xrotaryguy

The carb on my 84 rx7 is acting up. the fuel pump is in very good shape and the float bowls retain the correct ammount of fuel but after the carb warms up it stops delivering fuel. I mean that there after 20 minutes or so there is absolutely no fuel comming out of the little brass tubes sticking into the venturi of either the primaries OR secondaries. I have rebuilt the carb and found a couple of problems mostly that the gasket between the throttle body and the middle section of the carb that contains the floats and venturi and such. remadying that some of the carbs problems were solved but the failure of the carb with much running time continues. I cant figure this one out. Also the switching valve solenoid is missing. Thats the grey solenoid in the rack. The vacume routing on the driver side of the carb is correct im sure but on the passenger side it may well be wrong. I have not found a diagram of that yet. Any help would be apprecciated. Thanks,
Brian

Rx7carl

Hi and welcome. Are you sure its not the fuel pump quitting after it gets warmed up? At idle, there shouldnt be any fuel comming out the brass tubes. The idle jet supplies fuel at idle. Does it quit running? More info please?

xrotaryguy

Hello carl and thank you for the response. well you asked for it and here it is... more info. this is the third fuel pump I have had in it. and it puts out pretty bitchin pressure and volume. the others i did test and found that they were not up tosnuff all the time. but that turned out not to bve the problem. the fuel pump relay also seemed to be faulty. it would have the key in the on position and not have any fuel comming out. I dont know if the 84 85 cars require there to be oil pressure before turning the fuel pump on or something like that but it seemed to not run the pump even while the car was cranking from time to time. andy how the new fuel pump is currently running off the leading coil and goes like a mo fo. I am starting to suspect the venting solenoid but Im not sure that that would explain all the symptoms either. The car runs for quite some time at idle and under gentle driving conditions. we're talking like an hour and a half or so. At full throttle however it will die after a few minutes. I do this with the brakes on in second gear with the accelerator pressed flat to the ground. when it dies it will buck and jerk a few times and bretty much just stop trying to accelerate. then it gives up all together. I can usually start it one or two times more but only for a few secoinds the first time and for an even shorter time the second time. I have paid more attention to the level of the fuel in the float bowl now and it does empty out when it dies but will fill back up a time or two and then just stop filling any more. I can not really see the back float window. it would seem that both bowls yould have to be empty for the car to stop running. so that pretty much rules out needle valves that the floats actuate. is there a fuel shut off solenoid that im not aware of? can the venting solenoid cause the floats to run dry? The hanes manual calls it a venting solenoid but i hear people usually call it a fuel return solenoid. Im thinkin g that this could be the problem right now.

Sterling

Hi Brian,
That is the vent solenoid, and must be hooked up. Positive 12V causes a tiny electromagnet inside to retract a spring loaded plastic plunger, thus allowing the carb to vent.

It sounds like the problem is a fuel delivery problem, and not a carb problem- like you're simply running out of fuel. You've given much detail regarding the fuel pump, but have you replaced the filter?

Another possibilty comes to mind, so I'll ask this...
Does your fuel tank "whoosh" alot after you open the cap?

Also, is your replacement pump stock?

jayroc

Yes, I agree, sounds like a fuel delivery issue. What I would recommend is rewiring the fuel pump straight from the battery with a fuse and a switch. Temporary, or course, just to see if it is a wiring issue. Though, the fuel filter is a good thing to check, also. You can also try and clean out your hard lines and check for kinks in the soft lines. Good luck.

xrotaryguy

I agree that i am running out of fuel also. but I am really quite sure that iit is not a pre carb problem. The fuel pump is not stock and is wired to the coil. the pump puts out gobbs and bobbs of fuelregardless of wether or not the car is running properly. that is to say that if i take off the fuel line and supply power to the fuel pump by turning the key on then the thing pumps plenty of fuel regardless of wether or not the car is failing to run or not... I think

xrotaryguy

Ok ok I just checked the fuel supply after provoking the car to fail. I has almost no fuel comming out of the fuel line. but thats really weird. why would that happen only after running it for a while? It supplies fuel just fine when its been sitting for a couple of days. also the tank doesnt whoosh and i have driven the car without the cap so thats mucho bueno. and the fuel pump is hard wired to the coil. fuel filter is in excelent condition after removing the one that some idiot left in there when putting a new one in backwards. so i think im pretty much down to a heat sensative obstruction in the fuel line or a heat sensative obstruction in the tank Ie fuel strainer. which do you guys think is more likely?

xrotaryguy

I think i will provoke the car to act up again and see if the pump is putting out like it should just slightly after the pump. that should narrow it down some.

Sterling

Which coil is it wired to?
The trailing plugs do not always fire.

Jeff20B

iTrader: (13)

Uhg, another '84-'85 fuel pump weirdness thread.

red13brx7

It is pribably the return solenoid, the pump isn't pumping enough, that is being used.. its only a 12a it doesn't use that much fuel.. What kind of pump do you have? It honestly sounds like that venting problem because it sounds like your pump is cavitating or heating up and then stops pumping. I had this problem with mine when I did a 13b carb swap, if the car isn't using all the fuel that is being supplied the pump, pumps but not enough to keep it cool. But your probelm almost seems more than that.. because it is fine at idle. Just some idea.Does the pump still run when this happens? if you would leave the key in the on position?

red13brx7

I would hard wire the pump to the battery and not the coil, like someone already said in the forum.. just too see, if that could be a problem.

xrotaryguy

well I put a glass fuel filter in it to see what was comming out of the fuel tank and there was lots and lots of rust. I couldnt evendrive around the block with out the thing clogging up. so i put the tank out of my 8o in there... fudged which hoses go where and replaced the fuel pump again cause i think i ran it dry too many times or filled it with rust or something, and also put a new stock filter in line. now the car does not run out of gas any more but seems to run rich until the secondaries are open. It really has very poor power and runs rough and gassy smelling at part throttle acceleration, while maintaining speed and while idling. i can see fuel running out of one of the rear primary jet at idle and i dont think thats right at all. I imagine i got the carb float adjusted a little too wrong (I usually dont bother to adjust them all that well unless i get it wrong once ) also the thing is not making power quite like it should at full throttle. Its close but no cigar. For example... I got beat my a late model accord, and he didnt even realize we were racing. not at first any how.but he came from behind and spanked me. not good. any how. I think I need to rebuild the carb right this time and hopefully this time it will be right. By the way Im still missing a switching solenoid relay. any one wanna sell me one? Its the grey solenoid in the solenoid rack. I think it'll prolly run fine without it but better to have the engine compartment right in the phoenix area. any how thats whats up. I once again have actual carb problems.

xrotaryguy

oh by the way the fuel pump is running off the primary coil. and yea jeff i have a thing against the 84 85 cars too.

bbmac

as for your fuel drip in the rear venturi, my '83 did this as well and |I found out the problem was the surge valve aka purge valve. have your emissions been removed? if not take a cork and stuff the 1/2 inch line beside the idle compenator valve on the sirbox with the cork. Helped me tons and eliminated all my problems.

xrotaryguy

Well that definately sounds easier than rebuilding the carb again. Im not sure which hose it is that you're talking about but i will try to figure that out and effect a solution that way before doing another rebuild.
How about replacing the purge valve instead. I live in phoenix Az so I have to pass emissions. And besides I dont REEEEALLY want to molest another rx7. I think it would be cool to have a stock rx7 for a change lol.