Vacuum leak through carb linkages 79’ (1 Viewer)

[rghouse]

got the (CA 79’) cruiser at the shop and they hooked smoke up to it to diagnose vacuum leaks. major leaks coming out of the arms that move stuff inside the carb (throttle etc.) and butterfly valve post on the front side.

they recommended sending to someone to machine holes and put in new bushings.

anybody have input or experience this? havent cone across any threads specifically speaking on this issue. they did not put smoke through it after engine heated up. Is this normal? do I just need to purchase a new carb?

advice appreciated

 

[mattressking]

It's possible, some wear more than others and doing a smoke test will yield any leak. There aren't any bushings in the base for the butterfly shaft, they just wear. What is your vacuum reading at idle?

 

[B y r o n]

This info may help.

 

[rghouse]

it sits at about 15 hg, havent had a chance to test after some other minor leaks fixed.

 

[Fast Eddy]

got the (CA 79’) cruiser at the shop and they hooked smoke up to it to diagnose vacuum leaks. major leaks coming out of the arms that move stuff inside the carb (throttle etc.) and butterfly valve post on the front side.

Some silicone grease might resolve those issues. (Edit: Could hurt the throttle response though??)

they recommended sending to someone to machine holes and put in new bushings.

F' that. Rebuildable cores are readily available. It's the same core as an FJ60 if I am not mistaken.

it sits at about 15 hg, havent had a chance to test after some other minor leaks fixed.

15 is not so bad. You should try the grease trick and retest. If the grease helps, make sure you retest periodically to see if it eventually gets sucked in and ceases to help. It depends on how bad the wear is.

 

[ToyotaMatt]

it sits at about 15 hg, havent had a chance to test after some other minor leaks fixed.

Well then …

- you have answered your own questions and solved your dilemma
Most likely

Fix the other minor leaks …

- retest and report back

- I bet your reading Hg. Goes up


- use ONLY OEM toyota vacuum caps

There life time service parts

 

[rghouse]

thanks @Fast Eddy thats where i was going with it as far as the grease. also didnt know there was rebuilt cores .

the issue is come and go too so tearing my hair out. stalled at every stop sign this morning then ran great downtown, vacuum shuts down regardless of engine temp. will report back aftwr greasing some bad spots

 

[mattressking]

Your issue is likely your manifold gasket, 15inHg likely isn't your carb unless its truly trashed and missing a number of items. Check for leaks around the carb insulator and verify pcv hose isn't leaking or disconnected. Chase every item that is connected to manifold and verify they aren't venting to atmosphere, including your brake booster. Carb butterflies aren't your issue, they may show a leak, but extremely unlikely to be your issue. You want to be at 18-22inHg.

Also make sure you have properly done a lean drop tune and verified timing is at 7* and up to 10*-ish max if totally desmogged.

 

[rghouse]

it is not desmogged. the pcv is intact and connected. I didnt see any smoke coming out of the carb insulator during test, there was just lots pooring out of carb in general. I tested brake booster by plugging it off and issue persisted. timing was set at shop but i will see if it moved. I’ve done lean drop a couple times but will perform again.

what i can’t figure out is why it is intermittent. runs great 30% of the time, and idles in range.

wondering if it is a valve staying shut somehwere (vcv maybe), air pump cutting out (tested once, ok) or possibly issue with vac advance in distributor. Problem is the instructions in my Toyota engine manual are clear as mud and I cant make heads or tails of the vac advance instructions.

 

[mattressking]

Manifold gasket…..if it hasn’t been done, it’s time. Pull it apart, check for flatness, reinstall and test every single vsv/vcv/bvsv and vacuum routing as well.

wondering if it is a valve staying shut somehwere (vcv maybe), air pump cutting out (tested once, ok) or possibly issue with vac advance in distributor. Problem is the instructions in my Toyota engine manual are clear as mud and I cant make heads or tails of the vac advance instructions.

Air pump isn't vac related nor will it cause stumbling - it only adds air to exhaust for emissions, disregard. Make sure vsv's/vcv's are connected correctly and functioning (but not the cause of your vac leak).

Vac advance is not your problem, you can plug the vacuum feed, but again, even when they leak, it is off ported vacuum so at idle, you won't have vac leak (unless connected incorrectly). Definitely verify diaphgragm holds vacuum, but again, not the cause.

You're missing about 5inHg of vacuum, there isn't a system large enough to leak that much aside from large ports of manifold (booster, pcv) other than manifold gasket. Carb insulator usually only loses 1-2inHg if its leaking bad.

When the truck runs well at 30% of the time - is that when cold or hot? I've dealt with all of these issues you're encountering on multiple 2F's, don't waste your time chasing small systems, do the big job, move on.

 

[rghouse]

Happens regardelss of temp, no pattern noticed.

