Question about carburetors

Hey all,

I'm new here, this place seems like a great resource. I just bought an '85 Ram 50 with 160k miles (2.0L, 4 speed) that's had some fuel delivery issues. I cleaned and rebuilt the stock Mikuni carb and replaced the fuel pump (mechanical) and filter. It still runs like crap, stalling out or sputtering after a few minutes at highway speed or climbing a steep hill.

I'm thinking of buying a Weber carb to replace the Mikuni. My question is this - the OEM-style carburetors are complicated and expensive, and the Webers are cheaper and everyone says they're better. It seems that the extra cost of an OEM carb is because of the extra valves, solenoids, vacuum lines and the complicated internal passageways. I get that simpler is often better, but why is this the case? Am I losing anything by not having the extra stuff? Hopefully someone can help me understand this.

Another thing is that after my repairs it seems that the engine is running much hotter and losing coolant quickly. Could have been that I screwed something up, could be that I didn't notice the cooling issue before. At any rate, I plan to replace the water pump this week. Is there something to look for after a carburetor overhaul that could cause cooling issues?

Hi pinspanner, welcome to mightyram. The question about the Mikuni carb is valid. It is designed to deliver fuel below 5,000 rpm and provide a balance of fuel efficiency and torque. The water choke assemblies are like all things - does a good job when it's working correctly. Far as I can tell they also chose the carb based on the air flow demand of the engine which is about 170 CFM (which is 'accurate' for the 2 litre) and having a vacuum actuated secondary allowed for some flexibility in midrange to top end power. But it is lousy for performance as it strangles airflow. If it's running hot and cutting out check your fuel float level as it might be too low. The stock carb should not starve out under any circumstances.

You could've inadvertently created a coolant leak in the base of the carb when you pulled it off so check the mounting gasket and bolt tension. It would be able to pull coolant into the inlet manifold which will cause it to run rough as well. Start there.
As for other possible coolant leaks, they can be in the usual places like a dud head gasket, radiator/heater core or split hoses. But they also pop up in places you wouldn't normally look, like the base plate of the inlet manifold and the coolant circulation pipe from the water pump around the back of the head. They are notorious for getting corroded out. Good luck and let us know how you go. :)

Thanks man, I had a suspicion that I set the float too low. I'll check on that.

There aren't any visible coolant leaks that I can find, especially not between the intake manifold and the carburetor. The threads for one of the carburetor mounting bolts was stripped but I added some JB Weld steel stick and it seemed to tighten well enough. However, there is most definitely significant coolant loss and I can't figure how else it could be related to the carburetor. I did notice that the carb mounting gasket that was in there was handmade, maybe the last mechanic made one to block off a passageway for some reason?

Thanks in advance for bearing with me for a lot of basic questions. I hadn't driven or worked on a vehicle since high school before buying this truck and I am very much a beginner when it comes to auto repair.

If your exhaust is giving off an unusual amount of water vapour and smells sort of sweet like coolant it is entering your combustion chambers. Sign #2 are the spark plugs. If they're super clean, they're getting steam cleaned by coolant. You might not see coolant around the base of the carb as it is leaking internally. Some guys do bad things to engines - like using the workshop floor to grind off carb gaskets (some a-hole pulled this on my truck way before I got it and ruined the carb...) Hand made gaskets are o.k. and sometimes better depending on who and how it was done. I'm going to recommend you find a good intake manifold for your engine. If the mounting bolts are no longer capable of being tightened enough it will cause both vacuum and coolant leaks.
Good luck, it shouldn't take much effort to getting it sorted out. :thumbup: