86 720 4x4 Valve Rattle

[FritoVL]

I recently installed a 32/36 Weber manual choke on on my 86 720. After I Installed the carb I drove it down the road (less than a quarter of a mile) and didnt think I was going to make it back. The valves started rattling real bad, and coming up the driveway I had no power at all. I've tried to adjust the timing but it has no effect. I checked the advance and it seems to be functioning fine. The idle is bad the whole motor shakes and won't hardly run unless the choke is on. I've run through all the adjustments and talked to the redline people they say its not a carb problem. They sent me a jet kit but I had no adjustment with the bigger jets. I seem to be getting spark from both coils. I've put a vacuum gauge on it and it is very erratic. Okay any ideas or similar experiences? Thanks in advance for any help or suggestions.

[PEZi]

And you are indeed sure its valve rattle? Not pinging or anything like that? Because they are 100% right, installing a carb isn't going to screw up valves in any way. As far as the vac being erratic, could be something like the baseplate of the carb not being fully sealed or something.

Hopefully we can figure this one out for ya!

Welcome!

[synack7350]

sounds like you have a major vac leak, possibly one of your lines is hooked up wrong or you are loosing a ton of vac around the base of the carb, finally fire man, with a better carb you need better spark if your dizzy and rotor is tired and old....

[FritoVL]

I checked for vacuum leaks around the base of the carb with carb cleaner with no change in the idle quality. I even took the carb off and reinstalled it doubling the gaskets between the adapter and the manifold and between the carb and adapter with no change. I'm definitely hearing a valve rattle and not a ping. Although every now and then it sounds like a ping or more like a piece of metal bouncing around inside the motor but this sound is not consistent, and I didn't drop anything inside when I was installing the carb. There's only one vacuum line on the carb going from the advance port to the distrib. I've eliminated all the miles of vacuum lines and was running a Weber 34 (WeberCarbsdirect) before and never had these kind of problems. I changed to this carb because I was hoping to get better fuel economy. I'm wondering if I have a burnt valve or the valve seals are leaking. Would this create a vacuum leak or make the valves rattle when under load? As regards to fire: Its still the original distributor I've checked the advance by putting vacuum to it and I see that the advance works and holds the vacuum. The coils are also still original but seem to be functioning. I have E3 plugs on the intake side only, these are only about a month old, I pulled them a while back to check my burn and they were a whitish brown color, although when I pulled one a couple days back it was black in color but I figured this was from having to run it with the choke on to keep it running. Like I said before the idle is horrible but it only rattles when you put a load on the motor giving it gas. Any other suggestions or a way that I might be able to test the distributor to know if something internal is malfunctioning. One other thing I pulled the valve cover checked the timing chain and also checked the valve clearances. The chain is tight and I didn't see any slop, as I ran the motor with the valve cover off.

[heyman421]

A tapping valve could burn due to improper seat, but a burned valve wouldn't necessarily tap.

My truck sounds like a typewriter, and i've had the valve lash adjusted, and everything else checked out.

The tapping and loss of power could be unrelated.

Is it possible that it's been tapping for a while, and you're just now noticing it because you're trying to diagnose the other issue?

[FritoVL]

I wouldn't describe it as a tapping sound it's harsher than that. When I say rattle it's a killer rattle. Like if you were climbing a hill in to high of a gear. When I have tried to move the truck and put it in gear and give it gas it rattles so bad it almost dies and sometimes does.

[84Datsun720]

It could be as simple as some bad gas or a fuel filter(if u still have one). when i first got my 720 it had been sitting for a while and I had to put gas treatment and a new fuel filter on it because it rattled and cut off sometimes. Also, i had to replace both intake and exhaust plugs as well. Just trying to think simple.