Cuts out off centre stand

Hi folks,

I've run into a problem that I'm hoping someone might be able to help me with. I've got my 72 roadster (non-combat) running and have gone for a few test rides and everything seemed be working pretty good. Then one day last week I went to go for a ride and I stalled as I was pulling out of the shed. I thought that I had just not opened the throttle enough, so I started her again, and managed to going, but she was hating every incline and was threatening to cut out. And a few times she did cut out. I would put her on the centre stand and give her a kick, and she would start and run fine, but I started to notice that she was running differently on and off the centre stand. On the stand things are fine, but when I take her off she may or may not continue to idle, and will cut out with any throttle pretty much every time - especially going up a hill. And that's been the case pretty much ever since.

I've got a single Mikuni carb, that was in bad shape when I got the bike first (very dirty with blocked jets etc), but that was working fine earlier this season, and a Boyer MKIII ignition.

I've tried a few things so far, but nothing has solved it. First I made minor adjustments to the timing, and that seemed to help a bit. I was a little on the retarded side, just trying to avoid kickback, so I advanced it a little, and she sounds beautiful now... on the stand. I figure it's likely a carb related thing, so I pulled that off and cleaned everything, and blew all the jets out. I did this three times, and she is starting first kick every time when warm, and running beautifully on the stand. I can rev her up to whatever RPM I want and she seems to run perfectly on the stand. But if I take her off the stand she might idle, or she might cut right out immediately. Or she will cut out if I give her some throttle. Gentle throttle and out she goes. A quick blast, and she dies as I release it.

I figured maybe the fuel level in the float bowl would make a difference so I adjusted that a number of times. First I tried more fuel in the bowl. That resulted in immediate cut out off the stand, so I decreased the level of fuel, at one point not have any fuel in the bowl at all. Having the minimum fuel level seemed to help a bit, and I thought I was going to have it solved with these adjustments, but with the lowest amount of fuel in the bowl that will still let her run, it will sometimes idle decently off the stand but other times will die almost right away, and will pretty much always die if I throttle up at all when she is off the stand. But on the stand she runs like a champ! I've tried every air and throttle screw combination that I can think of and sometimes I think I'm on to something, and she'll die again off the stand.

A couple of possible clues are the fact that the engine is running rich (soot on the plugs), and that the weather has been warmer since this issue developed. I have no idea if cool weather would cure it, but its a good 10 degrees Celsius warmer than when I was able to drive around.

Anyway, I'm having trouble thinking of what to try next. Any ideas? Thanks!

Your post writing seems on a romantic love level : that's good. Unscrew the points cover and recrimp the connectors.

Given you think it's a carb problem means it's probably electrical. If you have a multi meter maybe check the earth on and off the centre stand.

Lol, thanks Torontonian for the kind words, and for the suggestion. I'll give that a try.

Hahaha, thanks Steves, good call. I'll give that a try too.

Years ago on an Atlas, it just died and rolled to a stop on a canyon road. Pulled it up on the center stand and started up first kick. As soon as I pushed it off the stand it would die. After a few repeats with the same results I found one of the blade type wiring connectors was loose on the ignition switch. The old wire was stiff enough to conduct current when on the centerstand but not stiff enough to stay in place when the suspension came into play. Pushed the connector back on and fixed. Might check any electrical connections going to ignition system.

Thanks brokeneagle - that's very helpful as well. I'm going to head out to the shed with a multi-meter and the ideas you fellows have given me and will report back in a bit .

Oh you awesome people . Within minutes of getting into the shed I discovered that one of the connections to the left hand coil was hanging off. The assimilator can, which I hadn't secured particularly well, was putting downward pressure on that wire and had worked it almost completely off the coil tab. I pulled off the connector, and hooked it up to the other option (there are two tabs that both go to the same bit on the coil) and she fired right up and kept on ticking off the stand, and would let me rev her as much as I wanted without any hint of cutting out. So I went for a couple of test rides, and I'm super happy and excited to report that she is running better than ever . I must have the cleanest carb in Labrador, and now that no wires are hanging off she runs like a dream up hill or down.

I'll tell you what, it's a good thing I've got an international team of Norton geniuses behind me on this project . Thanks a million once again!!! I really appreciate it, and I'm predicting some high levels of fun in the very near future.

Well done and have fun

Love this post! And proves once again that the old adage is true - if you think it’s a carburation problem, it will turn out to be electrical and vice versa.

Quick question from me though:

Is there any way around this?

For example, if I think it’s an electrical issue do I start looking at carburation first, what will it turn out to be?
Will the world implode or will I knock it off it’s axis?

If I keep blowing fuses after running for 15-30 seconds (either on stand or off) with the occasional go around the block, is it carbs rich or lean?

Lol. Not.

Gotta be a short somewhere . Can't find it.

For 100 years the old saying has been "95 percent of carb problems are electrical."