Jump to content
HybridZ

Pressure in fuel tank and boiling fuel in carb


Recommended Posts

Hey there, i have suddenly gotten a problem with my 280Z with a 302sbf. I installed a regular fuel tank instead of the fuel cell i have had in the car. There are 3 lines running from the rear of the car up to the engine compartment. 1 is 3/8" and i use that for fuel feed, the second is 5/16" and i am using that for the return line to the tank, the other is a 1/4" line and i think it is supposed to be hooked to the vapor tank in the rear hatch area because it has a check valve in it, question...where does the other end supposed to go too??? it is just open ended next to my firewall. I am thinking this supposed to be a vapor line for a charcoal canister, maybe, maybe not, I am also having a problem with fuel tank being pressurized during hot weather and i think this is because that 1/4" line is plugged. I plan to run new 3/8" lines on the outside of the frame rail to alleviate some of the heating of the fuel problems since the lines only clear the headers by about 1 1/2", but if i need to run another vapor line too i want to make sure that is what it is for and where it needs to go.

Link to comment
Share on other sites

You're running carb'd, right? If so, what are you even doing with a return line? (I'm generally a fuel injection guy, so I could be missing something, but all my sbf's are single line from the gas tank to the carb...)

 

By the way, are you only running aluminum spacers on your manifold to carb connection? When your carb gas starts to boil, see if your intake manifold will boil water too. My 65 Econoline would do that, as it has a shared intake/exhaust cast iron manifold. The heat transfer from aluminum to cast iron is pretty high, even with a thick gasket, so you need something else there. On the I6 Mustangs, Ford ran coolant through the side of the aluminum carb to manifold spacer block to draw heat away from the carb. I helped the boiling gas problem go away on my van by using a 1" phenolic spacer I made. It's not perfect, but it definitely helps.

Edited by yellowoctupus
Link to comment
Share on other sites

Well lets see, if you run fuel pump without a return line the fuel pump has to kick off and on to keep fuel to the carb, with the return line system you are allowing the fuel pump to run continously and recirculating the fuel to cool the pump and make it last a lot longer, plus with a return system you have better control of fuel pressures. I dont have any spacers between the carb and the intake because then my air cleaner wont fit under my hood. I am thinking my fuel boiling problem is because my fuel lines are parallel to my headers and only about 1 1/2" away. There is a heat shield between the 2 but when it is 108* outside that doesnt help much, i went and bought 25' of 3/8 tubing and am going to run a set outside the datsun frame and get them completely away from my headers. I am planning to fabricate a different air cleaner this winter so i will need to take into account the extra space needed to allow a phenolic spacer between the 2

Link to comment
Share on other sites

Hey there, i have suddenly gotten a problem with my 280Z with a 302sbf. I installed a regular fuel tank instead of the fuel cell i have had in the car. There are 3 lines running from the rear of the car up to the engine compartment. 1 is 3/8" and i use that for fuel feed, the second is 5/16" and i am using that for the return line to the tank, the other is a 1/4" line and i think it is supposed to be hooked to the vapor tank in the rear hatch area because it has a check valve in it, question...where does the other end supposed to go too??? it is just open ended next to my firewall. I am thinking this supposed to be a vapor line for a charcoal canister, maybe, maybe not, I am also having a problem with fuel tank being pressurized during hot weather and i think this is because that 1/4" line is plugged. I plan to run new 3/8" lines on the outside of the frame rail to alleviate some of the heating of the fuel problems since the lines only clear the headers by about 1 1/2", but if i need to run another vapor line too i want to make sure that is what it is for and where it needs to go.

 

 

The smaller 1/4 inch line is for the fuel vent, just like you said. And yes, it went to a charcoal canister that was on the left side of the car next to the strut housing. As far as the fuel lines go, I think that your lines are too close to your headers which will really heat the fuel up. I am in the process now of re-routing all of the lines since I have the same issues. I will have the lines routed on the outside of the frame rail and then into the fender near the strut to avoid the heat from the exhaust. Also try to set up a return line for your carb so that it is always routing fresh fuel thru the lines. This will keep it much cooler.

