Having a Blast with Ural Petcocks

Best read here: https://www.sevarg.net/2024/05/18/having-a-blast-with-ural-petcocks

This week, motorcycle maintenance! I have more or less valid reasons to replace the petcocks on all three of our motorcycles - both Urals, and also the Buell Blast, which I don’t think I’ve talked about much before - but I’ve done some interesting enough stuff to it over the years, so it’s worth sharing a bit of detail on it. I’m replacing two vacuum petcocks with manual ones, and replacing a leaking petcock with a less-leaking one.

An Overview of Petcocks, Vacuum and Not

If you’ve ridden a motorcycle of the pre-fuel-injection era, you’re (hopefully) familiar with the fuel selector or petcock down below the fuel tank. They normally have three settings - off, normal, and reserve. The difference between normal and reserve is that the pickup for reserve is lower down, so when the motorcycle either starts acting like it’s starving for fuel (ideally), or simply stops running suddenly (usually…), you switch from the normal pickup to the reserve pickup and have another gallon or so (depending on the motorcycle, of course) to go get yourself some fuel. This is a pain, and I’ve always relied on my trip counter as a fuel gauge, but sometimes fuel levels surprises me.

The Urals, however, both have a slightly odd system - vacuum petcocks. These also have three positions - but they’re normal, reserve, and prime. The concept behind these is that they’re automatic (for the most part). When the engine is running, a vacuum signal from the carburetors opens the petcocks up to let fuel flow, and when you shut down, there’s no vacuum - so they shut off automatically, and you’ll never have the awkward situation of a bad needle valve allowing fuel to seep into the carburetors and fill a cylinder, hydrolocking the motor when you next try to start it. Prime is the “Please let fuel flow into the empty carburetors” position. Of course, in reality, they tend to fail over time - either “not allowing enough fuel,” or “not shutting off.” Neither are ideal.

But there’s also another, somewhat overlooked problem with vacuum petcocks. When the throttle is wide open or nearly so, there just isn’t much intake vacuum - which means a restricted fuel flow. There’s enough, and the petcock obviously works well enough or you’d never get up a hill, but the Urals only use the vacuum from one cylinder to feed the petcock, and there are just a lot of times that wide open throttle for a long enough period happens. This is the last time you want a restricted fuel flow and low fuel levels in the carburetors - but it’s supposedly a thing, and after changing my petcocks around, I think it’s a thing that genuinely happens. I mostly ride the 2005, and after changing the petcock out, my top end is noticeably better, to the tune of about 5mph at similar throttle settings. I ride the bike regularly, so I’m fairly comfortable with what it takes - and I can’t argue with the fact that after I changed the petcock, the bike runs better at speed. It’s happy cruising about 5mph faster than it used to like in various conditions, and it’ll pull certain hills better than it did before. Maybe it was the colder weather, maybe it’s just the butt dyno, but I’m quite familiar with this bike, expected absolutely no change in riding, and I’ve noticed a difference. So, as far as I’m concerned, that’s a good enough reason to change the petcocks out.

We’ve also had some problems with the 2013’s fueling (especially on steep grades) that are solved by flipping the petcock from “normal” to “prime.” Running these engines consistently lean is just a good way to put holes in pistons, so I decided to simply swap both out. It’s a simple enough afternoon project, so if you’ve got a similar Ural, I’d encourage you to do the same.

I’m kind of shocked to say it, but after doing it, I really do think it makes a difference, and I really do think it’s worth doing, even if your vacuum petcock works perfectly.

2005 Ural Manual Petcock

I sourced a replacement petcock for my 2005 Ural from VintageCB750 - you want part #20-8038.

Assuming your petcock looks like this with a screw bung on the tank, this one should work for you. If mine looks a bit oily, it’s because I had a crack in the crankcase vent line (the big rubber line going from the crankcase to the airbox). It was a pain to find - it wasn’t obvious at all, but it was clearly venting some oil vapor when the engine was working hard, and eventually close examination revealed an inch or so crack. I don’t get too worked up over a bit of oil on my engines - I just clean it off every year or so.

The only annoying part of changing petcocks is that you need to drain the fuel tank fully. Wait until you really need gas, and it’ll be a lot less annoying. I picked up a new length of 3/16” fuel line to cut replacement line chunks from. The manual petcocks aren’t exactly the same arrangement as the older ones in where the fuel comes out, so you might need to make some new lines. Draining the tank is simple enough - hook up a length of fuel line into a gas container, set the petcock to prime, and go do something else until it stops flowing.

