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When good carbs go bad

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mrsprite

mrsprite

Jedi Warrior
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Hey everyone. I am having some driveability issues with my Bugeye and just need to know where to begin.

To start off, I have a non-standard engine. I am running an '82 Datsun A15 engine with twin Hitachi 38mm SU carbs. I have owned this car for almost 2 years and aside from a busted clutch last summer, it has been one of the more reliable cars I have owned. A couple of weeks ago though, it started acting up.

It began with being very hard to start in the morning. It normally fires right up with the choke pulled about half way, but lately it just cranks and cranks and cranks before it tried to fire. I replaced the plugs, points, condenser, cap/rotor, points, fuel pump & fuel filter. Initially I thought it was just getting a weak spark, but after today I am fairly certain it is the carbs.

Now it stumbles and pops and crackles when I accelerate and smells like it is running very rich (almost a raw gas smell). At stoplights I have to rev it several times to "clear" it out, but it still runs rough. I will pop out the new plugs when it cools down and see what they look like (probably fouled).

Anyway, my questions are.....generally speaking, what are the typical symptoms of a bad carb or two?

Does anyone know if the Datsun 38mm SU's have the same mounting points as a 1 1/2" SU? I am thinking about getting some regular SU carbs, but I'm not sure if they will bolt up to my intake manifold (anyone have pics of a 1 1/2" SU?).


Thanks.
 
Have you checked your floats?
Doh... I should read before I respond.
 
OK....so I'm thinking and it hits me.....check the floats! What an epiphany! /bcforum/images/%%GRAEMLIN_URL%%/laugh.gif

Alright.....I am carb ignorant here. I threw them in the tub and they sank, so how do I get them to float?

Seriously though.....how do I check the floats? What am I looking for, etc.?


Thanks guys!
 
After checking the floats I would also check the float valve it could have become stuck, and check for dirt in the bowl itself, and check to make sure the fuel runs free from the filter at the carb. Place the hose it in a can and turn the ignition on and make sure fuel comes out clean. Then check the timing, just to make sure it is not out.

There are several different float settings depending on which type of carburetor/float set up you have. Listed below are the most common options.

image-107.jpg


T1 (1 7/8ā€ OD) and T2 (2 1/4" OD) Float chambers. With the float chamber lid inverted and the hinge lever resting on the float needle, it should be possible to just slide a 7/16ā€ diameter between the radius of the hinge lever and the face of the float chamber lid. See diagram.

T4 (3ā€ OD). A 5/8ā€ test bar should be used.

Early HS carburetors with brass floats. A 5/16ā€ test bar should be used.

HS carbs with the early nylon float and steel needle. The gap between the lever and the face of the lid should be between 0.125ā€ and 0.187ā€.

HS carbs with the later all nylon float and delrin type needle. The gap between the float and the lid face should be between 0.062ā€ and 0.187ā€ with the float resting on the needle but not depressing it. This type is non adjustable.

Anyone else have anything to add, did I miss anything?
Ɛan
 
This would be a good time to invest in a shop manual. Checking the needle valves (which are probably the problem, not the floats per se) is simple, doesn't require much in the way of tools, and is well explained in any manual.
 
To check the needle valve (not specific to your carb so this may not work):

Remove the bowl but leave the float and valve in place. Hook a piece of hose to the fuel inlet. Gently blow through hose while slowly raising float. If air flow is stopped, you are good to go. If the float sticks or air flow cannot be stopped, get some carb cleaner and thoroughly clean the valve and valve seat. Either way, get some carb cleaner and clean the valve and seat.

PS. When you say your floats sink... do you mean they go to the bottom, or they just float below the surface.
 
One thing that you need to check as well as your floats is your spark plug wires. I had some go bad about 2 years ago and the symptoms were just as you describe.
Bill
 
Thanks guys. I actually have manuals and whatnot, but I am in the middle of moving and it seems these were boxed up and are now sitting in a storage facility in Vegas (750 miles away). Believe me.....I went looking for them as soon as this started happening.

I'll check the floats later today.....I am moving junk from one place to another in preparation for another run out to Vegas, so it's been hectic and just no time to work on the car yet.

Bill.....I'll look at the wires also. I replaced them about a year and a half ago with Magnecor's and figured they would last a bit longer. Maybe they gave up the ghost?

BTW Morris.....I was only joking about the floats (I threw the carbs in the tub and they sank, yada, yada, yada). /bcforum/images/%%GRAEMLIN_URL%%/laugh.gif It was my poor attempt at humor (although I thought it was chuckle-worthy).
 
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