An interesting note about exhaust popping on deceleration

[legaleli]

I have yet to properly tune my carbs because the long "fuel line" I bought to run the tank from my lift was too big in diameter and the gas leaked from the connection between the hose and the petcock. That didn't stop me from trying to set the mixture though.

Before the adjustment all my air screws were set to 1.5 turns out. I had just completed a full cleaning and 0-ring replacement.

The bike ran ok but had a very occasional "backfire" on idle on #4 or #3 (I think it was 4), a rough idle, and a whole lot of popping on deceleration. I have heard on this board that the popping is often the result of leaks in the exhaust. I assumed in my bike that the popping was coming from a leak somewhere in my exhaust (where I eliminated the h-pipe). Understand - there was a LOT of popping.

I then turned #3 and #4 carb air screws out 3.5 turns and #1 and #2 2.5 turns out. I did this because I had a hunch that I was running lean, and because I could not run my bike with the tank off I could not try out my colortune.

The result - the idle is perfect, there is no occasional backfire, and surprising to me - there is absolutely no popping sound at all on deceleration - the issue is gone.

The only issue is that on mild acceleration and revs around 4-6 k I think the engine is missing slightly - but the minute I roll on the throttle the engine is a monster!

So if you still have popping after sealing up your exhaust - try the idle mixture!

 

[1_v8_merc]

I like the exhaust popping!
Wouldn't give it up for anything!

 

[Steve]

Now that you know you were running lean and have fixed that problem, you might be running a bit rich.

This is when you tweak your mixture screws IN slowly, listening for highest engine idle speed. If the idle speed does not increase, keep turning the screw IN untill the speed decreases, then back it out about 1/4 turn. Repeat for the other carbs.

When you are done, turn each screw in until it lightly seats, counting the turns. Put it back where it was, record that number for future reference. You may find that it will run best between 2 and 3 turns out, so the two that you have at 3.5 turns are only sucking extra gas for you.

.

 

[legaleli]

Now that you know you were running lean and have fixed that problem, you might be running a bit rich.

This is when you tweak your mixture screws IN slowly, listening for highest engine idle speed. If the idle speed does not increase, keep turning the screw IN untill the speed decreases, then back it out about 1/4 turn. Repeat for the other carbs.

When you are done, turn each screw in until it lightly seats, counting the turns. Put it back where it was, record that number for future reference. You may find that it will run best between 2 and 3 turns out, so the two that you have at 3.5 turns are only sucking extra gas for you.

.

Sounds good to me! Also, when I get my colortunes on the go I can see how well the "ear adjust" works vs the "colortune" adjust. I get the feeling the old school way is probably going to win.

I'm also going to sync my carbs after this too.

1_v8_merc - I used to like the popping... but I can't help but think I'm destroying something at the same time! Also there's this little voice in my head that says the popping is because my bike is OUT of tune... and that bothers me!

 

[Turtleface]

Yeah, from what I understand, popping means one of two things, either a lean condition, or an exhaust leak. Assuming your exhaust is tight at the head, and you don't have any giant holes in it, a pop may very well be a lean condition. Which isn't an optimum running condition. Any plug chops yet? That reminds me, I need to pick up a couple sets of plugs this weekend for a nice long tuning session.