What Afr Should I Be Looking To Achive?

[M_R_205 5 1 Cars]

in my seemingly endless battle to get this car running properly i have forked out on a wide band kit and have managed to get things running, at the moment at idle it shows a very irratic reading somewhere between 12 and 14 a partialy open throttle revving prety much anywhere im getting 12ish and if i momentarily open the throttle fully it dives to 10ish, Unfortunatley i cant do any on the road tests asmy guage is not working, im running the sensor though a desk top pc!

 

Any way what sort of values should i be looking at, the genral conclusion i have come to is that 14.7 at idle is perfect, but what about at revs? should it stay around that figure or is a little rich fine? (obviously not quite as rich as im currlently getting!)

 

 

Cheers for any advice

Paul.

[Tom Fenton 1,542]

Don't get too tied up in getting it to 14.7 bang on at idle, just fuel it so it runs nicely, different engines seem to like different mixtures. When actually driving under load you want to be somewhere around 12.5 to 13 AFR. This is where you will get max power.

[petert 588]

You can only do the idle mixtures if the sensor is in the downpipe (or general area). There is not enough exhaust flow at idle to get an accurate reading from the tailpipe. I generally aim for around 13:1 at idle. Once off idle, get it anywhere between 14.7 and 13.5 initially, other than full load. Aim to get the mixtures progressively richer as the load increases. For example, on the 3000 map, aim for 14.7 at light loads, 13.5 at mid, then 12.7 at full load.

 

If you stick a meter on an lambda equipped Mi16 for example, it runs at 14.7 everywhere, except from 5000 onwards at full load when it goes to sub 13. They're a lot more responsive if you remap the mid loads to 13.5:1.

Edited May 11, 2009 by petert

[gti_al 1]

Peter, mine was down at 11 above 4500rpm when we ran them the other day. What could be going on there? Made good power, but ran out of revs!

[M_R_205 5 1 Cars]

well im going to have a fiddle with it tonight, im kind of learing as im going with it lol, the sensor is at the ver end of the 4 branch manifold around the gear stick area, i think i need to get my guage sorted as i cant test the egine under load, or get my lap top sorted which ever is easiest!

 

Thanks for the advice

Paul.

[M_R_205 5 1 Cars]

Now then, bit of step backwards here, iv managed to get the laptop to recognise the sensor, i also re calibrated the sensor to "free air" and the readings im getting are much richer than at first averaging 10ish at idle and as low as 7-8 at full throttle/load!!! so im going to pop in some smaller jets tomorrow and see what happens, probably going from the 180s in now to 165s/170s

 

Another thing iv noticed is how irratic the readings are aven off idle, they can range anywhere from 8 all the way up to 12 in a split seccond, is this normal? il try an post a graph up tomorrow when i can steal the laptop back.

 

Paul.

 

EDIT: will getting the AFR correct make that much difference to performance? i know im gpoing to sound like a tit here but the car fees... is bloody fast as it is, will i get better performance? or will it just be a case of the car running better? im not realy botherd either way its just out of curiosity.

Edited May 11, 2009 by M_R_205

[welshpug 1,661]

it'll run better AND be more powerful, AND more economical

[M_R_205 5 1 Cars]

[unariciflocos 49 1 Cars]

I had better get this sorted on mine as well.

 

Just to make sure, fueling on bike carbs is adjusted by the idle screws for idle, vacuum pins for mid range and main jets for high range?

 

What is common practice? Adjusting fueling and then ignition timing, vice versa or repeating one of the sequences several times?

[M_R_205 5 1 Cars]

I had better get this sorted on mine as well.

 

Just to make sure, fueling on bike carbs is adjusted by the idle screws for idle, vacuum pins for mid range and main jets for high range?

 

What is common practice? Adjusting fueling and then ignition timing, vice versa or repeating one of the sequences several times?

 

 

The way im doing ti be it the correct way or not is, set the high end fueliong first with the correct size main jet, then as you say get the mid range sorted with the mixture/vacume needles underneath and that uysualy sorts the idle fueling out to.

 

iv not touch my ignition yet as i only want to play with one variable at a time.

 

Paul.

[unariciflocos 49 1 Cars]

Thought I'd post here and not open another topic on the same subject.

 

Spent 3 hours on the dyno last night trying to sort the fueling on my R1 carbs, but synce the dyno here only provides power runs and software remapping for new cars had to get into the black magic of carbs myself and to be hones was a bit disappointed with what i managed to achieve.

 

Could anyone please have a look at my graphs and maybe give me some pointers on what I should try next?

 

Power graph - 180 mains, 60 mm trumpets

AFR - 180 mains, 60 mm trumpets

 

Power graph - 180 jets, no trumpets

AFR - 180 mains, no trumpets

 

Power graph - 190 jets, no trumpets

AFR - 190 mains, no trumpets

 

Power graph - 180 mains, Stock R1 rubber velocity stacks

AFR - 180 mains, stock R1 rubber velocity stacks

 

The last one is the final setup, but I'm tempted to go back to the 190 jets and sort the midrange from the height of the pins, but what puzzles me is the crap torque low down with the 190 jets.

