Trying to dial in the Carbs on my 84 1100 and been having issues getting it smoothed out.
Pilot Fuel jets are 42.5's, replaced all the o-rings and gaskets in the carbs. The carbs were cleaned in an ultrasonic cleaner.
When running, the bike responses quickly to throttle, but is showing other issues. When on the centerstand and holding the throttle in place, the RPM's will fluctuate up and down by 500-1000 RPM. Sometimes the fluctuation is quick, making the needle on the tac tick. Other times it'll take 4-6 seconds to fluctuate. RPM also hangs when coming down from anything at 4k rpm or above. Often taking 2-3 seconds to return from 4k to Idle.
We tried doing a leak test at the intake manifold and the vacuum nipples but couldn't locate one. Despite that, I still think part of the problem is a vacuum leak on the intake manifold. But I would like help sorting out all the issues so I can finally get this old girl back on the road for this riding season.
Quote from: Warp84 on February 26, 2026, 08:52:49 PMTrying to dial in the Carbs on my 84 1100 and been having issues getting it smoothed out.
Pilot Fuel jets are 42.5's, replaced all the o-rings and gaskets in the carbs. The carbs were cleaned in an ultrasonic cleaner.
When running, the bike responses quickly to throttle, but is showing other issues. When on the centerstand and holding the throttle in place, the RPM's will fluctuate up and down by 500-1000 RPM. Sometimes the fluctuation is quick, making the needle on the tac tick. Other times it'll take 4-6 seconds to fluctuate. RPM also hangs when coming down from anything at 4k rpm or above. Often taking 2-3 seconds to return from 4k to Idle.
We tried doing a leak test at the intake manifold and the vacuum nipples but couldn't locate one. Despite that, I still think part of the problem is a vacuum leak on the intake manifold. But I would like help sorting out all the issues so I can finally get this old girl back on the road for this riding season.
Slight Correction. When I say hanging RPM's, I mean slowly returning to idle. Not getting stuck at a particular RPM point.
The Bike was getting actually hanged up when it was using 37.5 pilot jets, not crossing past 2.5k RPM, shooting up to 4k and staying there. But haven't had that specific issue after I put in the 42.5 Pilot Jets.
Quote from: Warp84 on February 26, 2026, 08:52:49 PMTrying to dial in the Carbs on my 84 1100 and been having issues getting it smoothed out.
We tried doing a leak test at the intake manifold and the vacuum nipples but couldn't locate one. Despite that, I still think part of the problem is a vacuum leak on the intake manifold. But I would like help sorting out all the issues so I can finally get this old girl back on the road for this riding season.
Warp 84,
To find a vacuum leak, use aerosol spray-can ether (starting fluid). With the engine running, spray a little on each part of the intake system in turn. If spraying any one place causes a change in RPM (up or down), you just sprayed the vacuum leak place. Repair as needed. HTH. :good2:
Quote from: Warp84 on February 26, 2026, 08:52:49 PMWhen running, the bike responses quickly to throttle, but is showing other issues. When on the centerstand and holding the throttle in place, the RPM's will fluctuate up and down by 500-1000 RPM. Sometimes the fluctuation is quick, making the needle on the tac tick. Other times it'll take 4-6 seconds to fluctuate. RPM also hangs when coming down from anything at 4k rpm or above. Often taking 2-3 seconds to return from 4k to Idle.
This to me says that the idle mixture screws aren't set quite right. I'd try adjusting up or down until it smoothes out.
What is the ambient temperature? I had tuned my FJ in summertime and it ran perfect but when I started riding into the fall as it got colder out the 50F morning starts were difficult and I had a hanging idle that generally went away when the bike and day warmed up. I suspect it wasn't getting enough fuel with the colder ambient temps because I know it was set perfect when it was hot out.
Did you recently may any other modifications like air filter or exhaust?
Quote from: red on February 26, 2026, 11:50:48 PMQuote from: Warp84 on February 26, 2026, 08:52:49 PMTrying to dial in the Carbs on my 84 1100 and been having issues getting it smoothed out.
We tried doing a leak test at the intake manifold and the vacuum nipples but couldn't locate one. Despite that, I still think part of the problem is a vacuum leak on the intake manifold. But I would like help sorting out all the issues so I can finally get this old girl back on the road for this riding season.
Warp 84,
To find a vacuum leak, use aerosol spray-can ether (starting fluid). With the engine running, spray a little on each part of the intake system in turn. If spraying any one place causes a change in RPM (up or down), you just sprayed the vacuum leak place. Repair as needed. HTH. :good2:
We tried that but I'll give it another go incase we missed a spot.
