It's running

[brokabolt]

Hiya all'
After 14 months of hard work iv'e finally started my griff up. Had i not omitted to use the rotor that nametab supplied with the ignition system i could have started it a couple of days ago. I can only assume the original rotor needed re-magnetising. Anyway it starts on 1st-2nd kick now. Problem is now i can't seem to get it running that well. Iv'e rebuilt the carb entirely with all new parts as stated in the spec sheets,all jets and main jet holder are correct,new float,everything. Iv'e fitted original paper air filters as i was having a hard time locating foam ones. To start with i unscrewed the air/fuel mixture screw out 1 1/2 turns. Once warm i screwed the throttle stop screw in just enough to keep engine ticking over so that i could adjust the air/fuel mixture. Got it to peek revs and backed off a little and then backed off the throttle stop. The problem is it is not responsive to the throttle. It is slow on pick up when i open the throttle and slow when i close it. To get it to peek revs i had to screw the air/fuel screw in one complete turn which means the mixture screw is only turned out half a turn. The new float is all plastic so there is no way i can adjust the float level(or is there). I haven't checked the float height as i don't know what it should be. The carb is a 30mm and not a 32mm so i have looked on numerous spec sheets and some say original size is 30 whilst others say 32. It's a 1969 model from the states so i don't know if this makes a difference. I'm running on 25-1 castor. I'm sure(i hope) that it is only something simple. Any help or advise would be greatly appreciated. Many thanks. Mick.

[John-Boy]

You could try raising the needle one notch or going up one size on the needle jet (from .106 to .107) that should improve pickup off the pilot jet.

The Griffon parts book refers to the 250 and 380 having a 32mm concentric carb (usually stamped 932 on the body).

This assumes there are no air leaks on the inlet and the crankshaft oil seals are not leaking.

[brokabolt]

It's running

Cheers John A,
No air leaks on exhaust or intake. Simon at Nametab rebuilt engine so all seals are new. If you google greeves griffon 250 specs, scroll down to greeves scramblers and desert racers, scroll down to 250/380 griffon sales flyer page 4 it states 250 has a 30mm carb, also if you scroll down to 250/380 griffon technical data sheet it states 250 has a 30mm carb. Cheers. Mick

[John-Boy]

Mick,

I have looked at the Greeves Maintenance Manual for the Griffon, which includes a detailed examination by the US publication "Cycle World".

The test report does refer to the 250 having a 30mm Mk 1 Concentric and the 380 having 32mm!

The general data schedule then goes on to list out the carb settings for the 250 and 380 and says:

Carburetter: Amal 900 series concentric, 32mm bore.

In the British section of the manual it says:

Carburettor: For both engines: Amal 900 series concentric. Choke 32mm, main-jet 310, pilot jet 30, needle jet 106, throttle valve No 3, with needle clip in middle notch. Pilot air screw approx 2 turns out (variable).

The only difference between the above US and British settings is that the US setup specifies a smaller, 25 pilot jet.

Even if you have a 30mm carb it should run OK but you may have to make final adjustments to suit your engine.

There is a number of tuning sheets available if you google 'tuning Amal Concentric carburettors'.

I hope that is of some help.

[brokabolt]

it's running

Thanks John,
Will have a tinker with it. Let you know how i get on. Many thanks. Mick

[brokabolt]

It's running

Amal tuning instruction state float should be parallel but a little bit higher wth float chamber base. On checking mine it was no where near it so iv'e bent the tabs as best i can bearing in mind it's all plastic, raised the needle one notch and re-fitted. Took ages to start. Got it running a lot better but still not quite right. will order a stay up float and bigger pilot jet from amal tomorrow. Air screw is still only half a turn out as this enables peek revs. Would have thought it should be at least 1 1/2 turns out. Any suggestions folks. Mick.

[John-Boy]

Mick
the pilot jet and air screw should have no effect on peak revs. It only affects the slow running up to about 1/8 th. of the throttle opening.

Another thing to check is whether all of the parts you have purchased are intended for a two-stroke and whether the body of the carb. is worn (where the slide goes up and down)

[greeves246]

Gary

Hi
if i may throw my hat into the ring

amal say top end tuning is slide cut away might be float (fuel supply)
i have tapped the brass insert can be moved up and down cairfully and using a bolt with a pin can be ajusted using the banjo bolt check gauze in fuel tank and
check fuel runs free.

villiers singles and twins book states 32mm carb
310 main
25 pilot
number3 slide
106 jet needle check needle jet is not oval and needle isnt worn (dave harper told me)

my griffon - https://www.youtube.com/watch?v=TIgsjD5DlOM

[cray]

Just to add my bit, get the engine really warmed up before making adjustments and plenty of plug chops along the way!! Aaaaand check the timing again & again!!

Colin

[brokabolt]

It's running

Morning all,
When i said peek revs i was referring to slow running air/fuel mixture and not throttle wide open. Carb is in very good condition with hardly any wear on slide or carb body. All parts are definitely two stroke and brand new with two stroke jet holder(short). Rob checked carb and drilled out fixed pilot bush so i know that's ok. I could have raised float needle insert but that still wouldn't have made the float parallel with float bowl. Petrol flow is good as the tank and petrol tap are all brand new. Have checked timing several times and is all ok(nametab 5mm btc). Cheers. Mick.