPMs.
-cannot find any exhaust leaks (felt around and also used body powder).

I'm now at a loss and need suggestions for what to try next! Thank you!

[GregT]

If your model has centrifugal advance for the ignition, check it's moving freely and no springs are broken.
It'll be under the cover on the RH end of the crank.

[mrules]

checked. it is moving freely and no broken springs.

[GregT]

Not a common problem but have a look at the carb diaphragms - hold them up to the light and check for splits.
If one is split, it'll let air in under deceleration.

[mrules]

i examined those thoroughly when I had the carbs apart to dip them and they were in good shape. Thanks for your suggestions!

[LAB3]

The only other thing that comes to mind is an exhaust leak either at the head or crossover pipe. On my bike the pilot screws like to be tweaked when the weather gets warmer and again when it cools back down this time of year. If you put them back in the position they where in before the cleaning you might want to give those a tweak just in case.

[GregT]

I had a similar thing with a racebike. It'd always popped on the overrun - not a problem on track so I never did anything about it.
When I recently rebuilt the bike, I deleted an additional breather which was on top of the cam cover.
It now no longer pops on the overrun...I can only assume it was sucking air through the valve stem seals.

The 450 breather is on top anyway but it may be worth checking to see if the gauze packing in the top compartment is still there.

[fastbysuzuki]

With all the work you have done and the checks made then I would bet on an exhaust leak.

[mrules]

went to drop the exhaust to check it thoroughly for holes and take a look at the gaskets and a bolt on each header was LOOSE (which might have been the problem all along) and this awesomeness happened.

There is about !/8" exposed. Not sure I can get at it straight enough to use an extractor.

Any tips on getting those gaskets out?

[GregT]

Gaskets will lever out with a small screwdriver.

I wouldn't bother with an extractor for that broken bolt. There's more than enough there to weld another bolt onto it - and simply wind it out.
The heat of welding expands the head nicely and makes it easy.

[fastbysuzuki]

If you have a welder then there maybe enough stud/screw left to put a nut on and weld it, or weld another stud to the broken one, then applying penetrating fluid,heat and taking it slowly.
as for the gaskets tapping a screwdriver between the gasket and head (carefully) when it's under the gasket and hits the solid shoulder twist the driver so it collapses the gasket pull out with plyers.

[mrules]

I don't have a welder, nor do I know how to weld. Will have to try to find someone who can come to me.

[Burque73]

If you feel lucky you can grind a slot in that bolt with a dremel and use a large flat screw driver to unscrew it. It may break though and then you're even worse off than now.

[mrules]

got the bolt off (neighbor with a welder)! new exhaust gaskets (and studs) and problem not solved. pulled the carbs to double (triple) check for any potential sources of air leak, and found that the intake side of the carb (and into the airbox) was wet with gas. this was a few hours after running it. no gas in the crank case or leaking from anywhere. pulled the hose off the carb suction nozzle and the nipple was wet too. assuming the float heights are set right and the float needles are good (i checked them when I pulled the carbs apart to dip them, and checked them again on reassembly):

1) could the gas be from anything other than the petcock (coming down the suction tube); and

2) could that be causing the popping / sputtering (happens mostly on decel, which I thought was a lean condition problem)?

even with all the apparent excess gas, bike does not seem to be bogging. but I am boggled.

[chuck hahn]

decell pop can be from gasket leak where headers insert into the pipes...sucking in cold air