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lean K&N high rpm

  • Thread starter Thread starter catbed
  • Start date Start date
C

catbed

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i heard that if you put a k&n replacement filter for stock, not pods, that the bike would run lean in the high rpm range, with the needle and main jet. i also heard that someone tuned their needle by switching the plastic and metal washer so the needle would sit higher. i also hope to get a little more power by increasing fuel. is any of this true?
 
huh.. i'd like to hear about this as well, i was really considering a k & N filter, it's prettyy much the first thing i buy when i get a different car.
 
You may lean it out a little by fitting a K&N inbox filter, didn't seem to make a lot of difference when I put one on mine.
You can likely put a spacer on the needle just to bring it up a little if necessary. Unlikely to need a new main with just that mod... maybe one size max.

Just at a guess!

Dan :)
 
My 850 has a K&N in the airbox and it runs pretty well. A little flat spot in the mid range until warmed up but fine when up to operating temperature. In my experience most GS bikes with BS/CV carbs benifit from a little needle shimming. The needles have a spring which pushes up from the bottom so the needle height is controled by the spacer/washer thickness on top of the clip; the thinner the washer, the higher (richer) the needle.

Going to try shimming my 850 needles a little and see how it works. Made a noticable difference on my old 550.
 
Spoke With Rapid Ray

Spoke With Rapid Ray

The plugs on my CA 1981 GS750 are a little lean, and yes it seems to have that mid range flat spot (but then again it is not an 1100 8-[). I put in a K&N filter into the airbox and the plugs seem even whiter, The plugs are shown below(insulators are pretty white). I did not clean or swap the plugs after the filter swap so some of the build up is from before.

I got some washers from Rapid Ray fro shimming the needles on the GS750, just have not gotten around to it.


GS750_Plugs_Mar_2008.jpg


Posplayr
 
posplayr said:
The plugs on my CA 1981 GS750 are a little lean, and yes it seems to have that mid range flat spot (but then again it is not an 1100 8-[). I put in a K&N filter into the airbox and the plugs seem even whiter, The plugs are shown below(insulators are pretty white). I did not clean or swap the plugs after the filter swap so some of the build up is from before.

I got some washers from Rapid Ray fro shimming the needles on the GS750, just have not gotten around to it.



Posplayr
Click to expand...

If your carbs are stock there will be a plastic washer/spacer on top of the needle which is about 2mm thick. Remove this washer/spacer and replace with a stack of metal washers about 1mm thinner than the plastic washer. Works wonders.
 
You can't just pull your plugs and determine where you're at. You need to do chop tests. If you didn't, the pic you show might be where you're at on your pilot circuit, not WOT. Do some chop tests before you start changing things.
Putting a K&N in the air box will probably lean things out a bit, and that will be on all circuits. But each bike will be different depending on how well it's tuned, etc.
 
The stock airbox on the 850 is a labrianth of passages controling airflow and the stock air filter is open on the top and sides and has a good deal more surface area than a K&N. Due to these factors I don't think there is any serious concern with just poping in the K&N and running the bike - no rejetting should be necessary.
 
K&N in the stock airbox will lean it out slightly, more so at wide open throttle. If it was on the edge of being too lean as it came from Suzuki it is now past the edge. Try a bigger main and raising the needle. Those plugs look lean but as Renobruce says you have to do proper chop testing to have any useful info. Do it before you fry your engine.
 
Last edited:
Chop Test?

Chop Test?

As I recall reading of the chop test you need to be able to run on that carberator circuit and then cut off the engine and read the plugs?

Since I live in town on a kinda windy road with traffic, it would be difficult to do this and get back to the garage.

Is this something that you would do on the Highway? Bring a spark plug wrench, and a plug cleaner, and spare plugs?

Are there instruction for a chop test someplace speciifc? (I know I can search)

RapidRay gave me three washers per carb (12 total) so I was going to change the height by 1 washer and see how it runs.

It is getting harder to start sometimes without pulling the choke and the idle seems to wander sometimes, just right some other times low. I read here that that is also a symptom of lean mixture.

I think the 81 GS750 is California stock (exhaust , carbs, cams) Except someone had removed the (pilot ??) jet covers previously but the previous PO warned me to "not mess" with the carbs. I did buy a set of carb gauges so I plan on checking balance just running a little behind on projects at the moment.

Posplayr

P.S. Catbed sorry for hijacking your thread but my bike was exactly the situation you were asking about so hope you dont mind.
 