The old petcock comes off like a normally threaded nut - put a wrench on it and smack it towards the front of the bike. The interesting thing here is that the petcock nut is a “double threaded” nut - the top half is a normal right hand thread, but the part interfacing with the petcock body is left hand threads. This works fine, but it means you need to make sure the nut is roughly centered on the two halves, or it will bottom out a set of threads before the whole thing is tight.

Don’t forget the vacuum line to the carburetor. It comes off with a normal enough clip. Remove this, and the petcock should come free. Do NOT forget this vacuum port - if you leave it open by mistake, you’ve got a good vacuum leak into one cylinder, and you’ll eventually put a hole in your left piston.

You can see how the pickup works here - the primary pickup is the tall one with a filter on it, and the reserve pickup sucks from the very bottom of the tank. The good news is that the reserve position will get every last drop of gas in the tank.

The bad news is that the reserve position isn’t filtered, so it will also pick up every last bit of crud that’s settled to the bottom of the tank. If you seldom use reserve, and your tank is generating some debris from rust (or just crap in the fuel), you could easily enough fill the reserve pickup with junk and find it not working when you need it. I’ve got secondary fuel filters on the path to the carbs, and that’s a good idea on one of the older designs.

The new petcock comes with a nice fuel filter, and a clear plastic tube to protect it in shipping. The tube comes off… unless you want almost no primary fuel capacity and no reserve at all.

On mine, at least, the manual petcock filters both primary and reserve pickups. This is good - junk from the tank won’t end up in the pickup, even if you reserve, and at worst it will just clog the last tiny bit of fuel from coming in. This is a better design than the OEM one in terms of clean and reliable fuel delivery.

Of course, it also comes with a rather longer “primary” tube. This is easily adjusted by simply cutting the new petcock’s main pickup to match the length fo the hard metal tube on the OEM one. It doesn’t have to be exact, but if it’s longer, you’ll have more reserve capacity at the expense of primary capacity. Now is a good time to adjust it if you care.

Screw it in, and hook it up. I had to tighten mine on the next cold morning as it was weeping a bit - so don’t be afraid to use some (reasonable) force to get everything seated. If it’s not seating properly, you’ve messed up the alignment with the half-right, half-left threads, so take it off and try again after adjusting it. The nut should start on both sides at the same time and you’ll be fine.


It needs a cap like this. Either a 1/4” or 3/16” cap will fit. You could put a worm gear clamp around it if you wanted, but I’ve not had any issues with the cap on the right cylinder, so I’m not inclined to mess with it too much.

Refuel, check for leaks (ideally before you dump the whole thing in…), and you’re good to go! This is a 2 gallon fuel jug I keep around mostly because it fits well in the sidecars - and while I’ve not built a base for it, I’ve seen some clever little mounts that will fit one of these on top of the axle guard between the motorcycle and sidecar.

For the sanity of whoever happens across this part in the future in the “motorcycle parts” bin (which may very well be me), I’ve labeled it with what it is, and the general condition.

Again, even though I had no reason to believe the vacuum petcock was acting up in the slightest, I still notice a difference in how the bike rides afterwards. It was clearly being slightly starved of fuel at higher throttle settings, and this makes a clear difference. I can’t promise you the same, but I really did find a difference.

2013 Ural Manual Petcock

The newer carbureted Urals have a different style petcock - two hex bolts hold it on. If yours looks like this, you can get a manual replacement from Holopaw Ural (or a few other places - there are some Yamaha ones that work too). Same concept, different shape.

You start, of course, by just draining the fuel out. Fuel jug, prime, beer.

A standard enough Allen wrench will handle getting the petcock off once everything is drained and the fuel lines are freed. It’s a bit stiff - there’s some thread locker in there, at least on mine, in addition to the lock nuts. It’s not a bad idea to repeat the concept, because I’ve had fuel petcock bolts back off on other motorcycles before, and it’s never fun to find out that you’re covered in fuel and low on fuel at the same time.

The new petcock style filters both the primary and reserve pickup - and you can see why this is a good idea here, with all the random crud (mostly paint flecks, I think?) that have settled at the lowest point in the fuel tank. It’s not a half bad idea to, every now and then for more major maintenance, drop the petcocks and flush stuff out. Better that than sucking this through your carburetors.

