Carb settings with pod airfilters and cut exhaust....

[Goodhew11]

Hi folkes..

Right I have a 1992 fj1200 3xw, and she's running horribly.

She is a custom build with the only thing really being standard is the engine wheels and part of the frame.

There's no room for the original air box now so she has some pod airfilters fitted.

The exhaust has the original pipes that have been cut down and have slash cut tips on the end.

When started without the choke she just dies, and then with the choke she never has a steady idle. The first twist of the throttle she bogs out and cuts off.
Once warmed up the revs are erratic and she runs hot too. There's usually a very strong smell of unburnt fuel aswell.

The other day she bogged out on me while riding, I pulled over and she wouldn't start for a few days then she fired up again. I put this down to over fueling and possible flooding.

It's like one second she's sucking in too much air and the next it's too much fuel.

Any help would be appreciated.
Thanks in advance.

[fj1289]

We will need a LOT more info and details to try to give some good ideas.

How did it run before?
How long was the bike setting before/during the build?
What shape is the tank in?  Rust?  Crud?
Have the carbs been PROPERLY cleaned?
Stock wiring harness?  Stock ignition system?
Have the carbs been rebuilt?  Specifically new needle seat O-rings?
Any jet kit in the carbs?  What jets?  Idle and main?  Needle setting?

[Nova]

That's because as you roll through the throttle one second she's sucking in too much air and the next it's too much fuel.

You removed the airbox, which is an important part of the intake system on a bike with CV carbs. If you bought cheap podfilters the very LEAST you need to do is make sure they fit properly and aren't blocking any ports. You also went to an open exhaust, which means you have no back pressure.

In short, you have two options:

1. Prepare to do a mountain of tuning... including (but not limited to) re-jetting the carbs to compensate for the loss of a balanced, still source of air into the venturi with a consistent vacuum pressure.

2. Throw away the pod filters and find a way to put the airbox back on and replace the open exhaust with something using proper mufflers.

[racerrad8]

Or the third option:

Get a hold of Robert or myself, we can get you dialed in for your specific needs.

Email or call.

Randy - RPM

[Nova]

http://clevelandmoto.blogspot.com/2015/05/clevelandmoto-podcast-89.html

Pick it up at the 25 minute mark. Still the best explanation about podfilters I've ever heard.

[simi_ed]

I'd choose door #3! (Randy/Robert)

[racerrad8]

Still the best explanation about podfilters I've ever heard.

No offence, but I'll never get that 25 minutes of my life back.

Since we have been doing this for so long, the "pod" filter application on the FJ has been fully sorted. Yes, the carb jetting needs to be adjusted, but the benefit is worth it.

Those guys are lost...

Randy - RPM

[Nova]

Likewise no offence, but even though the jetting has been sorted, in the end you're still using a rack of CV carbs engineered to work with a reservoir of air at a certain atmospheric pressure (an airbox) and doing a workaround because that component has been removed. No matter how well the jetting is done, it's still a hack to compensate. In many cases you may be trading all around performance across the entire powerband for better performance in a certain area of the powerband. I'd be interested to see some hard numbers from a before and after test on an FJ with a stock airbox and then with rejetted carbs.

[fj1289]

Likewise no offence, but even though the jetting has been sorted, in the end you're still using a rack of CV carbs engineered to work with a reservoir of air at a certain atmospheric pressure (an airbox) and doing a workaround because that component has been removed. No matter how well the jetting is done, it's still a hack to compensate. In many cases you may be trading all around performance across the entire powerband for better performance in a certain area of the powerband. I'd be interested to see some hard numbers from a before and after test on an FJ with a stock airbox and then with rejetted carbs.

In the end, you want the carb to act like a carb - i.e. the slide should respond to your right wrist.   Unforunately, CV carbs add a lot of ambiguity between your right wrist and the slide.  CV carbs definitely are NOT the result of seeking improved performance - other than not having to equip a bike with a too small carb to make up for the "average consumer" that lacks appropriate throttle control to not whack open the throttle too quickly at too low of an RPM.  

I consider the whole CV carb concept to be a compromise -- and another one of those things that works better in theory than practice.   So adapting a set of pod filters just modifies the existing set of compromises - if that is to your favor, then good, if not, then easy enough to revert back.  

In the end there really isn't a "best" or "better", it's all about the set of compromises you like best - be it carbs, tires, seats, handlebars, engine tune, oil, clutch setup, pink stripes, etc!

[ribbert]

In the end, you want the carb to act like a carb - i.e. the slide should respond to your right wrist.   Unforunately, CV carbs add a lot of ambiguity between your right wrist and the slide.  CV carbs definitely are NOT the result of seeking improved performance - other than not having to equip a bike with a too small carb to make up for the "average consumer" that lacks appropriate throttle control to not whack open the throttle too quickly at too low of an RPM.  

I consider the whole CV carb concept to be a compromise -- and another one of those things that works better in theory than practice.   So adapting a set of pod filters just modifies the existing set of compromises - if that is to your favor, then good, if not, then easy enough to revert back.  

