New carbs, won't start warm...

I think I'm at number 98. Really looking forward to that 100th time

I just fired it up, held my thumb over the pilot air hole and the engine faltered on both sides. Good news. I dialed the slide in a bit more and viola, she idles like a purring cat. Now I just need to give it a good warm up and do a proper tune.

Thank you everyone for your help.

Sometimes it happens so fast you can't even see it...hate those kinds of mistakes but I make them all the time

Glad you got it sorted out.

I also just installed a set of the new Premiers on my 850 and kept having similiar problems.If you keep having this try
going to a #19 pilot jet.It cured all my ills and now running like a champ.I would also put the needle in the #3 or top
notch.
YING

I have had new carbs with the float level incorrect.

Double check.

Floats were definitely checked before the installation. Ran into that problem with my original AMAL's and didn't want that headache again.

How drastic a change can changing the needle height make? My old carbs were not tunable enough because of air leaks for the needle position to make any noticeable difference at any throttle position. I know that it fine tunes mixture, but what symptoms would I look for beyond looking at the spark plug colour for something that finite?

ioginy said:

How drastic a change can changing the needle height make? My old carbs were not tunable enough because of air leaks for the needle position to make any noticeable difference at any throttle position. I know that it fine tunes mixture, but what symptoms would I look for beyond looking at the spark plug colour for something that finite?

Click to expand...

The most important thing to remember is that the different circuits on the carb control the mixture at different throttle settings. Don't go by speed or rpm's. Plug color is not a factor in the lead free gasohol world. Check out the plug reading article. The final reading is basically seat of the pants. Does the engine pull, no faltering, missing. Set idle/pilot circuit first because if it's too rich it will mess up the plug when you try to read the plug for slide cutaway. Likewise slide and the needle/jet. The only circuit that isn't effected by the rest of the setting is the main jet, wide open throttle. So start at the pilot-air screw with a clean plug, you probably won't be able to burn a fouled plug clean even if you finally get the set up right by idling. Fred at OldBritts has a nice article.

http://home.everestkc.net/malsin/Motorc ... ry_101.htm
http://www.4secondsflat.com/Spark_plug_reading.html
http://amalcarb.co.uk/rebuilding-mark-1 ... arburetter
http://www.oldbritts.com/amal_tun.html

It's good to know that seat of the pants is an accepted route. After restoring this bike I did as much reading on the carbs as I could find and have the theory behind them memorized. It's the practical application that often kicks theory out the window though. I tuned the carbs this afternoon in the manner that all the literature suggests and found everything to be running fantastic. Pulls hard at all throttle positions, no sputtering or faltering. In fact, with these new carbs the power the norton provided was almost scary compared to what the old carbs could pull out of the engine.
Thank you for the articles. The spark plug info is super helpful as I mark sure to never let ethenol within spitting range of my engine.

It's taken me a year and a half but I think I now have my Amals dialled in. Nice idle and the plugs look good. I found the air mixture screw to be VERY sensitive. The final adjustment was 1/16 of a turn. Getting this matched for both carbs is tricky work. Further complicating matters is Shells vs Petrocan vs Esso.

Using the same technique on the 68 Triumph, I thought I had that one beat too. But just yesterday, the thing falted, die and the plugs are as black. Fine tuning required.

I try to keep the variables in check. Only us chevron 94 fuel. But I imagine the tuning will go on for a while. Like all good things, they get better with attention and love.