Quote from: 86FJNJ on February 27, 2026, 07:15:46 AMWhat is the ambient temperature? I had tuned my FJ in summertime and it ran perfect but when I started riding into the fall as it got colder out the 50F morning starts were difficult and I had a hanging idle that generally went away when the bike and day warmed up. I suspect it wasn't getting enough fuel with the colder ambient temps because I know it was set perfect when it was hot out.
Did you recently may any other modifications like air filter or exhaust?
The heated garage is 60f, outside was 24f. We started the bike with the door closed (over 2k square feet in the garage bay so this isn't immediately unsafe) And after 5 minutes opened the garage door. The smoothness of the response to the throttle improved as it warmed up, but the RPM flux and slow drop persisted the entire time.
No Mods to exhaust, P.O. put in a washable air filter, however I put in the filter I got from Partzilla, which should be OEM.
sounds like it needs some more fuel, my guess is if it was 75F out you won't have those issues. Maybe crank up the heat in your garage and put a space heater on the engine for an hour and see if it acts any better.
42.5 pilots should be fine for your setup. Maybe back out the fuel mixture screws a 1/8 turn and see if that improves things. Or if your slide needles are adjustable maybe raise the needles a notch by lowering the clip that could help get some more fuel off idle.
how many turns out are your fuel mixture screws?
Quote from: 86FJNJ on February 27, 2026, 11:48:20 AMhow many turns out are your fuel mixture screws?
About 2.25 turns out. I'm not sure these mixture screws are OEM, they seem longer. They were obtained before I learned my lesson and started getting my supplies from RPM.
In my early FJ days I went with some cheap china ebay stuff for carbs and learned my lesson too. Have you tried 2.5 turns out on the fuel mixture screws to see if that improves things?
Here in NJ it will be 50F tomorrow, if you have any warmer days in your area a test ride would be good if the bike responds/runs well in mid range and top end then it's likely a fuel issue in the pilot circuit either related to your fuel mixture screws, non-OEM pilot jets and/or clogged passageways in carbs.
I had a set of carbs I could not get fully clean, I put seafoam in the next few tank fill ups and went out for several spirited ride and that helped. Since then I run Yamalube Ring Free Plus Fuel Additive in each tankful of gas to help keep things clean.
https://www.amazon.com/dp/B002GU4SN2?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_3&th=1
Quote from: 86FJNJ on February 27, 2026, 12:39:36 PMIn my early FJ days I went with some cheap china ebay stuff for carbs and learned my lesson too. Have you tried 2.5 turns out on the fuel mixture screws to see if that improves things?
Here in NJ it will be 50F tomorrow, if you have any warmer days in your area a test ride would be good if the bike responds/runs well in mid range and top end then it's likely a fuel issue in the pilot circuit either related to your fuel mixture screws, non-OEM pilot jets and/or clogged passageways in carbs.
I had a set of carbs I could not get fully clean, I put seafoam in the next few tank fill ups and went out for several spirited ride and that helped. Since then I run Yamalube Ring Free Plus Fuel Additive in each tankful of gas to help keep things clean.
https://www.amazon.com/dp/B002GU4SN2?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_3&th=1
The jets are all original Genuine Mikuni parts, all have the maker mark on them. The 42.5 jets I had put in were from RPM. I currently have the flat bottom slides and y-0 Emulsion tubes in the carbs. But I also have a set of round bottom slides and y-2 emulsion tubes that came from an 85 FJ100. Should I switch it over to the Y-2 tubes and round bottom slides?
Forgot to put in, we started at 2.5 turns out and it seemed to be getting too rich hence we brought it down to 2.25. Was getting foggy grey exhaust instead of clear exhaust
If you can't get it dialed in as is it would be worth trying the other slides and tubes. Are you sure the grey exhaust was from too much fuel? My FJ smokes like a chimney after the fist 30 seconds for about 3 minutes because the valve seals are original and oil leaks past them when sitting so when I first start it that needs to burn off. After that it doesn't really smoke.
If your FJ was running well at 2.5 out but just had some smoke I'd be tempted to ride it like that and then keep tuning from there after you know how it's behaving more after warmed up and through the rpm range. It's going to be tough IMP to dial in the carbs without riding it. Is this a bike you had running well at one point in the past or is this something you got from PO and have been rehabbing it but not ridden it yet?
Quote from: 86FJNJ on February 27, 2026, 01:42:39 PMIf you can't get it dialed in as is it would be worth trying the other slides and tubes. Are you sure the grey exhaust was from too much fuel? My FJ smokes like a chimney after the fist 30 seconds for about 3 minutes because the valve seals are original and oil leaks past them when sitting so when I first start it that needs to burn off. After that it doesn't really smoke.
