jetting advice

[bronco70]

Your comment about it not doing the same blubber at 1/2 throttle in any gear except 2nd probably comes from the fact that the engine is not really "pulling" at steady 1/2 throttle in 2nd (and you just won't leave it at half throttle in 1st - note that I wouldn't either). Anyway, jetting is supposed to be checked with the engine "loaded" (made to work, not just "wind-mill"). So I think it is a good sign that it doesn't blubber in the higher gears - ASSUMING that you "found" the carb setting which DID blubber in the higher gears, then went ONE step leaner to arrive where you are now.

I kind of like the look of the plug. It MIGHT be showing slightly rich, which is what I sure as heck would want on a bike I'm just getting used to. But PLEASE don't do your jetting based on plug observations, OK? Take some time. Ride the machine. Carry a couple of spare plugs. If you find your jetting is indeed on the rich side and it is causing you problems with rideability or spark plug life . . . figure out what throttle position is rich and tweak that. Make ONLY one adjustment at a time, so you can gauge the effect of that ONE change - BEFORE making any other change.

By the way, what brand and heat range of plug is shown in the most recent photo?

How does a 200 main jet run at full throttle?

Ed

ok i know i keep bugging you about this so here is last run down that i did
fresh plug b8 hs note i did swap new plugs in during test after jet changes
93 gas mixed 28/1 amsoil
pilot jet is done and staying with 40 1 1/2- 1 3/4 turn seems good
ran with 210 jet sputters at wot
ran with 200 some times sputters depending on gear/load but fine most of time
190 jet runs great seems like better power at wot but after a few wot runs plug has little sign of ash/gray
so i dont know if i should play it safe and run 200 or is the 190 best.
looking to get best advise from you since you have the expert advice
thanks for the help and patience with me

[Bullfrog]

Bronco,

I'm going to go "all conservative" on you. Your mention of ". . . little sign of ash gray" makes me nervous.

Have you checked compression? Anything over 160-165PSI is going to require special fuel.
Have you confirmed the ignition timing with a timing light? Timing can be set by the "gap method" . . . but you don't know "where/when" it is firing till you check it with a timing light. And since expertise and "feel" with feeler gauges can vary, I always check my own bikes with a timing light.

Do you KNOW what throttle setting you are holding when you are doing jetting runs? WOT is easy, but 1/4, 3/8, 1/2, etc. are harder to discern. Have you set up something like the photo so you can really identify throttle position?

I've got a fair amount of confidence that you are gauging throttle position fairly well . . . but I'd like to be sure. I've had folks tell me they were at half throttle . . . when they really were assuming half throttle when at about half engine speed. It is more important to KNOW throttle position and how the engine is running, than it is to know engine speed and how it is running.

So, now to the "all conservative" part. I'd recommend the 200 main jet . . . and simply get some time on the bike. Carry some plugs and do some trail riding. If it won't "wind out" when you need it to take control of hills - you'll know it. When you get convinced it is rich on Main Jet . . . THEN you can go down ONE size. And while you are doing that riding, you'll get a "feel" for how it runs at various throttle positions.

Finally, if you are going to post spark plug photos, I'd like to look at the side of the "side strap" and down into the plug at a 30 to 45 degree angle - with good light on the insulator nose . . . and in good focus. A photo in focus from a few more inches away is far more useful than a blurry up-close photo.

Ed

[Bill2001]

Ed, this may sound like the Choir preaching to the Preacher but "you're right". After a year of twiddling around with my jetting, I'm making progress once I stumbled onto the "conservative and repeatable" approach you outline. Being in the thick of things I can say firsthand that it works.

Carry on...

[taber hodaka]

I think some oils are harder to get what we would call a normal plug reading. Amsoil is a 100/1 oil, 28/1 is a big variable and synthetic oil could be a factor. I like being just a touch on the rich side. Running and tuning chain saws for several years in early life was good experience, they worked all day, the week and the year. Different oil produced a almost instant comparison of oils as tuning only took a minute. The snow machines were choked to start and did not perform without tuning. On chainsaws and snow machines tuning was done with a screwdriver on adjustable jets. -----Clarence

[Hydraulic Jack]

Clarence is making a valid point here. Synthetic oils, and especially high end synthetics, produce little ash and don't mark spark plugs the same way petroleum oils and average two stroke oil does. While all oils will darker a plug with use, it takes longer with synthetics than is practical for reading a plug unless you are a road racer that stays pinned a good part of the time.

Any plug reading must be done at a nearly static rpm to give you any usable information regarding rich/lean condition. As is the case here, the bike runs normally over most of the rpm range and seems rich only at one throttle position, yet we see a plug with only a light color coat, and no rim coloration at all. So at what rpm should we conclude jetting condition based on the plug? We can't.

