250-500cc plugs keep fouling?

Just got done doing a new top end and my bike keeps fouling plugs. It had started to do this before i rebuilt it but plugs look fine but just foul after a minute or two. Could my gas/oil mixture have too much oil? Im prob gonna try fresh gas but it runs great until it starts to foul and bogs when you rev it and the just dies.

Well, what is your gas to oil ratio? We can't tell you if you have too much oil if you don't tell us what it is.

40:1 and 50:1 are both very common and should be fine. Even down to 32:1 is probably ok.

I'd be inclined to think it's a jetting problem, but I don't really have enough detail to be sure.

Trav...what carb are you running?

I have an older dellorto...Its on my 91 wxe260. I richened it up a bit on the mixture screw because the temps are dropping a lot here but I dont see how that would make it foul them so fast because it was perfect before. I am running 40:1. What kind of a jetting change would I need for about a 30 degree colder temp? Are the mixture screws real touchy on these carbs? I only went in about 1 turn. I might go back to what I had before and check it again.

I got rid of my OE Dellorto on my 95 WR360 for the very reason that they are so finicky that l often foul plugs to the point that l seized my bike when it suddenly leaned out in top gear. A respected Husky dealer/mechanic measured he slide bore and found it was worn so the whole carb was now too sensitive to tune - essentially they (Dellorto) are a great carb but don't last as long as the jap carbs.
So, basically ditch the dellorto and find a carb that 99% of the dirtbike world uses (Mikuni TMX or Keihin PWK).

ignition failing/fault

This thread is a few months old.

what the hell, check your crank oil seal could be knackered if it is acrid blue/ white smoke will be coming from your exhaust.

(yeh the threads old but it may have relevent info if we keep dragging them up).

Put a little gear oil in the tranny. If your crank seal is gone, you will smell it.

Haha yeah problem was resolved. cant remember what it was. Wasn't crank seals but I think it was a combo of too rich on the carb and too much premix for break in. It runs great now and have zero issues. Also think I had the wrong plugs at the time.