I put a rebuilt head on my 20R, tuned the carb to the Weber (32/36) best lean idle instructions, and set my timing to...mine just has the 0, 5, then two more lines but they don't have numbers. It's set to the highest line.

Before I did all this, I had decent get up & go right from a stop. Now there's a little dead spot. Before, my timing was set a little out past the highest line. But I don't know if maybe that's a bit too advanced.

Anyway I'm wondering whether you think it's a carb adjustment thing, or a timing thing that it doesn't respond right away from a stop.

 

Most likely it's too lean on the idle circuit. Low rpm stumble? Any pop-back through the carb? It's pretty easy to go too lean with a 32/36.

 

Also, you may advance your ignition timing as much as you like, just back it off if you have pinging issues. 20R engines are 8:1ish compression, so you can likely run higher than most 22R engines until you find ping issues.

 

Ok, cool. No popping out the carb, yet, but I just drove it to the neighborhood gas station and back. We'll see how it does on a highway test later. I'm still babying it since after I put the rebuilt head on, my first draining of the oil after letting it warm up was chocolate milk.

Scary. But since then it has been fine...so I think I just had a bunch of condensation in the crankcase from sitting all winter.

If it give it a little more gas, like rev it and burn the clutch a little, I actually get a big power surge from a stop. But if I just let out the clutch and go like I normally would, there is very little response. Not a jerking stumbling, just very little power.

So maybe I'll make the mixture just a tad more rich. If that doesn't help I'll advance the timing a little more.

Thanks.

 

One thing I see on the 22r is their is supposed to be vacuum on both lines and usually one does not have vacuum. I have not done the test in a while but when that happens, usually it is cheaper to find a whole distributor then to fix the part that is bad. I would assume the 20r is nearly the same.

 

20R only has one vacuum line to the distributer. I replaced my distributer a couple years ago. Doesn't mean it isn't bad though...I'll check it out.

 

My 20R (unknown year) has two lines to the distro...

I won't hijack your thread, but I just rebuilt my carb and am having the same issue you are, among others.

 

Interesting. Well, a 78 20R has a one-port distributer. That's how it was when I bought it, and the part I bought from Rock Auto was the same way.

My truck sat all winter, then had a rebuilt head put on, then I adjusted the timing and carb. Just drove it for the first time on monday. So it's a little hard to say...It might just need to get out on the highway.

I sprayed a lot of carb cleaner on it yesterday, and meant to make the mixture a little more rich but I guess I got distracted cause I just realized I never did that. I need to get out it out at highway speeds for a bit anyway, to make sure the head gasket is holding, and my new front main seal with speedy sleeve isn't dumping oil under higher pressures.

So we'll see how it accelerates during & after that.

 

Ports on the diaphragm for the vacuum advance are not causing this problem IF your throttle plate is not too far open at idle. As long as you tuned your Weber with the vacuum advance unplugged, and timed your engine 8*BTDC or above with the vacuum advance unplugged I believe this is a fuel/carb tune issue.


I have yet to see in person any R engine using both vacuum lines to the dizzy. The only one necessary for proper vacuum advance function is the front port, the other may be capped or not capped, individual choice. Many vehicles came with advance diaphragms with two ports, most I see and have worked on only use one. Number of ports on the diaphragm is inconsequential as long as the right one is hooked up. So many parts on R engines are interchangeable that it is impossible to know what came with or was retrofitted unless one has an appropriate accumulation of experience, knowledge and historical reference.


The vacuum advance should be non-functional at idle and at heavy throttle. The timing will only advance via vacuum at cruising speeds and only for economy. The vacuum advance will not affect performance unless you have a mechanical problem in the distributor/diaphragm or an improperly tuned idle. Most likely you'd have dieseling issues if your throttle plate were that far open. You can run into issues trying to use a vacuum advance with a monster cam, but if you were running a cam that big you wouldn't be able to use a 32/36. You'd be outstretching 38/38 territory at that point and moving onward to DCOE's or big Holley two-bbls.

just to rule it out, it's pretty easy to cap off the vacuum advance and drive around. If you find yourself combating this issue after more carb tuning try running sans vacuum advance for kicks. you never know what you might discover. I have had mechanical issues with Toyota distributors in the past. All mechanical advance issues, but the vacuum diaphragm and linkages can get sticky and corroded and cause problems mechanically as well.


