Basic carb tuning

[hxhettin]

So i have made the home made sync tool and sucsessfully set the carb sync pretty close . Now my question is how do Correctly set the A/F screw settings? is it simply by ear or for best RPM? they are preset at 2.5 turns out just at a starting point right now. bike runs pretty good but im guessing it can be better by setting the a/f screws correctly.

 

[Traumahawk]

Here were my initial settings....and other people have said the same thing

1-2.5
2-2.75
3-1.75
4-2.75
Some basic tuning tips that Ive been told is to set your rpms to about 1000, and the adjust A/F screw to the right until the engine starts to stumble, and them go back to the left 1/4 to 1/2 a turn. After that resync, set your idle at 1100 rpm, and enjoy.

 

[PATMAX]

Actually one needs a CO2 exhaust gas analyzer to set them. If you have Damon Ferriaolo's video, it explains it succinctly. Maybe a decent shop with a dump can use their "sniffer" to tell you where each cylinder is and if rich or lean.

 

[jfeagins]

I have found that by lowering the rpms to about as low as the bike will still remain running (around 800 rpms or less) and then slowly turning the A/F screw in very slowly until just that point where the engine begins to stumble, then backing it out the 1/4 - 1/2 turn as Tramahawk suggests, gets them very close. You may cause the bike to die while doing this. Just restart it and let it resume below normal idle speed, then take up where you left off. Do all four this way. I have the synch gauges set up at the same time and make sure the synch stays spot on as I do the proceedure. After all four are set, I put my idle back up to 1000-1050 rpms, and test throttle response. Usually spot on.

I have an exhaust gas analizer, and have done it that method too, but in a nutshell, can't get them set any closer than what I have done using the slow idle, by ear, method I've just described.

 

[carnut108]

I have found that by lowering the rpms to about as low as the bike will still remain running (around 800 rpms or less) and then slowly turning the A/F screw in very slowly until just that point where the engine begins to stumble, then backing it out the 1/4 - 1/2 turn as Tramahawk suggests, gets them very close. You may cause the bike to die while doing this. Just restart it and let it resume below normal idle speed, then take up where you left off. Do all four this way. I have the synch gauges set up at the same time and make sure the synch stays spot on as I do the proceedure. After all four are set, I put my idle back up to 1000-1050 rpms, and test throttle response. Usually spot on.

I have an exhaust gas analizer, and have done it that method too, but in a nutshell, can't get them set any closer than what I have done using the slow idle, by ear, method I've just described.

OK, followed your method exactly today. Problem is, on the right side (carb3 & 4) I can turn the A/F screws all the way in and the engine does not stumble. There exhaust on this side is also much weaker than the left. Engine has been running rough for almost two months now. Its better than it was ( bad gas, carbs out of sync) Just can't seem to get it dialed in.

 

[naughtyG]

Remember that the A/F screws mostly deal with idle and very low rpm engine speed. After that it's more a combination of needles and jets.
To tune the A/F properly, as said earlier you need a sniffer tool. I've tried the ear/idle/rpm method and it's never worked for me - could screw any of the 4 all the way in and no difference.

If your max is running rough, you may benefit more from a good carb cleaning - and I mean all the way by taking them off and properly cleaning every little orifice (there are many), checking all the seals, gaskets, slides and o-rings are good and replacing as needed. Then re-assemble and sync, having adjusted the floats properly. You may find that makes a BIG difference. Also replace your spark plugs, they're cheap and sometimes it's incredible how much that can help too.

 

[jfeagins]

Usually, when I'm tuning the a/f screws, I'll have my synch guages set up at the same time to make sure they are synched while doing it. If the carbs are not in synch, the a/f screw adjustments may yield diff results with engine rpms.

Naughty, if you aren't seeing any engine rpm change while screwing the a/f screws all the way in, I'd think you either have the idle set too high while doing it, or you have air infiltration from a different source preventing proper adj. BUT, I'd like to point out, EVERY single solitary time I've ever done this to a bike of mine, it has been with OEM factory original carbs and pipes. I've never attempted it with any mods, and perhaps certain mods make my method not work properly? It's always worked for me, not only on both 85's I've owned, but also back when I tuned the XS1100 as well.

 

[Coffinator]

It's also a good idea to check the carb rubber joints, vboost rubber joints, and o-rings under the intake manifolds.. Air leaks mess things up..

 

[Irtron]

I have found that by lowering the rpms to about as low as the bike will still remain running (around 800 rpms or less) and then slowly turning the A/F screw in very slowly until just that point where the engine begins to stumble, then backing it out the 1/4 - 1/2 turn as Tramahawk suggests, gets them very close.

Would it make sense to remove three spark plugs and run a single cylinder for one by one carb adjustment?

this is what I did on one cylinder engine some time ago.
so you have one cyl running (if it's possible at all of course)
1. set min rpm at which engine doesn't dye
2. turn A/F screw to lean the mixture that increases rpm slightly
3. repeat 1 and 2 in small steps until the engine stumbles
4. roll back a bit (1/4-1/2 as per previous suggestions?) to ensure stable operation

It might be too much for a single cyl to drag three other cylinders along while idling though. So the main jet gets involved and setup wouldn't work.

 

[Traumahawk]

I know that a Vmax will run on 2 cylinders...I don't know if it will run on just 1.