QT50 or QT60 mods

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QT50 or QT60 mods

Postby mholmes137 » Thu Apr 20, 2006 11:42 pm

It's finally been nice out in MN now and I've had my QT 60 out a few times but I can't stop thinking bout more performance for them. I just went through all the old posts from xrongor and tumbleweed and anything else I could find, but I was wondering what you guys have going on now.
YT60 cylinder bored out .50 mm
K&N filter straight off the carb
Boysen Power reeds for a PW50
Jetted to match (don't remember what I ended up at, it's a little bit rich by my standards, but I race snowmobiles with 114 octane and I like my plugs on the verge of white)
I've probably got other little things done, but I can't think of them right now.

Next on my list of mods is to hog out the intake around the reeds. WIth the Boysen reeds you can remove the center plastic piece and actually hog out a little more for more intake flow. I'm going to try to shine up the whole intake side of the engine too.
I'm also watching PW gears on ebay. They're on my list of parts to try, but I've got to drive up a big hill so I don't want to loose my low end. I'm going to give them a try, but I know I need more power if I want those to work.
I'm thinking bout bumping the compression up more too. I've checked compression with PW50 head and YT60 head on the 60 cylinder, I got the most with the 60 head (like 144 psi) and I know it can handle more compression than that with premium gas. I'm thinking maybe take enough off the head to get it to 155ish. What's the highest compression anyone out there's got with premium gas?
The biggest gains could be made with exhaust, and I'm trying to work something up for that, it's just going to be a biogger project because I've got to make sure to do it right....I've got access to a book on 2 stroke pipe building and the formulas and I'd really like to do that, but that's a huge ammount of time. I'm not exactly sure what RPM I'd want to build the pipe for either, I want top-end, but then again most of my driving would benefit the most from low to mid....I keep thinking about finding a decent pipe for something with close to the same bore and stroke, but havn't put the time into that yet either... Then I'd still have to put time into cutting and welding it to fit too....and ideally port timing and everything plays into that too....I guess I've still got a lot of pondering to do, but I was wondering what else guys were up to with QT mods....By the time I'm finally done I'm going to be looking for disc brake mod.....

Oh and there's a pic of my ped. It's a metallic red paint from some Mazada. I've got a buddy that works in a body shop and that color looked pretty good so we went for it...
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re: QT50 or QT60 mods

Postby TowerTower » Fri Apr 21, 2006 9:31 am

By inserting a thicker gasket (aluminum) between the cylinder and crankcase, you can increase the port timing of the engine (like putting in a higher lift/duration cam on a 4-stroke). 1 mm extra height is the equivalent of 5-6o exhaust and 7-8o transfer port timing. Shave the cylinder top and head to bring back the compression, something you planned to do anyway. You will definitely need a new pipe to take advantage of the extra port timing.
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re: QT50 or QT60 mods

Postby xrongor » Fri Apr 21, 2006 2:07 pm

ive got stock carb with a 70 jet needle in middle position, stock exhaust, many holes in the airbox, brand spanking factory new YT60 top end with stock QT head (compression is 155 psi after about 250 miles running 32:1 penzoil 2 stroke for break in), and 41:8 gears (5.125:1 which is between QT and PW). i tried midgrade octane and it slightly hurt performance so next tank im back to plain old cheapo gas which will also be my first synthetic 2 stroke and switching to synth has always increased performance in the past with QT's.

its running very slightly lean right now (nowhere near dangerous) but when i switch to 50:1 and run synth that should take care of it.

because of the QT clutch design takeoff is still slow slow, but once i get the clutch engaged at around 10-12 mph i can beat guys with 5 speed - 4 stroke 90's on the flats until i hit about 35-38. i just run along side it and push it up to 10mph if im racing... downhill ive topped it at 47. with the stock exhaust it still sounds like a kitten. with synth and a helpful wind i bet i can hit 50.

without modifying the clutch, i think getting anything resembling decent 0-10mph acceleration is impossible. If you wanted to go full monty, you should remove some weight from the bell housing and re-balance it, and get some pw racing springs.

if you want to go fuller monty, i think the next step is a full YT or YF bottom end with its stiffer clutch. unfortunately you cant just swap clutches. YT is wider and wont fit and i dont think its simple to work around. but supposedly the motor is a bolt in swap.

im still running 10-30 oil in the transmission but next change im going to try ATF in it as PW guys claim it gives better takeoff.

