Non-starting G9

ChrisD200 · Post by **ChrisD200** » Sun May 24, 2009 4:55 pm

Hi all, hope you can advise. My 1951 G9 used to start so easily - one prod and away we go. Now its a b----h to start and it runs for a few seconds only. Indeed it will even start on a single plug and idle for those few seconds. Yes there is fuel getting to the carb, the moment it stops I only need one touch on the tickler to make it flood and the tank cap isn't blocked and the tap flows plenty fuel.
No changes have happened to the carb since it last ran and there are no leaks. I've blown out the needle, main and pilot jets and there was no blockage. The slide is a bit sticky but whether I move the throttle or not, it still dies. One thing I notice is the air slide cannot be adjusted lower than the middle of the carb throat. Is that correct? (I don't know how this ever affected the slow running anyway).
The magneto is still firing fine even when the engine dies as a strobe light on one plug continues to fire.
So any advice would be most welcome - this is the fifth failed weekend ride where yet another problem arises!

Urbsam · Post by **Urbsam** » Sun May 24, 2009 6:00 pm

What carb do You have, ?
Is there a filter in the carb fuel inlet?
Do the fuel flow throw the carb with the bottom plug away?

Groily · Post by **Groily** » Sun May 24, 2009 6:34 pm

So hard to say why something does what you describe, but it can only be fuel or sparks assuming the engine's OK.

Thinking about your air slide: Did you used to have to use it, fully closed, to start from cold? If so, and it's only half closing now, that could be part of the problem, although a good flood with the tickler ought to make it unnecessary, especially in milder weather. But could be it's just a bit weak on start up, and so coughs and dies.

Have you tried some different sparking plugs by any chance . . . just in case? And does the strobe light continue to light up on the other plug? Ie will it start briefly on EITHER cylinder, or just on one side?

More often than not, things I have thought are fuel problems turn out to have been ignition, and . . . vice versa. So I'd have a quick look at the contact breaker on the mag and give it a tweak if necessary, I'd have a look at the HT pickups and wipe the slip ring through one of the holes, I'd swap the plugs, I'd flood the carb using fresh petrol if the thing has been standing over the winter (?), whatever carb it is, and try again.
Can't be much wrong if it used to run fine and nothing has been changed. Good luck!

ChrisD200 · Post by **ChrisD200** » Sun May 24, 2009 7:10 pm

Guys - thanks for your quick answers. I don't have a filter inline, but the fuel does flow easily. If I remove the bottom of the mixing unito, where the float chamber is bolted on, fuel flows.
Groily, I have thought of plugs - B6ES are on the bike so I'll buy a pair tomorrow. If the mag had failed, surely I'd get no spark then the strobe wouldn't fire either. I must admit I didn't test both sides with the strobe nor whether it would fire on both sides. But when it does start it fires on both cylinders and strongly too. For that reason I don't suspect bad petrol also the tank fill was very recent and I suspect thev spargks are OK. I will though check the HT pickups for dirt and the slip ring etc. The bike has stood for a couple of weeks whilst I was away so I still need to check for mousenests.
Don't know about whether the slide has always looked like this as I've never had it apart (I've only had the bike for ~500km so far despite the 18months ownership). It just doesn't look right but nothing seems wrong. How far down the carb throat should the air slide move - all the way down? If so, then I do have a problem. Hope it is nothing complicated as my RE Bullet is also down with a clutch problem. Such is life - cheers all, Chris

itma · Post by **itma** » Sun May 24, 2009 10:21 pm

first thing to come to mind is a sticky valve;
next time be prepared and run a quick compession check.
next; are you running on unleaded?
unleaded has been known to cause sticky valve stems in older machines, first brought to attention by some of the old car crew; I have had this as well, solution seems to be a good dose of Redex.

Groily · Post by **Groily** » Mon May 25, 2009 12:04 am

Air slide should, I reckon, come down pretty much to the bottom of the throttle slide. Certainly I'd expect to see the lower bit of the air slide sitting snugly behind the throttle slide cut-out when the air slide is closed. Have to admit I haven't fitted mine (on the same Type 76 carb) as it doesn't seem to need it even in winter. It's more important that the darn thing pulls cleanly and fully up and out of the way for normal running!
Could be a valve though, as itma says. This petrol we get nowadays is sticky old stuff. So might be worth whipping the rocker covers off just to see - although, I know, the tank mountings can be a major pain!

paul knapp · Post by **paul knapp** » Mon May 25, 2009 12:55 am

G'day Chris, one pecularity I have noticed with my 1951 twin is that from a cold start, it requires full choke, I.E., the choke slide must drop to the very bottom of the intake bore, If not, after flooding with the 'tickler', it will briefly run then stop. The choke must be used till the engine has a little warmth in it then it can be lifted.

Paul

wilko · Post by **wilko** » Mon May 25, 2009 1:00 am

Yes twins love tons of fuel for cold starts. But it will be dud plugs for sure, as proven a million times before. NGK's wont tolerate flooding no matter how well you clean and dry them out.

ChrisD200 · Post by **ChrisD200** » Mon May 25, 2009 8:30 pm

Ok Guys, problem solved or at least understood. Previously I had worked hard to stop the continuous petrol flooding - which made fuel consuption a bad joke. It now seems that was all that allowed the bike to start as the air slide never had any effect! Now if I disconnect the choke cable from the lever, the air slide drops to its correct place and the bike will start and run. So 2 problems, but one only apparent once the other was fixed. Not sure if the problem lies with the wrong cable for the choke or the wrong lever. Is there more than one cable length for the choke?
BTW the only text ion the Amal carb is the notation 76AG and 1AU on the connection between the float chamber and the slide barrel. Would gaskets for a 276 fit or is the 76 a different carb?
Cheers, Chris

Groily · Post by **Groily** » Mon May 25, 2009 8:58 pm

Good you've worked out what ails it.

Sounds as if the air slide cable inner is too short, although there is some adjustment usually via the screw and locknut on top of the carb (or even mid-cable or at the lever depending on what you've got). Most AMAL levers give the same amount of movement, I have found, so less likely the lever is the problem. But I am sure correct cables are available to suit from Burlens, the folk that sell Amals these days, or from Surrey Cycles. Or JSL, I haven't looked. Basically, you need the right length outer and inner cable, and small variations mess things up well and truly. Having said which, I have to say mine starts (with the same carb) without needing an air slide anyway, with the generous tickle wilko refers to.

Unless my mind deceives me, there aren't many gaskets on a Type 76 apart from the fitting to the inlet manifold . . . the tricky bit is the union - fibre washers - where the fuel passes to the float chamber from below (that banjo nut can have a painful habit of undoing and making a mess - as well as leaving you short of fuel miles from a petrol station before you notice).
The Monobloc is very different, and has its own set of problems, often centring on the float chamber cover (which uses a gasket) being distorted and not sealing.