Link to comment
Share on other sites

Ok, that makes sense. Do you have to run an adjustable low pressure fuel regulator then? This spells bad news for me too then, as my fuel lines are only 1" away from my right exh. pipe... I was working on welding those up tonight actually. How do you know if your fuel is too hot on an injected engine? I would think the higher flow would make a difference, but if you're running an electric pump and have a return line, that's almost the same thing as I've got going on, just with lower pressure.

 

BTW, Scott, have you had yours out for a test drive yet? Haven't seen any updates. I was in WA the other day and didn't have your phone number, I have to save it in my phone for next time.

Edited by yellowoctupus
Link to comment
Share on other sites

Hey-

 

I did put an adjustable fuel pressure regulator on my car, Summit has one made by Bosch really cheap, and I got a liquid filled gauge from Charleston Rubber and gasket in North Chuck. I think that the regulator was about 30.00 or so and the gauge was about 15.00. I am still quite away's from getting the motor started though, still need to do the wiring and clean up the loose ends such as exhaust and the steering linkage. Its been so hot lately that I can't get out in it to work in my garage. Plus work is keeping me really busy at the moment. I'll take some photos shortly and post them. Later-

Link to comment
Share on other sites

I got a liquid filled gauge from Charleston Rubber and gasket in North Chuck. I think that the regulator was about 30.00 or so and the gauge was about 15.00.

 

Often the liquid filled gauges have a rubber nipple on top which you're supposed to snip off to get a more accurate reading. The Bordon tube that's inside will slightly pressurize the gauge itself otherwise, however I would NOT recommend doing that, as they have a nasty habit of leaking out gauge oil all over the place if you do. Ack. Been there done that.

Edited by yellowoctupus
Link to comment
Share on other sites

Whenever it cools down enough i am going to run 3/8 lines outside the datsun frame and i guess that 1/4" line will just be run with a downturned loop in it so the tank can breathe and still keep trash out of it. make sure you use a return style regulator, standard regulators wont work. Right now i am dealing with major overheating problems. put on a brand new 600 holley and it is fine until i get into a cruise situation then it goes extremely lean and make the thing run 215 to 230 degrees. This is even with a rodded out radiator, i have been talking to holley techs and they dont seem to know why it would go so lean at cruise. I have a 16" electric fan on it now in a shroud but i might have to mount it directly to the radiator along with a 12" i also have. Never had a overheating problem until recently. On the highway it runs around 190, until i get into over drive and am cruising at 1600 rpm at 60 mph then away it goes

Link to comment
Share on other sites

How do you know it's running lean?

 

Is your ignition timing and advance correct?

Retarded timing causes high temps.

 

Under a heavy load in overdrive, pinging/detonation can cause high temps also.

Edited by jasper
Link to comment
Share on other sites

How do you know it's running lean?

 

Is your ignition timing and advance correct?

Retarded timing causes high temps.

 

Under a heavy load in overdrive, pinging/detonation can cause high temps also.

 

I know it is lean because i am running 2 o2 sensors and 2 a/f ratio gauges and they both agree, my timing is set at 14*btdc, and it isnt under load, when i get on it and do put a load on it the a/f ratio goes into a normal area and it runs cooler. Holley techs werent any help at all they just told me to check the plugs and go up or down from there, well i believe the a/f ratio gauges are a little more trustworthy than reading the plugs.

Link to comment
Share on other sites

Good info.

First, apparently 14* is your base ignition timing, what is your max/total advance???

 

From my experience, most coil/wire/plug/misfire/problems occur in high gear

at moderate throttle,..Kind of like a clutch slipping in high gear(high load, high torque),

....not at WOT in a lower gear!

Running in a lower gear may stress drive line componets, but not your ignition system, etc.

Coils, etc generaly fail under low rpm, high load.

 

Wild stab here.....what are your vacuum readings, and what are the

power valve/s rated at??

 

What is your rear diff ratio? Are you overgeared?? "Lugging" it??

1600 rpm is kind of LOW at 60 mph ! for most cars.

Most times..... I'm thinking approx 2200 rpm at that speed,is about the norm.

