Starts then Dies HELP!!!

[weazel]

Alright folks, here is the deal. I have this 81 ATC 70 that I have been rebuilding. Thanks to the great folks here I managed to figure out my spark issue.

Well now it is all together, I filled up the tank, got gas into the carb and started pulling. I get it to fire, maybe 3-4 times then it dies. The longest I have been able to get it to run is about 15 seconds.

Going off of the repair manual, I opened the pilot screw from 7/8 to 1 1/2 turns open from bottomed out. The Idle screw I have no idea where to set it.

I adjusted the points again and again and nothing.

I'm about to pull my hair out trying to figure this thing out. Please help me out if you can. Such as where to set the carb, etc.....

I guess I should also ask as far as the points go, they should be set just so that they start to open when at the "F" mark and measure the gap at the "T" mark. I think I'm reading the manual correctly. Please help on that also. Thanks again

[weazel]

I thought of something else, not sure if it affects anything or not.

I rebuilt the carb, I set the needle on the 2nd slot from the top. That was where the old one was at. Not sure of exact spot for that .

[weazel]

Anyone???:wondering

[daniel_250r]

i have read on other threads that this can be a bad cdi

[weazel]

This is a points machine.

[oscarmayer]

weazel, 1 suggestion is, pacience. your basically spamming the thread in less than a 12 hr period expecting us to jump. heck half the people on here are still asleep.

as mentioned above have you read through other "recient" threads concerning running issues? there are 3 newly started threads in the last 2 weeks reguarding this issue that i know of.

[weazel]

Sorry, was not my intention to spam the boards.

Yes I have read through many old threads and I'm trying to narrow down the problem off of them. So far none of them hit home, I have tried a few different things already and still nothing.

I'm still thinking it is a carb problem, and the setting of the Pilot screw and idle screw. I'm just not sure how many turns out they should be.

[big schott]

Weazel, I've been waiting around to see what others say about theis also. I have a 70 doing the same thing. It has good compression, the points are set properly(I think), and it is getting plenty of gas. I thought mine was a carb issue becaus my plug gets black in a matter of those 15 seconds.

How does your plug look? Like I said, mine gets BLACk fast and then won't run (of course). I have a hard time getting anything higher that a fast idel out of mine, How about you?

Maybe together we can get each other running.

[oscarmayer]

pilot shoudl be 1 and 1/2 turns out if i recall.
the idle, i would turn it 3/4 way in, then onc eyou get it running, slowly turn it out till it does. once it does, turn it 3/4 -1 turn in and leave it.

the carb may beed to be completely dissambled, cleaned and then put back together. that's a common issue.

---------------------------
if the plug is getting black, then you may have too much fuel. you may have to adjsut the needle up a notch. (up is lean and down is rich)

[big schott]

Your are right and that is why I think I need a carb kit. (its wore out:) )

[weazel]

alright, I found a thread that may help me out. I must of missed it last night. I will set the 2 screws to what was mentioned here, that seems to be the consensus. I think there are a few things in my carb that need to be checked again. I did put a new kit into it and was unsure about 2 things. I will get back to you on this.

I will also check out my plug, and let you know what it looks like. Thanks again for your guys help.

[weazel]

Well found one problem in my carb. When I rebuilt it I had one jet left over, that didnt look like the others, so I left it out. When I pulled the carb today, I decided what the hell I will see where it goes. It was my idle jet. I got the old one out, which was pressed or twisted in. It was plugged good.

I pushed hard and managed to get the other jet screwed in. There where no threads so I made my own. unscrewed it and screwed it back in a few times and it works great.

Well first pull it fired and died. Second pull SNAP!!!! the damn rope for the rewind broke, so there she sat. Will let ya know what happens after I got the new rope on.

[Derek]

You might be better off converting it to cdi from a pitbike stator, pitbike flywheel and cdi box and wiring harness. You can find all the parts on eBay and convert it for under $75 Its nice to because those pitbike stators have a lighting coil. Pit bike carbs will also fit on the 70.

[weazel]

hmmmm interesting thought.

I lost my spark again tonight. Made me almost throw my tools across the garage but I held my self back.

