250 Yet Another Jetting Question

RageD

RageD

I took the bike out for the first time since I rebuilt the top end and clutch this last Saturday. All was going well until fouled a plug at the bottom of a downhill and couldn't walk the bike back to the truck. I then proceeded to walk back to the truck and return to the track repair. Nice way to kill 30-40 minutes of valuable riding time :doh:. Anyway, I promise this story is relevant to my question and I'm done complaining now.

After I got the bike started again, I rode for another 20-30 min before I had to load up and head back home. When I got back, I decided to pull the plug and take a look at it; it looks about the same as the one that went out on me :thumbsdown: I haven't chopped this one yet because it's still starting and my new plugs are in the mail with some new jets (and I must have dropped the fouled one, so I don't have that one).

Here are some quick pictures of what it looks like:

IMG_0706.JPG IMG_0707.JPG

Maybe I really need to chop it before I can tell much, but I don't see even the faintest bit of white.

A quick rundown of temps, elevation, and my jetting for the day: day started around 50 degrees and then went up to about 65 degrees. I ride between 500-800 ft above sea level. At the time, the jetting was #170 main, #50 pilot, needle (N3VF) was on the 2nd clip, and pilot screw about 2 turns out. Generally speaking, I am thinking my main was probably a bit lean, but everything else about this seems sane to me (though I'm certainly no expert). I didn't have any hard starting issues that day though I did have a bit of hanging idle problem.

I pulled the carb and did a thorough cleaning (24 hour dip followed by a manual spray) and readjusted my float (which seemed to be a little bit high-- I was probably running rich there). Note that I had already repacked my silencer before this ride and had cleaned the air filter. Just to be safe, I have since replaced the air filter with a new one.

Now, on to my question: to me, it seems as though I have competing issues. I think the plug looks like I'm running too rich not to mention I fouled a plug while riding. Likewise, my float was set pretty high so that suggest to me that I was probably running rich from there. However, I thought hanging idle issues were related to running too lean. I was on the throttle coming off of a downhill when the plug died on me. Is it possible that one circuit was too lean while the other was rich? I'm not exactly sure what to make of this here :)

I was out working on it on Monday, but the temperature had changed rather drastically (70-75), so I couldn't exactly reproduce the issues (read: this has been the weirdest Illinois winter... Temperature swings from 20-70 in the matter of a week). The only issue that seemed to stick around was the hanging idle (but I had also dropped the jet to a #48 as part of my testing and never put it back to #50).

I had other odd issues this day too like leaking coolant though I couldn't find the leak (engine cases looked dry, so maybe overflow?) but I checked and the propeller seems to be fine and after adjusting air screw and riding around some more that issue seemed to stop... But anyway, that's mostly off-topic unless someone has additional thoughts (maybe running too hot, etc.?)

Well, there is my somewhat haphazard description. Anyone have thoughts on this situation? Should I try to go back to stock jetting and work my way out from there?
 
SRAD97750

SRAD97750

Moderator
Staff member
It is rich. I think float setting has most to do with the general black soot on the plug.
Hanging idle can be an indication of an idle lean condition, which is typically caused by an air leak at the carb boot/intake or an improperly adjusted idle mixture screw. Set idle and mixture while the engine is HOT.
Looks like you are on the right track. I would try again with the float set correctly. No reason to change brass unless it won't run at a particular throttle setting.

Slow drip from the weephole under the impeller housing is a sign of a bad water seal. But it is typically constant once it goes.
-BIG DAN:thumb:
 
2strokesteve89

2strokesteve89

I agree with Dan here,you may have found the issue causing the fouling plug with the rich float setting. Start small with jetting as in his suggestion of adjusting air/fuel mixture screw. If the idle rpm doesn't lower with adjustment you may be looking at an air leak which can be found with carb clean or propane around the carb boot area. On the coolant leak issue, why do you think you have a leak, is there coolant drips under bike or are you regularly topping off coolant without any other signs of coolant loss? Don't rule out a bad radiator cap.
 
RageD

RageD

2strokesteve89:
On the coolant leak issue, why do you think you have a leak, is there coolant drips under bike or are you regularly topping off coolant without any other signs of coolant loss?
Click to expand...

I was watching coolant drip from the bottom of the bike when it was hot. I topped the radiator off after it cooled down and after similar riding for a similar amount of time, the issue subsided. Like I mentioned, I couldn't find anywhere on the cases where this actually was coming from. Can this happen temporarily from a one-time overheat, maybe? When I got back I realized it was a pretty fast sounding idle.
 
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2strokesteve89

2strokesteve89

RageD:
I was watching coolant drip from the bottom of the bike when it was hot. I topped the radiator off after it cooled down and after similar riding for a similar amount of time, the issue subsided. Like I mentioned, I couldn't find anywhere on the cases where this actually was coming from. Can this happen temporarily from a one-time overheat, maybe? When I got back I realized it was a pretty fast sounding idle.
Click to expand...

If you top the radiator off when it's cool you may get some coolant that passes by the cap from expansion as it warms up.When I fill the radiator I usually adjust the level when it's warmed up. Like I said before though, it could be a weak cap also, maybe throw one on for general purposes and see if you stop noticing the coolant loss.
 
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RageD

RageD

Great, I'll take a look. I noticed my reed valves are slightly chipped-- could that be related? As I may have mentioned, I bought this bike from some guy that I'm pretty sure never performed any maintenance outside of changing the oil :) These are probably the stock reeds from '99 -.-

I bought some replacement Boyesen reeds and those should be here in the next few days.
 
RageD

RageD

Well the new ones come today :) I'll let you guys know how it turns out when I kick it over. Maybe even tonight if it's not too late after work (I try to be nice to my neighbors lol)
 
Mihylo33

Mihylo33

RageD:
Well the new ones come today :) I'll let you guys know how it turns out when I kick it over. Maybe even tonight if it's not too late after work (I try to be nice to my neighbors lol)
Click to expand...


Use blue loctite on the screws and let the bike sit for 24 hrs before running it so the loctite cures.
 
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