Topic: CB350F poor cold start

[Wilson]

My 1972 350F is very reluctant to start after sitting for a couple of days. With the choke on the starter spins the bike over but but it won’t fire. After several tries the bike finally starts to fire and eventually runs. After that the bike starts instantly as long as I don’t let it sit for more than a day.
The carbs have been cleaned, rebuilt and sync’d. Timing and valves set. Still running the original coils, regulator, rectifier.
Any thoughts?

[carnivorous chicken]

Fuel evaporates from the bowls, meaning they have to fill before it will start. Next time it's been sitting for more than a day or two, turn the gas on and count to 20. Same thing happens to mine, so when I go to ride it if it's been sitting for a couple days first thing I do is turn on the fuel before putting in my key and and getting on it.

[jonda500]

When cold, try priming it first.
 With the ignition off, the choke fully closed and the throttle held wide open kick it over a few times, then release the throttle, turn on the ignition and upon trying, it should fire immediately!
John

[newday777]

My 1972 350F is very reluctant to start after sitting for a couple of days. With the choke on the starter spins the bike over but but it won’t fire. After several tries the bike finally starts to fire and eventually runs. After that the bike starts instantly as long as I don’t let it sit for more than a day.
The carbs have been cleaned, rebuilt and sync’d. Timing and valves set. Still running the original coils, regulator, rectifier.
Any thoughts?

Welcome aboard the forum Wilson
You say you have the original coils. Have you tested the resistance of the coils and spark plug caps? This is an important factor. Do you have the service manual for your bike?
You may only have a bad connection to the spark plug caps in the plug wires allowing ambient moisture in. (Not knowing where you live, it being spring, cold morning temps and moisture possibilities???) After you get your bike started and warmed up it burns off any moisture in the plug caps/wire connections. To fix...
Unscrew the plug caps from each wire, cut off 1/4"(@6mm) of each plug wire to expose fresh plug wire, screw the cap back on if resistance checks good. This should help it start better.
Post back a reply of how you make out on this afterwards.

[carnivorous chicken]

Welcome aboard the forum Wilson
You say you have the original coils. Have you tested the resistance of the coils and spark plug caps? This is an important factor. Do you have the service manual for your bike?
You may only have a bad connection to the spark plug caps in the plug wires allowing ambient moisture in. (Not knowing where you live, it being spring, cold morning temps and moisture possibilities???) After you get your bike started and warmed up it burns off any moisture in the plug caps/wire connections. To fix...
Unscrew the plug caps from each wire, cut off 1/4"(@6mm) of each plug wire to expose fresh plug wire, screw the cap back on if resistance checks good. This should help it start better.
Post back a reply of how you make out on this afterwards.

After that the bike starts instantly as long as I don’t let it sit for more than a day.

Leads me to believe it's fuel not spark.

When cold, try priming it first.
 With the ignition off, the choke fully closed and the throttle held wide open kick it over a few times, then release the throttle, turn on the ignition and upon trying, it should fire immediately!
John

This is probably just buying time for fuel to fill the bowls. I don't do any of this, but just wait and it fires right up. To each his own though.

[dave500]

go right over your ignition first,also check the charging rate,if the battery isnt fully charged the spark can weaken when cranking,also have the headlight switched off.

[M 750K6]

New or old fuel? When you put the carbs back together, did you check the chokes were still adjusted so they all close fully?

[drodg33]

When cold, try priming it first.
 With the ignition off, the choke fully closed and the throttle held wide open kick it over a few times, then release the throttle, turn on the ignition and upon trying, it should fire immediately!
John

This is what I have to do with my 72 500F.  I had it for a year plus and had the hardest time starting it and someone on this forum recommended this starting procedure and it starts right up now. After turning the ignition on I do give it about an 1/8 of a throttle. 

[Wilson]

Problem seems to be solved. I now ensure the battery is kept fully charged by using a battery tender.  I turn on the fuel and wait a couple of minutes, choke full on, light off and hit the starter button. TaDa…the bike starts. Thanks for all the suggestions.