FJ1100 carburettor adjustment and synchronization

[Tom Nolan]

Hi all,

Recently got a FJ1100. As far as I knew it ran fine when I got it and we had a few short rides. Then we had a longer ride, to give you a picture, approximately 420 kilometres which I think converts to 260 miles. And a few days later, fuel overflow from carbs.

I soon had the carburettors overhauled by a motorcycle mechanic specializing in 70 and 80s Japanese bikes. Rusty water in the carburettors, and so I did one such three-step treatment of the tank, with a pack of liquids to remove rust, condition, and seal it.

As I removed parts on the bike, I quickly decided that the air box wouldn't be re-installed, and so I ordered and installed new pod air filters from RPM.

I've not changed the jets/ needles/ nozzles - whichever is the right part and term - so as to let the bike have more fuel which may be needed due to the new pod air filters. I know this may be needed and will ask the mechanic to help me out if so.

A few days ago I were to synchronize the carburettors, as the mechanic told me I probably would have to, and the bike were vibrating a lot from idle to approximately 4000 rpm, which he also told me probably was a sign that the carburettors needed to be synchronized. Besides that, though, the motor ran just fine as far as I could tell, though I didn't actually rode it, just blipped the throttle and gave it some rpm in the garage.

Got a carburettor synchronizer tool from the mechanic. It's one of those 'planks' with four 'clocks' with gauges, with a hose between each 'clock' and vacuum-thing in front of the carburettors. Warmed up the bike, mounted the synchronizer, and the gauges were spinning wildly around. Unknowledgeable as I am I thought along the lines that oh well, somethings clearly wrong with the bike. After some googling without any particularly good answers to what could be the problem, I tried to carefully adjust some back and forth on the synchronizing screws, but the bike either kept vibrating or 'bobbed' when I 'blipped' it by the throttle, so I set them back to where I began as I clearly was as good as blind anyway (also bear in mind that I've never done this before).

In frustration I tried adjusting some on the fuel/ air/ mixture screws as well just to see what happened, but that just made the bike run worse, it began 'bobbing' when I blipped it. Now that I think clearer it's obvious that would happen, as that mixture probably weren't a problem at all. Anyway, I didn't get the mixture adjusted back to scratch and took a break from it all for some days.

Today I figured that maybe the valves that came with the carburettor synchronizer should be mounted on the hose, so I can adjust the vacuum pressure that affects the gauges, or however this thing works, by adjusting this little screw on each valve in and out. Makes sense as that's what the instructions that came with the synchronizer really pictured...

So, now I've drained the carburettors and mounted the valves on the synchronizer. Before I touch anything, I need your help.

1) How many rounds out should I start with the mixture screws and how to proceed? Adjusting one and leaving the others if it works, or should all screws be in the same position wherever that may be working?
2) Do you think the carburettor synchronizer will work properly now that I can adjust those valves on it's hose?
3) What other thoughts do you have based on what I've written?

For info, the mechanic isn't available to help me out for some days or weeks.

All the best

Tom Nolan

[Pat Conlon]

Got a carburettor synchronizer tool from the mechanic. It's one of those 'planks' with four 'clocks' with gauges, with a hose between each 'clock' and vacuum-thing in front of the carburettors.

Hello Tom, welcome to the FJ forum.
I am unfamiliar with the tool that you're describing. Please send us a picture.
As your engine idles, you are equalizing the vacuum between 4 carbs so you would need 4 gauges with each gauge connected to a hose, for 4 hoses total. Those 4 hoses are connected to the 4 vacuum ports located on the intake manifolds. To use these ports, remove the rubber caps on #3 and #4 ports and remove the rubber vacuum lines on ports #1 and #2, then plug the 4 hoses to your gauges into these ports.
Pulsing: As the engine draws air (pulls in vacuum) the needles on the gauges will pulse in time with the intake event. This is normal. The small valve located on each gauge is used to tune down these pulses to steady the gauge needles.

