ATC 70 - Help Getting It Running

[brandonlowe2]

My '85 ATC 70 is having some trouble. I got it and took it to a mechanic... well that didn't do anything except take money from me. He claimed I needed a new Carb and an Airbox. What it was doing was dying when getting into the throttle.

The interesting part is that is actually ran before I took it in (not great, but it ran) and after I got it back it literally would not run. It would idle in Neutral, but as soon as you change to 1st it would die down. They said they would put the new carb and airbox on for free once it came in, but, I am pretty much done with that place now. When I got my Tri-Z, I took it in and asked them to go over it to find anything wrong... they found 1 thing wrong (clutch cable connector) charged me a ton and didn't find any of the 4 or 5 things that I have since then found and learned how to fix myself.

I am determined now to learn how to do all this stuff myself... which I am learning fast... the 250sx project helped alot with that.

Ok, back to the ATC 70. I went ahead and ordered a new Carb (figured a new one can't hurt) and I ordered an airbox and air filter off of eBay (an OEM off an old trike) The carb came in yesterday so I replaced it last night. Still no airbox so just the air filter off the back of the carb. The engine started right up on the first pull I let it idle for 10 or 15 seconds... jumped on and took off in 1st gear. Drove around the yard a bit into 2nd gear, no problems. Got up to 3rd gear, having a blast.... it was probably 2 or 3 minutes of riding (can't recall if I got to 4th gear) and then all of the sudden it starts spitting and popping and it bogged down and died. It would start back up, but pretty much immediately bog down.

I will admit I have no idea how to "dial in" a carb. Adjusting the screw on the side I was able to make it bog down differently but I was not able to make it run good after that first 2 minute ride.

The airbox will be here Monday or Tuesday... is it really going to make a difference? I can't imagine that being the difference in being able to ride and not. But, then again I don't know.

My other thoughts are if my gas cap open/shut is not working so there is no vent letting gas in.... OR the gas lines that are on it are installed by that same mechanic and he put some 1-way valves in the middle of the hose... I am wondering if those are not letting gas through quick enough?

Any thoughts or ideas would be much appreciated.

[yaegerb]

My '85 ATC 70 is having some trouble. I got it and took it to a mechanic... well that didn't do anything except take money from me. He claimed I needed a new Carb and an Airbox. What it was doing was dying when getting into the throttle.

The interesting part is that is actually ran before I took it in (not great, but it ran) and after I got it back it literally would not run. It would idle in Neutral, but as soon as you change to 1st it would die down. They said they would put the new carb and airbox on for free once it came in, but, I am pretty much done with that place now. When I got my Tri-Z, I took it in and asked them to go over it to find anything wrong... they found 1 thing wrong (clutch cable connector) charged me a ton and didn't find any of the 4 or 5 things that I have since then found and learned how to fix myself.

I am determined now to learn how to do all this stuff myself... which I am learning fast... the 250sx project helped alot with that.

Ok, back to the ATC 70. I went ahead and ordered a new Carb (figured a new one can't hurt) and I ordered an airbox and air filter off of eBay (an OEM off an old trike) The carb came in yesterday so I replaced it last night. Still no airbox so just the air filter off the back of the carb. The engine started right up on the first pull I let it idle for 10 or 15 seconds... jumped on and took off in 1st gear. Drove around the yard a bit into 2nd gear, no problems. Got up to 3rd gear, having a blast.... it was probably 2 or 3 minutes of riding (can't recall if I got to 4th gear) and then all of the sudden it starts spitting and popping and it bogged down and died. It would start back up, but pretty much immediately bog down.

I will admit I have no idea how to "dial in" a carb. Adjusting the screw on the side I was able to make it bog down differently but I was not able to make it run good after that first 2 minute ride.

The airbox will be here Monday or Tuesday... is it really going to make a difference? I can't imagine that being the difference in being able to ride and not. But, then again I don't know.

