Measuring exhaust gases...

[Guest]

So since it appears that the Colortune gizmo doesn't work very well with CV carbs (like on my '81 850G), we're left with setting the idle adjustment screws by ear. That seems less-than-ideal to me - especially considering how important the whole lean vs rich question is for these carbs. Has anyone ever heard of a device that sniffs the exhaust gases and displays the results? Any help would be greatly appreciated!

Scott

[hannibal]

You could use a wideband O2 sensor. Something like this: http://www.plxdevices.com/PLX-Wideba...uges-s/125.htm

In my former turbo Nissan days, it was common to add an extra bung to mount the wideband sensor. On a GS, I'm guessing you could remove the mufflers and place the sensor in the end of each header pipe.

[Steve]

On a GS, I'm guessing you could remove the mufflers and place the sensor in the end of each header pipe.

The only problem with that is that one pipe on each side of the bike is continuous from the head to the tip of the muffler, so there is no "remove the muffler" possible.

And, for the other pipe on that side of the four-cylinder bikes, you have to pretty much remove everything else to access the end of that header pipe, so drilling a hole and welding a bung is pretty much the only option.

I have heard it said that one bung at the collector is sufficient, but wonder if you don't need one in each header pipe. Have never seen it done, so don't really know.

So far, I have not had problems with the "tune by ear" method.

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[Guest]

You could use a wideband O2 sensor. Something like this: http://www.plxdevices.com/PLX-Wideba...uges-s/125.htm

In my former turbo Nissan days, it was common to add an extra bung to mount the wideband sensor. On a GS, I'm guessing you could remove the mufflers and place the sensor in the end of each header pipe.

So..... stupid question, but why couldn't you just stick the sensor in the muffler?

[hannibal]

The only problem with that is that one pipe on each side of the bike is continuous from the head to the tip of the muffler, so there is no "remove the muffler" possible.

And, for the other pipe on that side of the four-cylinder bikes, you have to pretty much remove everything else to access the end of that header pipe, so drilling a hole and welding a bung is pretty much the only option.
.

This is not true, at least on my 750. I have the four headers removed with the mufflers still attached to the bike. I imagine you could do the opposite: leave the headers installed and remove the mufflers.

So..... stupid question, but why couldn't you just stick the sensor in the muffler?

If you're trying to test the mixture in each cylinder, I think you'd want to be as close to the cylinder as possible and not read from multiple cylinders at once. If cylinder 1 was rich and cylinder 2 was lean, reading from the left muffler might tell you the mix is spot on when it's not.

[bonanzadave]

Do it by temperature. Lots of airplanes have a CHT /EGT combo gauge to measure each cylinders head temp and exhaust gas temp. Only drawback is the EGT probe needs to be about 2-3 inches from the head which requires a 1/8" hole in the pipes. I think Steve will be the second (me first) to say that would be over-kill....

[Steve]

I agree that temp readings would be good, but who knows what the proper temperature is?

Many, many years ago, I used to drive truck cross-country. All of our engines had a pyrometer (exhaust temp gauge), some of them were in the manifold, ahead of the turbo, some were in the bend just after the turbo. We were told to keep the temperature below 1250 if the probe was ahead of the turbo and below about 1050 if it was after the turbo. Keep in mind these are temps for a large diesel engine (Cummins). I also had a pyrometer in my car, which had an aftermarket turbo. My probe was after the turbo, and more than one time, I saw over 1800 degrees.

Now the question would be: at what throttle setting do you check exhaust temps? Since a leaner mixture runs hotter, you don't want to simply tune for highest temperature. Richening the mixture would cool it back down, but how far?

I guess we are just going to have to find someone whose bike works PERFECTLY and convince him that we need to drill some holes in his perfect exhaust system so we can record the temps and call those the "right temps".

Any volunteers?

.

[Guest]

I guess we are just going to have to find someone whose bike works PERFECTLY and convince him that we need to drill some holes in his perfect exhaust system so we can record the temps and call those the "right temps".

Any volunteers?

.

LOL! I vote for YOURS Steve! Your 850 really did impress me that day. It would be the perfect candidate!

I've already sent a PM to Ed Ness about WHAT to adjust when you're doing a vacuum sync, but I might as well ask here too:

When you bench sync the carbs, what you're actually doing is making sure all four butterflies are set at the same position rotationally, and that they move in perfect unison. Doing that gets them close enough to "right" to get the bike going, but it is probably NOT optimal. So when you hook up the vacuum gauges, you tweak those same adjustments to achieve perfect vacuum balance (or as close to it as possible). The air mixture screws are NOT used to achieve that balance, are they?

I've been under the impression that once you bench synced the carbs, you never touched them again except to adjust the idle speed with the big idle speed screw between #2 and #3. That wasn't correct, was it?

[bonanzadave]

Now the question would be: at what throttle setting do you check exhaust temps?

In an airplane you have a mixture control at your fingers. Its got a lot to do with altitude. 2500 RPMs at 25in of manifold pressure. EGTs are normally set to 50-100 degrees rich or lean of peak depending on whos engine camp your in. After that being able to see all six EGT and CHT temps becomes more of a tool to monitor the engines health.

[gustovh]

LOL! I vote for YOURS Steve! Your 850 really did impress me that day. It would be the perfect candidate!

I've already sent a PM to Ed Ness about WHAT to adjust when you're doing a vacuum sync, but I might as well ask here too:

When you bench sync the carbs, what you're actually doing is making sure all four butterflies are set at the same position rotationally, and that they move in perfect unison. Doing that gets them close enough to "right" to get the bike going, but it is probably NOT optimal. So when you hook up the vacuum gauges, you tweak those same adjustments to achieve perfect vacuum balance (or as close to it as possible). The air mixture screws are NOT used to achieve that balance, are they?

I've been under the impression that once you bench synced the carbs, you never touched them again except to adjust the idle speed with the big idle speed screw between #2 and #3. That wasn't correct, was it?

The screws for syncing the carbs are between 3-4 2-3 and 1-2. Carb#2 is not adjustable so the other 3 are adjusted to it. The adjustment screw has a lock nut which must be loosened first. Run the engine up to around 2500 with a fan on high and the engine fully warmed up to adjust the vacuum settings.

V

[Steve]

... I might as well ask here too:

When you bench sync the carbs, what you're actually doing is making sure all four butterflies are set at the same position rotationally, and that they move in perfect unison. Doing that gets them close enough to "right" to get the bike going, but it is probably NOT optimal. So when you hook up the vacuum gauges, you tweak those same adjustments to achieve perfect vacuum balance (or as close to it as possible). The air mixture screws are NOT used to achieve that balance, are they?

You are correct. The "bench sync" just gets it close enough so that it can run for you to do the "Vacuum" or "dynamic" sync.

The mixture screws are NOT involved at all in the sync process.

I've been under the impression that once you bench synced the carbs, you never touched them again except to adjust the idle speed with the big idle speed screw between #2 and #3. That wasn't correct, was it?

You are right, that is NOT correct.

If the bench sync was done close enough, the vacuum sync won't have to change it much, but you MUST to a vacuum sync to know for sure.

There will also be differences from one bike to another. The amount of vacuum on the gauge depends on how much air is being drawn through the opening. Differences in valve clearance affect valve timing, which will affect how much air is being drawn, so it will be different from one bike to another. It may be pretty darn close, but it will likely be different.

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