Dad put on CA legal headers about maybe 2000 miles before tear down (frame off) in 2008. so that gasket should be a baby in use, not so much in time. Just find it hard to believe thats it but looks like thats where i am going. Thanks much @mattressking

 

[mattressking]

Happens regardelss of temp, no pattern noticed.

Dad put on CA legal headers about maybe 2000 miles before tear down (frame off) in 2008. so that gasket should be a baby in use, not so much in time. Just find it hard to believe thats it but looks like thats where i am going. Thanks much @mattressking

Oh yea - headers. There's your problem. No header is perfect, they all leak ultimately.

 

[rghouse]

Okay so getting ready to tear down and just checked and tightened some mani/header bolts. The pressure is better, but another issue came back and wondering if this is also a symptom of the leaking mani. The engine races, surges, or drops up and down in the idle level. Guessing the air/gas mixture is just all screwed up because the vac leak is so bad? This is a smooth rev, rev, rev

Also, Dad saved the original exhaust manifold should I just re-install it? or is it worth pressure testing or something on the headers to see if they are good? Again, they have very little miles on them but just sat for 15 years. Guessing whichever I go with it will have to be machined flat for good measure?

 

[mattressking]

Okay so getting ready to tear down and just checked and tightened some mani/header bolts. The pressure is better, but another issue came back and wondering if this is also a symptom of the leaking mani. The engine races, surges, or drops up and down in the idle level. Guessing the air/gas mixture is just all screwed up because the vac leak is so bad? This is a smooth rev, rev, rev

Also, Dad saved the original exhaust manifold should I just re-install it? or is it worth pressure testing or something on the headers to see if they are good? Again, they have very little miles on them but just sat for 15 years. Guessing whichever I go with it will have to be machined flat for good measure?

Idle surge/hunting is the tell-tale sign of a vacuum leak. The engine is getting inconsistent amount of air per part of fuel, so the idle goes up and down. You can tune some of it out but once you fix the leak, that will sort it out.

I'd recommend putting it back to stock, you'll need some manifold gaskets then assemble loose on the head then torque nuts/bolts on head first then finish with the 3 manifold bolts that connect intake to exhaust manifold. Once they are tight, remove manifold from head then check for flatness, no more than .050" is factory spec. If it's more than .050 you'll need it machined flat.

Header won't benefit from a pressure test, the issue is the header flange warps/is inconsistent with the factory intake and to resolve you'd need either half-moon washers to compensate or a thicker gasket.

 

[Mcap1PA]

If you haven't taken your rig apart yet, to do some further testing, get a can of carb cleaner and lightly spray around the intake manifold ports where they meet the cylinder head. Use the little red tube that comes with the can so you can pinpoint the spray. If there is a leak it will show with a change in the engine speed.

MC

 

[MoCoNative]

Pretty much all headers are not the same thickness as the stock intake manifold. Typically you have to cut washers in half to make shims to sit in the recessed portion of the half hole on the intake manifold. This is still an imperfect way to assure that the nut and washer on each stud which clamps down the manifolds is exerting the proper force on the manifolds. If the nuts are just tightened down, and the they are seating on an unflat surface then one of the manifolds can come away from the head. Doesn't take much to cause a bad vacuum leak, or exhaust leak at the gasket. Can possibly be intermittent, or change with temps.

 

[rghouse]

waiting on the parts and went and messed with it some more today. Started and idled fine for 5 minutes, not sure what vacuum was. Hooked up gauge to brake booster port and it read 15 and slowly started stumbling but maintained idle without choke. Minute or 2 later it started surging. Didnt have my Tach setup but guessing it was going up and down from 900 to 1300 ish.

Sprayed all over manifold that I could reach, no effects at all. However, the below 'coupler' with gasket does have a leak. Tightening all the way down and didnt help, it seems bent a little in the middle.

 

[rghouse]

didnt find any obvious signs of a leak on the intake manifold. The EGR cooler fitting was not tight though and slid inside the fitting freely.
I do not see a ferrel fitting?? might check home depot before caling SOR.

going to have to use the headers again I think, I do not have an exhaust pipe to go from the heat riser to the next connection downstream. SOR says discontinued, and not sure if towing to a muffler shop is worth it. Ideas?

 

[rghouse]

back to the drawing board. new manifold gaskets etc did not fix. EGR was bad in all 3 unions, only suspect thing noticed. truck will not idle at all. will occasionally switch to racing at higher rpms, then i back off idle screw or choke and it dies.

moving on to electrical or ignition i guess, just can’t beleive this is vacuum. All the carb spots that spewed smoke are greased over to seal. new intermittent high pitch whine noise showed up too, will be taking apart again seems like its near the bottom of carb. just about at wits end now.

 

[fjc-man]

If you’re ready to punt, see if maybe @marksoffroad.net would consider sorting it out for you?