ATC 70 Help

[59bisquik]

Hi Everyone,
I just picked up a 79 Honda 70 ATC for my daughter. Its in really nice condition but I have a few questions. 1) it has a Takegawa intake and filter and a kiehn carb. Can anyone identify what it is from the picture posted? Is it bigger than stock, etc? 2) The bike stumbles a bit on the top end. I just adjusted the valves that were too tight and was thinking of looking into the points and condenser. Any other places to look? Thanks everyone!
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[59bisquik]

Looking at the DrATV website, it looks like the 20mm carb kit they sell in the ATC and performance section. It states in the info that the main jet needs to be changed for the 70. I wonder if that could be part of the stumbling problem.

[barnett468]

hi,

nice bike, wow.

your main jet might have been changed by the previous owners. plus if the big has a big cam and high perf pipe the carb kit mfg's recommendation might not work for you.

with eng cold, how much choke does it take to start?

how much throttle?

how soon can you turn the choke off and still have it idle and run ok?

what is the air temp where you are at?



you can do the following if you want:

install a new plug

on a flat or slight uphill, accelerate slowly and quickly from 0 and from around 5 mph in 2nd gear.

if it sputters/burbles then goes it is rich, if it simply fails to accelerate like it is out of gas it is lean.

if you do not have a new jet try lowering the needle if it is rich or raising it if it is lean.

see if it runs any better.

try a 2 size bigger or smaller main jet as needed.



look at the old plug

white to lite gray = too lean should have hesitation on hard acceleration.

lite tan = slightly lean

medium tan = ideal

dark tan = slightly rich, might have a sputter/burble on hard acceleration.

dry black = way too rich, should aputter/burble and have black smoke out tail pipe.



I would also check the following:

CARB

Take a 10” long piece of clear plastic tube.

Connect it to the float bowl drain fitting.

Hold the open end next to the carb even with the carb top.

Open petcock and bowl drain screw.

Gas should partially fill the tube.

The level should be from the bottom of the carb body to 3mm or 1/8" below the bottom of the carb body at the float bowl.

If it is off by more than around 3/32" I would correct it by adjusting the float.

High is richer, low is leaner.

[barnett468]

POST CORRECTION

Make sure the fuel mix screw is around 1 1/2 turns out. Turn it slightly in either direction until the idle is at its highest. Use idle set screw to adjust idle speed afterwards if necessary.

[59bisquik]

Wow! That is some great info!

As for the starting, no choke or throttle is needed and it normally fires on the first or second pull.

The plug is dry and black.

It has an aftermarket pipe, carb, intake and air cleaner. Any other items like a bigger piston or cam are unknown. Also the jetting is unknown.

I am going to replace the points and condenser when I get a chance also. Even thought of dropping in a CDI kit.

After I get the flat fixed, I will try your recommendations and post up what I find.

Thanks again!

[barnett468]

hi;

barstow? must be 50 degrees when you are trying to start it?

where did the bike come from?

have you changed the plug since you've had it.the plug indicates it is very rich. the polished cases and carb kit suggests to me that it likely has a high perf cam.

a high perf cam can cause a hesitation off idle and a dark plug even when it is jetted close.

based on the info so far, i would do the following until you get some jets and see if it helps.

clean the plug with wire brush and install a new plug the proper heat range when you get one and see if either helps.

either way, i'm guessing that thing is fatter than a xhristmas hog.

lower the needle 2 positions and ride it. if it develops a flat spot upon acceleration, raise it back up.

next, see where the fuel mix screw [not idle speed] is set and turn it in and out in 1/4 turn increments until the idle is highest then turn it in 1/8th turn. tell us where it was originally set and where you ended up setting it.

i suggest you but a 1 size smaller pilot and 2 size smaller main jet for starters and try the main first.

your bike should require at least 1/2 choke if it is around 65 degrees or lower out. the fact that it starts easily with no choke suggests the pilot is too large.

don't forget to do the fuel level test before changing jetting. changing the float level might affect your jetting.

you can do the needle and fuel mix screw though without setting the float level for now if you want.

[barnett468]

you can check the timing by connecting a continuity meter to the points.

remove the timing inspection plug.

set the points so they open when the F is lined up in the window.


a can of seal and air might work on the tire temporarily if needed.

[59bisquik]

The tire is leaking from the valve stem. Gonna need a new stem or tube. Not sure which until I get it apart.

As for the temp and location, we are in Pinon Hills now. Its been in the high 60's and low 70's lately when we have been riding it. We are also at 4200 ft of elevation. The bike came from down in the LA basin with much lower elevation and a bit warmer.

I will report back after tinkering with it.

Thanks again! :)

[barnett468]

hi;

your elevation will also cause it to run richer than it would at sea level or los angeles.

[59bisquik]

Updates:
Got the tire fixed today, was leaking at the bead. I also replaced the spark plug and the bike ran alot better on the top end. Im sure I still have some carb issues to deal with. I still need to go through and do the rest of the items listed in the previous threads.

However, to maybe add another issue to the mix. When I was changing the plug I did take notice to how shiny the cylinder is. I noticed it said 49cc on it. According to the DRATV website, a stock sized cylinder and the 88cc cylinder can both be marked 49cc. Any easy way to check without pulling the bike apart?

[fastatc70]

Just for giggles try replacing the air filter to a larger foam style filter lightly oiled. I have had problems with the small pleated filters not flowing air properly. Also don't trust the stamping a on the cylinder. I have boarded and purchased cylinders with wrong markings. Cheater cylinders.