Mix screws 4.5t out, still lean. What's the way forward?

[gorbys]

I just swapped in a gsx1100 engine in my 750gs(which ran 850 cylinders and top end, 4-1 race exhaust and podfilters).

I know nothing about this 1100 engine or its previous setup. 

I have it running now with the pods and exhaust from the 850engine. It ran lean(as expected) so I tried to adjust the mixture but its still running lean at a full 4.5 turns out! So do I increase the pilot jet or the main jet as I understand these are sort of intertwined in their operation? I have checked bot the 850 carbs and 1100 carbs and the included jetting is attached in the picture. Seems the 1100 is jetted slightly higher than stock so might have ran an exhaust previously? Mix screws where 3.5turns out. 

Have not road tested it yet, still on the bench as I'm working on brakes.

[TonyGee]

i think 3.5 turns out is generaly the max, its then down to the pilot jets. 

[Dezza]

My 1100 (efe), stock carbs (BS36), pod filters, Ledar kit, 152.5 mj, 2 1/4 turns out. If you run pod filters and don't have a dynojet/ledar air corrector kit you're going to find things difficult. First thing, ensure all is good with engine, i.e. compression test, valve clearances, give it an oil change. Then strip and clean carbs, fit appropriate carb kit to get you somewhere close, bench synch, and go from there.

[gorbys]

What size pilot jets are you running Dezza? 

With that big main jet it's almost tempting to try the 135's i have just to see if it gets better. 

I have been in touch with 6 sigma about a jet kit as I never expected it to run okay as it was. 

Engine got a slight refresh before it was put in so its in good health, need to check the valves again as they where set cold 

 

[Dezza]

They're stock - 47.5 according to the book. The cheapest and easiest key to  flat-spot-free smooth running when the airbox is junked is to use air-corrector jets as developed decades ago by Ledar. I thought Grumpy 1260 were going to remanufacture these again. What carbs do you have? Different GSX1100s had variations on (mainly) BS34s with the last 'EFE' models having BS36s.

Edited September 12, 2021 by Dezza

[no class]

my 1100 Kat with 4-1 pipe / stock airbox ( lid removed) 130 mains / 47.5 pilots / 1 1/2 turns out from seated ….. spot on .

[Gixer1460]

Its a GSX1100 so why not start with a richened up 1100 jetting to start - 4.5 out on mixture screw is waaay to far. ^^^ above doesn't sound a mile off?

[gorbys]

11 hours ago, Dezza said:

What carbs do you have? Different GSX1100s had variations on (mainly) BS34s with the last 'EFE' models having BS36s.

I don't know to be honest. It's an 82 engine as far as I know. 

 

9 hours ago, Gixer1460 said:

Its a GSX1100 so why not start with a richened up 1100 jetting to start - 4.5 out on mixture screw is waaay to far. ^^^ above doesn't sound a mile off?

No it doesn't, I think I'll start by just putting in the 135's to see if it betters. Untill I get a proper jet kit.  I'll order one but I also need to order an upgrade kit for the clutch basket springs. I've noticed the little time it has run it's very noisy and today I took out the basket while changing the oil and 3 of the springs where loose. And the threads in the oil sump for the plug are probably gone as te bolt just goes round and round when you try to tighten it. So happy days 

[gorbys]

Just a little update to let you know that it responded nicely to bigger mains. I put the 135's in and mixture screws are now at 3 3/4 turns out and the throttle is definitely more snappy.

Still need to get jetkit as it's not enough but at least I can take a little testdrive up and down the street hopefully to see if everything else is OK with the bike 

[no class]

3 3/4 turns is still waaay too much . 

[gorbys]

5 hours ago, no class said:

3 3/4 turns is still waaay too much . 

I know. 

[johnr]

if youve not actually ridden it on the road, how do you know its lean? revving it up in the garage on the stand isnt putting it under any load. if iy runs, take it up the bypass with fresh plugs in and do a plug chop.

[Gixer1460]

5 hours ago, TomP said:

Hi, can you post a picture of the screw you're adjusting? I always thought that the main jet doesn't  enter the picture until wide open throttle. However I'm still learning. 

Any fueling that is on the needle or WOT will be determined by the MJ.

[gorbys]

On 9/20/2021 at 5:19 AM, TomP said:

Hi, can you post a picture of the screw you're adjusting? I always thought that the main jet doesn't  enter the picture until wide open throttle. However I'm still learning. 

