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Post by icefly on Oct 5, 2021 0:34:06 GMT -5
So I notice around ~1/2 throttle at 35 MPH I can kill the engine but continue to have power. There is a narrow band in which I can adjust throttle and speed up/slow down where the engine "runs" and doesn't sputter out/pop and crackle.
What (if anything) does this say about my jetting / temps?
'04 Zuma, Airbox With Mods, Stock Carb (Pilot:57.5,Needle 1 clip rich,Main:105), 70cc Polini Air cooled, Ebay Leo vince knockoff, 6g rollers
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Post by Zino on Oct 5, 2021 7:22:16 GMT -5
If you hit kill switch .
The ignition should no longer be giving spark.
If you are still running on You have a rich mixture with a hot spot in your cylinder .
That is igniting the fuel keeping you with power .
This is called dieseling.
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Post by icefly on Oct 5, 2021 22:24:40 GMT -5
Is dieseling an indication of improper cooling in a 2T? Should I go to a colder spark? If it's happening in the midrange what would that suggest for my tuning?
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Post by Zino on Oct 6, 2021 7:23:40 GMT -5
Post up a picture of your well used spark plug.
The proper heat range spark plug will have a color change in the bend of the ground strap.
What style jets are you using Mikuni ?
Your jetting is much higher than I ever had to run.
stock air box a a 87 to a 90 mikuni was rich enough
I used Stock jets in the 82 and 84 size with a leo vince and a sport kit .
Stock pilot is a 44 Going to a 46 from the vino is as big as I have ever needed to go.
On the dellorto carbs I never went much over 40 on the pilot .
What airbox mods have you done?
Post pictures of that too .
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Post by icefly on Oct 7, 2021 0:01:14 GMT -5
Yes, Mikuni. Mikuni VM28 / 486 Pilots & VM11-22 Mains6 of these: www.zumasrusstore.com/products/air-box-mods-ysr Dremeled holes in the stock airbox, pressfit & glued the edges with contact adhesive. Pictures to come later this week.FYI I'm basically at sea level since I'm on the Florida coast. Dieseling would be indicative of running hot, no? |
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Post by Zino on Oct 7, 2021 7:43:35 GMT -5
dieseling is you have a hot spot such as built up carbon in the cylinder combined with a rich enough mixture to fire on its own .
Is your spark plug black like coal does it have flakes of carbon built up on it .
That would be a good indicator of way too rich.
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Post by icefly on Oct 10, 2021 18:59:27 GMT -5
Definitely running rich:    I had been idling a bit before this to test out some underglow i was installing... so I can get more pics later when the egine was actually hot & running full bore Airbox mods: Sorry for the weird angles but didn't feel like pulling it off. 2 on top:  One on inside nead engine outlet:  One near CVT:  Two on front:  Uni air filter (pulled out & cleaned ~200 miles ago) |
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Post by Zino on Oct 10, 2021 19:42:38 GMT -5
you look rich piston crown and plug plug is wet you are probably too big on the idle and main by a couple jets according to the heat range mark on the ground strap you might be running too cold of plug  |
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Post by aeroxbud on Oct 10, 2021 23:03:35 GMT -5
It's hard to tell from the pictures. Are all the inserts on the unfiltered side of the air box?
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Post by icefly on Oct 11, 2021 2:45:29 GMT -5
It's hard to tell from the pictures. Are all the inserts on the unfiltered side of the air box? All except for one are on the unfiltered side |
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Post by icefly on Oct 11, 2021 2:56:36 GMT -5
you look rich piston crown and plug plug is wet you are probably too big on the idle and main by a couple jets according to the heat range mark on the ground strap you might be running too cold of plug Thanks for the advice. I'll get a hotter plug and will lean my main jet. I will run it WOT and take a spark pic when I get back from work tomorrow. |
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Post by Zino on Oct 11, 2021 7:17:01 GMT -5
Do you have a rpm gauge ?
Do you have a temp gauge ?
When you are all warmed up
how does she idle ?
When you blip the throttle
1)does it stay at a higher idle for a while and then come down ? this indicates a air leak or lean on pilot we call this hanging idle
2)Or does it drop down right away struggle a little bit and then clean up and rise ?
This is rich on pilot racers tend to be here to hep with throttle braking
3)idle drops back to idle speed quickly this is perfect for a daily rider
Go slow dropping main jets
when you get close to where you think you should be try this .
With you scooter all warmed up go wide open till your speed levels off .
Then back off the throttle to 7/8 throttle this will richen you up momentarily
3 things will happen .
1) you will stay around same speed and then drop slightly main jet is very close to good
2)you go a little faster main jet is on the lean side
3) speed drops right away main jet is on rich side .
I tune mostly by throttle feel and sound .
I listen for mad hornet sound and good throttle response .
Then I Double check by plug chops and Temp Gauges .
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Post by snaker on Oct 11, 2021 11:27:07 GMT -5
Certainly something odd going on.
Most obvious thing is a bad/intermittent kill circuit
Any sort of run on or dieseling usually in my experience will fairly quickly drop rpm and be pretty obvious.
Not sure of your experience, could it simply be the engine being spun by the machine coasting down?
Like if your driving a manual transmission and kill the ignition while its in gear?
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Post by icefly on Oct 11, 2021 17:06:49 GMT -5
Certainly something odd going on. Most obvious thing is a bad/intermittent kill circuit Any sort of run on or dieseling usually in my experience will fairly quickly drop rpm and be pretty obvious. Not sure of your experience, could it simply be the engine being spun by the machine coasting down? Like if your driving a manual transmission and kill the ignition while its in gear? Switch will be checked with multimeter. Unlikely but will check. Flat land of florida... Unlikely that the drivetrain is pushing back through the belt. RPMs don't drop at all. |
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Post by icefly on Oct 11, 2021 17:09:35 GMT -5
Do you have a rpm gauge ? Do you have a temp gauge ? When you are all warmed up how does she idle ? When you blip the throttle 1)does it stay at a higher idle for a while and then come down ? this indicates a air leak or lean on pilot we call this hanging idle 2)Or does it drop down right away struggle a little bit and then clean up and rise ? This is rich on pilot racers tend to be here to hep with throttle braking 3)idle drops back to idle speed quickly this is perfect for a daily rider RPM nope. Temp just installed yesterday so no historical data yet. What's a reasonable temp range? When she's cold she idles high and warmed up is a nice low idle (no vibration) It does have a bit of a hanging idle. Going to check for air leaks again before changing jets a bunch. |
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