gents,
i did a search and i think i have this right:
i have an '87 fj1200 with stock everything and want to change to the pod filters offered at rpm.
i should run 125 main jet, 40 pilot jet and shim needle with 5mm washer, is this correct?
i'd like to know this is correct before i order from rpm.
thanks,
larry
That main jet will be way too large for just pods. You could use the stock main, or go up to a 115.
Shimming the needles is far more critical than changing the main jet.
DavidR.
Quote from: scarylarry on March 19, 2012, 01:29:12 PM
gents,
i did a search and i think i have this right:
i have an '87 fj1200 with stock everything and want to change to the pod filters offered at rpm.
i should run 125 main jet, 40 pilot jet and shim needle with 5mm washer, is this correct?
i'd like to know this is correct before i order from rpm.
thanks,
larry
Don't forget to purchase a crank-case breather filter. And ear plugs. The intake howl was too much for me so I ditched the UNI pods and reinstalled the air box. just my .02 of course.
Depending a bit on the air where you are, a 125 is still hilariously too much for stock exhaust. David's right on there. Jets are cheap, I'd probably buy a set of 115's and shim the needles slightly, and experiment from there.
Nah, let's be honest. I'd get 122.5's and try to make them work. By buying a pipe. :)
Quote from: Dads_FJ on March 19, 2012, 02:53:52 PM
And ear plugs. The intake howl was too much for me so I ditched the UNI pods and reinstalled the air box. just my .02 of course.
Damn, you must have great hearing.
I can't hardly tell the differance on my bike. At least not to the point of having to change back to an airbox.
Leon
Quote from: 1tinindian on March 19, 2012, 04:50:42 PM
Damn, you must have great hearing.
I can't hardly tell the difference on my bike. At least not to the point of having to change back to an airbox.
Leon
Speaking of that, how does it run?
Randy - RPM
so i should just keep the the stock main jet, go to a 40 pilot and shim the needle with a 5mm washer?
...and the crank case breather.
larry
A 5mm washer would give you interesting results. Try a 0.5mm washer to start perhaps?
Slow down, read a bit more carefully.
I think jetting threads can be as bad as oil threads or worse yet, which oil do I use on my chain threads! My opinion, and everybody has one... is that because you'll have more air entering across the board, that is throughout the whole rpm range, then you'll have to compensate by adding more fuel across the whole range as well - by increasing the main main jet as well as the pilot jet. When I went from air-box to sans-air box and back to air-box, the only jetting change I made was with the main jet. I don't recall which size jets I used with the pods, they went with the filters when I sold them. I should also add that the loudness I referred to earlier was when I was in the kookaloo zone above 5-6K RPM. Also... (don't worry, I'll stop soon!), although there was a bigger hit at higher RPMs, the loss in low end power conflicted with my 18 tooth front sprocket, 'nother reason I switched back. your results may vary.
In part, and in defense of those without airboxes, not mildly enrichening the midrange would have meant you were leaner than prior, and you likely lost some torque because of it, not just the lack of airbox.
In truth, the best way by a long shot is to put it on a dyno and see what's what, but that's an expensive proposition unless you're quite certain that you're done upgrading airflow into and outof the engine. Suggested jetting changes are just that, suggestions as a place to start. Nothing will ever take the place of fine tuning either via dyno time or careful chopped plug reads.
Quote from: andyb on March 20, 2012, 08:24:40 AM
A 5mm washer would give you interesting results. Try a 0.5mm washer to start perhaps?
Slow down, read a bit more carefully.
i was always decimally challenged! :dash2:
thanks, I'll start from there.
Quote from: racerrad8 on March 19, 2012, 07:14:53 PM
Quote from: 1tinindian on March 19, 2012, 04:50:42 PM
Damn, you must have great hearing.
I can't hardly tell the difference on my bike. At least not to the point of having to change back to an airbox.
Leon
Speaking of that, how does it run?
Randy - RPM
As of right now, I only have a little over 30 miles on it since getting it back together, but from what I have been able to tell, it runs great, and the top end sounds good. The pods can be heard at WFO, but hell, I love that sound!
Thanks for getting me through this Randy!
Leon
Quote from: 1tinindian on March 19, 2012, 04:50:42 PM
Damn, you must have great hearing.
Leon
If he's riding an FJ sans earplugs (airbox or not), he probably won't for long.
