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Discussion Starter · #1 · (Edited)
I have an 03 Rappy that I just had rebuilt. It is now a 686, 11:1 compr, stock head, stage 2 cam, has a full FMF system and a K&N cone shaped filter in it.

It is jetted with 148/146 mains, 22.5 pilots, 55 power jet in only one, clips are on the 3rd notch, and the screws are 4.5 turns out. The carb on the right as your looking from the back of the machine is the one missing the jet. How do I tell if I have dynojet or Mikuni's??

I am at 865ft above sea level.

The quad had all the mods done except the bore and it had a 12.5:1 piston in it. I ran 110 octane before but now run 93.

It was rebuilt because of a blown head gasket and once opened I figured I'd refresh it and go with a milder comp ratio. Before the rebuild it ran pretty good but when the weather got warm (75*) it would develop a hiccup/miss on a run down a road. It doesn't happen off idle but after it is halfway or more up in the rpm range it occurs.

I have only ran the quad a little since I had it rebuilt and it was in cold weather (40*) and it didn't have an issue.

I have not read the plug since the rebuild it looked pretty carboned up when I pulled it.

I am pretty sure there isn't a spark issue since it has a brand new stator, a newer coil and wire.

I plan to buy some plugs and go through the jetting process but I am hoping for some opinions on what the issue might be and how to remedy it. Also, where to start with jetting.

I have done some reading on what others have done and had success with but I don't have any experience with it and hope to get out riding asap.

Thanks
 

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Those numbers look like dynojet numbers. The right carb is missing the jet because it doesn't have the choke on it and therefore is meant to not have it. The right side (when sitting on the bike) should have the higher main jet number (because it feeds 2 valves instead of 1)

If the bike is running rich then it will run better cold than warm. It would also make the spark plug look sooty. My guess is this is your case.
 

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I am unique
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The carbs look filthy, time for a good cleaning.........
 

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Discussion Starter · #4 ·
Thanks for the input! Plug after 2hrs of run time...

This is what my plug looked like after approx 2hrs of run time.

I took the quad for a ride today.

It seems to run great off idle and during acceleration.

On long runs, once I reach 5th gear and get to the upper rpm's it has a definite miss or something seems to be slipping.

It pulls very good/hard until I get to that point.

The idle is not quite as smooth as I'd like either.

I hope to get some plugs tomarrow and play with the jetting to see if there is any improvement.

Thanks again for the help!

Willy you've been a great help in the past. It's nice to have such a great resource at your fingertips.
 

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Almost looks lean to me.
 

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Master of the Electron
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146/148 are DJ numbers, typical values used for full exhaust and open airbox... is your airbox modded?

If the hiccup arrives as weather warms up the circuit in question is too rich. Don't care about gear or RPM's - what THROTTLE position does the hiccup or bog occur?

You can't tell anything by looking at your plug unless you performed a plug chop test properly, other wise you have no idea where the plug's deposits came from. For that reason, I pay little attention to the plug's looks and a lot of attention to how the engine PERFORMS while riding.
 

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I am unique
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This is what my plug looked like after approx 2hrs of run time.

I took the quad for a ride today.

It seems to run great off idle and during acceleration.

On long runs, once I reach 5th gear and get to the upper rpms it has a definite miss or something seems to be slipping.

It pulls very good/hard until I get to that point.

The idle is not quite as smooth as I'd like either.

I hope to get some plugs tomorrow and play with the jetting to see if there is any improvement.

Thanks again for the help!

Willy you've been a great help in the past. It's nice to have such a great resource at your fingertips.
To start with, give the carbs a good cleaning, this may eradicate your problems, unless you have done some mods that are causing the jetting problem............
 

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Discussion Starter · #8 ·
Cont.

I did do an extensive cleaning of the carbs disassbled them and sat the parts in cleaner for a couple of hours. Used cleaner, a brush and shop towels to clean up the rest of the parts. I recorded the necessary info to return them to pre-clean settings.

The airbox is in tact but has two 11/4" holes cut in the top.

How can I tell if I have dynojets or mikuni's??

The miss/hiccup is much better than it was. It was extremely noticeable before, it wouldn't get close to top speed. Now it doesn't do it until it is nearly maxed out.

It only really happens when I am on a long high speed run, i.e. 1/8mi or so. It seems like I have to get to 5th gear to get it to occur. When I am going through the gears full bore on a 100yd blast it doesn't happen.

It could just be me but it doesn't seem to pull as hard as it did in the winter or when the weather was much cooler.

Today, I hope to get some plugs and some jets and play with it but if you have any other ideas or suggestions I would be most appreciative.

Thanks again!
 

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Usually mikuni's have a little mikuni symbol on them. Also you can look at the numbers themselves - Mikuni mains will go by fives (or is it 2.5) and the Dynojet mains will go by 2. Since you have 146 and 148 those are dynojet numbers. I don't think the pilot jets have any difference in the numbering.

Note that the dynojet mains have a different numbering scale and a 146-148 DJ combo is somewhere in the ballpark of mikuni 155-160 or 160-165 (someone correct me if I'm wrong there).

Could be your floats out of adjustment - did you do the clear tube mod? - Check the stickies for that.
 

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I did do an extensive cleaning of the carbs disassbled them and sat the parts in cleaner for a couple of hours. Used cleaner, a brush and shop towels to clean up the rest of the parts. I recorded the necessary info to return them to pre-clean settings.

The airbox is in tact but has two 11/4" holes cut in the top.

How can I tell if I have dynojets or mikuni's??

The miss/hiccup is much better than it was. It was extremely noticeable before, it wouldn't get close to top speed. Now it doesn't do it until it is nearly maxed out.

It only really happens when I am on a long high speed run, i.e. 1/8mi or so. It seems like I have to get to 5th gear to get it to occur. When I am going through the gears full bore on a 100yd blast it doesn't happen.

It could just be me but it doesn't seem to pull as hard as it did in the winter or when the weather was much cooler.

Today, I hope to get some plugs and some jets and play with it but if you have any other ideas or suggestions I would be most appreciative.

Thanks again!
Engines will have more power when the ambient temperature is lower........this could also indicate that your jetting is too rich...........
 

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in my opion the plug looks lean also i would try 25 pilots 22.5 seem to small for your build that is just me im at 4600 ele and runnin 160 160 with 25 pilots
 
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