Dynojet set up gsx1100 Katana

[Scott]

Hi,

I'm running a cobrra sr1 4into 1 pipe and pod filters on my 1100 katana withthe stock 34s cv carbs. I've fitted a stage 3 kit and everything is fine but I seam to have a stumble between 3 and 4 thousand revs I think this is the transition between pilot circuit and needle after that it goes well and tick over and pull away are OK

I was thinking of dropping the the clip by a half (washer) to richen the needle what do you think. The stumbling would normally be a lean problem right?

Cheers,

Scott.

[Billy Ricks]

Down low it's usually a lean condition and up top a rich condition.

[KEITH KRAUSE]

Yes, most likely a lean condition.
More important than the rpm's, what throttle position is the stumble at?
If right about 1/8 thottle or a bit more, it's hard to say which circuit is causing trouble because the pilot circuit is transitioning to the jet needle at that point.
I assume the carbs are vacuum synched well? The mixture screws responded well to adjusting them for highest rpm? What are the mixture screw settings right now. How much, if any, did you increase their richness?
What brand of pods? If K&N, did you oil them correctly?
If you have any floatbowl vent lines, did you remove them?
What size air jets did the kit supply? Did you try any?
Did the kit include lighter piston springs? Did you try them?
Have you taken any plug reads yet, especially at 1/3 throttle and minimal throttle (just above idle/steady low speed cruise)?

[Scott]

Hi keith,


I reckon its about 1/8th throttle position but I'm going to to tape the throttle tommorow and mark up the the exact positions. I'll pick up some new plugs and do some chops this week.

I'm running well oiled pods (not K&N)with a DJ134 main and a det of pilot air jets that DJ supply I have the carbs synced and the pilot air screws are out at about 2 3/4 turns. Apart from th needles and the larger vent hole on the slide everything else is standard.


I've heard that some people go up on the pilot jet size even withthe dynojet kit. Have you ever tried this?

It just feels like the top end of pilot circuit to me after that it goes all the way.

[KEITH KRAUSE]

The jet needle effect does kick in sooner than many think. If you have the e-clip in the DJ base setting suggestion, they are commonly lean by my experience. I'd first run a solid 1/3 throttle plug test to see what the jet needles are doing. If a bit lean at all, I'd raise the needle either 1/2 position with the jetting spacer or maybe 1 full position depending on the degree of leanness/color of insulator. You don't mention any performance issues at 1/3 throttle so I'm guessing the needles aren't far off? I'd get that right first. If you do raise the needles, then I'd take more plug reads to see how the pilot circuit was effected with minimal throttle tests/performance check. It's possible the stumble will be gone.
If you didn't need to make any needle changes/still have the stumble and (I assume) good jet needle plug reads, then I'd go at the pilot circuit. The mixture screws generally have an effect up to 4 turns out. If no joy at that point, then you have to increase the pilot jet size and return the screws to something close to stock and re-test.
I assume the carbs are very clean inside and float levels set to factory spec's.

[Scott]

I've raised the needle 1/2 a notch using th DJ spacer and the problem still there but not as pronounced . I'll try one full notch a see what happens.

Carbs are squeeky clean and float hieghts are set at 22.5mm which is stock height.

[chef1366]

I have my needle set on the fifth notch down. Runs like a champ.

[Dink]

Just throwing in a couple of thoughts.
1 are the vent hoses on the carbs removed?
2 are you certain the idle progression ports are spotless?
I did see you mention the carbs are clean, but are you certain about the progression holes? these carbs run quite a few fine ports so it doesn't take much to restrict them.
Dink

[Scott]

The carbs were ultrasonically cleaned the vent hoses are removed. The carbs ran standard on my 750 with a standard airbox before I fitted the dynojet kit and they ran fine. It's since fitting the 1100 dynojet kit and running them with pods on the 1100 that the problem began. So I know the pilot circuit is not blocked.

[KEITH KRAUSE]

I've raised the needle 1/2 a notch using th DJ spacer and the problem still there but not as pronounced . I'll try one full notch a see what happens.

Carbs are squeeky clean and float hieghts are set at 22.5mm which is stock height.

Sounds like you're getting there. Remove the jetting spacer and re-test.
How do the plugs look after a good 1/3 throttle run, if you can do that safely.
When you say the carbs are synched, I hope you mean with a vacuum tool. Bench synching is just to prepare for the vacuum tool synch. Hard to judge performance or get accurate plug reads without a good vacuum synch. The stumble could be related to a poor synch too.
I assumed before that you vacuum synched but re-read things and thought I'd mention it.

[Scott]

Thanks guys,

Kieth they are vacume synced. I won't get a chance to do any plug chops today so I'll post progress later this week once I've marked up the throttle positions and done a few chops.

[KEITH KRAUSE]

Yes, I'd first take 1/3 throttle reads and do what the plugs/performance say to.
If you end up raising the jet needles another 1/2 position, that may fix you up. You did say that raising the needles 1/2 position so far has improved the problem.
But just in case, if you have good performance and plug color while operating the jet needle circuit and still have the problem, you may have a vacuum lag problem. Hard to say and difficult to explain. But a lag, or throttle response issue, could be what's happening. That's why most jet kits supply the lighter springs. The vacuum port to the diaphragm chamber must also be drilled out correctly.
I wonder...does the bike stumble at 3/4K only under acceleration? Meaning, you're turning the throttle more and more as you approach, hit, and then pass the stumble point? No "fixed" throttle position? If so, it could be a lag in vacuum/throttle response issue. Happening just for a moment, after you open it up?
If you deliberately held the bike at 3/4K and made sure of no throttle position change, would it still stumble, almost continually? This would suggest a mixture problem and not a vacuum issue.
Not trying to complicate things. Just thinking. Hopefully, the richer needle settings will be the fix.
Let us know the fix because it helps others down the road.