no bottom end power

[Jprunck1]

I have a 2002 yz250 with FMF SST pipe, shorty silencer, V-force 3, 13 teeth (front), 52 teeth (rear) and i believe stock jetting (needle at 4th pos., or second highest pos.) I rebuilt top and bottom about 50 hrs ago.

I was a the track (Piru MX) today and found myself having a hard time getting enough speed out of the turns to clear the jumps. There is a lot to improve on my suspension and my cornering, but my bike doesnt rip until i get the rmps way up there. And when it hits (which is hard to predict), it hits hard. Most of the time the power really isnt usable for me. Should i just work on the high rpms and fanning the clutch out of the turns? Or anything that i could change on the bike, like go to a fatty or gnarly pipe?

I had a friend do a couple laps on it, and he came back and told me that his yz125 (2005 w/ 150 bore) hits way harder, and your got no bottom end power. Is this a common thing for the yz250s or 250s in general?

Also, i find myself riding mostly at gorman (3000-8000 feet) and Piru (i think 2000 ft.), any jetting suggestions for those altitudes. I just put the V-Force 3 in and did not re-jet.

Any suggestions for me? thanks

[B_Rad]

I have an 02 Cr250 and have both the SST (on the bike now) and the Gold Series Fatty. I also run the V Force 3.
In my circumstances I would have to say its the pipe. I did a complete top and bottom rebuild along with alot of extra bits and the pipe change was the most noticeable. Bottom is lacking and it hits really hard. It's fine in the range I need to do what I do, but small jumps (say 15-35ft) I find really hard. If I try to come in slow and power at the right distance to make the gap, I get a real hard hit mid ramp and tend to end up nose up beyond the point of saving with a rear brake tap.
I solved it by chopping at the throttle just in ban and giving the last squirt just before the lip to save nosing down or falling short.
It takes some time getting used to finding that right rev range but when you sort it you'll be sweet.
If your not getting enough squirt, then just get on the gas a little harder out of the burm. If you find your nosing up from the hard hit several times in a row, just maybe lean over the nose a little more than usual to balance it out

[Jprunck1]

B-Rad - ok, ill give that a try next time i get out, but the bike does not want to deliver any power out of a turn / burm, making it hard to get the the rpms up before the jump. You said that its probably the pipe, whats your opinion between the fatty and sst? You said that the SST makes it difficult to do the smaller jumps right out of a turn. Thats my problem, cause there will typically be a bigger jump right after the smaller one (which i gained no speed over and my body ends up taking a beating). Anyone who has a yz250?

Anyone think that adding weight to the flywheel might help this problem?

[dklassen]

I have a 2005 YZ250 and it does have good low end. My previous bike was a 2003 CR250 similar to B-Rad's bike and that model didn't have a lot of bottom end hit. You are already running a higher tooth rear sprocket so the bike should have more bottom end. At 50 hrs on the top end, you should rebuild it. It could be that it's lacking compression. Another issue might be the power valve govenor spring. This is located inside the clutch housing. Not the the clutch cover but the right side case cover. If the spring is worn, the power valve doesn't engage soon enough so you'll lose the bottom end hit. My bike is getting a complete rebuild (top and bottom) at the moment and I'll be replacing the spring as they do tend to go over time.

[AV8R]

I would guess that your problem is jetting, and the sst pipe. That pipe requires rich jetting just to stay away from detonation. Jetting too rich on the pilot and needle is what your symptoms sound like to me. Especially at the altitudes you listed. Before attempting jetting use a clean air filter and make sure the float level is set correctly.
Do you have spooge out the silencer? Is the plug dark brown instead of tan?
Start by getting the next size smaller pilot. Then get it idleing well using the air screw and fine tune it until the engine transitions smoothly from low rpms to mid range. Then start moving the needle clip up one notch at a time until it accelerates crisply from mid range to high rpms. Once the engine accelerates smoothly and crisply from idle all the way up to the over rev you got the jetting right. Keep in mind that you will always have to fine tune it for varying temps and altitudes. This can usually be done with the air screw.

[Beatty]

If this just recently happend it also could be your reeds. My RM 250 lost all bottom end power and when I took the reed manifold off one of the reeds had a chip in it. So you could have damaged reeds or some crap stuck in them.

[Jprunck1]

Thanks for your input. AV8R - When you say "detonation"... are you referring to premature combustion explosion do to the high temps?

