New guy from Ohio - '82 GS750T

[Chuck78]

Really by 1/4 throttle, the pilot circuit has less and less to do with the mixture. Almost out of the picture be then.

[yasser]

Have fun with explorations, hang onto that air box. I say that after seeing years of T owners struggling with pods.

[GSXR7ED]

Welcome Sailor Bob,

Love your "T". Wanted to see full-size pic:



So...you're going with Pods, huh? I've never had the inclination to pursue this but like yasser suggests, keep the original Airbox.

Also, post your "T" here:

http://www.thegsresources.com/_forum/showthread.php?228624-T-Nation-Thread-(My-2nd-Thread)-3rd-Overall-(I-think)&highlight=

Ed

[sailor_bob]

Hey guys, thanks for the advice! Over the past few weeks that I've been in active I have been trying different jetting combos, tried raising the needle jet around .040 so far, bigger and bigger main jets up to as much as 4 sizes above factory (112.5 is factory, 122.5 is highest I tried), one size larger pilot, and of course playing with my mixture screws til it's running at it's best. All this and still somehow running lean... I feel as if it should practically be drowing in fuel by this point but I can't get it to richen up. But the fuel mixture isn't even the biggest problem, my worst problem is still the dead spot in the throttle between 1/4 and 1/2 throttle. Closer to the 1/2 margin. I hate to say it but I think i've finally given up. Probably going to put the airbox back in and go back to factory jetting this weekend. It ran great there and I'm somewhat regretting ever messing with it. At least I tried but I'm missing to many riding days.

[Chuck78]

This is the biggest reason why a Dynojet kit is sometimes the easiest route for owners who are just starting to wrench, & are going pods & pipe with stock bore pistons & stock cams.
Having CV carbs complicates this even more, because in terms of carb tuning, "1/4 to 1/2 throttle" is when the slides are 1/4 to 1/2 raised. On direct linkage carbs, your throttle wrist only opens the butterflies at the outlet of the carbs, the slides still do their own thing based on airflow velocity through the carbs. There is often a lag in the slide raising to the same position as your throttle grip is twisted. So there is still a slight possibility that richening your pilot jets is needed.

Now if you go from running good at 3/4 throttle and back off the throttle down to say 3/8 throttle in the middle of the problem area, and it still acts up, your engine is definitely telling you that the upper area of the needle (largest diameter that the needle jet sees) and the beginning of the taper of the needle are too thick, or also that the needle jet opening on the top end of the emulsion tube is too small of diameter.
The needle jet emulsion tube/bleed pipe assembly (all 1 piece on those carbs, earlier vm carbs the bleed pipe /emulsion tube and Jet are 2 seperate pieces stacked onto each other) is what the main jet screws into. You can get smaller or larger needle jets readily from jetsrus.com or Z1 enterprises, and you probably need to go up one size to alleviate this problem. Problem is the needle jets are generally around $16.99 each! There are a million different types of them, but if you pull one of yours, you will see stampings on them. One will be the mikuni logo (little square inside of a big square, like a right triangle notation, but 4 sided square) then the type/style of needle jet (a number like 186), then the size, letter then a number - like O-6, or P-4. The jets r us site will tell you which is richer and which is leaner. So it really sounds like you probably need a needle jet that is one size larger. Putting in a needle with a skinnier base and sooner or more drastic taper would do the exact same thing however. Needles are much more complicated to look up with all different lengths, clip locations, tapers and dual tapers, taper beginning location, etc... needle jets are just #1 - one type only that fits your carb, & #2 - a single large orifice with only 1 measurement

Dynojet gets fancy with their needles and reconfigures the tapers and the beginning diameter as well, but Dynojet. kits tend to run you on the rich side just to keep them safe from ruining anyone's engine by running it too lean. Often, every one of the 3 sets of mains they give will be too rich, but better for them than melting a hole in someone's pistons.
Their jet sizes are also rated differently, a 120 Mikuni hex head main does not equal a 120 Dynojet. That is always confusing for people all across the board.

If I were you, I would experiment by shimming the needle up substantially, as in .080" or .120", and see if the problem was partially solved at at a small range closer to half throttle. This will probably make you way too rich above half throttle, but if you pay attention to exactly where the problem ended previously, and then do the exact same observation after shimming the needle up substantially, then that will tell you that your needle jets need to be larger but 1+ size. There is also the mod that some people do by cutting the diaphragm spring shorter. I will not recomended this as I don't work on CV carbs much to have any advanced knowledge on this. Shortening a spring makes it stiffer (slower opening side) as long as it doesn't get cut too short to have freeplay. Don't do this unless someone extremely well versed in tuning gives you very clear explanations on every aspect of it.

