Vacuum problem? No gas to Seca Turbo carbs.

I just rebuilt the carbs and for a few days they worked great. I then took off the gas lines to clean out rust which came from my tank, which I had just cleaned, then... gas started spray from the pressure in the gas lines while they were connected. I let it sit, tried again, and gas started flowing out of the carb air intake. I don't know what went wrong. 8O

Now, after cleaning it more, the gas is on, check valve works fine, the fuel pump works fine, but there's no gas flowing to the carbs. I'm assuming the check valve needs suction to allow gas to flow, but there is no suction. Is this wrong? Do the carbs need to be producing vacuum to allow the valve to open and allow flow?

Any ideas? Thanks for the help.

'82 Seca Turbo 650 (no turbo)

 

Check your pressure regulator. It may be plugged up with crud from the tank.

 

The check valve is supposed to open under pressure from the fuel pump, which should be approximately 3psi at idle. Put it in prime for a bit before you try to start it in ON.

 

I see in your signature that your Seca has no turbo.....you sure are missing out on some serious fun

I was wondering what you did for the exhaust since you are turbo-less....do you have a 4-1 system on there? Does the bike still run properly after 6000 rpm? Hope you get your fuel issues solved.....Make sure the fuel pump is operating.....put the bike in 1st gear with the key on and hit the starter button, you should here the pump running. Good luck!

-Nick

 

My exhaust is two 2-1s. And I don't know if I ever went over 6,000 rpms. I'm going to look again at the fuel pump this week, my neighbor said its not working but he didn't have it in first.

Thanks Everybody.

 

If you have no turbo, you don't need a fuel pump, or a check valve, or a fuel pressure regulator. You should be able to run the fuel line directly to the carburetors and be done with it. You are going to have piss-all top end if you are pulling through the reed valves in the surge tank, since they are meant to allow air to bypass the turbo under no-boost conditions (i.e. low to midrange). Come to think of it, with the cam timing, and compression ratio, you will probably have piss-all top end anyway, no matter what.

 

So I just by-passed the fuel pump, check valve, and fuel pressure regulator and went straight from the gas tank to the carbs, and it worked amazingly. Super nice. I took it 70 mph on the highway with ease. It fixed my backfiring problem too. Thanks a lot you guys.

 

Hey, that's great news.

INSTALL AN INLINE FUEL FILTER ASAP. Your bike has a history of rust in the fuel system, you don't need more aggravation. There is a fuel filter to the inlet of the fuel pump. Now that it is bypassed, you have no protection from debris entering your pristine carburetors.

I would strongly suggest that you turn your petcock to the OFF position every time you stop your bike though. Since this is a straight through petcock with no vacuum line to open and close the valve, the carburetor float valves are holding back against the weight of the gasoline in the tank all the time that the main fuel valve is open. Even the guys with vacuum petcocks sometimes end up with the dreaded crankcase-full-of-gasoline problem, and with the turbo's petcock having no vacuum dependent off function, it is even more susceptible to this malady.

I would think that installing some normally aspirated Maxim or Seca 650 cams in that motor would help restore some badly needed low and midrange torque.

As a side note, if you are sure that you will never use the pump, check valve and regulator ($$$) again, you could probably sell them on for a pretty penny.

 

If you went the route of replacing the cams with ones from a N/A XJ, I would figure out some way to get a regular N/A airbox in there, maybe even pods....Do you have the inlet on the surge tank that went to the outlet on the turbo closed off? If you do, then your motor is sucking all it's air in through the 3 tiny reed covered holes in the surge tank at all times.....which I would think might be starving the motor for air above 6000 rpm.....If you don't, then you'll be sucking up un-filtered air into your motor.

By the way, If you want to get rid of the fuel pump I'm interested :wink:

-Nick

 

SweetIrony - sent you a PM.

Fraps.

 

Now whenever I start the bike (cold). Gas comes out the exhaust????? Once it runs for about 15 seconds, no more gas out the exhaust, and runs smooth. Whats up?

Side Note: I've left the gas tank on 'on' for a week, and still no gas in the crankcase. , but could the gas still be seeping onto the pistons and when I start it, that gas on the pistons comes out the exhaust. Does that make sense...

 

are you sure it is gas and not just condensation (i.e. water)??

 

yup sounds like a condensation problem to me, after a long ride I get some condensation dripping out of my right side pipe.

 

Thats weird. I took it on a 30 mile ride or so, but its definetly gas.

 

That sounds kinda odd.....usually if the fuel is getting into the cylinders it seeps right past the rings and into the crankcase. I've had fuel get into the exhaust before, but it also got into the crankcase pretty good, all because I left the petcock on and my check valve wasn't closing. Have you tried shutting the petcock off for a few days inbetween riding since you've encountered this problem? If your petcock is fully functional I can't see how fuel could get into the exhaust. I know when I start my bike cold quite a bit of condensation spits out that little hole under the muffler....but like you said, if it's fuel you'll definatley know it probably by smell.

 

No, that does not make sense. Any gas entering the cylinder in that quantity would seep past the rings and get into the crankcase, and it wouldn't stop until it was full. As soon as the engine started, that gas would light, or at the very least, evaporate or ignite in the exhaust system. Gas is incredibly volatile, giving off vapor at -40 degrees. If it runs out of the muffler and puddles on the ground, it is 100% NOT gas. It probably smells like gas from coming out of the same pipe as the rich exhaust fumes while the bike is on choke. I've never seen a Turbo yet that didn't burp condensation out of the pipe.

 

yeah it just have to be condensation, but it smells like gas because of running through the exhaust pipes....

I highly doubt it is gas.

 

I bet its condensation.

Old School Test.
Wipe-up with paper towel.
Set paper towel on sidewalk outside.
Throw lit match on Paper Towel.
Ignites = Gas
Don't = Condensation

Condensation is by product of Regular Gas with high Ethanol Content and will drip from exhaust if Mixtures are Rich enough to allow for a quantity of unburned fuel while Idling.

The Ethanol Content will do a number on the Fuel Pump or the Pump may be clogged with Crap.
Pull the pump and emerse the Outlet hose in Carb Cleaner.
Cross the leads and make the Pump run backwards.
Flush Pump that way.