Heres my shmeal with jetting. I do have spog coming off the end of the silencer, between silencer and pipe as well as pipe and cylinder. I use high temp silicone to seal the cylinder to pipe spong (I can tell a large improvement in power when it is sealed). I might get 2-4 inches of oil dripping down the bottom of the silencer. (More so when im in higher alt.) I thought spong was a normal thing for 2 strokes. Am i wrong? Mixing 40:1 yamalube 4R (By the way.. i think they changed their formula.. the new bottle seems to have lower viscosity... it seems thinner. maybe im wrong)

I have a yz125 manual (not 250) it says to have fuel level to 11.5 -12.5. Does that sound about right? I assume that F.L. is that same as float level. I found a good forum by Faded for that one. ( How To Set Your Motorcycle Carburetor Float Level (more commentary). )

My plug - Ive been watching my plug a little bit. Not all proper plug readings. With clip in highest position w/ stock reeds @ 4000 ft ... plug was tan with white on the edges. It was still bogging on the bottom end, i checked plug after doing a 3/4 throttle hill climb. i noticed white smoke coming out the pipe! Not good, so i took it easy the rest of the day. Next time I lowered the clip back down to groove 2. I did a proper reading at about 3000 ft. with a new plug. I did 5-6 laps, and then went full throttle in the parking lot... plug seemed very clean. Could not see much on it. The tip looked healthy tan/brown. Last week was the first time ive ever fouled a plug. It was from warming up the bike with the pilot screw all the way in (I forgot i was messing with it. The screw would not go more than one turn out, but i fixed that and set it at 2-2.25 out. I have not checked the plug after that but noticed a noticeable improvement on the bottom end. A little crisper.)

Im not sure what size pilot ive got. I would assume that its would be stamped on the side when i take it out?

Thanks for your input guys! It might be 2 weeks till i get to try a new pilot. But it seems like a very reasonable start, especially if ive got my pilot screw all the way out.

[yathump]

Spooge is not a normal 2t thing, once you get the jetting dialed in, the Yamalube 4R that you mentioned did they change that from the previous 2R premix, i've only seen the 2R and 2S that Yamaha made for premix's. If your getting that far out on the pilot i'd definitely go for the next leaner, if its still stock it has a 50 pilot so going to a 48 will make a big improvement

Giving the overall mechanical condition of the motor, jetting for your Temperature/elevation and riding style will make a noticeable improvement on how the bike preforms

[Jprunck1]

yeas sorry.. 2R. Im definitely going to be doing a pilot swap sometime this week. Thanks guys.

[dklassen]

I hope things work out for you. If the jetting doesn't clear this up try the Power Valve spring. The part is cheap but getting to it is a little complicated because you have to take the water pump off in order to take the side cover off. The problem you describe sounds exactly like a bad spring.

[Jprunck1]

Yea i am planning on changeing the spring also. I figured see what I get from chaging the pilot. Also, yes i have lost some conpression. Do think putting new rings in would do? or would you think a whole new top end? Next time i change oil ill openup that side of the case. When i rebuilt my bottom end, i didnt touch the water pump cause i didnt have to. How does the spring wear out? Does it gets grooves from the shaft? or it looses its spring coefficent? Also, Do you think i would be able to reuse the case gasket? I guess i would if it starts leaking ? haha

[dklassen]

From what I understand the spring becomes worn out and doen't engage the power valve progressively. The power valve just slams open instead of opening slowly when the revs build up. I have my 05 YZ250 apart right now for a new crank and I had to take off the impeller to take off the right side cover. My opinion on whether to change just the rings or the whole top end is this. If you have more than 20 hours on it, just put a new piston in too. You can buy a Yamaha top end including pin, and bearings off ebay for $75 right now. If you're going to the work of taking the cylinder off you might as well throw in a new piston. I had to re-use a side case gasket in a pinch once and it worked with a little silicone but I wouldn't do it if it wasn't neccessary. Keep us posted.

[Jprunck1]

Hey, im back. I got to swap out the #50 pilot to a #48 pilot. Also my main is 178 with a needle N3EJ. on the 2nd clip. So i got to ride this past weekend in santa barabra (4000-5000ft i would guess) with the 48 pilot. I set it to 1.25 out and didnt play around with it. I noticed a slight improvement to my throttle response. When i first started riding, i noticed that my front wheel wanted to come off the ground a little more. . But it could have been the grip on the fireroad, not sure. The wheel stopped lifting up as the altitude increased. Also, i noticed that power band was not out of control. I would say the drop in pilot leveled my power out. I took some pictures of the spoog on the silencer tip and silencer/pipe connector. There is definitly less spoog than before. Can anyone tell me if this is not normal. Should i try a 175 main or try i different needle?

[AV8R]

Thanks for your input. AV8R - When you say "detonation"... are you referring to premature combustion explosion do to the high temps?

Sorry I didn't get back to you sooner on this, I must have missed the e-mail notification.
Detonation is the fuel exploding rather than burning. Pre-ignition is the fuel burning prior to the spark from the plug. Detonation can cause hot spots in the combustion chamber and lead to pre-ignition. Detonation can be caused by many things but running too hot or lean is one of them. I read an article in which the author belived that the SST pipe provided too much refection back to the cylinder and this caused excessive piston crown temps which lead to detonation problems when properly jetted. I tend to believe him because I had detonation problems with my SST pipe.
You can have detonation without pre-ignition. Of the two detonation is better tolerated by the engine, but neither is good for the engine.

