Air filter/running weak

ChrisD200 · Post by **ChrisD200** » Sun May 31, 2009 7:11 pm

My G9 came to me without an airfilter on its Amal 76, but I'd like to fit one. There is limited space behind the carb - basically a hole in the frame. What filter will fit there?
On a separate note, I fixed the leaking and flooding carb, then discovered the air slide was ineffective and fixed that too, then I flattened out the newly-discovered 20thou bowing of the carb flange, replaced the needle clip to where it should be (3 from top). But still the bikes needs lots of air lever to run. The main jet is 170 and it should be 180. Would that make so much difference or is there yet another problem to find? I have the long cold and wet winter nights ahead so I might as well fix something else.
Thanks for the input, Chris
Never knew I had any patience until I met my Matchy!

Groily · Post by **Groily** » Sun May 31, 2009 9:56 pm

A fair few things to fiddle with.

I've never had an air filter either (although of course I should). . . because neither have I ever figured out what would fit.
On my Type 76 (on a Model 20) supplied recently by Surrey Cycles and I'm pretty sure correct for the machine, I don't need the air slide. It starts and runs impeccably, just needing a good tickle from cold on cold days. I think it's on a 180 main. But the main jet is only relevant when the throttle is 3/4 to fully open, so I doubt the 170:180 thing is making any great difference unless you have to close the air slide at high speed.

The issue, barring ongoing air leaks from the bowed flange etc, will more probably be in the needle and needle jet department . . . . or with the throttle slide cut-away.

Suggest checking that all 3 are correct per book as a first move, to be sure what came to you is what the makers intended!

Long cold winter nights . . .!!?? It's just starting to warm up!! I rather hoped we'd had them.

GSAX1 · Post by **GSAX1** » Sun May 31, 2009 10:35 pm

The filter is fitted behind the frame tube, between the oil tank and battery. The intake goes through the hole in the frame and is "sealed" by a large foam ring. There is a rubber hose going from the carb and ending in the hole in the frame to complete the setup. Difficult to find items, as the filter was specially made by Vokes for AMC (there where at least four similar, but not interchangeable, types for different models that I know of), and nothing else but the original rubber hose will fit well due to the angle from the carb. You could try Surrey Cycles, I bought some rubber hoses for the 376 carb from them.

The filters crop up on eBay from time to time, I have seen a handfull the last four years. They are not cheap but well worth it as they are completely out of sight (no ugly K&N's) and protect your engine.

Michael

paul knapp · Post by **paul knapp** » Mon Jun 01, 2009 4:36 am

Low fuel level in the bowl could also necessitate excess choke use in a cold engine!
The level should be up to, but just beneath the mixture screw. (if any higher the fuel will weep through the screw thread)
This level can be checked by removing the small blanking screw on the bowl banjo (type 76 carb) and fitting a nipple with a length of clear plastic tube attached. When the fuel is turned on, the actual level can be seen rising in the tube.
Also, with the engine running, when the throttle is 'blipped' the level can easily be seen to quickly drop, due to the extra demand on fuel, but will also be seen to quickly rise up to resume the correct running level. If this level is slow to resume, it could indicate a fuel flow problem.
If the level is too low, the air speed over the needle jet will be not sufficient to 'pull up' a steady, continous flow of fuel to keep the mixture at the correct ratio for smooth running.

Paul

ChrisD200 · Post by **ChrisD200** » Mon Jun 01, 2009 9:18 pm

Gentlemen, thanks for the advice. Paul, I have also wondered about the fuel level. What thread is the "blanking screw" so I can get a suitable nipple for a level check?
GSAX, I will have to get a filter, many of the roads here are unmetalled so dust is a problem, on the other hand the bike has had a long life but compression still reaches 120psi so it can't be all bad (don't know if the bore is oversize though).
Groily, I agree the main is of little importance at this time (fact is I hardly ever get past about half throttle out of respect for her age) so the next step is the manifold to see if that too is warped. Actually I'll do that the easy way by running the engine and squirting water at the joint. Should make for an interesting reaction.As I've said, I lowered the needle by two slots (not enough) so maybe the slide or needle jet themselves are also wrong. Back to the books! Chris

paul knapp · Post by **paul knapp** » Tue Jun 02, 2009 12:25 am

Chris, I made the nipple thread 1BA x 3/16" long. With a fiber washer fitted under the hex. head, it screwed in and sealed nicely.

Paul

Eric · Post by **Eric** » Tue Jun 02, 2009 10:58 am

Just a moment! If you lowered the needle that makes the mixture weaker as more of the main jet area will be occupied by the needle at any given throttle setting.

I know you originally said you had put it back to where it should be according to the book, but check this out again as this maybe your problem.

ChrisD200 · Post by **ChrisD200** » Wed Jun 03, 2009 7:59 pm

Eric, I actually lowered the clip by 2 slots (from 1-3) instead of the needle. Correctly the needle was raised by that amount - on re-reading it is clear my English mislead you.
When it stops raining, and gets light again (this weekend) I'll try the fuel level trick - maybe that's where the problem lies. I have also just acquired a full set of washers for the 76 Amal (from Hitchcocks), they are definitely different from what is currently on the carb so I am hopeful that the problem is essentially solved. However, that said, every time I've solved one problem, another completely new one appears. My wife says I am impatient, but that's only with bad drivers not with an old bike that has soul but no life! Cheers
Chris