Puch Athena 70cc, phbg tuning

I read through all the articles on tuning and all searched, still having some problems.

Current setting: 75 main, 55 idle, needle is set with the clip 2nd from top. I tried 80 and 85 main (85 main wouldn't run well at all, 10mph tops). Idle jet started at 60, went up to 65 and it was much worse, down to 55 and it was better.

When I start from a stop, it bogs out and dies unless I go wide open. If I just crack the throttle a little bit while idling it dies. It only does then when fully warmed up. While testing different things, I found if I turned down the idle mixture to make the idle lean to the point where it was barely going then it behaved much better. Needle setting has little effect with the bogging.

Wide open, its running well but a little on the rich side. Plugs are a medium-dark brown.

To me it seems that my idle jet may be too big, but I see many posts with people running 55's and 60's with no issue and I don't want to run over lean. Does a 45 idle sound reasonable?

Re: Puch Athena 70cc, phbg tuning

yes.

Re: Puch Athena 70cc, phbg tuning

So I found an interesting problem when tuning today, apparently fuel was building up in the hose from the carb to the intake. When I would blip the throttle it would suck that gas in, causing it to nearly die. I remounted the carb so it was a bit higher than the intake instead of a little lower, hopefully that will help.

Re: Puch Athena 70cc, phbg tuning

Yeah, thats a common problem. Keep the hose as short as possible and try to keep the "in" side of the carb higher than the "out" side.

Re: Puch Athena 70cc, phbg tuning

Funking with the idle jets are nerve racking. The 45 ended up being the best at the moment, even the 50 would make it "boggy" off takeoff. 55 would eventually foul things out and the exhaust was way gassy.

Re: Puch Athena 70cc, phbg tuning

Things are looking well, I remounted the carb so everything points downstream, and now have a 45 idle jet. Mixture screw is at 1.5 turns out now, so things are looking good. Bike runs much better.

According to the dellorto manual, the phbg can be tilted quite a bit. I haven't had any issues yet with it at this angle, and after putting on an 18 front sprocket I hit a new top speed of 42mph.

Here's a pic of the setup now:

Re: Puch Athena 70cc, phbg tuning

Dude you're crazy... What size carb is it? I'm running a 105 jet with a 19mm carb. I think you're running way lean.

Re: Puch Athena 70cc, phbg tuning

Its a 19mm, running pretty sweet with the 75 so far. Plug chops looking good, 105 definitely wont work for me. Putting in an 85 main the thing was 4stroking like crazy and would barely move.

Re: Puch Athena 70cc, phbg tuning

Something is probably wrong then... What kind of filter are you using? It might restrictive.

Re: Puch Athena 70cc, phbg tuning

Using a K&N conical filter:

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