FCR tuning issue

[memper]

I looked in the search here and found only a bit of what I'm experiencing. When I first got them and didn't know a thing, thinking that the fuel screws were a/f screws like on cv carbs, I seated them and turned them out to 2 turns. After reading a bit I remedied that and now they are both at 3/4 of a turn out.
I was getting some hesitation/farting at idle when the throttle was cracked fast and hard so I set the slow air screws to 1,1/8 instead of the 1,1/2 recommended. Thinking the hesitation/near stall was from being too lean (no air box, just alum v stacks). Though throttle drops back to idle quickly and steadily.

Turns out the hesitation goes away after riding and its good and warm.

The other situation I experienced was a hanging idle while riding. I would be going 20/25 mph and approaching a red light. I would pull in the clutch and down shift to first (clutch still pulled) while I'm coming to the stop. But the idle would hang at like 1300-1500 rpm. I would then blip the throttle and the hang would go away.

My guess is that the slow air screw is too lean. However I have it turned in a bit (as stated above) which richnens the idle circuit yes?
The appearance of the hang is not consistent either.
I'm confused (again...lol)

[brad black]

i think i ended up with 45 pilot jets in my 750.  i tend to tune the lower end with the pilots and keep the screws close to std settings.  but i'm not sure how valid that theory is, could be complete crap.

not sure about what you're experiencing tho.

[memper]

I will put all back to std settings and get new plugs n go from there. Will report back.
According to Pat Burns using the screw is preferred...

[Cloner]

I had an identical problem when I installed FCRs on my 900 about 12 years ago.  I tweaked...and tuned...and fiddled....and finally removed them, cleaned the joints, and reinstalled them and they've worked well since.  I think they just had a small vacuum leak that made them really lean at idle and off idle, but was insignificant at higher throttle openings.  The idle didn't change with application of carburetor cleaner or other liquids, but the problem definitely went away after a quick cleaning of the manifold boots.

I, like Brad, got best results changing pilots to get "in the ballpark" then using the screws only for fine tuning.  My bike is fairly rich at idle, but that's largely on purpose to assist in cold starting due to lack of choke.  It's still as cold-natured as a hibernating grizzly on New Year's Day, but it runs great once it's warm.

[memper]

I had an identical problem when I installed FCRs on my 900 about 12 years ago.  I tweaked...and tuned...and fiddled....and finally removed them, cleaned the joints, and reinstalled them and they've worked well since.  I think they just had a small vacuum leak that made them really lean at idle and off idle, but was insignificant at higher throttle openings.  The idle didn't change with application of carburetor cleaner or other liquids, but the problem definitely went away after a quick cleaning of the manifold boots.

I, like Brad, got best results changing pilots to get "in the ballpark" then using the screws only for fine tuning.  My bike is fairly rich at idle, but that's largely on purpose to assist in cold starting due to lack of choke.  It's still as cold-natured as a hibernating grizzly on New Year's Day, but it runs great once it's warm.

Makes sense...I will take a look at what pilots are in there and double check the rubber flanges. Thanks. The rev hang is probably due to this. Aside from that intermittent rev hang when rolling to a stop, there seems to be no other issues. I have not checked for flat spots in the upper register yet. Kinda hard to get above 50mph in NYC.

[koko64]

Have you read Patrick Burns Keihin FCR Tuning Procedure? Its the word on FCR tuning.
Chris Kelleys Ducatitech site has a link.

In theory your slow fuel jet should be correct when you get the fastest, strongest idle with the Idle Mixture Screws between 1 and 2 turns out. So more than 2 turns out you need a bigger slow jet, less than 1 turn out need a smaller slow jet.
Thats the theory, unless you have an incorrect Slow Air Screw setting (or messed with it at the same time ) or have an incorrect needle. Chris sends good needle sizes ime and from what others have reported, unless you've done big mods.
You have open velocity stacks, thats correct?

Try and control low speed running with the Slow Fuel Jet as Brad suggested.
 If you want to use the Slow Air Screw instead, go ahead, but it takes some experience with these carbs to juggle both circuits, so play with one or the other to get what you want. A 1/8 turn of the Slow Air Screw can make a difference at points from idle to 1/4 throttle. I understand how turning a screw is more attractive than pulling float bowls off.

Another thing to consider is that snapping the throttle at idle is one thing and doing it under load is another. My testing would be under load.
These carbs are great, but the hardest part to tune is the off idle to 1/4 range.  Some of that range is personal preference, eg, snappy Vs smooth or acceleration Vs economy or wheelie nut Vs commuter.

[memper]

Yes, like I said, the hesitation while standing still and cranking the throttle disappeared after returning from a run. No issue with that part anymore.