I would also disagree that a slight ash on the electrode is a bad sign. There is not enough information here to base a conclusion regarding running condition using only the plug as a determining factor. Instead, we are told that the bike runs well in almost all throttle positions except WOT and even then, it doesn't always seem rich. This is a lot more diagnostic data than we can get just from the plug. I would much rather see a slight ash on the electrode than not, as long as the bike runs well and as long as the other plug factors are consistent with proper jetting, i.e., coloration of the rim and insulator, and whether the insulator is dry or damp.

We also don't know the protocol used to get the plug reading that we see. For example, was the bike warmed up fully, a new plug inserted, and the bike taken to a fixed rpm range, held there for up to a minute, and the ignition cut and the plug read right there. Or, was it taken for a ride, brought back to the garage, stopped, and the plug taken out for a look? If the later, you can't tell anything from the plug.

Clarence has rightly pointed out that plug readings are not reliable, and they aren't. They offer only one data point, and are reliant on so many variables that unless the operator has a good sense of how to do plug readings, the plug alone tells us nothing.

As for running rich for a while, I would point out that a rich engine tends to run hotter than a correctly jetted engine. There is nothing I can find in other than anecdotal form that suggests that you should run fuel rich during break in. Oil rich on the other hand has been supported for many years for breaking in a two stroke, and while I think 28:1 is probably more Amsoil than needed, unless there is a clear indicator that this ratio is doing harm, I see no reason to change it now.

Frankly, jetting anyone's bike is an art form. While the process can be reduced to writing, the nuance of experience and talent can't be written down. Some folks will always be better at playing piano than others, and so it is with engine tuning. Bronco is doing well here. Whether he uses a 200 main or a 190, he is in the ball park, and time will better tell which to use than one or two plug readings. It isn't going to help in doing plug readings to have a tape mark on the throttle without all the other process that goes with it. It will, however, help to isolate which throttle quadrant needs attention. That information, when used in conjunction with a jetting chart showing the overlap of jetting and throttle position, will get the job done.

[bronco70]

great info guys and i would agree this 2 stroke tuning is art form that i am trying to get better at
the 200 main seems to foul plug to soon so i am considering going back to the 190
had nightmare tuesday after fouling plug. threads came out with plug.this sucks threads seemed
loose from day one but didnt expect this. guess i get heli coil in this week .
could head gasket be reused?? only has few tanks of gas thur since replacing
also should top of piston looks super clean is this sign of to rich ??

[Bullfrog]

Uh-oh, there is prime potential that you had an air leak right at the spark plug. Someone on this thread suggested that an air leak may be causing your problems . . . looks like they could have been right. You now have another piece of evidence that a pressure test should be done to assure that DPO procedures haven't "built in" a fault (air leak).

Don't worry about the comment that slightly rich jetting may run hotter than proper jetting. As a practical matter that is simply not an issue for your mildly tuned engine and trail riding use without long term single throttle setting running - and is open for much debate elsewhere in the engine universe. It is still true that if you are "off" on jetting, it is better to be "off" on the rich side than on the lean side.

I do wish that you would scale back the fixation on looking at the condition of pistons and spark plugs attempting to discern "rich" or "lean". Use your ears and ride the bike. Note how the engine sounds/performs at specific throttle settings.
Ed

[bronco70]

Uh-oh, there is prime potential that you had an air leak right at the spark plug. Someone on this thread suggested that an air leak may be causing your problems . . . looks like they could have been right. You now have another piece of evidence that a pressure test should be done to assure that DPO procedures haven't "built in" a fault (air leak).

Don't worry about the comment that slightly rich jetting may run hotter than proper jetting. As a practical matter that is simply not an issue for your mildly tuned engine and trail riding use without long term single throttle setting running - and is open for much debate elsewhere in the engine universe. It is still true that if you are "off" on jetting, it is better to be "off" on the rich side than on the lean side.

I do wish that you would scale back the fixation on looking at the condition of pistons and spark plugs attempting to discern "rich" or "lean". Use your ears and ride the bike. Note how the engine sounds/performs at specific throttle settings.
Ed

so no concearn on piston being spotless? i was just assuming that rich was washing it off
i will put back together tonight and see how it goes

[Bullfrog]

That is correct - the piston being clean doesn't truly "tell" me anything. I could be telling me your oil is very clean and very heat resistant. It could be telling me "this is a very low mile" piston. But I would make NO judgements about jetting by looking at that piston. None. No.

Ed

[Bill2001]

Last year I read a lot of material on 2-stroke engines to get myself up to speed on the technology. One thing I saw referenced a lot was "piston wash" on snowmobile and watercraft 2-strokes. It's the holy-water of 2-strokes and can mean everything or nothing. Generate a heckuvva lot of discussion. So The Captn is undoubtedly correct.

Carry on.

[bronco70]

ok its back together and running again