Fuel feed rail/carb pipe pressure

[nospark]

The metal fuel feed rail obviously has a T off to to a "rubber" fuel pipe to feed each of the carbs. On most of the engine photos I've seen, each fuel pipe to the carb is looped up and over to the carb such that the top of this kinked loop is above the height of the return fuel rail.

I assume it is configured this way so that the RETURN fuel rail is always filled with petrol, is therefore pressurised as it should be and therefore avoids air locks in the return fuel system and lets it do its circulation job properly.
ANY THOUGHTS ? (Have a look at yours)

On my car the front pipe feeds downward from the rail to the SU carb. The rear pipe did the up and over loop to the carb over the throttle bar. Not so long ago I changed its path to go down and under the throttle bar so the fuel feed pipe fell downward to the SU carb. This MAY BE a factor in my rear carb flooding issue as the return fuel rail/sytem has attracted air and gunk into that return line. (I am speculating. PS Its NOT a float bowl/needle problem)
Just wanted observations on how the fuel feed system should be configured.

 

[anthon51]

Hi everyone. I am now getting a little miffed off over the problems I am having with my fuel supply to the carbs and engine. On the verge of sending for a mobile mechanic. After the episode of sluttering to a stop last year in the Ormskirk show,sending for the RAC, being told that my fuel pump was the problem the RAC mechanic got me on the road again after priming my pump with a priming bulb."I did,nt even know that there was such a thing".,After a couple of weeks went to start the car and after a couple of minutes it died on me. Replaced the fuel pump and in spite of priming the new pump numerous times and starting the engine it stops after 5,10,or 15 minutes. I am now so frustrated I have nearly started smoking again after more than 30 years. All help and advice sincerely appreciated. HHHHHHEEEELLLppppp please.

 

[jonbills]

Hi everyone. I am now getting a little miffed off over the problems I am having with my fuel supply to the carbs and engine. On the verge of sending for a mobile mechanic. After the episode of sluttering to a stop last year in the Ormskirk show,sending for the RAC, being told that my fuel pump was the problem the RAC mechanic got me on the road again after priming my pump with a priming bulb."I did,nt even know that there was such a thing".,After a couple of weeks went to start the car and after a couple of minutes it died on me. Replaced the fuel pump and in spite of priming the new pump numerous times and starting the engine it stops after 5,10,or 15 minutes. I am now so frustrated I have nearly started smoking again after more than 30 years. All help and advice sincerely appreciated. HHHHHHEEEELLLppppp please.

Hi, I think first thing would be to start your own thread. You can do that on this page:
http://zclub.net/forum/newthread.php?do=newthread&f=127
Please be explicit about what you're asking for - are you asking for someone to come and fix your car, for recommendations for a mechanic, recommendations for a cigarette brand, or things on your car for you to investigate.

 

[jonbills]

The metal fuel feed rail obviously has a T off to to a "rubber" fuel pipe to feed each of the carbs. On most of the engine photos I've seen, each fuel pipe to the carb is looped up and over to the carb such that the top of this kinked loop is above the height of the return fuel rail.

I assume it is configured this way so that the RETURN fuel rail is always filled with petrol, is therefore pressurised as it should be and therefore avoids air locks in the return fuel system and lets it do its circulation job properly.
ANY THOUGHTS ? (Have a look at yours)

On my car the front pipe feeds downward from the rail to the SU carb. The rear pipe did the up and over loop to the carb over the throttle bar. Not so long ago I changed its path to go down and under the throttle bar so the fuel feed pipe fell downward to the SU carb. This MAY BE a factor in my rear carb flooding issue as the return fuel rail/system has attracted air and gunk into that return line. (I am speculating. PS Its NOT a float bowl/needle problem)
Just wanted observations on how the fuel feed system should be configured.

I'm not expert on the SUs by any means, and don't have 'em to look at, but I wouldn't think this is a factor. if the return line is so blocked (by air and gunk) that there's extra pressure at the rear carb causing it to flood, then there will also be that extra pressure at the front carb doing the same there.
Here's a list of things I can think of
1) the float level is wrong,
2) the needle valve isn't closing (either because its got dirt in it, is worn or maybe the float has a leak),
3) the jet is too low or
4) the fuel in the rear float chamber is boiling
5) the needle is raised too quick/too much - is the damper spring missing?

I'm sure there are other possibles of course.

 

[nospark]

Jonbills
Thanks on two fronts
First, for telling Anthon51 not to hijack this thread. Something i was about to do myself.

Second, for your obs. This is NOT a float needle issue. Something I made a point of stating in my post. That base has truly been covered by me. As you know liquid in a system finds the weakest point and finds its release (of pressure) at that point. It is likely that the rear carb is the weak point and the pressure is relieved at that point (ie flooding) before the front carb has a chance to come into play.

THIS THREAD QUERY IS ABOUT CARB FEED "RUBBER" PIPES LOOPING AT A HEIGHT ABOVE THE METAL FUEL RAIL (my own issues are secondary to this "how/why is it configured/works? query). Have a look at my original post.

 

[jonbills]

Jonbills

Thanks on two fronts

First, for telling Anthon51 not to hijack this thread. Something i was about to do myself.



Second, for your obs. This is NOT a float needle issue. Something I made a point of stating in my post. That base has truly been covered by me. As you know liquid in a system finds the weakest point and finds its release (of pressure) at that point. It is likely that the rear carb is the weak point and the pressure is relieved at that point (ie flooding) before the front carb has a chance to come into play.



THIS THREAD QUERY IS ABOUT CARB FEED "RUBBER" PIPES LOOPING AT A HEIGHT ABOVE THE METAL FUEL RAIL (my own issues are secondary to this "how/why is it configured/works? query). Have a look at my original post.

Sure - I meant to say I know you're sure it's not float/needle stuff. I just had it in my list for completeness.

Happy to butt out so the thread can get back on track with how the stock piping is routed.

 

[MaximG]

This is taken from a Nissan brochure.

 

[nospark]

Thanks MaximG. I now think i have been barking at the wrong tree and my "theory" is wrong

 

[TimW]

I don’t know if this is relevant or not, I only mention it as I’d seen in the post about extra fuel pressure in one carb.

Being no expert and new to Z’s my knowledge is limited, but one of the first things I’d noticed on my carbs was that when blowing down the banjo joint there was a significant difference in pressure between the two, thus assumed difference in fuel pressure. I was having difficulties leaning up the rear carb which lead me to dismantle the them

Turns out the carb fuel filter was blocked and fuel plug hole crudded up/restricted with rust in the rear carb. Carbs are working fine now. I’d done a few other things which I think more relevant to them now being ok, such as floats and needles, but thought may be worth a mention.

 

[Mr.F]

As an aside - finally got new stock of the inlet basket filters for 240Z carbs. Often overlooked on rebuilds and been unavailable from Nissan for a while now...

 

[TimW]

Not wishing to divert thread....

Great stuff Mike, I now know what they're called. Much easier to investigate when having the correct terminology.

Yes, you tend see info on needles and floats, but little mentioning of inlet basket filters. I discovered my cruddy filters more so by curiosity and a little bit of luck.

Put me down for a couple of those. My list is slowly growing, nothing major just odds and sods, will be in touch soon.