Topic: Hard starting when cold

[club_c]

Hello boys and girls. 1980 CB650C. I’ve got it all reassembled, looking good and running well. When it’s warm. But it is a beast to start when cold. I have to give it a shot of carb cleaner in the intake to get it to start. Once warm it starts with a touch of the button. I’ve been into the carbs numerous times and paid attention to the accelerator pump too. It would seem it’s not getting enough fuel since it’ll go with the carb cleaner?  Dunno. Could use help on this. Please.

[TwoTired]

Are you certain the choke closes fully?

[club_c]

Yes fully closed

[pjlogue]

Try enrichening your idle air circuit a bit and see if that helps.  Be sure your carbs are balanced before you adjust the idle air mix.  I had this same problem with my '76 750K.  Slight enrichening of the idle air circuit helped the cold start problem I had.

-P.

[TwoTired]

Yes fully closed

Sorry, you need to be more specific.  Have you verified that each and every choke plate is closing on each carb, when the knob is drawn out?

[club_c]

Try enrichening your idle air circuit a bit and see if that helps.  Be sure your carbs are balanced before you adjust the idle air mix.  I had this same problem with my '76 750K.  Slight enrichening of the idle air circuit helped the cold start problem I had.

-P.

I will try this. But is it in or out to enrichen?  Carbs recently balanced in last couple of weeks with vacuum gauges.

[club_c]

Yes fully closed

Sorry, you need to be more specific.  Have you verified that each and every choke plate is closing on each carb, when the knob is drawn out?

All choke plates fully closed when knob is drawn out

[TwoTired]

When you cleaned the carbs, did you yank the pilot jets to clean them?

Do you have the stock mufflers on the bike?

[club_c]

When you cleaned the carbs, did you yank the pilot jets to clean them?

Do you have the stock mufflers on the bike?

Yes I did pull the pilot jets and clean them. Each carb was ultrasonic cleaned as well. Good point on the exhaust. It is now a 4 into 1 design. It is very mellow, not a “neighbor hater”.

[TwoTired]

If the new mufflers have less back pressure than the originals, it has the effect of leaning the carbs if still jetted to factory specs.  Same is true with air filter restriction mods.  Honda had to meet epa idle emissions tests for importation which meant very low hydrocarbon exhaust sniff tests to pass.  Muffler back pressure caused a reburn of some of the mixture and allowed carbs to be tuned leaner due to burning the leftovers. 

You might be able to compensate by enriching the idle mixture screws.
This assumes you’ve done all the standard tune up duties specified by the owners manual before ever tweaking the carbs.

[club_c]

SOLVED.  As I mentioned these carbs were in pieces and I had no history on the bike. The resolution to the hard start cold was: replacement of accelerator pump diagram (old one began to disintegrate once reinstalled) and most importantly, float levels triple checked and readjusted to 12.5mm when the bodies are held at an angle so just touching the float needle. Not completely upside down. With a couple of twists of the throttle (activating the accel pump squirts into the carb) it immediately fired up cold even without choke, tho choked it a little after it fired up. I believe the most significant issue was the float settings. For those that will go on after me…