81 FJ60 loss of power after warming up (1 Viewer)

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Hey all,

First time posting and just want to say thanks! I've learned a boatload on this site.

So I picked up my first Land Cruiser a couple months ago. I am very much in love. Aside from some electrical gremlins everything is solid, but I've been trying to resolve a performance issue and I think I'm starting to get it narrowed down. Basically, truck runs like a dream for the first ~5-15 minutes after starting. Once the engine warms up, there's a little loss of power, and it seems to get worse the warmer it gets -- for example, yesterday I drove up in the mountains and when I hit the foothills about 30 minutes out, I could barely keep it at 45mph (it'll hold highway speed in the flats okay, but it still feels sluggish). It seems to directly correlate to engine temp; once I got off the highway and did a little stop and go, there was a little more power, and mobbing up a hill is no problem at all at the very beginning of a drive.

Some background:
This is an 81 FJ60, ~275k mi. Previous owner did a lot of work, including desmog and a weber carb.

Vacuum lines look brand new, and the vacuum gauge doesn't indicate any issues. It idles steady at about 17; about 5 under heavy load, and around 23 on decel. After I got off the highway yesterday it was idling at about 16, which doesn't seem like a significant drop to me, but correct me if I'm wrong.

There's a fuel pressure gauge under the hood and it reads fine, but obviously I'm not sure what it shows when I'm trying to climb a hill, so fuel starvation or partial vapor lock might be an issue? I'm not sure.

It felt similar to some ignition issues I've had on previous rigs, so I replaced the spark plugs, cleaned the distributor contacts and checked the signal generator gap. I also adjusted the timing to factory spec. That made a difference, but it didn't resolve this power loss issue.

As far as I know, the distributor is not recurved for the desmog. I ordered springs and a bushing to attempt this poor man's recurve: Builds - The Rushing Turdle
If that makes a difference, I'll get it done properly down the road, but I'm not convinced that's causing this because I would expect it to have the same problem running cold.

My only other guess is that it's just getting really hot under the hood and the carb is sucking hot air. Judging by the temp gauges, though, this thing doesn't heat up much, but it would make sense.

Anyway, I've searched the forums and gotten a lot of ideas and information but I'm hoping you can help validate some of my assumptions and maybe give some ideas for where to look next. Sorry for the long post, but I figured I'd give all the info I could.

Thanks all, you guys rock.
 
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I haven't and after reading more about them, that seems like a really prudent next step. Thanks for the direction!
 

roadstr6

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Remove your carb and look under to check for a crack in the intake manifold. You may be sucking exhaust into your intake, running lean and hot when the engine is up to temp.
 
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Awesome, thanks @roadstr6. I had thought about that and wasn't sure how easy it would be to find a crack like that. I've heard some tricks like using an unlit propane torch to search for leaks around the carb gasket while the engine is running. Haven't tried it yet, but there's a first time for everything.
 

roadstr6

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A crack under the carb won’t show itself with propane or spraying carb cleaner around the intake. You will have to remove the carb and look underneath. Here’s what I’m talking about:
45E17A06-D057-4227-B32F-8ADE1AD92134.jpeg
 
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Oh yep, okay, not what I thought you meant. Great, I'll add that to the list. Got plenty of time this weekend, luckily
 
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Get rid of the Weber, for one. Second, when it seems to be lacking on power, does pulling the choke out do anything?

The Weber has an electric choke, so the choke knob isn’t connected to anything. I’lol consider finding a good aisin long term but this is bad enough that I’m skeptical it’s a carb tuning issue (aside from maybe jetting)

I just did the compression test this morning and got good readings. 130-150 dry across the board with a 10-20 jump wet. I noticed some oil and fowling on the plugs I put in about 1000 miles ago so I’m thinking valves. I’ll need to order a valve cover gasket before I dig in there
 
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The Weber has an electric choke, so the choke knob isn’t connected to anything. I’lol consider finding a good aisin long term but this is bad enough that I’m skeptical it’s a carb tuning issue (aside from maybe jetting)

I just did the compression test this morning and got good readings. 130-150 dry across the board with a 10-20 jump wet. I noticed some oil and fowling on the plugs I put in about 1000 miles ago so I’m thinking valves. I’ll need to order a valve cover gasket before I dig in there
Keep in mind, Weber’s on these motors typically run rich. A cold motor needs more fuel, and as it warms up, it needs less. It’s probably just running pig rich.
 
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Keep in mind, Weber’s on these motors typically run rich. A cold motor needs more fuel, and as it warms up, it needs less. It’s probably just running pig rich.

