Starting and tuning rebuilt motor...timing travails, vacuum leak vexations and carb conundrums (1 Viewer)

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No particular questions but sharing this as I go through the process of getting my freshly rebuilt 1974 up and running. Its a 1974 US market FJ40 I've owned for almost 20 years and dragged across the world and back. Here is a build thread that needs some updating...Builds - 1974 FJ40 Restoration Build Thread

I had some initial timing problems which many of you helped with along the way...https://forum.ih8mud.com/threads/methodical-first-start-process.1199635/post-12986555

Now I am tackling another round of issues which hopefully will be quick, but I am taking a methodical an involved approach this time rather that just following the FSM and Haynes...so here is what I am dealing with and doing...no particular questions but feel free to post observations and suggestions if you wish...

Truck was initially idling high but OK and was not responding as expected to mixture or throttle stop changes. I suspect vacuum leaks so I blocked off each vacuum hose 1 by 1 and didnt find any change. Vacuum gauge reads almost nothing when it was idleing and now even when briefly idling before it dies. Like 3". Sprayed some carb cleaner around different spots and found the carb was leaking at the horn-to-base gasket. Put the truck away for the night. That leak is above the throttle plates so it certainly needs fixing but wouldnt explain the low vacuum reading on its own.

Next day started the truck up but now it wouldnt idle at all without 1/4 choke and even then just sputters out. Ot would start with full throttle and rev but wouldnt idle on its own. I have a air-fuel mix gauge and it shows rich at the rough idle but I havent found those gauges reliable when the motor isnt running close to right.

My plan is to re-rebuild the carb and go through every single place an intake leak coule be coming from, down to the intake manifold.
For posterity, my carb settings are...
Primary jet 1.20
Secondary jet 1.80
Primary idle/slow jet 60
Secondary idle/slow jet 80
Primary Venturi has #2 stamped on in, secondary has #4. Both are double-ring.
Power valve 80

I disassembled the carb and using a pane of glass sanded the air horn section and carb bases flat. Made a new gasket and used curil-t.

Cleaned out every passage in the carb including removing and cleaining the idle circuit and testing the solnoid. I saw some threads mention an o-ring falling apart and blocking the idle solnoid. I didnt find any o ring and also no evidence of debris.

Put the carb all back together last night and will work on the base and intake later today....

Thanks all end enjoy!

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Well that was a fun garage session...I found out why it ran worse just before I put it away and wouldnt start or run well after...I was fine-tuning the dizzy just at the end and look what I did...
20200415_165611.jpg



Pinched and cut open the vacuum hose off on the battery tray...
20200415_165559.jpg


I also figured out why I kept having timing issues...the cap wasnt locating on the keyway squarely, so every time I put the cap back on the timing was different! Ugh....Also reclocked the distributor 1 tooth retarded to get in range and not pinch off the vacuum tube again.

20200415_165611.jpg


20200415_165559.jpg
 
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Still having problems...appreciate any guidance/troubleshooting here. Here is what I have done;

1. Sent the carb and had it rebuilt/returned by TLC
2. Checked timing again...10 degrees btdc at 800 rpm.
3. Checked compression...146, 150, 148, 151, 149, 150 psi compression warm
4. Regapped plugs narrower to 0.035
5. Tried all combinations of throttle position, idle mix screw settings
6. Installed wideband O2 sensor to assist with tuning
7. New DUI cap, rotor and new wires.

Here's the problems I am having;
1. Hard start warm or cold.
2. Low manifold vacuum. 10 inches is the best I get.
3. Very lean idle. I can get it idling but O2 sensor shows it at ~20 AFR. When I try screwing in the air mixture screw (starting at 4 turns out from TLC) I can get it richer, and it almost immediately dies. I tried opening the throttle idle speed to compensate for the reduced ait through the bypass but couldnt get it to idle happily. The carb was rebuilt by TLC, so i dont want to/havent messed with it internally (changing jets, float height, etc.) I suspected a problem with idle passage blockage as it was doing the same thing before the rebuild...any suggestions why/how to fix this lean idle condition?
4. Explosive off-throttle backfiring through the exhaust. Almost like valve timing is off?

I am at my wit's end here...I feel like I have ruled out easy fixes already...is it possible the cam is 180 degrees out? Is there a way to check that without disassembling the radiator/pump/timing chain cover?

Any other suggesions?
Thanks!
 
