Author Topic: Tuning by Head temperature.  (Read 7389 times)

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Offline Bruin

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Tuning by Head temperature.
« on: October 15, 2013, 02:41:57 AM »
I was told that you can tune your carb by monitoring the temperature of the head. Too hot = lean, too cold = rich. The key is to know the desired temperature. I run a '82 Honda XR 500 thumper. It is stock, single oversized mikuni, 4 valve, dual header. Anyone have any idea what the ideal head temp should be?
STD; Speed Team Doo
'82 Honda 500 APS-AF
'70 Triumph 250 MPS-PG
'71 Triumph 250 APS-PF
'70 Triumph 250 M-PG

Offline Jon

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Re: Tuning by Head temperature.
« Reply #1 on: October 15, 2013, 05:13:41 AM »
For the price difference between a decent under plug temp sensor and gauge and a wide band exhaust O2 sensor these days I would go with a Wideband O2.

http://www.innovatemotorsports.com/products/MTXL.php

Sorry, I know it doesn't answer your question, and its probably more than you wanted to spend but if you want to manage fuel ratio the best thing to measure is fuel ratio.

cheers
jon
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Offline redhotracing

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Re: Tuning by Head temperature.
« Reply #2 on: October 15, 2013, 07:53:51 AM »
We use one of these in our down pipe. It's
a great tool for tuning at a reasonable price.
Luke- Winston Salem, NC
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Offline Dean Los Angeles

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Re: Tuning by Head temperature.
« Reply #3 on: October 15, 2013, 11:32:04 AM »
Head temperature is one of the tuning tools available to you. It rates last on the list. Air cooled engines are affected by the outside air temperature and the amount of wind flowing over it. A sensor goes under the spark plug to read head temperature. The correct temperature on a cold day is different than a hot day.

Next would be spark plug color. Still a very rough way to tune.

Exhaust gas temperature tells you the heat of combustion, and it is directly related to air/fuel ratio. Unfortunately, as you lean out the mixture and the temperature gets hotter, you reach the peak temperature and leaning it out more drops the temperature. You can be fooled by being on the wrong side of the curve.

A wide band oxygen sensor will tell you how much oxygen is in the exhaust. Excess oxygen indicates a lean mixture, excess fuel indicates a rich mixture. A sensor, cable and gauge will set you back $200. It is the only true way to tune.

Because the amount of air entering the engine is highly variable depending on altitude, temperature and humidity, you really need an active monitor to be able to react to changing conditions. Changing the jets between runs may be required if outside conditions change.

Well, it used to be Los Angeles . . . 50 miles north of Fresno now.
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Offline Sumner

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Re: Tuning by Head temperature.
« Reply #4 on: October 15, 2013, 11:33:26 AM »
We use one of these in our down pipe. It's
a great tool for tuning at a reasonable price.

Agreed, we have one...

http://www.innovatemotorsports.com/products/MTXL.php

...... for each bank of Hooley's Stude.  I might be wrong but to tune by egt or head temps you really need to run the motor on a dyno and find the combination that makes the most power and then note the eg or head temp and later tune to that temp as conditions change.

With wide band O2 sensors and their required controllers coming down in price they seem to be the way to go.  I think most good dynos now use those on each cylinder for optimal tuning when you have a fuel injection system like MegaSquirt and others that will let you adjust fuel individually by cylinder.  Even with a carb you can see which cylinder is leanest and adjust the carb to make sure you aren't too lean in that cylinder even if you have to run rich in others.

Also the MTX-L can be part of a data logging chain with many other sensors.  We are datalogging 16 inputs in our chain.  For another $100 you could add the PL-1....

http://www.innovatemotorsports.com/products/pl1.php

... to the MTX-L and data log your air-fuel during a run  and any other sensors you add later.  It is a nice system,

Sum
« Last Edit: October 15, 2013, 11:36:14 AM by Sumner »

Offline Bruin

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Re: Tuning by Head temperature.
« Reply #5 on: October 15, 2013, 03:11:35 PM »
I see a lot of good info above and it is appreciated. Here is the fine print to my original temp tuning inquiry: Reading a plug is free and just what I can afford. A heat sensing unit has been donated by a kindly sponsor. Until I write the next best seller, those are my current options.

