by m3a1 » May 17th, 2018, 12:30 pm
I've reviewed your postings. Sounds like you're experiencing the bulk of your problems under a load and from that I conclude you probably have a air/fuel mixture issue or fuel delivery issue.
Start with the easiest check. Is your carburetor firmly seated and bolted down? No, seriously! Give it a little wiggle. If it's not..I guarantee you it's a big part of your troubles. You might be surprised how often carbs are found to be loose. People get busy and forget to tighten them down. It happens.
Is there fuel coming into your fuel filter? If you don't have a clear, disposable fuel filter, get one and install it. Actually, get two (one for later). Yeah, yeah...I know. They don't look cool. Neither does being stopped on the side of the road with the hood up. Yes, you can keep the metal fuel filter but replace it with new. Cheap insurance, right? NOW does it run better?
Examine the spark plugs. They may show evidence of running in a lean condition. Have you looked at them? Look for white powdery residue on the plug or plugs. If they are ALL showing a lean condition it's a general lean condition. If only ONE plug is showing lean, then the problem is localized to that cylinder or that plug.
But let's assume all the "supposed-to work fine" stuff is true and correct and you simply have an emerging condition. It happens in old cars and trucks, especially when change of ownership means a change in the manner or frequency of its use. By way of example, since I started driving my old MUTT regularly (far more frequently than the previous owner) little rust particulates in the tank are starting to break loose from all that fuel slowing around and those get into my fuel filter. With a clear plastic fuel filter, I can see it and get a general idea of when it's time to swap it out.
From a cold start, if your engine is reluctant to start, it may be timing or valve adjustment. From a cold start, if it is usually happy to start, but then runs poorly, we might rule out timing but not necessarily valve adjustment. But for the moment, let's put timing and valve adjustment aside.
You have been told it runs well and again, let's assume that's an accurate statement. I don't believe you have told us which condition your engine is in, starting-wise... but here are a few simple tests you might do before getting into all the more invasive stuff -
I conclude from your posts that your gut seems to be telling you you have a fuel supply issue, my first suggestion is to see if your engine likes to run better with a verifiably 'good' fuel supply. To do that, you're going to need a friend and a can of starting fluid. Here, you're going to eliminate most, but not all of the participation of your carb as a fuel supplier in this test.
Pull the air intake hose off the carb and with a friend trying to start the truck WITHOUT stepping on the accelerator, you give it some shots of starting fluid. Think safety. Do that at arm's length and from the side. Protect your face and eyes. Safety first. Some shots of starting fluid to start and some more to keep it going. Assuming it's going to start and run, do the starting fluid thing only for a moment. If it revs right up and runs strong with starting fluid you very likely have a fuel issue, n'est ce pas?
BUT, if it starts/runs with the starting fluid and still sounds weak and hesitant, stop there, put everything back together, Now start it and keep it choked a little. In doing so, you are enriching the air-fuel mixture by restricting airflow. Don't try to rev it up choked. That's not what we're looking for, the engine won't like it and higher RPMs really only mask problems. But, does it generally run better at idle while partially choked?
If it runs better partially choked, stop everything and start looking for a vacuum leak or an intake leak because that's probably what's causing your lean condition. For vacuum leaks, look especially hard at those out-of-sight areas such as the lines going to the distributor housing (particularly the one on the back side!). Those areas often get overlooked and you will find they often have very ratty hoses as a result. Those are very small hoses and they live in a hot environment and will degrade. They can crack and still look good so you are going to have to manipulate them a little bit and see if a crack opens up. Same with any of the other vacuum hoses. ALSO check to see if there's a decent rubber gasket on the distributor housing because if that housing is still hooked up to the vacuum line system the cap has to make a good seal.
NEVER EVER SPRAY ETHER OR ANY FLAMMABLE SUBSTANCE ON YOUR DISTRIBUTOR HOUSING!
IF YOU DO YOU MAY GET A BIG SURPRISE!
Raw air being drawn into the system anywhere after the air-fuel mixture point (carburetor) creates a lean condition. For intake leaks, it may be drawing air in at the gasket under the carb. There IS a gasket there under the carb, right? (Sometimes a guy will try to reuse a damaged gasket which causes a lot of headaches for the next guy.) It may even be drawing air where the intake manifold mates to the block. I'm not going to make any suggestions as to how you check that because even under the best conditions, the most efficient way of checking it is u-n-s-a-f-e and there is a risk of fire...but, if you take that route, do it only when the engine is not up to temperature, you've got proper PPE and a friend around to call 9-1-1.... and use something somewhat less volatile than ether.
So spend some time with your little truck and get back to us. We'll get you fixed up.
Cheers,
TJ