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Get a copy of the maintenance or shop manual for your engine.  Most likely you need the Honda Helix CN250 manual.  That's the 244cc engine.  Google it for free downloads.  It will show you how to properly adjust your valves.  You must align the engine to the proper TDC marks to adjust the valves.  If you didn't you might have bent the valve stem.  If you are lucky, you just adjusted the exhaust valve way too loose and hence the clanking.  Be sure you do this right, it will get expensive if you don't.  You don't have to pull the valve cover, there are view ports for aligning the engine for a valve adjustment.  It's in the manual. 

Once you have the valves adjusted correctly, make sure the spark plug is good.  If the spark is weak, change the plug before you go any further.  I had a hard starting problem with my Lance Duke Turing 250 that turned out to be a bad plug, after much gnashing of teeth.

I got the #118 jet in and encountered a problem. The engine would start with no throttle and then bog down it any throttle was added. The CV slide was not lifting. I put my finger in and lifted the slide (manual calls it a vacuum piston) manually and it worked. I thought the diaphragm might be damaged, so I switched in the one from my old carb. Same thing. I thought maybe the bigger jet was the problem, so I put the #110 back. Same thing. Finally, I cut about 2 turns off the diaphragm return spring and WOW. Not only does it work right but it develops a lot more horsepower. Does anyone have any experience with this? Am I correcting for a clogged port or a vacuum leak or are the stock slide return springs actually to long?

I got another carb for my Lance Duke 250.  The idle mixture screw had frozen in my old one.  The new carb (from China) didn't even have a brand name or model number on the body, but it works fine except that it runs lean according to the plug.

I took the needle up one slot, but still not enough.  Only one slot left which will be taken up today.  I do like that it will start and idle cold almost immediately, unlike than the old carb.  Never the less, it seems to run hotter.

I checked the main jet which is the same size as the old carb, a #110.  I think I'm gonna need a bigger jet.  Are larger jet numbers bigger or smaller?

It occurred to me that overheating problems I'm having and that I am reading about here may be due to a change in gasoline to include some ethanol, which mixture if I remember correctly, burns hotter.  I think the mixture here in California is 10% ethanol, but don't quote me on that.  It would also explain my idle mixture screw freezing.

If ethenol is the problem there may be a run on bigger jets before this is all over.

So from a #110 jet, which is a larger jet, a #108 or a #115?

Slick! Proboards reads a video url and inserts the video in a post in place of the URL. In the case of the 'Prevent intake flange failure' video in my last, you must click the YouTube symbol at the lower right of the video to go YouTube and be able to see the parts list and source in the author's comments.

Thanks a bunch gooter!  I would be interested to know if your Duke heats up after more than 10 min. of wide open throttle.  If it doesn't, and your replacement radiator is the same size as the original, it appears the original fan is inadequate and the rest of the system is OK.

I sure would like some pictures of your setup.

This is an attempt to get an upload of better resolution.

I took my radiator apart and rodded it out.



It had a pinhole leak where the tubes joined the end plate. You can see from the internal rust pattern of the radiator in the foreground that it had been running about 3/4 full. I fixed that leak and the tiny one at the tube coming out of the engine & going to the carb, a cooked hose end probably.

I had it out the other day in 95 degree heat in town. The temp pegged again. Arriving home I immediately got my temp instrument and read 210 F at the crank case. My guess is the cooling system keeps up until the oil temp rises and then it's peg city for the duration.

Either the cooling system is inadequate or there is a blockage somewhere. I'll be checking the hoses next. Other than that, I can't think of anything I haven't checked except the temp sensor.