I bought a 1975 Hilux with a rebuilt 20r. It runs and drives but has a flat spot or hesitation when you stomp on the gas. The problem doesn't seem to exist when you gently accelerate and I can drive it without it doing the sputter/hesitation. I don't know much about carbureted vehicles so looking for advice on where to start tinkering with this issue. I do know that the 20r has been rebuilt and only has maybe a few hundred miles on it since. All de-smogged. Has a brand new carburetor. Has distributor converted over from points. I notice the stumble at approx 1500-2000 RPMs and otherwise the truck idles smooth and when past that spot seems to pull great. The POs friend thought it could be something like a power advance in the carburetor or even the timing being off. I was reading up and didn't see anything regarding a power advance, but did see something about an auxiliary accelerator pump (AAP) and was wondering your thoughts on this being the culprit. Not sure since he said it's all brand new carb. This weekend I will verify the timing and see what I can do to fix the issue. I've got a crappy Harbor Freight timing light, hopefully it'll work. Thanks!
Whats the procedure? I kinda understand what it does - stomp gas and vacuum drops, so a diaphragm in the power valve senses this and blasts more fuel in the mix. Sounds like it could be the problem, but why if it's a new carb? I'm seeing from pics that this is an internal component of the carb? I found an exhaust leak last night too - header flange to exhaust connection. I need to cut off a frozen doubled-nut that's loose and replace with new hardware. I couldn't break it free to tighten the connection for the life of me and I think this is what the PO was talking about when he said he couldn't tighten the connection.
Is the point conversion a pertronix setup? If so I had a similar issue with my 75 celica/20R setup that I converted via the pertronix unit. I switched back to points to test my theory and my hesitation went away. I later converted to a later 20R electronic setup and had no more issues.
I don't know, I'll have to look. Is the logo obvious? I checked the receipts pile he gave me and didn't see distributor on any of them. also didn't find carburetor receipt either, but the guy moved recently and it could be somewhere else in his garage full of stuff.
not sure the logo is obvious, sorry. might try to look up images of the pertronix unit and compare them to whats in your dizzy.
So yesterday i had a little time to investigate. I didn't want to mess with carb stuff so I decided to play with timing and at least figure out where it's set. The trucks got an aftermarket oil pump without the timing marks like all the OEM ones have. I saw online that the one single mark that is provided is to be considered the 0-degree mark. I set my motor at TDC compression stroke and found my timing to be set at "0" according to the mark. Unfortunately the distributor is out of room to adjust in the slot, so I played with moving the distributor over one tooth in either direction. Neither got me to be able to get the timing to 8 degrees (which is left/counterclockwise of the mark for 8* advanced, right???). I think I need to file/bore out some more room in the distributor adjustment slot in order to get it set. Looks like someone did that already for when it is a tooth over, but it didn't work for me.
