Topic: Cb400f Misfires in the Rain

[philcarroll_1985]

Hello all, got caught in a heavy down pour last week, at first the bike misfired but carried on running, shortly after that it cut out altogether. Had 5 mins under a tree to dry off then the bike started fine as if nothing had happened. Can I weatherproof the bike in anyway? The pic was half hour before this incident, any excuse to post it

Sent from my VOG-L09 using Tapatalk

[The Sovereign Man]

Possibly spark plug leads and/or caps.

Get the bike running at home and spray the leads one at a time with a spray bottle (don’t drown everything) and see if you can replicate the problem.

Next culprit could be the coils.

[Nurse Julie]

My 400/4 does that, its the type of rain we have in the UK 😁😁😁. Starts off as a four in dry weather, down to a triple in a light shower, a twin in a heavy sharp shower and a single in a deluge. Always manage to get home on one cylinder though 🤣🤣🤣

[RAFster122s]

WD-40 carried on the bike might help if you can give the wires and caps a good spray down after they get wet. Often periodically spraying things down is enough to help get you through a light rain next time. I usually replace wires and caps having these issues. Wonder why the 400 seems to have this issue?

[scunny]

My old brain recalls something about the length and location of the carb drain lines causing problems if they are to long.

[BenelliSEI]

Do you have a good, well fitting gasket under the points cover?

[Trevor from Warragul]

My CB350F used to do that after I washed it. The solution was to dry the motor with an air compressor. Doesn't help you much, though...

Trevor

[bryanj]

"They all do that sir" was the standard dealer answer in the day. Besy answer from list, carry WD 40 (NOT PENETRATING OIL) and liberally spray plugs, caps, leads, coils and anything else under there

[Deltarider]

My old brain recalls something about the length and location of the carb drain lines causing problems if they are to long.

I've seen two reports on this. Both concerned a CB550K3/4. May also be the case on other models. Remedy is simple: just cut a few cm of the tubes.

[philcarroll_1985]

"They all do that sir" was the standard dealer answer in the day. Besy answer from list, carry WD 40 (NOT PENETRATING OIL) and liberally spray plugs, caps, leads, coils and anything else under there

Exactly what I was told by my Dad, he said it didn't like the rain but didn't think it would be quite so dramatic. Wd-40 it is

Sent from my VOG-L09 using Tapatalk

[philcarroll_1985]

Do you have a good, well fitting gasket under the points cover?

Nope, I'll have a look into that thanks

Sent from my VOG-L09 using Tapatalk

[philcarroll_1985]

My old brain recalls something about the length and location of the carb drain lines causing problems if they are to long.

Any idea what the theory is behind that?

Sent from my VOG-L09 using Tapatalk

[Deltarider]

Often wondered myself. All I know, is it takes just a tiny droplet of water to hinder proper carburetion.

[bryanj]

Remember the reports were K3/4 and they have different lean burn, therefore more finiky, carbs

[Old Moe Toe]

I have got a truckload of "Water Damaged" Umbrellas going cheap.

[Erny]

My old brain recalls something about the length and location of the carb drain lines causing problems if they are to long.

Any idea what the theory is behind that?

Sent from my VOG-L09 using Tapatalk

I had very similar issues on my CB750 K7. See posts from members wobbly & enwri that explained it - clogged upper body vents. It was confirmed recently on my K7, vents were totally clogged. Did not test again on wet road yet, but I believe this was route cause.
This is relevant for my PD41 carbs, but I assume can be similar on your carbs

http://forums.sohc4.net/index.php/topic,179023.msg2077590.html#msg2077590

[mattsz]

Do you have a good, well fitting gasket under the points cover?

Nope, I'll have a look into that thanks

Be careful if you purchase another.  I bought a "brand new, NOS" cork gasket - after waiting a week for shipping, I found that it simply didn't fit.  Its overall diameter was either too small from the get-go, or it had shrunk over time (see pic).  I'm going to make my own...

[BenelliSEI]

MattSZ. Old trick: If you soak an old, dry cork gasket in a pan of water, it will “grow”. Carefully clamp it in place and it will retain that shape when it dries.

[mattsz]

MattSZ. Old trick: If you soak an old, dry cork gasket in a pan of water, it will “grow”. Carefully clamp it in place and it will retain that shape when it dries.

You don't say!  I'll keep that in mind for next time - I already returned the "shrunken" one... and I've got some sheet cork from another project...