I messed around with the plug out and the points, then the plug out again. Couldnt for the life of me figure out what was wrong. Well after putting the plug in the last time I heard a crunching noise. I thought crap there went the threads. So I removed the spark plug and Whhhhhhhhhhaaaaaaaaaattttttttttttttttttt!!! I have never seen this before, the threads on the spark plug actually broke off at the base of the plug. That explains my mysterious missing spark. Well cant do much more for tonight until I get a new plug.

Oh and no I did not over tighten the plug. Just in case you where wondering.

But needless to say I still have not gotten it running. Saga to be continued.

[Tri-Z Pilot]

just because the plug is new doesnt mean it's good. thats a good piece of info to keep in the noggin.

[Autophysn]

dude, I had the same problem, changed the plug and wamo, no more prob's.
but if you rebuilt the carb and used the new needle, they are usually not the same as the OEM. play with that if the new plug doesn't help.

[weazel]

Well got the new plug in and Whooo hooo!! It started with and ran on the choke for about 15 sec. Pulled and pulled and got it fired again this next time it was about 1 minute. It started to die with the choke on so I flipped it off and died right away.

I cant seem to keep it running with out the choke one. I did move the needle to the middle notch. I'm wondering if I'm flooding it out.

After it dies it takes a lit of pulls to get it to fire again. When I took the plug out it was wet. I cleaned it off and it fires with in 3 pulls, but then dies again.

Any suggestions now. I was thinking putting the needle back to the 2nd notch from the top. But not really sure if that would help.

Oh I tried searching the pit bike stator's and none of those look like they would fit. Any suggestions where I can get a cheap CDI swap or ow to search for it.

[weazel]

Grrr, I dont get it!!!! Now I cant even get it started.

Is there anyone is the MN Twin cities area (Stillwater) to be exact that wants to come by and lend me a hand figuring this thing out.

[Autophysn]

just wondering, have you tried to see how strong of a spark you have?
We took a 70 for a swimm one time by accident, and the magneto was soaked, took forever for it to dry out and run again. We actually towed it with a buggy in gear forcing it to run, then eventually it dried out and ran pretty good since then. It does go thru plugs more often than before, but it works. Took along time to figure that one out.
Generally these things are not too difficult to wrench on, but it sure sounds like you are having a hard time. I feel your frustration and wish I could help, but I am in California, sorry

[weazel]

I have a nice strong spark, now that I changed the points and condenser.

I took the carb off and cleaned it again. I got air through all the passages. So I know my carb is clean.

I put it back on and pulled and pulled. Finally it fired after about 30 pulls, then died after a few seconds. I pulled a bunch more and I could not get it fired again. I'm starting to wonder if I dont have enough compression. I dont have any way to test it, but I'm also not sure how much I should have. Does anyone know the compression #.

Oh I checked out the valves again and they are still gapped to .002" so those are good.

[leokendall]

timming on the cam sproket off?

[leokendall]

compression should be arourd 150 WOT,


get a buddy and put your thumb over the spark plug hole and pull her over, if u can blow your finger of ther should be enough compression there for the bike to run.

i can keep my thumb on 120 psi on a 4 stoke no problem, i dunno about other people.

[weazel]

Timing was correct I know that for sure.

Compression seemed really low on mine, It didnt even feel like it wanted to push my thumb off.

So last night I was curious about the head and jug. So I pulled them both off. The jug mic. out at the specs in the book. No wear and no lip on the top side of the jug, where the piston stops. So I have to believe that the piston and rings are good. I disassembled the head I rebuilt and put my old head back together. Reason I disassembled the original head was because of a stripped spark plug hole. Well that got fixed and maybe the valves I had just didnt fit the other head I had. So time to reassemble the engine tonight and see if I have more compression and if it wants to start. I will keep you posted.

Oh and Thanks for the specs on the compression

[CRAZY70MAN]

I know where ya are coming from! My first rebuild drove me crazy. The points shoud start to open when the mark on case cover and the F mark align. Two ways to make it easier, leave the plug out and use a testlight with a battery or battery charger. Create a circuit, ground the light to the frame and hook positive or power to the test light probe. Rotate flywheel and watch for the light to dim which means points are just begining to open and check your marks. This works great and is very accurate. The carb issue is common. Take back apart and clean. Use torch tip cleaners for jets and check float level, should be in your manual. I had to clean tanks several times on my 70s before they were right. Also check fuel petcock filter, may need cleaned. Hang in ther, its worth the wheelies in the end!! on3eatin'4...........good luck.