I’ve seen grumbling about how hard it is to get the fuel filter off the end of the stalk - and you do need to get it off, because the new stalk is far longer than the old one. I found using an adjustable wrench as a slide hammer worked just about perfectly. Slide it on over, and catch the filter as it pops off!

You can see the problem here. The stock pickup is just way too high - so unless you only want about 3 gallons, it needs to be cut down.

There are no shortage of methods one can use, but I pulled out my best WWID (What Would Ivan Do), cranked some Dos Gringos, and got to work with a hacksaw. I also used the hacksaw to cut the bit of a groove that the filter sits in - just draw it back over the brass and it cuts a groove. Spray the whole thing down with carb cleaner, reinstall the filter, and it’s ready to install!

The new petcock is significantly smaller than the vacuum one, not that it makes any real difference. It even comes out with the fuel nozzle on the same side (when they’re facing the same direction).

Installed! And once again, it’s really important to make sure you cap that vacuum nipple.

The 2002 Blast

Finally, the petcock on the Blast started leaking in reserve - which is annoying. I don’t think I’ve talked about this bike before, but it’s one we’ve had for quite a while. My wife learned to ride on it back when we were dating, and over time, it’s been turned from the Rider’s Edge training bike it started life as into something that’s a bit more of a city bike.

Ours, if you’re familiar with the bike, is pretty heavily modified. The handlebars are mostly Buell XB parts now - hand guards, and the better mirrors. Heated grips keep hands warmer in the cold (my wife quite likes them).

The intake is a custom bit of work from a guy who used to build these for Buells. Stock, the bike comes with a rather restrictive airbox. I chucked that and replaced it with one of these - which is a nice little bit of work with a splitter plate inside that (supposedly) helps improve airflow.

If you’ve ever ridden a 500cc thumper, you’ll know that they tend to shake around a bit. Many years back, the Blast decided it was done with the stock exhaust, and informed me by cracking the pipe. I replaced that with something far better flowing as well, though I’ve got the “hush kit” in it right now. It’s very loud without the baffle plate in it - though it’s hardly quiet with it in.

And, finally, the back end is missing the mud guard (I don’t ride this one in the rain anymore and it looks far better without it), and I’ve got a bunch of custom work around the back for lighting. I’m a big fan of “stupidly bright, flashing LEDs” on motorcycles when I can manage it, and the center brake light on the Blast is now both a flashing brake light and a “running out” style chaser. But I’ve also gone from the stock incandescent turn signals to the LED 1125R turn signals - and the end result is that if I want to change lanes, you have to be blind to not see it. Doesn’t stop people, but at least it’s harder to miss.

The end result is a good bit more power than stock, while still being a very easy to ride bike. It’s a summer runabout for me - I’ve long since learned that riding “single headlight” bikes in the dark is a good way to die, so I won’t ride it when it’s dark out, and that ends up being most of my trips to town in the winter. Oh well - it’s still fun, and I expect our kids will learn to ride on it too, at some point. I just have to remember it’s a 21 year old bike.

Which, of course, brings me to the petcock. Try as I might, I couldn’t get it to stop leaking in reserve, so, out it comes.

Remove, replace - nothing fancy. But, if you’re curious as to what the inside of a petcock looks like, I did take this one further apart. They’re quite simple - some rubber gasket material and a few holes. The shape in the back of the lever allows opening or closing various holes based on position to give off, primary, and reserve feeds. Simple, straightforward, and held up for 20 years before giving me any trouble!

I Ride Old Bikes

It’s crept up on me, but at this point in my life, I’m riding bikes that are almost as old as the bike I rode back after college. In 2006 or so, I was riding a 1979 Honda CX500 - complete with CB and milk crate. It was about 27 years old.

Now? I ride a 2002 Blast that’s 21 years old, and my “daily driver” (not that it gets a lot of miles since I work from the property…) 2005 Ural that’s 18. It doesn’t feel like it to me, but they’re getting up there in years. Fortunately, I don’t mind older vehicles - my truck is 26 and still going strong! And, you know, they’re a lot easier to maintain, too.

This is a companion discussion topic for the original entry at https://www.sevarg.net/2024/05/18/having-a-blast-with-ural-petcocks