ATC70 only runs choked

**Frankencelery** · 10-20-2007, 08:38 PM

My son's ATC70, which admittedly desperately needs an engine overhaul, only runs when the choke is on. I moved this carb to another ATC70, and it did the same thing. To me that would indicate an air leak somewhere in the carb, but if the gaskets are good between carb and engine, what could it be? I replaced the o-ring, and I've tried spraying carb cleaner around while the engine is running, but I haven't been able to find the leak.

Any ideas?

**tecat-z** · 10-20-2007, 08:42 PM

Clean the pilot jet and thouroughly blow carb cleaner through all internal circuits, and finish off with blowing air through all circuits again. Should fix you up.

**ATCwithdrawals** · 10-20-2007, 09:34 PM

Originally Posted by tecat-z

Clean the pilot jet and thouroughly blow carb cleaner through all internal circuits, and finish off with blowing air through all circuits again. Should fix you up.

Tecate-z is right, your problem is internal.

**james9r9r** · 10-20-2007, 10:26 PM

Well I rebuilt my whole carb on my 1983 atc 70 and the damm thing takes forever to start. I have to push it in gear to start and when it does run it still has no power and boggs, almost dies when I put it in 1st gear and fouls plugs if I can get it started?

NOTE:I am missing the little cap that goes on the choke lever I am thinking I am sucking air threw it. Also it won't idle at all unless I push in where the cap used to be with my thumb???

**Frankencelery** · 10-20-2007, 10:43 PM

It seems like we gave it a good cleaning when we first got the machine, but I suppose I should take it apart again and give it a shot. Otherwise I'll have to buy a carb.

Speaking of buying carbs, Beatrice Cycle is selling a substitute carb for less than $50. The only thing wrong with it is the fuel barbs are on the wrong side. I'm thinking if I can't work this out, I may try one of those. Anyone have any experience with these carbs?

**Frankencelery** · 05-11-2008, 10:21 AM

In my long standing tradition of answering my own posts, I had to add a comment. Once I decided to rebuild the engine on the 70, I bought one of those carbs from Beatrice Cycle. It was several months until I got around to opening it and last night, I did. Turns out it doesn't fit! It looks like it will fit my CT70 intake, but not the ATC70. I didn't realize they were different! So now I'm back to trying to fix that old carb that only runs with the choke on. Arrrrgh!

**bigreddaddy** · 05-12-2008, 09:12 AM

Go through the carb man. Its probably a clogged pilot jet.

**J.D.** · 05-12-2008, 10:48 AM

I've had the same issue as you there fella. I've already pulled mine apart 3 times and cleaned it all out and blew through all passages. Now, I'm going a step further. I've taken the carb off, dissassembled, remove all rubber/plastic parts, and putting it in this stuff called "CHEMPDIP, carb/parts cleaner" by Berryman. This stuff works wonders, leave it in there for about a week, take it out douse it all down the carb cleaner and blow all the crap out. You can buy it at a parts store, Oreillys etc etc, it's about 20 bucks for the gallon, but it'll last you for several several carbs....it looks about like a 1 gallon can of paint. I'm positive after letting mine sit in there for a week and cleaning it out good, it's going to be fine.

My Big Red was EXTREMELY hard to start, took carb apart let it sit in this stuff for a week, put it back on....starts first kick now

**Frankencelery** · 05-12-2008, 11:22 PM

Ok, here's what happened: I rebuilt the carb completely. I took the unit apart and soaked it in solvent. Then I used some very good carb cleaner and made sure to spray out all the passages, making sure that the spray comes out where it's supposed to. Replaced main and pilot jet, needle, gaskets, etc. Adjusted according to specs. Today I put it all back together and with the top end completely rebuilt, the damn thing still won't run. Oddly, it ran for about 2-3 minutes, very badly, and only with the choke on, and now it won't start at all. Just sputters. Double-checked timing and all that, and it's right on.

There's not much to these carbs, I just can't figure out where the problem is! Anyone have any ideas what I might be missing? Otherwise I'm headed to Ebay for another carb.

**bigreddaddy** · 05-13-2008, 02:12 AM

Have you checked your compression? I don't know if the problem is just the carb. If the carb was the only problem then it should have improved a little after you soaked/cleaned it.

**Frankencelery** · 05-13-2008, 07:23 PM

Yeah, I was thinking along the same lines. I ran a compression test, and with my automotive compression tester, I got about 120lbs. I figure I'm losing at least 5cc with the tester, so that should be great. I'm thinking about pulling the cam cover and checking the valve timing and making sure I didn't do something wrong there. There's just not that much to go wrong with these carbs!

**hrc200x** · 05-13-2008, 09:29 PM

Sure sounds like carb, but you could also clean and adjust the points, make sure gas cap vent isn't plugged, air filter clean?

What is the difference between the new carb you bought and the stock one? I have a couple trail 70s both with carb issues if your willing to sell.

**Frankencelery** · 05-13-2008, 11:08 PM

The points are new and properly adjusted. I made sure to remove the gas cap to make sure I had fuel flow (besides, I'm using clear fuel filters, so I can see it) and there's no element in the air filter yet.

The replacement carb I bought from Beatrice Cycle has a different bolt pattern to the intake. I thought about trying to use a CT70 intake, but I don't think it would fit in the space between engine and tank. I have a CT70 that I will be rebuilding sometime, so I guess I'll keep it.

**300rman** · 05-13-2008, 11:14 PM

only runnning with the choke on would indicate a carb issue.
did you check the entire electrical system to make sure you are getting a good spark?

whats so special about these carbs? to they slip into a rubber boot, or are they like a lawn mower carb where the mounting flange is built onto the carb?

**Frankencelery** · 05-14-2008, 12:03 AM

Yeah, spark is a good strong blue spark. And I replaced the spark plug. Just now I went out to make sure I got the cam chain on correctly, and there's no problem there either, it's right on. So the carb is where I started, and the carb is where I'm ending up, I think. 300rman, you asked about the carb- the engine side of the carb has a mounting flange that has two bolts. The air filter side has the rubber boot.

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ATC70 only runs choked