Plug chop results.
- Thread starter Loctite77
- Start date
Tune-A-Fish
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Elevation where you are?
Tune-A-Fish
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Im running 105/35 1.5 out 3rd position up and things seem right, but I keep looking for a lean condition nothing yet but I run gas no corn.
Tune-A-Fish
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Re: Plug chop results.
Stock bores in Memphis 350ft N of water, reason I asked was because I lived in the high country in Colorado so swapping brass was a common chore.
Loctite77 said:
Stock bores in Memphis 350ft N of water, reason I asked was because I lived in the high country in Colorado so swapping brass was a common chore.
redwillissuperman
Keep it simple- engine, wheels, bars
Re: Plug chop results.
Loctite77 - your bike is stock. The little muffler and pods are done nothing. Take the carbs completely off and go through each passage with a thin gauge wire. Put in stock stuff. Verify your manifolds are sealing. Go back to factory settings and get it to run correctly. A 750 should "zing" to redline not sound like an old Russian tractor.
Verify that you have the right combination of resistor plugs and wires. What ohm coils are you running?
Loctite77 said:
Loctite77 - your bike is stock. The little muffler and pods are done nothing. Take the carbs completely off and go through each passage with a thin gauge wire. Put in stock stuff. Verify your manifolds are sealing. Go back to factory settings and get it to run correctly. A 750 should "zing" to redline not sound like an old Russian tractor.
Verify that you have the right combination of resistor plugs and wires. What ohm coils are you running?
Tune-A-Fish
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" hesitate and sputter"
Seems odd to be a lean issue, more of a starvation issue or ignition. at 3/4 to WOT we can eliminate the idle circuit so you are right to suspect the mains are lean, but I would expect at 2-3 sizes it would just not pull up top not stumble so much.
Get it back on the bench and make sure it's synced run the 115/35 3rd clip position cheap plugs and vacuum sync... another thing is the boots from the carbs to head need to be tight and leak free... maybe your pulling air in.
Seems odd to be a lean issue, more of a starvation issue or ignition. at 3/4 to WOT we can eliminate the idle circuit so you are right to suspect the mains are lean, but I would expect at 2-3 sizes it would just not pull up top not stumble so much.
Get it back on the bench and make sure it's synced run the 115/35 3rd clip position cheap plugs and vacuum sync... another thing is the boots from the carbs to head need to be tight and leak free... maybe your pulling air in.
Loctite77
Yeah Son!
So to clarify, previously if I would crack open the throttle abruptly it would hesitate/bog. If I would back off the throttle and roll back on slowly it would be okay. Raising the needle by putting the clip in the last spot fixed this issue. I know that 3rd from the bottom does not work so I guess I'll try 2nd from the bottom now. I am pretty confident the boots are sealed tight and I have vacuum synced.
Yeah Son!
Yeah Son!
Tune-A-Fish
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Looks like you are armed with a plethora of thoughts, the simple thing is it should run decent within a range of jetting setups... dialing it in to a tune is another step.
Other things such as the valve train adjustment and valve seating, spring rate, ignition and ignition timing bad valve guides/seals all can play in what the plug looks like. I tend to tune with my ear and throttle response first, I also always try to find a basline like your doing here.
Good lux mang!!
Other things such as the valve train adjustment and valve seating, spring rate, ignition and ignition timing bad valve guides/seals all can play in what the plug looks like. I tend to tune with my ear and throttle response first, I also always try to find a basline like your doing here.
Good lux mang!!
Raising the needle will make it way too rich mid range as long as the main jet is too small. I know that the plugs read rich, but try a larger main jet and keep going up until the 3/4 to WFO is right and put the needle back in the middle slot to start with. You may need to change needles later or get custom needle jets made. Honda used 2.6mm jets in almost all their bikes for years and changed the needle root diameter to moderate fuel flow.
IIRC there were a few different CB750 needles over the years. Not sure if I have any left from the experiments where we tried to get a CB77 to run cleanly on methanol (it did) and went through a few different needles before I "machined" them to a different taper.
IIRC there were a few different CB750 needles over the years. Not sure if I have any left from the experiments where we tried to get a CB77 to run cleanly on methanol (it did) and went through a few different needles before I "machined" them to a different taper.
