Carb Cleaning

[Triumph GT6]

Carb Cleaning.

Having removed the tank the fuel inside was cloudy on draining the float bowl that was full of crud plus black solids. The tank now also needs cleaning although I took out the battery box, it only moved the air filter about 25mm.

I heated up the boots to get them off also thinking of splitting the upper frame to gain safe refitting.

[FJ1100mjk]

Carb Cleaning.

Having removed the tank the fuel inside was cloudy on draining the float bowl that was full of crud plus black solids. The tank now also needs cleaning although I took out the battery box, it only moved the air filter about 25mm.

I heated up the boots to get them off also thinking of splitting the upper frame to gain safe refitting.

I always took off the whole subframe when I pulled the carb bank. So much easier to remove and install the carbs and airbox.

Yea, its some work to remove the subframe, but if the bike is needing a bunch of work (cleaning and greasing shock linkage, cleaning the main electrical ground, ...) that has not been done in a while, removing it provides easier access. And once done, you won't need to go in there again for a long time. Maybe never again, if you don't own the bike for that long.

Be prepared for the proponents of air filter pods, and their reasoning for taking the OEM airbox and throwing it in the trash.

[Triumph GT6]

Thanks for that, seen that mod what is the main benefit of individual pods in relation to performance.

[CutterBill]

I always took off the whole subframe when I pulled the carb bank. So much easier to remove and install the carbs and airbox...

+1  Honest, it's just not that hard (to remove the subframe.) Might be a little head-scratching the first time you do it, but after that, it's quick and easy. And you can clean everything.

As for the OEM airbox design vs. the foam filters... I'm no expert, but knowing just a little bit about intake and exhaust design, when I saw those long flared rubber inlet ducts and the large volume of the airbox, my first thought was "Yep, those Yamaha engineers knew what they were doing." (Hint: bottom end torque) Your mileage may vary. Feel free to disagree. Carry on...   
Bill

[fj1289]

Compare the FJ air box to any of the newer 1000's-1400's and you wouldn't call it "large volume"!

Some of those air boxes are huge - it's like they design the bike around the air box, then fit an engine under it

[racerrad8]

As for the OEM airbox design vs. the foam filters... I'm no expert, but knowing just a little bit about intake and exhaust design, when I saw those long flared rubber inlet ducts and the large volume of the airbox, my first thought was "Yep, those Yamaha engineers knew what they were doing." (Hint: bottom end torque) Your mileage may vary. Feel free to disagree. Carry on...   
Bill

Bill, how does the "long flared rubber inlet ducts" and "large volume of the airbox" affect the "bottom end"?

Just curious?

Randy - RPM

[racerrad8]

Carb Cleaning.

One of the most important kits you can buy while cleaning your carbies.

FJ11-12/XJ12/XJR13 S/S Screw & O-Ring Carburetor Kit

Randy - RPM

[Sparky84]

Carb Cleaning.

One of the most important kits you can buy while cleaning your carbies.

FJ11-12/XJ12/XJR13 S/S Screw & O-Ring Carburetor Kit

Randy - RPM

I can attest to those kits, I bought them for the screws but never thought I was going to use the Fuel Transfer O-Rings, its something you cannot see if you don't break the carbs apart and is much worse than stuffed screw heads.
FJ1100mjk also said he always breaks them and change O-Rings so its something I will remember for next time also, thanks Marty

[CutterBill]

Bill, how does the "long flared rubber inlet ducts" and "large volume of the airbox" affect the "bottom end"?

https://www.amazon.com/Scientific-Exhaust-Systems-Engineering-Performance/dp/0837603099/ref=sr_1_1?s=books&ie=UTF8&qid=1519308726&sr=1-1&keywords=intake+system+design#customerReviews
https://www.amazon.com/Design-Tuning-Competition-Engines/dp/0837601401/ref=sr_1_1?s=books&ie=UTF8&qid=1519308967&sr=1-1&keywords=design+and+tuning+of+competition+engines

And others...

[CutterBill]

Some of those air boxes are huge - it's like they design the bike around the air box, then fit an engine under it...

So that volume must be important, eh?   

[fj1289]

Some of those air boxes are huge - it's like they design the bike around the air box, then fit an engine under it...

So that volume must be important, eh?   

I would say it "can" be important.   For the volume to be that critical, everything else in the system would have to be designed on paper, and then optimized in the real world to compliment the entire package.   

In my mind, as easy as it is to see improvement from simple mods on the FJ, I think that design and optimization must have been greatly hindered by production, regulatory, financial, and longevity concerns the factory was dealing with at the time of manufacture.   

So, yes, I think airbox volume, header length, collector style, muffler flow, camshaft design, piston skirt and ring design, etc all "can" be critically important, in reality, most FJ engines are so far from their full performance potential, changes in any of those bring fairly minor non-critical changes to the overall package.   

The upside is - it leaves the FJ as a wonderfully flexible and reliable engine.   It's very forgiving of poorly executed mods (like poor jetting - whether airbox or pods), but rewards well executed mods (like a well jetted set of carbs - again whether airbox or pods). 

It's always fairly entertaining to see theoretical discussions on FJ performance since our engines are almost never at that level of development in reality.

 

[whyzee79]

So I'll open this door.  What are the best mods one can do for the FJ?  Open the stock airbox?  Junk the stock airbox?  Do either and go up one jet size to compensate for the increase in air?  Exhaust?  Cam swap?  Mine is stock right now but the potential for messing around is great.   

[racerrad8]

Bill, how does the "long flared rubber inlet ducts" and "large volume of the airbox" affect the "bottom end"?

www.amazon.com/Scientific-Exhaust-Systems-Engineering-Performance
www.amazon.com/Design-Tuning-Competition-Engines

And others...

Oh, I thought by your statement below you had a personal position on the subject. I know you said you were no expert, but I was hoping to hear your personal experiences, not your recommendations of books to read on the subject.

... but knowing just a little bit about intake and exhaust design, when I saw those long flared rubber inlet ducts and the large volume of the airbox, my first thought was "Yep, those Yamaha engineers knew what they were doing." (Hint: bottom end torque)
Bill

I have read many of books over the years and have taken them into consideration, but I don't base my opinion on the words of another until I have confirmed they are supported, especially when it comes to "those long flared rubber inlet ducts". I have almost 25 years of hands on experience with the Yamaha FJ1100/1200 Mikuni BS Carburetor and the effects of the velocity stacks on them. I was looking for your personal experience with them and how they affect the "bottom end torque" you refer to, not the generalization writing of someone writing about general engine design.

I will take your recommended reading into consideration, but at this point the perceived reduction of bottom end torque is still a myth when changing over to pod type air filters.

Randy - RPM

[chiz]

I think giant air boxes are significant... although long induction tubes into the ports are just a function of the distance of the box from the ports and the lay out of the frame design.
What is important though is the distance between the butterfly or on some older bikes the slide and the intake valve. On my old BSA R3  as fitted to the Rob North chassis I think they try to get 14 inches or is it 7 never the less this distance is important for gas flow and exhaust as well.
Lez

[Country Joe]

[/quote]



It's always fairly entertaining to see theoretical discussions on FJ performance since our engines are almost never at that level of development in reality.

 


[/quote]

I think this statement is the money shot in this thread.
Joe