If your FJ was running well at 2.5 out but just had some smoke I'd be tempted to ride it like that and then keep tuning from there after you know how it's behaving more after warmed up and through the rpm range. It's going to be tough IMP to dial in the carbs without riding it. Is this a bike you had running well at one point in the past or is this something you got from PO and have been rehabbing it but not ridden it yet?
When we went to 2.5 turns out, after it had warmed up for 10 minutes, it started emitting the smoke again out the pipe hence why we were concerned it was too rich at that point More specifically, when blipped. Turned it down to 2.25 and the smoke cleared even when blipping.
As for the bike. When I got it, it hadn't run in 17 years, and sat for 14 years straight with it's oil-pan off. Replaced the oil pickup gasket which was cut in half for some reason, as well as the oil pan gasket. The bike wasn't running right, as one of the top bowl section, where the slide sits, was cracked on Carb #2, and cylinder #3 was dead at idle. Carb #3 also had destroyed threads for the adjustment screw and pilot fuel jet. So The #2 and #3 carb bodies were replaced with the bodies from a 1985 carb stack, hence how I got the other slides and emulsion tubes. And why I replaced all the fuel jets with 37.5's (By mistake) from RPM, before being corrected on the forums here, and getting a set of 42.5's, also from RPM.
Right now she starts easy and idles at 1100 RPM on the digital man-o-meter, all cylinders running, (1.35k-1.4k reading on the tac) Just having the issues (That you've been discussing with me) when I give it power. So it's actually been running better than ever, compared to when I got the bike originally.
have you ridden it like this or is all the tuning based on the bike in the garage? I rehabbed my FJ from PO who let it sit 15 years, I was only able to get it about 90-95% dialed in on the center stand the rest came from riding it and then coming back and making minor adjustments. I can honestly say it took me like 300 miles of riding before I found the sweet spot for my set up. Have you tired fuel mixture screws in between 2.25 and 2.5? Are you using adjustable slide needs or are they the ones with the little plastic donut on them? I'm curious how your slide needles are set.
Also if tuning while idling be sure to put a big fan on that engine to help cool it and even then don't let it idle too long as even a big fan wont cool that engine the way air flow would cool it at even a low speed of 15mph.
Quote from: 86FJNJ on February 27, 2026, 02:25:01 PMhave you ridden it like this or is all the tuning based on the bike in the garage? I rehabbed my FJ from PO who let it sit 15 years, I was only able to get it about 90-95% dialed in on the center stand the rest came from riding it and then coming back and making minor adjustments. I can honestly say it took me like 300 miles of riding before I found the sweet spot for my set up. Have you tired fuel mixture screws in between 2.25 and 2.5? Are you using adjustable slide needs or are they the ones with the little plastic donut on them? I'm curious how your slide needles are set.
Also if tuning while idling be sure to put a big fan on that engine to help cool it and even then don't let it idle too long as even a big fan wont cool that engine the way air flow would cool it at even a low speed of 15mph.
We did one test ride when it had the 37.5 jets after the carb stack was put back together with undamaged carb bodies. That ride is when we uncovered the oil pickup screen gasket was cut, when oil started pouring out from the bolt hole just above the exhaust collector, after passing 55mph. That ride had the RPM ticking up and down the 1k rpm, several times a second, instead of the current slow fluctuation it has.
Like you said, it's nearly impossible to get a perfect tune on the centerstand, Since it's running so much better I'm prepping to check a few more things and set out on a test ride in a day or two. Wanted to make sure I dotted my I's and crossed the T's so I don't have another incident like on the first test ride.
-edit- The Slides for both kinds that I have are the fixed type with no clip for adjusting it.
I know you said you have stock intake/air filter, is your exhaust stock too or is it more free flowing aftermarket?
Seems like you have it tuned really close, if it were me I'd put the fuel mixture screws between 2.25 and 2.5 and fill it up with fresh gas and dump half a bottle of seafoam in there and go for a ride and see how it behaves through the rpm range and see how it is when you stop at stop lights and stop signs, what does the idle do then after it's warmed up, what does it do when you ask for some throttle off idle or ask for more throttle at 3k rpm in 2nd gear...make some mental notes and adjust from there.
If your intake and exhaust are stock I don't think you should need to shim your slide needles the stock position should be ok. If putting some miles on it doesn't allow you to dial it in I would probably try the other emulsion tubes and slides you have from the later FJ's maybe that helps smooth things out.