Not much has been said on when you did the chops. They're not going to do you any good unless you do them at every point of riding: idle, through all the gears, highway, etc. It's very possible to read lean and rich at the same time and get lost in all the adjustments. Also, make sure you're setting the idle mixture at 800 - 900 rpm, not 900 - 1100 rpm like the manuals direct. If you set it up with pods and an open exhaust that breathes easier, than you're probably using more than just the idle circuit above 900 rpm.
I have to politely and respectfully disagree. The ONLY time that a plug chop is useful in terms of fine tuning mixture is wide open under load. At anything less that WOT, the plug temps are much lower and often below the temperature at which they self clean and therefore very misleading.
A plug running cool at part throttle should look as if it's running rich - not because it's rich, but because it's too cool to self clean.
A plug running cool at part throttle should look as if it's running rich - not because it's rich, but because it's too cool to self clean.
Tune-A-Fish
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http://precisionmoto.com/2014/01/10/spark-plugs/
Fair enough, but this is the first time it's been addressed after three pages of advice. Also, motorcycles don't get nearly as hot as a V8 and don't do nearly the job at cleaning them. So, they really don't clean even at WOT since they barely get above 400° iirc. Carbon burns off at above 550°. Also, the rpm at idle mix needs to be addressed as it could be causing a false rich condition.teazer said:
And thanks for that page, Tune. I've been looking for something like that for a while.
Tune-A-Fish
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Seems rite:
Cylinder head combustion chamber and piston temperatures and heat fluxes were measured in a 2.2 L 4 cylinder spark ignition engine. Measurements for the combustion chamber were made at wide open throttle conditions, 1400 rpm to 5000 rpm at 600 rpm increments, additional measurements were made on the combustion chamber at part throttle conditions at 3200 rpm. Piston temperature and heat flux measurements were made at WOT conditions from 1400 to 3200 rpm in 600 rpm increments. Average combustion chamber surface temperatures ranged from 130 degrees C to 248 degrees C, while peak combustion chamber surface temperatures ranged from 142 degrees C to 258 degrees C for WOT conditions. Peak heat flux at the surface for WOT conditions in the combustion chamber ranged from 1.2 MW/m₂ to 5.0 MW/m₂. Central region heat fluxes were 2.3 to 2.8 times greater than those in the end gas regions of the combustion chamber. Piston temperatures were 10 to 25 degrees centigrade hotter than corresponding combustion chamber surfaces at WOT conditions. Peak heat flux values in the end gas region of the piston were 2 to 4 times greater than corresponding locations on the combustion chamber at WOT conditions. The Woschni heat transfer model correlated well with the experimental instantaneous local heat flux data. Long term heat flux data indicates that deposit formation greatly modifies surface heat transfer.
Under 500DF for sure based on that, but I don't think it "burns" off but rather changes color or builds up more or less.
Cylinder head combustion chamber and piston temperatures and heat fluxes were measured in a 2.2 L 4 cylinder spark ignition engine. Measurements for the combustion chamber were made at wide open throttle conditions, 1400 rpm to 5000 rpm at 600 rpm increments, additional measurements were made on the combustion chamber at part throttle conditions at 3200 rpm. Piston temperature and heat flux measurements were made at WOT conditions from 1400 to 3200 rpm in 600 rpm increments. Average combustion chamber surface temperatures ranged from 130 degrees C to 248 degrees C, while peak combustion chamber surface temperatures ranged from 142 degrees C to 258 degrees C for WOT conditions. Peak heat flux at the surface for WOT conditions in the combustion chamber ranged from 1.2 MW/m₂ to 5.0 MW/m₂. Central region heat fluxes were 2.3 to 2.8 times greater than those in the end gas regions of the combustion chamber. Piston temperatures were 10 to 25 degrees centigrade hotter than corresponding combustion chamber surfaces at WOT conditions. Peak heat flux values in the end gas region of the piston were 2 to 4 times greater than corresponding locations on the combustion chamber at WOT conditions. The Woschni heat transfer model correlated well with the experimental instantaneous local heat flux data. Long term heat flux data indicates that deposit formation greatly modifies surface heat transfer.
Under 500DF for sure based on that, but I don't think it "burns" off but rather changes color or builds up more or less.