Tuning by ear

[Prothec]

It is actually not a commonly known method to tune to highest vacuum. . .

I had to figure that out by looking at a few other websites before it clicked. I had posted about getting the mixture right and general tuning and no one had ever suggested by vacuum.

Once I figured that out, it made things MUCH easier. Doing it by vacuum a few times helps train you to the sounds to at least get it close by ear.

[jetmechmarty]

I'm not having success with this....yet.

I had scary white plugs. 110-120-120-110 mains all else stock. Removed carburetors and went through them. Jetted 115 across. Replaced pilots. (stock size) Replaced float valves. Adjusted float height, checked, rechecked, and checked again. Checked fuel level. Bench synced. Mixture screws to 2.75 out. Runs great. No white plugs. A bit rich. 28 mpg.

I have a Morgan Carbtune. I synced up the carbs. I don't see anything happen to the vacuum when I turn the mixture screws. Reset them all to 2 turns out. Still no popping on decel. 31 mpg.

This bike runs great, but it drinks more fuel than my cars do. Could an improper mixture setting be causing this?

[DAVINCI]

The mixture is just a baseline for idle, most of your riding is off-idle, on the pilots and at higher rpms, on the pilots + mains.

You can raise your MPG's by lowering the float height, that will lean everything out. However, you're right, your plugs should not be white. Do you have an aftermarket exhaust? They can lean things out too, not much backpressure = leaner mixture.

That said, the ONE THING that affects your MPG's most is........the twist of the wrist

[jetmechmarty]

The mixture is just a baseline for idle, most of your riding is off-idle, on the pilots and at higher rpms, on the pilots + mains.

You can raise your MPG's by lowering the float height, that will lean everything out. However, you're right, your plugs should not be white. Do you have an aftermarket exhaust? They can lean things out too, not much backpressure = leaner mixture.

That said, the ONE THING that affects your MPG's most is........the twist of the wrist

Yes. I have a 4 into 1 with a baffle. There is no packing in it. Stock air box.

I recently purchased a new MAC 4 into 2. Do you think that might bring the improvement I'm looking for? It's still in the box.

Last fall, I rode all day with Jeff and Brent. Jeff's is a '78 with stock headers and aftermarket mufflers. It's in fine tune and runs great. Brent's is an SG with MAC 4 into 2. His tune is less than perfect, but it runs OK off idle. Both of those bikes were consistently getting almost 10 more mpg than me!

[DAVINCI]

I can vouch for the Mac 4-into-2, had it on mine for 8 years (2 sets) and if I paid attention I could push it as high as 44MPG. That was with the 750 final drive and babying it all day. You should install them i think you'll be pleased.

BTW, I would also run it in it's sweet spot between 4500-5K rpm's in 4th gear. Evey setup will be different, but mine seemed to like that spot best. I think 5th gear on the 750 drive was too steep for it at normal highway speeds and it made me go deeper into the throttle, sort of a minor lugging of the engine, killed my MPG's

My setup was 117.5 mains, stock pilots, Mac 4-into-2, 25mm floats. Mixture screws were set as previously discussed, so don't ask how many turns, it don't matter.

[LoHo]

I've been out tuning with the vacuum gauges and have improved the idle, but not perfect yet. One thing is that turning the pilot screw has very little effect on the vacuum, or so it seems. In fact, I can hear the change before I see it on the gauge. As the needle closes, the engine stumbles; as the needle is opened the engine revs up and then starts to stumble again, so I turn it back half a turn to the smooth rev.

Now some weirdness: at one point the engine was running smoothly, reving very slightly, and hardly vibrating at all, but the vac gauges were not aligned. I made the adjustments to equalize vacuum, and the engine was not as smooth, but the vac readings all were equal. Is it possible for the bike to be synched with different vacuum values?

I know better than to claim I did everything right but it turned out wrong, but that was a puzzler.

[skids]

If you can get a good tune, why argue with success? The vacuum only gets you in the ball park and is mainly for the butterfly plate openings with the compression of the respective cylinders. If you can get a good tune without being too rich or lean at idle, you are there LoHo. All of that is for idle or just off idle.

[Prothec]

You could always check that your gauges are synced. Just use each gauge on the same cylinder one at a time and make sure they read the same.

[DGXSER]

If your using gages, it us a must to align, synch the gages. Hook each one to the same cylinder and note the reading or mark the reading on the gage face. That is the base reading where all four are the same. If you skip that all four cylinders could be off substantially from each other, meaning when you think your lining them up you may be moving them apart.

[Prothec]

And if you're using dial gauges, I started with dual gauges. Then, it was like night and day switching to the Morgan Carbtune. Well worth the cost IMHO.

[jwhughes3]

Just used the new SynchPro manometer gauges today vs the old dial gauges. Easy as pie and much easier to read.

John

[DAVINCI]

+1 on the Morgan Carbtune. No more fluids for me! (or so I thought). Got it a couple of years ago. Ironic, though that on the Goldwing I can't use the carbtune. Goldwing has two carbs serving three cylinders each and pulls over 40 inches of vacuum, just pins the Morgan full scale. Had to resort to building a two-column manometer lol.

Still like the carbtune, though for my GF's 650 V-Star.

[LoHo]

A side note: Running the engine at idle for forty minutes or so was enough to drain a new battery. Does that sound reasonable? I know our system doesn't charge the battery until 2500rpm or so....

[Prothec]

When my charging system wasn't working, I pulled unnecessary fuses - headlight, etc, then back on the charger during breaks. I don't remember having a problem with the battery draining, though, but I can't say how long for sure I ran it without charging. I was riding it for quite a while for my 10 - 15 commute to work and never had a problem. And that was with no charging whatsoever. I did that for a couple months before I got around to fixing it.