WEIRD jetting problem - ideas?

robwbright · Aug 21, 2008

Ok guys - I've been screwing around with jetting half the summer. went from a very sploogy 460 main to a 390. splooge is basically gone and plug is light brown.

However, the bike does not feel right. The "hit" is just not there and here's where I think the problem lies. . .

If I warm up the bike and then SLOWLY open the throttle, the bike runs smooth everywhere except right at 1/2 throttle.

At 1/2 throttle, the engine makes the bike vibrate noticably. It smooths out again at 5/8 to 3/4 throttle.

Changing the main jet is apparently not going to resolve the issue. What should I change next?

IndyMX · Aug 21, 2008

Have you done anything on the needle yet? Perhaps it's still too rich...

robwbright · Aug 21, 2008

Needle clip is one from the top. I haven't fooled with it for awhile.

helio lucas · Aug 23, 2008

and if you check the ignition? the flywheel could be loose and make the engine vibrate...and by the way check also the engine mounts...

whenfoxforks-ruled · Aug 23, 2008

Where is the air screw set at? Never recall a jetting and vibration issue in the same sentence. Lean surge? What does the plug look like if you run it where its having issues?

AV8R · Aug 25, 2008

Drop the needle one more clip position.
That "vibration" is probably blubbering from being too rich.
Reeds are good, right?

robwbright · Aug 25, 2008

Over the weekend I went down with the needle clip (raised the needle two positions and the bike would hardly run at all. It would not idle.

I then raised the clip to the very top position and the bike was much crisper.

I went for a WOT run yesterday and it's still rough in a couple spots - I think I'm beginning to recognize "richness" - but I'm still a bit hesitant about jetting because I haven't really experienced "leanness".

Still having issues, though, and with the clip at the top position on the needle, I suppose I'll order the next leanest needle and go from there.

Thanks for the assistance.

FNG · Aug 28, 2008

Not sure how the off idle performance is but the pilot is 10% of the overall fuel @ WOT. I am down 2 sizes on my pilot and it is getting better but not the way I want it. From 1/8 throttle to WOT it is really good tough I plan on dropping the main 1 size as my plug is still dark.

Normally tha mains are 1-2 sizes rich from the factory, and some tuners will push it a little farther, but if you go too far you can run into an over-lean condition will sometimes mimic a rich, or over-fueled condition which leads the tuner to go leaner yet until SQUEAK! If your needle clip is on the top then your needle is too rich IMO.

It is hard to keyboard tune, but I think maybe a more detailed explanation of the bike and what is done to it would help us.

Maybe the vibration is a clue that the power valve isn't opening all the way, or slowly? I know when I bought my YZ 250 the valve hadn't been cleaned for years and it felt like a good running 125 then fell on its' face on the big end until I cleaned it.

Your troubles may not be in the carb.

Hopefully this helps.

SpDyKen · Aug 28, 2008

Checked your reeds, like AV8R asked, yet?

AV8R · Aug 28, 2008

I would tend to agree with FNG try droppong the pilot one size and see where you are at.
If your airscrew is one turn or less out and bike runs well off bottom then leave the pilot and a leaner needle may be the route you need to pursue.

robwbright · Aug 28, 2008

The reeds are not a problem If they were, I would have made note of it. They were inspected with no apparent flaws.

I changed the reeds not long ago and I had the entire top end apart rebuilding it a month ago. The problem has existed throughout - before and after the reed change AND before and after the top end.

The bike is an Eric Gorr 144 cc overbore, head compression for race gas. Mo betta porting.

Bills Pipe and silencer. No other mods to speak of.

I went to the Bill's Pipe site. I realize that since I have the 20 cc overbore, it could/would potentially throw off the jetting. . .

For what it's worth, their baseline recommendations have a 450-460 main, 30 pilot, stock needle.

I've currently got a 390 main, stock 32.5 pilot, stock needle. I've tried 390, 400, 410, 420, 430, 440, 450 and 460 mains (started with the stock 460 and went down).

Before even reading the above posts, I was beginning to wonder if I'm too rich on the pilot and perhaps the needle, while being too lean now on the main - I ran that idea by my father-in-law last night and he thought it would be worth a try.

Since the switch to the 390 main from a 410, the bike is crisp off the bottom, but has a really wierd flat spot in the mid/upper mid range where the bike has no acceleration for approx 1000 rpm and then starts pulling hard again.

whenfoxforks-ruled · Aug 28, 2008

Put it all back to stock fast! Usually, after the EG mod, it runs good on stock jets. From stock, try to adjust the air screw to its highest idle. Count how many turns out you are. Under 1, bigger pilot. Over 2, smaller pilot. Because this circuit over runs the main, it is a complete circle jerk doing it any other way? The needle clip position after adjustment, will tell you if you have the correct needle. At the top, get a leaner needle. Bottom position, get a richer needle. Then you have 2 ways of finding the correct main. Being able to feel it, or cut the plug. Follow these steps, and if it does not make sense, you have an issue you are missing. How is the muffler packing and timing? When was the last time you replaced the float valve? What kind of race fuel are you running? Does your slide show signs of wear?

