Hesitation after warm engine

[Mark Maras]

 How many turns down are the mixture screws? It's possible the float levels are too low. It definitely is a lean condition.

[Palmettobug]

I've got what I think are '72 SU carbs. You can see them in the above pictures. They have the large screws instead of the flat screws. I turned the large screws all the way up and the backed them down two-and-one-half turns.

[Patcon]

The amount you thread them down is directly relative to the fuel level in the float bowls. Like Mark said if the float levels are low then the mixture nuts will need to be threaded down more or the float levels reset. I would screw them down 1/2 turn at a time and see if you can get it to act right. If you can, run it for a while and pull the plugs to check the mixture

[siteunseen]

My T plug doesn't look like your's.  Mine look like Ts.  Your's look more like an H.  Maybe it has the higher output alternator already?

[SteveJ]

22 hours ago, Palmettobug said:

I could use new friends that lived closer. You guys are on the coast and I'm stuck here in the middle. Haven't seen anyone from Tulsa on here.

Anyway, last couple of days I have sync the carbs with airflow. I think I got the fuel mixture right. I have the idle dialed in at 1000 rpm in park, 1200 rpm in drive. I make it out the driveway and step on the gas ..... I get jerking and hesitation. The carbs backfire, and the rpms drop to 500 and stall out. I recrank and put the choke on. I can make it around the neighborhood. Haven't been adventurous enough to jump on the highway.

Think I may contact a different shop this time.

The alternator thing I was saying because the headlights run dim. Most of the threads I've read say I should upgrade to the 60 amp and purchase the headlight harness from Dave. I also need the Honda upgrade swap for the windshield wiper motor and the heater blower motor. All of which can wait until after I deal with the carb issue.

I think @Zup and @S30Driver may live in Northwest Arkansas. That's a lot closer to you than most of us.

[S30Driver]

SteveJ is right, Zup & I live about 2 hours from Tulsa.

Zup's car is a 73 and he runs Dave's HL PL harness with the stock alternator - I can attest that his lights work great.

[Palmettobug]

S30Driver : Nice to meet you. Has Zup ever had the acceleration problem I seem to be having? 

[S30Driver]

1 hour ago, Palmettobug said:

S30Driver : Nice to meet you. Has Zup ever had the acceleration problem I seem to be having? 

He had some fuel related running issues last year when he completed the car.  Blue worked his magic on the carbs at Memphis Zcon and corrected the problem.  I think he richened up the mixture.  Zup has been happy ever since .... 

[Chickenman]

All good info. Owner needs to do some proper tests though.

Backfiring under load  can also be due to a weak spark. Something Siteunseen mentioned in an earlier post about checking the points and condenser..

A weak spark will allow a car to idle fine, but as soon as any real load is put on it car will lose power and can backfire. Will also affect plug coloring. Not to say he doesn't have a fueling issue or Vacuum leak issue, but don't over look the Ignition system either. A weak condenser can be an SOB to find. Solution. Brand new points and condenser if old ones are at all suspect.

Don't know if OP has checked spark quality, but he should . Get a cheap plug tester ( less than $10 )  and open gap to about .060".  With engine running you should get a strong blue spark and hear a bit of a " Snap". If spark is weak, intermittent or yellowish then you have an issue.

Same with fuel. By an inexpensive fuel pressure gauge and actually measure the fuel pressure. Better yet, buy a good combination Vacuum and Fuel pressure gauge. Quality tools and equipment are always a good investment and will last you a lifetime. Assuming that things are OK "because there is lots of fuel in fuel filter " is not the way to test.

Same with alternator. Put a volt meter on it and measure what it's putting out. Consider switching to an IR alternator down the road. Original Nissan regulators were pretty good in their day. But that technology is 40 years old now and the VR's available now are mainly Made in China crappola.

OP needs to take a methodical method of diagnosis and eliminate causes one at a time with the proper instruments. Otherwise you chase your tail in circles. Wouldn't be surprising if he finds several small issue.

 

 

[Palmettobug]

I did put in new plugs and cleaned the carbs. But you're right, I haven't even thought about the distributor. Maybe it is time to put new points in. I'll check on that. Thanks !

I'll check on the fuel pressure too. I did do the "there's plenty of fuel in the filter" test.

[Palmettobug]

OK, so today I go buy a fuel pressure tester. It won't hook up to a Nissan. Domestic fittings. In the mean time I decided to pulled the fuel hose off the fuel rail to see if the pump would work. Started with the back carb, turned ignition key to accessory, and Beautiful! We got gas coming out the fuel rail to the rear carb. Did the same thing to the front carb. Same results. So I'm thinking the fuel pump isn't the problem. It's idling at about 1300 rmps. I decide to see if it could make it up small hills today. I go driving around the neighborhood, no problems like before. No sputter, no hesitation,  Figure why not go down the road where there's huge hills. Made everyone with a loss of power. OK, let's see how fast this thing will go. Hit the highway and got it to a 100. While it did build up to it, there wasn't an immediately response from the throttle, it's still 10 times better than it was last week. No idea what I did to get it here.

However, when I get to a parking lot to check under the hood for problems; I have fuel coming out the air intake hose and front of the rear carb. It's squirting like its being pumped from the fuel pump. How the heck to fix this new problem?

[Mark Maras]

 Hmmm. Interesting method for verifying the pump is working. Most likely the needle and seat in the rear carb. float chamber is stuck open or the float level is way too high. Pull the float chamber top, inspect the needle and seat and check the float level. If you don't have a spare gasket, sandwich the gasket in wax paper or foil and put it in a book to keep it from curling as it dries. Also it would be a good idea to check the banjo fuel filters on each carb. They're on top of the float bowl covers where the fuel line enters. They often get overlooked.  Pull the spark plugs. Numbers 4-6 will be black due to the excess fuel. What color are 1-3? If they're tan in color, the front carb. is set reasonably close.