Carb Issues - 1987 3.5 V8

NMEXPAT

Well-known member
Long time lurker and first time poster. Looking for some direction.

Back in October 2017 I bought an Australian 1987 110 3.5 V8 from Royal Overland in Austin. On the drive home from Austin to Houston, it stopped running. Basically it felt like it was running out of gas, when of course it wasn't empty. It would do this a few more times over the next few weeks, but always start up and drive again after a few hours like nothing happened.

After doing some internet research I decided the fuel pump was slowly dying. I ordered a new fuel pump and other odds and ends from Rovahfarm.

While dropping the fuel tank, I found it was powered by a separate individual +12V source. I didn't trace the wire back, but the vehicle at some point was outfitted with a immobilizer. I think this separate wire could be grounding out randomly or the immobilizer would acting up. This also might be the cause of the random shut downs.

In the end I terminated the single +12V wire and rewired the pump wires to the original wires.

Two weeks ago the stars aligned, I was off work and it wasn't raining. I installed the new fuel pump and fuel filter. I confirmed the fuel pump was wired correctly and running by turning the vehicle without the filter in place. Fuel was coming out. I then installed the fuel filter and tried to start my truck. It initially fired up for a second and then stopped. It wouldn't spark anymore. It cranks but won't fire up.

I pretty sure the carbs are flooded. Due to the vehicle storage location and running out of time I couldn't confirm this 100% but I've flooded cars and bikes before. I'm pretty sure this fuel pump is pumping much better (higher pressure) than the old one that came out of it.

I also didn't check the fuel vapor separator or fuel return line to fuel tank. Fuel should be returning to the fuel tank under normal operation.

Here's my dilemma.
1. I could rebuild the SU carbs and replace the gaskets, needles etc. Hoping the float needle valve will now seal. Probably cost $200
2. Ditch the SU carbs entirely and go to an "american" style carb setup. Looking at $800 cost.

I'm leaning towards #2 since most people post positive results with changing the intake manifold. However, when the truck was running with the original equipment and it ran great. I just want the most reliable and easy to work on setup.

Any other tips before I drop money on carbs? I guess I could install the old pump back in and see if the truck will run, this would only serve to eliminate the suspect wire problem and over pressure but I'd be worried about it dying randomly. I couldn't find any information on the fuel regulator near / on the fuel vapor separator. Hopefully I'm just over looking something simple.

Thanks!
 

Red90

Well-known member
Adjust the floats, make sure they are not leaking and check the float valves. Sounds like that was the problem from day one. No need for $200, just a little bit of time. It is a simple job.

The Edlebrock (Carter) carbs are not better carbs. If changing to something new, you are better going EFI.
 

RDavisinVA

Technical Excellence Contributor
After all the years the 3.5 fuel pumps become suspect.
Why not install a new fuel pump and install a relay powered from the starter lug, but energized by the IG SW.
Then run the output from the relay to the fuel pump.
Wouldn't this ensure fuel delivery?
 

NMEXPAT

Well-known member
After all the years the 3.5 fuel pumps become suspect.
Why not install a new fuel pump and install a relay powered from the starter lug, but energized by the IG SW.
Then run the output from the relay to the fuel pump.
Wouldn't this ensure fuel delivery?

I don't have a fuel deliver problem right now. The new pump is definitely pumping fuel. I think I have a blocked return line problem or a float valve sealing problem.
 

NMEXPAT

Well-known member
Adjust the floats, make sure they are not leaking and check the float valves. Sounds like that was the problem from day one. No need for $200, just a little bit of time. It is a simple job.

The Edlebrock (Carter) carbs are not better carbs. If changing to something new, you are better going EFI.

I'm just unfamiliar with the SU carbs and despite having the workshop manual I remain a little fearfull. I figured if I was going to mess with the carbs I might as well replace the gaskets, seals, floats and valves. I've tried to skimp on rebuilding motorcycle carbs, and it always bites me back.
 

NMEXPAT

Well-known member
I also forgot to mention at some point in the trucks life it was outfitted with LPG fueling as well. Some of the hardware remains as well, but I'm no certainly no expert.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
I'm not an expert, but I'd say start simple. Just try cleaning the carbs as they sit, then work up from there. I've had several fuel issues go away completely with a simple cleaning.

Also, could it be possible that something is just stuck? Are both carbs being actuated in exactly the same way when the choke and pedal are moved?
 

Red90

Well-known member
I'm just unfamiliar with the SU carbs and despite having the workshop manual I remain a little fearfull. I figured if I was going to mess with the carbs I might as well replace the gaskets, seals, floats and valves. I've tried to skimp on rebuilding motorcycle carbs, and it always bites me back.

Pull the carbs, turn them over and pull the float bowls. Check valves to make sure they seal (blow into fuel line and then close valve). Check floats to make sure they float and then adjust float height. Super simple. No different than any other carb. All clear in the manual. Nothing to be fearful of.

Don't fix things that are not broken. Your description from the beginning was carb flooding.
 