Yeah the exhaust definitely smells rich. Could I counter that with smaller jets? I’ve also heard the mechanical fuel pump doesn’t pair well with a Weber and that an aftermarket electric one would be better suited, but I’m not sure that’s relevant here.
 
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Also maybe worth noting—ever since I adjusted the timing, I’ve had to run 92 octane to avoid dieseling. I had just chocked it up to carbon deposits in a 40 year old motor, but it occurs to me now that the spec timing might not be appropriate with an aftermarket carb
 
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Yeah the exhaust definitely smells rich. Could I counter that with smaller jets? I’ve also heard the mechanical fuel pump doesn’t pair well with a Weber and that an aftermarket electric one would be better suited, but I’m not sure that’s relevant here.
I know nothing about Weber’s other than they’re finicky on these trucks.
 

DFXR

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Also maybe worth noting—ever since I adjusted the timing, I’ve had to run 92 octane to avoid dieseling. I had just chocked it up to carbon deposits in a 40 year old motor, but it occurs to me now that the spec timing might not be appropriate with an aftermarket carb

One thing to consider.

Are you getting pinging/pre-detonation under load when you're warmed up and heading up the hills? If your EGR stuff is gone with the desmog, but the distributor vacuum advance is still setup in stock form, it can lead to overly advanced timing under certain conditions and a very hot, very lean burn.

My understanding is that the vac advance, in stock setup, is expecting cooler-burning exhaust gases sent from the EGR to be combusting, so it advances the timing well past the spec +7 degrees under certain driving conditions (not at idle or low RPMs though). If the EGR is gone or bypassed, but the advance still happens without the cooler exhaust gas, things get really lean under load. 92 octane can help but even that is not enough sometimes.

Many of us who have temporarily bypassed our EGRs between emissions tests just swap the two vac lines at the vac advance and that takes care of it. But ideally you either fix your EGR (if you have to keep it), or get the distributor re-curved.

How is your vacuum advance currently set up? It's circled in red here, on the front-facing side of the distributor. You should be missing most of the other crap in the diagram, and happy for it.

2F_emissions_schematic-1.jpg
 
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One thing to consider.

Are you getting pinging/pre-detonation under load when you're warmed up and heading up the hills? If your EGR stuff is gone with the desmog, but the distributor vacuum advance is still setup in stock form, it can lead to overly advanced timing under certain conditions and a very hot, very lean burn.

My understanding is that the vac advance, in stock setup, is expecting cooler-burning exhaust gases sent from the EGR to be combusting, so it advances the timing well past the spec +7 degrees under certain driving conditions (not at idle or low RPMs though). If the EGR is gone or bypassed, but the advance still happens without the cooler exhaust gas, things get really lean under load. 92 octane can help but even that is not enough sometimes.

Many of us who have temporarily bypassed our EGRs between emissions tests just swap the two vac lines at the vac advance and that takes care of it. But ideally you either fix your EGR (if you have to keep it), or get the distributor re-curved.

How is your vacuum advance currently set up? It's circled in red here, on the front-facing side of the distributor. You should be missing most of the other crap in the diagram, and happy for it.

View attachment 2523749
Also worth noting, is the mechanical advance bushing in the distributor is probably dust. I just replaced mine, and prior to it ( I disconnect my EGR between emissions tests and have my vacuum advance ports swapped like you) it would ping at anything over 7*. New bushing and it’s gone. I run about 10 degrees of base timing now with a new bushing.
 
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Okay, so taking into account the idea that FSM timing doesn’t necessarily make sense with a Weber carb, I adjusted for peak vacuum at the intake manifold. I didn’t have my timing light so I’m not sure where it’s at, but it’s rotated counter clockwise almost as far as it goes.

It is running MUCH better. I’ll give it a proper test pushing it up a good hill on the highway soon and report back.

I’m still going to recurve the distributor to compensate for the desmog. So I understand the distributor has a vacuum advance and a centrifugal advance. I’m not sure what order they engage in, and I’m also not sure why there are two vacuum ports, but to answer your question @DFXR they are both connected to the same vacuum port on the carb. And you’re right, I am missing most of that and very happy for it!
 
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89 fj 62 stock 3fe efi developed rough idle and engine misfire/ buck under load and climbing hills. She has recent plugs, wires, cap and rotor. Replaced fuel filter fram 67196 and it cured all issues. It’s wonderful when the easy fixes work. She’s running smooth and climbing strong now. As soon as I started her up after filter change I knew I had nailed it. It’s a cheap easy job to tackle before diving deeper chasing demons.
 

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