....... Mikini and Keihin carbs.

[Brook]

........ How hard, would it be, to convert a set of Keihin Flatslides, that are built for a different bike ,to fit a FJ. I have a set of Mikuni 38mm F/S. And have had nothing but problems. I found out, they do not build the Keihin F/S's for FJ's anymore.
                                      Jeff

[fj1289]

It can be done.  It may be more expensive than you expect.  The parts to do it are not available any more either and will have to be fabricated or modified.  If you find a set of carbs set up for wider spacing than the FJ, you might be able to mod the spacers and throttle shaft.  Otherwise, you are looking at having to fabricate new ones.  This truely is a job you kind of have to tear into to see what it will take.  The devil's in the details.

You might be $$, time, and hassle ahead to do a fuel injection conversion.  I think there are some posts on this sight and some on the Yahoo sight that talk about it - but no step-by-step instructions!  Steve Conklin has done a lot of work on this - don't know the current status on it though. 

I think Steve is using the Microsquirt controller with Hayabusa TB's and I don't know what for a fuel rail, pump, regulator, sensors, etc.  Another option would be one of the later Hayabusa ECMs since they have hacked those and have a lot of capability built into them from the factory.  They are finding out that these are full on race controllers with abitly to switch maps, contol outputs (like N20), etc.  I'd imagine an FJ with a 1314 or 1349 bigbore and a nice head would have similar fueling requirements and would only require minor tweaking to the existing maps. 


Chris

[Brook]

..... Yes, I remember, Steve and Frank, talking about it, [injections converson's] But, like you said, do not know the results. If I could find a set of Keihin's for a good price. I would try it. I bought the F/S's. from CPW,[new] and when I got them, I could tell, that the slide shaft and the carb. bracket has been apart and redrilled. The hard part would be, the fuel lines, going from one carb, to the other.

[simi_ed]

I was looking at Sudco's site a week ago, and noticed that they still list a p/n for Keihin FS for the XJR.  Since this is still a FJ motor, they **might** fit.  I don't have the $1100+ they want, so I have no reason to inquire with Sudco, but they could be available.

[Brook]

...... Back to the Mikuni F/S, I wish I could afford another set of carbs. ... But, I am going to have to deal with the set that I have .. I hope Chris or anyone that has experience with Mikuni F/S will reply.>> It's not fun riding any more.<< The problems that I am having is, first, The overflow coming from the overflow tubes, ...I hope this is fix, I lower the floats from 17mm to 18mm from the base of carbs. the last time I went for a ride, no fuel on the ground>> after... Next,>>> The throttle sticking open<<<.. this is what I have done.... made sure no leaks from the boots, having the push-pull system. No bends.....they seem to work well... Adjusted the airflow screw> 1/4 to 1/2 turn out. Clean and check all needles and jets. Changes main jets and needle clips. I do not know what else to do. I was told, It's running lean, How could it stick wideopen when it is not getting enough fuel?.. I have check out the >> Mikuni carb.and tuning 101<< But, I did not see anything that would cause or fix this problem. One other thing, with the bike at idle and the filters off. and running. there is a tremendous amount of vaccum. ..... How can that be, with the slides down, where is the air coming from??.... Put my hand over the back of the carbs. and the RPM's drop. Also, I was told that the vaccum, from the motor is so strong, it it pulling and holding the slides open and to the walls of the carbs. But, that is were the push-pull cables come in to play..... So, Can anyone give me there thoughts on this.  PLEASE                        Thanks Jeff   

[fj1289]

Jeff,

You have two different issues.  The overflow issue I have always thought of as a float seat issue.  Are you running a fuel pump on your FJ?  If so, you may need smaller seats.  I'm pretty sure the ones from the stock carbs will swap out.  If you have the large seats made for gravity flow, the fuel pump can over power the float and still force in fuel.  Smaller seats solve this issue.

The sticking issue is definately a tough one.  I've seen people go both ways with the Mikuni RS carbs.  Some are bothered enough by the sticking to buy the Keihin's (that's what I did).  Others deal with them.  I don't know if some sets or set ups stick more than others.  On the other forum (Psychobike for Dragbike.com - I don't remember which) was the first time I've heard the running lean explanaiton.  Try going up a couple of sizes on the main jets and see if it helps.  Or to do a quickie test, use duct tape to cover up 2/3 to 3/4 of each air filter (to richen in up at high power settings) to see if it helps.  If so, then go to larger main jets. 