IMHO,
The size of the inlet air hole in the bottom of my air box has alot more to do with making a rich or lean condition than the type of airfilter.
 
posplayr said:
P.S. Catbed sorry for hijacking your thread but my bike was exactly the situation you were asking about so hope you dont mind.
Click to expand...

no such thing as highjacking for me, as long as it helps all of us.
 
posplayr said:
As I recall reading of the chop test you need to be able to run on that carberator circuit and then cut off the engine and read the plugs?

Since I live in town on a kinda windy road with traffic, it would be difficult to do this and get back to the garage.

Is this something that you would do on the Highway? Bring a spark plug wrench, and a plug cleaner, and spare plugs?

Are there instruction for a chop test someplace speciifc? (I know I can search)

RapidRay gave me three washers per carb (12 total) so I was going to change the height by 1 washer and see how it runs.

It is getting harder to start sometimes without pulling the choke and the idle seems to wander sometimes, just right some other times low. I read here that that is also a symptom of lean mixture.

I think the 81 GS750 is California stock (exhaust , carbs, cams) Except someone had removed the (pilot ??) jet covers previously but the previous PO warned me to "not mess" with the carbs. I did buy a set of carb gauges so I plan on checking balance just running a little behind on projects at the moment.

Posplayr

P.S. Catbed sorry for hijacking your thread but my bike was exactly the situation you were asking about so hope you dont mind.
Click to expand...

Find a road where you can run at steady fairly low speed, and where you can accelerate hard, and especially where you can pull over to remove the plugs safely. Just need a plug wrench, and a pencil and paper.

BassCliff has a section on plug chops for VM carbs on his website. I wrote it a while ago and will write a better one soon, but it may help you out.
 
Last edited:
catbed said:
i heard that if you put a k&n replacement filter for stock, not pods, that the bike would run lean in the high rpm range, with the needle and main jet.
Click to expand...

I can't comment on the K&N replacement filter, but why do people continuously make the mistake of equating RPM and carb circuits? RPM has NOTHING to do with which circuit you are running on. Throttle position determines that alone. You can be at 2500RPM and on the main jet and you can be at 9000RPM and be on the pilot circuit. You must measure throttle opening to figure out which circuit you are on. The easiest way to measure throttle is to put a piece of tape on the throttle housing and on the grip. Put a mark on the grip one and then mark throttle openings in 1/8 increments (mark 0 and WOT, then divide that by 8 to mark off the others). After you have done this, you can go out and do some choke tests and plug chops to see where you are at on the various circuits.

Mark
 
sorry! how about this?

i heard that if you put a k&n replacement filter for stock, not pods, that the bike would run lean at WOT. i also heard that someone tuned their needle by switching the plastic and metal washer so the needle would sit higher. i also hope to get a little more power by increasing fuel. is any of this true?
 
catbed said:
sorry! how about this?

i heard that if you put a k&n replacement filter for stock, not pods, that the bike would run lean at WOT. i also heard that someone tuned their needle by switching the plastic and metal washer so the needle would sit higher. i also hope to get a little more power by increasing fuel. is any of this true?
Click to expand...

OK, better, but the needle has nothing to do with WOT, that is the domain of the main jet.
 
catbed said:
sorry! how about this?
Click to expand...

Better.:-D

I'm not ridiculing you, but it drives me mad that this keeps floating around. It is a misconception that can hurt engines and makes it very hard to diagnose and tune carbs until the realization hits that it is throttle position that dictates which circuit you are on. Doing the tape bit and using the choke to test for rich/lean makes it pretty easy to get close in only a couple of tries on the jetting. Plug chops on top of that will get it sorted completely.

Carb tuning is not rocket science, but it requires a careful, methodical approach. Try to do two changes at once and you will be chasing your tail for a long time.

Mark
 
catbed said:
i heard that if you put a k&n replacement filter for stock, not pods, that the bike would run lean at WOT. i also heard that someone tuned their needle by switching the plastic and metal washer so the needle would sit higher. i also hope to get a little more power by increasing fuel. is any of this true?
Click to expand...

All depends. This is why you tune a motor. If you were on the rich side of things and you added even more fuel, no you will not make more power. Leaner is Meaner, until it blows. Of course, you could be so lean the motor would not run but that would be a stupid setup.

I would doubt you would see much change by brand of the stock air filter.

Previous posts are correct. RPM by itself has little to do with circuit being used. I guess if you tied in torque you could figure it out. Also the needle has little to do once with the A/F ratio at wide open throttle.
 
the carbs are all stock, so no increase in fuel flow from before. it is my understanding that these bikes cam e very lean from stock. am i wrong about this?
 
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