 

So please, if anyone has any suggestions, shoot. My engine is a standard Mi16, R1 carbs spaced out to match a cut mi16 inlet manifold, Megajolt ignition and a 54 mm exhaust.

[Galifrey 1]

180 Mains rubber inlets, drop the needle a notch, adjust the idle air screw slightly leaner.

 

You can try the different main air jets, (not to be confused with main jet) needles and emulsion tubes that come with an R1 dynojet kit maybe?

 

With the dynojet kit you should get new springs, mains, tubes, needles and pilot jets.

 

I recommend THIS page purely to help you understand how each jet and adjustment interacts with the overall outcome.

Edited October 20, 2009 by Galifrey

[unariciflocos 49 1 Cars]

Thanks for the quick reply.

 

I just want to make sure I got this right, you're suggesting I get the midrange leaner by moving the clip on the needles up a notch and get the off idle leaner by getting bigger air jets.

 

I have a Dynojet kit from a friend, but it's for a V-Maxx 1200 bike so springs and needles don't fit. I'm really not keen on spending an extra 100 Euros on an R1 dynojet kit as I chose this fueling method just to be on a budget. If I'm going to spend any more money I'd be better off getting a proper ECU and bike bodies.

 

My main goal is performance, as I use this for amateur rallies, but I'd also like decent mpg as I drive it to stages and blast it to work every now and then.

[Galifrey 1]

Thanks for the quick reply.

 

I just want to make sure I got this right, you're suggesting I get the midrange leaner by moving the clip on the needles up a notch and get the off idle leaner by getting bigger air jets.

 

I have a Dynojet kit from a friend, but it's for a V-Maxx 1200 bike so springs and needles don't fit. I'm really not keen on spending an extra 100 Euros on an R1 dynojet kit as I chose this fueling method just to be on a budget. If I'm going to spend any more money I'd be better off getting a proper ECU and bike bodies.

 

My main goal is performance, as I use this for amateur rallies, but I'd also like decent mpg as I drive it to stages and blast it to work every now and then.

 

Well you won't get decent MPG unless you get the fuelling at its best, to be honest, you will probably save the 100 euros on the dynojet in fuel costs after a few thousand miles, if it cures the overfuelling.

 

Yes, 1 notch up the needle, drops it and leans the midrange, I think with the idle circuit, (mixture screw) more air = leaner, and on the main air jet, more air = less fuel midrange

 

Dynojet kits often use a drill on the pilot jet, so maybe if someone has an existing kit, check to see if they have the drill, but make sure its an identical kit for your carbs model & year!

 

Good luck with it, I have spent a lot of time doing bike carbs on bikes (was a BSB technician) and on kit cars with bike engines. It is fun getting it all done, but ultimately more rewarding than Fuel Injection, if not ultimately as good performance.

[unariciflocos 49 1 Cars]

It used to do 30 mpg in this setup, but if I think about it more, I only do like 1 or 2000 miles/ year in it so doesn't really matter.

 

I read somewhere that i should block the air corrector on the front of the carbs but all that did was flood the cylinders with fuel, so I dumped that idea.

 

I'll try and adjust the mixture a bit per your directions and see how it goes. I have a rally this weekend 60 miles from home and I'll see how it performs now.

 

Currently I'm running without a filter, will adding a Piepercross px604d change the mixture significantly or should I go for an airbox with a cone filter?

 

Thanks for all the info you've given me so far.

[Galifrey 1]

An airbox will probably do more harm than good in terms of how it will affect the performance. A pipercross 600 should be ok, but may richen the mix a little at higher throttle settings.

[unariciflocos 49 1 Cars]

Right, being a bit dissapointed with my peak power i stared digging and found that there was a 3 cm gap between the carb face and manifold so the connecting hoses got sucked in and over time hardened to 70% of their diameter. I changed the hoses to new ones and got the carbs closer to the manifold (under 1 cm) so they can't get sucked in. I think it's now flowing much better because the plugs are clean as new so I'm guessing a lean mixture, so you could say I'm back to square one and need to book the dyno again.

 

The car is quicker now, but i need to fork out some more cash for the dyno, wish I had done this before the previous attempt to tune it.

 

At least now I kind of know what I'm doing. Thanks again for the advice.

Edited October 23, 2009 by unariciflocos

[pee vee 1]

quick question..

on your graphs, why don't the torque and bhp lines cross at 5252 rpm ?

 

not a dig, just thought they have to.

Edited October 30, 2009 by pee vee

[Galifrey 1]

quick question..

on your graphs, why don't the torque and bhp lines cross at 5252 rpm ?

 

not a dig, just thought they have to.

 

Only when they use the same scales ie ft/lbs and BHP

 

If you use nm and BHP they dont cross

[pee vee 1]

ah so the torque is in NM on there. cool!

[unariciflocos 49 1 Cars]

Powers of 10 scaling and metric system FTW! Damn I hate your imperial system .

 

I spun a shell on the last stage and the rings have seen a lot better days, so I won't be doing anything of what i was planning with the engine for a while.