Honda-SOHC

Right, you are all going to think this is my imagination and i'm going crazy but here goes:

74 CB550, has electronic ignition and a solid state regulator / rectifier all new. New bog standard lead acid battery.

Bike starts on the button, rides fine.

If I don't use it for say 2 to 3 weeks, when I put the key in the ignition and turn it on (just on, no attempt to start it), the bike makes a brief hiss then wont do it again.
Bike fires up perfectly, idles fine, rides fine.

The hiss noise will not come back for a least a couple of weeks if the bike is not used.

Hiss is nothing to do with the fuel tank, petrol tap is off when it happens.

Just wondered if there was some kind of valve in the battery maybe to release pressure?

It sounds like it comes from below the seat so i'm thinking battery. Battery is fine, holds a charge.

Please, no Snake comments 

https://www.ebay.co.uk/itm/Honda-CB550-CB-500-Four-Exhaust-Rat-Bike-Homemade/323831734666?_trksid=p2485497.m4902.l9144

Just had the company car MOT'd by that well known company, 2 words first one begins with K.

If it was my own car I wouldn't touch them with a barge pole, but the lease company say we have to use them.

From them getting my car out of their car park to finishing and parking it up, 15 minutes exactly 

I know the MOT rules have changed but didn't realize it was way quicker now.

Anyone know anything about them, my mate has had one in his shed for must be at least 10 years.

Hasn't moved in all that time. He's now thinking of selling it so I may go for it. Think the engine needs a bit of work.

Been watching a few bikes on Ebay over the past few months.

Can't understand why people are having bidding wars when there are days and days to go before the auction ends.

All it does is push the price up, great for the seller but not the bidders.

One I was watching recently, 6 days to go, 2 people out bidding each other, whats the point?

Am I missing something?

I'm really confused.

I messaged Bob and asked him if he could do a cover for my 74 550 and sent him some pics.

He said he could for a very reasonable £35 plus postage but then he said that Silvers do them for around a tenner cheaper.

I asked him if his were better quality but he said he doesn't compare his with others.

Has anyone had a cover from him, are they better than Silvers?

In the attached pic, there has never been a pipe on the outlet at the bottom, I'm assuming it should be blanked off?

My 550 K0 with 022A carbs has been running perfectly except for number 2 overflowing.

I have stripped the carbs today, with new o-rings from Gerben.

Just done the bench sync with a 3.2mm drill bit, throttle stop screw all the way out.  Adjusted for the same gap on all 4 carbs, repeated several times, all bang on the same now.

Noticed that there are more threads showing on the adjuster for carb 1 than the other 3, does this matter?

Haven't refitted the carbs yet, wanted to know if it was ok first.

First pic is 1 and 2, second 3 and 4.