I'm just confused, considering the leanness of my intake setup that after enrichening the slow air screw the throttle would hang, inconsistently when coming to a stop.
For the most part (say 80%) low speed running was fine. Just occasionally it had that hang... So weird..
The settings that were originally there had the bike *seemingly* operating fine. I just got in there to fiddle because of my free flowing intake. Thought I'd be doing a good on it but I guess not.

And who makes a carb with no bowl drain so every time you go to inspect shit you get covered in gas?? Keihin that's who....lol


*Edit: I just read a great thought on the matter:

"...Even though the first impression of hanging is that it is lean, it may be just the opposite. You may have the idle set to high, after blipping the throttle, RPM returns to normal idle, which is to high, then the motor loads immediately from over rich condition and RPM's drop. You can test this by turning of the fuel valve when the motor is idling, if after a few seconds the RPM starts to rise, then it's to rich. Now turn fuel back on while RPM is in elevated position and it should immediately start to drop..."

[koko64]

Just checking. The Slow Air Jet screw in the carb mouth. Controls air.  In for richer.
Idle mixture screw in float bowl recess. Controls fuel. Out for richer.
Try turning the Idle mixture screw out 1/4 turn see if the hanging stops.
Like to see if the hanging stop with the IMS between 1 to 2 turns.

Could be a cable routing, adjustment thing. Probably not, you got lots of room under there.

Maybe Brad can chime in, he sourced some velocity stacks designed to work with K&N pods. I was thinking of testing them. Maybe the K&N site has them. I worry about your motor life with no filters and alloy stacks (looks mean as sharkshit though).

[memper]

I'm gonna shoot at the easy stuff first. Could simply be a bad seating at the boots. Those connections could be better, but alas..
I'm not skeerd about running stacks. I have thick nylon filters over the openings which have similar micron levels as k&n filters just minus the oil (which in some camps is believed to attract and hold dirt to choke up airflow and possibly act as a snack for the motor later on).

I know dudes that have totally open stacks, run em hard for years with no issues. I'm not worried. Next year I'm ditching the 750 for a 900 anyway  


Another odd thing. Any other fcr owners notice that its hard or near impossible to create slack at the grip? The tensioner at the middle of the pull cable is all the way in (loosest possible setting) and I have zero play. Well maybe 1/16". If I move the barrel up one hole on the butterfly, I can get some slack but the result is that the cable doesn't pull the butterfly all the way round then.

[brad black]

no air filters (or air filters without oil) will wear rings and piston skirts.

if it's in neutral then idle is the only relevant test.  anything else is irrelevant.  i remember one dickhead who was going insanely mad that when he held his 900 with new fcr at 3,000 rpm in neutral the pipes glowed, which indicated in his belief completely wrong jetting (too lean).  wouldn't be told otherwise.

aside from that, i tend to find playing with the idle mixture and slow air screws frustrating and often largely ineffective.  which is why i change pilot (slow fuel) jets.  plus they always idle much richer than i would idle anything else, around 8% co rather than the 5 i'd usually use.  i've gotten over the compulsive need to have 5%.

to drain the float bowls you put a little container under the main jet caps and remove it.  fuel drains out.  easy.  i use a plastic bottle cut lengthways, so it's long and shallow and can be jammed between stuff.  wearing nitrile gloves helps keep the pinkies clean too.  the ladyfriends tend to appreciate that.

i bought some plastic trumpets to mount k&n filters on fcr while maintaining a decent trumpet form, from k&n - http://www.knfilters.com/psadapter.htm  haven't tried them.

[memper]

no air filters (or air filters without oil) will wear rings and piston skirts.

I have a plan to take my ru-1750s and cut the flange and affix the blue keihin v stacks to the filter base.

if it's in neutral then idle is the only relevant test.  anything else is irrelevant.

Well the occurance happens (if and when) while in gear but with the clutch pulled

to drain the float bowls you put a little container under the main jet caps and remove it.  fuel drains out.  easy.  i use a plastic bottle cut lengthways, so it's long and shallow and can be jammed between stuff.  wearing nitrile gloves helps keep the pinkies clean too.  the ladyfriends tend to appreciate that.

Didnt even consider that cap. Thanks!

[memper]

It works. Though I wish the blue v stacks had a bigger opening. Might choke the airflow a bit??

[memper]

But after installing the blue v stacks I noted that the pilot screw and main jet just kinda "hang out" there in the breeze. Is that ok? I guess the carbs are typically attached to a filtered air box so those openings are filtered. The blue stacks probably were not intended to be run without an air box correct?

So basically I just cut up a pair of filters for nothing. Good thing I got them for only 8 bucks!

[brad black]

the k&n adaptors cover the slow air and main air jets, like the alloy adaptors, but longer.

[memper]

I'm a dope. But I'm just going to fashion new flanges. Unless I find a steal on ebay again for new filters