Spark Plug Issues

[Alson]

trouble shooting carb

I put the brass arms that regulates the float hight from my stock carb, which looks much higher. Took it for a ride, and the sputter is gone, it runs very good and cruses nice in slow movement. I dident have a mm mesurment, but runs good but seems like I lost a litt,e top end, when Im going slow and open it up it bogs then goes. I dont know if its to ,ean, I didnt take the spark plug out and look yet. If its lean should I bend the brass things down a bit. When I have the carb upside down the float and the the top of tbe brass valve are flush, your pitcher it was up above the float a little. Ill check the plug and go from there

 

[Alson]

Thanks Steve for the info, jt was tbe float level

 

[Alson]

My plug is a light chocklet brown, like nesley quick

 

[AussieSteve]

Good timing. I was just about to reply. Been pretty busy.

I knew that it had to be something simple. (There's nothing complex in these engines.)
I'm glad it's sorted.

Regarding final adjustment, it's best to set the float at about 21mm, then use the slide needle height and main jet size to get things just right. Altering the float level to adjust the mixure will lead to problems.

The plug colour doesn't sound too bad, possibly very slightly rich. If it was lean the plug would be grey or whitish.

Best to do plug chops at mid-throttle and WOT with a new plug, as described in 'NT Carb Tuning Basics', to do the final adjustments.

Good luck.

P.S. It's better that the mixture is slightly rich, rather than lean. If it's not 4-stroking, I wouldn't be overly concerned if I were you.

 

[Alson]

It seems like I lost just a little top end about 3-5 mph, I dont have a speeddometer, but I can tell, I thought about lowering it just a little, I dont knowl mabe I should just leave it a,one ,ike you said, see I realy dont know if its set right, I had no mm mearsUment deal to measure jt. I looked real close at your pitcher and your nedel valve was just a little up from your float, mines even wjth the float, makes me think jt might be why I lost a little top end

 

[AussieSteve]

Still best to actually measure it if you can.

Then you should ideally do what I suggested. Anything else is just messing around.
Hopefully I don't sound rude, but i've already said it all.

I do re-iterate, though, don't try to tune your bike by float level adjustment. Just set it at 21mm. (Buy a steel rule if necesary, they're only a couple of bucks.)

 

[Alson]

Alright, Steve, thanks, Alvin

 

[AussieSteve]

No worries, glad I could help.

 

[Alson]

tuning

Thanks again, you realy did help

 

[Fabian]

Hi Alson,

Please be careful with your comment: "I took my bigger jet out and put the stock jet in jt, it runs the same."

From my experience, the engine may appear to run the same, but if it runs well on the larger jet and you replace it with a smaller jet, it will only run hotter, and most likely detonate, causing the connecting rod big end bearing to fail.

I've had 5 engines all fail with exactly this same problem (big end connecting rod bearing failure) and since replacing the main jet with a larger Dellorto No 84 (through trial and re-trial) i've not had any more engine failures.
Every one of my engines would fail at 700 kilometers (approx 450 miles). The distance figure of 700 was so repeatable it was almost laughable.

Fabian