2002 400ex 416 kit stage 2 cam - Honda TRX Forum
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post #1 of 4 Old 05-26-2019, 03:25 AM Thread Starter
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2002 400ex 416 kit stage 2 cam

Took my bike out today to do break in ride and get the carb setting correct. Having a couple issues though. I pulled the carb when I put the 416 kit in and it has a 170 main and 38 pilot. It seems to me that it’s running rich on the low end to quarter throttle. I had the air/fuel screw at 2 1/2 turns out and turned it in about to 1 1/2 turns out and that seemed to help some but what it does it once it warms up good is it kinda stumbles a little in the low end and kept having issues where it would die on me and then take some time to start back up and spit and sputter when it finally did start and I would have to lightly feather the throttle before I could get going again. On decel in gear it would backfire bad, turning the screw in helped with that. I didn’t look to see what my needle was set on when I was in the carb, if there is an adjustment, so I’m wondering if that doesn’t have something to do with it

I was also having issues with it kinda sputtering a little and blowing some black smoke out when cracking the throttle open. I took the air box lid off and rode for a while and that seemed to help with the sputtering but would still pushing out a little black smoke.

This bike has always seemed to run rich, not sure what the previous owner did to it but someone had been in carb before I was.

Any tips on how I can fine tune the carb to get it to run right.
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post #2 of 4 Old 05-26-2019, 05:23 PM
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148 is the standard main jet and from my experience you are simply too rich all around.

First do not make any changes using a fuel more than 21 days old (alcohol blended fuel) or more than 90 days old for non-ethanol fuel. Use a minimum 91 octane (non-ethanol blended fuel) or a 93 octane ethanol blended fuel, but no higher than a 95 octane either alcohol blended or alcohol free fuel.

The stock pilot jet is a 38, but engine modifications do not necessarily necessitate bigger jets (more fuel) - I highly modified a Kawasaki F7 175cc in 1972, my pilot jet was fine, but I had to reset the air screw from 1 1/2 turns to 3/4 turn to make it idle acceptably (I modified it for racing and idle was not a priority - the original Suzuki RM400 had no provision for idle - close the throttle and the engine would die and was then flooded on the restart). You may have to turn you fuel screw in more for a good idle. If it will not idle cleanly at 1/2 turn or more, change the pilot jet to a 35. Changes to the intake that may require more fuel include a free-er flowing air filter and lid removal or modifications to the air box or lid to allow a less restrictive intake. Changes to the intake that require less fuel (smaller jets) include larger venturi carbs, higher valve lift, larger valves and larger intake openings (ported heads usually require jetting down).

Once idle is fine (set idle mixture on a hot engine - if set immediately upon start up, it will be rich when the engine warms to normal operating temperature), work on the mid range (slide needle) - in third or higher gear with the throttle set at about 1/2 opening and cruising at a steady speed, the engine should not surge (lean) or blubber (too rich) - generally, the middle notch on the needle is adequate (unless you run a high or low octane fuel or an alcohol blended fuel) - you should not be using a fuel higher than 94 octane unless the engine builder has made changes requiring the slower burning and harder to ignite high octane fuel.

Now that the idle and mid range are set, take it out and stab the throttle wide open, a stumble from idle to WOT is not abnormal, but indicates a momentary lean condition upon the instantaneous vacuum drop caused by the sudden opening of the throttle. The accelerator pump on the carb may need adjusted or modified to deliver a stronger shot of fuel during this moment. If the stumble is not severe, it can be worked around by a change in fuel, setting the idle fuel screw on the rich side and (if adjustable) raising the float level can help.

Beyond the stumble, you want to get the WOT to run clean with the engine at maximum RPM - I think a 170 main jet is a bit on the big side - try a 160 or a 165 - standard was a 148

Jetting is as individual as the machine - when they come off the assembly line, they are all the same and the jetting installed at the time of manufacture is generally adequate for most locations, but each machine can benefit from tweaking for the specific location, fuel quality and changes like exhaust and air filters.

If you are happy with it and is is not fouling spark plugs or pinging, it's fine.
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post #3 of 4 Old 05-26-2019, 06:11 PM Thread Starter
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Obviously I think the previous owner put the 170 main jet in possibly because of aftermarket slip on exhaust. Ill try adjusting the fuel screw in more than what I have. I’m running 91 octane ethanol free. Like I said ever since I bought this bike I’ve had issues with it running rich. Taking the air box lid off helped with the blubber on accel but still couldn’t get the idle set right. I’ll check the setting on the needle and see where it’s at and try adjusting it to what you said, thanks
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post #4 of 4 Old 05-27-2019, 01:22 AM Thread Starter
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I just checked on the air/fuel screw.. I’m only about half/ 1/4 turn from fully seated and still having the issues of dying after riding a while and pulling throttle in and then hard to start and feathering throttle after starting like it’s flooded. so any ideas what this means?
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