People always complain that you will never get your bike tuned right with pods, but the thing they never considered is they are only raising the needle and changing the pilot jet and main jets. That jet that dictates quarter throttle to half throttle is not something that people think about changing, and that is generally always why people say that you will never get your bike to ride with pods.

You CAN tune your bike properly with pods, the only thing that you will have trouble with his heavy cross winds making your bike go extremely clean, or heavy rains making your bike go extremely rich. Your air filters on 2 carbs are now completely exposed to the elements on the outside. After an unfortunate carburetor theft, I am now running individual pods as opposed to dual oval air filters that I much preferred (Google k&n RC-2222), and in doing so, I have grown even more accustomed to the fact that I really need to clench my legs around the outside of the air filters when I ride in the rain or when it gets very windy. For the rain aspect, I almost put my factory air box back on, but the 1977 air box was just too heavy and bulky when I had it in my hands about ready to swap it in place, so I threw on a pair of 30 year old K&N pods after heating the old rubber up on my halogen work lamp to get them flexible enough!

Best of luck

Chuck in Columbus

[sailor_bob]

Thanks a bunch Chuck. I see what you're saying now, i would have never though to try and change the needle jets really, to be honest. Didn't cross my mind as a tuning type of adjustment. I have contemplated the dyno jet kits but I've heard of people having trouble with them too as far as buying them (fairly pricy) putting it all in and still now fixing the problem fully.

My manager at work (vintage bike guru pretty much, has arpund 30 something old bikes) has been giving me lots of advice and looked into the problem online everywhere and found the same info other guys have said here that the 750's don't seem to like pods. I'm no doubtful at all that it CAN be made to run with them, but the problem is my huge lack of time to work on it constantly and I hate dumping money into it and not seeing many results. If I could dump a bunch into it knowing for sure it would work I would in a heart beat. The other problem and probably the biggest is the fact that it is my only bike. If I had a second bike to be riding until I get this one tuned in I'd be more eager to dial it in, but being that I'm completely missing out on riding right now altogether I just want it running as fast as possible even if that means back to factory settings and then maybe I can try again once I pick up another bike down the road.

Another coworker suggested at least trying the factoy setting onces because I haven't since I had the top end all apart. He said try it because it ran that way before, so if it runs that way again that at least confirms I put everything all back together correctly and the timing is right. He said maybe my timing chain is off by a half link or something but I triple checked it before putting it back together and am 99.9% sure it's all correct, although you can never be too sure. People make mistakes, So I think i should at least try throwing the airbox back in this weekend to confirm everything is mechanically right. I wish I would have just done that in the first place after tearing the engine down instead of messing with the carbs before I tried running it. But, you live and you learn. It's a mistake I won't make a second time.

[Spyder]

I was running 140 mikuni jets in mine with pods and a 4-1 pipe setup in the stock carbs. I have since then installed DynoJet kits with the tapered, and adjustable needles and still run the 140 jets. Runs awesome. You may want to keep coming up with your jets, and I strongly recommend getting the DynoJet kits. Not too expensive and WELL worth your savings in aspirin... I also recommend staying with the mikuni jets. With a stock exhaust you shouldn't have to come up to a 140, but ...

[sailor_bob]

Hmm not sure, if finally just put my factory airbox and jetting back in today. wasn't excited about it but I just want a bike to ride. If I pick up a second bike this summer or fall I might try again and even invest in a nice 4 into 1 next year when I can have it down and not miss out on riding any more. but for now, factory settings will have to do. Did not get a chance to start it up and tune the mixture but I'm confident it should run no problem now. I did manage to snap a few pics with everything together and the side covers on now before I covered it up.

Really just needs a tad more cosmetic TLC (polish forks like I did the side cases and black out a few more small pieces) and she's ready for bike night.

[GSXR7ED]

Sweet looking bike! Enjoy the ride once you turn her on!


Ed

[Spyder]

Very nice! Someone around here should have a front fender for it layin' around...

[GSXR7ED]

Good catch Spyder,

Yeah...someone should have one lying around.


Ed

[sailor_bob]

Very nice! Someone around here should have a front fender for it layin' around...

I actually have the front fender! Took it off when I had the pods and all still on. Was trying to eventually go for the bare bones, stripped down look but that's not gonna happen til fall or next summer now probably. I like the way it looks with no fender but have a feeling the first time I get caught in a downpour I'll be kicking myself in the ass for taking it off.

[GSXR7ED]

I actually have the front fender! Took it off when I had the pods and all still on. Was trying to eventually go for the bare bones, stripped down look but that's not gonna happen til fall or next summer now probably. I like the way it looks with no fender but have a feeling the first time I get caught in a downpour I'll be kicking myself in the ass for taking it off.

You'll need the front fender because it serves as a fork brace. I put a fork stabilizer on mine for peace of mind. No "wow factor".


Ed