1982 GS650E carbs- correct jets???

[cmj]

Hello, I have a 1982 GS650E and last year installed a header and Kerker muffler. I was thinking of installing individual pod filters also. My question is- which jets should I switch to to come up with the correct air/fuel mixture? I was wondering if anyone else here has done something similar to their bike? After the first of the year, I'll start pulling the carbs and cleaning them, so I'd like to also switch out the jets at the same time. Thanks very much in advance for any help or info. This site is full of friendly enthusiasts with great advice.

[KEITH KRAUSE]

Well, no one else wants to try so I'll take a stab at it.
I haven't jetted your model though so these are just suggestions. You may want to check out Dynojet or K&N, etc, to see if they have a jet kit for you. With pipe AND pods, you'll need a stage 3 kit.
If no kit, you can still look at what general jetting changes may need to be done by looking at other similar kits/asking here (as you're doing) or visiting jetting websites. Once you see what may need to be done, then it's a matter of finding the correct jet sizes.
Be sure the bike is ready for re-jetting. That means clean/adjusted/vacuum synched carbs with fresh o-rings, no intake leaks, new gaskets for the pipe, clean filters, good compression/valve clearances, good spark/timing, etc. Re-jetting can be hard enough on a correctly set up bike.
I don't know what pipe and pods you'll choose but here's a ballpark guess to start at.
Increase the main jets by 30-35.
If your model has adjustable jet needles, try raising them two positions richer. If no adjustable jet needles, you'll have to shim them with spacers from Radio Shack or ? Try raising the needles about .09"-.10".
Increase pilot jet size by 5 and possible richer mixture screw adjustment to fine tune.
Increase pilot air jet one size larger.
If your model has floatbowl vent lines, remove them so the bowls breath better.
You'll probably need to increase (drill out) the vacuum orifices to each diaphragm chamber too. This improves throttle response. This must be done carefully and is part of jet kit info.
You may need lighter piston/diaphragm springs too.
You may need larger primary air jets.
As you can see, the CV carbs your model uses can involve many parts, not just main jets or something that simple.
I never try to talk anyone out of tinkering with their bike but ask yourself if you really want to play with it for an extra 5/6 HP or ? You can also expect to lose a bit of low end torque, though the higher rpm's should show some noticable improvement.
Some people find checking/adjusting the cam timing correctly may help you get more power than the pipe/pod mod's, though doing all three is even better.
Then you get to test the jetting. If you get to that point, let us know and we'll try to help.
By the way, If you're going to get pods, I suggest the K&N's. Expensive but worth it. If you get cheaper pods, be aware any jet kit info you may gather will not be as accurate because the jet kits were designed with K&N filters in mind, not other brands.

[txironhead]

If you go to www.dynojet.com, look up the jet kit for your bike, and next to the part # will be a .pdf file you can download that says what comes in the kits and how to install it. You can decide from there if you want to go to that much hassle. As my bike came with a V&H 4-1 and no airbox OR pods, I didn't have much choice.

Regardless of how you want to jet it, if you don't have a friend that has a carb synchronizer like I do, you'll have to fork out the money for one of those, too.

[cmj]

Thanks for the info

Thanks very much for the info from both of you. To tell the truth, the bike runs great now. I've read of others who have installed pod filters and have had problems with the bike dogging out at higher RPMs, so that was my main concern if I chose to do that. Considering the info from both of you, I may just let it go as is and let well enough alone. I doubt very much if I'll notice the difference in performance. I like to go quick sometimes, but I'm a pretty casual rider, so I'll probably just let it go. I would think that any small gain in HP would be offset by the loss of low end and mid-range torque, which is more important in every day riding anyway. Thanks again for the help. It's nice to see informed people willing and able to help out other riders. I hope to post a couple of pics of the old bike soon. I always had a soft spot for the old Kawasaki GPZs, so I sort of morphed a GPZ themed paint scheme onto the 650. I'd much rather ride an old GS though. I've had 7 different GS's of one kind or another in the past 9 years. Hope I don't upset too many Suzuki traditionalists. I just like the way it looks.

[txironhead]

It's your bike, do what you want with it. 'Course, I'm a firm believer that stock sucks, so I'm a little biased. Definitely would like to see pics.

As long as you're not running lean, you should be okay. Running lean is a quick trip to a dead engine. A quick plug read should tell you, or there are several threads here on the subject. Running rich isn't great, but it'll affect your mileage more than anything.

