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[Andy C]

Just before Christmas I treated the 612 to a new Premier Concentric - the old Concentric was past its best so decided on an "upgrade" to the Premier Concentric.

I have only just got around to fitting it and was very disapointed to find that the bike will not run with it fitted.

All it will do is kick / cough / backfire, it simply refuses to start - put the old card back on and guess what, it fires up straight away.

I have completley dismantled the Premier, and blown everything through with an airline, but still no joy.

I assume that these will work (just like the original MK 1) without the choke mechanism fitted i.e. just tickle and then start.

The premier carb is setup exactly as per the MK 1 that came off.

As I say runs fine with the old carb,but refuses to even start with the new Premiere one.

Anyone any thoughts?

[Daiwiskers]

Throttle stop ?
Air leak?
Float needle not seating?
Float height?
I also remember trying to set up a monobloc with not enough fuel in the tank! that took some time for me to work out! putting the tap to reserve helped here (it was just on the edge between main and reserve)
Can't think of anything else
Hope this helps Dai

[Wheaters]

I had a similar issue when I first fitted a 26mm Wassell Concentric to my 350; it was difficult to start, misfiring, spitting back.

I swapped the standard 160 main jet for a larger one, (170 then a 180) which made no real difference. Then I tweaked the float height higher (to put slightly more fuel in the bowl) which immediately cured it.

I had already ordered a choke cable and lever for cold starts, seeing that the carb came with a choke flap type slide but so far have never needed to fit it, so it's still in my spares drawer. From cold I tickle the carb until fuel just shows, two slow kicks over compression with the decompressor pulled, ignition off. Then it will usually start and run first "proper" kick.

[black fingernail]

Check the 'drillings' in the main casting are as they should be, I know there is no comparison, but, the pilot hole in the body of the new Micarb that was fitted to my bike was not round, there was casting 'flash' there that needed drilling out. It needed a magnifying glass to find and micro drills to sort out, that was probably why my bike was for sale.

[mauri]

the stationary circuit is much leaner on a MK1 premier than on the standard MK1.

you'll need a three line stationary jet at the very least.



Even with a four line jet it will not start without the choke.

[Daiwiskers]

Stationary jet?
That's me lost

[Andy C]

All.

Thanks for everyones input, Mauri is refering to the removable pilot jet.

To cut a long story short, I had the bike running with the original worn MK1 and then swopped over to the new one, yet again it would not start, out of frustration I tried a new plug - started 3rd kick, but was clearly very weak as it was spitting through the carb a fair bit, which supports what Mauri has said.

The spark plug may have been coincidental - I'll see if it will start from stone cold later today.

So it looks the permier carb is much weaker on the idle circuit than an original concentric and loks like I'll need to at least fit a choke. As I bought the carb from our hosts I'll see what they recommend.

[singleminded]

I would check the size of the pilot jet in the Premier carb.

There has been a lot of discussion on Access Norton regarding Premier carbs and the received wisdom is that the original jet supplied with Premiers is too small, causing the bikes to run weak at tickover and hesitate slightly on pulling away from a standstill.
I have a pair of Premiers on my Commando and have fitted larger pilot jets. The result is better idling and starting and the 'hesitation' has gone.

Also, out-of-the-box my Premiers didn't work......

One cylinder ran, the other would not (apart from 2000 rpm upwards.)

I stripped the carbs and put them in an ultrasonic tank. After cleaning, there was a lot of gritty sediment sitting in the bottom of the cleaner. I reassembled and refitted the carbs and the bike then started and ran on both cylinders. (Fuel lines were clean and had inline filters, btw, so the sediment was in the carbs when purchased.)

There have been many reports of dodgy QC on the new Premiers - perhaps they have now been sorted.

[Wheaters]

A shame that quality control isn't up to expectations when paying for a "premier" carb!

Apart from (not too unexpectedly) having to adjust the float level setting, my "cheap" Wassell concentric, which some warned me off (after I had bought it) has so far proved to be a really good carb for my 350, especially as those reservations were mainly about the pilot "bush" fixed jet, rather than a replaceable item.

[Andy C]

Singleminded - thanks for your comments.

Judging by how the bike ran when I eventually had it running on the premier carb, it was definately way to weak which bears out what people have been saying.

I'll raise it with our hosts to start with and see what they say, but as you looks like I need a larger pilot jet.

Cheers