Exhaust temps - fine tuning carbs

[darrell3001]

Bike: 83 11E

Background: Carbs and bike are performing beautifully. Im running stock exhaust with pods and Dynotec stage two kit. Mixture screw at 3 turns. Idle rock solid, mid-range and full have good power and response. Carbs balanced, valves adjusted, new plugs, new coils. Im could not be more pleased with setup. Im now to the point of doing very fine adjustments. One of the things that i saw UrbanMonk do on his channel was to use an IR sensor to check the exhaust temp to fine tune rich/lean condition. Im starting to measure temps on exhaust about an inch from the block. The temps im reading are certainly within tolerance (i think), but there is some variance. From left to right (4-3-2-1), im reading, on average 165, 104, 128 and 131 (C).

Q1: Is this method of measuring exhaust temp a valid test that i can read anything into? The readings do seem to stay fairly consistent from ride to ride, but im just not sure if the variance is really telling me anything or not

Q2: is slight adjustment on mixture screw going to have any affect? Mixture screw is only going to affect pilot jet. Im just not sure that it would have that much effect on engine running at speed. But then again, bike is probably running for 5 minutes at low RPM just before i pull into into garage and test temp.

Q3: Is a higher exhaust temp a sign of a rich or lean. I assume lean. I was going to try to richen up the number 4 carb a half turn for tomorrow ride to see if it affects the post ride temp.


Thanks and Best Regards,

[zed1015]

Answer 1 = NO !

Answer 2 = Mixture screw only for pilot fueling... Negligible effect on anything above.

Answer 3 = All depends on header thickness, Material and whether single or double skinned and unless you know the correct running temp of that particular exhaust on that particular engine under a specific condition ( which no one does ) measuring the temp is pointless.

Waste of time measuring exhaust temps for anything except to indentify a dud cylinder..

If the bike runs fine just ride it..

[Suzukian]

Does 2 and 3 cylinder connect at the bottom, like a manifold connect, and 1 and 4 run separate? On stock Suzuki exhausts, since 2 and 3 share the exhaust at the collector, those two inside cylinders should be synced a 1/2 ball lower than 1 and 4. You have to extrapolate that with a dial gauge. This is due to the scavenging between 2 and 3 cylinder. This does not apply to a 4 into 1 exhaust.

[rphillips]

I wish someone would answer # 3. Back in the day it was known if you leave the choke on too long, pipes would turn purple, thought from too much heat, but also when rejetting the carbs, too lean would also make the pipes turn purple, also thought too much heat. I've always wondered... Another thing about the heat, the GS1150's came with 1 size larger main jets in the inside carbs, inside were 122.5 and the outside carbs had 120. Rumors were to make the inside cyls. run closer to the same temp as the outside cyls.... Wondered if running a cooler sparkplug in inside cyls. wouldn't have done the same thing.

[zed1015]

.. Another thing about the heat, the GS1150's came with 1 size larger main jets in the inside carbs, inside were 122.5 and the outside carbs had 120. Rumors were to make the inside cyls. run closer to the same temp as the outside cyls.... Wondered if running a cooler sparkplug in inside cyls. wouldn't have done the same thing.

Running different size jets in the middle cylinders is nothing directly to do with controlling cylinder temps or to cool the inners in relation to the outers but to simply ensure the A/F ratio is equal across all cylinders.
Certain airboxs because of frame design perameters etc deliver a slightly larger or smaller ratio of air to the middle or outer cylinder depending on which way you look at it.
To ensure the correct A/F ratio the jetting on the affected cylinders need adjusting to suit.
An exaggerated example would be to run open carbs on the inner cyls and an airbox on the outers.
The inner cyls would need bigger jets to maintain the correct A/F ratio.
On machines with that jetting configuration once the airbox is removed and pods or stacks fitted the jetting across all four carbs would be set identical to each other.

[bonanzadave]

I've installed many EGT monitors in air cooled 6 cyl airplane engines. Yes, 6 probes in each stack about an inch from the head flange. Most were fuel injected engines with a mixture control that the pilot can move which controls a fuel servo. Lots of debate on running 100 degrees F lean or rich of peak in cruise. There are very few throttle movements once set up and cruising.

[Rob S.]

"Running beautifully...could not be more pleased..."

I'm old school, so I say, "if it ain't broke, don't fix it." More to the point, if it ain't broke, DON'T BREAK IT!

Just ride it, and be patient. All too soon, things will need fixing.

[darrell3001]

Hello all. Thanks for the feedback on this topic. So i did do run this test. Sorry, this is just my nature to need to understand things. My findings:

Originally with all carbs tuned to 2 3/4 turns, i measured exhaust temp (immediately after ride), directly at first bend on exhaust pipe on all cylinders. Readings were (4,3,2,1) 165, 104, 128 and 131C. To be clear, my test is not to get them to a specific temp, but to have them all read about the same. This is an 83 1100E, so all four pipes are independent, then 3&4 and 2&1 join just before the muffler.

