550 Seca owners...I have questions...

Hello,

I just picked up a 1982 Seca 550 up in PHX and I am working on tuning it up right now...have yet to break anything apart because I would like to have my ducks in a row before beginning any overhaul...

Pertinent info:
- Mileage: 31,780 miles
- Obviously, it is a 550. Currently running champion plugs...going in the garbage when I get time to pick up a set of D8EAs
- Has an odd cyclic throbbing...rpms cycle kind of like a thrum, thrum thrum...a bouncy kind of wave around about 1200 rpms...thought it was the cam chain tension but adjusted that and it still is there...
- running pod filters and a 4 to 1 ehxaust...running lean because I don't think the bike was properly jetted...
- I believe it has some valve train noise...intermittent tapping from right side of motor (cylinder 3 or 4 not sure which)


Questions:

1) How come I had never heard about this bike...I think i have permagrin right now just from riding it around the block

2) What are the stock jet sizes...I ahve heard the main is 112.5...? I can't seem to find it in my Clymer manual, funny as that may be...

3) Are these motors prone to losing their top ends? The bike sat for three years so i am wondering if something up top could be bad...

I guess that covers it for now...any input/advice is greatly appreciated.


Semper Fi,

Jon

 

112.5 sounds, right but on mine I have 137.5's with k&N filters and a spec2 exhaust. I also have the FJ 600 motor in mine. Top ends are pretty good just don't do long burnouts on them.... Lost a valve that way For the most part it's a quick and nimble bike for the time with decent power. Just change the oil often and keep the chain lubed and adjusted. When the chain wears out replace both sprockets and chain. I have had two chains break on me and they both went through the starter and ripped it off of its mount. If you can get the braided stainless brake lines. The one disc setup is mediocre at best.

Sean

 

ee) OEM and aftermarket Mikuni brass MAIN FUEL JETS, sizes as follows, fits all XJ550, XJ650 Turbo, all XJ700-X and XJ750-X, XJ900RK, and XJ1100 models.

NOTE: stock Mikuni XJ series carbs used the following original main fuel jet sizes:

#100 1985 all XJ700-X models
#102.5 XJ900RK US & Canada
XJ550L (1984) on cylinders #3 and #4
#105 1986 all XJ700-X models and all XJ750-X
XJ550L (1984) on cylinders #1 and #2
#107.5 XJ900 1983-84 except USA or Canada
#112.5 XJ550 all models and XJ1100
#127.5 XJ650 Turbo carbs for cylinders #1 and #4**
#132.5 XJ650 Turbo carbs for cylinders #2 and #3**




Alas, the Mikuni BSxx series carbs used on XJ models---unlike their cousins the Hitachi HSCxx series carbs---did not have replaceable main air jets. The MAIN AIR JETS on these models are in the carb throat, facing the airbox, and are a small, brass pressed-in tube that is non replaceable, and which we suggest you do NOT try to modify by drilling or enlarging.

And just in case anyone is wondering, here are the sizes of these non-removable main air jets in the various models:

#45: XJ900RK
#70: XJ550 all models and XJ650 Turbo models.
#120: XJ700-X all models and XJ750-X all models*
#140: XJ1100 models*



ef) OEM and aftermarket Mikuni brass PILOT FUEL JETS, sizes as follows, fits all XJ550, XJ650 Turbo, all XJ700-X and XJ750-X, XJ900RK, and XJ1100 models.

NOTE: stock Mikuni XJ series carbs used the following original pilot fuel jet sizes:

#32.5 XJ650LK Turbo (1983)
#35 XJ550 all models, XJ650LJ Turbo (1982), and XJ700-X all models
#37.5 XJ750-X and XJ900RK USA & Canada only
#40 XJ900 1983-84 except USA or Canada
#47.5 XJ1100




ef2) OEM and aftermarket Mikuni brass PILOT AIR JETS, sizes as follows, fits all XJ550, XJ650 (except Turbo), all XJ700-X and XJ750-X, XJ900RK, and XJ1100 models.

NOTE: stock Mikuni XJ series carbs used the following original pilot air jet sizes:

#120 XJ750-X models
#140 XJ700-X and XJ750-X models
#155 XJ550L (1984) models
#160 XJ900RK all models
#165 XJ550 Maxim models (1981-83)
#170 XJ550 Seca models, XJ650 Turbo, and XJ1100

 

Answers: 1: That way there's more for us. 2: I knew Len would come thru. 3: Dunno. From what I know they're bulletproof, suffer the common XJ "achilles heel" (carburetors) and I think I know what you're hearing: Most likely the primary chain. These bikes have a massive, short primary chain from the center of the crank that drives a jackshaft that has the primary drive gear on one end. The Clymer book IS woefully inadequate I am sorry to say. I am currently suffering by with one waiting for the FACTORY service manual I found on eBay for $15 (yes fifteen dollars) to get here. Anyway, back to the primary chain. There is apparently a tensioner of some sort for the primary chain, it appears in one photo in the Clymer book, and also appears to be "automatic." I have 2 Seca 550's, one has a bit more primary noise at idle but it works and rides just fine and the noise goes away as soon as I come off idle. I also notice there is a certain amount of trans/clutch noise associated if the bike is in neutral with the clutch out. None of this seems to affect operation one bit, the bike runs and shifts just fine (including finding neutral when hot) so until I start finding giant bits of the primary adjuster (guide?) in the sump I have elected not to worry about it. All in all, you have stumbled upon what is in my humble opinion, the "purest" of the XJ's, being chain driven and of a relatively small displacement. The sweet high-revving powerplant in the compact, rigid frame makes for an awesome little backroad bomber. I strongly recommend a decent set of rear shocks and that's about all since you already appear to have lower than stock bars. I would dearly LOVE to get my hands on an original Euro-spec 1980 XJ400R, the original Seca. Enjoy!