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Discussion Starter #1
Is it just me? Anyone getting consistent (repeatable) results with the Gunson Gastester?


Mine frustrates me to no end. I warm it up for ~15 minutes and get a stable 2.0 reading. Testing is another matter, it never stabilizes. The reading moves every 10 or 15 seconds, I've tried testing for more than 10 minutes without getting a stable reading. Then when I remove the probe it never returns to 2.0.

If I follow up with another test (after 10 or 15 minutes to let it stabilize again) the result will vary.

I might as well stand behind the exhaust and use my senses. If my eyes water, it's rich.
 

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Koop said:
Is it just me? Anyone getting consistent (repeatable) results with the Gunson Gastester?


Mine frustrates me to no end. I warm it up for ~15 minutes and get a stable 2.0 reading. Testing is another matter, it never stabilizes. The reading moves every 10 or 15 seconds, I've tried testing for more than 10 minutes without getting a stable reading. Then when I remove the probe it never returns to 2.0.

If I follow up with another test (after 10 or 15 minutes to let it stabilize again) the result will vary.

I might as well stand behind the exhaust and use my senses. If my eyes water, it's rich.
+1, I bought one last year and took the thing back within 2 hours, even if I just lifted it up and down the zero went berserk.

In the end I bought a secondhand snapon/blue point one from e bay, it's spot on every time.

(quote)I might as well stand behind the exhaust and use my senses. If my eyes water, it's rich.[/QUOTE]............. not always true :ahhh: if the mixture is weak you will get a very high hydrocarbon reading due to the engine not burning all the fuel............that makes the eye's :bawling: a bit!
 

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Hi Koop,

As mike said if you jolt the unit it will jump but it should return very quickly in my experience. I guess I've been using it for a couple of years and quite a few tunes of my bike and other's. Something is going on if it's not repeatable and back to baseline normally. Are you placing far lower than the probe and draining it properly? I took off the double sided tape and use 3M dual-lok instead.

Mike's sounds great but I've good success with mine.
 

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Discussion Starter #4
JamesC said:
Hi Koop,

As mike said if you jolt the unit it will jump but it should return very quickly in my experience. I guess I've been using it for a couple of years and quite a few tunes of my bike and other's. Something is going on if it's not repeatable and back to baseline normally. Are you placing far lower than the probe and draining it properly? I took off the double sided tape and use 3M dual-lok instead.

Mike's sounds great but I've good success with mine.
Hmmm...far lower than the probe, maybe that's the issue. It's not much lower, maybe even level with the probe.

I would expect it to drift if I jolt the unit.
 

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Put it far lower so the condensation can drain readily and see if it improves. It will help keep air movement from teh exhaust from disrupting the external sensor and the condensation out of the way gives a better and more stable reading. I also put the probe on the ground during calibration to ensure all condensation can drain from that part of the tubing.
 

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Discussion Starter #6
mikef4uk(quote)I might as well stand behind the exhaust and use my senses. If my eyes water said:
............. not always true :ahhh: if the mixture is weak you will get a very high hydrocarbon reading due to the engine not burning all the fuel............that makes the eye's :bawling: a bit!
Quite right, high HC comes from lean misfire as well as rich mixture.

The Blue Point unit sounds good. I'm going to try again, following JamesC's advice on lowering the unit to makes sure the H2O drains properly.
 

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Discussion Starter #7
JamesC said:
Put it far lower so the condensation can drain readily and see if it improves. It will help keep air movement from teh exhaust from disrupting the external sensor and the condensation out of the way gives a better and more stable reading. I also put the probe on the ground during calibration to ensure all condensation can drain from that part of the tubing.
Thanks, I'll give it another shot.
 

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Koop said:
............. not always true :ahhh: if the mixture is weak you will get a very high hydrocarbon reading due to the engine not burning all the fuel............that makes the eye's :bawling: a bit!
Quite right, high HC comes from lean misfire as well as rich mixture.

The Blue Point unit sounds good. I'm going to try again, following JamesC's advice on lowering the unit to makes sure the H2O drains properly.[/QUOTE]

The snap off unit is spot on, warms up virtually instantly to with 0.2 co and returns to zero every time I pull the tube from the bike, one interesting thing though, and this is with the pipe pushed about 1 foot down the exhausts, if you get a stable reading then blank off one of the four outlets it alters the co quite considerably with RG3's fitted :jsm: back pressure I suppose?
 