Here is a video showing 2 different types of carb sync tools, the gauge type and the liquid column type.
Look at the gauges, is this what you have?

https://www.youtube.com/watch?v=Ne3qqfW_dXA

Remember the goal, equalizing the vacuum between all 4 carbs.
Once you get the pulse on the gauge needles calmed down, you can start.
There are 3 adjustment points on our FJ carbs, (as you sit on the bike)  
1) Left side screw balances carbs #1 with #2
2) Right side screw balances carbs #3 with #4
3) Center screw balances the 2 left side carbs (#1-2) with the 2 right side carbs (#3-4)
Adjust the vacuum in the above order....work fast, don't overheat your engine. Get a box fan to keep air flowing.

The air/idle mixture screws: Turn them in (clockwise) until *lightly* seated, then turn them out (counterclockwise) for 3 turns. That should get you in the ball park.....fine tune only after you sync the carbs.

Cheers.  Pat

[Sparky84]

G'day and Welcome Tom

There's also heaps of info here in the Files section

https://fjowners.com/index.php?board=21.0


Good Luck

[Tom Nolan]

Hello Tom, welcome to the FJ forum.
I am unfamiliar with the tool that you're describing. Please send us a picture.
As your engine idles, you are equalizing the vacuum between 4 carbs so you would need 4 gauges with each gauge connected to a hose, for 4 hoses total. Those 4 hoses are connected to the 4 vacuum ports located on the intake manifolds. To use these ports, remove the rubber caps on #3 and #4 ports and remove the rubber vacuum lines on ports #1 and #2, then plug the 4 hoses to your gauges into these ports.
Pulsing: As the engine draws air (pulls in vacuum) the needles on the gauges will pulse in time with the intake event. This is normal. The small valve located on each gauge is used to tune down these pulses to steady the gauge needles.

Here is a video showing 2 different types of carb sync tools, the gauge type and the liquid column type.
Look at the gauges, is this what you have?

https://www.youtube.com/watch?v=Ne3qqfW_dXA

Remember the goal, equalizing the vacuum between all 4 carbs.
Once you get the pulse on the gauge needles calmed down, you can start.
There are 3 adjustment points on our FJ carbs, (as you sit on the bike)  
1) Left side screw balances carbs #1 with #2
2) Right side screw balances carbs #3 with #4
3) Center screw balances the 2 left side carbs (#1-2) with the 2 right side carbs (#3-4)
Adjust the vacuum in the above order....work fast, don't overheat your engine. Get a box fan to keep air flowing.

The air/idle mixture screws: Turn them in (clockwise) until *lightly* seated, then turn them out (counterclockwise) for 3 turns. That should get you in the ball park.....fine tune only after you sync the carbs.

Cheers.  Pat

Thanks!

Seems like I've been on the right track at least. I have the gauge type carb sync tool. I've mounted the valves now, so my next try should work out better than the first!

The carb sync I've got is some variant of this one: https://www.walmart.com/ip/Leke-Motorcycle-Fuel-Vacuum-Carburetor-Synchronizer-Tool-Carb-Sync-Gauge-4-Cylinder/1275910251?wmlspartner=wlpa&selectedSellerId=101183488, which comes in many versions with slight differences when I google it. I don't have the nuts and o-rings that's on the photo in the link, but the rest of it. I've now cut off a piece of the hoses, mounted it below the gauges, then fitted the valve, and then the rest of the hoses to the valves; and then the end of the hoses to the vacuum ports. The 'sticks' you can see in the photo have no use for me as far as I can tell, as you probably are aware since you know our carbs well.

G'day and Welcome Tom

There's also heaps of info here in the Files section

https://fjowners.com/index.php?board=21.0


Good Luck

Thanks! I've noticed that carb adjustment guides posted in the files section have opposite logics at certain steps. One guide, by David Raforth (https://fjowners.com/index.php?topic=655.0), states that if the bike slowly goes back to idle after blipping the throttle, the mixture is rich, and if the bike cuts off dropping below idle rpm and then goes back up to idle when blipping the throttle, the mixture is lean. Another guide (https://fjowners.com/index.php?topic=580.0) states the opposite regarding which symptom represents rich/lean mixture. I think the guide by Raforth is right, but can you confirm?

[gdfj12]

David Raforth knows the FJ carbs very well. I follow his advice and the advice of Randy or Robert at RPM Racing. My '89 has been running awesomely since the last carb rebuild. It's set for 600' altitude and it ran fine even all the way up Pikes' Peak in Colorado, to somewhere around 13,000+ elevation.

George D