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Max Power 285cc kit

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Finally got my bike put back together last week with a new Max Power 285 kit and went out yesterday for the first time.

I had ridden it up and down the street a couple times, but never past half throttle.

Yesterday we went out to our favorite spot in the dez. The bike seem to run pretty well at home, but in the dez when I started to let it rev out a little, it seemed to fall on its face pretty early and didn't have much of a punch. I was a little disappointed to say the least.

I started thinking about why it didn't want to rev and thought about I had put a new Hot Rods crank at the same time, but didn't check the timing. I marked the stator before I took, it off so I could put it back in the same place.

It didn't dawn on me at the time that the crank may not be indexed the same. Today I checked the timing and found I only have .002'' advance. I reset it to .007" and gave it a test ride in the street. Now it rips like I had hoped it would.

I have a Gnarly pipe and a Q-Stealth silencer and thought that may have been chocking it, but for now I'm going to ride it again, before changing the pipe. I like it quiet and I think it will be fine.

At this point, I think I'm going to be pretty happy with the Max Power 285 kit.

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Who did the motor work and curious, what's the cost? Any dyno numbers that mod?

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I did al the work myself except the cylinder and crank. Cylinder was $675 (cylinder need a repair), usually $599. Crank, bearings and seals were $230 I think, came as a kit. Also spent about $325 doing WR the 3-5 gear swap.

No idea on dyno numbers, but it hauls the mail. Faster than I'll be going for sure.

I have way more money in this bike than anyone would ever pay for it, but its works really well and I plan on riding it until one of us wears out..

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17 hours ago, Ron W said:

 

I have way more money in this bike than anyone would ever pay for it, but its works really well and I plan on riding it until one of us wears out.

We ALL do. 

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18 hours ago, Scott_72 said:

Did you change anything much with the jetting?

Right now I have the standard JD jeting with a #8 slide. The plug is on the grey side after Saturday in the dez, but I haven't done any wide open plug chops yet. Since the plug is showing lean, I raised the needle a notch for now.

Now that it's reving out, I'll check the main jet in the dez.

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Not sure what I was thinking, but I wanted to tap into Big Bore knowledge bank. Made better sense when I did it, than it does now. I do apologize.

I pasted my hack and the response below, hopefully my "hack" can be removed.

I appreciate the response to my issue. I too feel it's a jetting problem, but I think I kind of shot myself in the foot with the JD Jetting kit. Without knowing anything about the JD needles I don't know where to start with OEM needles. I will get the NECJ and NEDJ needles and other jets recommended and start from there.

I did install a new Hot Rods crank at the same time, so I'm safe for now. But for safety's sake I think I will have the squish opened up to .045". Can you recommend what "cc" I should have in the combustion chamber, for 91 octane?

I tried to do a compression check when I first put it together, but I'm not sure if my gauge is to cheap or I couldn't it kick it fast enough, but it only got up to about 180 psi. Didn't make sense given how hard it was to kick.

The power valve was cut and installed by Max Power and seemed to move properly on the bench. I installed the cylinder the way I received it from Max Power (except cleaning the bore of course).

 

Sorry, I don't mean to hi-jack this thread, but you guy's are talking about Big Bore YZ's and I'm having a problem with my Max Power 285. Maybe I can get some help?

I've had the bike out twice now. I reported in a previous thread I didn't verify the timing after installing a new Hot Rods crank and found the bike wouldn't rev. The plug looked a little grey so I raised the needle a notch and planned to do some wide open plug chops next time in the dez.

Turn's out the key-way on the new crank is not the same as the OEM and I had very little advance. After adding some advance (.007") per the manual, it felt much better in the street in front of my house.

However, yesterday in the dez, it has a flat spot in the mid range. Right when it feels like it should come on the pipe and pull, it goes flat momentarily and the rev's out.

I have the JD Jetting kit with the #8 slide. As a 250 it ran perfect, better than any bike I've ever owned. With the 285 kit installed, the only change I've made was to raise the needle as stated above.

One thing that still bothering me is that, I had asked Max Power to set the 285 up to run on 91 pump gas. In the instructions I received from Max Power, they were very adamant about checking the squish clearance before running the motor and if it was .035" or less call them. Mine came in at .036". When I called them they said not to worry, it will be fine? Just for safety sake I'm currently running a 50/50 mix of 91 and 100 race gas. BTW, I contacted Ron at R & B via email about re-cutting my head and he responded, he only does stock 250's.

Anyone have any idea's on what's going on here.

Thanks for any help.

 

 

 

Like you said, I don't wanna clutter up this build thread with off topic posts, but I will take a quick stab at your questions. RockerYZWR seems like a cool dude, so I don't think he will mind, but if you need to discuss it further, it might be better to start another thread, or post in the one you already started about your 285.

Anyways, first off I'm surprised that Max Power suggests going that tight on the squish clearance, but they would know better than I would. So if they say that it is safe to run it at .035" then its probably okay. My only concern/ suggestion would be to keep a very close eye on your big end bearing to make sure there is no UP/DOWN play, as you only have .89mm of clearance between your piston and head at TDC. I'm not sure, but I would be worried about the piston contacting the head if you let that big end bearing get too sloppy. Moving on, it is possible you would still be safe to run pump gas with that head, but it all depends on the volume of the dome. If they removed enough material from the dome, and your compression is not super high, pump gas will be fine. You can still have low compression AND tight squish. This is actually ideal IMO, it is my belief that your squish should be the same no matter what octane fuel you are running (then CC the dome accordingly). I personally would feel more comfortable with around .045" of squish clearance though, and this is what Ron at RB Designs recommends. I would recommend doing a compression test and see where you're at, and maybe ask Max Power what they set the volume to. 