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Discussion Starter #10
OK, I set up the Gastester well below the probe - about 4" above the floor. I allowed the maching to warm up, calibrated to 2.0 and ran four tests. Each test was at least 2 minutes to allow it to somewhat stabilize. In between each test I let the machine purge for 10 minutes and rechecked the calibration. Here are the results:

Test 1 - Calibrate 2.0% Test 3.6% After Purge 2.5%

So, my CO% could be as high as 4.1% allowing for the .5% drift.

Test 2 - Recalibrate to 2.0% Test 3.1% After Purge 1.8%

Hmmm...now CO% is probably around 2.9% ???

Test 3 - Recalibrate to 2.0% Test 4.5% After Purge 3.4%

Now it looks like 3.1% - not far off of the last but the huge drift in calibration makes me suspicious.

Test 4 - Recalibrate to 2.0% Test 2.7% After Purge 1.2%

What???? Is it this lean, 1.9%? :banghead:

Have I done something wrong? I think I have a real POS on my hands, should've guessed at that price. :eek:nthecan:

I'll have to take the bike across town and use a real gas analyzer on it again. :ahhh:
 

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Had you ridden the prescribed time/distance to purge your exhaust of as much condensation as possible and was it heated beforehand until the fans were on? I realize you are talking about % error drift but want to ensure you are setting things up in the proper conditions to get repeatable results.

When I pull the probe I can't think of more than one or twice out of many many many samples on a number of bikes that it didn't return to exaclty 2%, and then it was on the order of .1% off?
 

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Discussion Starter #13
JamesC said:
Had you ridden the prescribed time/distance to purge your exhaust of as much condensation as possible and was it heated beforehand until the fans were on? I realize you are talking about % error drift but want to ensure you are setting things up in the proper conditions to get repeatable results.

When I pull the probe I can't think of more than one or twice out of many many many samples on a number of bikes that it didn't return to exaclty 2%, and then it was on the order of .1% off?
Yeah, I always tune with everything fully warmed up. Also, we have very little condensation here, humidity is around 8-10%. Maybe my Gastester is just NFG.
 

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Discussion Starter #14
Problem Solved!

OK...I take back all of the bad mouthing :stickpoke

Yesterday I pulled the hoses from the Gastester preparing to pack it up. Then I noticed something funny about the fitting where the exhaust probe goes into the diaphragm housing. I dug out a little black sooty ball of something foreign. I'm guessing that a little piece of packing material got in there somehow - it's too sooty to tell exactly what it was.

Anyway, I removed this foreign bit, let the Gastester warm up for half an hour (while I rode the bike) and tested.

Calibrate 2.0%, test 4.1%, 10 minute purge 1.8%
Result ~3.9% CO.

Today I did the same thing, plugged the Gastester in to warm up while I went riding, then repeated the test.

Calibrate 2.0%, test 3.9%, 10 minute purge 2.0%
Result 3.9% CO.

Bingo. My bad for not looking at everything before calling the Gastester a POS. :baddeal:

BTW, the 910R is awesome with the "off road" exhaust and EPROM at this mixture (originally I was at 4.5% but I leaned it slightly).
 

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What did you decide on Mike? 3.9% you referenced? I think I put a recent 910R that was having problems to 4.2% to good effect. His TB's were well off and we also swapped to eix's but I guess all of his problems are gone now and fuelling is in good shape. Do you do a lot of high rpm running that would enable comment on high rpm throttle transitions at that CO%?
 

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Discussion Starter #16
JamesC said:
What did you decide on Mike? 3.9% you referenced? I think I put a recent 910R that was having problems to 4.2% to good effect. His TB's were well off and we also swapped to eix's but I guess all of his problems are gone now and fuelling is in good shape. Do you do a lot of high rpm running that would enable comment on high rpm throttle transitions at that CO%?
I'm happy at an indicated 3.9%, it was 4.5 - 4.6%. At the richer setting getting back on the gas was smoother but a little fluffy. Top end didn't seem to suffer though. I also rechecked TB balance and it's good. I don't do a lot of high RPM, I want clean transition from off throttle to neutral throttle or accleration in a turn.

The road I usually run has mostly tight switchback corners with a few sweepers. Sometimes I'm opening throttle mid corner at 7 -8,000 rpm and it's pretty snappy. On the slower corners I'm in second gear at 4,500 - 5,000 when I transition back on the throttle. Like I said, I'm happy with the set up now.
 
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