Problems with power arch or amal?

just started my 73 750 i've been working on yesterday. the motor was totally rebuilt by a brit bike shop thats been around since the 60's, so i'm pretty sure they know what they're doing. The owner of that shop said he wanted to start the bike for the first time and confirm oil pressure and everything was assembled right before he would warranty his work on the motor. so he started the bike yesterday, and told me everything was good, except the left side was running rough, and he thought it was a problem with the carb because he couldn't get a good adjustment from it. I took it home, and started the bike, heard the left side idle rough, and when i pushed down the tickler on that side the engine would surge and the miss would go away. Sounds like a fuel problem. So today i decided to go ahead and switch the plug wires around and just rule out anything in the power arch system. For whatever reason, when i switch sides with the HT wires, the bike won't even start. It kicks back, back fires, smokes out the airbox. Switch the wires back, fires right up, and idles rough on the left side!? What the heck could be causing this? multiple factors adding up?

the fact that it performs strongly on the left side when you tickle that carb seems to confirm that you have a fuel starvation problem there

take the left fuel line off and hold a cup under the petcock and turn the flow on, does fuel come on with a steady stream?

is so, then I would suspect the left carb's float is set too low and it runs out of fuel too quickly

"the motor was totally rebuilt by a brit bike shop thats been around since the 60's, so i'm pretty sure they know what they're doing. "

Sounds to me like they don't! How can any repair shop overhaul an engine and then return it to a customer in essentially non-running condition?

But, as noted, it's either fuel or spark. If you switched wires and the symptoms changed - whether for good or ill, that would indicate there is at least some sort of issue with the wires themselves. If the plug wires are good, it should make no difference at all if they are swapped. Of course, there could be more/other issues. You need to sort through it one thing at a time. Improper timing, of course, can cause the backfiring/kickback. The bike running better with the tickler down would indicate that carb is very lean. Is the balance tube between the carbs attached? That will cause an etremely lean condition which could cause the symptoms as well.

TWO faults at play here

concours said:

TWO faults at play here

Click to expand...

thats what i was thinking. one fuel, one spark. The wires came from old britts as part of the kit, and they need to be cut to length then have the one end crimped on. I looked at the wire i think is bad, seemed like the crimped end might have been a little too loose and allowed the outside jacket to push back when pushing it up onto the coil. Don't know if it was enough to cause a problem (not allowed to work on the bike after 5PM! :evil: ) but i tightened it down and will check tomorrow if that has any effect. Also going to use a timing light on the wire and see if the light is effected by the miss.

mike996 said:

"the motor was totally rebuilt by a brit bike shop thats been around since the 60's, so i'm pretty sure they know what they're doing. "

Sounds to me like they don't! How can any repair shop overhaul an engine and then return it to a customer in essentially non-running condition?

But, as noted, it's either fuel or spark. If you switched wires and the symptoms changed - whether for good or ill, that would indicate there is at least some sort of issue with the wires themselves. If the plug wires are good, it should make no difference at all if they are swapped. Of course, there could be more/other issues. You need to sort through it one thing at a time. Improper timing, of course, can cause the backfiring/kickback. The bike running better with the tickler down would indicate that carb is very lean. Is the balance tube between the carbs attached? That will cause an etremely lean condition which could cause the symptoms as well.

Click to expand...

yes on the balance pipe, i bought a brand new one when putting things back together.

mike996 said:

"the motor was totally rebuilt by a brit bike shop thats been around since the 60's, so i'm pretty sure they know what they're doing. "

Sounds to me like they don't! How can any repair shop overhaul an engine and then return it to a customer in essentially non-running condition?

Click to expand...

I don't understand that. I took them a motor, they took it apart and replaced bad parts, did all the machine work, set it and handed it back to me with a large bill. Basically the same exact work you would see mick hemmings do on his dvd.

One item that can cause the carburetor to run super duper lean is that the needle clip could have been knocked off the needle while putting the slide assembly into the carburetor. Installing the slide assembly on an assembled motorcycle can be a little awkward, and if the needle hangs up on the needle jet and if you force the slide at all, the needle easily pops off of the clip.

Many years ago I experienced this problem while riding my BSA 350 dirt bike. The needle clip in my carburetor broke which made the motorcycle only idle afterwards and made for a very long journey home.