Dies after warm up!

rhoadesm

True Classic
My '80 carb version has not been on the road for a few years but I still go out and start it about every other month. The last time I started it up (about 2 weeks ago) it started and ran fine until it warms up. As soon as it gets warm and the choke goes off it dies, I can restart it with no issues but again it will die when it goes back to an idle. I also noticed that when you up the RPMs to keep it running, it is not running real smooth. I was thinking carb rebuild but thought I would check to see what all the experts on the subject have to say. If I do need to rebuild the carb, how difficult is it going to be, I believe this to be a stock carb.

Thanks
 
Given what you are saying it is doing, I personally would stop your periodic starting and running of the engine until after you rebuild the carb.

In all likelihood you have some clogged jets as a result of sitting and having deposits building up in the carburetor bowl.

There are a few other things it could be. You could have a very clogged fuel filter, you might change that as a first step to see if that clears things up and would need to be done in any case. Another area that could be the root of the problem is the fuel pump may be failing. You might check to see if your oil is getting contaminated by gasoline (though this can happen from running very rich under the choke) by a torn/failed diaphragm allowing fuel to go directly into your crankcase. I doubt this is the case but it is something to check. You might also very carefully ensure the pump is actually pumping properly after the car has been shown to start by pulling the supply line to the carb and turning the engine over with the end in a plastic cup. It is low pressure but a decent volume so be careful.

When running on the choke it is likely running quite rich at idle and that also applies to running at higher rpm. Once the choke goes off and you try running at something greater than idle it may be running lean when off the choke due to a clogged jet reducing the fuel available.


Rebuilding a carb is not a difficult task in general but it does require you keep things organized and be scrupulous about being clean.

I find that keeping the body of the carb in the same orientation to you, working in a shallow cooking pan so parts can’t roll away and taking a cardboard box and poking small holes in it to hold the parts as you remove them Is a good work process that will aid you in keeping track of things and the order of assembly.

As you are taking jets, emulsion tubes and so on off that you write down the tiny numbers and letters on each part down and where it came from. The numbers/letters can be hard to see but they are there.

Print out the exploded view of the carb and have it close at hand when you start taking it apart.

I would use some carb clean and a brush to clean the exterior of the carb before taking it apart as they can get quite grimy and nasty. You don’t want any of that getting into the carb or being a part of the detail cleaning process.

Get both spray carb cleaner to go through the various passages and a gallon of dip to place the larger sections into which you will then use the spray clean to clear passage ways. Ensure the gallon has a dipping cage or use a metal screen colander to hold the small parts in the gallon dip bucket.

The other Carl is much smarter than I and has lots of experience in rebuilding carbs and will be along shortly to correct the misconceptions I am spouting... ;)
 
Follow all of Karl's advice on determining the possible causes. Then.... If the carb is still the stock Weber DHTA 28/30 found on the 79 and 80 Xs, check the cost of a new or NOS unit compared to the rebuild kit. The linked items are only examples, but with a little research you might find the proper carb ready to go at a reasonable price.

Anyway. Just a thought based on my experience with the DHSA on my 124 sedan. The car ran like **** when I purchased it. Following the advice here, I replaced the fuel pump, fuel lines, fuel filter, basically everything in the fuel system except the tank. When none of that made a noticeable improvement, I took the carb off and cleaned everything I could. It ran a little better, but still pretty poorly. So I got a rebuild kit and replaced every part supplied in the kit. Again it ran a bit better, but it was still fidgety about actually driving down the road. I finally bought a new Redline DGEV carb kit intended for a Spider. Stuck it on the car and was amazed that I could actually drive the car all around town. Sometimes you need to balance how much your time is worth against a ready to go part.

If you decide to look for a new/NOS carb. Seek guidance on that too.
 
Also, before starting to rebuil your carb, try to be sure it is a carb related problem. Sometimes, bad timing could cause similar problems. Try to become familiar with the timing marks (at the crank and at the cam). Nothing is more frustrating than overhauling your carb to discover it is still running like crap... 😵 (Damn, there are too many emojis to choose from...)
 
If you are going to all the trouble of cleaning and/or replacing the carb, you might want to find out what is happening inside the fuel tank before hooking it up to your clean carb. If that fuel has been sitting for a few years, the best it can be is not good. The worst it can be is not fuel. At the very least, I would drain the old fuel and inspect the inside of the tank. If you spot buildup or sludge anywhere, remove it. If you don't, it may get dissolved when you put fresh gas in and clog up your filters or worse.
 
Back
Top