BS32 re-jetting...

[GS650LCM]

Not rushing into modifying the bike I just acquired, but I know it won't stay stock forever. So, while reading the Pods, Pipes, Panic thread, I found a post by Bonehead back in 2012 referencing information he had apparently found somewhere, listing various intake and exhaust mods and corresponding jet changes. He had asked if the information was valid; I didn't see whether he ever got a response. My questions are now: is the information indeed valid? Are the changes to be made primarily to the main jet? And, are the changes good for both VM and CV carbs?
I have the BS32SS CV carbs on my bike. These are a bit of a challenge to find parts for, but I have located a few sources with the help of this forum. Also, I found the link to Motorcycle Wiki in the PPP thread that gives a little different list of jetting changes. Which one to use? Looking forward to input from other members. Thanks in advance... Chris

 

[Big T]

Chris,

Unfortunately, there is no magic jetting formula for YOUR bike, and everything you read is pretty much a guideline. It's all trial, error and plug reading.

Many recommend a Dynojet kit, mostly to get a needle with more taper and adjustments. IDK if they have a kit for your carbs

 

[GS650LCM]

Thanks, Big T. Yeah, been to the Dynojet website, didn't see a kit for BS32's. Looking at Jetsrus and Z1 Enterprises for some parts, ebay for others. For carb internals, I would like to stay genuine Mikuni if at all possible, just for the sake of consistency. I guess I'm going to get good at carb rebuilding, syncing and plug chops/reading. Oh, well, it's all part of the fun. Still open to input from others...

 

[Steve]

You are not going to find a kit for "BS32" carbs, you are going to find kits for specific bikes.

Speaking of which, ... what bike do you have? The BS32 carbs were fitted on bikes from 550 to 850.

Also, what mods are you planning? Knowing what challenges we might be facing while trying to help you would make the job a LOT easier.

.

 

[GS650LCM]

Thanks, Steve. Ya, I did kinda neglect to include some pretty vital information, huh? It's an '83 GS650GLD, so a "shaftie". Mods I plan to make to the engine include either pod air filters or a large single K&N in a custom housing, no airbox, and very minimal mufflers behind the factory 4-into-2's, almost open pipes. I was reading another thread about whether to rejet for one mod at a time or do all planned mods then just rejet once. Opinions seemed to fall into two camps - do it all at once, and don't touch anything! Seems like, with a couple of guideline "formulas" to go by, it would be cheaper and/or less time-consuming to go the "all in" route. Not to open the same can of worms here, but I would appreciate any other's experience. I mean, the bike is going to be more toy than necessary transport, but if its running well and fun to ride, I'll want to be on it as much as I can...

 

[UKPR1]

Rejetted my 83 650GL with a dynojet kit, and AFTER I invested the time to balance the carbs (homemade balancer), the bike ran great. A little gravelly when cold for the first mile, but smooth and sweet thereafter. All I did was install the kit per the directions and not skip on anything. It also relies on your BS32's being in stock form, so make sure that all the jets, etc, are correct for your bike.

 

[GS650LCM]

Thanks, UKPR1. Just got off Dynojet's website and saw a Stage 3 kit for '81-'82 GS650's, but goose eggs for '83. Seems like 6Sigma had a kit for '81 to '83. Maybe the Dynojet kit would work in the Mikunis on an '83, too. Might be worth a phone call or email.

 

[UKPR1]

Came to the same impasse as you, but did some research and looked at the internal orifice sizes for an 82 CV carb versus an 82 CV carb and saw that even though there were some minor differences (bypass sizes if I remember correctly), that they really shouldn't affect running. One of my old question posts dealt with that and got the overall feedback to try the 82 dyno kit and see what happens. I bit the bullet and found that it still worked great for me. I too contacted Dyno Jet and got the lukewarm reply that they only sold an 82 kit.

Geoff

 

[Steve]

Mods I plan to make to the engine include either pod air filters or a large single K&N in a custom housing, no airbox, and very minimal mufflers behind the factory 4-into-2's, almost open pipes.

