best way to confirm gas to carbs?

[bounce]

I smell gas in the engine area when trying to start but still have the base of the air filter attatched to the su carbs on my 240.... if I am starting to troubleshoot a fuel issue after eliminating spark as a problem how do I proceed?

also, is there a return fuel line which would somehow endup back at the rearmost vent hose line on the gastank? I put some gas in it the other day and noticed it was leaking at that rear vent hose after giving up on starting it for the day... Either it was caused by me adding gas to the tank or all the work the fuel pump was doing when trying to start.... any input?

thanks fellas... I've been doing my searches on the forum but not having such a great keyword hunt....

[MikeW]

The most common cause of fuel smell in the engine compartment is a needle valve that is stuck open even when the float attempts to shut off the supply to the bowl. This is why there are overflow hoses from each carb to the air cleaner. If you smell fuel it's got to be leaking out somewhere. It's possible that the amount is small enough to smell but not readily see since it will quickly evaporate.

Often needle valves will get stuck shut as well but that causes fuel starvation and a car that tries to run on only three cylinders.

Yes, there is a return line to the tank but it's far more likely that the vent hose has deteriorated and that filling up the tank caused the leak. Did you fill it all the way up?

[bounce]

no, I was told it had half a tank before winter....and with me adding about a gallon...it leaked for a little bit from the rear vent hose attachment...so I still think it has half a tank...allthough the gauge says it's closer to a quarter now...(yeah, it started working again)

[Shade133]

if you see any leaking around the gas tank. thats a dead give away. as to the smell in the engine compartment, who knows might be a leak there to, im sure you have checked all the rubber hoses for cracks and made sure they were tight. also i dont know SU carbs but a lot of carbs have a clear bowl window so you can look in it. id see if its filling up to much or not filling up enough which would indicate a leak in the line somewhere and possible performance issues.

[bounce]

if you see any leaking around the gas tank. thats a dead give away. as to the smell in the engine compartment, who knows might be a leak there to, im sure you have checked all the rubber hoses for cracks and made sure they were tight. also i dont know SU carbs but a lot of carbs have a clear bowl window so you can look in it. id see if its filling up to much or not filling up enough which would indicate a leak in the line somewhere and possible performance issues.

well I think I'm smelling gas in the engine compartment because I've been trying to start the motor for about 15 minutes....I though the fuel pump was knock-knocking away and pushing gas up to the carbs....and then it was going back to the tank and leaking...but it could have also been leaking because I added gas to the half full tank... and no, I only added maybe about a gallon....

I'm going to figure out how to confirm there's gas actually arriving at the carbs....any ideas?

[Bruce Palmer]

Take a fuel line loose at the float bowl. Hold the loose end in a jar. Crank the motor and see what happens in the jar.

[Shade133]

bruce i was just about to suggest that . or you could do a fuel pressure test if you have the tool. you'd notice the pressure being low after the engine has sat for a few minutes, then raise and should be steady at crank.

[bounce]

I think I'm dangerous around these carbs....around this car without a manual....

what's that fluid on top of the carbs? is it dot3? with the little black screw top lids that says finger tighten? I thought it was stabil that I have dumped into a possibly empty tank then tried to start it....but no....it doesn't smell like Stabil...and my fuel filter on the right hand side fender well is full of good clean fuel ....

I cleaned off the windows on the side of the carbs but do not see fuel sitting there...I can only see a some motion around the circum. of the window when opening the butterflys....pushing accelerator down....

so i took off the base of the air filter housing....and the three screwed "float bowls?" and could see the butterfly on the carbs... i dumped the red fluid onto a rag out of the float bowl...so that needs to be refilled....

bottom line...: I've got fuel to the filter in the engine bay, but still do not know if I'm getting proper flow to the carbs... I will research and try to find the fuel line to the carbs themselves and do the miracle whip jar test....

lazy question: what manual do I buy, where, and can I paypal it? or does someone have one they wanna sell/ship for a paypal payment?

Edited July 16, 2010 by bounce

[MikeW]

20 weight oil goes in the top of the carbs. Some people use ATF. It's a dampener, not a lubricant. It will only affect throttle response, not whether the engine will fire.

I think you may have bad gas. If it sat over the winter it's likely too old to be good, even with a gallon of fresh gas added to the tank. Since your other posts indicate a possible ignition problem the first thing to do is simply try to start the engine after spraying starter fluid into the air cleaner. If you have a spark it should fire right up. If it doesn't then you've got an ignition problem to get sorted out first. If it fires and dies down after a few seconds then you have a fuel problem after all (either no fuel or bad fuel). No fuel could be a blockage somewhere before or after the pump, a non-operational pump, or a hole in the line between the tank and the pump that would cause the pump to only suck air. The glass jar test mentioned above will be the easiest way to make sure that gas is making to all the way to the carbs. If it is then you might take the float lids off and see if the bowl is empty. If so then it's likely stuck needle valves or clogged banjo filters.

[bounce]

The glass jar test mentioned above will be the easiest way to make sure that gas is making to all the way to the carbs. If it is then you might take the float lids off and see if the bowl is empty. If so then it's likely stuck needle valves or clogged banjo filters.

TOMORROW!!! is the day....

[Bruce Palmer]

Tell me more about these windows on your carbs......

For the Hitachi SUs we sell a JUST SUs dvd that will be a big help for you de-bugging your carbs if they ar Hitachis.

[Casey_z]

My 2cents

On tuesday I changed my dist cap and rotor on my 72 240z - stock ignition.

Turned out the rotor was defective.

I put the old parts back and could not get the car to fire up.

I checked everything and it would not fire.

I spoke to my brother in law who apprenticed as a mechanic at a Datsun Dealership in the 70's and he told me to change the spark plugs.

The plugs were a year old and looked fine.

I replaced them and the engine started on the first turn.

He told me back in the day this happened when you soaked the plugs with unburnt fuel it soaked into the carbon on the tips and the plugs just would not spark well enough to fire up the engine.

These plugs looked great and I wonder if I upgraded to electronic ign. the spark would have been stronger but that is a different topic.

My brother in law told me that at the dealership they cleaned the plugs and sand blasted and basicly tried everything but replacing the plugs was the only solution.

This may or may not be your issue Bounce but I had pulled the little hair I have left out trying to figure out what was wrong and this worked:beer:

It is always nice to have the phone a friend option:cool:

Casey

Edited July 16, 2010 by Casey_z
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