Last edited:
Joined
Nov 21, 2017
Messages
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Still having problems...appreciate any guidance/troubleshooting here. Here is what I have done;

1. Sent the carb and had it rebuilt/returned by TLC
2. Checked timing again...10 degrees btdc at 800 rpm.
3. Checked compression...146, 150, 148, 151, 149, 150 psi compression warm
4. Regapped plugs narrower to 0.035
5. Tried all combinations of throttle position, idle mix screw settings
6. Installed wideband O2 sensor to assist with tuning
7. New DUI cap, rotor and new wires.

Here's the problems I am having;
1. Hard start warm or cold.
2. Low manifold vacuum. 10 inches is the best I get.
3. Very lean idle. I can get it idling but O2 sensor shows it at ~20 AFR. When I try screwing in the air mixture screw (starting at 4 turns out from TLC) I can get it richer, and it almost immediately dies. I tried opening the throttle idle speed to compensate for the reduced ait through the bypass but couldnt get it to idle happily. The carb was rebuilt by TLC, so i dont want to/havent messed with it internally (changing jets, float height, etc.) I suspected a problem with idle passage blockage as it was doing the same thing before the rebuild...any suggestions why/how to fix this lean idle condition?
4. Explosive off-throttle backfiring through the exhaust. Almost like valve timing is off?

I am at my wit's end here...I feel like I have ruled out easy fixes already...is it possible the cam is 180 degrees out? Is there a way to check that without disassembling the radiator/pump/timing chain cover?

Any other suggesions?
Thanks!

Any help out there please? The low vacuum had me chasing any possible vacuum leaks but I couldnt find any...had the intake planed too...pinched off the brake booster and the crankcase vent and the dizzy vacuum (those are my only 3 vacuum sources) with no change.

I had to use some permatex to get the valve cover fully sealed, which I now regret and am removing to check valve operation...
 
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Try advancing your timing...
Hi, and thanks for chiming in. I did advance timing all the way to ~40 degrees while idling, but it would not start when left there and the backfiring out the exhaust off-throttle was explosive!

I pulled the valve cover tonight and found #1 was tight at ~0.9 mm intake, ~0.2mm exhaust. Reset to 0.20mm intake and 0.35mm exhaust. I ran out of patience and time before moving back...would tight valves cause this? I am curious to see if I find any that weren totally closing, though I doubt it since I got good compression across the cylinders?
 

Pighead

Stop calling it an FJ
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The thing is, the more you build your engine, the less you can rely on the FSM settings. My rebuilt engine likes a lot of advance, so much that the BB is lost behind the bellhousing and I time by vacuum. Advance timing, turn out idle screw. Repeat until best vacuum then retard a degree or two. drive and listen for pinging...
 

Dizzy

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When I advanced my static timing beyond range, it failed to start easy. I say try to keep your spark relative to the crank angle for most torque, akin to 7 deg. BTDC.

Mine has low vacuum when I installed it, and I'm at high altitude. I'm pretty sure that when the valve stem seals were leaking tons of oil, that it was getting baked on the top of the intake valves, making it hard to pull air in. I've been monitoring it with an O2 sensor and readout (mostly works), but O2 sensors don't necessarily measure incomplete combustion. It runs better now, but during the beginning of tuning, I had to over-jet it, now, I think that I'm burning rich because driving it has removed deposits. I don't have a bore scope, but you can see it with the intake manifold off, and I've seen it on a couple of my other heads that I pulled the valves and did a wire wheel cleaning.
 

Dizzy

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Make sure that you are on the right camshaft turn (2 crank turns = 1 camshaft turn). IIRC cylinder #4 will be way off on the rocker arm, if the crank is 360 degrees off. It might account for your goofy .9mm on the intake for number 1. I must have set mine two times correct, getting lucky with the crank turns before I hit the wall, adjusted like numbers 1 to 3, then realized that something was way wrong on number 4.
 

