Stage 3 Dynojet not enough?

[Guest]

1980 GS750L
Uni pod filters (oiled foam)
V&H 4-1 (standard fiberglass packed baffle)
all else stock

I first tried a Sigma 6 jet kit for these mods and they send me though a mess of jetting changes and nothing but frustration. I finally broke down and bought the Dynojet III kit (keep in mind it was a NOS kit never opened) I started with just their normal settings but have had to mess around with other jet sizes. I am in need of some help figuring things out.

I started by syncing the carbs before making changes.

Settings were:
-needle 5 clips from top, one washer under
-Stock 42.5 pilot jets
-DJ 700 main
-Pilot screws 5 turns out (WHA??!)
-Installed air restrictors

Bike started ok, didn't idle well, sputtered with throttle

So I made a few changes:
-Needle same
-Stock pilots drilled out 4 drill bit sizes
-Newer DJ140 mains
-Pilot screws 3 turns out

I tried the DJ130 mains wouldn't idle worth a crap, no power up top. Tired DJ150 mains, idled better, slowly rev'd out up top. So I split the difference and went with 140s. Now the bike idles fine has ok mid-range OK top end. Now for the butt. It sometimes comes to life and really pulls crazy hard with the power I would love it to have all the time. Pulling away from a light you have to play with the clutch, it's like as soon as there is a load it falls on its face.

Where do I go from here?

[mmattockx]

I tried the DJ130 mains wouldn't idle worth a crap, no power up top. Tired DJ150 mains, idled better, slowly rev'd out up top. So I split the difference and went with 140s.

First off, your main jets have no effect at all on idle and getting onto the needle. You don't even need main jets in the carbs to get the pilot circuit sorted, the bike will idle and putter around town just fine until you open the throttle enough to start getting well into the needles where it will bog as gets fuel dumped in from the hole where the mains should be. The pilots cover idle to ~1/8 throttle, needles 1/8 to ~3/8 throttle, then the mains from 1/2 on up. There is overlap of course, but that is close enough to get things sorted. I always tune from the bottom up, starting on pilots and working up to mains because the lower circuits affect the ones above them but not the other way around.

Put a piece of tape on the throttle housing and mark the throttle openings in 1/8 increments from 0 to full. Then go out and test ride, using the throttle opening marking as a guide to what circuit you are running on. I like to go out to a back road where I can run up to highway speeds and change speeds without any traffic around to bother me. I will get into 3rd gear and let the revs drop to 2500 or so, then open the throttle and hold it in each circuit zone. When it is pulling steady and the revs have climbed some into the midrange I then open the choke. If it cleans out and runs better it is lean, if it bogs just a bit it is pretty close and if it bogs badly then it is rich. I test each circuit this way to get an idea of which way it needs to go, then go home and make the changes indicated by the testing.

My thoughts:

1) You should be fine with the stock pilot jet or one size bigger, definitely no more. You will probably be at 3.5-4 turns out on the mixture screws with the stock pilots and 2.5-3 or so with one size bigger. Sort the pilot circuit first until it starts properly, idles well and will take a bit of throttle as you ride around town at small throttle openings.

2) Once it will run well on the pilots then start testing the needle. I would start with it in the middle clip position and running the largest main jet you have. Do the above tests and adjust as needed until it will pull cleanly off the pilots and get close to 1/2 throttle without problems.

3) Checking the mains requires that you let the engine rev some at full throttle before you pull the choke because it has to be flowing enough air to really get the slides open. Pulling the choke at 4000rpm on the full throttle test won't give you a true reading.

Once you have the circuits sorted then you may have to tweak things a bit to get the transitions between them really nice. It can require a bit of compromising depending on how things work out. For instance, this spring I put a set of the APE pods on my 1100E and they flow better than the pods previously on the bike. With the APE's I got a lean surge coming onto the needles so I raised the needles one notch and that got rid of about 90% of it. It was so close that at most I needed a washer under the needle clips. I didn't feel like chasing that very fine difference so I added 1/4 turn to my mixture screws. It is a tiny bit rich on the pilots now but the surge is gone and it runs great. I did this because I plan on building a new exhaust for the bike soon and it will flow enough extra air over what I have now that I will have to revisit both the mains and the needles and I will get it 100% at that time. There is always a bit of give and take trying to get that last little bit.


Mark