THE OFFICIAL QT50 THREAD!

[84qt50]

[sloped]

[sloped]

[hypermiler]

Great idea for a thread!

Do we want to start a PN cross reference (PW50/YT60)?
Upgrades?
QT50 specific jets?

I know there is info somewhere about identifying year. I can't seem to find it, perhaps someone else would have better luck and drag the link here?

[xrongor]

as to cleaning out the port in the cylinder, pull the cylinder. scrape it with wood or plastic so you dont scratch the metal. an old toothbrush can be filed to a chisel and works well. replace the cylinder base and head gaskets when you get done (less than 10 bucks from a yamaha dealer).

as for the yt60 swap, i did a full compare for myself when i upgraded. the only different parts you need are the piston, rings, cylinder, and head gasket. the rest are exact matches with the QT50. (base gasket, bearing, rod, pin, clips, etc..) and i think some people are still using the QT head gasket although imho its better to get the YT one. same price for both...

as for oil, 1 cc = 1 mL (mililiter) and most measuring cups have mL markings right on them. no need to convert to ounces. 300 mL will do it.

as for jets, youll just have to do plug chops. somewhere between 60 and 75 will likely be the correct size (lower altitudes require higher numbered jets). from what ive seen you should expect to go up 5 in size if you switch to a 60 from a perfectly jetted 50. but again, chops are the only way to be sure.

randy

[spankydog]

I'm having a problem. I asked about this on another forum but they're not very helpful.
I've got a 81 mj50 (i know not a qt50 but very similar) that came with homemade air filter. Runs great. So, I get a proper airbox and now its running rich an 4 stroking a bit. Did my chops with an without airbox, plug looked best without. I'm assuming it was up jetted, not sure. My question is should i get a smaller or drill a few holes in the airbox. Thanks in advance!

for comedic value i'll post a pic of the very flaccid old filter

[xrongor]

unless you want really poor performance, you definitely need to drill holes in the airbox (on the side of the piece that allows the filter to still work). the stock airbox just doesnt let much air in. you didnt say, but i assume you bought a new stock filter. if not get one

you may still need to change the jet after you do this.

there is lots of posts already about drilling holes in the airbox. search the forum.

i have seen no evidence that the stock airbox/filter with holes in it performs worse, and lots that shows its the same as these valve cover filters that dont filter anything but gravel. i suggest you don't go that route.

the filter that is in that picture is useless. you were smart to dump it.

randy

[spankydog]

[xrongor]

[pedmister]

Can anyone tell me how to adjust the "clutch"?
Mine seems to slip a lot until it is finally fully engaged, which is often after I have travel some distance.

[hypermiler]

Replaced the piston, rings and gaskets on my QT50. Lightly honed the cylinder and put standard guts back in. The engine and trans are removed from the bike. Both front and rear wheels were siezed when it came to me and I have never heard it run. Turns out the piston was siezed also.

Is there a way to check for spark? I put the kick lever back on, on the bench and jammed it a couple of times, but haven't done a compression check. Sounds like a 50cc motor without fire.

So the question I have is this: Is there a way to provide power to the coil to bench check for spark?

Can I use a 120VAC multi adapater that puts out 6VDC @ >100mA? If so, how/where do I ground it? Ideas? I don't have an official battery for the bike yet, but I was hoping to fire it up by Tuesday.

Thanks!

[xrongor]

providing power to the coil will not do anything to help you test for spark. the spark system works because of transitionary wave functons not static ones.

other than the tests provided in the manual in the moped repair section of this site which will tell you if the components are good, the easiest way to test for spark is to remove the plug, lay it on the cylinder so it makes contact with the side of the plug, kick the bike over, and see if the plug sparks. if you have ANY spark, you got spark.

randy

[hypermiler]

That's what I thought. I'll have to delve into the manual I guess and begin checking out the components. Seems to me like it should have done something without a battery. I live in the NW and handled my share of chainsaws, I've never seen a chain saw with a battery. I thought it would self excite enough to jump a spark with a couple of kicks, but no joy.

Thanks xrongor, I'll start T-shooting stuff....

[xrongor]

you are correct. you do not need a battery to get it to spark or run. one of my QT's has never had a battery in it and it runs fine. the horn works, as do the headlights and tail lights. you need one to get the blinkers to blink though, and if you have a pre '83 without the voltage regulator you will probably burn your headlight out unless you have a battery installed, and charged, and the fuse doesnt blow, etc... basically if you dont have the voltage regulator i would either buy one, or use a 12v replacement for head and tail lights.

if you do not have spark, it could be as simple as a shorted wire, a broken plug wire, a bad plug boot, a broken kill switch, or a number of other things. no spark does not necessarily mean any of the main ignition components themselves are bad (coils, cdi, etc..).

in any case the manual has a decent procedure for troubleshooting spark problems. as does fred's guide in the moped repair section.

randy

[dcbarner]

I have a 79 yamahopper that isn't running. My guy says that I need a stator. I have no idea what he is talking about or where I can get one. I'm just getting into this hobby, any help would be greatly appreciated.

Dane