2003 Suzuki LTZ400 Fuel Cock

[ougaf]

I have an 03 Suzuki LTZ400. I made the mistake of letting it sit a couple of months with some apparent bad gas. I tore the carburetor apart and the needle & seat were completely seized up. I replaced them and cleaned the jets. I put everything back together and it still ran really bad. I went ahead and took into the motorcycle shop. They tore the carb apart and gave it a thorough cleaning. When I went to pick it up the mechanic said that he got it running good, but the pet cock was bad. He said that he recommended putting a new one on it (~$110), but he would have to order it and that he had "rigged" it to where it would run fine in the meantime. He capped of the vaccum line at the carb and flugged the line coming from the pet cock and put the cock on Prime. He was right in the fact that it runs fine that way. I decided to try to find a cheaper alternative than paying the $100+ for the valve. I found a used one that came of a bike that was supposed to be working good when the motor seized up. I changed out the fuel cocks and hook back up the vacuum line. When I started it, it started missing and back firing. I plugged off the vacuum line again, put it on Prime, and it ran fine again.

What are the odds that I have 2 bad pet cocks? Can the pet cock be taken apart and cleaned? Could this still be a carb issue with the vacuum?

Any help would be greatly appreciated.

[DirtDemon]

I suppose it is worth a try to clean it out, if it works it would certainly be cheaper than buying a new one.

[Ajmboy]

It's possible I guess....but it seems to me that he Rigged something else to make it work because your vacuum is seems messed up. Did he tell you what he did to Rig it?

All the Petcock does it set fuel flow...shouldn't cause backfiring or misfiring. It should have an on, off, and reserve..positions..right?

Where does the vacuum line that you plugged go? To and from...

[ougaf]

I am thinking the same thing about the vacuum being messed up. The vacuum line goes from the backside of the fuel cock to the side of the carb. Last night I took the fuel cock apart and so no damage to the diaphragm or any real grime in it. After I put it back together I tried to test the operation of the fuel cock. In the Prime position, you can blow through the gas line and air will go through the valve. In the On and Res positions, you can blow through the gas line and air will go through the valve until you put your finger over the vacuum port. When you plug the vacuum, it closes the valve. There isn't an Off position which seems odd to me. I believe that the fuel cock is working the way it is supposed to??? It makes me wonder if there is a restriction in the carb that is keeping a vacuum on the fuel cock and keeping the valve closed.

As far as the backfiring and misfiring, I am not sure why it runs fine when vacuum is disconnected from the fuel cock to the carb. He said that the only reason he plugged each end was to keep gas from coming out of the petcock and to keep trash out of the carb port. Is it possible that if a fuel cock is bad that the gas would flow through the vacuum line and into the carb and cause it to misfire?

Thanks again for your help!

Edited May 20, 2009 by ougaf

[DirtDemon]

It seems like the vacuum signal from the carb is what keeps the petcock open, when the motor dies, the valve closes, thus shutting off the fuel supply. That is probably why there is no off position. If there is not a sufficient vacuum signal coming through that line the fuel flow will be stopped or insufficient. You could have one of three problems. There may still be some kind of blockage in the carb that was not removed, or the carb was damaged in some other way. The vaccume line could be damaged. Or the petcock is indeed bad. Also keep in mind, vacuum lines like that aren't like a regular fuel hose, they need to be made of a more ridgid material that won't collapse when pressure or vacuum is applied. At any rate, I don't see any reason that you can't just block the vacuum line from the carb and use a standard three position petcock instead.

[Ajmboy]

It seems like the vacuum signal from the carb is what keeps the petcock open, when the motor dies, the valve closes, thus shutting off the fuel supply. That is probably why there is no off position. If there is not a sufficient vacuum signal coming through that line the fuel flow will be stopped or insufficient. You could have one of three problems. There may still be some kind of blockage in the carb that was not removed, or the carb was damaged in some other way. The vaccume line could be damaged. Or the petcock is indeed bad. Also keep in mind, vacuum lines like that aren't like a regular fuel hose, they need to be made of a more ridgid material that won't collapse when pressure or vacuum is applied. At any rate, I don't see any reason that you can't just block the vacuum line from the carb and use a standard three position petcock instead.

Good points, I forgot that the vacuum line to the switch would be because of fuel shut off on engine stall.

[Sc0tt]

This is such an interesting thread. I can't wait to hear what the solution turns out to be.