Are the rubber diaphragms in your carbs OEM or aftermarket? Did you inspect them for any pin holes or tears? Do your slides all go up and down at the same rate or are any of them a bit "sticky" and slow to lift or return?
I had hanging idle, you'd give it a quick blip and it'd stay up before going down .... Turned out to be electronic ignition module
Update: Rechecked the floats via a float test. The level in the tube was low, so re-adjusted the floats. Went back to 2.5 turns on the idle's and it's running so much better now. No burbles or coughing. Easy smooth start up. Still having it go up to 4 thousand RPM and not wanting to go passed it. But going to continue doing road test's and tune out the wall.
Warp84,
No doubt, you are fairly close on mix & tune. Good show!
Kinda basic, but . . .
- Are your throttle cables in good condition, and lubed?
- There should be a slight amount of free play in the throttle cable system. No-slack there can cause a hanging throttle/ RPM issue.
Just a coupla thoughts, shooting in the dark here.
Quote from: red on March 09, 2026, 06:03:25 PMWarp84,
No doubt, you are fairly close on mix & tune. Good show!
Kinda basic, but . . .
- Are your throttle cables in good condition, and lubed?
- There should be a slight amount of free play in the throttle cable system. No-slack there can cause a hanging throttle/ RPM issue.
Just a coupla thoughts, shooting in the dark here.
What lube should I be using? I replaced the Carb side Push cable with a unit from RPM. All the cables move freely and with no noise. There's a small amount of play on the grip before the pull cable is engaged, so it's not constantly applying pressure.
Quote from: Warp84 on March 09, 2026, 07:17:09 PMWhat lube should I be using? . . . All the cables move freely and with no noise. There's a small amount of play on the grip before the pull cable is engaged, so it's not constantly applying pressure.
Warp84,
Any light petroleum grease (*NOT* WD-40, which is just kerosene) will do the job there. Get the aerosol can with the skinny red straw. No Lithium (white) grease, there.
Then this gadget, at most bike shops and Amazon, will make cable lube easy:
Cable Lube Tool
(https://user.xmission.com/~red/CableLube%20Tool.jpg)
HTH.
Hi Red, I'm curious why not to use WD-40 for throttle cable lube?
Back when cable sheaths had a lining of nylon inside then the application of the WD40 caused the nylon to expand in the sheath and "grab" the cable and stop it from sliding.
Whether cables sheaths are made like that now i don't know but i never use WD40 on cables because the problem once happened to me.
thanks Billy, been using wd40 for years without issue but sometimes you don't know what you don't know so I'm open to changing.
Those cables are pre lubed you won't need to lube them for awhile.
We use tri flow to lube ours. Has a little bit of teflon in it and that helps them slide in the plastic tube liner.
The pull cable might a have a bit of slack but is the push cable adjusted properly?
Positive you don't have a vacuum leak somewhere? Depending on year the igniter box had a vacuum timing advance that can fail and cause a vacuum leak.
Quote from: RPM - Robert on March 10, 2026, 12:00:16 PMThose cables are pre lubed you won't need to lube them for awhile.
We use tri flow to lube ours. Has a little bit of teflon in it and that helps them slide in the plastic tube liner.
The pull cable might a have a bit of slack but is the push cable adjusted properly?
Positive you don't have a vacuum leak somewhere? Depending on year the igniter box had a vacuum timing advance that can fail and cause a vacuum leak.
Greetings Robert,
This bike was pretty neglected by it's P.O. There's a solid chance there might be something wrong the ignition box. Do you have a testing procedure I can run through on it?
The intake boots were just replaced due to vacuum leak around the brass nipples on the previous set. Also replaced the caps and vacuum petcock line. (Also rebuilt the petcock with the RPM kit) I'll have to double check the line that goes from the boot to the box here soon.
Quote from: 86FJNJ on March 10, 2026, 08:30:51 AMHi Red, I'm curious why not to use WD-40 for throttle cable lube?
86FJNJ,
WD-40 is mostly kerosene, not a lubricant. If it works at all, it's because the solvent is just re-locating some lube that was already there. Then the kerosene evaporates, leaving a sticky, gummy mess that attracts dirt. Spray some WD-40 on a glass pane, and see if you like what you find there in a week.
The solvent can also deteriorate the inner lining of some cables, bad plan.
Besides all that, I get pissed when stuff that I can buy in gallons is being sold by ounces, for more money.
All IMHO, of course. :bye2:
Quote from: Warp84 on March 10, 2026, 12:22:32 PMDo you have a testing procedure I can run through on it?