[KEITH KRAUSE]

And remember that the pipe you have now, if freer flowing, is effecting the jetting. If that pipe flows better than stock and you have stock jetting, you're lean. How lean and at what throttle positions requires you to take some plug reads at 1/3 and full throttle and after some general slower/city riding.
Different pipes require different changes.
A lean mixture at slower/city speeds (minimal throttle) may be fixed by simple richer mixture screw adjustments of maybe 1/2 to 1 more turn out?
If lean at 1/3 throttle position, that would mean you need to raise the jet needles a bit.
Lean at full throttle means the mains need to be larger.
I suspect the mains will need to be increased if you still have the stockers in. If it flows better, it's for sure. Probably 7.5 to 10 larger (1 1/2 to 2 full sizes richer). For pipe only, the mains commonly need to be changed more often than jet needle positions. Still depends on testing and what the plugs say.
Warm up the bike completely and "chop off" at a safe place and read the plugs. Chopping off, if you aren't familiar, means to run the bike at the desired throttle position for several moments (level or uphill only) and then quickly pull in the clutch lever, shut off the throttle and turn off the key and coast to a stop without releasing the clutch lever.
For hot plugs, I take a rag and a piece of fuel hose that fits snugly over the plug end. The hose allows you to remove the plug when you just have a few threads remaining and also to re-install the plug into the first few threads. As always, be careful of cross threading. Be safe too. This is high speed testing, something I'm lucky to have a nice "test area" to use.
Any amount of lean condition isn't good, but just a little lean isn't going to cause real problems if the bike is ridden mostly around town/slower speeds. Longer trips could mean more heat than desired though. If leaner, pinging and pre-ignition could result that can cause serious damage. I doubt just a pipe would cause pre-ignition but pinging under loads is possible.
I'm not trying to say a little lean is OK. It depends on how the bike is used. Obviously, you want the perfect mixture. I don't want you to think you must re-jet all three jetting circuits just for the pipe. I just want you to be aware of how a pipe can change things and make a good decision, which is to trust the plug reads and go from there.
If the bike is in good tune and the carbs synched, you're ready to check those plugs.
By the way, I assume the stock airbox lid is still on? If not, this WILL require re-jetting all three circuits.

[snowbeard]

hey keith, when you say longer rides, how long are you thinking? half an hour? more or less?

[KEITH KRAUSE]

hey keith, when you say longer rides, how long are you thinking? half an hour? more or less?

You know, I almost didn't make that comment because it can be taken the wrong way. I was just trying to give as complete a thought as possible.
Running lean is not good. It would depend on just how lean we're talking about as to how soon you need to correct things. An air cooled engine relies quite a bit on the correct amount of fuel in the mixture to aid in cooling. A lean mixture will also cause pinging because the spark won't ignite at the right time. Lots of bad things can happen.
In this case, the bike has only a freer flowing pipe and no other changes. It will run a little leaner but it shouldn't be so much that it causes a problem at city speeds and shorter rides. I know that many bikes have been ridden for many miles with the same condition and no apparent problems. But the fact is the bike will run hotter than it should and you KNOW that will decrease engine life. The leaner it is, the worse the wear and the worse the problems can be.

[snowbeard]

I believe you, I'm just trying to guage the damage vs fun factor. In a few of my threads I've posted about a similar change, opening up to a freer pipe. It causes some limited backfiring on decel from a hard windup, and when I checked my plugs last night they were white and ashy. The pipes have not blued, but I've been riding mostly in very cold temps (32-45F)

I actually turned around this morning, the nicest for some time, and put the ol girl back in her stable, took the car instead because I surely don't want to end the life of my engine immediately. I took the mtn bike as a consolation for the day.8-[

so, aside from changing my jetting, could I restrict the flow of the new pipes to fix my leanness? any thoughts on how that might be accomplished?

here's some more info on my self induced dilema, thanks for the help!!

http://www.thegsresources.com/_forum/showthread.php?t=101248

[KEITH KRAUSE]

Well, I can't give advice about deliberately trying to cause restriction in a pipe. Never bothered with something like that.
I can't even say how this modded pipe flows but you say it appears to be leaner.
The decel' pop and "white/ashy" plugs you have suggest that.
Just removing the pipe could create the need for new exhaust gaskets and that would cause the decel' pop. The plugs suggest you're lean though, regardless.
Do what the plugs say. Test at minimum, 1/3 and full throttle to determine what jetting changes are needed.
If just that pipe mod (and it really does flow better) and completely stock airbox, I'd guess about 2 full sizes richer (10) on the mains. An additional 1/2 to 1 full turn out on the mixture screws would help with lower speeds/city riding.
If you're lean at 1/3 throttle, then you'll need to raise the jet needles a bit, which is the most work.
But before bothering with plug checks, be sure the bike is tuned in other areas. Good compression, valve clearances, good spark/timing, carbs synched, etc. Then do what the plugs say.
"Home made" exhausts can be more trouble than they're worth in my opinion. What about finding a stock exhaust? Not a good idea?

