YPVS Loses Position(?)

2steve · September 23, 2025, 09:10:10 PM

Took the carbies loose and twisted them so the float bowl could be removed and the float lowered. Ran a little better after that, but still not right - wet left plug and imbalanced.
Took them all the way out again and I had only accomplished 1mm lower on the float in the less than ideal twisted state. They were really both at the proper 21mm.
Sighted the carbs and saw they were not really lined up with each other, so loosened the joining brackets and realigned - doubting that will accomplish anything. Gave the left float another 1mm lower for a total of 2mm down. ALSO dropped the left needle 1/2 step, leaving the right one where it was. Maybe that will do it.
Really annoying that the slides do not agree with each other mechanically. I swear there is a difference in slide stroke from one side to the other. The only way that could happen is if the rotating lever in the carb top is longer on one side.
Buttoning it back up. Will ride soon. This has been a real mystery with the carbs having been dialed in really good at first.

mnein · September 24, 2025, 08:11:26 AM

Man what a hassle. I hate to suggest this, but you don't have a broken piston ring on the left side or something like that do you? My 75 350 had a broken ring on one side and it ran, but it was always a bit off and I think that side kept fouling plugs. That's what I remember from 45 years ago...

2steve · September 24, 2025, 08:26:52 AM

Compression has been really good, but haven't checked lately. Assuming that would indicate that sort of problem.
I'll check compression and try ripping around the neighborhood one more time. Just need to put the intake filter back on after last night.

mnein · September 25, 2025, 08:10:30 AM

Yeah I guess broken ring is a long shot, seems a compression test should show it. It's just so strange that there's not an obvious thing with a carb, only so many avenues to pursue there.
If you were made of money I guess it would be time to buy a set of aftermarket carbs and ditch the originals with the conjugal relations linkage/bracketry and the pain they are to remove.

2steve · September 25, 2025, 08:34:40 AM

I'm getting pretty good at removing, operating on, and reinstalling though.
(He says as his thoughts turn to forgetting an oil line hookup or some such disaster).

1976RD400C · September 25, 2025, 08:46:38 AM

Quote from: 2steve on September 25, 2025, 08:34:40 AMI'm getting pretty good at removing, operating on, and reinstalling though.
(He says as his thoughts turn to forgetting an oil line hookup or some such disaster).

After the 5th time of taking my carbs off I ditched the throttle return cable. It's easier to get the carbs back on and it snaps back better.

m in sc · September 25, 2025, 10:49:10 AM

all I have to say is: flatslides

Kawtriplefreak · September 25, 2025, 11:41:53 AM

Yep

2steve · September 25, 2025, 03:59:00 PM

Rode it during lunch with the lopsided settings mentioned above.
It's streetworthy now. Just a little disagreement-congestion at low throttle, lower rpm. Improves as it warms up. Not perfect, but at this point, riding it will take priority and can actually be fun.
Wondering how much of all this was the left carb.
Thread title should be "VM26 carb from outer space and whatever electrical issues combo platter"

m in sc · September 25, 2025, 04:45:06 PM

def something wrong if carbs have to be staggered.

2steve · September 25, 2025, 05:40:58 PM

Your 2mm lower suggestion on the float was right on target though, along with dropping the needle 1/2 step more than the other one. Also opened that left air screw another 1/4.
It's art, not science

2steve · September 28, 2025, 08:47:40 PM

Simple question(?)
Starts and idles great. Before it's warmed up, it acts like before; running on one cylinder at low throttle and lower rpm. Enrichener is on ONLY for start up. Yanking the "choke" doesn't change anything.
After warm up, it transforms to running normally.
After the ride-that-became-normal, both plugs are equally wet-ish around the circumference with a dry/normal electrode.
I can live with that, but shouldn't really have to. Wondering what gives?

2steve · September 30, 2025, 03:04:43 PM

To simplify the above, does the bike tend to lean out as it gets warmed up?

m in sc · September 30, 2025, 03:14:23 PM

lean out or get richer feeling? is it actually dragging a cyl at idle? its hard to diagnose that w the crossover tube, i have plugs to isolate the intakes fir this very reason

2steve · September 30, 2025, 03:53:04 PM

Feeling rich. Starts and idles fine. Dragging a cylinder only under load at lower rpm when cold. Spooky when you have to pull out into traffic like that.

THEN, it all goes away after warm up and we're running normal.

After lowering the float level 2mm and dropping the needle 1/2 step, it got better and I'm almost home except for this.

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YPVS Loses Position(?)