RDavisinVA

Technical Excellence Contributor
We use the Moss 386-390 Grose-Jet on MGs with SU carbs as a trouble free replacement for the older and problematic needle & seat.
This may fit your carbs, Moss could tell you.
 

NMEXPAT

Well-known member
Pull the carbs, turn them over and pull the float bowls. Check valves to make sure they seal (blow into fuel line and then close valve). Check floats to make sure they float and then adjust float height. Super simple. No different than any other carb. All clear in the manual. Nothing to be fearful of.

Don't fix things that are not broken. Your description from the beginning was carb flooding.

With the old fuel pump the carbs didn't flood. I'm guessing the new one pumps at a higher pressure.

Before I dig into the old carbs I'm going to get a pressure Gage and check both pumps.

I see aftermarket adjustable fuel pressure regulators for cheap. If the new pump is above spec, cleaning, new floats and valves won't matter.

Thanks for the help everyone.
 

Red90

Well-known member
The explanation of the original problem was carb flooding. I think you were mistaken that it was a pump issue.
 

Roverman2010

Well-known member
That fits in the tank or mounts to the frame? I have an in tank pump.

I take you got PRC7020? the one I use is frame mounted. couple of things to check, fuel return tubing is clear, if you still flood your going to have drop the carbs and check that the needle Valves are clean this means taking the bowls off and do it carefully so you don't tear the gasket. you should check the float height as well, but nine times out of ten its the needle valve gets crap on it. The new Viton tipped needle Vv's are the ones to fit. The rubber ones just don't seat well.

What is the general condition of the carbs, are the butterfly spindles a tight fit no wobbling allowed lol

I am hoping you got SU HIF's

http://sucarb.co.uk/technical Hope this helps
 

NMEXPAT

Well-known member
I take you got PRC7020? the one I use is frame mounted. couple of things to check, fuel return tubing is clear, if you still flood your going to have drop the carbs and check that the needle Valves are clean this means taking the bowls off and do it carefully so you don't tear the gasket. you should check the float height as well, but nine times out of ten its the needle valve gets crap on it. The new Viton tipped needle Vv's are the ones to fit. The rubber ones just don't seat well.

What is the general condition of the carbs, are the butterfly spindles a tight fit no wobbling allowed lol

I am hoping you got SU HIF's

http://sucarb.co.uk/technical Hope this helps
That's super helpful thanks! Yep that's the fuel pump I ordered and paid in.
 

Roverman2010

Well-known member
I do have some new carb parts here on Galveston Island not sure if I have a complete set, I know I don't have new needle valves but some good old ones that can get by. Let me know.
 

NMEXPAT

Well-known member
Well yesterday the stars aligned. It was sunny and in the 70's and I got a few hours to work on my 110 to investigate the problem. I also bought a fuel gauge and a regulator just in case.

I pulled the massive airfilter off to get access to the rear bulkhead. I traced the fuel and return lines to the carbs. It quickly became obvious my truck fuel system is not plumbed up according to the figures in the defender manual. The fuel vapor separator shown in the manual is completely missing. The fuel line runs straight to the right carb. At the right carb there is a T junction and a fuel line runs to the left carb. The left carb also has a T junction where the fuel tank return line is connected. The hard fuel lines on each carb don't look stock. The line between the carbs is a strange hard thin wall plastic line.

The new fuel pump is pushing fuel at 4psi, right smack in the middle of the range given in the manual. So it's in spec.

I'm still at the same spot but now I have a better idea of what's going on. Right now I think I'm going to go the edelbrock intake manifold and carb route and add in a fuel pressure regulator on the rear bulkhead with a return line to the fuel tank.

Thanks everyone for the advice and offers. I'm going to order the parts in a few days and attempt this myself.
 

Roverman2010

Well-known member
The fuel lines you describe sound normal, don't forget the the manuals are written to take in count for many markets. Fuel vapor thingy? Not all have and in the 8 or so V8 carb powered RRC's have has been fitted.

Are you still having a flood issue? Is the return line clear? One tip give each carb a puff of air as sometimes this clears curb off the needle. Use a push bike tyre pump is best for this. A shot of sea foam into the carbs and let it sit for a bit helps clean them as well.

Where in H town are you?

Good Luck!
 

NMEXPAT

Well-known member
The fuel lines you describe sound normal, don't forget the the manuals are written to take in count for many markets. Fuel vapor thingy? Not all have and in the 8 or so V8 carb powered RRC's have has been fitted.

Are you still having a flood issue? Is the return line clear? One tip give each carb a puff of air as sometimes this clears curb off the needle. Use a push bike tyre pump is best for this. A shot of sea foam into the carbs and let it sit for a bit helps clean them as well.

Where in H town are you?

Good Luck!

Just north of the heights.

Thanks for the tips. I think these carbs are nearly original / untouched. They still have a tamper proof band installed. I ran out of time to replumb and check return line for fuel coming out.

I think for nearly the same amount of time fixing the old I can get new up and running. Yes parts will cost a little more but my issue is time.
 
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