1984 720: Just bought this little beauty. Last one I had was a 1975 620 (should've kept it!).

I bought it from a kid who said his brother and dad overhauled the engine.

Now, it starts hard, sputters like crazy, then will finally get an idle. Once warm will idle pretty good. Once on the road it has little power. Max speed with a slight downgrade = 55 mph.

Ready to get started.... so, you clever fuel, carb & timing guys... where would you start?

Thanks.
Modified by wesradford at 10:11 AM 11/17/2009

well... did they say anything about the carb? as to whether they rebuilt it or anything?i'd also be worried as to whether or not they did everything properly on their overhaul

the sputtering when you first turn it on isn't exactly fun, but its not uncommon. mine does it too but that's just cause of how i have it set up more or less... it runs 100% fine once warm

do you know if its a stock carb or aftermarket?

Nope, not a word on the carb... I will have to dig in a little and see if I can tell. I agree, I hope the overhaul was done properly, I am a little bit worried on the timing chain, hope they aren't off a link or two.
Modified by wesradford at 10:12 AM 11/17/2009

Oh, also. . . it sputters a lot.... kills a few times, then finally gets going...

Do a tune up. Its mostly the carb that causes the sputtering with these engines. If you do not have to worry about smog regulations then try a webber, 32/36 is best to dial in for these engines.

i used to have some sputtering problems a while back... this was when i still had all the emissions controls and it was fixed when i replaced all the vac lines... it could be that as well i suppose

Thanks Guys. I will rip into it this week. Dang it started snowing ! I'll let you know how it goes.

also make sure your fuel filter isn't ancient and that your pump looks in good condition.

Doing my visual inspection tonight. Realized that the tming was most likely way off since the distributer cap was rotated as far as it could go counter-clockwise. ( then hoping that it wasn't an intentional adjustment because the timing chain was off a link)..... I turned the cap to the aproximate center postion, and wha lah...! Starts and runs 100% better. Now trying to find the factory specs since my repair manual I bought on ebay hasn't arrived. I will keep looking...but if one of you chaps has it handy I would appreciate it.
Modified by wesradford at 10:13 AM 11/17/2009

Called Autozone-- they said timing is +3. I expected something BTDC... anyway, made no diference tonight...can't see the mark on the pulley..going to have to crawl under in the day and put some white on it. At acceleration I have pinging now...so I need to get it right.

Can anyone confirm that I use the Intake sparkplug wire #1 for the timing [ front cylinder, passenger side wire) ?

confirmed on the intake plug 1

Thanks for your help guys. Got the timing pretty close...but had to stop at 10 deg BTDC (spec is 3), just would not run well at 3. When I bought the it was set at about 30 deg. no wonder it ran so bad. Now is running well except under acceleration...just doesn't have the kick I wish it had....

I think....that this low horsepower issue is now due to low electrical output from the alternator, but like a second opinion.

Symptom: When I accelerate or head up a hill it struggles, lights dim and the battery light blinks. At idle the alternator checks OK with a tester. I have a brand new beefy battery in it.

Does this sound like an alternator problem? Or maybe a regulator (does my 720 have a regulator) ?

They all came with built in IC in the alternator, that means no regulator. When the battery light blinks what kind of rpm are you doing. It could be a loose belt or worn bushings in the alternator.

OK, I am glad you asked about the RPM, 'cos it made me observe a little more and realized that I could get the same behaviour sitting in the driveway as I could on the road. Sitting in the driveway at idle the voltage gauge reads about 14v.

As I slowly rev it up, and it hits 3200 rpm, the voltage drops rapidly to 11.5 to 12.5 and it starts running a little rough. When I slow it back down towards idle, at about 2900 rpm the voltage bounces rapidly back to 14ish.

I also noticed that at idle the votage tick/tocks - 14.5 to 14.0 to 14.5 to 14.0 etc...

As far as the belt goes: It looks new and tensioned properly, but I don't know for sure since I just bought it. It also sat for a year, so maybe the belt got stiff ?

Thoughts? Alternator?

Question: I have rebuilt non-Datsun alternators in the past, put in new diodes I think....Has anyone rebuilt one of these out of the Datsuns? Know where to find the parts?

Well that is not good. Dropping off volts on increase in rpm denotes either a bad commutator (the part where the brushes make contact) or a bad/damaged stator (the part that turns in the center of the alternator). Either way on a test bench it will show good because there is no real load on the windings during the test. It needs repair or changing.

Update on getting the truck running better: * cleaned the carb the easy way (can of cleaner).* Installed the carburater pre-heat tubing (HUGE difference in warm up time !!)* dialed the timing to factory spec of +3 (no more ping)

Running real well. But is still lacking power. I ordered the alternator, since it has gotten even worse... sometimes at 12v even at idle now. Hope it helps with power issue...next step will be fuel filter . . .then deeper carb work...I hope not...

It is shaping up nicely: got dash and dome lights working this week. What a pain that was...spare tire fixed, antenna installed, radiator pinhole leak repaired, chasis lube mostly done.

Next week: replace alternator, rear end lube and install a couple of grease zurks...and stereo install.

Slow but steady.

Installed alternator...wha whoo ! Voltage constant 14.5 no matter the RPM.

Not ready for drag races yet...still not enough power, but I won't get stranded with a dead battery now.

Bought the carb kit - $33 at Checker Auto, and a solvent bucket $20... wish me luck... hopefully sometime the next two weeks I will get it rebuilt...

Getting just 7 mpg and blowing unburned gas out the pipe .... ouch



Also got heater working properly this week...instead of a little drift of air I have a hurricane, defrosts much better in this 10 degree frozen wasteland.

One of these days this thing is going to have ALL WORKING PARTS....

Keep at it and keep us posted.

hew youve done alot of work keep it up did you ever get it to where you can go past 55 mph?

I've had the same problem on two different trucks.

First, make sure your distributor is in correctly and that someone didn't put the oil pump in a little off. With your timing that far advanced, I'd guess that you're firing on only 1 of the two coils or sets of plugs

Which leads me to the second thing to check...make sure that coil #2 is getting power from your fuse block. There's a nasty kink in the wire from the factory where the fuel pump relay enters the main engine harness. Over time, this wire overheats and seems to melt down. If your fuse hasn't blown for the secondary coil, test the resistance in the wire and make sure there isn't a short.

Hope that helps.

ha ha Project Trucker....One of these days I might take it out to the tracks and give the stock cars a run for their money.... but if not, I would be happy with 60 mph.

Hey thanks Dlarsona, good ideas. I threw the timing light on all eight plug wires and have strobe. I haven't pulled the plugs to see if they are actullay firing though.

I will check the distriburter when I get a second. I have actually had a lingering concern about that in the back of my mind because the previous owners did an overhaul.

wesradford wrote: have actually had a lingering concern about that in the back of my mind because the previous owners did an overhaul.

Given all the things you've replaced and fixed it sounds like they did one hell of an overhaul