Rg500 problem

[2strokejamoke]

Hi everyone, I just got my hands on my dream bike, rg500 1986! It starts and runs fine but I have an issue. It's hard to explain but here goes: when I take off on a warmed up bike it scoots away just fine, run it up thru the gears and very shortly it stumbles like it's out of gas. It will recover and you can rip it again but it is will fall on its face again. It is weird, it seriously feels like it's out of gas. It has the gross ball valves and LG airfilters. Mains are 240. It will ride around fine at low rpm, but even if you keep it under 7k eventually it will start hiccuping. It has plenty of gas in the tank, full to the top. And it's flowing very well throughout the fuel system, the overflow from the carbs is full blast if you open the drain. I'm going to do a leakdown test cause something is not right . Thanks -ian

[Jeff B]

Is the tank properly vented?

[TwoStrokeNut]

Is the tank properly vented?

I would definitely check this. I had a clogged vent on a cap once and it would start up and run fine for about 5 minutes and then it would start backfiring and hiccuping bad (this was a Suzuki thumper dual sport). Mine never would recover fully though once it started. I don't know how many times I had that carb apart looking for a problem

I found and corrected the vent issue finally and it ran perfectly. It turns out some rubber had swelled over the years, nearly blocking off the cap vent passageway. They say if you catch it while its starving for fuel, you can hear a suction sound as you open the cap. Mine didn't have a sound because it was venting some and I suppose by the time I stopped and took the cap off, pressure had equalize some. Just guessing.

[2strokejamoke]

Yes the tank is vented fine, the fuel dumps outta the lines like crazy

[2strokejamoke]

This was one of my initial thoughts too, I went as far as drilling the vent spigot out bigger, I guess I could try riding with the cap off but like I said the fuel is gushing out of the lines and drains if you open them. It feels like a fuel problem but I just don't see how?! Frustrating

[2strokejamoke]

A thought I just had, maybe a clogged vent line? When the engine is running I know it pulls a lot of fuel in and the carbs have a few vent lines and plumbing that I will inspect. I know I will get it but please keep the ideas coming, no wrong answers!

[Brad Winchester]

When it stumbles, switch the fuel off and undo the drain screws and see how much fuel drains out. If a heap of fuel drains out then you can assume that the carbies have enough fuel. If little or no fuel drains then there is a fuel flow problem.

[2strokejamoke]

It does it when I'm riding under load so I don't think I can perform that test.

[silverstrom]

The bowls need to vent air to allow fuel in. No air going out means no fuel going in. Very easy to check the 4 vents.

I'd suggest stripping the carbs to get to the root of the problem. I would be betting on plugged jet needles.With carbs that have sat for a while with fuel in them, the fuel can go bad quickly and and the tiny holes in the jet needles can become plugged. Once that happens nothing will help except a strip and clean. Completely strip the carbs and go through every jet, passage, nozzle, etc until things are spotless.

[TwoStrokeNut]

No RG500 expert here, but just throwing out some ideas...

You say fuel dumps out of drains when opened. That can happen two ways. If you open the drains, and they pour a lot for a short period and then run dry, the fuel supply is shut off or blocked somehow and air is simply replacing the fuel through the carb vent line. If fuel continues to flow indefinitely once a drain is opened, that means fuel supply from the tank is making up the lost fuel out the drain by coming in through the float valve.

I would suggest you try draining each carb independently for a longer period of time (longer than would be enough to drain just the float bowl). All should be checked independently because all four need to be working properly. One or two carbs starving will cause ill affects.

I'm with silverstrom... a good carb cleaning never hurts and a dunk in the ultrasonic bath really made my RZ500 come to life.

[2strokejamoke]

Holy cow Boys I think I found it! I went to my suspect cylinder first and there is a huge leak at the base gasket. Under the exhaust looks like someone was prying on the cylinder and deformed the hell outta it. It's breathing big thru this spot! Jeez I'm glad I only barley rode it

[silverstrom]

Did you just buy this bike?

Where?

[2strokejamoke]

I bought it from a friend in Ohio, yes recent purchase

[silverstrom]

I was checking as a few have been sold lately and was curious if it was one of those that had been widely advertised.