Largest main jet & still lean as can be!!!

[pmptrk]

I can't quite figure out what is going on here. I just got done (only a couple rides on the 426) doing all of the engine mods as listed in my sig. I also have a 450r carb and am trying to tune it. I ended up with a 55 keihin pilot and 2.5 turns out on the a/f screw in order to get good idle and plug color. However, when testing the main jet with a 230 keihin in (the largest they make) I can only get a pure white plug.

I am not asking for correct settings for a 450r carb on this bike, because I know that topic has been beat to death. I'm just curious what to do in this situation from a general tuning point of view.

Thanks a lot.

[Pappy]

with a main that big you are probably throwing so much fuel on the plug that it wont color up

***sorry, i did not see you said white. is it white or no coloring at all?

[pmptrk]

After a main jet test run the plug shows definite signs of being too hot. The only color it gets if any would be whiter. Howerever, I get a perfect brownish color at idle, but once the main jet test has been done, it is back to white as can be.

[Pappy]

any chance you have an air leak either at the carb boot or the intake itself?

[pmptrk]

I triple checked both and they are tight. The 450r carb requires the hotstart hole to be plugged and I did that with silicone.

[2004exrider]

Are you sure your checking it right (not saying your doing it wrong, so no offense meant). The way to do it right is to crack it full throttle while under a load for about 5 seconds and then turn it off. That will give you an accurate reading, the main controls
3/4 - Full throttle. Just curious, did you mess with the needle position? Other than that, i'd think that would be way to rich?

Jimmy

[GPracer2500]

Contrary to popular belief, when doing plug chops to test a main jet size, it is perfectly normal for the tip of a plug's insulater to be BONE WHITE--even when the main is too rich. The heat of WOT operation, even when rich, can keep the insulator of a new plug completely white except for the "mixture ring" that forms at the very base of the insulator. That is where you look to read a plug when evaluating air/fuel ratios.

See my post in this thread for more information: http://www.exriders.com/vbb/showthread.php?s=&threadid=237664&perpage=15&pagenumber=2

Performance tuning using plug readings isn't quite as simple as most people think. I'm (slowly) working on a "How To" in which I'll elaborate on using plugs to tune carburetors.

Plug readings aside, how does the bike run at WOT? With a jet that big, I've gotta believe it's exibiting rich running behaviors that you're misinterpreting as being lean running behaviors.

[pmptrk]

Originally posted by 2004exrider
Are you sure your checking it right (not saying your doing it wrong, so no offense meant). The way to do it right is to crack it full throttle while under a load for about 5 seconds and then turn it off. That will give you an accurate reading, the main controls
3/4 - Full throttle. Just curious, did you mess with the needle position? Other than that, i'd think that would be way to rich?

Jimmy


That is exactly how I checked it. I have not messed with the needle position at all, which is in the middle or 3rd spot, and I think that is its stock position on the 450r carb. Would richening up the needle have any affect on this problem?

[A A R O N]

Maybe out of time:confused:

[GPracer2500]

Originally posted by pmptrk
That is exactly how I checked it. I have not messed with the needle position at all, which is in the middle or 3rd spot, and I think that is its stock position on the 450r carb. Would richening up the needle have any affect on this problem?

What do you mean? You've looked at the mixture ring at the bottom of the insulator? A picture would help us diagnose what's up.

Forgeting about the plug, how does it run at WOT?

I don't think the needle is relevent here.

[pmptrk]

Originally posted by GPracer2500
Contrary to popular belief, when doing plug chops to test a main jet size, it is perfectly normal for the tip of a plug's insulater to be BONE WHITE--even when the main is too rich. The heat of WOT operation, even when rich, will keep the insulator of a new plug completely white except for the "mixture ring" that forms at the very base of the insulator. That is where you look to read a plug when evaluating air/fuel ratios.

See my post in this thread for more information: http://www.exriders.com/vbb/showthread.php?s=&threadid=237664&perpage=15&pagenumber=2

Performance tuning using plug readings isn't quite as simple as most people think. I'm (slowly) working on a "How To" in which I'll elaborate on using plugs to tune carburetors.

Plug readings aside, how does the bike run at WOT? With a jet that big, I've gotta believe it's exibiting rich running behaviors that you're misinterpreting as being lean running behaviors.

That is a very interesting post, I had not seen any of that info before. I thought that if it was in fact rich, I would be able to tell as well, but I would by no means say that it stumbles at WOT.

In your post showing that the tip can remain white, how long does that last? I do get a light brown color on the tip at idle.

ANOTHER IMPORTANT PIECE OF THIS PUZZLE (so i think) IS THAT I AM RUNNING THE DPR9Z (hotter plug) if that info helps any.

[GPracer2500]

Do not modify a plug and still use it afterwards. That's asking for major problems.

A DPR9Z is actually a colder plug than the DPR8Z stocker. The 9 transfers its heat to the head more easily/faster than an 8 and therefore operates at a lower temperature. There are ways of reading the plug's ground strap to determine if the plug is the correct heat range--but that's another discussion. The DPR9Z should be fine.

http://www.rpmoutlet.com/images/ngkheat2.jpg

The white tip will pretty much last as long as the engine is kept at WOT. The mixture ring will slowly climb up the insulator at WOT but it may never reach the end. The high combustion chamber temps of WOT keep it clean. At idle and lower RPMs the temperature of the plug is not as extreme and that's why it's showing color so much more easily.

All of this assumes a new plug. An old plug that allready has color on the tip of the insulator may or may not ever go white at WOT. Old plugs don't tell you much--but I think you allready know that.