On last ride, i leaned 4 by 1 turn (1 3/4) and i richened number 3 by 1 turn (3 3/4). The results did have an effect on exhaust temp (145, 125, 130, 132). However, now i have a "mushy" spot at about 3000 rpms. So i can say, fairly conclusively, that mixture does have an effect on exhaust temp. But... I dont think its a direct correlation to stoichiometry, ie now i have a mushy spot at 3k.

Anyway, im going back to 2 3/4 turns on all 4 which give me near perfect all around performance at idle, mid and full. It was a fun experiment, but, in the end, did not yield any useful results.

im taking Rob S. advice and just ride the damn bike and enjoy. Another bigger problem will be just around the corner.

Thanks and Best Regards,

[rphillips]

Zed, thanks, that's something I'd not heard but do see how the air flowing through air box can be different for inside and outside carbs. Inside would be more of a straight shot, faster air flow, and the outside carbs., the air would kind'f have to make a dog leg turn, slightly slower air flow to the carbs...

[Big T]

Hello all. Thanks for the feedback on this topic. So i did do run this test. Sorry, this is just my nature to need to understand things. My findings:

Originally with all carbs tuned to 2 3/4 turns, i measured exhaust temp (immediately after ride), directly at first bend on exhaust pipe on all cylinders. Readings were (4,3,2,1) 165, 104, 128 and 131C. To be clear, my test is not to get them to a specific temp, but to have them all read about the same. This is an 83 1100E, so all four pipes are independent, then 3&4 and 2&1 join just before the muffler.

On last ride, i leaned 4 by 1 turn (3 3/4) and i richened number 3 by 1 turn (1 3/4). The results did have an effect on exhaust temp (145, 125, 130, 132). However, now i have a "mushy" spot at about 3000 rpms. So i can say, fairly conclusively, that mixture does have an effect on exhaust temp. But... I dont think its a direct correlation to stoichiometry, ie now i have a mushy spot at 3k.

Anyway, im going back to 2 3/4 turns on all 4 which give me near perfect all around performance at idle, mid and full. It was a fun experiment, but, in the end, did not yield any useful results.

im taking Rob S. advice and just ride the damn bike and enjoy. Another bigger problem will be just around the corner.

Thanks and Best Regards,

Um, you've got that backwards. On BS carbs, turning the idle mixture screws out richens the mixture.
also, are you numbering carbs from Home left (clutch hand) to right Groups (throttle hand) ?

[darrell3001]

Hi Big T Sorry.. typo. I wrote it backwards. I leaned number 4 (+1 turn to 1 3/4) and richened number 3 (-1 turn to 3 3/4). I’ve updated that in my original post. Im counting 1-4 from clutch side to throttle side. Just like they are numbered on spark plug wires. I normally write my reading in my log book as 4 to 1, left to right as I’m looking at engine head on.

[Burque73]

...........................................use an IR sensor to check the exhaust temp.............................

Your results may be inaccurate, especially if the pipes are polished chrome.

3. Confused by Bright Shiny Objects?


"Infrared thermometers have good accuracy when measuring most objects, but shiny, reflective surfaces can be a challenge. You should be especially wary when measuring the temperature of shiny metal objects, but even reflections off of glossy paint can affect accuracy. Putting a piece of non-reflective tape (such as electrical tape) over the shiny surface or applying some flat paint gives you a target from which you can get a better measurement."

https://www.fluke.com/en-us/learn/bl...ect%20accuracy.


I was trying to do the same thing a while back. Found more satisfying results measuring the metal collar holding the pipes to the head. In the end, however, I decided to focus more on the color of the spark plugs than the readings on the thermometer.

[Who Dat?]

Let's start in the first post. You mentioned something about checking temps "left to right, 4-3-2-1". The cylinders are NOT numbered the way you see them when looking back at the bike. Number 1 is under your CLUTCH hand, Number 4 is under your THROTTLE hand. All references to directions on the bike are made as if you are sitting on the bike, ready to ride.

.... Wondered if running a cooler sparkplug in inside cyls. wouldn't have done the same thing.

Just in case you were not aware, spark plugs do not control the temperature of the engine. In other words, a "cooler" plug will NOT lower engine temps (at least, not directly). The temperature rating of the plug is determined by the length of the ceramic insulator in the middle. A longer insulator will take a while for the heat of combustion to be sinked to the cylinder head, resulting in a "hot" plug. A shorter insulator will sink the heat rather quickly, resulting in a "cool" plug. A "cool" plug might eventually foul, leading to misfiring or not firing at all. THAT will give you a cooler-running engine (if it runs at all).

[rphillips]

Just seemed, as the colder plug, dissipates heat quicker from (out of) the combustion chamber, through the metal of the head, cooling fins, and water jackets, there would be less remaining heat to come out the ex. Just as if less heat is dissipated through a hotter plug, that should leave more heat inside the combustion chamber to be released through the ex.... I dun'no, it can be really confusing.

[pdqford]

Just seemed, as the colder plug, dissipates heat quicker from (out of) the combustion chamber, through the metal of the head, cooling fins, and water jackets, there would be less remaining heat to come out the ex.

The way I think of it, the colder plug gets colder by dissipating heat OUT of the plug faster, and into the head, thereby making the exhaust gases a smidgeon warmer.