Popping Carbs and Dies on throttle input

I'm really getting annoyed here, Today I took the carbs apart and checked everything for clogs, I found one clogged pilot jet, solved that problem, everything else looked really good, there isn't even any grime anywhere. So I have been having this constant problem. The bike will idle, sometimes only with the choke on, sometimes I can get it to idle for a short period with the choke off. But the carbs constantly pop like the timing is off or something, so I went in and checked the advancer and it was frozen solid. No problem, took that apart, cleaned and oiled the whole thing and it functions as it's supposed to now. Started it up, same problem. It's almost like the carbs are coughing or something and it doesn't make any sense. I dont know a ton about motorcycles, but I am definatly a car guy and coughing out the intake usually means the timing is off. but I dont see any adjustment for the timing on these bikes. It just looks like you set it static and then the cyntrifical advance goes into play from there. My 82 has no points, it's electronic ignition, so points is not the issue. I'm very much at a loss. Only running with the choke on, that would potentially be a lean condition wouldn't it? If so, how on earth do you richen these things up, it's a stock bike, it shouldn't need bigger jets, etc. Oh, and I can't check the float levels, the screws are stuck in the bowls, I tried all morning to get them loose and they woudln't budge. But they havn't been messed with, I dont see how the float levels could be off if they weren't messed with before.

I'm about to pull my hair out here and I'm bald!

John Jones

What's the bike?

Definitely sounds like a lean condition. Which could result from leaky carb holders or poorly adjusted floats.

Lots of people say they can detect leaky carb holders with either WD-40 or some propane (look it up on YouTube). I've not had any luck with this method though.

For your floats, the best thing to do is measure with what's called the clear tube method. You basically stuff some clear tubing into the drain hole (wrap the end with plumbers teflon tape) and then let the float bowl fill up and use the fuel level in the tube to measure the distance from the float bowl gasket to the fuel level.

You adjust the float level by bending the little tang on the float itself.

The bike is an 82' 750CSR Twin. I did the brakeclean trick on the carb holders today and there was no change. Great, I get to blindly adjust the floats because the bowl drain screws wont come loose...I still dont see how it running lean would cause the carbs to cough.

I'm still a relative noob myself, but running lean will definitely cause a popping. You've got to have the right fuel/air mix for the fuel to combust properly.

When you give it gas and it dies, that could be because there's not enough fuel in the bowls to meet the demand of the engine so it just quits.

I don't think you will be able to do this blind. You're going to need to get the carb drain screws out.

If they just won't come out, the closest you're going to get is to take the carbs off, flip them upside down, remove the bowls and measure the height between the gasket surface and the top of the float. Pick whichever one is closest to the gasket surface and make them all match that. Then you may end up with a rich condition.

I guess I'm just gonna have to work at those screws some more. both carbs are popping, so setting them the same wont do any good. I appreciate it

John Jones

Running only on full choke is a classic symptom of clogged idle circuits, your carbs are still dirty. Your pilot circuits are clogged. You said you cleaned out one pilot jet well there are tiny passages in the carb body behind the pilot jets. When you "clean" your carbs insure ALL those little tiny passages in the CARB BODY are clear.

Choke makes the bike run richer than normal, so all signs point to lean. I haven't figured out why lean causes popping either, but all the elders here say it does, and that always seems to be the outcome for others. At idle, the pilot circuit being clogged will definitely cause a lean condition, so it's likely.

You also had that overflow condition before, from your other thread. Presumably that's at least fixed now? That would have been causing a rich conditionon whichever cylinder that was. Maybe you bumped the tang on the floats while you were in there, they aren't particularly stout, so it'd probably be easy to knock out of adjustment.

For those stuck screws on the drains. The best results people around here get tend to come from Kroil. I can't eveer find it anywhere but online, but it's not expensive, might be worthwhile. You'll be chasing all sorts of problems if you never get the floats set right. Impact screwdrivers are also useful, but I'd exercise extreme caution using one on the floatbowls, they're small and would be easy to break, and probably hard to replace without buying another carb with it.

On the timing, you're right, it's just that one piece that sets it. There's two marks on it. I believe the correct adjustment is to ave it set at the T mark with cylinder 1 at Top dead. Others can yell at me if I've said the wrong mark, but I seem to recall that being it. Do be careful you didn't install it 180 degrees around, it goes on that way, and doesn't work right that way.

ok, I got the screws loose on the float bowls. I'm glad I didn't break them. they are both lean, one way more than the other. Which way do I bend the tabs to make it richer, toward the bottom of the bowl or towards the top of the bowl?

You want the float to float higher before it cuts off the fuel. So bend the tab towards the bottom of the float bowl.

After I posted that I figured that was how it was done so I went and did it, the fuel level in the bowls is now 3mm from the body of the carburetor. I got it started again and with the choke on the bike screams to 5k rpm and stays there. If I turn the choke off, the bike dies. If I give it throttle, the bike dies. Is there some other adjustment that I'm missing? Fluid passes through all ports in the carb without any issues, I checked that earlier today, I found no more clogged pieces. Damn I hate carbs!

Do you have mixture screws you can adjust or are they blocked behind blanks?

Are you talking about the ones that are on top of the carbs? little tiny flat head screws that lead from the pilot jet? If so, yes, they are accessable