QT50 60cc keeps seizing.

got an 86 qt50. after cleaning the exhaust and giving it a tune up it ran mint.

shortly after i installed a 60cc kit with the stock head, bike soft seized twice. no matter how rich i tried it always kept getting hot.

my current setup is yt60 jug

qt50 head

ngk bp7hs plug

pw80 carb (jetted rich)

and a pocket bike muffler welded to stock header.

bike runs pretty good.

occasionally will bog at wot because its rich

but after about a 8 mile ride today it soft seized again on my way home.

any thoughts?

im running one base and 2 head gaskets

i was considering picking up a 70cc high compression head off treats but dont know if that will help my cooling issue

any help is appreciated.

Re: QT50 60cc keeps seizing.

Probably Fred /

Too hi of timing

No head temp gauge that's not smart with a new kit

Re: QT50 60cc keeps seizing.

Justin Cabral /

i dont believe the timing can be adjusted on the qt50.

also i did use a temperature probe when i first got the kit.

i was getting 400 plus degrees at idle but once i went up to a 7 range plug it dropped to the 330-360 range.

i then added another headgasket in hopes of dropping the compression some but i dont think it was enough

Re: QT50 60cc keeps seizing.

you cant take the flywheel off the woodruff key and slide the timing around like that?

Re: QT50 60cc keeps seizing.

matt boda1nz /

Air leak.

Re: QT50 60cc keeps seizing.

matt boda1nz /

Arnie Grape Wrote:

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> you cant take the flywheel off the woodruff key

> and slide the timing around like that?

Funny, I just had a flywheel key on a qt50 push back and out of the keyway.. torqued it down to 35 ft lbs and thought I was blowing cdi's because the timing kept changing. Finally was going to switch out the complete stator with a good working stator and noticed the key was gone and the crank was blued a bit where the flywheel meets the crank. Sooo.. it might just be my bike, but

Torqued to spec, the flywheel on mine either spun or rocked back and forth.

To the op.. you should be idling 340 max.

Re: QT50 60cc keeps seizing.

The header is to small. Also check the piston ring gap not enough for expansion? Air leak? injected or pre mix????

Re: QT50 60cc keeps seizing.

Justin Cabral /

Injection is still working.

i cannot source and air leaks ive tried spraying the motor while running and no difference.

as for the exhaust im not sure if changing it will help with cooling. I will post oics later

also i read that the yt60 cylinder with qt50 head will hit the pistin and raise the compressiontoo much.

Re: QT50 60cc keeps seizing.

Change your exhaust. A cheap biturbo for a tomos will work. Just cut off the header and rotate it and re weld it. That pipe works suprisingly good. That carb will work but you should buy a clamp on vm16 or vm18 and delete the oil injection. b7hs Plug. Stock timing is fine. Also i've always ran a few tanks of gas through those kits before ripping.

Nick

Re: QT50 60cc keeps seizing.

What is your compression? Try a quick run with no pipe?

Re: QT50 60cc keeps seizing.

Nick are you run the vm16 & vm18 with a stock intake?

Justin Cabral you using a stock yt60 piston?

Re: QT50 60cc keeps seizing.

Bog eh? When I hear bog I think lean.

Re: QT50 60cc keeps seizing.

Todd Keingeshaft /

I had similar issues with my Towny... I found that the stock head did not have enough "cooling capacity" to handle the higher temps that came with the kit, AND the increased RPMs. (Especially running at WOT for more than a couple miles at a time)

For a while, I ran a stock YT60 head, but now I have a Treats 70 cc high compression head on it, which I modified the combustion chamber on to bring the compression down to a more reasonable level. (Generally, the higher the compression, the hotter it will run)

The timing is not adjustable, but if you run a Yamaha Jog CDI or other CDI with a curve, the CDI will retard the timing at higher RPMs and keep the temps down. This alone worked wonders on mine...!

Originally I tried a pocket bike pipe with a homebrew header, and it didn't improve performance all that much. I also tried the Tomos Biturbo on mine, and it worked well. I later made a custom header and used the Treats Black Chamber, and that worked well, too. Currently I am using a MLM Sidebleed, and top be honest, the performance is only slightly better than the Treats Chamber... There is a guy on here that has a YT60 topend on his QT with a PW80 carb and STOCK pipe, and it consistently runs in the high 40's. His setup defies the logic about the smaller header, but it works for him...

I'd definitely get a head temp gauge as soon as possible, so you can keep an eye on temps and prevent another soft seize. I always try to keep mine below 400-degrees if possible, although sometimes it will peak higher when going up a long steep hill...

Re: QT50 60cc keeps seizing.

Todd Keingeshaft did the yt60 head work by its self? also what about the yt60 CDI or would the jog CDI work better? I have heard of a few Towny guys using the yt60 CDI to help with a kit.

