Low RPM stumble

[chawks]

My 80G tends to stumble and almost fall on its face when leaving from stop or when applying throttle in other gears when running at low RPM's. I spend most of my driving time just putzing around town so it is rather annoying at times. From where I started on this bike a year ago I'd say it runs real good but not perfect. She screams when I am laying on the throttle. I suspect she's running lean. I think I did a good job of getting the floats heights set right but I suspect I have a pilot circuit problem. Perhaps I did not get the passage from the main jet to the pilot cleaned well or the pilot itself. Am I on the right track here?

[TopCatGr58]

Low RPM Stumble?

Hey there Chawks,

I'll let the real GURU's answer your lean/rich question, but I think you may need/want to provide a little more info about the condition of your bike first. What kind of exhaust, stock or aftermarket, 4-2 with/without crossover, or 4-1 set? Type of filter, stock box, or indy filters. Stock jets, what sizes?

Also, what RPM's are you talking about? These bikes do have decent torque, but aren't designed to walk away at 1.5 k, they like to run at around 3k or above, so if you're running it at even 2k in 4th or 5th, and expect to have it pull quickly from there, IMHO, it doesn't happen that way, at least with my bike.

On my 81, the pilot screws were sealed, capped, and I had to drill them out to get access to them, not sure about the '80 series? They have a 1/4" thick brass cap stuck in the top with a little hole in them, right infront of the mount to the intake boots. I drilled thru them being careful to only go thru the cap, not to let it keep drilling into the pilot adjust screw, then screwed a sheet metal screw into them, and then tapped them out by putting a lock pliers around the screw, and then tapped on them with a hammer until they pulled out. Then I was able to get to the pilot screws, remove them, and ensure a thorough cleaning and adjusting. Okay, I'll shut up now before I really show how dumb I am about the rest of the carb adjustment process!!!!

T.C. "not a guru!"

[chawks]

I agree my bike does like to run better at 3k and up. If what you say is true maybe I am not running as bad as I thought.

The carbs and filters are all stock. I had already gotten the brass caps out last year when I stared working on an idol problem. I have Jardine slipons with cross over on the stock headers. I had been told no rejetting was required for these. I adjusted the pilot (idol) screws earlier today and have not been getting the periodic back fire I had been getting when coasting to a down hill stop in gear, which I attributed to being a lean idol condition.

Maybe I just need to drive harder and faster all the time!

Or maybe not.

[GtrMn]

My '80 LG did the same thing, BADLY! especially when it was cold.
Between 1500 and 2000 RPM the engine would start to stumble and almost die. After syncing the carbs it's awesome now.

[Bill]

Re: Low RPM stumble

Chawks wrote:

My 80G tends to stumble and almost fall on its face when leaving from stop or when applying throttle in other gears when running at low RPM's.

Here's my guess: As TC suggested, it may be related to the pilot circuit, which is made up of the pilot jet and the pilot screws. This circuit controls mostly idle and low RPM fuel, so the problem goes away when the engine is running faster

In TC's case, the situation was corrected by adjusting the pilot (idle mixture) screws. In the case of my old '79 Standard, the pilot jets were clogged and had to be removed. They were full of sediment because the bike had sat for a long time before I bought it. After removing the pilot jets I was able to gently clean out three of them, and one had to be replaced. Problem solved.

TC also mentioned the other components of the intake and exhaust. My old '79 Standard also ran generally rough because of rotten mufflers. One side had much more "stuff" in the muffler, causing uneven power from idle to WOT. In fact, that problem masked the pilot jet problem until I replaced my mufflers.

Good luck and keep us posted on your progress. (Not a guru, just learned a few leXSons the hard way).

[dragxs11]

My 80sg had the same problem. It got progressively worse over a couple years until it became unridable. I opted to go to war against it and bought rebuild kits and dyna-jet kits. While I was at it, I found wear marks on the diaphram boots. Some had more wear than others, but all needed replacement. My float height was also considerablly off and I had to sync the carbs after rebuild, of course. I don't know which fix did it, but the bumbly low end went away. Now, it takes some effort to stall it at take off. Bottom line?, I suggest a full carb job on every carb and maybe valve adjustment. Mostly to save time. Now is no time to have your bike down.