I'm going to have to face this again myself since the Keihins were among the stuff I had stolen.  They were spec'd for a late model XJR1200 - one that had TPS (I used it for datalogging).  I have seen a couple of different places that there are no more FCR's setup for FJ's nor XJR's.  I think anything you are seeing online is old info.  After paying for pistons and headwork for the dragbike, THEN having to buy a new trailer, I don't have the funds for FCR's even if they are available. 

Some people have talked about using some later model CV style flatslides from an FZ1 or something.  I don't know if anyone has taken this past the theory stage yet, or how much better than stock they would be.  Stock carbs are great for putting around on the street, but greatly restrict the Kookaloo!  I'm seriously contemplating running the stock carbs on the streetbike once again while trying to chase down all the parts to do an FI conversion - especially since the Busa and GSXR ECUs can be flashed now. 

Check your float seats sizes if you have a fuel pump and try riching the mixture (mains for WOT) to see if it helps.   

R/
Chris

[Brook]

.....Hey Chris, ....... I have the gravity feed pet cock, no pump. When I first bought my FJ, about eight years ago. I had to get another gas tank. The shop, that was working on the bike at the time, got it from Ebay. So, I do not know the year. Just know it is the small pet cock. Also, I forgot were, I heard that the bike setting on the kickstand, can cause the float level to change.   I bought the F/S's from CPW. They are the ones , that said it was a > lean < problem. And I have changed the Main jets many times from 130's 135's to 140's. Those are the only ones that I have. [Did not change]. But, I am told, that the main jets, should not have anything to do with the throttle issue...... One other thing Chris,,,, do you know, what the small spring, that is on the arm, that controls the lowering and raising the slides. What is it there for??   What is the big differents  between the Mikuni's and the Kiehin's is it the Kiehin's have the bearing on the slides?? ..About dealing with the throttle hanging up, Really, there is no way, I could not deal with it. It is so bad,....... What are the deal tails, was everything stolen at your home? was it lockup?? Do you know, that Steve C. has or had a set of the Keihin's for sell. The last time I talk to him, He said, he was going to wait to the summer months. You might what to call.  ...... I have a set of the FZ1 carbs, [Water damage]  for parts. Steve said, that they can be used, on FJ's. Not sure if I have ask before, do you have any pic's of your bike?? If I can remember right, you said, you spent some time at Mac Dill Air Force Base. Do you live in the Bay area?? 
                   Jeff

[joew]

Not sure this is even worth two cents, but the carbs on my '86 were stuck and it turned out to be the white plastic sleeve in the throttle handgrip rubbing on the bar-end that kept it from snapping back to idle. 

[racerrad8]

Jeff,

I am trying to read your posts but they just run together...

From what I think you wrote and like Chris said you have two different issues.

The overflow is related to leakage at the fuel supply float seat. The o-rings that seal that area are prone to leak over time. If you did not have any issues and now you do, it is something in that system. The o-rings, bad float or bad needle(s). I doubt changing the float height will fix you problem.

Secondly, even if the slide does stick up the idle speed is not affected. You can raise the slide while the engine is idling the the idle speed will not change. I would unhook the throttle cables and see if the problem still exists. If it does, then you might be to lean at idle which will cause a high idle once the bike is warmed up.

If you are speaking of the small spring on the throttle plate adjustment that is used for balancing the carbs.

And finally, I don't know if you saw my post about new carbs, but I can sell you a new set of carbs for $400.00.

Or send me your carbs and I will rebuild them and take care of any carb related problems. I have the ability to run and adjust them prior to sending them back to you.

