75 Jet Surprisingly Good Results, But, ...

yuckfoo

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Joined
Nov 21, 2020
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705
I put a 75 jet in, clip second from the top. My top speed is lower, about 28 MPH but it runs surprisingly well. Throttle response seems perfect throughout the entire range. Really! No bogging at all no matter how I use the throttle or where it is between idle and WOT.

I bought a fine-tuning set of jets from Bikeberry so I'll be able to try 74 next, then 73 and then 72 again. One of those three should get me my top speed. I'm hoping to see top speed at 74 or 73 with a decrease with the next lower jet. If not, I can try the 71 jet and see what happens.

The other thing I noticed about jets is that if it is too big it becomes very difficult to set a good idle. Almost every setting was too high. I'd go lower and lower and lower until it was too low. Very difficult to find a sweet spot.

I expected the spark plug to be black and sooty again. It's not. Almost completely dry. The plug wasn't a new one so I'm not sure it's worth talking about the color of the electrode, except that I don't think it changed at all since I cleaned it. On my run a few days ago I put the clip to the middle (was using 70 jet that day) and did a low throttle ride and the plug was COMPLETELY black afterwards. I moved the clip back to where it was and when I got home, I cleaned the plug and put it back in for today's ride.

Anyway, I think I've finally got enough experience messing with the tune that I will be able to properly tune it now by down jetting then setting my clip and idle.
 

Sidewinder Jerry

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Mar 14, 2011
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2,523
Are you using a tachometer to do your tuning with? Ears can play tricks on you. A tech let's you know exactly what your engine is doing.
 

yuckfoo

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Joined
Nov 21, 2020
Messages
705
Are you using a tachometer to do your tuning with? Ears can play tricks on you. A tech let's you know exactly what your engine is doing.
I'd think my ears are more sensitive than those tachs that wrap around the spark plug cable. The way those numbers jump around they can only be good for getting a basic idea of what the rpms are. But, how would I use a tach to tune?
 

Sidewinder Jerry

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Joined
Mar 14, 2011
Messages
2,523
I'd think my ears are more sensitive than those tachs that wrap around the spark plug cable. The way those numbers jump around they can only be good for getting a basic idea of what the rpms are. But, how would I use a tach to tune?
First you get your max high rpm at full throttle. Then leave it there. Next you get your max low rpm at no throttle. Then adjust back just under max low rpm slightly towards the rich side.
 
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