Hello. 85 720 stutters when going uphill. Work done, no dice

[macklen]

Hello everybody. First I wanna thank you all for lending such helpful info in the forums, specially that Fastboatman dude. I can't believe the amount of dedication he's put into helping others.
I have been reading the forum for about a month and already got some stuff done in my recently aquired 85 720 4x4, most of it by following advice I found here. I'm a somewhat proficient mechanic and have no trouble following instructions, but I'm new to Datsuns, been a GM guy my whole life.

My truck has a problem going uphill, or otherwise under torque, it starts to stutter as if starving for gas, when I let go of the pedal it idles normal and comes back, but it does take quite a cough and fart to finish long climbs.

I have done the vaccum delete thing, no emissions to be concerned about where I live and the vaccum system was a total mess anyway, I thought if that did not fix the truck's problem I could rebuild the whole maze of hoses from scratch following Fastboatman's post.
I have replaced spark plugs, wires, cap and rotor, set timing, adjusted idle and mixture in the carb. The problem persists.

I have NOT:
-changed fuel filters, fuel pump.
-double checked spark plug wiring. I found a diagram that supposedly is for my engine, but it doesn't match the way it's wired at this time, I wanted to share with you guys and double check if it is indeed the right diagram, or maybe one of you could point me to it. Here's the one I found, does not match the order on my truck

Any help will be greatly appreciated, I will do my best to help others with whatever I learn on my rig. I like it already and I'm a stubborn SOAB, the truck will stay with me and I will fix it. Period.

[macklen]

BTW, my brother had another truck that was exactly the same engine but wasn't a 4x4 and had the same problem. Rode it for about 2 years and sold without fixing, as it does not prevent the truck from being driven. Two out of two with the same exact issue may ring a bell somewhere, perhaps a weakness in the original carb or something? I'd venture it's a common thing, since they are the only datsuns ever in the family and both had the same problem. The only thing my bro did was replace the fuel pump, which did not fix the problem. Just wondering, thank you.

[foxfan1992]

I had a similar problem with my truck a few years ago... after much ado of replacing the fuel pump, filter and resetting the carburetor float, we finally resorted to disconnecting the gas line and blowing through it with an air compressor. Did that and it finally solved all the fuel starvation problems! Might want to give it a try ;-)

My truck was doing it on steep hills and also on roads (highways) with speeds greater than 30mph.

[macklen]

My truck was doing it on steep hills and also on roads (highways) with speeds greater than 30mph.

Yeah, it's doing exactly that. Thanks for the reply, I'll do that next.

[flinterman2000]

If you are serious about keeping the truck, I advise replacing the carb eventually with a webber

http://s658.photobucket.com/user/flinte ... ort=3&o=67

[macklen]

Yeah, I'm saving to do that, from what I've read it's totally worth it. In the meantime I gotta make do with what I have, it's my daily driver at the time.

[macklen]

BTW, I was looking at Webers on ebay and saw that electric choke is cheaper than manual. Is manual choke better or what?

[flinterman2000]

BTW, I was looking at Webers on ebay and saw that electric choke is cheaper than manual. Is manual choke better or what?

Not really. The difference is whether it's activated by electric or water. The connection is more difficult with water but more reliable.

[macklen]

Yesterday I replaced some fuel hoses that were a little rotted, hooked some loose wires (one of them went to one of the coils) replaced crappy coil wires and blew some air in the fuel lines from the tank. While it does run better and the idle revs jumped up a bit, which I adjusted with the idle screw in the carb, the problem persists. Still had to pull over on a long climb and allow the truck to catch its breath before she could finish. I didn't allow it to stall, but it felt as if it would if I had not pulled over and got off the throttle.
Next will be a change of fuel filters.
Tomorrow I will upload a diagram of how my wires are connected, perhaps a good samaritan will look at it and let me know if something is wrong with them.
TIP:
I don't own a compressor, so to blow air through my fuel lines I used a regular hand pump for bicycles, adapted with a valvestem and one of those rubber nipples that fix wires that go through the firewall. It fit perfectly and worked great. Just saying, in case someone needs to do the same without a compressor.
More to come.

[macklen]

Wire order and connection double and triple checked, no dice. Truck will complain when under throttle. I will replace the fuel filter by the pump. There's another filter looking thing at the output line from the tank, before the pump and filter, read somewhere that it's a check valve.
Can it be bypassed/discarded? What does it do?

[macklen]

My bad, it's actually on the return line and it's to prevent fuel spillage in case of a rollover, according to other forum. I'll replace the fuel pump tomorrow. Not sure if anybody's reading this, but I will keep making a record of the work I do on the truck.

[flinterman2000]

when you change the filter try blowing through the line again, just to see if there is any more or less resistance. Less means that the filter was chocked or partially chocked.

[lego126]

I noticed you said you had done the vacuum line delete thing? what all did you delete? also, what type plugs did you use? gap? fire? filter on the banjo fitting in the carb? fuel level in carb sight glass? Reason I ask, mine just done the exact same thing, I found a guy who had pic. of how to disconnect the EGR valve, plug lines, and disconnect BPT valve, plug lines. I done that and it fixed my trouble. Or at least it got a hellvu' lot better.

[PEZi]

I know this is a dumb question, but you have triple checked your vac delete, right? There is still a hose running to the distributor and the rest are all capped, no leaks anywhere? Next on my list is getting around to checking that firing order. You should see the numbers on the distributor cap, as far as what goes where. The diagram looks close to what I remember, but going off of the numbers on the cap will help. If all else fails, new dizzy cap has fixed issues like this before. That might be where you're at!

[macklen]

Thanks all for your suggestions. I'm glad to report this lil' gremlin DEAD. The truck runs ok now. Last thing I did was replace the fuel pump, blow the lines some more, replace fuel filter and resolder the fuel pump relay behind the glove compartment, as I read in another post. Problem fixed. I tend to believe it was the fuel pump relay, as the contacts were very corroded but since I did everything on the same afternoon I can't say for sure. Yeah, I know, dumb and pretty much useless.
But hey, maybe it can still help others if they follow the path, huh?

Cheers y'all, next thing is a front end rebuild, my bushings, ball joints and tie rod ends are toast. I leave you for now with a pic of how the Lil' B1tch stands today.

[lego126]

Think I'm gonna replace my Fuel pump. I notice when I wiggle the wires that go into the pump, the pump will cut out only in 1 spot, it may be related to my sputtering, sluggish behavior during acceleration. Think I'll do that .... in 2 days.

[macklen]

Before you do that maybe you should just scrape the wire terminals a bit with a screwdriver and some sand paper, see if it gets better. A new fuel pump ain´t a lot of dough, but hey, a penny saved... right?
Good luck.