Your flat spot in the mid range could just be a matter of dialing in the jetting. Typically, a big bore is going to require LEANER jetting, but this depends on how well your jetting was dialed before the BB mod. It might do you well to get yourself one of the Suzuki needles (NECJ or NEDJ) as they seem to be easier to fine tune. Without knowing your altitude, temp, etc I would suggest a starting point of NEDJ clip 3, #8 slide, 165 or 168 main, 45 pilot, and 1.5 turns on the AS ... You may have to go one or two steps leaner or richer on the main & pilot, but this should get you in the ball park. 

It also wouldn't hurt to make sure everything else is working properly, including checking the powervalves... IIRC, @Monk was chasing his tail on his YZ250, only to discover that the previous owner installed the PV upside down. Another guy on here recently discovered that his gov. spring was bent and not functioning properly... I'm guessing your problem is simply a jetting issue, but it never hurts to check over everything. Did you install the PV's yourself? If so, make sure to note whether the side valves were fully closed before you tighted the two small outside allen bolts on the PV rod. If they weren't closed this will throw off the timing, and PV issues can make the bike run very off. 

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44 minutes ago, Ron W said:

Not sure what I was thinking, but I wanted to tap into Big Bore knowledge bank. Made better sense when I did it, than it does now. I do apologize.

I pasted my hack and the response below, hopefully my "hack" can be removed.

I appreciate the response to my issue. I too feel it's a jetting problem, but I think I kind of shot myself in the foot with the JD Jetting kit. Without knowing anything about the JD needles I don't know where to start with OEM needles. I will get the NECJ and NEDJ needles and other jets recommended and start from there.

I did install a new Hot Rods crank at the same time, so I'm safe for now. But for safety's sake I think I will have the squish opened up to .045". Can you recommend what "cc" I should have in the combustion chamber, for 91 octane?

I tried to do a compression check when I first put it together, but I'm not sure if my gauge is to cheap or I couldn't it kick it fast enough, but it only got up to about 180 psi. Didn't make sense given how hard it was to kick.

The power valve was cut and installed by Max Power and seemed to move properly on the bench. I installed the cylinder the way I received it from Max Power (except cleaning the bore of course).

No problem man, I don't think Rocker is the kind of guy that would get upset about posting a question on his thread, but you'll probably get more responses if you keep it in here. 180 PSI compression might actually be accurate since you asked them to cut the head for pump gas. The YZ250X is around 165 - 180 from what I've seen posted on here. You might get a bit higher reading now that the rings are seated if you checked it before breaking it in. 180 - 200 PSI compression should actually work pretty well with the big bore kit, and it should be safe to run on pump gas despite the tight squish clearance. I wouldn't blame you for taking the squish up to .045 if you can find someone to do it for you, but it should be safe to run for now. 

Your PV's should be fine if they were installed by Max Power. I think you'll be happy with the Suzuki needle, and I'm guessing it will solve the issues you're having. Jetting on a big bore can be a bit finicky (especially if it wasn't jetting perfectly before you bored it), but the NEDJ will be easier to dial in. Remember, my recommendation on the jetting is just a starting point, so you'll want to get a few sizes bigger and smaller so you can adjust if need be. 

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Thanks again Chevy_97.

I just had a friend lend a hand and re-checked the compression. Got just a little over 200 psi (throttle wide open/PV closed). I have maybe 3 hrs on the motor now.

I ordered the NECJ and NEDJ needles, the 165 -168 main jets and the 45 pilot you suggested. I think it has a 172 in it now. I did the compression test tonight got lazy and decided I pull the carb tomorrow to verify the jet sizes (aside from the JD needles).

As a 250 with the JD jetting kit, it ran really good with a nice tan colored plug. I went ahead and bought a #8 slide, just because of all the good things I've read about it. I have to say the #8 slide made my bike seem almost electric. It completely eliminated the off idle 1/8th throttle stumble. With my Rekluse Z-start Pro it was near perfect.

BTW, I ride in the SoCal high desert around 4500 - 5000 ft. elevation.

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Just a follow up.

Today I installed a NEDJ needle #3 clip, 165 main jet, 45 pilot jet, air screw set at 2 turns out.

Testing in the street in front of my house (600 ft elevation) the bike runs awesome. Pulls clean from idle, no flat spots or hesitation, throttle response is instant.

I'm not much of a WFO rider (never was) so I'm thinking when I get up in the desert around 4500 ft elevation this time of year it should be fine.

I'll be checking the plug color in the dez, my neighbors have heard enough for today.

Thanks to Chevy_97 for helping with the jetting spec's.

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Had my bike in the dez again yesterday. Tested with a NEDJ needle in the 3rd clip, 45 pilot and 165 main jet.

The bike ran pretty good, but when tuning the air screw, I was out a little more than 2-1/2 turns, so I'm going to try a 42 pilot.

I checked the plug after a short ride and I think the plug is still a little light.

I didn't want to do any wide open plug chops until I put in a larger main jet, maybe a 172 and work my way down from there.

Getting close. BTW, riding at about 4500 ft elevation

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Still have a jetting issue. Bike runs pretty well, a bit rich still I think.

The question I have is when I'm accelerating, the motor pulls cleanly. But if I back off and then roll it back on again, I have flat like hesitation, before it starts to pull again. Not a bog just a no response feeling.

Is this a mid throttle or wide open throttle condition? I'm assuming it's lean causing this, but not sure.

I'm running a NEDJ #2, 165 main, 42 pilot 1.5 out on the air screw.

Thanks for any help.

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