[CRAZY70MAN]

sorry, wrote info wrong. Ground testlight to frame and hook power to light probe. Connect probe to black wire out of stator, this will make circuit which lights the testlight. Just watch for it to dim which means points are beginning to open,

[weazel]

Thanks for that tip!!! I will for sure give it a shot when I return from x-mas.

I just want to make sure that my cam and crank are timed correctly so I will tell you how I have it set.

On the Cam Sprocket i have a small "O" stamped into the face of it. I lined that up with the "v" shaped notch on the head, the notch is at the front of the head pointing towards the wheel. I have my Crank on the T mark for TDC on the compression stroke. I assume that is correct. Please inform me if I'm wrong.

Other than that I will do the test light trick when i return. I will also check the carb again for the 4 time LOL.

I installed that other head and the compression doesnt seem to be any different. If I have low compression, does that make a difference on how it starts and runs?? Thanks again guys for all of your help.

[oscarmayer]

ok the reason the valves didn't work and will nto work is you did not "lap" them in. if you download a manual (link to one in my sig) you will see it talks about using valve palling compund. go to a local auto store and ask for a tube of valve lapping compound. the smallest tube is all you need as it takes just a tiny bit. you'll never even use that up. (done 6 atc head and still nearly a full tube the guys around here keep asking me to redo their quads and atc heads. hehe) anyway back on track.. you will need a small lapping stick.t he one at they parts store there are for car sized valves and will not work for your bike. you will need to order one from the local bike shop or online. you need a motorcycle lapping stick. (tiny valve one)

once you lap them in the valves will then have a matching seat to the head. also look at the lip of the valve itself where it sits onthe seat. most ATCs i have seen have the valve edge so word it's not reuseable. this means, if it hs not perfectly level and flat but has a worn lip it's trash. by the time you get ti right it will have machines off most of the thickness and will crack very shortly after usage and blow the motor. don't trust it. replace the valve if they are that worn.

get a wire wheel for the drill and put the drill in the vise. then manually wire wheel off all the carbon off the valves and see how they look. do the entire valve not just the seat but the stem and botton too.

good luck!

[Gag_Halfront]

Personally, I can't help but think it sounds like a fuel delivery problem. If the bike fired and ran for a minute, the compression is good enough and the spark is hot enough. If the floats are not set right, it could be running a bit rich or lean. That might explain only wanting to run with the choke on. If it's lean and you choke it that could make it just rich enough to run. Also, is the air cleaner installed? If the jetting assumes you have the stock cleaner and you actually have no cleaner, that will make it run lean.

Also, your description of how you set the valve timing sounds right on.

[weazel]

Ok guys, here is the latest

I did the test lite deal and got the points set exactally where they should be. Just opening on the "F" mark.

Put my finger over the spark plug hole and pulled it over, blew my finger off of the hole. Seems ok.

I double checked the key and key way to make sure that the flywheel did not move on the crank. That is OK

I bought some of that Heavy Duty Carb cleaning solution (where you soak your carb). I did this for over 24 hours and the carb looks almost new again. Reassembled it and checked the float and it all seems good. I get good gas flow into the bowl and all jets are clear.

I double checked the timing marks again. They are ok. The only question I have here is, is it possible to have the timing 180* off???

Checked the spark from my plug. Lots of little spark, blue to purple in color. Should I have one big spark??? I'm used to snowmobiles and they seem to have a bigger spark and less of them.

I also dont have the air cleaner. Never came with one. I will buy one but wanted to get it running first. Will this affect the starting of it.

The other thing I noticed is that when I was checking the timing marks, I rotated the crank and seems on the compression stroke I could hear air, I had the big round cover off, while turning the crank. Does that mean my valves are not holding???

I guess once again I'm at a loss. I am very good mechanically, but this little 70 has got me pulling all my hair out.

[weazel]

1 other question. I dont think it is possible, but can you get the slide in backwards??? I have the cutout side, facing to the air filter/rear of machine. I've looked in manuals and it doesnt say or give a good pic of what way it goes. I just assumed it went that way.