My other thoughts are if my gas cap open/shut is not working so there is no vent letting gas in.... OR the gas lines that are on it are installed by that same mechanic and he put some 1-way valves in the middle of the hose... I am wondering if those are not letting gas through quick enough?

Any thoughts or ideas would be much appreciated.

Time for process of elimination.

Rule of thumb...its takes 3 things for a motor to run. Fuel/Spark/Air. Fuel and Air are the easy ones. Ensure your plug is getting wet by good fuel flow from the bowl to the combustion chamber. Ensure you are getting fuel to the bowl by unscrewing bowl puke screw and watching for fuel. If that's OK, then get your new box and air filter on, then check for air leaks around the carb and intake by spraying carb cleaner around the joints and listening for increased RPM's or killing the motor completely. If any of that happens then you have an air leak and it must be addressed. Finally, ground your plug to your the head, shut all the lights off and watch for a FAT BLUE spark.

The way this is behaving it sounds electrical to me.

[brandonlowe2]

I will work on testing all of that tonight and report back after the weekend or after I get the airbox on. I have no lights or battery on this particular one... its all mechanical

[RubberSalt]

Now that you have a new carburetor, you'll need to make sure you have the correct jets in the carburetor. The manual should cover the jet numbers, but you can check the old one for the jets(assuming they are original). You may have been lean, got to hot, and died. The other possibility is that it go to rich, and died from to much gasoline.

These carbs are pretty easy to tune. There's 3 basic adjustments, and the main jet. Fuel screw(air screw on a 2 stroke carb), needle position, and idle screw.

Once the engine is warmed up, adjust the fuel screw. As you richen it up, the RPM will drop, use the idle screw to raise it back up. This will determine how it runs from an idle till about 1/4 throttle.

Next is the needle position. This covers 1/4 throttle till about 3/4 throttle. Lowering the needle
(raising the clip) makes it more lean. Typically in the middle is the spot you want.

Last is the main jet. No adjustments, only a replacement on these. Bigger jets=more gasoline.

To check your jetting, you install a new spark plug. Put the machine and hold the throttle at different position. Kill the trike and pull the plug. The white should have turned kinda tanish brown, like cinnamon or chocolate. If it's black, your rich. If it's white or grey, your lean.

Get to 3-4th gear in WOT and hold it for a little bit. Pull the plug and look at it.
Check it again at 1/2 throttle
Then at 1/4 throttle.

When it's said and done, you should have a well tuned bike. Most people don't check 1/2 or 1/4 throttle.

[brandonlowe2]

Ok... I will first off admit I feel stupid and admit that I still have no clue what I am doing. The bad part is I think I still know more than the local dealership's mechanics around here.... which is very frustrating. There should be a 3WW shop somewhere (I guess there is at Trikefest!)

Anyway.... the new carb arrived and the airbox. I got it all put on.... I have the exact same problem as before. I have adjusted the carb needle to every slot (I think there are 5 different slots on it) and every position gave the same problem. The only thing I can get it to do now at least is idle. It will idle all day long, but, as soon as I give it any throttle at all it dies. I can almost breath on the throttle and it dies.... so, needless to say I have not been able to try to WOT test for spark plug color.

Again, admitting I am still learning, I have attached a couple pictures of my carb. I have circled the two adjustment screws that I believe to be what I am supposed to be adjusting. The one on the right of this picture being the idle screw which is the only thing that seems to make any difference at all that I can make.

The left (or front) screw I assume (possibly incorrectly) is the Fuel screw, but it doesn't seem to do anything. The screw on the bottom of the bowl is all the way in. Is there another (or different) adjustment that I don't know about?

Here is a list of what I have tried so far and I get the exact same results with every combination.

