Z80, Flat spot at top rev's

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cyclepro101

cyclepro101

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I have put the larger #76 jet in and have pulled the gutts out of the muffler. Now that the run in period is up I opened her up today and noticed that it was pulling hard then a high revs appeared to be starving for full as it flatted out. Whats the best way to fix this? What about bending up the 2 tynes on the carb float to raise the float level?


Steve
 
JD-StukNchaoS

JD-StukNchaoS

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hey cycpro, I don't recommend bending anything, if you just move the "c" clip on the needle to the #1 notch setting. (the 1st slot from the flat end) you'll see a major decrease of wot fluttering,.,.good luck
 
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Pablo

Pablo

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cyclepro101 said:
I have put the larger #76 jet in and have pulled the gutts out of the muffler. Now that the run in period is up I opened her up today and noticed that it was pulling hard then a high revs appeared to be starving for full as it flatted out. Whats the best way to fix this? What about bending up the 2 tynes on the carb float to raise the float level?


Steve
Click to expand...

IMHO you are running too rich. The stock jet is typically too rich at WOT. What does your plug look like after a hard, hot run?
 
cyclepro101

cyclepro101

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As I am new to this stuff, what is WOT? The plug is always pretty dark and oily but I have only just started riding it hard/fast. I did move the circlip down one notch on the needle, thus lifting the needle up higher (I guess) I will give that a go after this bloody rain stops but I fear this will make it richer and maybe thats my problem as I have installed a larger jet (0.76mm)
So go leaner you reckon? That would be lifting the circlip up to the highest position, thus pushing the needle down lower?

Steve
 
Pablo

Pablo

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WOT = wide open throttle. (Some guys say WFO. Wide flat out, Wicked ****ing Open, etc)

Plug seems too rich.

Your issue is at near or full throttle, you write:confused:
The needle is just for off idle and up to WFO control, but if the jet is too large, too much fuel is blowing in - regardless of the needle setting. Yes even the factory setting is rich, so going with a larger jet will cause WOT bog.

I have a fairly modded engine. I run a .65 main jet, ran great at WOT until I got a slantplug head - now it's too rich again. May go .62...........
 
Goat Herder

Goat Herder

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I can't wait for my walbro carb to come in! I spent to days calling around on the phone vi the INTERNET. I do believe I found the right one. When I get it up I will post results!Theres is nothing cooler than re jetting my carb just by turning a screw. Last but coolest high low Idle circuit Just to cool!!
 
cyclepro101

cyclepro101

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OK I had a go with the clip in the 3rd spot down from the top and it was too rich, so I moved the clip up to the top spot (pushing the needle further down) and its better. Also I am running the hotter NGK B??5?? plug in lieu of the b??6?? plug. I had it set at 0.80mm and I have closed the gap up to 0.60mm and its a lot smoother. I also changed to the same plug but the one with the longer electrode and it made heaps of diff.
Could somene please explain what this POWER BAND is I keep reading about.
Just putting around my bike runs a little ruff but then I give it a little gas or go up a hill and the engine jumps from chugging to running really smooth and fast and the speed increases dramatically. It normally kicks in at about 25km's and max's out at about 35kms, thats with the 44 tooth sprocket. Even under load at 18 or 20km's this apears to happen too. Is this the POWER BAND?
 
Masterm222

Masterm222

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I have soldered shut and drilled my jet smaller to lean my bikes out and I have had pretty
good luck. I would like to know where to buy jets of the proper sizes. (.62-.65)
 
cyclepro101

cyclepro101

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I put the original back in (0.70mm) and it was guttless/worse. So I put the 0.76mm back in and I might drill out the original to 0.80mm and see how it goes. Its not bad though.
What I would like to try and do is just get it to run smoother, like when the power band kicks in. Spark plug gap appears to play a big role in this too.

Steve
 
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D

DIYMark

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To get it to run smoother first thing would be to jet it correctly. If your running a complete stock set up with no mods you will need to drop a jet size or 2, but instead what Id do is chop off the internal pipe thats welded to the exhaust muffler cap. This will lean out the pipe and give more power. Now Id play around with the needle to see if you can fine tune it more.

Also try a touch of acetone to the fuel. Add 2ml to 1 litre of 2 stroke fuel - ive tried this on 3 bikes and have never had a problem. This will smooth out the bike over the rpm range and will allow you to cruze at higher rpms with less rattling and a smoother exhaust note (and combustion).
 
Masterm222

Masterm222

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Does the engine vibrate much? On one of my bikes I discovered vibration was foaming the fuel in the carb making it run bad. I have a hard time believing going richer will help! Leaning the main jet helped my daily driver through-out the rpm range and I gained 5 mph at the top end. Also, remember a motor is just an air pump. Grind or file your intake to match the port on the engine and do the same with the exhaust. These ports do not match at all from the factory! Get some bulk gasket material from an auto parts store to use it as a template. Smooth air-flow = smooth power! I agree with Pablo too. You are to rich at WOT.
 
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cyclepro101

cyclepro101

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gavmiester said:
36t sprocket fixes a lot of problems the 66cc needs to be under load thats why they go so well up hill
Click to expand...
YES! Something I do understand. It does go much better/smoother/faster/morepower under load, so I am waiting for the 36t sprocket to arrive. I think this will sort out a lot of problems. The motor does love it under load.

Steve
 
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