Motorcycle Repair: 78 cb 125 idles but wont run, point gap, yellow tank

Question
I recently bought a 78 cb 125 that didn't start.After cleaning the carb with compressed air and changing the plug 3 or 4 times(seems to get a little oil).I also replaced the points and set the timing as close as i could (seems to start opening slightly after "T" maybe 2 degrees).Now the bike starts and idles lovely .It also revs up good in neutral however if i try to ride thye bike it just splutters like it's not getting gas or something.It seems to run smooth in all the gears for a second then more splutterring
I seem so close because of the start/idle
My spark is not the fat blue one the manual says i should have it's more like fat and yellow
tank is clean
fuel is good
changed oil
What do i check next
Any help would be great
THANKS

Answer
Eric, thanks for the great clue...  you said you set the timing at 2 degrees AFTER the T mark, right?  Timing is set at the F mark which is about 5 degrees BEFORE the T mark. Now, after sitting for years, I would check the function of the spark advancer unit, located behind the point plate.  They can stick and hang up to where they don't move properly. Mark the point cam to the advance base relationship, because you can reassemble it 180 degrees out of phase. Once the advancer is clean, lubed and installed correctly, you can put the point plate back on, turn the motor over to find the widest point gap and set it to about .014" then move the point plate until the points just open at the F mark. If you put in new points, be sure that there is a little lubrication on the point cam and set the point gap a little wider, as it will decrease as the point cam wears down in the first few hundred miles. FYI T mark is Top dead center and F is the Firing mark. So, F comes before T, okay?

Be sure that the gas cap is venting properly and that the float level is set according to specs, if adjustable. You don't mention the mileage and the condition of the engine, overall. If the bike has a lot of miles or was seized, then the oil consumption may be excessive for good operation. Check the compression. Should be around 150-175psi in good condition. If there is blue smoke coming out the muffler, then either the rings are stuck in the piston or there is wear on the valve stems/seals or the piston/rings. Excess oil will foul the plug fairly quickly.

Did you clean out the petcock screen and is the tank clean inside? Be sure that there isn't any kind of corrosion, dirt or buildup inside the fuel lines and in behind the float valve in the carb. If you blew air through the passages, then it should be okay.

Don't worry too much about the spark color. Do make sure that the battery is new and fully charged. It is only a 6v system and with the headlight running so often, the battery voltage available to the ignition system is too great, so the spark isn't going to be big, fat and blue.

Bill Silver