imho you need to get PW gears before you do anything else. after that you will likely rethink going much further with a QT unless you only plan on using it at the track. at these speeds i am seriously considering having my wheels/tires professionally balanced/trued. my QT60 as described climbs much hills better than a stock QT50 with stock gears and i even accelerate up smaller hills. i ride in montana mountains on dirt/gravel roads and i havent had to walk it up anything yet although some steeper hills will slow me to 23-24. easily does 35 on the flats with no wind. rode it home couple days ago into a 20-30mph headwind and still kept it around 31-32. that would have brought my stock QT down to the low 20's.

tumbleweed has a real PW gear (4.82:1) at his house and should be posting soon about its performance. his bike is closer to yours than mine. reeds, K&N filter, gutted his exhaust, etc.. im very excited to see what he has to say. i suspect he will top out higher, but i bet i have better midrange since he gutted the exhaust.

also im running a BP6HS right now but i think a BP7 would be slightly better. im holding off on fine tuning it until i switch to synthetic and the 50:1 mix that will go with it.

i know i could get better performance, but including a brand new cylinder, new tires/tubes, and several misc parts i still have less than 300 in mine after selling my stock QT gear on ebay. imho taking it further would cost significant amounts of money.

yeah baby welcome to the QT60 club hehe.

please post some performance numbers on your bike for comparison. i have a cateye bike computer thats calibrated as close as it can be so my numbers are accurate.

randy
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re: QT50 or QT60 mods

Postby xrongor » Fri Apr 21, 2006 2:08 pm

ps, what tires are those? are they knobby?

one other thing, it took 150-200 miles for the rings to decently seat. performance and compression slowly increased until its hit its peak and is much better than when it had only 50 miles on it.

and definitely, if someone finds an easy way to get a rear disc, please post it!!!

randy
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re: QT50 or QT60 mods

Postby tumbleweed » Fri Apr 21, 2006 2:56 pm

im running a stock qt-50 head with 175 lbs compression and good gas with no problems,i had a shaved 50 head and it gave me 255#but i was scared it would blow up but it was FAST!!!ps i run pure synthetic in both mine 1 is stock except the 60 cylinder i has reeds and k&n etc.the stocker has more tourqe but allways has,the more modified 1 is a top end screamer.
working on the fastest 2 qt60's
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re: QT50 or QT60 mods

Postby mholmes137 » Fri Apr 21, 2006 3:15 pm

Yup those are knobbies. Not exactly DOT legal, but I figure of I ever get pulled over, looking for a DOT approval on the tires is the last thing that they'll do anyways....I think they're Chen Shin tires. If you're really interested, I can go look and get you the model and everything. I just went through the Parts Unlimited Dirt catalog and looked for a set with the right rim size that had some harder terrain knobbies so it still handles pavement well. I also looked for the closest to stock size I could find. They are a bit bigger though, both fenders have custom mounts and cutouts to clear the tires. Do yourself a favor and just buy some flat aluminum (like in the picture) and make new ones. I spent hours trying to bend and stretch and modify the stock ones to keep the stock appearance. I had a few sets of extra mounts anyways from some ebay auction parts lots, so I was just out the time and some random extra spare parts. Making new ones with aluminum was really easy if you just follow the design of stock and chop away some plastic like I did on mine. For the rear, it's a just a spacer to raise the front of the rear fender. The rear rear fender mount can stay stock. It's tight but it works. I can get you more and better pics if you want. I'd post more pics on the thread, but I don't have the software to change file size easily and all my pics are like 311KB.

I've actually got the PW race springs in the clutch, I forgot to list that mod. Makes a HUGE difference in low end. I had them both on the 50 and 62+ cc motors and I'd never go back to stock. It just makes it rev higher before the clutch grabs and you start moving, so it just puts you at a higher RPM to start. I never thought about how that would probably take some away on top-end because the motors got to work harder against the springs. I guess someone could set up a test if they were really that interested. I doubt it would be much of a loss, but it could be some. I'd never go back to stock just because I like the grunt out of the whole, if I wanted to push off the line, I would have bought a real moped with pedals...wait my QT was free, but either way I don't like to push....

I've actually got a whole YT motor too. I bought it for the top-end (big bore kit). I think the owner said the bottom end wasn't too great (he had to have the cylinder overbored so the engine had some sort of issues) but I never really checked it out too much. I think I did notice some broken bits in the clutch though because I was going to steal that side cover off of it because it was already painted black (I've kind of been going to the paint everything black look) so I'll have to see what I could possibly steal from there for the QT. If nothing else I'll just look at sizing and if it would fit and then see how much new parts from Yamaha would be....

