Son of SoCal Fix-Up: We just can't resist improving them, can we?

[threejagsteve]

Correction: I have the FZR front wheel, with new bearings.  Correct OD, 15 mm ID, pound 'em, tap 'em in, new rubber, ride away.  That extra 1/2" of wheel adds about 1/2" of width to the contact patch (at least when vertical).  More stopping power to use. stick better in turns, leaps higher, faster that a locomotive ...

Yes, I'm just waiting for the right front wheel to come along... So far, the cheap ones all look scraped and/or battered (and/or painted some offensive color), while the good ones all cost too much. But eventually a nice one at the right price will jump out and say, "Here I am!" Of course winter is always the best prices for used parts...

[simi_ed]

I didn't worry about color.  I used Duracoat 2 stage gun paint, and it worked well, and seems tough enough, so far.  It doesn't like impact, but not many paints do!

[threejagsteve]

Sorry, not trying to pick on you, but I just have to ask: Why are you spending money on pods and jets?
Are you trying to add speed?  If your FJ is stock then you're just wasting time and money.  The only thing pods will help is simplify the carb removal process.  You can shim the needles and run the stock air filter and get the same performance as "pods and jets."

Now, if you want a "better" motorcycle that's quicker, then spend your money on suspension upgrades.  The payback is 100X better than what any other "performance upgrades" will get you.

Unless you're wanting a drag racer, then nevermind...

DavidR.

Hello, David,

No, I don't feel picked on; I'm always open to a conversation that might increase my knowledge and/or save me money.

My funds are quite limited until I find another job. Unfortunately, once I have that job, I won't have nearly as much time to mess around with the FJ. C'est la vie!

As I said earlier, since I improved the forks I've been noticing how marginal the rear is. And no, I didn't crank up the preload in the back, but I probably ought to make sure I have the damping at or near the top of its range (I think it is...). There's just no way I can pay the freight for a good shock right now.

But here's my current plan: My primary goal is to improve throttle response and pick up any available power gains, off-idle to midrange. I rarely twist it over 8K anyway. $100 or so for "pods and jets" will be doable in the near future. I'd also planned on needle shims as well, but those are chump change even for me, so I didn't bother to mention them in the previous post. The stock airbox could be drilled, I suppose, to open up the breathing. But I do hate that airbox, and since it seems that the carbs are going to be in and out quite a bit going forward, pods just seem to make sense for their frustration diminishment alone.

My bike is a '91, which as I'm sure you're aware came with smaller jets than the original 1100 in spite of the increased displacement and slightly higher CR (9.7 vs. 9.5:1). I have the strong suspicion that the original sizes were what were actually correct if you ignore smog and mileage considerations. My plugs always came out bone white, but it didn't seem to hurt anything, so I never did anything about it.

The other parts of this plan are to slot the advance rotor the way Randy has described, and do the coil relay mod. I'm figuring that 115 or 117.5 mains (110 was stock for '91; 112.5 on the original 1100) and 40 pilot jets (37.5 standard on all) ought to be about right. I'll start with .020" shims on the needles, and see how she runs...

However, in doing the research I also noticed that the pilot air jets were originally 160s and by '91 had been decreased to 155s. So this seems like a good time to ask... Do you think I should also bump those up as long as I'm gonna be in there anyway?

Constructive criticism is welcomed!

Cheers, and TIA!

[SlowOldGuy]

Steve,
Glad you didn't take offense at my question, as none was intended.

Allow me to clarify a few things.
Larger displacement does NOT necessarily mean more fuel needs to be added to the intake air flow.  At the top end, the larger displacement may have a greater airflow requirement than a smaller displacement, so if the engine was to spend a lot of time at WOT, then an increase in the main jet is probably a good idea.

Yamaha proved this when the idle jetting actually decreased between the '85 1100 and the '86 1200.  The '85 had a 110 main jet and a 40 idle jet.  All following models (at least US models) used a 112.5 main and 37.5 idle jet.  AFAIK, all models used the 155 air pilot jet.

I also "learned" this lesson when I installed a Wiseco 1200 kit in my 1100.  Thinking that more displacement needed more fuel, I bumped the main jet and raised the needle.  After several weeks of suffocating in raw gas fumes every time I rode, it finally occured to me that the larger displacement will breathe more air, but a carb's job is to supply the correct amount of fuel to a steady-state air flow such as when the bike is cruising and also supply an increased amount of fuel during a variable air flow condition, such as when the bike is accelerating.  Unless (or until) the demand from the larger displacement "out runs" the ability of the carb to supply the required amount of fuel, the jetting should be fine (or at least adequate).  Top end is the main concern as that's where the carb has the opportunity to be the limiting component in the equation.  But, once a carb begins to limit the airflow, it starts delivering an overly rich fuel mixture anyway (that's what the main air bleed attempts to correct for to some extent).

The same argument also applies to the airbox.  The stock airbox supplies adequate volume for 99.99999% of riding scenarios.  Maybe at WOT it could begin to limit airflow into the intake.  I've never experienced any problems with my stock airboxes.  But, I don't spend a significant amount of time at WOT either.  Some poeple have run the airbox without the cover.  Pin the filter retainer(s) so they don't fall out and you will open up a significant area of the airbox.