- I have tried the jet needle in every one of it's 5 slot positions
- I have tried the OEM jet and the aftermarket Jet (which both look identical)
- I have tried the left (or front) screw (in the picture) all the way in, all the way out and everywhere in between
- I have tried with choke on, off, half, etc.
- I have tried with the gas cap take off (just in case the vent was clogged)
- I have tried with the airbox and without
- I have checked to make sure the petcock was allowing good gas flow
- tried the carb cleaner trick to check for air leaks.... no leaks

236589236590

[Evan Hagenow]

Does it still have the metal gas tank on it? The tank might be rusty inside and letting a lot of crud into the carb. That would explain why it ran good for a couple of minutes and then shut down. It took some time for the crud to block the new, clean carb.
The screw on the bowl is the drain bolt. it doesn't do anything except drain your carb of fuel.

[yaegerb]

Ok... I will first off admit I feel stupid and admit that I still have no clue what I am doing. The bad part is I think I still know more than the local dealership's mechanics around here.... which is very frustrating. There should be a 3WW shop somewhere (I guess there is at Trikefest!)

Anyway.... the new carb arrived and the airbox. I got it all put on.... I have the exact same problem as before. I have adjusted the carb needle to every slot (I think there are 5 different slots on it) and every position gave the same problem. The only thing I can get it to do now at least is idle. It will idle all day long, but, as soon as I give it any throttle at all it dies. I can almost breath on the throttle and it dies.... so, needless to say I have not been able to try to WOT test for spark plug color.

Again, admitting I am still learning, I have attached a couple pictures of my carb. I have circled the two adjustment screws that I believe to be what I am supposed to be adjusting. The one on the right of this picture being the idle screw which is the only thing that seems to make any difference at all that I can make.

The left (or front) screw I assume (possibly incorrectly) is the Fuel screw, but it doesn't seem to do anything. The screw on the bottom of the bowl is all the way in. Is there another (or different) adjustment that I don't know about?

Here is a list of what I have tried so far and I get the exact same results with every combination.

- I have tried the jet needle in every one of it's 5 slot positions
- I have tried the OEM jet and the aftermarket Jet (which both look identical)
- I have tried the left (or front) screw (in the picture) all the way in, all the way out and everywhere in between
- I have tried with choke on, off, half, etc.
- I have tried with the gas cap take off (just in case the vent was clogged)
- I have tried with the airbox and without
- I have checked to make sure the petcock was allowing good gas flow
- tried the carb cleaner trick to check for air leaks.... no leaks

236589236590

Its not running cause your fuel is off :) Just kidding.

Have you checked the manifold and surrounding areas for leaks with carb cleaner?

[brandonlowe2]

It does still have the original gas tank. I will pull the carb off and clean it again and see what happens. I put a filter in the petcock last night (the original one had one, the new didnt so i took the old one) I guess I will also drain the gas tank and try to clean it out good.

Yea I checked for leaks with the carb cleaner and best I can tell there are no leaks :-(

[yaegerb]

Brand new, clean air filter? Good, fat, blue spark?

[briano]

Change the points. I've had a few that were doing the same thing, I chased carb problems forever. I put new points in and everything was good.

[Hurley250R]

I bet he has rust and junk in the tank also. Maybe even a gas cap not venting. Check the lines/petcock and carb for rust and junk. Make sure the cap is operating properly. Start with the simple things before spending money on parts you may not need.

[brandonlowe2]

What are points? I keep hearing about them but have no clue what they are are how to replace them

The air filter is brand new... i will blow it out just to make sure. I put an air box on... not sure why thats needed.

[brandonlowe2]

I assume this is what you are referring to..... http://www.ebay.com/itm/like/391450701799?lpid=82&chn=ps&ul_noapp=true

[Rob Canadian]

Points are the triggering system for spark. The condenser is a storage unit of voltage. They work hand in hand. Primative stuff.

I like to see fuel flow to the carb myself. Pop the fuel line at the carb off. Take a bucket or whatever. See the flow. Let it flow for a bit. Does it taper off? This will rule out tank, vent, lines

[coolpool]

I'd get ready to learn about points real quick if you're to join the 70 club; they seem to be the root of all evil if they're out of adjustment. This adjustment also determines your timing. Spend a few bucks and get a flywheel puller also, it will save a lot of hassles.