Pighead

Stop calling it an FJ
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When I advanced my static timing beyond range, it failed to start easy. I say try to keep your spark relative to the crank angle for most torque, akin to 7 deg. BTC.
Which might go towards illustrating my point. At almost 50 years and maybe a rebuild away from Factory, the FSM specs are more of a suggestion than Gospel.
Dizzy's won't start when too far advanced, mine seems to require the advance. Mine might be a bit more "built" than Dizzy's, I dunno. I'm running a 2F block with Late F head, bored 0.50 over, 60 series dizzy, Jim C. carb on a '69 wide-runner intake, headers (naturally) and an RV cam. And other stuff.
I think, what it comes down to, is learning to really "tune" your individual engine to your particular location and needs. I'm over 5K' elevation and like an idle 550 to 600 RPM. I adjust my tappet clearance a bit tighter than stock, 'cuz that's what the RV cam people said and it hasn't hurt anything yet (this rebuild is 16 years old, still pull 15in/Hg vacuum at idle and get 70psi oil pressure cold idle (engine was balanced for rebuild)).
So, JohnJL, I suggest that you're going to have to learn what your engine likes (once you get past the basics of adequate tappet clearance) instead of what the book says. Use your ears, use your SOP. Carry a 10mm wrench and a screwdriver in your center console (I do). Tweak as you go.
Also, that is a good-looking carb. But, do not think one carb rebuild cures all. I rebuilt my carb 5 times in the first two years I owned it (pre-interwebs) and probably once a year thereafter until I sent it to a pro. Just something to consider.
 

Dizzy

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I actually have my valves about .003" tight. It helps me with rocker arm clack at the oiler groove. Performance folks do it for upper end horses. As long as the valve can fully close, then it is not a problem.

However, if you get the valves adjusted correct, in the bigger picture, then you will have not much else to adjust on that end. I feel that valves would best be checked by a compression test. Vacuum measurements help but they require a well firing motor as a baseline.
 
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Hi Guys,
Thanks again for taking the time to get me back on track. Last night I went through the rest of the valves - checking each is at TDC with the plugs removed and following the valve action as I turned the motor over by hand. There were a couple that were .02 mm +/- but none way off and none so tight that they werent closing fully. I was kind of hoping to find something so obviously off and fixed with a 17mm wrench feeler gauges and a screwdriver.

I measured 146, 150, 148, 151, 149, 150 psi compression warm. I was barely getting 7-10" vacuum though, and while the truck would drive, it barely idles despite all kinds of experimentation. When I advanced ignition to say 15 degrees, the wideband shows 18-20 AFRs. I can get those down by screwing in the air bypass, but I have to get the air mix screw down to 1 turn out before AFRs become reasonable (~13-15) and then the motor dies. Also when advanced I get crazy backfiring when backing off the throttle.

Before buttoning up the valve cover and carb (I had to remove it to get at some RTV holding the valve cover on) is there anything else mechanical I should check? Like, is it possible to have the cam timing off? I reassembled aligning the dots and following the FSM but it it possible that they are out-of-phase? I dont cherish draining the radiator and removing all the front of the motor but I also dont want to keep chasing my tail...

Thanks!
 

Dizzy

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The camshaft is gear driven. I could imagine that, but, that is something that I'm more unfamiliar with.

Sometimes, or often, the vac gauge is off.

Remember, an O2 sensor needs to be silly hot hot, or it reads rich. Also, make sure grounds, connections (less a chance, but check with a jumper to a known ground - I had this problem). You might induce a small vac leak via stock 'gas filter' or an orifice in a vac hose to see if you are really rich.

The symptoms suggest lean not rich, as a hard to to idle without choke are band-aided with a slight choke. You have to be really rich before you have trouble running (as a the flame is governed more by the necessarily larger volume of O2, then the excessive fuel load, IIAC), and it is harder for a carb to be rich (leaking fuel, or bowl overflowing) then lean (restricted passage, or not enough vacuum). Is your bowl level with the dot on the window? If the throttle plate is excessively opened, and the slow circuit is not feeding enough fuel, then a bit of choke seems to help. You get an audible click on the idle cut solenoid when you use a jumper wire from the battery?
 
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The camshaft is gear driven. I could imagine that, but, that is something that I'm more unfamiliar with.

Sometimes, or often, the vac gauge is off.

Remember, an O2 sensor needs to be silly hot hot, or it reads rich. Also, make sure grounds, connections (less a chance, but check with a jumper to a known ground - I had this problem). You might induce a small vac leak via stock 'gas filter' or an orifice in a vac hose to see if you are really rich.

The symptoms suggest lean not rich, as a hard to to idle without choke are band-aided with a slight choke. You have to be really rich before you have trouble running (as a the flame is governed more by the necessarily larger volume of O2, then the excessive fuel load, IIAC), and it is harder for a carb to be rich (leaking fuel, or bowl overflowing) then lean (restricted passage, or not enough vacuum). Is your bowl level with the dot on the window? If the throttle plate is excessively opened, and the slow circuit is not feeding enough fuel, then a bit of choke seems to help. You get an audible click on the idle cut solenoid when you use a jumper wire from the battery?
THanks for taking the time and great advice!