Quote from: rktmanfj on March 20, 2012, 11:07:50 AM
Quote from: 1tinindian on March 19, 2012, 04:50:42 PM
Damn, you must have great hearing.
Leon
If he's riding an FJ sans earplugs (airbox or not), he probably won't for long.
I was waiting for an earplug thread! I am a firm believer in them, I use the the yellow cylindrical ones, gotta save what hearing I have left. I attest that my bad hearing is from rock concerts of the 70s & 80s.
Quote from: Dads_FJ on March 20, 2012, 11:16:59 AM
Quote from: rktmanfj on March 20, 2012, 11:07:50 AM
Quote from: 1tinindian on March 19, 2012, 04:50:42 PM
Damn, you must have great hearing.
Leon
If he's riding an FJ sans earplugs (airbox or not), he probably won't for long.
I was waiting for an earplug thread! I am a firm believer in them, I use the the yellow cylindrical ones, gotta save what hearing I have left. I attest that my bad hearing is from rock concerts of the 70s & 80s.
Well, why didn't ya start one? :biggrin:
I'm having a new set of customs made up soon... lost one of the originals, and the custom earbuds got chewed up by the (now ex) GF's Pekingese. :diablo:
There are some good generic 'plugs out there, but, IMO, none of those compare to custom-made ones.
Quote from: Dads_FJ on March 20, 2012, 08:41:34 AM
My opinion, and everybody has one... is that because you'll have more air entering across the board, that is throughout the whole rpm range, then you'll have to compensate by adding more fuel across the whole range as well -
I've ranted on this too many times to count. The air filter DOES NOT control the amount of air the motor gets! The THROTTLE PLATE does.
The type of air filter, or airbox, or no airbox changes the restriction to airflow through the carbs and, thus, changes the VELOCITY of the airflow. Velocity is what's important to a CV carb, not the amount of air. Filters clean and restrict air, they don'ty control the amount, unless your filter is totally clogged up.
DavidR.
Quote from: SlowOldGuy on March 20, 2012, 11:47:14 AM
Quote from: Dads_FJ on March 20, 2012, 08:41:34 AM
My opinion, and everybody has one... is that because you'll have more air entering across the board, that is throughout the whole rpm range, then you'll have to compensate by adding more fuel across the whole range as well -
I've ranted on this too many times to count. The air filter DOES NOT control the amount of air the motor gets! The THROTTLE PLATE does.
The type of air filter, or airbox, or no airbox changes the restriction to airflow through the carbs and, thus, changes the VELOCITY of the airflow. Velocity is what's important to a CV carb, not the amount of air. Filters clean and restrict air, they don'ty control the amount, unless your filter is totally clogged up.
DavidR.
Would you agree that running an engine sans air filter, be it with CV carb or anything else, runs leaner?
Hello John, yes the bike will run leaner but with the CV carbs it's due to the slower air velocity thru the carbs. The slower air velocity results in the vacuum slide not lifting as high as it would with a higher velocity. Attached to the slide is the jet needle, therefore the needle is in a lower position in the jet nozzle resulting in a leaner mixture. That's why we suggest shimming the needle to a higher position.
80/90 percent of our street riding is on the pilot jet and needle, only at WFO are we on the main jet.
A good primer on the subject can be found in the Files section under carbs.
Take a deep breath David. There is a reason we saved your discussion in the Files.
John, it took me years to figure out what David was saying.....
Quote from: Pat Conlon on March 20, 2012, 01:04:42 PM
...slower air velocity thru the carbs...
Higher air velocity = lower pressure, if memory serves.
The harder part to consider is that the volume of air entering and exiting a motor doesn't change with throttle position nor with load, only with rpm. The density of that air is what changes, and that's what matters. Air's damned compressable stuff!
David knows this bit also, the tuned airbox function, which at some resonant frequency will cause the motor to be slightly supercharged and flow more air than typical, but that's not the filter's fault, it's the airbox. Moral of the story, you don't need to know exactly how everything works at a physics level if you can see cause and effect of jet changes.
And while i'm nit-picking. The main jet does have some influence over fueling at any time that the motor's getting fuel from someplace other than the pilots. If the main jet is sized appropriately, it won't be the restriction so it won't matter too hugely though. It'll mostly be important when you're at WOT
and above about 6krpm. WOT at 2k won't give you a good idea on the mains effect, as it's minimal down there.
