Diagnosing exhaust leaks By jjoshua20213 (Read 728 times)

[jjoshua20213]

When i put on my bbk, I don't think I ever put the exhaust pipe back on right.


A metal peice (Gasket?) fell out when I took it off. It looked dis-formed.

The bbk came with a brass looking O-ring that fits perfectly into the port where the pipe plugs up to, but the piece that fell off looks completely different, its round and kinds flat....


I put that piece in today, but still suspect a leak.


When I put my finger over tail pipe shouldn't it push my finger off?

If not where do the gasses go?

When I do it the engine bogs down dramatically but not completely. And I hear a sssssss noise. Due to the fan being close I can't tell where the sound is coming from or feel for air. I haven't held my finger there long enough to find out, all I need is another problem

The pipe gets extremely hot fast and theirs a decent amount of hot air coming out.

After I put that new piece in I smelled what was a cross from oil to carbon burning and a little smoke came out the exhaust for like 3 secs.


What do you think?

[jjoshua20213]

Also when its decelerating fast I think its backfiring? Its not a loud pop like a gun shot, put a a few low pitch pop, pop. I thought I was too lean but, messing with the mixture screw dident change anything accept when set to too lean it does it more.

[rob63]

The popping could be due to a leaky gasket, instead of putting your finger over the exhaust hold something like a bunched up rag over it to block it completely. I generally stick the sole of my work boots against the hole as it`s quicker. The engine should die eventually as it can`t breathe. There are a few types of gasket, the copper ring, and a ring made of metal and fibre which has a flat face. Both do the same job.
It could be that the exhaust isn`t correctly mated to the cylinder, loosen the mounting bolts a couple of turns and the exhaust nuts at the cylinder. Give the exhaust a wiggle then re tighten the nuts at the cylinder first, then re tighten the mounting bolts last.
If you need another gasket there`s loads on ebay under '139qmb exhaust gasket'.

[Alleyoop]

Yes popping on decel it running lean and if it is not at very low rpms coming down to idle, it it most likely the Exhaust is leaking by the Flange where it attachs to the motor. When you put on a new gasket or putting attaching it to the motor you put the two nuts on and turn one nut up SOME then the other NUT and so on. You want it to come up even so that that gasket tightens evenly otherwise it will push the gasket to one side that you tighten down on.

The TRICK IS TO it up evenly then give them both a nice tightening.
Alleyoop

[jjoshua20213]

Thanx!

So Rob63 confirmed that the metal piece I was using is a gasket.


Lets say that the gasket looks like a cooper ring.(Non flat) It fits perfectly into the exhaust port;without exhaust hooked up and holding it in.

Is this the correct placement?

When I place my hand over a car exhaust it makes a hissing noise but builds up pressure and I can feel it pushing my hand.

When I put my finger over my scooter's exhaust it makes a hissing noise, but does not build pressure and push my finger off. Is that normal? Someone told me it could be valves. BTW the car has a brand new exhaust system done by a pro. When I installed my bbk I did not did not adjust then right away and it would not start.(Too tight) When I did it started. Did I bend a valve or valves? I re-adjusted my valves by eyeball, but their over .006 maybe .007 possibly .008 without ticking or any noises. I'm gunna un and re-righten the bolts accordingly, and post back.

[Alleyoop]

Yes, the ring should fit the indentation built in the head of the motor. Then when you tighten up the FLANGE it squishs it a little and seals around it.

Adjust your valves correctly, just go and get a set of feeler gauges at the auto parts store.
Make sure the set has feeler gauges with .003 .004 .005 some sets start at .008 which is to WIDE of a gap.
Alleyoop

[jjoshua20213]

I have a gauge, but one day when It was getting hot outside, it died and seemed to loose compression, so I did a quick readjustment eyeballing. Later I found out it was not getting gas correctly. Should I set them back? Also thanx for confirming my installation of the gasket. When I put I put my finger over the exhaust pipe, it should build pressure and try to push my finger off like the car right? I didn't hold my hand long enough to build too much pressure in the car. Didn't wanna mess anything up. I was able to rev my the bike without it building pressure.

[davec]

Hense the term "Crush gasket"

[jct842]

I suppose you could squirt a little oil in the carb intake to get it to smoke then try to plug up the tail pipe while it is running and see if you could see where the smoke comes out. Be aware you might foul the spark plug though.

[jjoshua20213]

I got a separate hose and unplugged the fuel pump vaccum and used the hose to suck in the oil. Leak was at manifold. The exhaust won't reach the mount holes on the bike. When I first put it on I had one screw in to hold it up, thus not lining the manifold up correctly. I guess the bbk's exhaust port was further out then stock. Not when I plug the exhaust hole she builds pressure and dies :-) Thanx for the help guys.

[gilbertbarocio]

My scooter sounds like a mini Harley Martinez what could be the issue to this awesome sound of this Harley sound

[jjoshua20213]

When I take off my airbox, mine sounds like that. Have you changed the stock air-box or changed or gutted your current exhaust?