The 02 sensor is a heated one, and I drive the truck around a while gently before working on this idle issue. It does indeed read and I agree the symptoms indicate lean. The carb came back from TLC 2 turns in on the idle throttle and 4 turns out on the idle mix/bypass. I progressively backed out the idle throttle until the throttle was closed in an attempt to create more vacuum and pull more fuel at idle, but it just dies rather than get richer.

Creating a new experimental vacuum leak doesnt seem to effect the motor, which originally led me down the path of a vacuum leak...hence planing the intake and pinching off all the vacuum hoses to see if any of them are leaking (they arent, or they arent the only leak if thats the cause.)

Yes, the fuel level in the bowl is in the middle, and I havent opened the carb since TLC serviced it and returned it to me.

Yes, the idle solnoid clicks.

You are also right that even when warm, the motor idles better with 1/4 - 1/2 choke. When I choke it, I can see the AFRs come down to 13-15. Its like the motor has a vacuum leak (I honestly cant find any more sources and have re-torqued the intake manifold) or is somehow mismanaging the air intake, which is why I suspected the valves and perhaps now the cam.

Yes, I put the cam in and matched up the dots. I am second guessing myself whether there is any way to have matched up the dots but overlooked another timing consideration?

Thanks again everyone!
 

Dizzy

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When the idle mix screw has little influence for the engine rpms, it usually is because the throttle plate is opened beyond a certain point, and the fuel mix is coming from higher up in the throttle bore.

Personally, I'd get bigger jets for the sake of fiddling with things. Also, I'd tripple check the spark. Is the coil hot enough, are the plugs clean, is timing and sequence right. A lean reading can just be unburnt fuel and O2, and you had exhaust backfire when spark was advanced too much which is usually a misfire.

Also, if your throttle plate is at a steep angle at idle, then you are pulling thru the ported vacuum source. Cap the advance barb on the carb until you get a good idle. Otherwise, it won't let you time and te correctly.
 
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Thanks guys. So I am standing on the bumper looking down on this thing contemplating whether to put the valve cover back on, carb and trying to start her up again, or to keep tearing down to check I didnt screw up the cam timing somehow...so am I right in thinking that as long as the dots on the cam and crank are lined up, there isnt any way to screw up the cam timing?

Dizzy, my coil is in the DUI distributor cap, and is new along with the plugs and livewires. I reduced the gap down a bit to .035 on the plugs to try and make sure I was minimizing misfires.

All advice and opinions welcome? Tear her down further to slap her back together? I will clean up the valve cover for a bit....

j
 

Dizzy

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I'm more skeptical about the carb rebuild. There are quite a few things that could go wrong. With two carbs, and one rebuild kit, I noticed three different spring rates on the needle valve on the float, and I had different o-rings to choose from with the idle cut solenoid. Also the replacement solenoid that I bought had a different profile on the o-ring groove, IIRC. I could see something like a pinched O-ring giving you trouble in the air horn. Also, my rebuild kit came with a significantly courser screen on the fuel inlet, which was a bit disappointing, so I swapped to one of the originals.

A couple of months ago, I had a strange idle lean burning issue like yours. I bolted on a spare 32/36 Weber, no problem, aside from the top end of throttle. So, I ordered a 38/38 Weber. While it was in the mail, I started chasing down the problem on the OEM carb, the problem seemed to go away (my motor is tired regarding compression and vacuum). The manual choke for the new Weber got me hung up, so I put the 38/38 carb and the idea of the swap on the shelf. Either way, the 2F runs great now. I can start it with no choke, it has a bit lean tendency on the A/F readout on the highway, and a bit rich at idle, but, I'm still likely blowing out old carbon deposits from the top of the intake valves, and I'm at 7,000-feet, so no worries there.

Again, I'm not experienced in the camshaft installation. However, there was one incidence where the Mudder had a woodruff key issue. The harder part seems to be getting the distributor on the 7 degrees BTDC of the compression stroke. However, with that, I don't know if the engine can run, or if you don't do rocker assembly or push rod damage (firing on an open valve). Plus, your compression test suggests that the valves are closing, and you had the camshaft dot line up with the gear on the crank, so that also leads me to believe things are okay in that realm.

I hope that others would chime in here.
 
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Thanks. Yes, I suspected the carb too, and finally gave up and had TLC go through it...
 

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