AFR tuning

[VJ]

Hi guys and girls, I'm looking for some advice on tuning. I've set up a wideband o2 sensor setup on my old ratbike now and will be going out for trial runs over the next few days and noting the AFR at WOT,3/4, 1/2, 1/4 etc ready for me to make adjustments to suit.

 

My question is: is there a clean cut number between jet sizes and AFR ratio to help me dial it in without having to buy too many jets? e.g -5 on jet number = 1afr etc. Also same question with needle heights.

 

If anyone is interested in specs its a gsx1100g with a DOT head and cams, 36 CVs with pipercross sock filters and a cut down micron on a 4-1 pipe.

 

I'll update this as I get the runing done incase it helps anyone in the future.

 

Cheers

John

[MeanBean49]

All dependa, on bike, carbs the whole setup. 

But as a rough guide on 1100/1200 motors with carbs around 36mm I have found a change in jet size of 10 (130 to a, 140 for eg) equates to an AFR change of about 0.5  (12.5:1 would become richer to 12:1)

[VJ]

Thats great cheers, To be honest I'd have been very suprised if there was an x=y straight ratio for it condisering how many variables there are but its good to have a ballpark idea of how many sizes to jump.

 

Cheers

VJ

[VJ]

So ive just been out for my first ride with the AFR display on.

Im getting around about 10.5-11:1 at idle all the way up to 7k rpm (ish) then it leans out to 14.5 and even dips into high 15s. as I hold it at 8.5k

Now these figures are all by eye not data logged to the rpm so I cant be 100% accurate, im more trying to hold an RPM and see what I get, It has told me I need bigger mains in it so I'l go from 150 to 160 mains and see how it looks on the top there.

Im also not going to change anything else until I've got mains dialed in, seen as fuel through the emulsion tube past the needle will be effected by the main jet size it seems a bit like pissing in the wind to change that before Ive got the mains happy.

 

Cheers

VJ

[Gixer1460]

For a NA engine those numbers around idle / mid range are waaaay to rich, almost potentially bore wash rich! Yes address the MJ but that is an area the gets used the least and it the carbs are off anyway you might as well jet and needle down the bottom end at the same time! Also for consistency, tuning on the road needs the engine under load so you need a looooong uphill stretch - a long flat just flatlines the load once you hit a particular rpm! Not knocking the enthusiasm but this could all be done in an hour on a dyno?

[VJ]

Yeah Im glad its rich rather than lean but it deffo needs fixing, its easy enough for me to do needle height with the carbs still on the engine so im not too fussed about doing it in one hit. Luckily Ive got an NSL road near me that is a long hill so im sorted for loading, yeah its not going to be as quick or as accurate as a dyno but im mostly doing it as a learning exercise.

[GSX1100dreamn]

Do you know what size your pilot jets are ?

They will affect your A/F at idle to 3000rpm (they did on my 38 cv) that was roughly where my pilots and mains crossed over.

[VJ]

So I popped into allens in bingham on friday and got some 157.5 mains (they didnt have 4 160s avaliable) 

Ive just put them in and also dropped my needle one as suggested by say what now!?.

as for pilot jets I realised they are unbranded '30' size so in the interest of knowing where I am and getting a better baseline figure Ive put some actual mikuni 15s in to see what I get there.

Work stops play for a few days now though, hopefully I can nip out on thursday afternoon and see how its running now.

[VJ]

weather is absolute shite here today so I havent had the chance to go out on the road to test today.

 

Ive now got 157.5 mains fitted, 15 pilot jet, and the needle on the middle position.

When I fired it up with 15 pilot jets and 2 turns out on the screw my gauge was pinging very lean (off gauge even) so I dialed the pilot screw out half a turn at a time to see what I could get it down to. I came to a comprimise and stopped at 4 turns out being 15.8/16.5 on my gauge. Ideally id like it a lot richer but I dont want to unscrew the screws anymore incase they fall out. I think I'll be putting some meatier pilot jets in when I get the time but I think that will do for now on the bottom. 

 

Just waiting for a dry day to go test my main and needle afr and see if I need to buy any more brass other than pilot jets before i trek back to allens.

 

Cheers

John

[GSX1100dreamn]

Normally baby steps with the pilots too.

I had the same AFR at idle low 11:1 and went from 37.5 to 35 pilots and that gave me around 12.7:1 or so. Close enough for me as I avoided taking my cabys off like the plague.

But atleast you have seen a change be it waaay the other scale of AFR.

The o2 gauge takes alot of the guess work out.

Cheers Andrew.

[VJ]

Interesting, that would suggest 20 seems to be a good size for me to try next then for pilots. I know what you mean about not wanting to take carbs off.

 

Yeah im glad I got the wideband setup, ive been fucking around with 'seat of the pants' dyno tuning for years but its really reasuring to see a gauge co oberate my thoughts.

[MeanBean49]

7 hours ago, VJ said:

Interesting, that would suggest 20 seems to be a good size for me to try next then for pilots. I know what you mean about not wanting to take carbs off.

 

Yeah im glad I got the wideband setup, ive been fucking around with 'seat of the pants' dyno tuning for years but its really reasuring to see a gauge co oberate my thoughts.

Personally I would stick with your origional plan of getting the main jet size right before dicking about with the needles for the mid range stuff because as soon as you change the main jet needles will probably need changing again, its basically pissing in the wind. 

Difficulty on the road is being able to find a decent enough bit of road to hold the bike open full throttle from low revs all the way to the top of the rev range in a high gear, ideally 4th or above, and being able to watch your gauge while doing it, unless you can go-pro it maybe

Also worth noting at steady throttle and idle your afr wants to be a lot leaner than when accelerating, ideally around 14.7 ish so your idle isnt far out as is. 

[VJ]

Well ive been out on the bike this weekend and found it was a bit lean on midrange so I popped home and lifted the needle, its running a lot better now.

Im a bit confused now with my readings though. If I cruise at 8.5k then I get around about 13:1, 7k is around about 14.7:1 5k is around 12:1. However if I do a WOT pull from 3k up to 9k in 3rd I get around about 11:1 all the way through.

Im a bit confused about where to go now but I think its close enough to be safe for now.

 

 

[dupersunc]

3 minutes ago, VJ said:

Well ive been out on the bike this weekend and found it was a bit lean on midrange so I popped home and lifted the needle, its running a lot better now.

Im a bit confused now with my readings though. If I cruise at 8.5k then I get around about 13:1, 7k is around about 14.7:1 5k is around 12:1. However if I do a WOT pull from 3k up to 9k in 3rd I get around about 11:1 all the way through.

Im a bit confused about where to go now but I think its close enough to be safe for now.

 

 

It's not fuel injection, you simply won't get it spot on at all loads and all revs.

Doesn't sound like you are a million miles out.

Get it right for WOT, then see how if feels else where. 

[Arttu]

Like @dupersuncsaid. I guess you are reaching the point where it starts to get tricky to improve with carbs. For sure it's possible but probably would need experimenting with different needle shapes and all that kind tricks.

I would try smaller mains to get WOT around 13:1 and then see if you can still improve cruising areas with needle heights.