FNG · Aug 28, 2008

Typically mod shops, as well as manufacturers will deliver "safe" jetting specs, sometimes too safe:)

I have been modifying, racing and riding snowmobiles for 25 years as well as 2 and 4 stroke 3 and 4 wheelers and just about anything that has an internal combustion engine.

Thanks for the rundown on the machine in question. With that said, I would be willing to bet a steak dinner and beers that you have gone too far on the mains and now are experiencing a lean/detonation condition with your motor. I have been there more than once myself.

The thing with dirtbikes is we usually don't run them WOT long enough to generate the internal temps to actually melt the piston but we can still experience the affects of a lean condition without major damage.

What fuel are you running? Altitude? air temps?

As for jetting I would start with 1 size leaner pilot than recommended by Bills, put the needle in the 2nd from top and try the 450 main. I think their 450-460 comment means they are not quite sure and are making sure to cover their behinds.

And lastly, what is the stock jetting for referance and how did it run before the mods and what jetting was in it before the mods?

robwbright · Aug 28, 2008

whenfoxforks-ruled said:
Put it all back to stock fast! Usually, after the EG mod, it runs good on stock jets. From stock, try to adjust the air screw to its highest idle. Count how many turns out you are. Under 1, bigger pilot. Over 2, smaller pilot. Because this circuit over runs the main, it is a complete circle jerk doing it any other way? The needle clip position after adjustment, will tell you if you have the correct needle. At the top, get a leaner needle. Bottom position, get a richer needle. Then you have 2 ways of finding the correct main. Being able to feel it, or cut the plug. Follow these steps, and if it does not make sense, you have an issue you are missing. How is the muffler packing and timing? When was the last time you replaced the float valve? What kind of race fuel are you running? Does your slide show signs of wear?

Dude, thanks for the help, but it was back to stock when I got the motor back 2 years ago. I ran it really rich for a year and a half and finally decided to try and fix the problem.

The plug is lite brown now - not as light as it should be, but not NEARLY as rich as it was.

Slide is brand new because the old one broke. float is fine. 110 octane mixed 50/50 with 93 or 94. Mobil 1 Racing 2T.

robwbright · Aug 28, 2008

FNG said:
Typically mod shops, as well as manufacturers will deliver "safe" jetting specs, sometimes too safe:)

I have been modifying, racing and riding snowmobiles for 25 years as well as 2 and 4 stroke 3 and 4 wheelers and just about anything that has an internal combustion engine.

Thanks for the rundown on the machine in question. With that said, I would be willing to bet a steak dinner and beers that you have gone too far on the mains and now are experiencing a lean/detonation condition with your motor. I have been there more than once myself.

The thing with dirtbikes is we usually don't run them WOT long enough to generate the internal temps to actually melt the piston but we can still experience the affects of a lean condition without major damage.

What fuel are you running? Altitude? air temps?

As for jetting I would start with 1 size leaner pilot than recommended by Bills, put the needle in the 2nd from top and try the 450 main. I think their 450-460 comment means they are not quite sure and are making sure to cover their behinds.

And lastly, what is the stock jetting for referance and how did it run before the mods and what jetting was in it before the mods?

Stock jetting before and after the mods. When I ran 460 main, the splooge covered the side panel by the silencer - completely black in an hour ride. Plug was black and wet.

440 to 430 reduced the splooge, but still dripping onto the swingarm and rear brake caliper.

410 cleaned up the excess splooge pretty good (not much in the way of droplets, but still black and wet in the end of the silencer) and the plug started getting lighter and "drier". Still not as light as it should be.

SpDyKen · Aug 28, 2008

robwbright said:
Stock jetting before and after the mods. When I ran 460 main, the splooge covered the side panel by the silencer - completely black in an hour ride. Plug was black and wet.

440 to 430 reduced the splooge, but still dripping onto the swingarm and rear brake caliper.

410 cleaned up the excess splooge pretty good (not much in the way of droplets, but still black and wet in the end of the silencer) and the plug started getting lighter and "drier". Still not as light as it should be.

If you indeed changed your main first, as it sounds here, you are working bass ackwards, and will be chasing your tail until you get tired. And frustrated, too.

WhenFoxForksRuled speaks the truth. Do not overlook the things he said to check. There are good reasons to work from the pilot to the needle, and then adjust the main last. Sure, you will have to clean up some extra spooge, and it is likely you'll have to repack your silencer, as well.

You'll get it right, though. :nod:

FNG · Aug 28, 2008

I am lost... Maybe a stuck dirty needle/seat?

On sleds they have water traps on the bottom of the bowls, well after many years the hose started to deteriorate and small pieces of rubber would infiltrate the seal on the needle/seat causing a progressively worsening rich condition that would go away with a carb clean. It took me a full season to figure this one out.

