new member needs help!

hey everybody! to start this off i should tell that ive been obsessing over nortons for the last year or more. A friend of mine introduced me to these beautiful bikes and ever since there on my mind 24/7. I finally found a 1974 850 and its in great shape. Ill post a pic in this thread as soon as i get the photo bucket part started. I bought it with bad plugs, battery and a broken throttle cable. Fixed all of those items and it starts first kick! you can imagine my excitement. but the idol was wayyyy up at like 4000 rpms, it does have the twin amal carbs. So adjusted the idol down and went for a short ride. The problem i need your experienced help with is that during the ride around half throttle it pops and cracks really bad and wont accelerate. If i grab a handful of throttle it will clear past that bad section and take off like a bullet in the top end. I really need your advice because this little hiccup is the only thing stopping this bike from being a daily rider. thanks in advance!

chris

If it is stuttering at part throttle - constant speed - around town driving then I'd guess needles and needle jets in the carbs. They wear out fast. I replace the sets every 4 or 5000 miles but probably you can do with just the needle jets.

Needlle jet sizes are specified by diameter not flow rate like most jets. So .001" wear makes a 106 needle jet into a 107. Doesn't take much.

Welcome to the group.

Welcome !!!.

If it were me, I'd pull the carbies off and give them a good clean out, a pair of vaccum gauges and the bushmans tuning tricks will help you ( perhaps run the bike and spray half a can of carby cleaner down its gullet might help ).

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

Keep it simple, the bike probably ran fine before being neglected in someones shed, I'd replace nothing until I knw what was going on, or wrong more importantly.

Good luck, its an awesome journey and there is a huge amount of knowledge on this Forum, just so you know, I'm hoping to be voted in as the 2011 Norton Commando Forum Village Idiot, so do not expect too much useful advice from me.

You didn't say how many miles on your bike, but a full service including a torque check, valve adjustment, timing chain tension and all fluids is a good place to start before wresteling with those Amals.

Batrider is very correct about needle jet ware especially when the needle is made out of harded material than the jet it rides in. On top of that Amal has gone through many changes, as a company, in the past 2-3 years that has resulted in poor batches of every part they offer at different times. Needle jets are at the top of the list. I attended a tech session at a recent English bike meet in my state and heard that the best way to determine if you actually have a 106/107 needle jet is to check it with a gauge; that 106 offerings have actually measured bewteen 102 and 109, that the new jets have a small recess cut in their base. If this isn't enough to make you crazy the actual pilot jet (idle jet) is almost impossible to get at, is not repalceable (a new Amal offering may have this covered, as reported in another thread) and does not like our new fuel; it will clog at the drop of a hat.

Before you have kicked yourself in the backside to the point of not being able to sit down, get yourself a Mikuni. A single 34mm VM will out accelerate a pair of Amals in the low and mid range any day. I realize that this may be a bit self serving, but I converted my Mk III about 3 weels ago and was blown away buy how much more responsive the machine became in the speed ranges I like to ride in, idle to 5500, and the greatly imporved starting, WOW! I went from pure-ist to Mikuni-ist in less than a mile.

RS

Make sure the choke slides aren't closed. It is an easy mistake. Tight cable = chokes off (normal riding), slack cable = chokes on for starting.

Russ

Yes it does sound Rich at half throttle, which is where the Needle and Needle jet do their thing,
A sign of the very common complaint... worn needle jet.
It probably wouldn't clean it self out at Full throttle if the chokes were partially closed.
An entertaining read, Roadscholar.
The Mikuni conversion has been helping people for probably.... 40 odd years.?

wow everyone! thank you for the quick replys. i did forget to mention the bike was rebuilt about 8 years ago completly, and only has 2000 miles since then. everything is super clean on this bike. Also, it starts first kick every time since the new plugs. I am pretty stuck on using twin amals for now because i love the original look, although it did come with an extra mikuni After some idling and short riding to get a feel for the problem it does seem to be running a little rich. Which one is the needle jet? is that the one that runs next to the throttle cable and has three clip settings? if it matters my clips are set in the middle, wondering if i could move it up to get the desired effect? thanks all!

chris