[cmj]

Very interesting information

Hello Keith,

I've been away for the last two days. Just now getting a chance to check in. I will do as you say once the weather warms up in the spring. I'll not be riding too much more now, and if I do it'll be just short trips around town. I'd like to find out what needs changed, so I'll definitely check the plugs as you suggest. I don't want to fry the motor prematurely. I've never heard it ping or anything like that, and only hear any backfireing on decel every once in a while. I know this might be a stupid question, but would changing to a slightly hotter or colder plug help in any way if carb adjustment is minimal? And by the way, the stock air box and new stock filter are in place, and I think I'll just leave them as they are. Thanks again for the info and suggestions from all of you. Much appreciated.

[KEITH KRAUSE]

The factory will tell you the ONLY time you may need to run a colder plug is if the bike is used for high speed running almost exclusively, such as racing.
The ONLY time you would possibly benefit from running a hotter plug is if the bike is used for very short trips all the time or the majority of the time.
In both cases, you STILL look at the plugs after running in the above conditions and let the plug read determine what needs to be done.
Of course, an accurate read depends on the engine being in excellent tune with no issues(such as an incorrect mixture)that can effect the reads.
Some people will tell you that they have run colder/hotter plugs with no problem. I'm not an expert about plugs and heat ranges, etc, but if your bike is running correctly and under "normal" conditions, you should always run the factory recommended plug.
Many of the people who have run colder/hotter plugs do so because their plugs aren't burning the way they should. This is because of compression, mixture problems, etc, and they try to compensate by changing the plug. Some change to a hotter plug because they have sooty plugs when they should be finding what's causing the sooty plugs. But I undertand how easy it is to be lazy or on a budget and these people just want a quick "fix".

[snowbeard]

wow, you say add as much as 10! I thought I was possibly overdoing it by changing to my 850 jets of 115 (the 650 had 110 originally)

I did try this, and it runs much more happily, and I can feel a difference in the power! I get 65 mph at 4800 rpm where it used to be 60 at 5000!

so with a plug reading, just how long would you suggest running the engine before checking them??


thanks for letting me hijack your thread a bit cjm!! it's really helped me!

[KEITH KRAUSE]

so with a plug reading, just how long would you suggest running the engine before checking them??

The plugs must be relatively clean/normal condition to start. If sooty, clean or replace. If carbon stained, replace. I just go about 1/2 mile at full throttle to check the mains. That's not very long when you're at that high speed.
Keep in mind I have a safe place to test with little/no traffic and no cops.
To be exact about what I do...
With fresh or cleaned plugs, the test area level or uphill, the bike completely warmed up/hot, I run it normal through the gears to reach top gear and then just open it up for about 1/2 mile or so. I then back off a little, make sure it's safe, then I open it up one more time for about 1/2 mile, then chop off and get my reads. I don't know if the second blast is absolutely necessary but I feel better about the reads that way. I just want to get a good read at full throttle and to positively burn off any deposits/previous coloring that may be on the plugs because of operating on other jetting circuits (smaller throttle openings) just before the run. Works for me.
Generally, according to people/books/websites I've visited, the best main jet will be the one that gives the best top speed. However, I don't think that's the advice that works best for some of the bikes I've done.
I choose the largest main I can run WITHOUT causing a bog during roll ons. A roll on is basically having the bike in top gear at about 60/65 mph and rolling on, not jerking it on as fast as you can, but just a normal deliberate twist to open it up fully. It should pull immediately.
On a street bike, any bogging isn't acceptable. In the real world, roll ons/passing is more important than squeezing a couple more mph at absolute top end. Some bikes will seemingly handle the larger main well at higher rpm's but they need to "clear themselves" (a bog) first before pulling hard. You shouldn't need to go down a gear to try to eliminate the bog either. Not on our type of engines. If it bogs, I'll drop the main to the next smaller size.
This isn't always necessary on every bike. Some do run best with the main that delivers the absolute highest top end. Others bog during roll ons. If I know I have the jet needles set correctly, I know there's no bog created by jet needle/main overlap and I can blame the main for the bogging. And since I usually adjust the jet needles first (not the choice of many others), I know it's the mains I'll be changing.

[snowbeard]

thanks again Keith!! great pics of the british show btw!

so would you think a white ashy plug would brown up nicely if I change the main and have corrected the leanness?