It's all good, I'm just trying to get a better understanding of the how's and why's, sort of educate myself... I don't like spewing misconseptions anymore than I like hearing them. I'd read up in the files section. Now what chain lube is best?
Quote from: Dads_FJ on March 20, 2012, 01:42:26 PM
...Now what chain lube is best?
Did somebody say Chain Lube (http://www.rpmracingca.com/proddetail.asp?prod=tri-flow)?
Randy - RPM :biggrin:
Sorry, didn't mean to come across so negatively.
K&N's "flow more air" advertising is mostly responsible for all the misconception. Yes, their filters are capable of flowing more air (at the significant expense of not being a very good filter, but they don't mention that). What they don't tell you is that engines don't need more flow from the air filter. Unless the air filter itself is the choke point on airflow, it doesn't matter how much air it CAN flow if the engine is not asking/needing more air. Usually the ultimate restriction to air flow is the carb size, but the only happens at WOT approaching redline (a place not visited often unless you're a drag racer).
If you take the air filter off and the engine speeds up, it's because the mixture leaned out, not because it's suddenly getting more air. It's getting the same amount of air because the throttle plate is controlling airflow, not the filter.
Most auto carbs work on the venturi (velocity) effect also so when you remove the air filter on your car, it will lean out because the air filter restriction is now gone and the air flow has slowed down and is not pulling in as much fuel (lean!).
I could go on (and on, and on), but I'll stop for now. :-)
DavidR.
Quote from: SlowOldGuy on March 20, 2012, 05:32:16 PM
If you take the air filter off and the engine speeds up, it's because the mixture leaned out, not because it's suddenly getting more air. It's getting the same amount of air because the throttle plate is controlling airflow, not the filter.
im not trying to be an ass but for my knowledge: how would it lean out if the filters do not control the flow.
i get that the throttle plates limit the air so what does it matter how much is air is getting to the throttle plates :wacko3:
No worries Matt, that's what we are here for....
You know that our BS36 CV(Constant Velocity)Mikuni carbs meter fuel to the motor based the various vacuum levels induced by the opening or closing of the throttle plates, right?
In other words, the opening and closing of the throttle plates do not mechanically add or subtract fuel.
The opening and closing of the throttle plates affect the air velocity (or speed of the air) and as the air whistles thru the carb it produces a vacuum which raises and lowers the slides which actually meter the fuel.
High speed air produces high vacuum (slide raised= more fuel) Low speed air produces low vacuum (slide lower=less fuel)
Unipods are less restrictive. (I think we all get that)
1) Less restrictive means that the air flow (velocity) is slower thru the carbs. (this point was hard for me to get)
2) Slower air flow results in lower vacuum levels.
3) Lower vacuum levels result in a lower slide position (which is run on vacuum)
4) Lower slide position results in a lower needle position and thus a leaner mixture.
http://www.fjowners.com/index.php?topic=4714.0 (http://www.fjowners.com/index.php?topic=4714.0)
Quote from: Pat Conlon on March 20, 2012, 09:12:45 PM
No worries Matt, that's what we are here for....
You know that our BS36 CV(Constant Velocity)Mikuni carbs meter fuel to the motor based the various vacuum levels induced by the opening or closing of the throttle plates, right?
In other words, the opening and closing of the throttle plates do not mechanically add or subtract fuel.
The opening and closing of the throttle plates affect the air velocity (or speed of the air) and as the air whistles thru the carb it produces a vacuum which raises and lowers the slides which actually meter the fuel.
High speed air produces high vacuum (slide raised= more fuel) Low speed air produces low vacuum (slide lower=less fuel)
Unipods are less restrictive. (I think we all get that)
1) Less restrictive means that the air flow (velocity) is slower thru the carbs. (this point was hard for me to get)
2) Slower air flow results in lower vacuum levels.
3) Lower vacuum levels result in a lower slide position (which is run on vacuum)
4) Lower slide position results in a lower needle position and thus a leaner mixture.
http://www.fjowners.com/index.php?topic=4714.0 (http://www.fjowners.com/index.php?topic=4714.0)
Pat, I think that was well put, even a 5th grader should understand that.
Thanks Mark, I 'think' I described it right.