However, providing the CAPABILITY for increased air flow doesn't necessarily mean the engine is making USE of that AVAILABLE airflow POTENTIAL.  Again, airflow limits are ONLY an issue at WOT.  When you're cruising (or accelerating) at anything less than WOT, the motor is getting all the airflow it is asking for, or needing.  Anytime the throttle plate is not sitting horizontal in the intake (meaning WOT) then IT is the limiting factor in airflow; not the airbox, not the filter (stock, K&N, UNI, pods, etc).  

Jack with anything in the intake chain that removes a restriction to airflow (i.e. that high flow filter) and you create the potential to run lean on the needles.  Is this because of EXTRA airflow from the new filter?  NO, NO, and NO!!!!!!  The intake mixture has become lean because in removing an intake airflow restriction, the velocity of the airflow DECREASED.  In a CV carb, the fuel delivery circuits respond to the VELOCITY of the airflow, not the QUANTITY.  When you remove an intake restriction and thus slow the airflow down, the vacuum produced in the throat of the carb (which is a function of velocity) is reduced which causes the vacuum slide seek a lower position which puts the jet needle in a leaner position in the needle jet.  This is Bernoulli at work.  Quantity of airflow or providing a greater airflow potential has nothing to do with it.

Wow, that was reminicent of the old carb discussions of a few years ago.  
Be sure to turn in your homework.
CLASS DISMISSED!!!!!

DavidR.
Forgive any spelling errors, I'm too lazy to proofread that diatribe.  :-)

[SlowOldGuy]

Also, on the air pilot jet since it is metering air, then smaller is richer.

DavidR.

[threejagsteve]

 In a CV carb, the fuel delivery circuits respond to the VELOCITY of the airflow, not the QUANTITY.  

Ah, the missing piece of the puzzle! Thanks, David!

Therefore it actually made sense that they should have gone to smaller jets when they increased the displacement, as that would have raised the airflow velocity through the same-size valves, ports and carbs.

So I gather that, in spite of the fact that the plugs have always come out bone white (but it never gave any symptoms of being overtly lean in the light-to-moderate duty that it saw) AND allowing for my intent to advance the ignition a bit (trying for 5-6*, but who knows how exact it'll come out grinding the slot by hand), about all I really need to do is raise the needles a bit?

[racerman_27410]

David is spot on....

the stock carbs i am running right now have 37.5 pilots and 117.5 mains

1349cc....    the big pistons dont have any trouble keeping the velocity up in the carb throats.... ran great at altitude on my recent western trip....Brutus has so much extra power that it felt like a stock FJ when at altitude     ..... averaged 38mpg too (cruising)   though if i hammer on the beast i can get into the low 20's pretty easily   

according toe the guy who built my engine the FJ has a very inefficient combustion chamber and as a result makes the best power when run on the lean side of the scale.

KOokaloo!   (and i truly mean that )


Frank

[andyoutandabout]

well that's probably saved me a whole heap of bother. Thanks Dave R

[threejagsteve]

Yamaha proved this when the idle jetting actually decreased between the '85 1100 and the '86 1200.  The '85 had a 110 main jet and a 40 idle jet.  All following models (at least US models) used a 112.5 main and 37.5 idle jet.  AFAIK, all models used the 155 air pilot jet.

Forgive any spelling errors, I'm too lazy to proofread that diatribe.  :-)

Please forgive this humble unwashed one . . but just to set the record straight, according to my official Yamaha shop manual (got the book right in front of me), the '84-'85 FJ1100L had a 112.5 main jet, 37.5 pilot jet and 160 pilot air jet. The FJ1200S ('86-'87) kept the 112.5 main jet and 37.5 pilot jet but did go to the 155 pilot air jet. '89-on FJ1200W and FJ1200B have 110 main jets, 37.5 idle jets, and 155 pilot air jets. Couldn't expect even a guru to keep all that trivia in their head, after all!

However, in a bald attempt to keep the Socratic dialogue going... I suppose that I will still have to pull my carbs one more time. I hadn't yet run across the discussions concerning the criticality of float height when I did my rebuild, so I was only concerned that they were within the book-specified range. When seeking that spot-on state of tune, apparently 1-mm differences count! Or maybe the "conventional wisdom" is wrong again...

[SlowOldGuy]

If you can get a clear tube on the float bowl drain port while the carbs are on the bike, you don't need to remove them to check the fuel level.  Of course if any of the floats need to be adjusted, then you'll need to go down that route.

On the jet size;  You are correct that the '88+ models got the 110 main jet.  The numbers may be correct for the '84 model, but I know for a fact that the '85 FJ came with a 110 main, 40 idle, and 155 air pilot since I still have those jets in my "spare carb parts" inventory.  The '85 model was a N/NC designation. 

And we all know how bad the GYSM (Genuine Yamaha Service Manual) can be, mine tells me to torque the oil drain bolt to 350 ft-lb!!!  :-)

DavidR.

[threejagsteve]

Hmmm, the 'N' designation isn't even mentioned! LOL (And my copy is c. 1990.)

Interesting that there's a 5th version I didn't even know about. ('85 only, I'm guessing...)

And yes, I know about the tube-on-the-drain float-level measurement trick. But I also recall that there were a-few-mm differences between 'em. So one more time...

Thanks again, David!