Hi, mine fj1200 is poping from exhaust while decelerating. I have stock everything but it's still happening. Carbs were twice disasambled and cleaned in ultrasonic cleaner. One thing that I changed is I dethrottled my bike as it was from Swiss and capped at 100hp.
I upped intake manifolds to stock 36y, opened blocked airbox air intake ( Swiss 3CY has half of it blocked so I drilled and cleaned edges so it looks stock like in unthrottled FJs) replaced jets to 110 on main and it was popping and kinda sluggish so now I installed 42.5 pilot and 112.5 main jet, air jet is 155. Bike and throttle feel snappier but it's still popping. Should I upp jets one step up or I'm missing something?
I used EBC jets maybe they are not up to spec and actually smaller than what's written on them?
I had a slight popping on my 1100 on deceleration. Nothing major. I accidentally cleared it by turning the mixture screws out a bit.
I have heard the you want to stick with original jets for that reason, aftermarket jets run one size leaner or richer. I forget if its leaner or richer. Or both depending on brand? Not sure. I've always stuck with Mikuni jets for that reason. Like balky said, you may be able to tune it out with the mixture screw. Just remember what you do so you can undo it if need be.
Are you sure there aren't any exhaust or intake leaks? Sounds unlikely based off what you've said but wanted to throw it out there anyway.
My 89 also pops on decel. Likely its a bit rich. Extra fuel igniting in the exhaust. Uni pods, RPM exhaust so not an OEM system. It's a minor issue for me, I will sort it next carb work.
Quote from: FJmonkey on September 19, 2023, 10:17:55 PM
My 89 also pops on decel. Likely its a bit rich. Extra fuel igniting in the exhaust. Uni pods, RPM exhaust so not an OEM system. It's a minor issue for me, I will sort it next carb work.
Mine pops like a racing bike and it's definitely a too rich mixture in my case. I love it though :pardon:
I always believed that popping on decel is sign of lean condition. My other bike yamaha fzs600 pops the same way after exhaust swap to some Chinese "acrapovic" so it is also to rich?
I thought the vacuum advance on the fj caused some of that. Especially in a lean condition.
Quote from: giantkiller on September 21, 2023, 09:24:24 AM
I thought the vacuum advance on the fj caused some of that. Especially in a lean condition.
I believe you are correct Dan. Upon closed throttle FJ ignition advances to 50 degrees BTDC
For poping, try disconnecting the vacuum advance (don't forget to plug the intake port) see if the problem goes away.
There is No performance drawbacks with the vacuum advance disconnected. The advance only activates under closed throttle conditions.
(http://i949.photobucket.com/albums/ad337/craigo987/FJ11001984ServiceManual269-1.jpg)
Sorry i didn't specify my bike is fj1200 1989 and i don't have vacum advance, all "digital" :>
My 89 has the advance. There's a vacuum line running from the number 2 intake boot to the ignition box under the right side fairing..
This is my exact igintion module TID14-65
Its been a while since I had my fairing off so I had to search for some info. I found this thread: https://fjowners.com/index.php?topic=20000.msg204629#msg204629 (https://fjowners.com/index.php?topic=20000.msg204629#msg204629)
My mistake. Looks like it runs to a separate vacuum advance box, not the ignition box.
Quote from: Pat Conlon on July 25, 2021, 09:36:17 AM
Be sure you are looking at ignition boxes from the same generation (84-87 vs 88-95) because there are 2 flavors of oem FJ ignition boxes
1) TCI (transistor controlled ignition) uses a dual pick up coils which were installed on the USA 84-87 FJ's
The TCI boxes have a built in vacuum advance module. See exception below.***
2) DCI (digital controlled ignition) uses a single pick up coil which were installed on the USA '88 to 95 FJ's
The DCI boxes used a remote vacuum advance module (better design, easily replaceable) therefore, there is no vacuum port on the DCI box.
You can not mix these 2 different systems together. You can not use the DCI box (no built in vacuum advance) on a early FJ and a TCI box on latter FJ's.
Quote from: Pheasantplucker on July 25, 2021, 04:16:12 AM
Mine has a vacuum pipe coming from the opposite end to the connections, another 1tx that I have broken for spares has an ignition unit without, what's going on here then?
Again, be sure you are not comparing a DCI (no port) to a TCI box (with port).
Apples and oranges systems.
***Here's an exception: Not all FJ's with TCI came with vacuum advance. It's been reported by our FJ brothers in Australia that their FJ's do not have this vacuum advance feature. Early TCI boxes in Aussie land do not have a vacuum port on the TCI box. All USA bikes do have the vacuum advance.
If you *are sure* you have Ignition boxes from the same 1TX model, perhaps you have a USA box with a vacuum port and your other box is an Australian box without a vacuum port?
What does the vacuum advance do?
*The vacuum advance has nothing to do with performance*
It is a emissions control feature. It advances the timing when you close the throttle to burn off unburned hydrocarbons. Your FJ will run just fine without this vacuum advance as I can attest along with our mates from the land down under.
If you want to bypass the vacuum advance, no worries, just be sure you cap off the vacuum port on the intake manifold. Use the heavy oem Yamaha vacuum caps down there, it gets plenty hot on the engine side of the heat shield. Thin wall vacuum caps are not appropriate.
Aftermarket Ignitions (Dyna, etc.) do not have any vacuum advance features.
Here you can read more about the vacuum advance: http://www.fjowners.com/index.php?topic=11690.0 (http://www.fjowners.com/index.php?topic=11690.0)
Cheers. Pat
Either way, if you don't have a vacuum line running from your intake to under the fairing then it may have been disconnected. My understanding is all FJ1200s had the advance, maybe they didn't in Poland?
Edit: I just saw your other thread where you mentioned you relocated the ignition box. I'm guessing the vacuum advance box is right next to the ignition box from the factory. So you likely would have removed or relocated it if it were there.
The purpose of the vacuum advance is to advance the spark to flash burn off any unburned hydrocarbons left in the cylinder upon decelerating...it's an emissions device, so it's not surprising that not all FJ's have this feature.
Certainly all FJ's sold in the states have the advance.
Quote from: Pat Conlon on September 22, 2023, 03:16:04 PM
The purpose of the vacuum advance is to advance the spark to flash burn off any unburned hydrocarbons left in the cylinder upon decelerating...it's an emissions device, so it's not surprising that not all FJ's have this feature.
Certainly all FJ's sold in the states have the advance.
My 1100 is from Switzerland like his bike and has (had) it so... I don't know.
The advance runs off a vacuum signal on an easy way to see if you have the advance is to look for the vacuum line, typically connected to the #2 intake manifold. The gravity flow bikes ('84-87) will have the petcock vacuum line connected to the #1 intake.