The spooge in the pictures I would consider unacceptable if it were my bike. My YZ250 is a 2000 so same engine with maybe small differences. I have a stock 05 pipe with a radvalve (which requires leaner jetting) and an adjusted squish to .050". I run at 3500 feet with a 165 main an N3EW needle on second clip position and a 45 pilot. This is for temps from 50 degrees f to 35 degrees f.
Looking at your jet numbers I would try a 45 pilot. The nice thing about the pilot is that there is no real penalty for too lean other than a low end bog. If that happens then you know that you need the next size larger.
I would also try a main around 175 or172. Unless you plan on going lower in altitude or riding WOT for long periods like in the dessert.
Your needle sounds like it might work on second clip after dropping the pilot jet size but you may also need to move it to the top position if it doesn't run cleanly in the second slot.
Always work from pilot to needle to main and change only one thing at a time.
Otherwise you end up not knowing what is causing the bog or drool on the pipe.
Put tape on the throttle housing and then mark 0,1/4, 1/2, 3/4 and full throttle on the housing and then mark the throttle grip next to the housing with a line as a reference point so that you can test the throttle in the appropriate positions for each jet.
When jetted right for your riding style you should be able to achieve a spooge free pipe. As your style or speed changes you may need to change the jetting accordingly.

i noticed white smoke coming out the pipe! Not good,

The white smoke coming from your pipe was probably old spooge burning off.

[yathump]

Originally Posted by Jprunck1

Hey, im back. I got to swap out the #50 pilot to a #48 pilot. Also my main is 178 with a needle N3EJ. on the 2nd clip. So i got to ride this past weekend in santa barabra (4000-5000ft i would guess) with the 48 pilot. I set it to 1.25 out and didnt play around with it. I noticed a slight improvement to my throttle response. When i first started riding, i noticed that my front wheel wanted to come off the ground a little more. . But it could have been the grip on the fireroad, not sure. The wheel stopped lifting up as the altitude increased. Also, i noticed that power band was not out of control. I would say the drop in pilot leveled my power out. I took some pictures of the spoog on the silencer tip and silencer/pipe connector. There is definitly less spoog than before. Can anyone tell me if this is not normal. Should i try a 175 main or try i different needle?

If you haven't cleaned out the pipe and changed the silencer packing you'll still get the residual oil that is in the pipe and soaked packing coming out. You could easily go another step leaner on the pilot with no worries, then start playing with the clip positions and needles

[Ford]

Hey all, was just wondering if the next time you are playing with the needles and jet screw if you could also have a look see if there might be a small hairlione crack in the rubber intake or even a small hole. This would make for bottom end and erratic rpm problems too. Its something to consider if you have run through all the needles and combos and it doesnt quite fix the problem. Also when you rebuilt the top end you didnt happen to swap the power valves around did you? They have to go back in the same side they came out or you will loose the bottom end and powerband too. Something extra to consider if re jetting doesnt work out for you.

Goodluck!
Ford

[Jprunck1]

Update....
I took my suspension to get revalved, should get them back this week. I also ordered that governor spring, #45 pilot, and a 175 main. Ill change the jetting, but not sure if im going to change the spring. I figured one reason my i had no power..... see anything wrong here?


lol...

I took my cylinder off to change my top end then i checked the power valves. I put the bolts back and the seem to be working. I guess i will put a little red thread lock with the blue. So im going to put a new topend. My piston looks ok, just wear on the sides. NO carbon build up on the cylinder head or piston crown. Does that mean anything?

Is this normal wear for a cylinder? I assume that it is ok to hone the cylinder with medium stones... or should i use fine stones too? Any tips for honing? use a drill press? or hand drill? Keep honing till the wear marks go away? My cylinder got replated last time, i did not get a new sleeve put in. Im assuming its ok to hone a replated cylinder.





my piston has the same wear and they are all on the intake and exhaust ports/side.

[dklassen]

I'm glad to see that you traced the source of the problem. I thought it was powervalve related from what you described. The cylinder can be honed but take it to a reputable shop. My local Honda dealer has honed all kinds of plated cylinders and I trust their work. I have used cylinders similar to what you have posted with good success. The biggest issue is the depth of the grooving. Make sure that you can't feel the grooves with your fingers. If it's smooth you'll be fine. Also use some anti-seize on all the power-valve bolts and torque them properly. I have a cylinder with a bolt seized and the allen head stripped out. Not fun!

[AV8R]

That scraping on the cylinder looks a little harsh. Probably it's from the powervalve not opening at all.
I use a ball hone on my cylinder with good results. I believe the brush hone is the best for plated cylinders to avoid chipping the nikasil at the port openings. I would try cleaning it with scotchbrite pad first and see if it is just deposits.