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Thursty

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Well, it has been a minute since I was last active, and thanks to the business of fall as a bricklayer, I haven't been able to work on the bike much. In one of my previous posts (I'll reply with a link to it), I talked about my struggles with the right cylinder and it's 'weakness', or 'inconsistencies' in regards to how it's firing. I left things off with a focus on the exhaust before moving forward, and have since then postponed my focus on the exhaust, with a desire to try dialing things in better. I can't seem to get good reads on my spark plugs. That's where I'm at now. I've rejetted the carbs multiple times, and currently am running a 27.5 pilot and 32.5 main. I've also leaned the needle one notch. The bike 'cuts out' and has a dead spot at the bottom end. Pretty much as soon as I apply the throttle, it cuts out. Mid to top end seems good as far as I can tell, with the exception of how the plugs read. I'll leave pictures in the comments. I can't seem to achieve a nice 'tan/brown' plug. No matter what I do with the jetting, I get a primarily white or dark plug. Sometimes both. Almost like it's marbled? I currently have uni foam filters and straight pipe. Again, the straight pipe is not staying. But for now, would at least like to get things running a bit better. Thanks.
 
Left, stronger running cylinder
PXL_20221105_235021247.MP.jpg
 
Right, weaker running cylinder. The right side carb was seized due to varnish when I acquired the bike. I am currently cleaning it once again (fourth time), to see if there's any stubborn varnish still hanging on in any of the small ports, and causing it to run inconsistently.
PXL_20221105_234957208.MP.jpg
 
That black "looks wet", is it oil?
without wading back through that whole thread what haven't you tried yet?
 
The plug reading will be a result of how the motor was run; the choke and warm-up period put some soot on them and if the motor is not run at operating temp. and higher rpm for a goodly period, the soot remains and the readings are muddled.

It actually looks like it could be a bit lean, but not run at temp. (guessing). Your symptom sounds like it could be lean. Does it need to stay choked for a long time to warm-up and take throttle?

In the FWIW category: a '76 model is right at the beginning of emission restrictions and a lot of changes to carb design. Because jets were changed (emulsion tubes and fuel screws too) between each year ’75 through ’78 – and Canadian bikes didn’t always match US – I think a lot of jetting got mismatched in the ensuing 45+ years. You’re running a pilot in the range of ’76-'79 US specs and a big main jet for a '76-'77 US set. The only way to understand what’s going on is to hope for original needle jets, needles, fuel screws or other parts and examine them to be able to match all the parts together as intended.

Did you happen to take any pics of the above parts?
 
That black "looks wet", is it oil?
without wading back through that whole thread what haven't you tried yet?
Oh gosh... I feel like I've tried everything.

Ignition system: I've replaced majority of the ignition system. Coils, condensor, points (which are not only new, but I also cleaned), plug caps, plugs. Timing is on point, following valve clearance, cam tension, and points gap.

Fuel system: both petcocks, and both carbs have been rebuilt. Started with stock jetting for 76 (year of my bike), and worked up in jet sizes. Right now I'm at 27.5 pilot and 132.5 main. The reason I worked up was due to the 4200 uni pods I installed and temporary straight pipes. Hoping to install some emgo shorty mufflers tomorrow that were graciously given to me by my uncle from his assortment of goodies and trinkets.

I may have forgotten a thing or two, so feel free to ask and I can update you in regards. Since I made this post, I actually took a couple steps forward. As I stated before, when I got the bike, the right carb was seized due to varnish. The bike hadn't ran since 82. So tonight, I decided to clean the carb again for the 5th time, and try not to be as frugle with my carb cleaner. Not only that, but step back the needle jet to the middle notch. Previously, it had been suggested that I lean it out one notch, but decided to back it off to the middle notch and see if that clears up the dead spot in acceleration.

Result: unreal. Right cylinder seems to be running way better with a consistent thump out of the exhaust. Now seems to be running as good as left cylinder. Throttle transition is smooth all the way from idle to high rpms. Backfiring out of right cylinder seems to be eliminated.

But I still feel like improvements can be made.
 
