the t-mod has to do with the vent lines coming out of the carb. the theory is that if you go in deep enough water and both lines get submerged the bike stalls and won't restart while your still in the water. putting a "t" shaped fitting i one of the lines makes it possible to have the original line go down to the swingarm while the second line coming off of the "t" goes up underneath the seat. i go in deep water all the time and never had that happen but did the mod anyway as i was bored one day.

 

Here is a great link on Mikuni's site on how to diagnose and tune mikuni carbs

http://www.mikuni.com/fs-tuning_guide.html

 

According to Mikuni the back firing in the exhaust is caused by












4: Backfires in Exhaust

Note:

It is normal for many high performance exhaust systems to moderately backfire or pop when the throttle is closed from mid-to-high rpm. In fact, one should expect a well-tuned high performance engine to "pop" and "crackle" when the throttle is closed at high rpm.

The popping is a result of the air/fuel mixture becoming very lean when the throttle is closed and the engine is rotating well above idle speed. It is also necessary that the exhaust system have rather open mufflers.

Why This (normally) Happens:

1) When the throttle valve is in the idle position, fuel does not flow out of the main system (needle, needle jet, main jet). Fuel is only delivered to the engine by the pilot (idle) system.
2) The combined effect of the closed throttle and elevated engine rpm is to create a fairly strong vacuum in the intake manifold. This vacuum, in turn, causes a high air flow rate through the small gap formed by the throttle valve and carburetor throat.
3) Under these conditions the pilot (idle) system cannot deliver enough fuel to create a normal, combustible air/fuel ratio. The mixture becomes too lean to burn reliably in the combustion chamber. It gets sent into the exhaust system unburned and collects there.
4) When the odd firing of the lean mixture does occur, it is sent, still burning, into the exhaust system where it sometimes ignites the raw mixture that has collected ---- the exhaust then pops or backfires.
5) Completely stock Harleys do not do this until open-end mufflers, such as the popular Screamin' Eagle slip-ons, are installed. The exhaust must be both free-flowing and have an open exit for the popping to occur.


Other possible causes:

Air Leaks:

Any source of fresh air into the exhaust system can create or worsen the conditions that bring about exhaust backfiring. The most common entry point is the junction of the header pipes and mufflers. Even a small air leak can dramatically increase the intensity or likelihood of exhaust system backfiring.

A high temperature silicone sealant, as can be found in many auto parts stores, may be used to seal the pipe/muffler junction.

Lean Carburetion:

While exhaust system popping may be considered normal, it is certainly made worse by an overly lean idle circuit.

Be sure that your carburetor's pilot jet is the correct size and that the idle air mixture screw is correctly adjusted before looking for other causes of popping. The procedure for adjusting the pilot circuit is covered in the Tuning Manual.

Ignition:

If exhaust system popping is very loud, irregular and accompanied by loss of power, then you should suspect that the ignition system is not performing as it should. If, for some reason, the ignition sometimes fires at the wrong time, then exhaust popping can become very energetic (loud). Look for failing high tension leads (plug wires), failing ignition coil(s) and especially switches or connectors as possible causes.


I think i am going to increase the pilot to a 40 from 37.5 so the idle circuit has more fuel when closing the throttle and see how it works. Hopefully it is the ticket to take care of the backfiring. I think I might have to drop the main as well as the guy I bought the carb from when running a big bore 331kit, something I dont have.. One thing at a time though.

 

My set up is 142.5 main, needle on 3rd clip, pilot as shipped to me from Bill fuel screw out 1.5 turns.
Result?


Other factors are, 300 kit fitted, BG full system, no air box lid and altitude is sea level.

I was told that this was a good result.

I find a slight on/off affect when operating at 0 to 1/8 throttle position.
Not sure why and the Dyno guy didn't notice anything.
It may be normal.
It may also be that compared to the "soft" standard carb set up, the extra spring tension combined with the heavier action the Vortex throttle gives, it's just a feel thing.

 

To plug the the hole where the smog crap goes just go to an auto parts store and find a pack of variable sized vacuum pump plugs. You need two different sizes to plug each side of the smog system you are removing.

 

Is the purpose of that tube to act like a pcv valve? What is the big diaphram looking deal that comes off it and plugs into the top of the stock carb?

 

The stock carb has a connecter which has a throttle position sensor on it. The tps is used for spark advance. When you remove the old carb and replace with with the Bill Blue carb you have no where to mount the TPS sensor. No TPS sensor=no spark advance. How is everyone getting around the fact that there is no more spark advance with the Bill Blue carb?

 

I took my bike to the pros, aka the kawasaki dealership. Here is the break down. With the air box lid on and big gun pipe installed, air injection tubing removed the carb was set at 127.5 main, 37.5 pilot, and af screw 3.5 turns out.i forgot to ask what they put the jet needle at. It runs pretty well. The pipe is dirt bike loud but sounds killer. I am happy.

 

Can't help.
Aus 06 didn't have a TPS.

It's interesting how different the various country versions are.

What I had to deal with was the stock carb had a de-icing circuit and the Mikuni pumper doesn't.
I just pulled all the hoses, thermostat etc off, blocked the hole in the engine with a short bolt and blocked the hose at the other end.
I had to laugh though, carb de-icing here in West Aus?

 

That's exactly my setup. What's your altitude?