Best way to build an atc70 engine for hill climbing power?

[blue83ranger]

I have an '85 atc70 that's in need of a little more power. I use it for trail riding and hill climbing, or at least I want to climb some hills with it. I need the power both off idle and on the top end. The mid range power is great but it needs to get reved up first to get there and once it is, it does great to a point, then the power just drops off on the longer hills. So, I was wondering what's the best way to go as far as getting more power where I described? I want to stick with the main part of the 70 engine (no crappy china engines) and I don't want to use a stroker crank either. So far I have a crf50 exhaust installed, the Malaysia ebay electric ignition kit, clamp on filter, and I put all the guts of a crappy china 70 carb in mine and it turned out to be jetted perfect, I just had to adjust the idle mixture and the needle. Any suggestions? thanks

[rg97]

If you want to stay at 70cc, the your best bet is a stage 2 web camshaft, high comp piston, and a engine port n polish. Shortline10 does very good porting, you could pm him about it. If you don't want a stroker, then i say do the above and see if you can find big bore kit.

[blue83ranger]

I was thinking of getting a big bore, I just wanted to keep the 70 bottom end. Would DRatv's 88cc kit with their race cam be any good? and the only reason I don't want a stroker crank is the electronic ignition won't work with one unless I told the guy I had one then he said he could modify the stator to work with one. and if I go with an 88cc kit would a bigger intake and carb be a good idea too?

[rg97]

A larger intake can be done by someone who does porting like shortline10. an 18cc increase will probably need a carb that is 2-4 mm larger than stock (i dont know what stock is). i jumped 20cc on my X and put on a +4mm carb.

[hippyplz]

I used the tbolt 88cc big bore and carb kit. Good quality and definitely added some grunt to the motor across the power range.

[Dirtcrasher]

DEEPA has that 88mm kit here at my home in a 70.

But, if you want power/torque, install a larger displacement AM motor....

[oscarmayer]

i have build and raced many 70cc engines and up to 131cc engines. (my son is a sponsored ATV racer at age 10) if your going to build it for fun and just trying to do the best you can then fine, if your trying to compete, honestly, KX65 engine swap.... i build a 125cc engine up to about 17hp. (YES on the crank dyno 17.2hp.) in 4th gear WOT the 2-smokers passed him by as if he was tapping the breaks in the last ATV race we had. that was when i asked a few questions and decided the kx65 was the next motor to be mounted into the ATV frame. I jsut traded one of his practice bikes for a compete good shaped kx65 bike. but you can get them on Craigslist for anywhere from $450-$1400 depending on work done. remember you want the motor assemble, electronics, and water stuff. once stripped own the rest of the bike you could sell for $150-$200 and make some of your $ back.
anyway to make a 70cc compete, they do offer lots of options.
DR.ATV is a good guy, but lately i have had issues getting them on the phone to discuss details i need to know. I now spend most of my $ with www.tboltusa.com . Pricing is typically the same, but i have more options. He also sells drop in motors that you can bolt into the 70 frame and run a 155cc engine if you wanted. but you can get a yes 88cc BB kit as well as many other parts from him. Vince is a good guy and they typically answer the phone. rarely do they not answer.

good luck with your project. once you get the new kit with the new bigger valved head and performance cam, you want to make sure you get it ported. But make sure it is properly ported. i use this place. www.theoldone.com tell them mike sent ya. it will take them about 4-6 weeks to get to the head, but no one will ever offer a better porting job. they use CNC valve work and high end flow benching to test all porting work. our last race head we gained 2.5hp after they ported a so called "worked head" we purchased from an online vendor. YES they are that good. so well worth the wait.

again, good luck and enjoy. a well build properly performing engine that will be reliable for racing is going to run about $750-$900 for the top end. An over all engine for my son costs me about $1400-$1600 to build when i drop in the stroked cranks and do custom machining to get everything to fit right, and that's with me doing all the final assembly and testing and machining once I get the machining to my specs.

I have his last 4-stroke racing engine i am building, but it will never see an ATV frame. it is a 125 stoker to a 132 with electric start. Since we are switching to 2-smokers for him to be able to compete against the 70cc 2-smokers it will sit or i will sell it. So yea poor engine will be wasted. :( but i may toss it up on the for sale to see if someone wants it. Semi-auto shifting as class required no manual trans. 3-speed w/reverse.

well gotta get back to work. boss coming. cya guys

[tblumer]

TBparts make a stroker crank for vintage motors that has the same flywheel taper as your stock crank

http://tboltusa.com/store/vintage-honda-108cc-stroker-big-bore-24mm-carb-kitbrct70-all-speed-80-81-speed-p-2636.html

this a whole kit but I'm sure if you contact him they sell the crank separate.

I've built several stroker 117's all based off ATC70 bottom ends.

