missfire till warm

I've resurrected three bikes that have sat for long periods of time. I've found that no matter how well I have soaked and cleaned the carbs, I usually have to clean them more than once to get them thoroughly clean. I've also made the mistake of replacing the petcock after cleaning the carbs, only to find my nice clean carbs filled up with rust and other debris.

When done properly, one rebuild per set of carbs should last for more years than the typical ownership duration.

In Steve's case, I think he's just lucky. He also gets "free" motorcycles, how often does that happen to the rest of us?

[chuckycheese]

Which only leads to the question ... WHY?

When done properly, one rebuild per set of carbs should last for more years than the typical ownership duration.

.

OK... I'll take a couple of minutes to explain it. I've owned my 750 for about 7 1/2 years and my 1100 for a little over 2 years. The carbs on both bikes were in poor shape when I bought them and one was filled with the wrong size jets. I rebuilt both as soon as I bought them.

I travel a lot on trips of long duration and don't take my bikes with me; the airlines won't allow it and I woudn't even if I could. Consequently, they sit, idle, often for weeks at a time. I've found that they seem to run best when the carbs are rebuilt about every 2 years. Every time I've done it, I've found the carbs to be filled with crud, so I don't think I was wasting my time. I also have an extra set for both bikes and, you guessed it, I rebuilt both when I bought them. Now.....there's more.

When I mentioned that I've "rebuilt them a bunch of times", I was also referring to other bikes, as well. I own 2 now but I've owned more than a dozen others in the past (I think 16, counting my dirt bikes)...and I've rebuilt the carbs on the majority of them. Each time I've done it, they've seemed to run much better. So....that's how I came up with my "bunch". Based upon the many posts I've read through the years, I doubt my rebuild schedules are probably all that unusual. Maybe I'm filling up at the wrong gas stations!!!!!

What shape is the coil. Plug wires. Boots. And plugs themselves in? What about condensation under the plug cap?

[Steve]

I've rebuilt my carbs a bunch of times ...

Which only leads to the question ... WHY?

When done properly, one rebuild per set of carbs should last for more years than the typical ownership duration.



Now, as to how the "choke" works ...

When your "choke" knob is pulled, there are pistons on the top, front of the carbs that move. If you looked into that area when you rebuilt your carbs, you should have noticed that it opens a large-ish hole in the side of the chamber under the diaphragm. This chamber is vented to the carb throat on the intake side, it's that large oval opening at the top. Opening the "choke" piston allows air to flow through this hole, instead of the closed throttle butterflies. Also connected to this air passage is the tube that sticks down into the float bowl. When air is allowed through the passage, it sucks fuel up from the float bowl, providing its own rich mixture to the cylinders. The outlet is on the engine side of the throttle butterflies, so it relies on the high vacuum generated to pull the gas up from the bowl. If you open the throttle AT ALL, that vacuum is greatly reduced, along with the effectiveness of the "choke".

To make sure the fuel pickup tube is working, use a single strand of copper from a wire. Poke it up as far as you can, then put on your safety glasses and spray carb cleaner through the tube, then follow with some compressed air. Also check the well in the float bowl that the tube lives in. Be careful spraying in there, it will come right back at you from the other end of that passage.

I always put "choke" in quotes when talking about these carbs because there is nothing that phisically blocks the intake of the carb throat, "choking" it down to force it to draw extra gas, like a car's carburetor does. Instead, our carbs have what is known as an "enrichener" system, but everybody knows what you mean when you say "choke".

.

[chuckycheese]

Check the choke circuit in the left carburetor, and the choke feed passage in the float bowl itself.

Something may be clogged in there.

Tkent....I understand where the "choke feed passage" is in the float bowl but which part is the "choke circuit" in the carb body? Thanks! (I've rebuilt my carbs a bunch of times but have never understood exactly how they work!)

[tkent02]

Check the choke circuit in the left carburetor, and the choke feed passage in the float bowl itself.

Something may be clogged in there.

[hampshirehog]

Hi and welcome to the nuthouse.

It's not rings unless it's smoking so you're quite right to suspect either the valves of the carbs. If you've lurked in these corridors for a while you'll know how important it is to make sure that both of these are sorted.

I would adjust your valves if you have not done it, clean the carbs and see if the problem goes away.

hi ive read alot of the threads and no one seems to have my type of problem so i hope someone can help

its a 1981 suzuki gs 400

runs nice when on the street , at first start up with choke out (on) it only fires on right side then when warm and choke is in ( off) left side starts to sputter and back fire and starts to fire and then runs fine ?

carb?
valves?
rings?

anyone else have this problem i'll be pulling the carbs tomorrow after work to clean again

thanks