Yep, that is an '81 Rochester Q-jet M4ME.

It wouldn't hurt anything to change the pump. Since I had one go out on my Chevelle (a long time ago) and got lucky that I had a new pump in the trunk and the proper tools to change it on the side of the road, I have always kept another fuel pump on hand. They are cheap enough!

I would get a new float and a rebuild kit. Both should be available from your nearest autoparts store. Since the carb is likely original to the motor, just tell them that you need a float and rebuild kit for your q-jet and give them the 17081220 number to make sure that they select the proper parts.

 

Do you still think its down to either the fuel pump or float then?

I think this might be linked to the engine starting trouble I was experiencing.. Anyway I should note, after I fitted the new fuel filter it took a while to start but I put that down to the fuel having to run through the new filter. Anyway she fired up and I left her idling for a good ten minutes - no problem. I sat and revved her to around the top off the RPMs (no tach by the way) - no problems. It only seems to happen when its in gear and reaching a certain amount of RPM. Is this whats referred to as "under load"?

When it cut out on the highway last night, I couldn't rev it back up, instead it would almost stall 2-3 times before revving up on the 4th time but then as I eased out the clutch to launch it would almost stall again :/

 

Your fuel requirements to raise engine RPM while in neutral are different than when the engine is under load. From the sounds of it, it is starving for fuel when under higher loads. Whether that is caused by a clogged fuel filter (already replaced so that's not it), a weak fuel pump (typically these work or they do not), a bad float, a bad accelerator pump, or just a carb in need of some help.

If you were closer, I'd say send the carb over to me and I'd do a basic rebuild on it for you.

 

Ah ok, I never knew that.
I'm going to see if I can grab a fuel pump at Canadian Tire tonight otherwise I'll go to Napa tomorrow morning and I'll try that out. Hopefully one of them have it in stock. I'll let you know how that goes. If its no good, I'm going to have to learn how to dismantle and rebuild a carb pretty quickly haha.

 

Ok so I changed out the old fuel pump this evening. I haven't had a chance to drive it out on the highway yet but I can say this.. When I got the old pump out, the trigger on the pump that gets pushed by the rod in the engine only moved about half an inch whereas the new one moved a good three quarters of an inch - could this have been the problem component?
Also what and where is the accelerator pump?
Oh and I have to say I really, really appreciate the thought about rebuilding the carb and I understand about the distance. I think if it comes down to being the carb I'll concede defeat and get it into a shop but atleast I've tried. Don't laugh but a week ago I'd never changed a spark plug but in the last 4 days I've changed 8 plugs, fitted a steering wheel, replaced a fuel filter and a fuel pump so I'm a little proud of myself and I'm learning constantly so it's all good. I just wish I could get the truck sorted and start to enjoy it finally

 

The thing in your third pic looks like a battery isolator. If you ever want to add a second battery to your truck, that's a good thing to have.

 

Ok cool. Thank you for the info.
How does it work?

 

It allows the alternator to charge both batteries, but keeps one discharged battery from discharging the other. They're used a lot in RVs and on boats, but more people are using them in vehicles for bigger audio systems, etc.

 

That sounds pretty cool. I might look into fitting a second battery then if I decide to install a winch or upgrade the sound system. Thanks alot for that

One last thing, I've been filling up my truck at a petrol station here in Canada called Husky with fuel that they advertise as "Mother Nature Fuel 90". It's where I always fill up my Ford Focus mainly because its 90 octane for the same price as 87 octane but now I'm wondering if the 90 octane has been bad for my truck and perhaps that is what is causing the problems... I don't really understand the octane differences so maybe someone will know if using 90 in a vehicle mean't for 87 would be giving me the vehicle problems I'm having. The thing is my Focus is meant for 87 but seems to run stronger on Husky's 90 octane but then it is a newer vehicle and its all electronically controlled and all that.

What do you think?

 

I have come across your problem with other peoples trucks doing the same thing and every time it has been the fuel pump..Im not saying that its your problem but worth a try. Good luck