Intake leak???
- Thread starter Island FJ
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I don't see a crack in the bottom of the intake. I hunt vacuum leaks with a can of WD-40 and a pee tube. Quickly and lightly spray along the intake manifold surface - when rpm's kick up there is your leakly spot. Do the base of the carb and the connecting joints between the pieces. Do it outside and have a fire extinguisher handy - just in case.
On my header installation I made custom brass stepped washers - 1/4" thick for the aluminium intake and 1/8" thick for the steel header. I planed the manifolds on a big piece of glass with sand paper to get them flat. I made longer studs and used 2 man-a-fre header gaskets (soaked in warm water for about 1/2 an hour) with stainless nuts and high temp anti seize compound. Torque in pattern by 1/3, then 2/3 and finally at 100%. Fire it up and let it get hot - torque again in sequence at 100%. After a dozen or so heat cycles re torque again at 100%.
On my header installation I made custom brass stepped washers - 1/4" thick for the aluminium intake and 1/8" thick for the steel header. I planed the manifolds on a big piece of glass with sand paper to get them flat. I made longer studs and used 2 man-a-fre header gaskets (soaked in warm water for about 1/2 an hour) with stainless nuts and high temp anti seize compound. Torque in pattern by 1/3, then 2/3 and finally at 100%. Fire it up and let it get hot - torque again in sequence at 100%. After a dozen or so heat cycles re torque again at 100%.
Three thoughts from my experience from 20+ years ago when my 40 had an aftermarket carb.
1. Does the carb have an electronic choke that could explain the RPM’s at startup?
2. I found that the adapter plate for the aftermarket carb had hardware that was too long that bottomed out and prevented proper torque. For me that was a huge vac leak.
3. Lastly, vac leaks can be diagnosed using a vacuum gauge attached to manifold vacuum (I’ve used the hose to the brake booster). With the motor at operating temp and idle set to 660 or so, you should see roughly 18HG and it should be stable. If it’s lower, or bouncing around then it’s time to spray the carb base and manifold with carb cleaner, the idle will jump up when you find a leak.
1. Does the carb have an electronic choke that could explain the RPM’s at startup?
2. I found that the adapter plate for the aftermarket carb had hardware that was too long that bottomed out and prevented proper torque. For me that was a huge vac leak.
3. Lastly, vac leaks can be diagnosed using a vacuum gauge attached to manifold vacuum (I’ve used the hose to the brake booster). With the motor at operating temp and idle set to 660 or so, you should see roughly 18HG and it should be stable. If it’s lower, or bouncing around then it’s time to spray the carb base and manifold with carb cleaner, the idle will jump up when you find a leak.
Those straight thread bolts jammed in the tapered threads in the intake?
- Thread starter
- #6
Thanks for the advice. The more I look at it, seems like a leak between intake and block. What are the best bolt / stud setup for a good seal? The intake use to seal, so would sanding be needed as stated in a reply?
- Thread starter
- #7
What should be used to plug these?
Pipe threads are tapered, pipe plugs are tapered. Those two big bolts - Lots of sealant, or drill and tap to standard bolt size either metric or SAE.
Since you are in a cold area consider making (I did) a fluid heat riser or buying a man-a-fre unit.
Since you are in a cold area consider making (I did) a fluid heat riser or buying a man-a-fre unit.
Stock hardware is still available. You can have the header flange machined to the same thickness as the intake to eliminate any spacers. Get a straightedge on the intake and use a stock or remflex gasket(a polarizing topic).
I’d definitely redo but also want to confirm that it’s an intake leak first.
All the bolt / stud locations where half the intake is shared with the header are problem spots. If one flange is thicker than the other, torque is not applied evenly to both surfaces. Having the surfaces of the header and intake machined to match helps a lot. I went further and measured each flange at each shared bolt or stud location and recorded them. IIRC Jim C told me .010” was the max tolerance. I shaved one half of the flat machine washers by the measured difference at each location and marked with a sharpie the other side. I assembled with a Toyota gasket, dry and torqued to spec some 15 years ago and it’s been fine. IIRC I used 5 studs which made hanging and assembling easier, as @Jdc1 pointed out, the hardware is still available from Toyota.
If you fix the leak with stepped washers and 2 gaskets, factory studs are too short. Machining the header down to be the same thickness as the intake and running 1 gasket might work with oem studs.
My same header and gaskets, stepped washers has been installed on 2 engines at least 3 different times and has never leaked since like 1985
While you are at it cut a notch in the air cleaner mount so you can easily get a socket on the nut for torqueing.
My same header and gaskets, stepped washers has been installed on 2 engines at least 3 different times and has never leaked since like 1985
While you are at it cut a notch in the air cleaner mount so you can easily get a socket on the nut for torqueing.
I find that OEM studs are plenty long. I have run two Fel-Pro gaskets in the past without a problem
I'm like the 8th owner and I knew the 7th. I got it in 82 when the rig was 10 years old, so no clue what the 6 previous owners did to oem stuff. My stepped washers are like almost 1/2 thick on the long side and 1/8 on the short side. They were made from the base of 50 BMG brass cut off at the web head. Drilled out primer pocket, then turned the hack saw cut flat and followed by step cut into the side with a hack saw and a file. The short side is at extractor grove towards the case head. They could be made shorter, but work holding was easier with thicker material. Plus the thicker brass hold up better to the heat.
The man-a-fre header gaskets are thick, and 2 of them is really thick, maybe 1/4'' plus prior to being compressed in place.
So on my install the studs that were there were too short. YMMV.
The man-a-fre header gaskets are thick, and 2 of them is really thick, maybe 1/4'' plus prior to being compressed in place.
So on my install the studs that were there were too short. YMMV.
I just bought thick flat washers at a bolt store and used the bench vise and a file to make the necessary corrections. Each location was a little different, that way I was dead on.
IIRC, the manifold studs on a '72 are a smaller diameter than a 2F, probably shorter too...
I made mine (very carefully) on a bench grinder.