I'm not exactly sure how many miles I've got on the new cylinder. It's over 50 but I don't think I'm to 300 yet....
I'm just running whatever stock is for spark plugs. I bought a box of them too, so hopefully I don't need to switch to a different plug....
I don't have any good performance numbers to post. I havn't rigged up my bicycle speedo on it yet, so all I can say is that I've burried the needle to what look to be approximately 37-38 on close to flat (possibly slightly downhill) with a decent (15-20 mph?) tail wind. Going the opposite way on that into the wind I was pullin 27-28. I go up a good sized hill on my daily commute with it and I pull 26ish up it once I hit full speed (I don't get much of a run at it if any).
I've got lots of ideas that I want to try, but I know that what it really needs is an exhaust, it's just going to be the hardest thing to do right, and I don't really want to spend time and money doing it any other way. I've got 2 more weeks of college and then I'll have a lot more time and I'll be able to actually go spend some days in the garage. I'll try to get more pics and info and testing info for eveyone when I do it. So far eveything is seat of pants feel and how far I bury that needle on the lil speedo. Oh yeah and the speedo is off because of my bigger tires. My #'s shouldn't compare exactly to yours because my front tire was big enough to require full custom fender mounts which means I'm going faster than it says I am.
Now I only need to find a way to mount a disc brake (well actually two disc brakes), have Fox build me a custom rear shock, Ohlins build me a custom front fork, and add gears to it......
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re: QT50 or QT60 mods

Postby xrongor » Fri Apr 21, 2006 8:09 pm

if you're running stock plugs for a QT, thats a bp4hs, i'd switch to at least a 6 which is stock for the YT. in any case, just read the plug. it will tell you if its too hot (read it on the ground strap not the porcelin)

i never tried the 60 with a stock gear. it was such an ordeal i already had the new gear on the bike waiting for the cylinder. now i have another perfectly good bike in pieces that i just painted so im in no hurry to swap the stock on on just to compare. but based on what tumbleweed has posted and what we've talked about in email i think the gear is the ticket. youll get all the speed without fear of winding it out too far. then when you do wind it you're well into the 40's hehe.

if you work out an exhaust definitely post pics and instructions. i'd like an exhaust that showed off the 'free' side of the rear wheel. instead they just ran the stock pipe next to it and it doesnt look cool.

randy
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re: QT50 or QT60 mods

Postby dustin » Fri Apr 21, 2006 10:38 pm

hey, just wanted to know how to get a kit for a yamahopper, like who makes then, and how big
slow cooked hobo mum mum mu thats good eating
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re: QT50 or QT60 mods

Postby xrongor » Sat Apr 22, 2006 1:02 am

here's a rough draft of everything i have to offer in regards to the QT. sometime ill finish it and have it posted in moped repair section.

After having gone through a couple QT's I thought I would share what I have learned and try and compile all this information in one locaton.

The service manual for this bike is available here:
http://www.mopedriders.org/article_cat.php?fldAuto=2

This guide will assume you have basic technical competence and will not cover such basic procedures as cleaning/tuning the carb or replacing the air filter. Personally I have stripped mine down to the frame and the engine, regreased everything, blue locktited all the nuts and bolts, and basically given it the love it needs to run virtually maintenance free for years. You should do these things of course but there is already information out there and these things should be done to any used bike. I am trying to stick to things specific to the QT.

BUYING PARTS: I see all sorts of parts for these things on ebay at up to 10 times the price you can get them for at the Yamaha dealer. Before buying any parts on ebay, check the dealer first. Almost every part is still available and at 1980's prices. If you are making a large order I have found www.motogrid.com has the lowest prices and you can use their online fiche to check prices. For small orders i just pay an extra 10 cents on the dollar and let Yamaha pay the shipping. If you are going the 60cc route I would just make one large order from motogrid.

The dealer has another use. Most dealers will order from Tucker Rocky catalogs and pay the shipping so you can get the same prices you see online without paying shipping. There are a few items in particular. Kenda 14x2.25 tires (about 12 bucks each), EBC brakepads. (about 10 bucks a pair), NGK spark plug wire splice (6$, since the wire is attached to the coil and the wire is probably worn, this is the best solution i have found). Your dealer should be able to order cables for between 10-15$ each. Some of them are out of stock from yamaha but motion pro has some. Your dealer probably has catalogs that have these items.

AIRBOX: The stock airbox is too restrictive. The best solution I have found is to drill holes on the sides of the airbox because I have noticed after riding in the mud that it splashes up everywhere else but the sides are almost mud free. If you have the stock side covers this is less of a problem, but drilling on the sides gives you plenty of clearance between the airbox and the cover to allow good airflow. The stock QT comes with a 70 jet which is too big if you dont drill the airbox, and about right if you do.