In the end there really isn't a "best" or "better", it's all about the set of compromises you like best - be it carbs, tires, seats, handlebars, engine tune, oil, clutch setup, pink stripes, etc!

So, what would be better and how would it improve real world riding?

Noel

[candieandy]

Here's the videos we did on my bike. Not CV carbs, but exhaust and chrome pod filters. Wideband tuning will make your life easier. You don't even need to datalog.

https://www.youtube.com/watch?v=JpAXXBQRlng

BTW - if you end up tuning with a wideband. My FJ is stock except carb tuning and exhaust/intake upgrades. My AFR is 14.5:1 at idle, 13-13.5:1 at Cruise, and 11.5-12:1 WOT. Since this engine is air-cooled, its much more forgiving on rich tuning. The other cool part is that a WOT blast produces some sweet black smoke. It looks cool and I know its making max power for the 87 octane fuel I'm using.

Andrew

[fj1289]

In the end, you want the carb to act like a carb - i.e. the slide should respond to your right wrist.   Unforunately, CV carbs add a lot of ambiguity between your right wrist and the slide.  CV carbs definitely are NOT the result of seeking improved performance - other than not having to equip a bike with a too small carb to make up for the "average consumer" that lacks appropriate throttle control to not whack open the throttle too quickly at too low of an RPM.  

I consider the whole CV carb concept to be a compromise -- and another one of those things that works better in theory than practice.   So adapting a set of pod filters just modifies the existing set of compromises - if that is to your favor, then good, if not, then easy enough to revert back.  

In the end there really isn't a "best" or "better", it's all about the set of compromises you like best - be it carbs, tires, seats, handlebars, engine tune, oil, clutch setup, pink stripes, etc!

So, what would be better and how would it improve real world riding?

Noel

For carbs, I prefer FCR flat slides.  Works for MY "real world riding" ..... although I'm using EFI now.  I prefer the EFI for all the control it gives (including ignition, kill for air shifter, nitrous enrichment and retard, etc.) 

What's better for YOU for YOUR "real world riding"?

[ribbert]

For carbs, I prefer FCR flat slides.  Works for MY "real world riding" ..... although I'm using EFI now.  I prefer the EFI for all the control it gives (including ignition, kill for air shifter, nitrous enrichment and retard, etc.) 

What's better for YOU for YOUR "real world riding"?

Well, "real world riding" for the the rest of us could reasonably be interpreted as use linked to the bikes intended purpose, in this case, sports touring. It sounds like you have some sort of track bike. Injection, nitrous, air shifter, hardly representative of the membership nor something to aspire to for road use.

As for your original point about CV carbs, they have been around for more than a hundred years and stood the test of time so well they were still in use into the 90's until FI became the norm. The Japs not only started using them on bikes (ditching slide carbs) but also on cars such as Nissan/Datsun "Z" cars and others, Volvo used them until moving to FI as did Rolls Royce, Aston Martin, Jaguar, Triumph etc. Stromberg, Zenith and many other carby manufacturers (such as Mikuni) made them also.

I don't believe any of these cars had performance "compromise" on their list - well, maybe Volvo 

These were not a compromise but a design so good the world copied it and its widespread use lasted 90 years and was only then eclipsed by the universal adoption of FI.

I know why you think slide carbs are better, but in everyone else's real world the difference goes unnoticed and they get to enjoy a wonderfully simple, reliable, economical, easy to service, easy to tune carby.

I've worked on everything at some point and still think the CV carb is the best for road use.

This is of course only my opinion.

Noel

[fj1289]

I know I fall a little outside the "norm" of FJ riders...

I think one aspect of FJs that appeal to many is the opportunities they offer for modification - and how well they respond to many of them (if well executed).  I also fully understand the inherit abilities of the bike for its intended role with very little if any modifications.  For me, my motorcycles are my outlet for fun.  My 4 wheeled vehicles are mostly utilitarian and serve a purpose and tend to stay close to stock.  My bikes satisfy my desire to modify, learn, use it hard, learn more, modify more, challenge myself, etc.  None of the modifications I've made can be classified as "required" - but fall under "desired" instead.  Anytime you modify something you have to take ownership for the consequences - both intended and unintended.  As I began drag racing my street bike, I wasn't happy with the compromises it made for daily riding - so the parts bike became a race bike.  With the land speed stuff, I've re-learned that lesson twice more since then!

But, back to the original topic, just because CV carbs were "designed" to work with an airbox does not automatically mean they can't/won't work well without the airbox if appropriate supporting modifications are made.  I'm sure any set of carbs can be made to perform poorly under any set of situations -- that doesn't mean that it becomes a universal truth that this or that carb with or without that is bad.  Usually the opposite -- put them in the hands of someone that knows and understands them from a point of experience vice theory and they can make them sing most any tune you want...

[fj1289]

Actually, back to the original post - I still think the carbs are full of goo and crud - regardless of what filters and mufflers are on it.