help sq 4 wont run

[kevinpender]

1951 sq4 laid u p for 10 years . was a runner then. Has had the head off and new gasket. New distributor . Starts with solex carb eventually until it runs out of fuel. Then will not start when hot. Fuel tank not fitted yet. Valve settings appear ok Timing has not been changed and I think I have timed the distributor correctly.
Will not start with new amal carb by drags. Compression seems ok . Measured with gauge when cold.
What am I missing or doing wrong. This is a simple engine which should run. Can anybody give me a check list?? Where do I begin?

[simon.holyfield]

Welcome to the forum! Is this bike yours? what do you know about the state of the engine rebuild? do you know when & who built it?

It's very, very risky to run one of these without knowing some history. The crankshaft oilways are very small and block easily if they have not been cleaned and a modern oil used.

[Simon.Gardiner]

Well, I'm absolutely no Square Four expert but the main things I know of that can deteriorate with just sitting around are electrical. They also change characteristics from cold to hot.
What does the ignition system have in the way of capacitors?
(Someone will know )

Edit:
Cripes, you might have a coil to play up as well!
If you can manage to wade through this thread guess there might be something useful.
viewtopic.php?f=4&t=8278&p=58787

SG

[simon.holyfield]

You says it starts with the solex until it runs out of fuel and then won't restart when its hot? There's nothing wrong with the Solex - you don't need to change it for an Amal. It doesn't surprise me that it won't start hot - mine is easy to flood and may be running rich - mine needs the bistarter for less than a minute if its very cold - if its warm, no bistarter and it will go. I'd get a temporary fuel supply rigged up and try again, from cold, and let it go for a while before you start worrying about other things.

As Simon says, it may be the condenser or the coil either of those can play up if it's hot.

[kevinpender]

Hi guys Thanks for the replies.
I have owned the bike since 1990. It had been in storage in a shed in yorkshire since 1970?? I ran it last in 2002 with solex carb and it ran perfectly.
When I bought it originally I used flushing oil on it . There does not appear to be any problem with the oiling system. I bought an AMAL carb from Drags as the solex was difficult to operate. However I have stripped and cleaned both carbs with acetone and compressed air yet amal no start solex run from cold and no start when hot Solex needs bistartr to continue running?

[simon.holyfield]

Let's go through the starting routine I use. After freeing the clutch plates, I pull the bi starter out all the way and kick - it will go first kick. I push the bistarter in as soon as the engine sounds rich, almost straight away, and I push it to the mid position. The engine will then run for a few minutes until it starts to labour & sound too rich - then I drive off and push the bistarter in after a couple of hundred yards.

I don't touch the bistarter again unless the engine is stone cold.

Have you tried giving it some throttle when hot starting? I find it quite easy to flood mine when warm, and a handful of throttle is useful to get it going.

Have a look at the points; the HT leads, the HT connections to the distributor and make sure it is all clean and shiny. I'm using NGK B5HS - I was finding B6HS would soot up quite quickly.

Do you know how to check the coil and condenser with a multimeter?

[simon.holyfield]

I wrote this in another thread:

The capacitor looks good. Using a multimeter set to ohms, one can observe the resistance rise to some 25 MOhms over a period of a few seconds - a smaller capacitor (new) I have for a Lucas 25D4 distributor rises to a similar figure in much less time.

The coil also checks out - 10 MOhms or so to earth from the HT connection, and suitable low resistance in the primary; 10,000 x that in the secondary. I didn't record those readings, stupidly.

Obviously those are cold figures - they may be quite different when hot.

[roger.fellows]

Is fuel getting through from the tank properly?

Any problem with the oiling system is likely to appear first as an exposed con-rod.

[chris.shearwood]

I have owned the bike since 1990. It had been in storage in a shed in yorkshire since 1970?? I ran it last in 2002

Hello Kevin,
Are you saying the motor hasn't been opened up to clean the sludge traps since the 1960's, if ever? If that is the case I would advise not to even think about running the motor until the sludge traps have been cleaned out.
Regards, Chris

[kevinpender]

Thanks Everybody for your input. Much appreciated.
The problem appears to be electrical. Now after removing and cleaning every HT lead and and distributor associated bits its running until fuel loss. And restarts when hot.
Chris Thank you. I will use flushing oil again before a big run . I do not really have the expertise to breakdown the bottom end. it ran well 10 years ago with no problem after flushing . My next step is to fit the Amal carb and then hopefully get back on the road. Any opinions on Amal carb??
I have a new one as supplied by dragonfly which I am going to try next.