exhaust pops

[Alf]

You cant imaging how much time I´ve been keeping a battle with the pops & explosions when closing the throttle when riding hard
It is a long war that started with my 1st FJ 1200, 18 years ago!!!! My tunned 1100 didn´t do that. When rebuilding and cleaning my carbs last week to change the emulsion tubes I renewed float bowl valves & seats, jets....everything new inside the carbs, so I try again resolve the problem

At the moment that I fit race cans or a 4/1 exhaust in a FJ1200, I have the pops & explosions with me

Today i´ve been testing 45 pilot jets. The pops were reduced to virtually nothing, only on very hard downshifttings with the brake applied on. And then there was only a occasional explosion. BANG!. But... (a very big BUT) the bike doesn´t maintain the idle below 2000 rpm

My carb settings: FJ 1200 3CV european spec
Dynojet kit: needles, holes drilled, springs....
Dynojet 104 mains
42.5 pilot jets (obviously the 45s don´t work)
Std pilot air jet
Open airbox (big windows opened at the sides) with KN filter
Open cans with open exhaust pan
5º factory advancer

Everything is correctly fitted. There are no vacuum leaks and the bike runs like a dream, accelerate in 5th from 2000 rpm until the red line like a missile

Any idea or the pops at the exhaust are produced for the valve overlap and it is impossible to fix?.

[Mark Olson]

drop the level of your floats by a small amount at a time and it will go away.

I had this problem as well and was resigned to deal with it on hard engine breaking when I learned of this trick.

If you have raised the rear of your fj it gets worse.

[Alf]

Thanks. In fact is a little complicated trick, because, how I bend the little tang exactly the same in the 4 carbs?, and how much?
Now those are set exactly the same, OE level
And yes, I raised the rear in my FJ. But the pops were there then. But sounds logic, Mr spoke 
Thanksagain. Next week I´m going to dissasemble the carbs again and I will try 

[RichBaker]

A little bit of popping on decel is normal to a properly tuned engine with open exhaust, it's caused by the rich mixture which is the result of the high vacuum produced when the throttle is closed at high RPMs. When the rich fuel mixture hits the cold, oxygen-rich air outside the exhaust, it ignites.... trying to tune the carbs to eliminate it only causes the engine to run poorly. Later-model (NOT FJ) carbs have a "coast" valve built into them, which actually shuts off fuel to eliminate this popping..... both my '97 Suzuki Intruder and my '03 Yamaha WR450F have these valves. I blocked the one on the WR off, because it causes other problems and I prefer it that way.... She runs much better without the fuel cut-off.

I consider the popping, "burbling" on decel as the bike happily laughing when being run briskly through the twisty turns.   

[Alf]

drop the level of your floats by a small amount at a time and it will go away.

so do I have to bend the tang to reduce the fuel level?

[Alf]

A little bit of popping on decel is normal to a properly tuned engine with open exhaust,........
I consider the popping, "burbling" on decel as the bike happily laughing when being run briskly through the twisty turns.   

Really, my 1200 FJs are the only bikes that have had that popping. No other bike I´ve owned has had that problem, included my ex-FJ1100, or bikes that I´ve tunned for my friends. My present CBX750 with 4/1 Mac race can, Dynojet, KN... don´t pop too

[Pat Conlon]

so do I have to bend the tang to reduce the fuel level?

Hola Alf, yes.

To lower the fuel level in your float bowls (by raising your floats) you need to physically bend the tang (down) just a little bit at a time, be gentle.
Measure often. Get all your floats within 1mm of each other.  Cheers!

[andyb]

Wear earplugs and tune the carbs to perform optimally.  Meh!

Even things like ferrari's burble on decel, it's a normal thing.  Repack your muffler, stick earplugs in, and ride it!  The easy way to prevent it is by leaving the stock pipe alone.

[Alf]

Thanks. Done today. Not still tested cause my choke cable is near broken, so I´m going to get a new one
I will inform
cheers

[Alf]

Wear earplugs and tune the carbs to perform optimally.  Meh!

Yeah, good solution. And its an easy one!

And I prefer the brubling before the OE silencers, thanks

[yarin]

good luck with that choke cable.  i searched everywhere for a new one.  i finaly found Boats.net to be a great source for OEM parts. has microphish. it took two weeks but i think it was only 25 dollars.
Tommy

[terryk]

I got my choke cable for the 87 FJ from Yamaha, no problems.