With all this said, would a cheap trick to make your bike ride better while riding through high allevation be to remove your air filter? It may not help with idle or start up, but if you could get your bike running in theory this may help while driving, right?
The key to the CV carb is the vacuum controlled slide. It responds to the velocity (and vacuum) produced by the air flowing through the throat of the carb. CV stands for CONSTANT VELOCITY, and that's what the slide seeks to maintain. At a steady state throttle position, the slide is held at a position that results in a certain air flow velocity. During acceleration, as the throttle (and thus the throttle plate) is increased, more air is allowed to flow through the carb.
For more air to flow, it has to speed up. When it speeds up, it creates a higher vacuum which initially picks up more fuel (kind of like an acceleration pump on a Holley). The slide diaphragm also sees this increase in vacuum and reacts by pulling the slide further up, exposing more throat area to the air flow. The larger throat area causes the air flow to slow back down to the steady state (i.e. constant) value. The slide tries to keep the air flow velocity through the carb at a constant value under all conditions.
This is where Andy's reference to RPM comes in. Pinning the throttle allows the maximum air flow for a given RPM. Because you can't instantly accelerate from 1000 RPM to redline (at least not while riding, not counting missed shafts), the engine doesn't need a bunch of fuel when you stomp on it. As the engine RPM increases, more air is drawn through the intake, and the slide rises to maintain the constant velocity throught he carb. As the slide comes up, the needle exposes more of the needle jet and allows a proportional increase in the amount of fuel pulled into the flow.
If you do anything to an intake component which disturbs the speed of the air, the carb needs to be adjusted to compensate. The best example is air filters. A "less restrictive" filter will allow air to flow "easier" which results in a lower velocity. The slide reacts to a lower velocity by dropping to a lower position which reduces the carb throat area and thus speeds the flow back up to the desired "constant" value. You're now too lean because the jet needle is lower in the needle jet and not flowing as much fuel for the given amount of air passing through the carb.
davidR.
Quote from: SlowOldGuy on March 21, 2012, 03:10:40 PM
The key to the CV carb is the vacuum controlled slide. It responds to the velocity (and vacuum) produced by the air flowing through the throat of the carb.
In truth, it's relative vacuum, not absolute vacuum, so it's really the pressure differential. Doesn't really matter unless you're setting up a blow-through turbo system though.
Quote from: SlowOldGuy on March 21, 2012, 03:10:40 PM
The key to the CV carb is the vacuum controlled slide. It responds to the velocity (and vacuum) produced by the air flowing through the throat of the carb. CV stands for CONSTANT VELOCITY, and that's what the slide seeks to maintain. At a steady state throttle position, the slide is held at a position that results in a certain air flow velocity. During acceleration, as the throttle (and thus the throttle plate) is increased, more air is allowed to flow through the carb.
For more air to flow, it has to speed up. When it speeds up, it creates a higher vacuum which initially picks up more fuel (kind of like an acceleration pump on a Holley). The slide diaphragm also sees this increase in vacuum and reacts by pulling the slide further up, exposing more throat area to the air flow. The larger throat area causes the air flow to slow back down to the steady state (i.e. constant) value. The slide tries to keep the air flow velocity through the carb at a constant value under all conditions.
This is where Andy's reference to RPM comes in. Pinning the throttle allows the maximum air flow for a given RPM. Because you can't instantly accelerate from 1000 RPM to redline (at least not while riding, not counting missed shafts), the engine doesn't need a bunch of fuel when you stomp on it. As the engine RPM increases, more air is drawn through the intake, and the slide rises to maintain the constant velocity throught he carb. As the slide comes up, the needle exposes more of the needle jet and allows a proportional increase in the amount of fuel pulled into the flow.
If you do anything to an intake component which disturbs the speed of the air, the carb needs to be adjusted to compensate. The best example is air filters. A "less restrictive" filter will allow air to flow "easier" which results in a lower velocity. The slide reacts to a lower velocity by dropping to a lower position which reduces the carb throat area and thus speeds the flow back up to the desired "constant" value. You're now too lean because the jet needle is lower in the needle jet and not flowing as much fuel for the given amount of air passing through the carb.
davidR.
This I actually get... but say we we're looking at a non-CV carb. Does removing the air filter also slow down the velocity of the air creating a lean condition? Or does it just induce dirt and wear out your rings faster?!
