2300 Off-roading upgrades?

JohnnyC

JohnnyC

Member
Ok I have a 77 Scout II with a 304/727/d20/44f&r combo. I finally ahd a enough guts to take my Scout for a romp in the mountains. It was doing awesome until I hit about 7500-8000 ft and then I noticed it would die on pretty much any incline. I popped the hood and noticed my fuel filter was empty (my fuel pump was replaced with a mech new one about 5 mths ago). I coasted to some level ground turned it over a couple times and it fired right up.

I was reading on some other posts about getting a fuel pressure regulator cause it helped on inclines/declines/sidehilling. I am also woundering if purchasing a inline fuel pump would be a good idea. If so do I just bypass the mech fp?
 
Don't take my first question the wrong way but are you certain you had enough fuel to keep the in tank pickup in fuel?


At high altitude fuel at altitude will boil and thus vapor lock at a much lower temperature. The pressure of the air column above your truck is shorter and exerts less pressure on the highly volatile fuel allowing it to boil earlier.


Do this, inspect your fuel line routing and make sure it is far away from any high heat source especially before the pump where the suction of the pump can magnify vaporization. The slow driving and low air flow doesn't help either.

The regulator won't help if vapor lock is the issue.
 
I'm with Robert here, what you describe is a classic "running out of fuel" situation.

You've prolly seen all the jawwin' we do around here regarding blocked and grungee fuel delivery systems! It May well be that the syndrome has hit your rig now. And if there is trash in the system chunks will enter the oem fuel pump also and take it out or greatly reduce it's ability to deliver adequate fuel volume at correct pressure.

I don't know where this myth regarding "fuel pressure regulator" use at higher elevations started. But that is just a band-aid for a carb that is not set up correctly and/or a fuel pump that is out of spec. This same idea has been bounced around on these forums for years!

A fuel pressure regulator is certainly a valid "upgrade" for a carbureted application, but only when used with fuel pressure gauge to both "set" the regulator and then monitor fuel flow.

There are several small "issues" that can arise when operating a carbureted engine at altitudes above say 5,000ft. But nothing that can't be tuned for! And if the vehicle lives between say 4,000ft. And 9,000ft., then that certainly needs to be done.

But my suggestion here is...determine exactly what happened at the time of the engine stall fuel delivery-wise. Is that a repeatable occurrence?? If it is, then the same issue will occur at a lower elevation also. And, what was the attitude of the vehicle at the time, steep climb?...steep descent??...side slope???...flat?

As for off-road enhancements for your carb, there are some things you May do. But I can't remember which carb you are running! So refresh my memory hole. But those mods won't have any impact on your root issue if in fact it's due to restricted fuel delivery.

Running a "back-up" electric fuel pump is certainly a good idea on any vehicle used in the serious backcountry (that is called insurance!)! And it can be used to "boost" fuel delivery (with an operator-controlled switching system) if needed as long as a suitable regulator is installed and adjusted before it's needed! It can certainly be used to push through on oem fuel pump also, just install a regulator with gauge before the carb inlet and after the final fuel filter.
 
My vehical lives at 6500 ft and plays at 7500+ ft. It uses a 2300 series, I forget the list #, remaned holly (45 power valve and 56 jets).

It usually happens when I'm on a steep climb, not on a steep descent. The first time it happened I got 3/4rs up a hill and then it would die. It also felt extremely sluggish. I was wheeling at about 8000ft.

Is it better to have the electric fuel pump as a back up to the mech or to just get rid of the mech fuel pump all together?
 
I prefer to never use an electric pump as the primary. I always install as a back-up that is "jogged" regularly to keep the mechanism free.

There is nothing wrong with an oem mechanical pump that operating correctly. If...your mechanical pump is starving, so will any electric. That is because they would both be pulling from the same dip tube in the tank.

It's entirely possible that you have an issue with the pick up tube itself inside the tank. So if you have never pulled the tank and purged it and checked it's internal condition, that is the first thing I'd do. And that costs nothing but time!

I'd look at installing a pair of 52 jets for your operating conditions and trying that, but based upon your description of the issue of "running out of fuel", that is not the root cause! If it does this again, quickly pull the sight plug out of the fuel bowl and look inside, if the bowl level is way low, then you have a fuel delivery issue. Run the engine with the plug removed and adjust the fuel level at idle so that the liquid is 1/16" below the thread in the hole.
 
Robert,
honestly I can't say that I did have enough fuel. It is going to really suck if I have to keep the fuel tank completely topped off just to do a little trail riding.

Ssgt john d. Colvin
 
johnnyc said:
mayben,
what do you use to measure 1/16"?

Ssgt john colvin
Click to expand...

Not tryin' to be a smartass john...but I use my eyeballs!

This does not have to be an exact measurement, but it should be done with the vehicle sitting perfectly level. The intake manifold on these engines is machined so that the carb is mounted "level" even though the engine has a tilt to the rear when installed of about 6*.

And it needs to be done with the engine running at idle, so take appropriate cautions to prevent fuel spill on the hot intake manifold!

When any Holley modular carb is serviced, the float height is set statically before the fuel bowl assembly is installed. Then, once the engine is running, the fuel level in the bowl is verified/fine-tuned if need be. This "tunability" of the fuel level is what makes the Holley modular mixers so infinitely adjustable for any application under any type of operating conditions, what works for the drag racers does not work on the circle track...and what works on a trial rig doesn't work on the drag strip!
 
Ok, good, I eyeballed the fuel level and it seems to be doing better. I,m gonna try going up to a few trails this week and see if it fixed or at least helped it. Thanks for your help.
 
So I went out on the some trails yesterday and the Scout did way better then before. Didn't stall out once all up hill, I even it some sidehillin at it did great. The trouble started as I was coming back down hill. The thing died on me five times. The tank was at least 3/4s full but my fuel filter was bone dry. I had about 5 psi all the way through the entire ride but the fuel filter had barely any gas in it. I replaced my jets from 58's to 53's, bought a fuel pressure monitor and a regulator. Placed them both right before the carb. After about 2 hours of driving at 6500ft the regulator stopped allowing fuel to get to the carb. So I removed it and the Scout ran well.
Now im not sure where to go from here.....:confused5:
 
From the fuel pump inlet backward all the way into the fuel tank, clean it out!!

Drop that tank, yore gonna find mung in there that is blocking the "sock" on the dip tube (if it's still present), or there is stuff that is clogging the pickup point on a random basis.

The last one of these that gave me fits exactly like this involved a huge turd of swollen rtv (shit expands about six times it's normal bead size when exposed to gasoline). Someone had "sealed" the sending unit into the tank instead of using the correct seal ring, must have been two tubes of rtv floating inside the tank that looked like maggots outta science fiction movie!

By the way, unless the fuel filter is tiny (like for a lawnmower) it will never exhibit completely full condition. At idle...maybe 2/3 full. Under load, 1/3 to 1/2 full.
 
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Thanks,
the fuel filter wasn't even a third full coming down from the trails. I will drop the tank as soon as I get the chance to. Thanks for all your help, I'll keep you infomed of the progress.:cornut:
 
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