Need help! Bike will not start!

[Lee Bowen]

I have a Honda CM400 Custom, 9,355 miles.
The bike has been running great until a few days ago when it was very difficult to start.
When it did start it would only run for a few seconds to about a minute. But once it did start and I drove it for 5 or 6 miles no problems until a few hours later it would not start again.

I have checked the fuel flow out of the tank, no obstructions, can drain fuel out of the carbs using the drain screw. Replaced the plugs (checked gap before installing .028) checked the coil (by removing the plug and grounding it) it works.

In trying to start the bike it seems that I would have to flood the engine (it would back fire a couple of times) and then start and run for a short time.

Also I open the air box and found fuel in the air box. I don’t the cause.

Given I have fire to the plugs and fuel flow to the carbs my guess is I have a float problem?

[TechTMW]

Since you have fuel in the airbox I would say that you are probably correct in your assumption that it's a float problem. It would be good to take off the carbs and open them up and check the float heights. Another possible problem is that one of your jets has vibrated out of the carb and is sitting in the bottom of your float bowl allowing too much fuel up into the engine. Either way, You need to take the carbs off and check out the insides.

Good luck!

[Lee Bowen]

Thanks!

Lee

[Lee Bowen]

TechBMW,

I have taken the carbs off, no jets in bowel, a thin layer of sediment on inside of bowels, removed same.

Took off the tops of both carbs, found an oily substance (probably varnish) coating the round thingie (I don’t know that it is called but it slides up and down in the carb and is pressed down by a spring) that holds the needle. I have carefully cleaned the oily substance and a black film (I think this was carbon) from the inside of both carbs and reassembled.
Didn’t have time to re-install carbs tonight. Will tackle tomorrow.

I found nothing obliviously wrong all jets were in place and tight and not clogged. The needles were free and relatively clean wiped off easily.

The “thingie” in the top was slightly sticky with a small amount of résistance (Don’t know much resistance is to much) cleaned up easily.

What would be my next move?

Thanks for your help.

[TechTMW]

it slides up and down in the carb and is pressed down by a spring)

That is called ... The Slide ! or if you want to get technical, the "piston Valve"

If you reinstall the carbs and still have the prob, let us know.

[Lee Bowen]

OK, here we go, again!

Re-installed carbs, it took several tries before the engine would start but it do start ran great even restarted three times. Now it won’t start again.

Plugs are firing and have fuel.

Help!

Lee

[Lee Bowen]

Update!

Pulled plugs, left plug had no spark and right plug showed weak and intermittent spark.
I have ordered a repair manual, however it has no arrived.

What could cause weak and intermittent spark?

Points? Where are they?


Lee

[Gadjet]

What year is your bike? if it's newer than about 1980, it shouldn't have points and condensers.

Sounds like a bad coil or cracked plug wires.

[Lee Bowen]

Honda CM400 Custom 1981

If no points what and how do I trouble shoot?

Lee

[TechTMW]

You need to get an electrical multimeter and run through the Ignition system troubleshooting tests laid out in the manual. You need to test the Coil, Plug wires, plug caps, Ignitor ... etc etc.

Your manual will have all the deatils.