If you have to tune your Weber a little lean vs a little rich, always go rich. The 32/36 is a pretty simple carb to tune, but not quite as simple as the synchronous varieties. Having both sides be exactly same simplifies the process for sure. I put a very mild cam in my otherwise stock 20R and had to upjet the 32/36 considerably. It's very easy to want to under-jet them.


Ignition timing would cause a problem like this only if it were very low or very high, meaning if you left your advance plugged into the vacuum port, and your carb was misadjusted just enough to add vacuum to the advance line at idle, you could have over-timed your initial advance. Having a timing light with a degree knob is also quite handy. Usually when your timing is too far off you'll get popping through the carb or sputtering like chitty-chitty-bang-bang. Not always, but reading your posts I assume you've done this kind of thing before and have basic procedure down solid.

 

Rebuilt a stocker or a Weber? Start a thread or post more info, would love to try and help.

 

My 1980 20R came stock with two vacuum lines to the distributor. I replaced the dist with a DUI single wire single vacuum line unit. I agree with jimbyjimb, too rich is better than too lean. Check your carb settings.

 

How do you like the HEI? They look funky, sitting so far out from the head. Do love that all in one packaging. One of GM's better ideas.

 

I desmogged it, put a header on 38/38 Weber and the dui dist. I love it!!!!
looks funky with that thing sticking so far out from the head and it is as big around as a number 3 coffee can, but it works great. It a 4X4 with 31X10.50 Firestone Destination MT's.

 

It's feeling a bit better. I'm going to drive it for a bit and see how I feel. Some of it is that I got used to driving a newer car all winter, and I think it was a bit of shock getting behind the wheel of the Chinook again!

But I'm sure it could use some fine tuning. I'm about to leave the flatlands and get back into the higher mountains, so I think I'll wait until then to do anymore tuning. For the most part, it seems to be running pretty well. We'll see what my gas mileage is like...

 

If it is lean now, it will be leaner in the mountains so that could be a good indication.

 

We'll see how it goes. Heading to Utah on Monday.

 

Take your jets and timing light. Above all,have a good time.

 

I don't have any extra jets, but if it seems like I need to re-jet, I'll buy the kit.

 

I have a spare. Pm me your mailing address and I'll mail them to you. It's not complete, but most of them are there and you can order the couple missing jets individually and inexpensively via carbs unlimited if you need to. Been wanting to hand this off to a 'techer in need for a while.

 

DUI? Where I come from that doesn't mean anything as far as engines go, though I suppose we could call it running rich, in one sense...

Is it possible to install a 22R distributor on a 20R? Would it run any different?

What does that other port do, then? Mine has an inline "capacitor" looking thing (sorry, I know more about electrics than carbs, and that's saying something).

Idle, yes. WOT? I thought the whole point was to advance timing under WOT to ensure that all that air/fuel mixture gets burned.

I just ordered a National stocker rebuild with a lifetime warranty.

I considered a Weber, but given my plans to swap in a diesel, the extra ~75 bucks and uncertainty, I decided against it.

I'm a mechanic for a living, I've rebuilt manual transmissions, diesel injection pumps (well, minus the governor spring), countless chainsaw/lawnmower/weedwhacker carbs, rewired an ABS/traction control computer on a BMW, all successfully... and this Aisan carb that's older than I am utterly defeated me. It's a humbling experience.

I don't quit easily and may again attempt an automotive carb, but not when it's my daily driver that I need ready for a 1000-mile trip soon.

I gotta say, jimby, I appreciate the support. It's resources like this forum that make DIY - an essential part of owning older vehicle, for those of us whose pockets have bottoms - possible, and it's people like you that make forums work.