Any OEM carb choices for the FJ ?

[turbocamino]

  Curious if anyone has had success fitting other ,larger, OEM type CV carbs ,,i think i read that FZ1 or maybe ZZR Kaw have been tried?  This would be for a 1300cc 150+ HP motor.

[fj1289]

I thought there was a post or two about FZ1 carbs, but can't find it now.

I did find this: http://www.fjowners.com/index.php?topic=3381.msg28526#msg28526

If you are looking for performance though, I'd really have to recommend performance carbs - the Mikuni flat slides or the Keihin FCRs.  I've run both - both make great power.   The Keihin's are amazing carbs - can be difficult to get setup, but very worth while.    You can easily adjust both air and fuel for all circuits to get them to fuel perfectly.

[turbocamino]

  Thanks for that link Chris,,it answered several questions.  I see that FZ1 carbs are 37s and the FJ's 36mm ,,may not be worth the effort?  No doubt i am leaving HP on the table without good carbs,,I have had a couple different sets of Mikuni's over the years and it always made for a jumpy ride compared to the vacuum carbs.  There was mention of zx1000 carbs ,, hoping they are at least 38mm?  thanks. 

[fj1289]

Another option - but not CV's (at least I don't so) - some GSXRs came with flat slides from the factory.   They may be a bit more well behaved - but will be very hard to find!

Sounds like you would really like the roller slides of the Keihin FCRs -  really smooth compared to the Mikuni flat slides. 

[turbocamino]

 The FCR's do seem to be a solution the more i read about them,,  big pill to swallow though @2K !  gulp.  These days all out HP is not at all why i ride.  This new engine was a fun project with minimal stress involved, Web,540 cams Andrews 1297,, and a somewhat local guy ,that did ProStock bike heads for many years ,,even a world championship to his credit,,got mine in and done in 5 weeks,,not a big valve head but the bowls and runners are a work of art to my eyes. Degreed to 106/108 (thank you Robert) ,, should be peppy : )

[Pat Conlon]

See my reply #26 on this thread: http://www.fjowners.com/index.php?topic=19232.msg195814#msg195814

I found in the UK some Mikuni 38mm CV semi flat slides off the '90-94 GSXR 750 (Mikuni BST38SS aka slingshot carbs)
The USA/JDM GSXR's used the 36mm carb, not the 38mm carb. You gotta go to the EU to find the 38's.

I don't have these installed yet, but *in theory* these have the potential to be the best of both worlds, a CV carb that compensates the fuel mixture for density altitude along with a 38mm bore for high rpm volume.
They have a unique slide design looks like this  —U— hence the nick name "slingshot".



The GSXR's rack needs to be shortened in the middle from the 77-93-77 spacing to the FJ's cylinder spacing of 77-85-77

Cheers

[fj1289]

Nice find Pat.  Pretty sure those were the carbs I was thinking of - so they were CV's

[MarioR]

Another option - but not CV's (at least I don't so) - some GSXRs came with flat slides from the factory.   They may be a bit more well behaved - but will be very hard to find!

Sounds like you would really like the roller slides of the Keihin FCRs -  really smooth compared to the Mikuni flat slides. 

Here you go: Mikuni flats 38mm

[Pat Conlon]

Yes, the Mikuni RS38's are common. IIRC Travis is running a set on his FJ.

[MarioR]

Yes, the Mikuni RS38's are common. IIRC Travis is running a set on his FJ.

I have my 86 engine rebuilt with 1219 Wiseco's and 38 MIKUNIS on it. Started today first time.....Mozart sound....

[Pat Conlon]

The Mikuni TMR flat slides would be my choice. They have rollers on the slides.
https://www.ebay.com/itm/116885339938

They do have a unique jingle jingle jingle as roll down the road.

[T Legg]

I love the RS-38 carbs. My bike runs smooth from 2500 all the way up through 9500 rpm. The bike had loads of power with the 1100 engine and the RS-38's now that I have the 1249cc xjr1300 engine in the bike with the RS carbs this bike really runs strong. My son has a zzr1200 which is a rocketship but when he rides mine he notices the extra snap when you roll on the throttle due to the accelerator pumps. On a side by side roll on my FJ will pull away from him until his cv carbs catch up.This spring we are going to do a side by side 1/3 mile run down the alpine county air strip to see how they compare. I doubt I can beat his bike but I don't think he will be leaving me in the dust. He was hitting 156 mph on his runs a few years back despite being at an altitude of 5,900 feet. One of the guys in our group who was riding his fjr1300 was dissapointed that his bike was only getting up to 145 mph .
 The RS-38 carbs are easy to tune. Ive found the suggested settings on the mikuni spec sheets were right on the money except the pilot screw settings. The specs say to set the pilot screw to 1/4 to 1/2 turn out. The carbs will run very lean and rough at those settings. I have my pilot screws at 1-3/4 turns and it runs very smooth. The accelerator pump needs to be set to start at 1/4 throttle and end at 3/4 throttle or you can get a stumble at about 5,200 rpm.It is also important to have the carbs balanced. One other consideration is to make sure the accelerator pump nozzles are turned correctly to spray down the carb center.

[Warp84]

I was actually looking at doing Mikuni RS36 carb's in place of my torched BS36's that came on the bike. Do you actually need to go to the 38 size, in leu of the 36's, to get it to be more plug and play? I do intend to go with the Wiseco 77mm piston's in the future but haven't done that change yet, so still running stock piston and rings.

[T Legg]

My first FJ1100 had RS-36 carbs and it ran great with those carbs. The carbs were the old versions with bakeolite plastic slides and they started to have a hanging idle problem I couldnt fix so I bought a set of RS-38 carbs. I didn't get much if any improvement over the 36 mm carbs in HP with the stock 1100 engine and the larger carbs didn,t run as smoothly .When I put The larger 1249 cc engine in with the RS-38 carbs they seemed like a perfect fit and the bike runs very smooth.I think the RS-36 carbs would be a better fit with a stock 1100 engine.

[Warp84]

My first FJ1100 had RS-36 carbs and it ran great with those carbs. The carbs were the old versions with bakeolite plastic slides and they started to have a hanging idle problem I couldnt fix so I bought a set of RS-38 carbs. I didn't get much if any improvement over the 36 mm carbs in HP with the stock 1100 engine and the larger carbs didn,t run as smoothly .When I put The larger 1249 cc engine in with the RS-38 carbs they seemed like a perfect fit and the bike runs very smooth.I think the RS-36 carbs would be a better fit with a stock 1100 engine.

Do the RS36/38's have the same bracket spacing as the BS36's? And use the same intake boots. Or do I need to find custom boots as well when I go to change out the carb stack?