Edited by jasper
Link to comment
Share on other sites

yeah 14 is base and i have a total of 38 that is fully in at 3800 rpm. I have a HEI distributor with a MSD digital trigger with a 65K ciol and 9 mm MSD wires, running Bosch platinum plugs at .050. Gettting 12" vacuum at idle in drive at 650 rpm. my gearing isnt ideal, i am running the stock 3.54 gears but plan to put my 3.92 gearset in this winter. that will bring my 60 mph up to about 1800. Going to go into the cooling system this weekend, even in 110+ heat to try and see if anything else may be wrong. Maybe when i had the radiator boiled out they blocked off some tubes or something.

Link to comment
Share on other sites

You need a bunch more timing at idle. Especially with only 12" of vacuum.

 

Here is a nice timing article for an old school 350 chevy which should also apply for an old sbf.

 

http://www.corvette-restoration.com/resources/technical_papers/Timing101.pdf

 

I didn't see a vacuum advance canister on your distributor. If you don't have one, then you really need one for a street car.

 

also get a ford taurus or t-bird fan from a mid 90's car. You can pick them up for $25 from a u-pull-it type junk yard. You need at least 3000 cfms. The ford fan is a 2 speed fan, and even low speed would be strong enough. They come with a build in shroud. nice.

 

a cross flow radiator would also help.

Edited by Pyro
Link to comment
Share on other sites

Ok here is what i have as of today with a little bit of tinkering, 14* at idle in gear at 650 rpm, my mechanical advance bring in a total of 18* at 2600 rpm, wacuum brings in a total of 38* at 3800 rpm. I jetted up to 70's in the primary and that is a little rich but close, now i am only running 190* to 200* around town instead of 215* to 220* after i get the engine flushed out with chemicals i am installing a new aluminum radiator with center top inlet and drivers side outlet to fit the ford inlets and outlets on the engine with 3 rows of 1" tubes, ($150.00 delivered)and 165* thermostat. It is not a crossflow (hate those things)and i am presently using a 18" electric fan set to come on at 175* as a puller with a full shroud and a 12" on the outside set to come on at 190* as a pusher right beside my oil and trans cooler.

The factory timing for this engine is 8* btdc so i think 14* should be plenty. I could be wrong but that seems to work best for me. So far i have been having to a lot of trial and error with this engine since it isnt fuel injected anymore and isnt pushing a 4600 lb lincoln towncar

Link to comment
Share on other sites

  • 2 weeks later...

honestly radiator isnt an issue. I know theres a lot of info on here that said you "should" upgrade but PERSONAL experience when I run my 260z with 302 i used the STOCK radiator kept the temp at 180*

 

THEN NOW ITS BOOSTED-61mm holset and guess what Stock radiator and temp is at 180*(Im in California weather)

 

I am using a ford taurus 2 speed fan but the 2nd speed NEVER kicked in b/c it does not get that hot.

 

 

btw is your a/f a wideband?

Link to comment
Share on other sites

Well i bought some cooling system cleaner (evaporust cooling system cleaner) and ran it through the entire system for the recommended 2 hours and flushed and then refilled it with antifreeze, now when it is 110* outside it gets right up to 200 then drops slightly. and even though the datsun radiator had been rodded out and block and heads hot tanked 3000 miles back when i rebuilt it this stuff got out chunks of rust up too 1/2" and what a difference it made, before it would go to 220 and pretty much stay there.

The main reason i am wanting to go to aftermarket radiator is it does get hot as hell here and when i want to go autocrossing i dont want to worry about overheating the thing since it dont get much airflow autocrossing off and on all day long. I now have a 16" puller fan that kicks on at 160* but when i put in the new radiator i will mount it flat against the inside and mount my 12" fan on the outside to kick on at 190* if needed, i know i really need it right now but i only drive the car 2 days a week for a total of 65 miles a week.

 

I am using 2 1 wire sensors right now when i put it inside for the wintger i need to weld different bungs closer to the headers, right now they are about 16" behind the header collector right in from of the exhaust cutout and they cool off too fast at adle and take almost 5 minutes to heat up when cold.

-

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...