Tuning FJ1200 carbs on a FJ1100

[Slick]

For those who dont know the bike background:
1985 FJ1100
16k miles
V&H 4-1 Exhaust
Original Airbox



I have had various issues with the electrical system as well as idling problems. At some point in 2011 I rebuilt the carbs with new floats and seals. The bike ran much better, but I still have problems due to rust being in the tank (Not the issue for now).


So I'm sitting here tearing down the carbs(again) and wanted to write down all the jet sizes. When I went to look them up I realized nearly all the jets in my cabs are to the specs of FJ1200 carbs. Guess the PO did a little swap for some reason.

Here is what I have:

Main Jet  -  115
Main Air Jet   -  Y-2
Pilot Jet  -  37.5
Pilot Air Jet  - 155
Needle  -  5FZ72
Mixture Screws  -  3 ½ turns out


Does anyone have any suggestions or comments for this Jet combination on a FJ1100 with V&H 4-1?
Any suggestions on "Mixture screw" or "Float Height"?

Please keep the "pod" recommendations to a minimum, I would like to maintain as much original setup as I can. 

[Pat Conlon]

Looks ok to me. Why are you concerned?

[oldktmdude]

Looks ok to me. Why are you concerned?

I'm with Pat. Jet sizes are certainly in the ball park. Mixture screws should be closer to 2 1/2 turns out. What issues are you having?  Pete.

[Slick]

I'm just asking for a general opinion as well as suggestions. I have to finish the battle with the rust in the tank before I know just how well she can run. This thread was just to get an idea of how much the PO "tweaked" things since I just realized that my carb-set must have come from a FJ1200.

Some of my symptoms are:

POORRR cold starting
Rolling-on the throttle has a break-up around 2000rpm that drops down to 1200rpm, and then back up as you continue to roll-on the throttle.
Some popping from the exhaust(not back-fire loud, just pops of air)

So yea, they are some of the things that I was experiencing last season. I have replaced a number of things since then, and I just want to put everything together nice and "Right"!
 
Float Height anyone?

[andyb]

There is no 'right' that anyone can tell you.  The best you can get will be 'close', and getting to right from there is up to you.  Every bike is different.

Clean the choke circuits and ensure that they're all fully actuating.
Clean the pilot circuit, including the jet and the passageways from it to the mix screws as well as the ones straight into the airstream.
Ensure the float height is level accross the lot.  It'll probably need adjusted after, but I don't think it's all of your problem right now.


As has been said, those jets are all quite in the ballpark.  Most likely something is dirty or leaking a bit.... particularly if there is a bunch of rust in the fuel!  Start with a good source of clean & fresh fuel, and run it through a set of carbs that are clean and not leaking.  Only then is it worth bothering to adjust the sizes and settings.

[yamaha fj rider]

Andy gives good advise, clean the pilot circuit should fix the the flat spot and maybe change pilot jets to #40. Hope this helps?

Kurt

[SlowOldGuy]

Poor cold starting with choke on is plugged orifice in the float bowls.

Low RPM stumble is plugged idle jet or something clogging the circuit.

Your jets should be fine, but SHIM the needles

DavidR.

[Slick]

Well, everything sounds good then. I wanted to make sure that the PO didnt have some mix-match jets, that would lead me to hours of tuning without a success. Thank you all for confirming that my jets are workable.

The carbs were pretty gunked up again I have them really clean now and will work on ridding my tank of rust. Does anyone have a link to a thread or guide pointing me in the direction of removing rust and "sealing" the tank?

[Pat Conlon]

Sure, look in the Files section under General Maintenance

[movenon]

Well, everything sounds good then. I wanted to make sure that the PO didnt have some mix-match jets, that would lead me to hours of tuning without a success. Thank you all for confirming that my jets are workable.

The carbs were pretty gunked up again I have them really clean now and will work on ridding my tank of rust. Does anyone have a link to a thread or guide pointing me in the direction of removing rust and "sealing" the tank?

This is a good read on the tank issue. Scroll down a bit, lots of pictures for us slow ones . http://www.svrider.com/forum/showthread.php?t=154997&highlight=tank+rust+removal
George

[bigbore2]

Put a filter on the gas line to deal with the rust,dirt issue getting to the carbs. Randy has them. or I can send you one that I have and have been using that still flows enough under WOT.

What is your altitude there?  1000 ft.?   My 84-1100- when I bought it [35,000 mi] had a Yoshimira 4 into 1and I added a K&N air box filter [which I now have for sale].  My local guy suggested I go up to a 115 main and shim the needles with this. He is familiar with these engines as he does work for the Legend racer guys here.  [Altitude here 5000 ft.] So I did and not much difference than the 112.5. Then I went up to a 117.5. Suggestion from reading on this site.  gearing of 17/42   The difference was simply amazing. I thought the front end was going to come up in 1st, 2nd and 3rd gear from 5500-9500. Bike is a monster now. But at your altitude with my bike I would need a 120 or 122.5 main to get the same response according to the charts. [1 main size change for every 2500 ft.]