[DirtDemon]

Yeah, I never knew that there were petcocks that were that complicated. Some motors use a fuel pump that is driven by a crankcase vacuum signal. I fixed a PWC for a guy that had a setup like that, the problem turned out to be the signal line that drives the pump. He just had a regular rubber fuel hose on it, when it got warm, the line would get soft and then the pump wouldn't work.

[nick4891]

hiya,

I have the same problem at the moment, but not sure on the vaccum pipe, im a complete novice, can you send or post up a pic of where the vaccum pipe is?

Thanks

[ougaf]

I went ahead and ordered the a new petcock. I put it on and it is running great. Apparently, those petcocks have a lifespan of ~5-6 years. That's all that I can figure since mine was bad and the used one I put on had the same problem. It would be nice to find a simple way of testing one.

Thanks again for all of your input!

[DirtDemon]

Good to hear that you are up and running again, I'm sorry to hear that you had to pay that much for a fancy fuel valve.

[Guest ecapuano]

I'm in the same boat... Quad acts as if it's fuel starved when operating with petcock in "On" position... After running engine for about a minute, it'll start dying. Must turn valve to "Primary" which opens the valve all the way for unrestricted fuel flow regardless of vacuum signal. The only problem with this is, when I turn engine off, I must turn valve back to ON or else fuel will run out of the carb over-flow onto the floor after about 5 minutes of engine not running.

Where did you buy your petcock and how much was it?

[ougaf]

I found mine at Bikebandit.com. It was $75 + s/h.

[PROFILL]

Hi guys...

As a suzuki mechanic I can say that ALOT of Suzuki fuel taps with the vacume lines are BAD.

They are just like every other brand bike, when it comes to the fuel tap, they are made by a third party company.

The last 7 to 8 years have been very bad batches of fuel taps for suzuki.

the bikes like, LTA400F Eiger LTZ400 LTA/LTA 500 Quadrunner LTF300 LTF250

All had diffrent shape fuel taps, but clearly come from the same maker...

Needless to say that they all die all to easy!

The two main faults is that some taps dont "shut off" so that when ever the carbi is dirty and the needle and seat dosnt shut off like its ment to, the bike will fill up the carbi... then the air box.... then the motor... untill the sump is full of fuel and the fuel tank is empty!

Because the fuel tap is "on" and fuel can flow out of the fuel side of the tap.

This is due to the little oring that is operning and closing with the bladder, it either gets dirt under it and cant close off or the oring getts little cracks in it... either way it stops working and lets fuel through.

then there is the problem with the vacume bladder leaking. (the thin rubber sheet with the round metal disc on each side) with a spring pushing on it.

either the suzuki sucks harder than what it should be, or the bladder is thinner than it should be.

Either way the bladder gets millions of little holes and fuel can be sucked through it and down in to the innlet manifold where it goes in to the motor.

often it will just make the motorbike run a bit richer than normal. or it can get to the point where the bike will be sucking so much fuel that the bike stalls, blows smoke, and runns very very very bad.

the next level is that straight fuel will flow right through the bladder and in to the motor without the motor even running (applying vacume) thus filling the motor with fuel!!!

the sneaky part is that the rubber bladder part looks fine, you cant see a tear or hole... it looks good. even to the point that it can trick the best mechanic for many hours.

now not all bike die from it, but it must be common for a suzuki shop to fix and replace a fuel tap once a week.

some fuel taps can die in 3 weeks, some may last 3 years.

every year suzuki mechanics have been wanting a change to the part.

and every year there is a "new batch" even with diffrent superseeded part number, but the problem is still there.

one of the best ways to test for the broken fuel tap is to turn your fuel tap on to "prime" so that fuel will flow to the carbi, and while the bike is running, get a pair of plyers and squees the vacume line so that it is stopped from working.

if exess fuel is causing the problem, then the bike will suddenly come right!

also pulling off one end of the vacume line, and looking in side should show that the vacume line is wet with fuel...

Where as a good tap will be always dry inside the vacume line.

odds are that either the guy with the old tap was lieing about the tap being good, or he was starting to have problems and diddnt know.

Thankfully the LTZ400 is better on fuel taps than the farm ATV's

it must be somthing to do with the DRZ400S motor and the amount of vacume it makes, or is fed to the tap.

Also there was a recall on the LTF300 Suzuki in about 2001 to 2004 and most owners were given a "restricter" that was to be put in the vacume line, that limmited some of the vacume.

This was because there were so manny fuel taps dieing that time....

people can still order that part, if you have a good suzuki store with a good memory!

I hope that this has helped.