I should probably warn you that there are a few on the forum that are VERY vocal about "loud pipes". Personally, I will just say that I am happy that you are not in my neighborhood, although I will be spending a few minutes near your neighborhood later this year. Loud pipes really just irritate anybody that is within earshot (and by going with loud pipes, you just extended that range), especially those that don't agree with your philosophy that "it sounds so good". I don't mind a bit of extra "rumble", but I tend to ride a bit farther than just down the block, so I want something that I won't mind hearing for hours (days) at a time without damaging my hearing. Yes, I do have a 4-into-1 header on my bike, but those that have heard it don't believe how quiet it is.

Anyway, before hacking up your pipes, consider offering them up to someone on the forum that is looking for a decent set of stock pipes (assuming they are in decent condition, of course). If you are going to go loud, you really only need the header pipes and whatever else you plan to add, someone else might be interested in the mufflers.

Finally, be aware that the jetting needs for (virtually) open pipes are different than the jetting for a quieter system, whether that system is stock or aftermarket. If you ask for jetting suggestions, some of those vocal opponents will say "no changes necessary", just so you burn up your engine and restor peace to the neighorhood. Sad, but true. I have no experience with jetting for loud bikes, so have nothing to offer there, except to say that you will need a LOT bigger jets.

.

 

[GS650LCM]

Thanks again, Steve and UKPR1. The heads-up about the opponents of loud pipes is well taken. I get a little bent out of shape myself when somebody rides (or drives) by with loud exhaust just so it's loud. If it doesn't give a performance benefit, it's not going to be likely to hold my interest. But the factory set was cut apart by a previous owner thinking he could make his Asian inline 4 sound like an American v twin, so... Anyway, a little research has me scratching my head some; elsewhere in this forum, the specifications listed for Mikuni BS32's on a 1983 GS650GLD should be: pilot fuel jet, 47.5; pilot air jet, 160; main jet, 107.5; needle jet, X-2. What is actually in the carbs is: pilot fuel, 42.5; pilot air, 150; main, 110; and needle jet, 270 / Y-7. So, either someone has already been in these carbs, or the factory or dealership jetted differently for whatever reason. Anyone else run across this? Seems like it's set up with everything richer but the pilot circuit. Am I thinking correctly here? And do I need to go back to the specs listed on the forum ( or from Mikuni, if I can find them) for a baseline before starting the re-jet?

 

[UKPR1]

With you saying that the PO had hacked at the exhaust, my guess would be that the PO tried to capitalize on that by going into the carbs. I too found jetting changes that allowed the bike to run on cheap pods when I first got it.

 

[Steve]

..., the specifications listed for Mikuni BS32's on a 1983 GS650GLD should be: pilot fuel jet, 47.5; pilot air jet, 160; main jet, 107.5; needle jet, X-2. What is actually in the carbs is: pilot fuel, 42.5; pilot air, 150; main, 110; and needle jet, 270 / Y-7. So, either someone has already been in these carbs, or the factory or dealership jetted differently for whatever reason.

I have not verified this with a manual, but my chart says this is what you need for an '83 650G:

[TABLE="width: 527"]
[TR]
[TD]83
[/TD]
[TD]US
[/TD]
[TD]GS650G
[/TD]
[TD]BS32ss
[/TD]
[TD]110
[/TD]
[TD]42.5
[/TD]
[TD]160
[/TD]
[TD]5c45
[/TD]
[TD]y-7
[/TD]
[/TR]
[TR]
[TD]Year
[/TD]
[TD]Ctry
[/TD]
[TD]Model
[/TD]
[TD]Carb
[/TD]
[TD]Main
[/TD]
[TD]Pilot
[/TD]
[TD]Air
[/TD]
[TD]Needle
Jet
[/TD]
[TD]Needle
[/TD]
[/TR]
[/TABLE]

.

 

[GS650LCM]

Thanks again, guys. The factory exhaust was bobbed right where the mufflers were welded to the pipes, and I got the mufflers with the bike as loose items. The factory air cleaner is (and was) in place, but the foam filter medium was destroyed. I know the old owner was riding it that way, and convinced he had less than no idea what he was doing. It's starting to look like it's actually close to correct for a factory configuration. If I weld the exhaust back up and replace the air cleaner, I could optimize jetting for the stock setup, then collect/build my performance parts and get a jet kit. Yeah, I see me spending a LOT of time with this bike getting it just right...