The pilot jet gets its fuel supply via the main jet.

I can recommend this video for how a cv carb works.

The difference for us though is that the mixture screw is at the top and like I said, the pilot is supplied via the main jet. 

 

[Gixer1460]

10 hours ago, gorbys said:

The pilot jet gets its fuel supply via the main jet.

I can recommend this video for how a cv carb works.

The difference for us though is that the mixture screw is at the top and like I said, the pilot is supplied via the main jet. 

 

I may be old and stupid ( some say definitely) but looking at that picture - and assuming the circuit on the left is the pilot / low running circuit) how and where is that connected to / influenced by, the Main Jet apart from they share the same float bowl? You can remove or can block a MJ on most carbs and the engine will still idle - how, if interconnected?

[wraith]

Very very basic, 

Pilot jet = low revs and up to 3 rpm 

Needle = mid range and overlaps pilot over about 2.5 rpm

Main jet high revs overlaps needle at about 5-6 rpm 

This rpm may differ to revs engine goes to. Like I say very very basic

All 3 are linked by the float bole be separate fuel system affecting different parts of the rev range

Pilot won't affect top end and main jet won't affect bottom end, I've ran GS a gs1000 with a set of carbs gone from a 130 main all the way up to 160 main with no difference at bottom end but you can see it mid to top end

[gorbys]

2 hours ago, Gixer1460 said:

I may be old and stupid ( some say definitely) but looking at that picture - and assuming the circuit on the left is the pilot / low running circuit) how and where is that connected to / influenced by, the Main Jet apart from they share the same float bowl? You can remove or can block a MJ on most carbs and the engine will still idle - how, if interconnected?

It's either a simplified scheme or the Harley carb separates the two. But on the suzuki carbs the pilot jet is blocked by a rubber plug and gets its fuel via MJ. 

 

 

[gorbys]

Okay so here's what's going on after today's test ride after installing the dynojet kit:

Still lean on the slow circuit. DJ instructions says mix screws should be 2.5t out from seated. I have them at 4 now and it's still stumbling/surging at low throttle sub 3-3500rpm's. Giving it some choke seems to clear it up slightly but not enough to stop it surging completely. 

Acceleration : Stumbles/slow accel upon opening the throttle until you get higher in the rev range/get on the needle. 

Cruising at 4-5000rpm:

Not surging, stable, plugs show maybe a slight tinge of a light beige. Definately leaner than the tan/brown you would hope to see. 

Acceleration: it does, but doesn't pull as hard as I would think an 1100 would do. 

Plug chop at 8k wide open throttle shows again, white plugs. To lean. 

Following the DJ troubleshooting guide: 

https://www.suzukicentral.com/threads/official-dynojet-troubleshooting-guide.69659/

A possible solution to the surging would be to raise the needle. And I can always try but how does that fix a problem with the slow circuit /pilot circuit? Is it the tapered design of the DJ needles that allows fuel to enter the venturi? 

Also every other guide I've read about tuning carbs says to start with the main jet and make sure that's correct before addressing the needle, and lastly the pilot/mix circuit. And it's pretty clear here that the mains are to small if its lean at a wot pull, or is the needle still in play at 8k?

[TonyGee]

you could try and wrap some tape round the filters just for a test and see if it runs better. it will confirm if its running lean. 

[gorbys]

54 minutes ago, TonyGee said:

you could try and wrap some tape round the filters just for a test and see if it runs better. it will confirm if its running lean. 

One of the things I'm thinking about 

[no class]

you could have made 1 run on a dyno to see your fueling and get it running proper…… fuckin’ about with needles and jets and mixture screws and trying to diagnose with plug inspections…… 

[gorbys]

2 hours ago, no class said:

you could have made 1 run on a dyno to see your fueling and get it running proper…… fuckin’ about with needles and jets and mixture screws and trying to diagnose with plug inspections…… 

Yeah cause I wouldn't have to fuck around with needles and jets and mixture screws if it was on a dyno...... 

plugs chops are fine, they tell me what I need to know, I have a wideband O2 sensor if need be but for now what is that gonna tell me that I don't already know... 

[no class]

…… yeahhhhhh….., go on then ….. a few turns out with the mixture screws and you’re almost there ! 

[no class]

..,,,. put your mixture screws at 1 1/2 turns out from seated  and go try it out . 

[gorbys]

Username checks out at least....