380 Twin Port Griffon.

[dave higgins]

hi everyone.
This is my 380 twin port griffon, i`ve rebuilt it through out & took it to a few pre 74 meetings this year.
Its extremely quick for an old girl & always draws plenty of interest in the pits, the tank & side panels are new & finished in red metel flake but you can`t really see it in the pics.
Every thing is right about the bike except the age old fuel probs with griffs, it starts easy & runs nice if you keep flooding it untill warm but has no low range response.
Its ok from tick over to full throttle stood still, but under load it has no power pulling away & then mid range it takes off big time.
I have tryed all carb re jetting varations, new slides, floats etc, to no avail, now i want to fit a mk 2 amal, can any one advise on choke size & jetting etc, and where can i obtain a barrel to carb converter?.
Has any one else had this problem, crank seals are fine & ignition is new from nametab. any thoughts anyone!

[John-Boy]

Dave
the bike looks great, very pretty.

Although my Challenger was originally a 360, at some stage it has been converted to a 380. According to the Greeves bible (Carrick and Walker) the 360 and 380 carburettor settings are almost identical, the only difference being the 360 has a 30 pilot jet and and 380 a 25.

My bike is a bugger to start when cold and needs to be warm before it will pull away without stalling. In cold weather (e.g Marks Tey 7 Nov) I have to pour fuel in the sparking plug hole to even get it to fire.

I too have the Nametab electronic ignition which helps to reduce painful kick-backs.

Once the engine is hot it will pull quite strongly from fairly low revs without any 'choking-up'.

When I first put a new Mk 1 Concentric on my Greeves it had similar symptoms to yours. I eventually discovered that it had been supplied with a four-stroke throttle needle which is longer than the two-stroke needle. I know of another Greeves owner who had the same problem. It was a bugger to start, would tick over when warm but there was no power between that and half-throttle.


The four-stroke needle is longer than the two-stroke needle which should have 3 shallow grooves machined into the top of it (these are for identification, not the grooves for adjusting the needle depth).

The needle jet and jet holder are also different between the 2 and 4-stroke carbs.

The only other thing I can think of is that somebody may have 'tuned' your engine by altering the ports or shortening the inlet side of the piston skirt.

I presume that you have the thick 'tufnol' spacer under the cylinder base.

I hope this is of some help to you.

[dave higgins]

380 griff.

Thanks john.
Very helpfull info, i did replace all the carb jets, needles, float & slide, but like you say they may have been supplied in error, i`ll check again.
The base gasket is in place & as the bike was bought with proof of a engine build by an ex greeves mechanic all i have done interior wise is take the barrel off to check the bottom end.
I have read various articles of the same sort of problem & the mk 1 carb always gets the blame, you can understand the cold start problem, no choke & it draws a lot air but it did not leave the factory like that! ( or did it).
Most tuning people i have spoke to suggest a mk 2, but i would like to keep it origanal, i will try your suggestions & hopefully find the problem, again many thanks john.