How to tune an engine with a temp gauge?

That's a good setup to have and at a decent price too... Basically what you want here is to stay below 360 degrees F which can happen on a properly tuned engine on a really hot day if ridden really hard, but for tuning, just set it up where it's not 4 stroking or if it is, it's doing it at an rpm you're rarely or never at. This gauge is a good tool to warn you if you're too lean or too hot so you can either ride less agressively to cool it down or add a little more fuel to the mix.
Using a temp gauge is more for your reference to know when to back off the throttle and let things cool off than it is for tuning, you can tune with it, but it's better for keeping from blowing your engine by riding it too hard too long, basically, think of it as cheap insurance for your engine because you'll now be able to know when to back off before any potential damage can occur.
 
Too lean will cause the motor to over heat, this is what will damage the engine.
Too lean can also give slight power increase, so can be that you might think your motor is running better, but it's lean and getting hot.
My C to F conversion isn't very good, but I find if my motor runs up around the 150 C or more it will start staining the underside of the piston, and in my opinion is starting to get to hot, I've heard of people getting their motor hotter, I've been told 180 C is OK.
As you probably know extra fuel helps to cool the motor.
I like to ride my bikes fairly hard and live in the tropics, So I generally like my motors to 4 stroke unless I'm on the throttle, which tends to give best acceleration as the motor wants more fuel under load. That's generally how I tune mine, by ear, but I have been around engines all my life and can hear when one is running right, then check the plug. A better pipe tends to make tuning by ear a lot easier.
The only time I have had over heating problems is when running higher compression with an angle fire head. The Puch head is the go if your going to try and make some real power.
My case induced motor with the Puch head does over 50MPH and runs cooler than my milder motors with less compression and a straight fire.
Any one after performance, throw away your angle fire heads!
 
I fully agree about the angle fire heads, they just can't get rid of the heat fast enough, then add a few performance upgrades and the problem only gets worse. The Puch heads do the job very well and cost half the price of a Fred head, not saying anything bad about Fred's heads because I run one on mine and it keeps the engine way cool. The fred head is more compact so it fits better in tight frames, but other than that, either head will keep your engine plenty cool enough.

I'm not completely up on my C to F conversion either but 150C should be around 330F or so, which is still in the safe zone but getting close to your limit. I like to keep mine under 360F which is about the max allowable temp for short bursts, not good to run it that hot constantly so try to tune well under that temp.

Be careful with the tuning here because like Theon said, it will make more power when you go leaner but it's also running hotter and won't last as long, many people have blown their engines going with the "lean is mean" tuning, there are other ways to make big power without burning up your engine and we can go over that later on if you want to know.
 
Here's what I do to tune. All testing is done with engine at operating temp.

Set it slightly lean and the. Apply the choke a little at a time. If there is a power increase then go a tad ritcher. Repeat. I do it for WOT and for cruise. Pilot circuit ( cns) is bit finiki though.
 
Thanks for that converter... I was off by about 20 degrees F in my "off the top of my head" conversion for 150C..
Bookmarked
 
a.graham52 said:
Here's what I do to tune. All testing is done with engine at operating temp.

Set it slightly lean and the. Apply the choke a little at a time. If there is a power increase then go a tad ritcher. Repeat. I do it for WOT and for cruise. Pilot circuit ( cns) is bit finiki though.
Click to expand...

That's one thing I like about the CNS carb is that it has an enrichener circuit like most motorcycles have and it's a good tuning tool or if you need an emergency cool down you can just feather the choke enough to give it that little extra it may need on a really hot day or right after a hard run.
 
Davezilla said:
That's one thing I like about the CNS carb is that it has an enrichener circuit like most motorcycles have and it's a good tuning tool or if you need an emergency cool down you can just feather the choke enough to give it that little extra it may need on a really hot day or right after a hard run.
Click to expand...

Indeed, I too appreciate the "in-flight" fuel/air mix adjustability offered by an enrichment circuit over the more basic "choke" design - while cold starts are made about equally easier with either, at speed & with a warmed up motor an enrichment circuit is far more useful for determining and/or optimizing fuel/air for those conditions.

Much like as what's found on small aircraft to enable the pilot to manually adjust to compensate for altitude, an enrichment circuit provides a measured amount of additional fuel, the amount variable to suit the application - unlike a choke, which just cuts off air, not nearly as handy for determining jet size modifications for example as you're reducing venturi size, not your typical tuning method when addressing jets.

[the following is not advice, can be harmful & is just silliness I do]
When I have a carb that has an enrichment circuit, generally I don't fuss about adjusting my carb's jets quite as precisely as otherwise, if I do it'll be a touch on the lean side (needle clip adj) as I tend to run with the enrichment circuit partially engaged to some extent anyway. As I've a temp gauge and am somewhat familiar with the preformance characteristics & assorted behaviors of the motor in question I'll simply adjust to suit as needed, when needed (friction lever on bars). An interesting example was the last rally I attended, meant for scooters & most being 150cc+ it was all my lil 49cc four smoker could do to keep up - so that meant I was running overspeed & overtemp all day in the sweltering summertime, redlined & screaming it's guts out I'd give it a touch of extra fuel not for preformance, but to quench the heat a bit. Once normalized (or less stress/speed/hilly terrain) I'd readjust back to "normal" cruise/preformance mix.

A bad habit I s'pose, one I picked up from small aircraft whose fuel/air mixes aren't really "set" anyway ;)
 
Last edited:
Update: Had the gauge on and went for a 12 mile ride. Temperature outside was 75F Maximum temperature on my ride (WOT) 275F. Most of the ride, I was between 230 and 265 F. It was a little four-strokey at bottom end, can I down jet just a little bit more? Or do you think making it leaner will be harmful?
 
Personally, I think you'll get better pulling power from leaving it a little rich in the low end.
If it's not 4 stroking when you hit the gas, only when your backing off, perfect.
 
It four strokes when I go from 0 throttle till quarter throttle, taking off. Every time I have down jetted it has improved slightly.
 
I'd just let it 4 stroke a little down low if it's running good on top or at the rpm range you ride it at, of course, if you're looking for max power, you can down jet until it feels strongest but keep the max temp below 360F and you should be ok.
 
personally in my opinion you want to go just lean enough to stop the for stroking. JUST enough. my bike fourstoked at cruise and when i swapped heads i found the plug fairly dark as well as a lot of carbon built up on the piston and head. i since have adjusted my needle (cruise setting) and much happier. still need to ritchen WOT though.

good tuning tip. always asses how well your bike is running when its up to temp. might take a mile or two but a cold engine will never run consistently.
 
Agree, you don't want it 4 strokeing while your at cruising speeds,
A little bit low down is OK, and you may find it will pull a little better if a little rich down low.
But shouldn't be 4 stroking while your accelerating, that is defiantly too rich.
But I think it should 4 stroke a bit when off the gas, and maybe a little while riding slowly with gentle throttle inputs. Then when you give it a squirt it should 'run clean'.
 
Last edited:
You must log in or register to reply here.
Back
Top