So if I understand correctly, you cannot tune to head temp because of varying air temps. What I have seen at Bonnie is maybe a 10 to 20 degree swing but usually in the high 80s, low 90s. I've seen references of 400-450 head temperatures for the XR-500. Does that mean the air changes are only a 2-5% variant? (I don't suppose it is that simple.)
STD; Speed Team Doo
'82 Honda 500 APS-AF
'70 Triumph 250 MPS-PG
'71 Triumph 250 APS-PF
'70 Triumph 250 M-PG

Offline Peter Jack

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Re: Tuning by Head temperature.
« Reply #6 on: October 15, 2013, 03:32:28 PM »
Why not install it and then ignore it unless it's suddenly significantly hotter than normal during a run. In that case you may save yourself a problem although at that point it will probably show even more on the plug if you're cutting clean at the end of your runs.

Pete

Offline Sumner

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Re: Tuning by Head temperature.
« Reply #7 on: October 15, 2013, 05:15:37 PM »
Why not install it and then ignore it unless it's suddenly significantly hotter than normal during a run. In that case you may save yourself a problem although at that point it will probably show even more on the plug if you're cutting clean at the end of your runs.  Pete

Good advice if that is all you can do.

I will add that data logging equipment isn't cheap and most of us would like to spend money on items that directly increase HP, but I'm almost positive that we have saved way more than the cost of  the equipment over the years by not having major engine  problems to this point.  That money saved can go towards speed equipment  :-).

Running blown gas to the 5 can be very expensive in engine parts and we have avoided that.  Not saying we will always be as lucky but having data can be invaluable.  Considering the cost of just getting to the salt and running $160+ for an MXT-L isn't a huge investment, but there has been times in my life where $160 might as well of been $1600  :cry:,

Sum

Offline Bruin

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Re: Tuning by Head temperature.
« Reply #8 on: October 15, 2013, 06:51:13 PM »
I can see where if I marry the two, temp and plug read, I might have a useful tune monitor. Run plug chops until I get the best read, then note the temp. If it starts to vary I at least will be aware of it and have an idea which way to go.
STD; Speed Team Doo
'82 Honda 500 APS-AF
'70 Triumph 250 MPS-PG
'71 Triumph 250 APS-PF
'70 Triumph 250 M-PG

Offline Peter Jack

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Re: Tuning by Head temperature.
« Reply #9 on: October 15, 2013, 08:42:09 PM »
The plug should be read after every run. The only time you'd use the gauge is if it shows out of whack part way through the run. Cut the throttle, exit the course and figure out what happened before the next run. The plug knows what's going on in there because it's in there!

Pete

Offline saltwheels262

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Re: Tuning by Head temperature.
« Reply #10 on: October 15, 2013, 09:54:18 PM »
I have looked into the mtxl and talked to innovate about it.

should be getting one for the V twin from Summit.
as soon as the card cycles.
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Offline Sumner

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Re: Tuning by Head temperature.
« Reply #11 on: October 16, 2013, 12:34:20 AM »
I have looked into the mtxl and talked to innovate about it.

should be getting one for the V twin from Summit.
as soon as the card cycles.

It is very bright and I found it very easy to read up to about 150.  Above that I was busy with other things. 

One nice thing about it is that you can program the lights around the circumference.  Say green is up to 12.2 then you could have yellow for 12.2 to 12.9 and red above 12.9.  You pick the ranges, but if it is where you can see it damage might be prevented if you see the red lights come on  :-),

Sum

Offline wobblywalrus

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Re: Tuning by Head temperature.
« Reply #12 on: October 16, 2013, 01:22:22 AM »
The method I use is to do all of the tuning at home or in Beaverton and to correct for salt flat conditions using mathematical formulae and charts.  It is so much easier to tune the bike down here where I have all sorts of equipment and time.  Remember the Mikuni jetting slide rule?  It was used for that method.   

Offline Bruin

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Re: Tuning by Head temperature.
« Reply #13 on: October 16, 2013, 10:15:02 AM »
I do have one of those slide rules but I don't have a place to run the bike to full speed. I tried the local dyno ONCE. Its sensor kept reading rich, right up to and including the point where the plug tip melted and piston got lunched. Not a fan. But I get that the point is to tune as best you can and adjust accordingly.
STD; Speed Team Doo
'82 Honda 500 APS-AF
'70 Triumph 250 MPS-PG
'71 Triumph 250 APS-PF
'70 Triumph 250 M-PG