[oscarmayer]

if you take it apart and measure the dimensions, you could probably find a 125cc crank that would drop in and then use the larger 57mm bore cylinder and piston setup. then you would have a 70cc bottom end with a 134cc top end. honestly it really depends ont he amount of $ you have to send vs. what your goals are. by the time you finish messing around trying to get the 70 to run a hill climb decent, you probably could have purchased a 140cc manual clutch kick start motor complete and would run circles around that build setup with lots of room for growth.

http://tboltusa.com/store/pitster-pro-140cc-enginebr-fits-pit-bikes-and-other-minis-p-2439.html
$439 for this motor.

this includes everything to run it. engine, harness, carb. just no filter. no biggie, local auto store has a 1 1/2" k&n style v8 breather that will work perfect for the carb. I use these for racing. they usually run about $12-$18 each.
no more points, no more hoping it will make it,. just bolt and BAM. up the hill she will go. also you will need a pitbike exhaust. you can get one off ebay for a 125 pretty cheap with alloy muffler.

[blue83ranger]

Thanks for the replys. I'm just building the motor for fun, not racing. and since I bought the cdi conversion, I can't use a stroker crank. So i'm just looking for info on a top end build, what head, cam, big bore kit, intake, and carb. and I already have exhaust. thanks again.

[tblumer]

Like I said before, you can get a stroker crank that is compatible with your cdi. TBParts makes one with the shorter flywheel taper for the 70 motors. Just so there isn't any misinformation being spread.

[blue83ranger]

I'll definitely look into that. thanks

[Rex Racing]

for the money just bolt on a 140cc pir engine and go ride, I have had several combo,s of engines out there, the 88cc kit will cost you more and not even close on power, you can make stock engine as big as 102 or with some work 108 but not worth it. I will sale you a complete 88cc ,4speed ,hotcam, ported, springs, 20mm carb, 25mm intake. check out mad 70's most of them 3wheelers are mine or have helped build. let me know if I can help :D

[blue83ranger]

From what I've found there are a few 88cc kits with a carb that say they'll double the stock power, which should be good enough for what I'm using it for. But I found it cheaper to buy the stuff separately. here's the route i'm thinking of going.
88cc $100
high volume pump $28
atc110 carb, which I have, just need to get a kit for it. $15
bigger intake $32 +shipping.
and i'm looking for a complete head off a SL70 w/cam or a xl/ct70 head and get the dratv race cam for $30.
Plus I already have a cdi conversion which noticeably helped, and a aftermarket exhaust. and I pretty much know for sure i'm not going to race it. I might drag race someone but nothing crazy. I would like to convert it to hand clutch too but I haven't researched that to much, but from what I did see it said the conversions are for 3 speeds and I have a 4. But If you can beat any of those prices or have a head pretty cheap I would be interested. thanks

[briano]

Put a china 110 in it and convert it to pull start. Cheaper than the big bore kit and more power. You can get a 125cc 4 speed manual clutch pretty cheap also. I know my china 110 powered 70 will pull away from an 88 kit from bottom end all the way to full speed.

I had a 70 with a 140 Piranaha motor that was very quick, I had another with an atc110 motor with a big bore kit, cam, pipe, and ported, it was also very quick. But the china 110 motor is my favorite so far, I'm using the stock 70 exhaust and was using the stock air box up until a few weeks ago when the rubber tube broke off. The pull start conversion is fairly simple, do a search on it.

I'm 250 pounds and riding a stock 70 compared to my lil 110 powered 70 is a night and day difference.

[barnett468]

serious hill climbing requires a gear change. its as simple as that. put a 1 tooth smaller front sprocket for a cheap, quick, easy change.

[Dirtcrasher]

He still needs some more motor torque/power - balls!! :D

That kit posted is amazing. I may grab one for my 2nd ATC 70!! :D

[barnett468]

He still needs some more motor torque/power - balls!!oh i certainly agree but untill he has the bank to buy the bigger balls he really needs to do the job he has in mind, the gears will make the balls he currently has seem bigger than they really are.

[Rex Racing]

I will sale complete engine 4 speed, 88cc kit , ported atc70 head, 22mm intake, 20mm carb, hotcam, and will put hand clutch off of a sl70 on it also $200 plus shipping 740-five02-7320 if interested :D

[Rex Racing]

engine is in a 70 now that we just raced last weekend !!!

[CRAZY70MAN]

I will sale complete engine 4 speed, 88cc kit , ported atc70 head, 22mm intake, 20mm carb, hotcam, and will put hand clutch off of a sl70 on it also $200 plus shipping 740-five02-7320 if interested :D

Now ya got me wanting it for that price....... Not to hijack thread but how does it hang with the 140's and such on the flat track Rex??? I am lookin' to build a 3rd...... Andy