One method of reading plugs without using the mixture ring at the bottom of the insulater is to read the "base ring". This part of the plug is not on the insulator but on the metal outer housing. The base ring is at the very end of the threads--the flat ring that faces the piston. It's the part that the ground strap (the "hook") is connected to. I'm hesitant to recomend this method because it's somewhat less accepted than examining the mixture ring. Nonetheless, what does this part of the plug look like? I'm guessing it has a very light coating of completely black soot??

[pmptrk]

The base ring had a lighter scorched look to it like it got extremely hot. I will take a pic of it when I ride it again soon.

It was my understanding that the pilot jet and a/f screw must be correct before adjusting the main jet. If that is so, does it sound like I have that adjusted right since I am getting a light brown color at idle?

What is the exact procedure that I should follow for the run before I take the pic? I have been doing it in 5th, but does it matter what gear I use for the WOT test? Thanks a lot for the help.

[cals400ex]

what kind of fuel are you running?

[GPracer2500]

Originally posted by pmptrk
The base ring had a lighter scorched look to it like it got extremely hot. I will take a pic of it when I ride it again soon.

It was my understanding that the pilot jet and a/f screw must be correct before adjusting the main jet. If that is so, does it sound like I have that adjusted right since I am getting a light brown color at idle?

What is the exact procedure that I should follow for the run before I take the pic? I have been doing it in 5th, but does it matter what gear I use for the WOT test? Thanks a lot for the help.

You're right that the pilot circuit should be adjusted before any other circuit. This is because of the overlap between circuits. There's a guide to adjusting your fuel screw in the "How To" section--check it (http://www.exriders.com/vbb/showthread.php?s=&threadid=229923) out. But, the affect of the pilot circuit on the other circuits is quite small. At WOT the pilot circuit is probably contributing less than 1% [shrug--I'm guessing] of the total fuel supply.

The standard gear for test runs while on a dyno is 4th gear. I'd probably choose that gear for throttle chops. The important thing is to maintain a load on the engine without letting it loose RPMs.

400exstud pretty much spells out how to do a run in that other thread I linked earlier.

I really prefer to use what I call "seat-of-the-pants protocols" to evaluate jetting. Basically, there are a bunch of "tricks" for determining whether you're lean or rich. For example:

--What affect does removing the airbox lid have (and for very brief trials you can even remove the airfilter alltogether)? But don't be thrown by increased intake noise.
--Does is run better when the engine is hot or cold?
--What happens when you engage the choke slightly? Do things get better or worse?
--What happens when you hold WOT in a tall gear at middle RPM and then quickly back off to 8/10ths or 3/4 throttle? Does the engine monentarily sputter, breifly increase acceleration before decreasing, or....

And there's others too. Each "test" will provide specific feedback that gives clear indications of richness or leaness. And it's not nearly as subjective as "it felt faster/slower." Plus it's quicker and cheaper than pulling plugs and cutting them up.

Ever wonder how some guys can jump on a quad/bike for 1 minute and come back with recommendations for each circuit that are right on the money? They aren't just randomly riding around and feeling for "power". They are performing specific tests that tell them whats happening.

Cals400ex's question brings up a good point that highlights a limitation of plug readings: differences in fuel. Brand to brand, location to location, and other factors will change what looks lean or rich--mostly subtle changes (I think) but changes nonetheless. Some people (professionals whos' oppinions I respect) don't believe in plug reading at all because they feel today's modern fuels, with all their detergents and additives, will have you chasing your tail. Something to think about....

[pmptrk]

I'll do a few more runs and take a pic when weather permits, taking into consideration all these helpful hints. I am running 100 octane unleaded.

[cals400ex]

many of the additives in some fuels these days will give false readings.

[pmptrk]

I could not get any pictures to turn out good since they are so close up. The ring at the ends of the threads had a flakey almost yellowish tint to it and the insulator as far down as I could see was still white. I haven't really had a whole lot of time to ride it but I will try some more things when I do.

Would it be worth the money to put it on a dyno and get it jetted perfectly? Once I got it close I don't think I am experienced enough to feel changes between a one jet size change.

[GPracer2500]

I'd flat out forget trying to read your plug. It's not getting you anywhere. I think it leads many people astray...

Having a quad dyno'd is worth in (IMO) just for the sake of doing it. Even if was tuned perfect, I'd still encourage one to do it--cause I love dyno charts. But in your case I think it would be especially revealing.

Have you tried something in the 180 range to see how that feels? If you can't detect a difference in performance between WOT operation with a 180 vs. a 230 then I've got to believe there is some unknown factor at play here.

[pmptrk]

I will go from 230 down in 10th sizes and see where that gets me so I can at least be close to spend less time dyno tuning.

Do most/all dynos have air/fuel meters? How much should I expect to pay? I have always wanted to get it on the dyno, but with these jetting troubles I think now is the time.

[GPracer2500]

No, not all Dyno's have air/fuel meters integrated into them. They are nice and give you unequivocal info about jetting but aren't mandatory for getting things dialed in. An experienced dyno operater can tune a carb without air/fuel data--it'll just take that same guy longer than if he did have air/fuel data. I'm not sure what costs to expect. Probably depends on how many dynos are within 100 miles of you.

I'm gonna go out on a limb and make a prediction: As you step down in main jet sizes, your WOT operation will improve. You'll notice that the exhaust note starts to change. It will sound less "wet". Each power pulse will sound less like a "blap" and become a sharper, dryer, "I'm-not-sure-how-to-describe-it" sound (if the exhaust note starts to get "tinny" than you've gone too far). Also, the engine will begin to rev with more immediacy. You'll notice it's more eager to race to the redline. HP will be improving as well but that's where the dyno comes in....

Good luck!

[pmptrk]

Looks like I'll dyno it. thanks a lot for all the help, I really appreciate it.