Carb work with vacuum gauges

[Mysuzyq]

OK, I give up. What's a plug chop? .... Thanks!

INGREDIENTS
2 loin cut pork chops with pocket
1 small egg, beaten
2 tbsp all-purpose flour
1 tbsp vegetable oil
1 tbsp butter
1 tbsp onion

...Things get a little complex now, so pay attention. We need to do what's called a "plug chop". This is where you pull the clutch, kill the ignition, and pull to the side of the road (carefully of course) WITHOUT ALLOWING THE BIKE TO IDLE. Still using your mechanic gloves, remove a plug and look at the color. If they are black and sooty, you are running rich on the pilot jet and need to reduce the amount of fuel by installing a smaller jet. If they are clean white, you are lean and need to give the engine more fuel by using a larger pilot or turn the mixture screw out a 1/4 turn. If they are brown no change is required. To aid in tuning, when you go in with the mixture screw, you get a leaner mixture. Out you richen the mixture. As a general rule of thumb the idle mixture should be 1-1/4 to 1-1/2 turns out when you have selected the right pilot jet. Repeat your test with fresh plugs for 1/2 throttle. Here in order to make a change, we can add fuel only with a stock needle by shimming with tiny washers under the needle. Every shim you add richens the midrange. The Dynojet tuner kits are equipped with a needle that has grooves in the end to adjust the position with a clip. Remember the higher on the needle the clip is the leaner the midrange becomes.

Install the appropriate jet you have decided upon (or make needle change), and a new set of plugs and redo the test. Repeat this until you have the correct light chocolate appearance.

The main jet is your cruising jet and needs to be tested above 3/4 throttle. It requires nice stretch of open road, or better yet a drag strip. Repeat the same type of test as before at 3/4 throttle and full throttle, doing your plug chop. Make changes accordingly. An additional test that is handy is to get up to, fourth gear at about 4000 RPM. Open the throttle all the way then immediately let off the throttle about 1/8. If the engine slows just a bit, the jet is close, if it seems to pick up speed or RPM; the main jet is too lean. If it hesitates or stumbles, the main is too rich. Change jets and test again.

After you have the jets close, I just ride about 50 to 75 miles observing the performance of the bike at different speeds. Poor acceleration, pinging, knocking, surging and popping or spitting through the carburetor suggests you're still lean. Black smoke, sooty exhaust, smell of unburned fuel and a rough idle suggest too rich. When I get back from the ride, I pull the plugs once more and see what I've got. If they are tan, light chocolate and the bike runs good, I'm done.


Full version here.

Tony.

[kungpaodog]

Thanks, guys! I'll give that a shot.

[Nightmare]

Seeing how I don't think anyone answered your questions about the vacume guages... yes that should work just fine (i was going to adjust my carbs the same way, but then i bought an inductive pickup digital tach (on my new multimeter) and figured that would be easier/more sensitive).

Before adjusting ANYTHING, it is very important that you get your float levels adjusted properly as this changes the fuel metering for all of the circuits. If i remember correctly, the fuel level (measuring using a fuel gauge) should be 4mm below the split of the bowl and top of your carb, although this MAY differ for your particular model.

[kungpaodog]

Seeing how I don't think anyone answered your questions about the vacume guages... yes that should work just fine (i was going to adjust my carbs the same way, but then i bought an inductive pickup digital tach (on my new multimeter) and figured that would be easier/more sensitive).

Before adjusting ANYTHING, it is very important that you get your float levels adjusted properly as this changes the fuel metering for all of the circuits. If i remember correctly, the fuel level (measuring using a fuel gauge) should be 4mm below the split of the bowl and top of your carb, although this MAY differ for your particular model.

Thanks, Nightmare. I think I may need to readjust the float levels AGAIN, since it doesn't seem to be running right yet. I tried the plug chop (low rpms and mid) and the 3 cylinder was rich, the rest looked ideal. When I get some warmer weather I'll do the high rpm plug chop. I still want to know why I can't get it over 65 mph in fifth, when it used to be able to do 90 mph in fifth up a hill! Other than that, it seems to be running pretty well, but I'm really starting to think about an EFI conversion...grumble...grumble.

[Nightmare]

Just to make sure you aren't wasting your time, plug chops are only useful at throttle positions and not as much at RPM range, check your plugs at closed throttle (idle), 1/3 throttle (Pilot circuit), full throttle (Main circuit). This page is useful for seeing which circuit is affected by which throttle position and I hope it helps you...

http://www.650motorcycles.com/CarbTuning.html

[ryder60]

I'm not sure this can help you or not but here goes.
I wouldn't adjust for maxinum vacumn for two reasons. First, when I did tune for maximum vacumn with my79 GS1000, it would stall when I cracked the throttle from idle. I had to reduce the vacumn until I had the preformance I wanted, even if it did carbon up #1 and #2 plugs a bit faster than #3 & #4.

On another bike I rebuilt I assembled and adjusted the carbs lean without guages and had it run hotter than I wanted. In fact I could smell the heat unless I ran a bit of choke. I ran it like that very little and later a valve spring broke. The spring was new when I did the engine assembly and tuned lean. I figure the heat led to its giving out.

I am also curious what your bike would run like through 5000 if you pulled a bit of choke.