No offense guys but i´ve been doin this with carbs for quite some time,so here´s my two cents.
In fact,it´ll be an essay almost..
Much good advice to be had within the previous posts,however i lack an order of progress TBH.
When tuning anything out there...
1/Start with pulling a simple engine diagnose. Set valveclearance,check valve timing.
Sure a compression tester is what most will use as these are easy to use,but TBH a tool that delivers a MUCH more valid diagnose is a leakdown.
Leakdown testers however demand that you´ve got compressed air around.
Simply put,check everything that even remotely might affect engine performance that´s in sight from a purely mechanical POW.
b/Check exhaust as well as intake system for any visable leaks et al.
Remedy if present,and no...it doesn´t have to be beutiful.
Ie;cracked intake rubbers are more or less the norm for bikes that has some miles/yrs on ém.
A quick TEMPORARY fix is to glue the cracks with superglue.Bonding rubber-actualy o-rings-is what superglue was basicaly developed for.
If your exhaust leaks the least...have it fixed.Leaks WILL affect engine performance.
Yamahas are notorious for their intake valves being to soft and as such intake valve clearance being out of whack.
2/Now turn your attention to the ignition system.
For an engine to deliver the goods this HAS to be up to snuff.
Simple as that,and luckily most spares that wear down are relatively cheap to replace.
DO NOT cheap out.
Fresh plugs,boots asf are...fresh.
The advice given how to test an ign coil is a shade tree one but is by any means valid.
Most spark plug wires for bikes see tremendous amount of heat and as such get both brittle and hard over time.
Just replace if needed.
To measure resistance and/or inductance of various components per above is GOOD practice.
3/Now check the not so obvious.
As you´re to adjust and tweak the carbs most likely you´ve got the gas tank off of there anyways.
So....get a jeep can or whatever and dump the remaining fuel in there.
Blow the tank out as best as you can with compressed air AFTER unbolting the fuel tap.
Check for rust and residue as you do.
Bike tanks seldome carry any innard protection vs rust,and as most just place their pride&joy into winter hybernation and do so without regard to amount of fuel in the tank...it kind of works as a condenser...and sure enough...many many bike tanks simply rust from the inside out.
Ergo...lesson learned,as you put your bike away for the season ALWAYS do so with it filled up to the brim.
That way...no chance for the condensation to take place.
As a fuel filter is cheap...just install a fresh one and be done with it already.
4/NOW at first is when we turn our attention to the carbs.
Don´t even bother with the occasional needle or whatever...
Simply put,rip the whole bridge out of there and either pen or paper...or have your laptop ready.
Read various installed jets asf and write them down.
Log EVERYTHING in sight,and that goes for the number of turn on the idle needles as well.
As for replacing the float needles...i can´t speak for US models but the ones we got over here,the Mikunis,all the later ones-inc the Yamaha FZR and YSR ones-have had their needles tipped with a pliable rubber like material called Viton.
Viton tipped needles very very seldome require replacement and they very very seldome wear.
There are basicaly only two different carburettor types.
The Solex principle and the SU one.
The latter one being what the Mikunis are an option of as they carry a variable venturi.
None the less the Miks are sort of an intermix between the Solex and SU principle from many respects.
Ie;carries more than one circuit as-a´la the Solex principle with its fixed venturi.
Basicaly to work on ANY carb it need to be clean,and then i mean clean as in eat off of it.
As long as the aluminium hasn´t pitted asf common petroleum based degreaser and a tooth brush works wonders.
If you got compressed air around,just rinse with common running water.
Do however NOT use petroleum based anything to clean the rubber diaphragms within the carbs!!
That coupled with compressed air.
...and...have ONE mere thing in mind.
When everything else fails...read the F-ing instructions.
In short,get a hand of the OEM manual for the bike or carb type one way or another.
Specs are specs,and you can rest VERY assured that the boys at the factory has something you don´t and that´s a couple of millions to blow shit up for to find crap out.
IOW,if the OEM manual specs one thing or another adhere to it.
If your particular carb shows signs of corrosion the ONLY way i´ve seen that WORKS to refurbish that is blasting it with baking soda.
WHATEVER YOU DO DO NOT EVER EVER EVER blast it with anything else!!!!!!!
I´ve seen people beadblast carbs...and good luck is all i can say.Those guys could just as well toss their carbs directly into the bin.
On a sidenote...this goes for pulling down on the various screws and bolts of a carb too.
Leave Mr Schwarzenegger out of it.Easy does it as most carbs are an investment casting out of zink alloy.
There is a REASON that most screws on a carb are philips or pozis and that is to PREVENT people from over torquing them!!!!!
That said...
To use an IR thermo MIGHT work for idle as the pace of the engine is slow.
For ANYTHING beyond that...fugedaboutit.
There are two tools that actualy work,and one of them is a wideband O2 setup and the other is an EGT probe that is INSERTED into the gas stream CORRECTLY via a weldbung.
As a tuner i´ve lost track of how many fools i´ve had come running excited with their panties in a wad...explaining to me how they run EGT at WOT or midrange in the 4-500degC territory.
Wideband O2 setups are readily available and getting cheaper by the day.
Most work with the Bosch LSU4 sensor,and when calibrated these can be trusted to the point where you can take what they show on the display to the bank.
Yes,there are more expensive WB O2s,but for the common DIY tuner the LSU4 based units are da bomb IMO.
As for "real" EGTs...leave that to the pro´s,cause even when installed right it is an entirely different matter to analyze the info correctly.
Likewise many many many EGTs are simply to slow to be of any good under load.
Probe dia is a balance.
To small and the probe might break...to fat and it WILL be to slow...
Another tidbit of advice.
