DJ stage 3 kit seems to small.

[Spiff]

Hi. So I installed a gsx1100 engine in my gs750. Since the engine was a junkyard engine I didn't get any ancillaries except carbs and used the pods and exhaust system from the 750(which actually ran a 850engine). Also had to swap the points ignition over since I didn't get that either...
Now Of course it was really lean and stumbled/surged when trying to drive it at low speed just off idle. So I ordered a jet kit from dynojet, installed it and hoped it would better. But it didn't, it still stumbles. And plugs are showing a lean condition. By giving it some more throttle the stumbling goes away and it accelerates fine(but not hard by any means). Plug chops indicate lean both at cruising and full throttle(I only pulled up to 8000rpm though).
The dynojet troubleshooting guide says to raise the needle but every other carb tuning guide says to install a bigger main jet. I'm also wondering how raising the needle is gonna help with the stumbling which seems to be a problem with the slow/pilot circuit.
Anyone else experienced this with a DJ stage3 kit? I installed the biggest jets (dj138) as instructed.

 

[Who Dat?]

If it is stumbling at low speed, why bother with the main jet? What are the settings on your pilot (mixture) screws? Before the carbs left the factory, they were supposedly run against a machine that would tune them for emissions then they were sealed. Most of those carbs had the screws in the 1.5 to 1.75 turns out from lightly-seated range. As the bike has aged and the fuel has changed, we find that at least two full turns are required, sometimes even up to 2.5 turns. It doesn't hurt to go a bit richer, but only for setting up and tuning. Start with the screws out 3 full turns. It will richen the mixture a bit, so you won't need the "choke" as much, and the bike will warm up quicker.

Once the bike is warm, you should be able to turn each screw in slowly until the engine slows down just a bit. When the engine slows, back that screw out about 1/8 turn, go to the next screw. When finished, verify that you have crisp throttle response. Turn the engine off. Turn each screw in, counting the turns. Record that number for future reference then turn the screw back out, move to the next screw.

As far as the needle and main jet are concerned, be aware that you need throttle setting, not engine speed to be your guide. The needle (and its jet) come into play about 1/2 throttle, regardless whether the engine is running 2000 or 8000 RPM.

 

[salty_monk]

got any air leaks elsewhere? The Air corrector might also be wrong in those carbs for the kit you bought.... What brand of pods? Properly oiled?

The main jet feeds everything on these carbs and is definitely the point to start. DJ's stage 3 is usually too rich not too lean if anything so something's up..

What pilot jets? Sometimes you need a size up. The screws will probably be 3-3.5 turns out from lightly seated.

Plug chops have to be done & read straight away. You can't just ride around & then check them, that gives you a reading from all of the circuits combined & who knows in what ratio.

 

[Spiff]

I didn't get any air correctors in my kit. Only needles with clips and washers, jets, and drillbit for the slide hole.
Mix screws weren't plugged, and the pilot jet was a 47.5 versus 45 stock and the main was a 122.5 and I think its a 115 stock. So I think the engine might have been running a vance and hines exhaust in its previous life.
Anyways, DJ recommends to put the mix screws at 2.5t out as a baseline after fitting the kit so that's where I put them but turned them further out to try and richen it as the idle will hang when revving it. But it still hangs.
Intake rubbers are new. I've tried to spray some carb cleaner around but that didn't produce any result unless I sprayed directly on the filters. Pods are of an unknown marque, dry filters.
Also my exhaust is a Harris 4-1 so pretty much just a straight pipe... I wonder if this screws it up too much in comparison to what DJ expects?

I did two plug chops at a full throttle pull and both times the plugs read lean.
Then I rode for five minutes just cruising and killed it, read lean.

Yeah something might be up

 

[Guest]

Also my exhaust is a Harris 4-1 so pretty much just a straight pipe... I wonder if this screws it up too much in comparison to what DJ expects?

It is somewhat surprising, but differences in exhaust don't matter nearly as much as differences in intake, when it comes to jetting needs. Even though the stock exhaust is quiet, it is amazingly free-flowing.

 

[Spiff]

It is somewhat surprising, but differences in exhaust don't matter nearly as much as differences in intake, when it comes to jetting needs. Even though the stock exhaust is quiet, it is amazingly free-flowing.

So I've read, so it might be my filters that are throwing it off perhaps since they're not the kn type that DJ specifies for this setup.
But regardless I think I'm going to tear the carbs to bits and see if something is up with the pilots or that circuit.

 

[Spiff]

A little update here: so today I disassembled every carburettor completely to make sure everything was open and clear.
Then put them back in again and no change. So then I started spraying brake cleaner again and it turns out there was a small air leak because the clamps weren't tightened as hard as they should be.
Took it for a ride, not a huge change, adjusted the mix screws a little further out(now at 3 ? turns out) and it got a little bit better.
A definite improvement but not completely rid of the surging, so I have lifted the needles now one notch per the DJ troubleshooting guide and I'm gonna see if it betters. The guide says its not uncommon to have to go two notches in cases like this. We'll see.

Plugs are nice and tan now so I don't think I'm gonna mess around more with the mixture screws

 

[Spiff]

Last update i think: so after spending most of the afternoon riding, adjusting, riding and adjusting some more I ended up with the mix screws just over 4 turns out. Needles where raised one more notch for a total of 2 notches all in all.
Overall the bike rides pretty well now and power is there when I ask for it.

The surging/hesitation isn't 100% gone, there is still a little bit on low speed/low throttle(20-40kph) but higher speed/low throttle I really can't feel it and I ended the night with an hour of cruising and some "spirited" driving.
It felt really nice and I think I'm just gonna be contempt with this for now, I'm gonna order the correct k&n filters since I need new ones anyways and maybe it'll become better, maybe not.
Maybe I'm just gonna have to live with it being like that at low speed.

Reminds me of the Sv1000s I used to own to be honest, that one didn't like low speeds either, which is kind of fitting since I sold that to prioritise getting the gs back on the road...

 

[gs11ezrydr]

Last update i think: so after spending most of the afternoon riding, adjusting, riding and adjusting some more I ended up with the mix screws just over 4 turns out. Needles where raised one more notch for a total of 2 notches all in all.
Overall the bike rides pretty well now and power is there when I ask for it.

The surging/hesitation isn't 100% gone, there is still a little bit on low speed/low throttle(20-40kph) but higher speed/low throttle I really can't feel it and I ended the night with an hour of cruising and some "spirited" driving.
It felt really nice and I think I'm just gonna be contempt with this for now, I'm gonna order the correct k&n filters since I need new ones anyways and maybe it'll become better, maybe not.
Maybe I'm just gonna have to live with it being like that at low speed.

Reminds me of the Sv1000s I used to own to be honest, that one didn't like low speeds either, which is kind of fitting since I sold that to prioritise getting the gs back on the road...

Most carbs I have ever worked on at about 3-3.5 turns out on the mix is wide open passage...Straight pilot jet...Anything after that is basically useless..I have been told..Every machine is different..What you did seemed to help..I've had to re-jet several DJ kits..Mainly bought them for there needles

 

[salty_monk]

Your filters are the problem. Get the K&N ones or the APE copies & oil them properly & the DJ kit will be fine.

 

[Rob S.]

As reported by Cycle World in 1982, some slow/steady surge was endemic box stock.