Advice for ATC 70 88cc Big Bore installation

[DuneAddict]

Hi 3WheelerWorld,

I recently picked up a 1984 ATC 70, my first time owning a 3 wheeler and I love it! I grew up riding on the tank of my Dad's 250r, so much fun. Now I ride my 18month daughter on my tank and she is addicted! I just say "Vroom vroom" and she runs right to it and jumps on lol. I'm about 6'1'', 230lbs and found out quick that I'd like a little more umph, but I don't want to put all the money into a lifan 125 or piranha 140, so the 88cc big bore kit looks like it will work nicely for me. I bought it already, but beings how this is my first time installing one, I'm looking for some resources and any advice anyone has to offer. I have done a top end on my CRF450 and YZ250, so I'm not a complete newb, I just want to see if there are any gotchas, stuff I should be looking out for, etc. Do you end up having to go up a jet size in the carburator? Any recommendations on sprocket sizes, I want to pull wheelies, but I don't want to throw a huge 44T on it and loose much of my top end. I'm thinking a 38T with the big bore might be good.

Please share any of your experiences installing the 88cc big bore kit. If you have links to threads on the subject, they would be greatly appreciated as well.

Thanks!

[dgm635csi]

Did you get the big bore kit with the head and carburetor? The big valve head make a huge difference in power, but the sheng way carbs are just OK. I upgraded my carb to a mikuni vm20. Much better tunability. As far as installation goes, it pretty straight forward. Just take your time, and stay organized. You should upgrade you oil pump while your in there, and inspect everything else thoroughly for wear during disassembly. Timing chains are also prone to stretching over time, so its a good idea to have one of those on hand. There are several good videos on youtube that show big bore kit installation on a Honda ct70 / ape 50. The process is pretty much the same for your atc70. I don't recall and "gotchas" when I did my 88cc kit on my ct-70.

Duncan

[Crazyktmmatt]

Id recommend doing a engine swap after getting my 88 running. It runs way better but still need more go. Im tempted to ad a stroker crank in it. I already have to much $$ in this 88cc build for the power it makes.

[DuneAddict]

Did you get the big bore kit with the head and carburetor? The big valve head make a huge difference in power, but the sheng way carbs are just OK. I upgraded my carb to a mikuni vm20. Much better tunability. As far as installation goes, it pretty straight forward. Just take your time, and stay organized. You should upgrade you oil pump while your in there, and inspect everything else thoroughly for wear during disassembly. Timing chains are also prone to stretching over time, so its a good idea to have one of those on hand. There are several good videos on youtube that show big bore kit installation on a Honda ct70 / ape 50. The process is pretty much the same for your atc70. I don't recall and "gotchas" when I did my 88cc kit on my ct-70.

Duncan

Thanks Duncan! The kit I bought didn't come with a carburetor or a big valve head. This is the kit I got: http://www.dratv.com/88ctalalc7.html
I'll have to look into the mikuni vm20 and big valve head. Do you have any links to these parts for me to checkout? Thanks

[T-Sox]

Put an ad on CL for a wrecked Pit bike. I've bought 2 low hour bikes in the last couple months. A 125 for $80 and a 110 for $70. Both started first kick after a carb cleaning. the 125 was supposedly wrecked the first day the kid had it. People buy these and give them to their kids who don't know how to ride a dirt bike. They end up broken in pieces in thier shed and you can get them cheap. I turned down 2 more today cause I don't need anymore motors.

[DuneAddict]

Thanks for the advice! I already bought the cylinder kit, wasn't planning on spending more money on a new head. Is the new head with big valves a must have? Already $100 into the cylinder kit, another $150 on the new head and that would put me at $250, I might as well just bought a lifan! lol.

[DuneAddict]

That's great advice T-Sox, think I'll post a CL ad and see where it goes. Thanks

[Crazyktmmatt]

Dont have to have a new head. I ported mine. Runs good for the most part, cept the jetting.

I also cut the compression down a touch.