Awful newbie question: fuel delivery and hesitation

[hyouriittai]

Hey guys,

 

I picked up an 1979 HA10 (unfortunately named 1979's "510" in the American marketS) a couple of months ago. It has an inline-4 L20B in it.

 

The thing ran great, I mean awesome, when I drove it down a good 180 miles from where I bought it. It's supposed to have the original 75k on everything. However, as soon as I got it in to town, it started having this had hesitation problem.

 

Past (approximately, because I don't have a tachometer) 3k RPM, it would stop giving the motor any gas (maybe not an accurate description, just how it felt.) This was while driving. So, I picked up an FSM and took a look at what the problem might have been.

 

I decided to overhaul the carb (DCH-340 series, I believe), as that seemed to make the most sense to me: dirty jets, bad float, something. When I took it apart, the float (made of some sort of synthetic) seemed to have been eaten away. Made sense; constant exposure to gasoline for nearly years. So I replaced the float and all the little bits that came in a NAPA carb rebuild kit that was specific to my carb model (of course.)

 

Anyway, I got it running. However, the problem seemed worse. I estimate that it revs only to about 1.5 - 2k RPM. If you open up the throttle any further past that, I just hear his hissing sound, and the engine wants to die.

 

So, what are the possibilities? I know there are a lot. Fuel pump? Fuel line/hose leak? More carb problems? Or something else entirely?

 

I appreciate any input, and thank ya all in advance.

 

-Matt

[zerow]

Could be the secondaries. It would seem that at 3000 RPM, that would be the point where the secondaries would open. IF the secondary fuel circuit is blocked, or worse, that would cause too much air to get into the engine giving you the hesitation you describe. If you have a carburetor shop local to you, have them bench test fro flow, over both the primary and secondary fuel circuits. Having it attached to a motor makes it difficult, if not impossible to tune, as the engine is relying upon the carb to work properly to stay running in the first place.

[racerx]

Heard that rebuilding the stock carb on our Datsuns is not the way to go...if you can get away with installing a 32/36 weber then this is it. Assuming that your car does not need to be smog tested.

 

The other thing too could be the distributor, rotor, points, coil, tune up etc..When I bought my 510 awhile back, the car started to hesitate and would backfire..so I thought it was fuel, after some troubleshooting come to find out my coil was going out.

 

You can also have a vacuum leak somewhere. This is easy to troubleshoot. Spray some carb cleaner around carb area, intake and even vacuum hoses. If the car's RPM jumps then theres a vacuum leak. Also check to see if you have any fuel leaks, maybe a hose was not tighthen down good. I don't think its the fuel pump since your cam turns the fuel pump, provided that it's mechanical which I assume, so as long as the engine turns, you are getting fuel. BTW how old is that gas, maybe it's been sitting there for quiet a bit. If it smells like acetone, that gas is old...and being old it's not igniting properly.

 

Good luck let us know, what's up.

[racerx]

forgot to mention to check you choke, maybe it's getting stuck

[Phlebmaster]

WELCOME TO THE FORUM!!

 

I would also check the fuel lines for rust or blockage of some type, maybe even pull the hose from the carb and, (useing a long hose to get away from your distributor), crank the motor. See how the gas flows from the pump. :D

[moparvwfreak]

I don't think its the fuel pump since your cam turns the fuel pump, provided that it's mechanical which I assume, so as long as the engine turns, you are getting fuel. BTW how old is that gas, maybe it's been sitting there for quiet a bit. If it smells like acetone, that gas is old...and being old it's not igniting properly.

 

Good luck let us know, what's up.

 

that is not always true. i have had a fuel pump that worked great at low speeds but at higher would fall on its face. the pump had a bad seal in it and at higher speeds would cause a vac leak internally so it wouldn't suck the fuel from the tank. then again it was a Schucks el cheapo fuel pump on a Plymouth.

[bonvo]

in my car i have noticed (specially when its cold) that the sceondary opens at around 2500 rpm you can feel the car pull a little harder (entering its powerband) though this is sounding an awful lot like a vacume leak

[SHADY280]

when rebuilt were you very specific of float level, most ppl seem to get this one wrong. it has to so close to perfect. and make a huge difference in performance. also did you install a new accel pump? i had one that did simmilar things, it was that. check fuel line pressure, can also cause starvation. good thing to try and have a perm mounted guage inline, just as a handy always there tool. and as said b4, vaccum leak test, super important.

[datzenmike]

Check the fuel level on the glass bull's eye on the front of the carb when idling. As long as it's close it's fine.

 

A poor fuel delivery caused by a bad pump, clogged filter, fuel line kink or clog, or sticky carb float needle valve will still usually fill the bowl at lower speeds and it usually takes a long hard pull through the gears or up hill climb to drain the carb and cause what you are describing. If you check that the fuel bowl is filled to the correct level and immediately drive it and find that it 'falls on it's face' then it's not delivery TO the carb but possibly the carb itself. Seems to be when the secondary opens, there is no fuel there.

 

Shady I agree the lack of a working accelerator pump will cause hesitation, but mostly at just off idle when air flow is not great enough to start pulling fuel from the primary circuit. This is much higher in the rev range.

 

I recently cleaned my Z24 carb. I got a can of carb cleaner with one of those red straws like the WD-40 cans. You can poke into all the holes and blow shit out. I try to blow it both ways. The solvent also loosens the gunk in there.