Runs on Gas, Sounds like a Diesel, Hybrid???

[Flyn Z]

OK, I give up!!!!
It knocks and pings like a diesel, but its not. And nothing I've tried has fixed it.
not at idle, but as soon as you put a good load on the motor and about half throttle, near the middle of the power band is the worst, but if I stomp it to the floor it quiets down, I've been under it and listened with a scope, if its a rod, I can't hear it.
Before you ask, Yes, it has new, wait, there is a long list, cap, rotor, wires, plugs, distributor,
( OH by the way, its cheaper to buy a new dissy/w ICM then it is to buy a ICM alone at aut ozone)
ICM, fuel pump, fuel filter, fuel lines, fuel tank sending unit, and the list goes on, but nothing else that would relate,
it has all new vac line straight from the carb, a weber came on the truck, to the dissy.
the carb is fairly new and in good working order I believe, good fuel pressure
I've lashed the valves three times, well once and just checked them twice, no change and all good.
I've tried thinner and thicker oil, premium, no ethanol, and 104 fuel mixes,
It runs great, but feels a little down on performance, I've put 20k on it in the last 4 months, and its getting 22.5 MPG average from the last 5 tanks,
Should i just turn the radio up a little louder and put my foot down a little hard and stop complaining?

Drive Friendly

[synack7350]

that's horrible gas mileage somethig has gotta be wrong. with a weber you should be making 25mpg to 30mpg. pez was getting 30mpg on a 38 syncro. Sounds like you are running lean with too much advance. midrange says the vacuum advance. whats your fuel pressure at the webber? have you done a compression check?

[Flyn Z]

Thanks for your reply,
last pressure check at the carb was 4.5 lbs, yes on comp check, all good, i didn't do it, but i hear it was rebuilt, feels nice and tight,
right now its in the shop with the bed off, broken spring mount, good chance to change all the wore out rubber under there, new brake lines, shocks, clean the tank out, change the sending unit, all that fun stuff, i'll drop a post when its back on the road,
Thanks again
Drive Friendly

[synack7350]

also big deal you might have a big vac leak somewhere. if you haven't done a vac delete are any of the vac lines not terminated? you don't have a vac line hooked up to say purge on the charcoal canister or anything do you? check for intake manifold leaks. leaks around the base of the carb / adapter plate. Vac leaks would definitely cause a bad lean condition.

[synack7350]

one last thing if you go greater than 1.5 turns to 2 turns out on the mixture screw on the weber you need to rejet with bigger jets. The carb wont accurately meter fuel past that threshold.

[synack7350]

s*** one more thing. if your idle screw is turned in to far so the throttle plates aren't seated well that's a no no too for tuning.

[Flyn Z]

Hey, thanks for the suggestions, I'll try a few today, I don't know a thing about these weber carbs,
I have deleted all the vac lines, plugged the holes, and sprayed carb cleaner around the carb and 'fold without finding anything drawing air, I put a hand throttle on the truck a while back, but had the same knock and ping trouble before, could it be pulling the butterfly past closed?
I'll be tinkerin later, let ya know
Drive Friendly

[synack7350]

no I don't think the butterfly is past close. you only have a vac line going to the dizzy then right. ping is too much advance. have you set timing via turn the distributor. also recheck all the plug wires. make sure you don't have cyl 2ignition on like cyl3 exhaust or something. that could mess things up. timing via light is 3degs btdc if memory serves.

[dirtdog]

So I have been experiencing a similar condition. Have you found a resolution?
If so, what did you find?
Thanks for what ever help you can offer.
DD

[Flyn Z]

Hey Thanks again for your help,
that carb info was great, all though for some strange reason it runs like crap if i don't put the gas petal to the floor, after i turn the ignition on, and before i try and start it, but if i do that it runs great, carb wise at least, still knocks and pings, right now i have the vac line off the dizzy and everything plugged off, and the timing set near 3, but as soon as i hook the vac up to anything the idle goes way up, and the light shows it way to far advanced, i would adjust it back down and it would all be fine i think, but there isn't anymore adjustment on the dizzy, yes i have checked all the wires, its there and advance setting on the dizzy? to control how far it pulls?
I work on heavy equip at work all the time, Its just embarrassing not to be able to time this little truck,
Does anyone know if these motors can jump a notch on the timing chain? or if this is a known sign of the chain tentioner fixing to go out?, just guessing?
Oh, the latest, now she jumps out of 5th gear when you decel from highway speeds, anyone got a transmission?
Drive Friendly

[Flyn Z]

Datsun update,
due to the heat i've been doing more driving than fixing, the ongoing timing issue is closer, but still not perfect, feels a little down on power still, but not knocking, best as i can tell it was just badly out of adjustment, has anyone else had to remove one of the dizzy hold down screws to get the timing in the right place?
5th gear is gone, running in 4th the last week, went from 22-23 mpg to 25-26 mpg, which seem weird to me, found a guy that has tons of datsun/nissan p/u parts, gave him nico's addy, hope he puts his parts on here, i got a transmission but its a newer one, won't work, going to try again today,
Drive Friendly

[dirtdog]

I have been having a similar problem, and while searching for possible reasons came on a vacuum line that was disconnected. I reconnected it and most of the knocking(pinging) has subsided. Seems to have slightly more power. I am considering removing all the vacuum lines that are not really necessary.
Hope your guy puts up his parts too. Every source available helps.
DD