When working a carb adjust ONE thing at a time.
I CAN NOT stress this enough,and indeed...to this day,having done this crap for a living for over 25yrs by now...even i still err from time to time when it comes to that thinking that experience is to outsmart Mr Murphy.
Not so.
To make this whole thing with carbs,floatlevels asf hopefully a bit more understandable to the newcomer and maybe even the slightly more seasoned vet...
Be 100% clear on that the level of fuel in the bowl with be the highest at the LEAST load of the engine.
Ie;idle.
Float level is NOT static!!
Further,this is also where we have the least SIGNAL to work with.
A carb doesn´t really "carb" anything.Its job is to emulsify fuel.
Ie;let the energy of the moving air "smash/drag" hydrocarbons(fuel) into itself at a proper level.
In short the fuel is to the letter sucked into the engine,and the ONLY force used is the air at hand.
That renders that the fuel for lack of better explanation is ripped layer for layer out of the carb and into the intake manifold.
From thereon out the high and low end aromatics of the fuel is starting to do the rest...
Circuits then.
We for instance know that we have an idle circuit.
Amount of fuel to pass into the engine is done via a separate orifice meaning that the emulsion tube itself isn´t involved instead the fuel is delivered via a metered orifice close to the butterfly.
This to take advantage of the rather weak signal at hand and to get better control of ADJUSTMENT.
Even so,the fuel for an idle circuit is still emulsified.
For a given circuit the following rule of thumb holds water any day of the week.
The fuel jet/orifice affects the ENTIRE curve for that given circuit while an air jet will affect approx the upper 40% of the given circuits range.
Simply put u use the air jet to fine tune the upper part of the given circuit.
As load increases on the engine the fuel will STOP to come out of for instance the idle circuit at a given point.
The point of the exercise is to have the various circuits intersect each other,but with a carb anything there ALWAYS will be areas where two circuits next to each other so to say have to intervein and this area will ALWAYS be somewhat rich by nature.
It is unavoidable.
Remember that as load increases floatbowl fuel level DECREASES...have that in mind,and as such any and all deviations from stock setting will affect the entire carbs various circuits.
If we for instance set the float level higher it will be easier for the engine to pull the fuel out...and we create a rich condition.
There is however SO much more to be said for floatlevels...SO much more..and what i just touched on is just ONE aspect.
Foaming,anti statics asf asf are just to name a FEW others.
Again...i appreciate that i might be peing on someones parade right now,but chances are that Mikuni in this case got it right the first time out.
The whole idea of altering floatlevel height is one of performance,and that is what the jets are there to handle!!!!!
That...and for instance an emulsion tube.
Speaking of which...this entire cascade of advice on never trying to alter a given jet.
What a load of BS...
Look...and engine could care LESS if it says 105 or 110 on the jet per se...the engine knows ONLY what it "sees".
Ie;fuel vs load.
So..if you are of the anal type and want to REALLY start learning this crap invest in the following small tools.
Look up your local welders supply.They sell "clean out" sets for gas welders that are like small bundles in 0,05mm increments.
These are THE tool to interpret various holes,jet or whatever.
Then pick up a set of jet reamers from VW wholesaler Gene Berg or similar.
Then get a phileateist loup.A lighted one pref,and this you use to read spark plug insulators.Just google how.
Work SLOWLY and read the results.
That jets are flowed by the factory...yeah yeah,yadda yadda...
PLUUUEASE tell me that they wet flow each individual jet.
PLUUUUEASE do.
AGAIN.
The engine could care LESS what it says on the jet...
Racers have been doin it this way for the last 70 yrs with success...so screw Weber,Mikuni,SK,DeLLorto asf asf...
I appreciate that they wanna sell jets,but let´s get friggin real here..
On occasion i´ve made my own even in the lathe of mine...
All in all i for one find the WB O2s an absolute must when doing this kind of work,but then again i´m originaly trained the old fashioned way so the prime reason for using a WB is that it cuts down tremendously on the amount of time used up to reach satisfactory performance.
The WB O2 to me is a "must have" tool these days and indeed at the shop we have like 6-7 sets that we toss in and out of cars,bikes and what have you.
Weldbungs are cheap as are plugs for them and we buy em by the bundle.
Engines are indeed individuals and TBH very few understand the practical needs and neccesitys of carburettors these days and i have to admit that i enjoy bringing out the laptop more...
However carbs are by many frowned upon as some sort of black magic and obsolete.
Not so.
They are remarkable devices that can be had to deliver very very close to EFI performance when setup right.
They are logical devices,and like in the issue above...when they don´t "answer" something IS amiss.
Be 100% sure of that!!
Simply put,YOU are overlooking something.
Take it from a seasoned racing mechanic..and like stated..i´ve been doing this crap pro for some time by now.
Carbs are just hydro mechanical devices,and as such can be understood by anyone interested.
FWIW...when it comes to syncronization i for one have left anything "bubble" or "air" way way way behind since long.
There´s one way to do it in my book and that is by fluid.
Mr Isaac Newton would have loved it cause building a sync setup can be done VERY cheap with common household supplies.
I for one that do this for a living i use an old sync instrument by Weber that uses mercury.
These days more illegal than owning a cannon...but...what the heck...i use it with judgement at least.
I appreciate that this one of my first few posts comes off as cocky,and be that as it may....it still IS the truth.
There..
*gets off the soap box*
So..to wrap it all up i´ll enclose a pic of what i´m working on at the shop right now as we speak.
Gearheads are gearheads all over the world,so i hope someone will enjoy it as it isn´t exactly the norm *LOL*
I've already used it 8 times 4 carbs, all measured then adjusted to the correct height
thats 8 times right? OOOH i feel special