There are 2 vacuum lines on our Early FJ's. Cylinder #1 port vacuum line goes to the petcock and cylinder #2 port goes down to the ignition box. The purpose of the #2 vacuum line is to advance the ignition timing *upon closed throttle* (for emission reasons) as discussed here:
https://fjowners.com/index.php?topic=11690.0
On the early FJ's ('84-87) the vacuum diaphragm is internal in the TCI ignition box and is non serviceable, non replaceable and the later '88-95 FJ's have the vacuum advance as a stand alone module, separate from the DCI ignition box. As our bikes age, this diaphragm can become cracked, thus leaking vacuum...causing a hanging high idle, what Robert was referring to....
How to test? We call this the suck test. Disconnect the vacuum line at the #2 intake port, clean the end, and suck on the hose. Put your tongue over the end of the hose to hold the hose under vacuum. The vacuum hose should stay under vacuum...if it bleeds off or if you can draw air through the hose, either the ignition box diaphragm is leaking or your hose is leaking. The hose replacement is easy, not so much the ignition box internal diaphragm.
Solution: Cap off the #2 intake port, use the heavy rubber oem Yamaha vacuum caps. It's hot in this area in front of the heat shield.
As discussed above there will be no performance loss with this vacuum feature disconnected.
Cheers....hope this helps.
Pat
Quote from: Pat Conlon on March 10, 2026, 03:18:33 PMQuote from: Warp84 on March 10, 2026, 12:22:32 PMDo you have a testing procedure I can run through on it?
There are 2 vacuum lines on our Early FJ's. Cylinder #1 port vacuum line goes to the petcock and cylinder #2 port goes down to the ignition box. The purpose of the #2 vacuum line is to advance the ignition timing *upon closed throttle* (for emission reasons) as discussed here:
https://fjowners.com/index.php?topic=11690.0
On the early FJ's ('84-87) the vacuum diaphragm is internal in the TCI ignition box and is non serviceable, non replaceable and the later '88-95 FJ's have the vacuum advance as a stand alone module, separate from the DCI ignition box. As our bikes age, this diaphragm can become cracked, thus leaking vacuum...causing a hanging high idle, what Robert was referring to....
How to test? We call this the suck test. Disconnect the vacuum line at the #2 intake port, clean the end, and suck on the hose. Put your tongue over the end of the hose to hold the hose under vacuum. The vacuum hose should stay under vacuum...if it bleeds off or if you can draw air through the hose, either the ignition box diaphragm is leaking or your hose is leaking. The hose replacement is easy, not so much the ignition box internal diaphragm.
Solution: Cap off the #2 intake port, use the heavy rubber oem Yamaha vacuum caps. It's hot in this area in front of the heat shield.
As discussed above there will be no performance loss with this vacuum feature disconnected.
Cheers....hope this helps.
Pat
Pat,
Low and behold that was part of the issue. The Diaphragm in the DCI had failed, as instructed, I put a cap over the vacuum nipple. A bit more fiddling with the needles and it no longer stops at 4k rpm either. Both on centerstand and under power. Thanks to you and Robert for your input and solving the vacuum leak.
Happy to help
Update, finally had a good day for more testing and putting more miles on the bike.
60F outside temp, low wind's. Brand new Metzeler Lazertek Tires. Stock 1100 pistons. Stock exhaust. Replaced exhaust header gaskets to correct exhaust leak. Replaced intake boots recently. Resynced Carb's on digital man-O-meter. Pilot Fuel Jet's are 42.5's. I'm not sure if the mains are 110's or 115's right now.
Idle adjust screws are currently at 2.25 turns out.
Bike doesn't hesitate at 4k rpm, but still has the rapid ticking up and down by a thousand rpm, every second, whenever the RPM is between 3.7 to 4.5k rpm. Above or below those RPM's and the needle on the cluster is behaving.
Bike is also wanting to rocketship as soon as it touches 4k rpm, taking only a moment to hit 6-7k, when in first gear. I've been told that is normal. For the bike to "Wake up" and want to go.
I'll keep fiddling with it to get it more dialed in.
The rapid ticking up and down on the rpm:
Option 1: Is it just the RPM gauge needle that is bouncing around but the engine RPMs are consistent?
Or
Option 2: Are the engine RPM's going up and down and the RPM gauge is just accurately reflecting that?
My RPM gauge need does the same, seems to get drunk between 3k-6k rpm and bound around but the engine RPM's are fine so I chalk it up to the bike being 40 years old
It seems like the RPM's are stable even while the needle is ticking, going by the sound. Good to know that it's not just my bike that has a RPM needle that likes to dance.
I'll stay tuned if anyone has a cure but my bike rides fine