Randy - RPM
rpm@rpmracingca.com

[Brook]

....RPM and racerrad8, Yes, I know some times it sounds like I do not know, what is going on. >> Well, some times, I don't....LOL....RPM>>About the hand grip and plastic, I have had everything, in that area apart and clean. everything moves freely. Thanks,...racerrad8, I am not sure what you mean, about the o-ring and pump,  Because I can't think of were the O-ring your talking about. and the pump, I do not think that anything will exchange with stock carbs. I have tryed. About, lifting the slides manually, and the idle not changing, I don't understand, because that is not going to happen, when riding.... I have had the carbs. apart to many times.[ We are talking new Mikuni 38mm flatslides > right<] I still have the stock carbs. and they work fine. But, of coarse they do not have the kick, like the F/S>>> and that's what has me hook <<<.. When I have the bike on the jackstand's, filters off and the tank off, with A good sourse of fuel, from another gas tank.[.pic in the gallery ] With the bike running, at idle, [and it starts up first time], it sounds great. But, when I give it the gas, half or wide open, it stays at that RPM, I am looking into the back of carbs, and the slides are down..... and the RPM's stays up,.. to the point,>>> I have to turn it off with the key. or I put my hand over the back of the carbs. and when I do that, There is great amount of vaccum.... I can not understand, were is the air flow coming from, [The slides are down] ......I have called CPW, many times, he is telling me it is running> lean< OK, turn the airflow srew, 1/2 to 1/4, turns out,... 130 to 140 main jets,<<<< big, for a 1219cc???..from the second clip to the fourth .>> jet needle<<  this has not work..... I ask, about the overflow,.... I have four sets of carbs. two of them are used for parts, I notice that the stock carbs. have a little rubber point on the needle that stops the fuel, from coming into the bowls.  the F/S's do not. He said, they do not come with them, could that be a issue?? The throttle cables are working well,<< WD40. When turning the throttle,  it pops back, not real fast, but, it returns. The springs on the carbs. are on the tightest setting, and that is rough on the wrist when riding. ........ About the spring IN the carbs. you take the tops off of the F/S... there is a rod that runs thru the four arms that pulls up and push down the slides. were the arm connects to the slides, there is a elbow, inside of the elbow is this spring, I have know idea, why it's there. So, at this point, I have the carbs. setting on the work bench, I am coming very close to doing something very drastic, I am thinking,.. why are the Keihin better than the Mikuni,  I need some ideas, soon....before I go to cutten, I can not use the F/S's, the way they are.... $400.00 for a set of >Keihin 39mm flatslides,.. check is in the mail.
                       Jeff

[rktmanfj]

Man, if I wasn't lost before, I sure am now.      

Randy T
Indy

[racerrad8]

We are talking new Mikuni 38mm flatslides > right<]

Nope...I don't have much experience with the flat slide carbs...By your posts I thought you were still using the Mikuni's...I have worked on several sets for some Suzuki & Kawasaki applications, and I am sure I can run them on my run stand to try and get them tuned for you. I know that Sudco is probably the people you need to be taking to about these.

why are the Keihin better than the Mikuni,  I need some ideas, soon....before I go to cutten, I can not use the F/S's, the way they are.... $400.00 for a set of >Keihin 39mm flatslides,.. check is in the mail.
                      Jeff

I have no idea why the Keihins are are better than the Mikuni. I was told it was due to the "accelerator pump", and they are bigger for more air flow. For a street bike, I think the Mikuni's will do everything you need.

The ones I have worked on were on Suzuki and Kawasaki powerplants in mini-sprint cars. I fought those carbs, and finally ended up changing both cars to Kinsler Fuel Injection.

$400.00 for a set of new Mikuni's

Randy - RPM

[Brook]

..... Rktmanfj... Why are you lost??... What part do you not understand??....Let me know,  I will put in simple words.

[the fan]

 I think its your typing style. Its very difficult to read esp for guys using their cute little hello kitty notebooks. I had to "translate" your posts myself to figure out just what you were trying to get across.

here is an example:

....RPM and racerrad8, Yes, I know some times it sounds like I do not know, what is going on. >> Well, some times, I don't....LOL....RPM>>About the hand grip and plastic, I have had everything, in that area apart and clean. everything moves freely. Thanks,...racerrad8, I am not sure what you mean, about the o-ring and pump,  Because I can't think of were the O-ring your talking about. and the pump, I do not think that anything will exchange with stock carbs. I have tryed. About, lifting the slides manually, and the idle not changing, I don't understand, because that is not going to happen, when riding.... I have had the carbs. apart to many times.[ We are talking new Mikuni 38mm flatslides > right<] I still have the stock carbs. and they work fine. But, of coarse they do not have the kick, like the F/S>>> and that's what has me hook <<<.. When I have the bike on the jackstand's, filters off and the tank off, with A good sourse of fuel, from another gas tank.[.pic in the gallery ] With the bike running, at idle, [and it starts up first time], it sounds great. But, when I give it the gas, half or wide open, it stays at that RPM, I am looking into the back of carbs, and the slides are down..... and the RPM's stays up,.. to the point,>>> I have to turn it off with the key. or I put my hand over the back of the carbs. and when I do that, There is great amount of vaccum.... I can not understand, were is the air flow coming from, [The slides are down] ......I have called CPW, many times, he is telling me it is running> lean< OK, turn the airflow srew, 1/2 to 1/4, turns out,... 130 to 140 main jets,<<<< big, for a 1219cc???..from the second clip to the fourth .>> jet needle<<  this has not work..... I ask, about the overflow,.... I have four sets of carbs. two of them are used for parts, I notice that the stock carbs. have a little rubber point on the needle that stops the fuel, from coming into the bowls.  the F/S's do not. He said, they do not come with them, could that be a issue?? The throttle cables are working well,<< WD40. When turning the throttle,  it pops back, not real fast, but, it returns. The springs on the carbs. are on the tightest setting, and that is rough on the wrist when riding. ........ About the spring IN the carbs. you take the tops off of the F/S... there is a rod that runs thru the four arms that pulls up and push down the slides. were the arm connects to the slides, there is a elbow, inside of the elbow is this spring, I have know idea, why it's there. So, at this point, I have the carbs. setting on the work bench, I am coming very close to doing something very drastic, I am thinking,.. why are the Keihin better than the Mikuni,  I need some ideas, soon....before I go to cutten, I can not use the F/S's, the way they are.... $400.00 for a set of >Keihin 39mm flatslides,.. check is in the mail.
                      Jeff

converted to the way it looks is easier to understand and therefore more likely to be read and responded to.

....RPM and racerrad8,
Yes, I know some times it sounds like I do not know, what is going on. Well, some times, I don't....LOL...

RPM: About the hand grip and plastic, I have had everything, in that area apart and clean. everything moves freely.
Thanks,

racerrad8, I am not sure what you mean, about the o-ring and pump, because I can't think of where the O-ring you're talking about is located.

About the pump, I do not think that anything will exchange with stock carbs. I have tried. About, lifting the slides manually, and the idle not changing, I don't understand, because that is not going to happen, when riding.... I have had the carbs apart too many times.
[ We are talking new Mikuni 38mm flatslides  right]

I still have the stock carbs and they work fine. But, of course they do not have the kick, like the F/S... and that's what has me hooked.

NOTE: racerrad / RPM / Randy (same guy) seem to mistakenly think you are tuning stock carbs

When I have the bike on the jackstand's, filters off and the tank off, with a good source of fuel from another gas tank.[.pic in the gallery ] and the bike running at idle, it sounds great. [and it starts up first time], But, when I give it the gas, half or wide open, it stays at that RPM.
Looking into the back of carbs, the slides are down, and the RPM stays up. At this point, I have to turn it off with the key or put my hand over the back of the carbs. When I do that, There is great amount of vacuum.
I can not understand, were is the air flow coming from, [The slides are down] ......I have called CPW many times, he is telling me it is running lean.
OK, turn the airflow srew, 1/2 to 1/4, turns out,...(presumably from the prior setting tf ) 130 to 140 main jets,is this big, for a 1219cc?
I moved the jet needle from the second clip to the fourth. This has not worked.
I ask, about the overflow (possibly in an earlier post? If so what did you ask?)
I have four sets of carbs. Two of them are used for parts, I notice that the stock carbs have a little rubber point on the needle that stops the fuel from coming into the bowls.  The F/S's do not.
The supplier said, they do not come with them, could that be a issue?

The throttle cables are working well, and I lubed them with WD40. When turning the throttle, it pops back, not real fast, but it returns. The springs on the carbs are on the tightest setting. This is rough on the wrist when riding, and does not solve the problem.