You should also pin the side covers to the airbox so they dont fall off. I have explained this procedure here:
http://www.mopedriders.org/viewtopic.php?t=5530


--MUFFLER: The muffler is probably clogged. They seem to clog easy. The easiest way to deal with this is to throw it in a fire for an hour or two and just burn it out. Then clean it off, lightly sand it, and paint it with some stove black paint. While you are at it check the exhaust port for carbon. If its bad, you should probably pull the top end, clean it, and rering/hone/bore as necessary. If you follow the 60cc path at the end of this document you will be doing this anyway.

--GAS and OIL: You should premix your gas and oil for much better performance. I use Amsoil Intercepter at 50:1 but I'm sure any of the synthetics would be fine. Since you no longer need the oil pump, you should pull it out and remove the gear from the end of it, and re-install it. This prevents any problems with the oil pump seizing or dragging from lack of oil and gives you a teeny bit more power to the wheel. In doing this you get an extra benefit.

The oil tank capacity is .2 gallons. Now that you aren't putting oil in it, why not use it for gas. .2 gallons doesnt sound like much, but the stock tank capacity is only .6 gallons. So its a 33% improvement. First disconnect the oil sensor. You need it to plug the hole in the gas tank, but I dont like the idea of power going to that sensor while its sitting in gas. If you want to chance it, go ahead. Next, head down to the auto parts store and buy a fuel filter, 2-3 feet of 1/4” gas line, a T, a fuel shutoff valve, and about 9 clamps for the 1/4” hose. About 10 bucks.

First, you want to use the T to run a line from the bottom of the oil tank into the gas line. Just rip out the existing gas line and replace it all while you are doing this. Then put the shutoff valve in the line from the oil tank before it hits the T. Put the fuel filter after the T so it filters both tanks.

When you fill the tank like this you can just fill the gas tank and it will slowly fill the oil tank as it goes through the T. But I've found it takes a while so usually i just pop both caps and fill the oil tank first, then the gas tank. Once both tanks are full, you can shut the valve off to the oil tank and you have a nice .2 gallon reserve tank. If you do this, I would open the valve once in a while and run that gas through so it doesn't get old.

I consider this a 'Must do' upgrade because the fuel line probably already needs replacing, the oil pump sucks, and although it may not seem like much, it's still 33% more capacity than stock.

FORKS: When you take the forks apart to grease them, You will see that there is a rubber 'bullet' in one of the forks. This prevents the forks from bottoming out. If you can get some bent forks somehow you can get a second bullet to put in the other fork for extra damping when you hit a nice pothole.

60CC UPGRADE: Ok this is the one you have all been waiting for. If you do this right it will cost you very little.

The cylinder off a YT60 (1984-5) or YF 60 (1986) will bolt right on your QT. You can get them used and bore them, but motogrid has them for 120$ brand spanking new. You can reuse parts, but they are all cheap so lets just do the entire top end and be done with it. You need to order all of the following parts to pull this upgrade off.

YT60 parts: Cylinder, Piston, Piston Rings, Wrist Pin, Piston Bearing, 2 piston clips, head gasket, cylinder base gasket.

QT50 parts: exhaust gasket. This may not be necessary, but its cheap and you are already paying shipping on everything else. If you have any other parts you need now is a good time to order them from motogrid instead of your local dealer.

You use the stock QT head. This will increase compression and you will want to get a BP6HS or maybe even a BP7HS plug (colder plug, stock is a BP4HS) to avoid engine damage. Plug chops will tell you what plug you will need.

Once you get all this on, the stock gearing will not be able to take advantage of all this power. What you need to do is find a PW50 ring and pinion gear for the rear end on ebay. I have seen these go for as little as 10 bucks including shipping for just the gears, and you see full rear ends for 35ish shipped all the time. This gear has a 4.82:1 gear ratio vs a 5.7:1 stock gear ratio and will give you more top end, and lower rpm's all through the range. Stock the QT somewhat struggles with this gear, but with the increased displacement and compression of the new top end, you can cruise at an honest 35 and ive hit 47 with mine. The PW gears use a longer axle than the QT so you have to take the ring gears to a machine shop with a press and have them swapped. You MUST switch the pinion gear in your rear end. I have found that the spark plug wrench in many motorcycle toolkits can be used to remove the pinion gear nut. If you mix the PW and QT gears they will not mesh properly or maybe not work at all. QT gears have 10 and 57 teeth so if you get them mixed up, start counting.

