Smoking 400/4

Hi all

I’m new to your forum and after some advice please with the great weather recently my 1975 400/4 came out of hibernation started straight away no problems but burning a lot of fuel and ticking over at about 3000 revs when hot the white smoke I’m guessing is condensation but it smells of petrol any thoughts please

Hello and welcome. I’m sure someone will be able to help.

Hello and Welcome

If it's been stood over winter I'd let it get warm a couple of times and see how it is

Hi yeah I’ve tried that took it out for a good ride came back and smoking again on tick over

White smoke is usually related to water but on an air cooled you can rule out head gasket, fresh petrol, checked the oil, is it using any, small amount may be very light blue.

Do a plug check then report back here. Have you got a compression tester? If so, what's it saying? Tickover sounds high - should be about 11 - 1200 rpm IIRC?.

Welcome aboard.

How long has the bike been stood up,just over the winter?

Assume it was running ok when you last rode it?

A few things I'd check;

Has the choke mechanism stuck,gummed up

Throttle slides all moving freely.Throttle cable free.

Carbs overflowing,stuck float valves.

Inlet rubbers not perished or gone hard.

Air filter ok.

Presume all the basics; points,ign timing and valve clearances all ok?

When I were a lad in the 70's a guy in our village had a 400/4 with an aftermarket exhaust,you could hear him miles away redlining the thing

Welcome aboard.

How long has the bike been stood up,just over the winter?

Assume it was running ok when you last rode it?

A few things I'd check;

Has the choke mechanism stuck,gummed up

Throttle slides all moving freely.Throttle cable free.

Carbs overflowing,stuck float valves.a

Inlet rubbers not perished or gone hard.

Air filter ok.

Presume all the basics; points,ign timing and valve clearances all ok?

When I were a lad in the 70's a guy in our village had a 400/4 with an aftermarket exhaust,you could hear him miles away redlining the thing

Hi Bianco - I had similar thoughts especially with high idle but if it was excess fuelling then I would expect darker or black smoke, not white. I suspect a stuck ring but a plug check/chop will reveal more.

Hi checked plugs all wet with petrol cleaned and set gap runs better but still smoking

I had 1 that colour years ago! loved it!

hope you get it sorted

I had 2 of them......blue and red!

Did you replace the fuel? Empty carbs over winter and put a tea spoon of oil in each cylinder to stop them rusting? I had a Smokey CG 125 the piston rings had worn out. Replaced them and it was fine again. Yes you're meant to rebore but bike was worthless. Had over 40k on clock

Are you sure it's white smoke? is there any smoke coming out of the crankcase breather hose? Being air cooled eliminates a water leak. l would go for an oil change anyway. A good run should normally vent off any moisture that built up in the engine and exhaust system, and a tank full of fresh fuel should take care of the fuelling end of things.

Do you have alcohol if your petrol over there?

Here, if you don't fully drain the carbs, they corrode internally.

I had to fully strip and clean carbs on my bike- a 1980 Yamaha, quite regularly.

The symptoms were: flooding, not starting, not idling, or running like a dog.

Modern carbs post 1995, may be a bit more fuel resistant?- no brass parts...

Dirty float valves and seats may allow running, but could run rich, or allow petrol to run out the overflow pipes.