FJ-600 Carb Nightmare!

Okay okay... it's not an XJ, but I'm sure it has a common engine with an XJ-series bike. The carbs on this bike are Mikuni BS32.

So. I recently picked up a beautiful 1985 Yamaha FJ 600, with one major problem: it had been sitting for 10 years, literally (last registration sticker was 1998). Previous owner had bought it at an estate sale, took it home, and dorked around with the carburetors - which were, of course, plugged tight.

He gave up, and so now the bike is MY project. He had taken out the plugs over the pilot jet screws (good) so he could clean out the carbs. I've since pulled and inspected, and they look okay, but are still plugged somewhere, I'm sure. The bike won't start on its own... with hard-start spray, I can get it to finally fire, and then run at 5,000+ rpm, but nothing below that. I checked the pilot jet screws and they were randomly set: one was 4 full turns out, the next 2 turns, the next was all the way tight... like he had just randomly installed them. OUCH!

So the question for the group: what is a good starting point for each of the four pilot screws? I know this is sensitive setting, but I don't even know where to start.

This for Mikuni BS32 carburetor. Any help at all... any starting point... would be wildly appreciated. Thanks!

 

3 turns out should be close enough for it to run decently.

By 2000 rpm though the screws have little to do with things. If you can only run 5k and up the pilot circuits are likely still dirty.

 

2.5 is were we start on the xjs.when i bought (rescude) my 700 it really ran like crap.
would not go over 65 mph though it ran well enough in town.
this site saved the bike from being re-sold as junk.
when i read how to pull the pilot covers i found them set from 1/2 a turn
out to 4.5.
thats from the factory! after a comlpete cleaning ( thxs again guys)
i set @ 2.5 and since have made adj to comp altitude, carb synq, etc.
now there all arould 3 with minor adj to bring the color in on each plug.

 

Hey THANKS! A place to start!

Amazingly on this bike, gas tank rust is not an issue: whoever stored it filled the gas tank before doing so. We've disposed of that gas.... but checked the tank and no signs of rust. Put a gallon in and drained it into a glass jar, a little at a time, NO rust flecks.

My big Nervous about this bike is that someone else dorked with the carbs. If I knew for sure that the bike was put away running and nothing was touched, I wouldn't be so nervous.

Side question: anyone have experience with the performance Jet Kits that appear on eBay? Like this one: eBay item #330302872202

I like the idea of making the fuel flow more rich, the bike has Kerker mufflers on a stock header. Other experience with bikes of this vintage (1980-1985) is that they are jetted quite lean, for emissions and other considerations.

THANK YOU to all who reply... this will be a nice bike when I get it done, and I will post pics!

 

Gonna have to take them off and open each up one at a time. Need to remove the jets, pilot screw(spring,washer,O'ring), slide, emulsion tube, float/valve and seat. Pay close attention to orientation of all removed so you get them back in the right place. Clean them all and spray carb cleaner through every port until clear. Clean the orfice in the float bowl if it has one. Wear SAFETY GLASSES when spraying carb cleaner. Then re-asemble and set your pilot screws. Don't dip the carb bodies in carb cleaner or you'll have an even bigger job...

You'll want to make sure you still have the spring, washer and O'ring on those pilot screws or that will cause Idle problems.

Adding a fuel filter is always good.

 

Be sure to clean all the air ports too. I had a problem like this with my little enduro. The airport near the top of the intake of the carb was plugged. No air getting into the carb to mix with the idle fuel. I thought it was clear, but after poking it with a strand of wire, a big clump came out and the port hole was bigger than I thought.

 

you wont go wrong pulling the carbs and doing a thorough job cleaning.
you may need to soak the carbs for a couple of hours or even over night
to get all the ports free of gunk.
some use carb dips, others steaming hot vinager,simple green, etc.
but if you don't make the carbs absolutely spotless-you will never be sure
that they are not the prob if it will not run right.

 

WOW - Great info, and I can't thank all of you enough. Serious. I consider myself a competent bike mechanic, but there is so little solid info from these bikes of a quarter-century ago. Yeah, junky Haynes manuals, or Clymers, but they usually beg off on the fine details of carbs.

The bike I'm working on now is so cool... very intact, paint good, 50K miles... I know it's the detail stuff to make it all right. I bought this bike so my wife can learn to ride: I think it's the right size and certainly the right price. After her, my pastor at my church wants a turn with it, and then finally, my step-son will use if for daily transportation. At least that's the plan.

My last serious work on motorcycle carbs was with Amal Concentrics... so YES I'm an old fart. Hope I can be teached new tricks. Thanks again!

 

i think you will find that most of us on this site are in or quickly heading
to old fartdom

 

Then there are those of us that have actually passed old fartdom several years ago :roll: ...

skillet

 

Hi, I havn't pulled my carbs yet - but the bike IS an XJ. Yamaha decided to call it an FJ in the US for some reason.

My biggest issue has been with the previous owners poor maintenance - and the fact the rear suspension needed all ned bushes!

I'm not sure I would like to learn to ride on it though - It's definately got two sides to its character. It'll poodle around in town but has a definate kick above 7000 rpm!