This will run you about $230 or so. Now you are saying WOAH MAN thats too much!!! but wait. I have saved the best for last. You now have a QT ring and pinion gear with a PW shaft already installed. If you sell this on ebay and market it to PW50 owners they will buy them. The PW50 is a small dirt bike that has been made for 20 years and by switching to a 5.7:1 gear they get much needed acceleration and hill climbing ability. I have sold just the gears with no PW shaft for 150$ and again for 140$. If you bought a complete PW rear end, swapped the shafts, cleaned it up and regreased the bearings, I think you might get as much as $200 for it as a ready to go bolt on gear swap package.

Now im not saying you will get this much, just that I have. But even if you only get $80 out of them that brings the total cost of this upgrade to around 150$. money well spent.

Lastly, I lied. I do not actually have a PW gear on mine. I have a gear off a chinese PW copy that is 41:8 or 5.125 to 1. If you ever get this gear do not bother trying to swap shafts. Just grind 1/4" off the end of the shaft and make a spacer. I love this gear. Even on a stock QT50 if fully tuned up it works well. On the 60 its awesome. But good luck finding one.

Now you have the QT that should have been. Much more rideable, and plenty of power.

Well, I'm tired of writing. I hope you have found this guide useful or interesting.

randy's QT guide V0.1 copyright randy
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re: QT50 or QT60 mods

Postby xrongor » Sat Apr 22, 2006 1:16 am

heres some pics to help explain how to convert the oil tank:
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re: QT50 or QT60 mods

Postby xrongor » Wed May 24, 2006 1:37 am

i didnt mention this before, but if you denut the oil pump as described, make sure to cap off the injection port in the carb, dont just leave it open. you can buy plugs for exactly this purpose cheap at the hardware store, or just be creative.

randy
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re: QT50 or QT60 mods

Postby 82QT50 » Thu Jun 01, 2006 7:55 am

dude I dont see how premixing your gas will give you "much better performance". If you could go into more detail bout that, I would be interested. You might be able to lean it up alittle more or less but nothing major. Keeping the stock oil injector is a much more advisable idea, for the convenience alone. why the heck would you want to premix? thats ludicrous.

anyways, I dont know what everyone here is talking about, running pw50 gears only on 60 motors. dude, iv ran pw50 gears with a STOCK engine all year last summer with just a opened up air box, and she ran like a champ. slightly slower up hills but overall faster. over the winter I did a top end with one step bore, reeds, port polished, uni filter, lowered needle clip and cleaned pipe. the performance gain was slight, with just alittle more mid and top, so it feels. I believe that higher compression and/or playing with the ports would set my motor free, and she would rip. right now I can get 32-33 on a flat, running with my friends jog and vino. any slight downhill or breeze and shes pullin 35. down steep hills it will do 40 but only when screaming, which iv only done once.
either way, I want to beat my friends yamaha jog, which will do near 40 on a flat.

xrongor, your bike is a monster, why dont you use full pw50 gearing?
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re: QT50 or QT60 mods

Postby xrongor » Thu Jun 01, 2006 10:16 pm

ive ran it both ways. its definitely better premixed. i have lots of theories why but it comes down to one basic premise. with the oil pump connected to the throttle the way it is, it alters the oil/gas ratio getting to the combustion chamber constantly thus changing the richness or leanness of the air/fuel ratio in the combustion chamber using both RPM's (more rpms = more oil pumped) and throttle position (more open throttle = more oil pumped) to determine what mix is getting there. by premixing you eliminate both variables and can better tune the carb.

also if you premix you dont have to worry what happens if the injector fails for any reason (you can search the forum, lots of people premix just for this reason). but you do have to mix the gas. im used to doing it so i dont find it much trouble. i just keep a 2 gallon container premixed and handy.

if i lived in a city i probably would use stock PW gears. but i have mountains to climb in montana.

randy
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re: QT50 or QT60 mods

Postby xrongor » Sat Jul 01, 2006 1:24 pm

since ive adopted this thread as the QT mod thread, i have another update.

I ran ATF type F in my transmission for a while (both in the 50 and the 60). it did increase takeoff performance for a while, barely. after about 300 miles i started having clutch slipping problems so i drained out and it was absolutely black, burned, thin, and useless. So im back to 10-30.

so imho, ATF might be your best bet for racing a PW50 dirt bike where you might put 10 miles on it all weekend and change it after every race weekend. but for running it 30miles or more a day, day after day in a QT50, i would recommend against it.

randy
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re: QT50 or QT60 mods

Postby mholmes137 » Sat Jul 08, 2006 7:35 pm

Just a curious question, but what kind of ATF? I swapped to some Amsoil synthetic stuff and havn't had problems yet, but I'm going to be more careful checking it now. Can't say that I really noticed much of a difference either way though....
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