1972 Honda 350 Scramble Carb Issue

My sons friend bought a 1972 Honda 350 Scrambler and while idling it will suddenly die.

He used a strong Sea Foam solution thru several tanks.

When initially starting, with the choke on it will start up and run then with choke off run good.

Then he takes off and when he comes to a stop within 5 to 10 seconds it dies.

Both carbs were rebuilt from a cafe racer shop.

New plugs and wires, points and condensor.

Any ideas?

Brian:

Let me preface this with the comment that I don't know anything about Honda 350s, but here is what I would check (not necessarily in this order):

1. Plugged fuel filter.

2. Plugged vent line from fuel tank causing a vacuum.

3. Floats in carbs stuck.

4. Junk in fuel tank partially plugging pickup.

5. Kinked fuel line preventing fuel from filling bowls in carbs fast enough to keep up with demand.

6. Electrical fault due to heat after engine warms up.

As I said, I don't know anything about this bike, these are just things to check of a general nature.

Jim

Brian:

 

Let me preface this with the comment that I don't know anything about Honda 350s, but here is what I would check (not necessarily in this order):

 

1. Plugged fuel filter.

2. Plugged vent line from fuel tank causing a vacuum.

3. Floats in carbs stuck.

4. Junk in fuel tank partially plugging pickup.

5. Kinked fuel line preventing fuel from filling bowls in carbs fast enough to keep up with demand.

6. Electrical fault due to heat after engine warms up.

 

As I said, I don't know anything about this bike, these are just things to check of a general nature.

 

 

Jim

Thank you Jim for your suggestions.

A couple thinks to mention is that while during continuous riding the Scrambler runs fine.

Also at a stop as long as he continues to slightly feather the throttle the engine keeps running.

The engines runs at an idle after the choke is off during start up, but as the engine begins to warm up, the engine at an idle eventually dies.

Pull the bowls off the carbs and check for idle jets being at least partially blocked. If Iremember right the idle mixture screws were on the side of the carbs. If you can't get it to keep idling you may have to back out on these a quarter turn to richen th idle mixture. Also if the bike is idling too low then it will probably die after a short time idling.

quality of gas or idle jets blocked. I would drain the gas and run fresh gas with no additives, new gas filter and fresh plugs first. Start with the easy and cheap

Ahhhh yes,, the good old Honda 350 Scrambler,,, my oh my its been a long time...

I remember when I was young and our local Honda shop had a big sale on them in 1972, 380 bucks out the door... Gettin side tracked a little:whistling:

Those 350's vent thru the cap, have him run it till its acting up and pop the cap and see if it changes..

Since the carbs have just been serviced and assuming the folks who did the work took the time to do it right:

I would take a peek inside the tank and see if he is picking up rust, stick your finger in there and rub around the internal edge of the filler cap and check for rust dust.. An inline filter wont help if the tank is rusty, small stuff will still contaminate the carbs. If you find rust he probably will need to clean the pilot jets again..

Another question.. Hows his battery/electrical system? Those ol Honda's are battery ignition..

Also, might wanna check the valve clearances on her, toss a timing light on her and make sure the points timing is dead on..

If it idles cold but not warmed up it is probably too rich.

Check for:

1) float valve not completely shutting

2) float level too high

3) idle mixture set too rich.