Re: QT50 60cc keeps seizing.

matt boda1nz /

you have an air leak or super high compression, or not enough cooling.

start with step 1.

presurize the engine with 5psi + and -, if it loses air quickly, you will know. google: mityvac for leakdown mopedarmy.com

block off the exhaust and intake. get a mityvac. how are you going to test a crank seal with the engine running?????????????

check compression

google: the right compression tester mopedarmy.com

$100 on air leak, could be at the base or head gaskets since you just put the top end on.

dude has a 45 mile an hour setup with stock exhaust. it's not the exaust.

Re: QT50 60cc keeps seizing.

Justin Cabral /

yes im running stock yt60 piston.

as for compression i will try to get my hands on a tester this weekend.

im going to look for a cdi to purchase. i guess anything for a jog will work on a qt50?

Re: QT50 60cc keeps seizing.

Justin Cabral /

Re: QT50 60cc keeps seizing.

Justin Cabral /

just let the bike idle for about 15 minutes.

gradually creeped up to about 290-295

gave it a few revs and it got up to 309 and hung around 300 or so until i shut it off

is this hot?

ambient temperature here today is 79

Re: QT50 60cc keeps seizing.

matt boda1nz /

I know it sounds as assholeish, but man, you gotta check your compression and do a leakdown. If you plan on doing mopeds/nopeds and you love the hobby you gotta pay to play. Three tools you will thank me for is a mityvac, compression tester and an inch pound dial torque wrench.

Your idle Temps sound good. But seizing doesnt.

Re: QT50 60cc keeps seizing.

matt boda1nz /

Oil? Pump? Premix?

Re: QT50 60cc keeps seizing.

Justin Cabral /

oil pump.

Re: QT50 60cc keeps seizing.

Todd Keingeshaft /

Arlie Endsley Wrote:

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> Todd Keingeshaft did the yt60 head work by its

> self? also what about the yt60 CDI or would the

> jog CDI work better? I have heard of a few Towny

> guys using the yt60 CDI to help with a kit.

The YT60 head helped, but to keep the temps down I still had to run the jetting pretty rich, AND use a "thick" head gasket with it to lower the compression some. I never soft-seized with the YT60 head, but by then I also had a head temp gauge, so I could keep an eye on the temps and avoid soft-seizing. Once I added the Jog CDI, though, my overheating problems were gone!

There is NO difference between the QT50 CDI, The Towny CDI, and the YT60 CDI. I have had all of them apart, and drew schematics for each of them, and the circuits are identical, despite the different part numbers. I posted about this a long time ago, but the last time I looked up the post for someone, a majority of my post was deleted for some reason.

The CDI I am using now is one of these:

http://www.ebay.com/itm/2-STROKE-CDI-IGNITION-JOG-Minarelli-1PE40QMB-Yamaha-JOG-cy50g-/151298876796?hash=item233a1da57c&vxp=mtr

If I remember correctly, that CDI retards the ignition about 6 degrees above 7000 RPM. That alone does wonders for keeping the engine temps down!

I bought one of those "blue aluminum" CDIs last year sometime, took it apart to draw a schematic of it, then never did anything else with it. One of these days I'll get around to trying it out, but from what I remember, the circuit wasn't anything special...

Keep the advice about air leaks and stuff that others have posted in mind while you troubleshoot this though. I posted my experiences because my engine was airtight, my jetting was spot-on, and yet I still soft-seized. Once you are sure that your engine has none of the issues that others have posted, you should then look into what I have mentioned...

Re: QT50 60cc keeps seizing.

Todd THANKS for the CDI info saves me some time and $$.

Re: QT50 60cc keeps seizing.

Justin Cabral /

ive purchased a 70cc head and new plug from treats.

and im going to get one of those cdis

while i wait for the parts im gonna see if i can borrow a compression tester tomorrow.

and also try and get a leakdown on the case

thanks for all the info

Re: QT50 60cc keeps seizing.

don't eliminate backpressure from the pocketbike muffler, weld job restriction.

it very well could be contributing.

Re: QT50 60cc keeps seizing.

Would an air leak not show it's self with the stock set up? Or no way to tell with out temp gauge for it running in stock set up? Just wondering.

Re: QT50 60cc keeps seizing.

Todd Keingeshaft /

Justin Cabral Wrote:

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> ive purchased a 70cc head and new plug from

> treats.

Keep in mind that I modified the chamber on mine to get the compression down. I don't remember the exact number, but unmodified that head made the engine have WELL OVER 200 PSI compression! I used the tennis ball/valve grinding compound trick to open up the combustion chamber and get the compression ratio down... Just my .02.

Re: QT50 60cc keeps seizing.

matt boda1nz /

I used a ball grinding bit in a drill press to drop the psi down to 200 and then an extra head gasket to get it to 160. It would not be good to use until modified.

Re: QT50 60cc keeps seizing.

Don't think it is the same for the stock yt60 44mm that head is for 45.5mm I think and the stock piston is not domed like the malossi kit is, don't how much that makes a diff. But i would think that the difference in piston would drop compression?

Re: QT50 60cc keeps seizing.

Justin Cabral /

I got the bew treats 70cc low compression head so im hoping it helps keep the compression down.

but not too much

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