Do you guys think I need to take it for a good run? I don't think I've ran it more than 4kms in one run since I've gotten the bike. Lots of 1km tests. Scared to run it too hard if it's not running right. However, after tonight's improvements, I'd be more apt to give it a better run. I don't think the dark deposits look wet, but can examine closer after running tomorrow. Looks more like a soot. But maybe that's because I often let it cool off before checking? Also, could intake manifold leaks cause inconsistent readings?
 
The plug reading will be a result of how the motor was run; the choke and warm-up period put some soot on them and if the motor is not run at operating temp. and higher rpm for a goodly period, the soot remains and the readings are muddled.

It actually looks like it could be a bit lean, but not run at temp. (guessing). Your symptom sounds like it could be lean. Does it need to stay choked for a long time to warm-up and take throttle?

In the FWIW category: a '76 model is right at the beginning of emission restrictions and a lot of changes to carb design. Because jets were changed (emulsion tubes and fuel screws too) between each year ’75 through ’78 – and Canadian bikes didn’t always match US – I think a lot of jetting got mismatched in the ensuing 45+ years. You’re running a pilot in the range of ’76-'79 US specs and a big main jet for a '76-'77 US set. The only way to understand what’s going on is to hope for original needle jets, needles, fuel screws or other parts and examine them to be able to match all the parts together as intended.

Did you happen to take any pics of the above parts?
Based off of my recent findings, I believe you're 100% correct. Too lean. And I wonder if your right that the initial start-up and enricher use has muddled my findings. It seemed too dark before, so I leaned the needle which caused the dead spot. I changed it back, and it ran really good. I might clean it AGAIN tomorrow, and I'll try to take pics of the above parts. My phone camera is shotty, but I'll try my best.
 
That's sounds like significant progress. Don't take it back apart just yet (and not for my curiosity). The plugs can cool back off and not affect the readings, it's the motor that needs to get up to temp and get things cleaned-out and the start-up soot burnt-off. If the bike is otherwise safe, give it a good 20km run and note how it operates at different rpm and different throttle openings.
👍
 
Agreed: do an Italian tune up. I find 1 or 200 miles, up to several tanks of fuel, a reasonable run in time before starting to chase small tuning issues. If it's running pretty well, explore the full range of RPM multiple times. Aides in freeing gummy rings, seating valves. Check reset valves, cam chain.
Doesn't hurt to drain and inspect gas from the float bowls a time or two either.
 
I rode the bike 12.5kms today. These were the plugs following the test. From what I can tell, that reads super lean doesn't it? Bike handled rpm transition quite nicely I thought. No dead spots. Maaayyybe had a bit of sputter at very bottom end, low rpms. Other than that, handled all rpm ranges very well. Makes me nervous riding it if it's too lean...
 
One of my wise friends always suggested, when tuning carbs, to keep going richer until it's too rich and then go back. As you're getting a bit of "sputter" low, perhaps go one richer on pilot and also one richer on the main and try it.
 
One of my wise friends always suggested, when tuning carbs, to keep going richer until it's too rich and then go back. As you're getting a bit of "sputter" low, perhaps go one richer on pilot and also one richer on the main and try it.
I'm currently @ 27.5 pilot, and 132.5 main. Do you think it's ok to go bigger yet? Again, they are 76 bs38's
 
Yep - given the plugs shown. You could verify there are no air leaks at the intake - just to be sure. Let us know....
 
Yep - given the plugs shown. You could verify there are no air leaks at the intake - just to be sure. Let us know....
Will check for leaks at the intake first. Then go from there. Any recommendations to testing intake leaks?
 
I use an unlit propane torch directed at intake boots & gasket @ idle, some use contact cleaner, etc.
 
So I did not have any propane or acetalyne on me, so I went with carb cleaner for the time being, in order to check for a leak at the intake manifold. I honestly don't think it's leaking. Ran the bike again another 20km. Still white plugs. It must just be running lean, no? I had previously heard that my 76 bs38's don't run very good on anything bigger than 132.5 mains and 27.5 pilots. I completely respect the guy who gave me the advice, but was wondering if maybe the newer jets I have could still be too lean, though they are '132.5's and '27.5's. should I try going bigger? Again, bike seems to run good through all rpms. No flat spots, no sputtering. I think my clutch is maybe slipping a bit under load, but that'll have to be a later project lol...
 
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