About the spring IN the carbs, you take the tops off of the F/S and there is a rod that runs thru the four arms that pulls up and pushes down the slides. Where the arm connects to the slides, there is an elbow, inside of the elbow is this spring, I have know idea, why it's there.
So, at this point, I have the carbs setting on the work bench, I am coming very close to doing something very drastic. I am thinking... why are the Keihin better than the Mikuni,  I need some ideas, soon....before I go to cutten(?). I can not use the F/S's, the way they are.... $400.00 for a set of >Keihin 39mm flatslides... the check is in the mail.
                      Jeff

I personally have not had to tune out major jetting problems on multicylinder bikes equipped with flatslides but I have tuned several singles and tamed a few multis.

First, Keihins are a more modern design but do not necessarily operate better than the Mikunis when working properly. All flatsides have issues, which is why the manufacturers quit using them, but the performance boost is well worth it if you are willing to sacrifice convenience for performance.

It sounds like your bike will start and idle but when you hit the throttle they hang at a high RPM. Is this correct?

I also note that your throttle does not snap shut. It should, especially with flatsides. Do you have a push/pull type throttle (2 cable) or a single cable? either wat disconnect the cables at the grip and see if the throttle plates will snap back into place by pulling the cable and releasing it. This will help in locating the issue.

• The hanging idle can be caused by several things:
  Vacuum leak causing a very lean condition
  poor sync
  lean low speed jetting
  worn slides

Most likely it is a mix of 2 or more issues.
It could also be as simple as a throttle cable that does not have enough slack to allow the slides to shut once the engine has been spun up enough to create excess vacuum. On a pumper carb this is a common issue as the carb itself is jetted lean down low to run crisply and avoid rich mixture induced flat spots. This system relies on a squirt of fuel from the accelerator pump to give the engine enough fuel to accelerate properly when the slides are opened. If the pump does not work the mixture will go lean and causing the engine to race and can generate enough vacuum above the slide to prevent it from closing completely.

It could also be from a bad bench sync as listed above. In the few multis I have tuned I have found that the slides need to be adjusted so that all of them open at the exact same time. if this is not the case the RPM will rise until all of the carbs have equalized. this is often at a higher rpm than any single carb is tuned for.

The first thing I would do in your place based on the post above is to call sudco and confirm the jet sizes, needle number and settings as well as the size of the float needles to ensure that you have the right starting point for this project. I would also check to see if they were set-up to run with or without an accelerator pump.

Next I would have the carbs ultrasonically cleaned to ensure that all of the tiny internal passages are clear.

once this is confirmed get back and I will let you know the easies method for bench syncing. Then we will all be on the same page.

BTW, I attached a diagram of a Mikuni RS smoothbore.

[fj1289]

Jeff,

The biggest thing that's better about the Keihin FCR is the rollers on the slides.  That design overcomes the natural slide sticking instead of using a strong spring to overpower the natural slide sticking.  On one of my early trips to the dragstrip (when I would ride to the strip vice trailer to the strip) I broke the end off the "pull" cable.  With the Keihin FCR, I was able to swap the "push" cable over to the "pull" side and ride home that way - no sticking slides.  If I had to do that with the Mikuni RS, I would have had to use the kill switch whenever I needed to slow down!

OK, back to troubleshooting by keyboard (from my experience, the only thing more difficult to fully understand than a mechanical problem far from you is a woman close to you!)...

I think you may have a throttle cable with not enough play and the two are fighting each other instead of each doing their own job.  With as heavy a spring as the Mikuni RS uses, the throttle should definatley "snap" back - "SLAM" back is probably a better term.  I'm beginning to think that is the primary symptom of your problem and makes the slide sticking worse than normal while riding.  Just have to find out what is causing it - my first guess is cable tension, possibly cable routing (does the throttle "snap" back with the tank off?  Or is it better with the bars turned one way or the other?), possibly a throttle cable end not centered in the bellcrank at the carbs and rubbing on something.  Maybe something rubbing inslide the throttle housing - try slacking the screw a hair and see if it improves.  Are you using the stock throttle and cables or the Mikuni throttle and cables?

Chris