Triumphrat

jimmyj900 · 04-29-2005

I've been saying all along that a dyno run without an air/fuel plot was useless. I screwed up. I was wrong and I apologize for having provided incorrect information.

I had a lengthy conversation with Marc Salvisberg of Factory Pro about the validity of exhaust gas analysis with gasohol fuel.

Out of that conversation came an "Ohhhh...DUH!" moment. While I was concerned with CO levels versus O2, Mark informed me that the gas curves were largely meaningless on a sweep test and the only thing that mattered was the maximum horsepower reading!

The rpm is read directly from the engine and is an instantaneous value, but the results from the exhaust gas sensors are several seconds old by the time they're plotted onto the graph at the current engine rpm.

It takes time (seconds) for the exhaust gas to reach the sensors and for the sensors to make their readings. That means that the A/F ratio plotted at 8,000 rpm might be the result of combustion at 3,000 or 4,000 rpm and useless for tuning!

Marc says the correct technique is to set the main jet for max power and then try and figure out the A/F curves later -- or ignore them altogether! That means multiple test runs with increasing jet sizes until the peak power drops off and then stepping back to the set that produced the best power. That's the only real option since the A/F curves are useless for high rpm testing.

For me that means more carb teardowns, more dyno runs and another handful of main jets. I had previously tested with #150 mains but the A/F curve showed extremely rich conditions at high rpm. After changing to #145 main jets and adjusting the needles the A/F curve looked pretty good -- but 4 horsepower down from the peak reading with the #150 jets. I chalked the difference up to air density variation since the A/F ratio looked pretty good.

I think now that I was seeing the A/F ratio from the incorrect needle adjustment when I thought I was looking at the main jet mixture. That means the #150 mains go back in for a verification of the previous run and then trying #155 and maybe #160 jets to see what happens on the power curves.

Agan, my apologies for providing incorrect information.

Jim

jimmyj900 · 04-29-2005

I've been saying all along that a dyno run without an air/fuel plot was useless. I screwed up. I was wrong and I apologize for having provided incorrect information.

I had a lengthy conversation with Marc Salvisberg of Factory Pro about the validity of exhaust gas analysis with gasohol fuel.

Out of that conversation came an "Ohhhh...DUH!" moment. While I was concerned with CO levels versus O2, Mark informed me that the gas curves were largely meaningless on a sweep test and the only thing that mattered was the maximum horsepower reading!

The rpm is read directly from the engine and is an instantaneous value, but the results from the exhaust gas sensors are several seconds old by the time they're plotted onto the graph at the current engine rpm.

It takes time (seconds) for the exhaust gas to reach the sensors and for the sensors to make their readings. That means that the A/F ratio plotted at 8,000 rpm might be the result of combustion at 3,000 or 4,000 rpm and useless for tuning!

Marc says the correct technique is to set the main jet for max power and then try and figure out the A/F curves later -- or ignore them altogether! That means multiple test runs with increasing jet sizes until the peak power drops off and then stepping back to the set that produced the best power. That's the only real option since the A/F curves are useless for high rpm testing.

For me that means more carb teardowns, more dyno runs and another handful of main jets. I had previously tested with #150 mains but the A/F curve showed extremely rich conditions at high rpm. After changing to #145 main jets and adjusting the needles the A/F curve looked pretty good -- but 4 horsepower down from the peak reading with the #150 jets. I chalked the difference up to air density variation since the A/F ratio looked pretty good.

I think now that I was seeing the A/F ratio from the incorrect needle adjustment when I thought I was looking at the main jet mixture. That means the #150 mains go back in for a verification of the previous run and then trying #155 and maybe #160 jets to see what happens on the power curves.

Agan, my apologies for providing incorrect information.

Jim

Gdsila · 04-29-2005

I for one (I dont know about others) always admire someone who admits a mistake and takes steps to correct it.
In forums such as these when that happens evryone(hopefully) gains a little more knowledge. Which is always a good thing.

Gdsila · 04-29-2005

I for one (I dont know about others) always admire someone who admits a mistake and takes steps to correct it.
In forums such as these when that happens evryone(hopefully) gains a little more knowledge. Which is always a good thing.

Saigon5 · 04-29-2005

Jim,

Thank you for the valuable information. On a different note, you sure found a way to end my pleasure of tuning my bike. Now I have to consider where to start again.

On a good note, better now since I was about to re jet, than later.

Saigon5 · 04-29-2005

Jim,

Thank you for the valuable information. On a different note, you sure found a way to end my pleasure of tuning my bike. Now I have to consider where to start again.

On a good note, better now since I was about to re jet, than later.

jimmyj900 · 04-30-2005

Quote:

...you sure found a way to end my pleasure of tuning my bike. Now I have to consider where to start again.

Well, if it's any consolation that's a "me too" situation.

Jim

jimmyj900 · 04-30-2005

Quote:

...you sure found a way to end my pleasure of tuning my bike. Now I have to consider where to start again.

Well, if it's any consolation that's a "me too" situation.

Jim

tri-900 · 04-30-2005

Well since I'm still waiting for my Factory Pro kit after 3 weeks this is a God send of info, carbs still on the bench.Thanks for the news Jim. :hammer: :knkknk:

Saigon5 · 05-07-2005

Jim,

It really seems like you took the worm out of the can.

On the last dyno run that was made after reading on the subject of fuel and air mixture curve. I decided it was time to talk to the dyno operator. He did agree that it was quite useless to look ar the curves printed on the graph. His way of doing was like described, tune for the highest output and fix the rest after. The other point he brought is that when he has the bike on the dyno his screen his besides him and he runs the engine at various RPM steady. For example he is keeping the throttle at 4500 for a while and move across the range that way. This is the method he is using to tune the jetting. He feels that way is more accurate, which too me make sense. A fast full on opening of the throttle will bring too much gas for a moment.