Quote from: SlowOldGuy on March 21, 2012, 03:10:40 PM
"....... When it speeds up, it creates a higher vacuum which initially picks up more fuel (kind of like an acceleration pump on a Holley)......"
Hey David, just a quick comment: I'm not sure that is a good analogy.
The Holley accelerator pump is a mechanical pump which (for a double pumper) squirts fuel down the primary and secondary barrels.
It does not use vacuum. You can tell when the engine is off (no vacuum) look down the throat and quickly open the linkage.
See the 4 little squirts of gas coming from the center of the carb? That's the accelerator pump. It's mechanical and works with out vacuum. That's why you can flood your engine by pumping the gas pedal, all those little pesky squirts...
The Mikuni TMR and Keihin FCR flatslide carbs have accelerator pumps. Crank the throttle a couple of times on those puppies and you can flood your engine real quick. The Mikuni FS and CV carbs do not have pumps.
Thank you for your continued explaniation on the functions of our CV carbs. Now I know why they call them "Constant Velocity".
I hope you don't mind but I saved this explaination in our carb files. Pat
Pat,
The accelerator pump analogy was a comparison of the effect rather than the actual mechanism. In a Holley (or Rochester, or Quadrajet, or Carter, I've worked on them all), yes the accelerator pump is a mechanical driven pump. It adds fuel for smooth acceleration because the typical auto carb does not have the advantage of a variable venturi (the diaphragm slide).
When you abruptly open the throttle on an auto carb, you get a quick in-rush of air that the fuel flow can not respond to which creates a very lean condition that is not conducive to smooth acceleration. Thus the use of an accelerator pump to prevent an accel bog. In a CV carb, the slide inertia helps prevent the sudden in-rush of air be forcing the air through a small throat that keeps the velocity up and the fuel flowing to prevent an acceleration stumble. DJ kits include stronger slide springs to help this effect.
This is related to Dad's question about manual carbs where the slide is directly controlling the air flow and there is no separate throttle plate. This setup is very similar to an auto carb. Snatch a big handful of throttle and bog the crap out of the motor with a big gulp of lean air/fuel ratio. That's why the "good" flatslides usually have an accelerator pump, to compensate for the lean acceleration.
Running a manual carb without an air filter will affect the mixture because the fuel flow is a function of the velocity induced vacuum just like a CV carb. Manual carbs are just a sensitive to intake restriction and jetting as a CV carb. Change an intake component on a manual carb and you will affect the air/fuel mixture. Re-jet accordingly.
Oh yeah, the auto carb accelerator pump is a great means to check your idle mixture setting. Gently tap on the pump mechanism to add just a touch of fuel and see if the idle quality improves. If it does, the idle mixture is too lean, richen up the idle. If the engine stumbles when given the extra shot, then you're either okay or rich on the idle mixture. Of course, fuel injection has taken all the fun out of this. :-)
DavidR.
okay so if i read this right more air flow = less vacuum like in a car with a turbo at idle you have vacuum but with the turbo spooled you have pressure?
so with less vacuum to move the jets your have to manually move them via a spacer or jet kit?
im pretty sure i understand
Quote from: SlowOldGuy on March 21, 2012, 05:16:59 PM
Pat,
The accelerator pump analogy was a comparison of the effect rather than the actual mechanism.
Ok, got it, thanks.
Moonrunnah, you don't move the jets anywhere. You move the jet needle (up) via a shim (washer) or via the clip on the needle, if you have a adjustable needle.
yes that was what i meant
is the stock fjs adjustable if so how i would like to do a 4-1 exhaust with the uni pods
The stock FJ doesn't have a true adjustable needle, but it can still be shimmed up if needed. A true adjustable needle will have mutiple slots in it for a wider range of adjustment. The other common adjustment is the idle mix screws, though they are behind the pilot jets, so you're replacing brass if you really want to make big adjustments.
Though, with a 4-1 pipe, you would also need to replace the main jets, and quite possibly the pilots.
Jets aren't moved as such, they're simply replaced. The needle can be moved, arguably it's a needle jet, but that's just arguing definitions.
well how much is involved to change the jets for a 4-1
Not much. There's more involved that shimming needles, but that's only because you can do those without taking the carbs off. Take the bowls off the carbs and you'll be able to see both the pilots and the mains.
if i take the carbs out to change them to i screw up the sync of the carbs