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Tuning carb with wideband o2

  • Thread starter Thread starter beingblueeyes
  • Start date Start date
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beingblueeyes

Guest
back ground:
Over the years I have built many turbo fuel injected import cars and 2 turbocharged fuel injected Chevy small blocks. So I know you need to put the motor under load to make the turbo spool up and add positive atmosphere. As well as make the ecu go through its timing table and fuel table

Question 1:
To tune the gs550's since it is older (no ecu) do I still need to put the bike under load to tune the carb? Because the ign. is points and it is a carb bike why can?t I just rev it standing still with the laptop on my lap? The only info I want from this is the Air/fuel. Would the air/fuel change under load in riding conditions? (I know the air flow will change slightly but no enough to be a huge shocker)

Question 2:
if the bike dose need load on the motor to tune the carb is there a way to put load on the bike without moving it without going to a dyno (because I don?t have a pda to keep in my pocket and holding a laptop and driving the bike would be really tuff);)
 
I am almost certain that the air/fuel is much different under load. You use a lot more gas under load at a certain rpm than you do just free-revving it in neutral.

Short of builting some sort of resistance roller at home, i think a dyno is your best bet.
 
You need to hold the throttle open long enough to get a good reading, the RPMs would go through the roof with no load, and would not be accurate as the airflow would be different at this extreme RPM, fuel flow changes with airflow as it is not fuel injected....

Hook up the laptop and Bungee it down on the seat?
Maybe inside a protective box or something?
 
The good news is that your VM carbs are at least predictable as far as air flow. The BS carbs, with their diaphragm and slide, depend on engine load to create the vacuum to lift the slide. So, not only would you have to load the engine, you would almost have to have a vacuum gauge while riding to see what "normal" vacuum levels are so you can match them, if you are interested in getting a/f readings for 'normal' riding.

.
 
No personal experience bit I’ve hear about people running their bike around with a couple of plug wires pulled so they can judge fuel mixture, including full throttle, much easier.
 
I have a little 200cc bike that has an Innovate LC1/DB gauge.

Also have used a LM1/LMA3 on the same bike to monitor RPM w/inductive clamp, MPH w/magnet pickup, MAP, Acceleration, and AFR.

A little overkill on a 200cc bike, but what else am I supposed to do with my spare time. LOL

The LM1 data logger just rides in a tank bag. Get back to the garage, make the adjustments to the carb, do a verification ride, and usually spot on without even pulling the plug.

Will set it up on the 700E once road ready..

Don't really need it to tune an engine, but it is fun to play with.
 
You could put it under load by having bike on centre stand, bike in gear and apply rear brake to put motor under load. Don't know how well it would work. Just thinking out aloud here.
 
Have you tuned the bike using the standard, shop manual procedures yet? That should be your first step.
 
Suzuki_Don said:
You could put it under load by having bike on centre stand, bike in gear and apply rear brake to put motor under load. Don't know how well it would work. Just thinking out aloud here.
Click to expand...
thats pritty good thinking, i might try it

DimitriT said:
I stumbled across this recently.

It talks about the CV carbs but it may be useful:

http://www.zrxoa.org/webpages/techinfo/carb/carbtuning.html
Click to expand...

haha small world, i just read that just about 100% in a book the other day "101 sportbike performance projects"

no i havent tuned the bike to standard yet, im just geting an idea on whats needed to tune with a wideband
 
Suzuki_Don said:
You could put it under load by having bike on centre stand, bike in gear and apply rear brake to put motor under load. Don't know how well it would work. Just thinking out aloud here.
Click to expand...

You'll burn the pads up and still get ****ty results, not only do you need a load but you also need speed. Best way would be a dyno. There's no difference in the requirements for tuning EFI or carb. I know the OP mentioned having to spool up the turbo but that's not the actual reason for having the load on it---the load simulates real running environment and forces the motor to do work, the turbo spooling is just part of what goes on when the engine is running/working. Granted someone surely has mentioned this already.

Back to my original thought, holding the rear brake is a bad idea unless you want to find out how easy it is to burn/glaze the pads, warp the rotor, and cook the brake fluid.
 
Keep the garage door open...........

Yes, best results the engine should be under load.
 
You need to test each circuit of the carb; pilot, needle, and main jet. Therefore throttle position under load is what is important. Read your plugs by doing plug chops at each throttle position. That will be the best way to determine and fine tune your air/gas mixture. Short of a dyno, I think that's your only alternative.
 
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