And with all due respect, did you put the piston on the right way? Odds are you would have hooked a ring by now but I have seen respected mod shops send motors out with pistons installed backwards. It happens......

Good luck.....

This is why I run my stuff "dialed in stock" now.

whenfoxforks-ruled · Aug 29, 2008

Rob, this stinks to high heaven of a bad float VALVE, and seat if its applicable. It may even seem to work properly, NOT! You had Eric do up the engine, and its his knowledge that I will tell you that the float valve should be replaced YEARLY! If that does not do it, you need to do a leak down test. That would be, something is not sealed properly in the bottom end. The right crank seal, base gasket, or case seal. Anytime someone has other issues, they start to believe jetting is difficult. Keep it simple, there is something else awry!

2strokerfun · Aug 29, 2008

And if you are jetting it and can't seem to get the needle right, don't be afraid to try another needle. I can't tell you how many times I've seen friends fight jetting, changing jet after jet after jet; oil/gas mix etc., but for some mysterious reason simply terrified to spend the $7 for a new needle to try and fix a midrange problem.

robwbright · Aug 29, 2008

FNG said:
I am lost... Maybe a stuck dirty needle/seat?

On sleds they have water traps on the bottom of the bowls, well after many years the hose started to deteriorate and small pieces of rubber would infiltrate the seal on the needle/seat causing a progressively worsening rich condition that would go away with a carb clean. It took me a full season to figure this one out.

And with all due respect, did you put the piston on the right way? Odds are you would have hooked a ring by now but I have seen respected mod shops send motors out with pistons installed backwards. It happens......

Good luck.....

This is why I run my stuff "dialed in stock" now.

The piston is in the right way.

robwbright · Aug 29, 2008

whenfoxforks-ruled said:
Rob, this stinks to high heaven of a bad float VALVE, and seat if its applicable. It may even seem to work properly, NOT! You had Eric do up the engine, and its his knowledge that I will tell you that the float valve should be replaced YEARLY! If that does not do it, you need to do a leak down test. That would be, something is not sealed properly in the bottom end. The right crank seal, base gasket, or case seal. Anytime someone has other issues, they start to believe jetting is difficult. Keep it simple, there is something else awry!

If it's in the bottom end, it's not getting fixed until Winter. . .

I have wondered about that, but I'm not taking on that project until riding is over for the season.

Never thought of the float "valve". By "float valve" do you simply mean the black thing that I call the "float"?

If so, I was thinking in terms of "if it's not stuck and leaking gas, then it's not a problem."

robwbright · Aug 29, 2008

SpDyKen said:
If you indeed changed your main first, as it sounds here, you are working bass ackwards, and will be chasing your tail until you get tired.

I changed the main first on the recommendation of a pro ATV racer who runs a 1986 250R motor bored and stroked to approx 320cc.

And the fact that before all the changes, the bike didn't run that bad - it was smooth on the bottom and quite rich in the mid and top. It just didn't have the "hit" that it should have.

Incidentally, with stock jetting, the thing ran like a scalded dog as soon as I got it back from Eric - rich but still smooth. Sometime thereafter, it lost the "snap". I had supposed it was ring and piston wear, but changing the ring last year didn't help and changing the piston and ring this year didn't help, either.

Thinking about it. . . would that imply a possible/probably bottom end seal issue?

FNG · Aug 29, 2008

robwbright said:
The piston is in the right way.

LOL!

The needle/seat is the pointed thing that is attached to the float pin. Sometimes they are rubber tipped, others are polished aluminum or steel. When you do replace it make sure to clean the seat if you do not replace it as well. A Q-tip and some mothers chrome polish does a great job of removing any varnish or other deposits in there.

Only other thought is to try the stock pipe. Maybe something isn't right internally with the new Bills.

whenfoxforks-ruled · Aug 30, 2008

Order parts 21 and 22, http://www.bikebandit.com/houseofmotorcycles/suzuki-motorcycle-rm125k2-2002/o/m6558, and the leak down kit will tell you if your bottom end is sealed, http://www.motionpro.com/motorcycle/tools/view/2-stroke_leak_down_tester/. And if anyone advises you to start monkeying with your main or needle first, you should know that they do not know what the heck they are talking about? It is real possible that when you remember when it changed how it ran, either the float valve started screwing up or the right crank seal took a crap? Even if you view the fuel shutting off, does not mean it is functioning correctly while you are riding. It wears and/or gets a build up, and causes unperceivable issues, and just needs to be replaced yearly. Did you always run the Bills pipe?

robwbright · Aug 30, 2008

FNG said:
LOL!

The needle/seat is the pointed thing that is attached to the float pin. Sometimes they are rubber tipped, others are polished aluminum or steel. When you do replace it make sure to clean the seat if you do not replace it as well. A Q-tip and some mothers chrome polish does a great job of removing any varnish or other deposits in there.

Only other thought is to try the stock pipe. Maybe something isn't right internally with the new Bills.

The Bills has been on the bike since I bought it in 2005.

WEIRD jetting problem - ideas?

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