I'm beginning to suspect I may have an intake manifold leak, probably between the head and the manifold. Vacuum is around 16.5 inches at idle, and the car acts like it's too lean, especially when cold. It's sputters and sneezes right after startup even with the chokes pulled out on the Mikuni's. I also can't get a stable idle below 1000 RPM, and low RPM torque is poor.

I'm running premium fuel, timing is at 15 deg., distributor has the Pertronix kit installed with Flamethrower coil. MSD6 ignition, NGK plugs gapped at .035, spiral wound silicon plug wires. The engine is stock B20F specification with injector holes plugged with threaded hole plugs, with less than 1000 miles on a complete rebuild.

I'm using a FI exhaust manifold with the aluminum intake manifold. The mounting flange thickness of the intake and exhaust is different, so I had a machinist buddy at work fabricate some stepped washers for me; beautifully and precisely made... but I'm starting to wonder if they could be part of the problem, here's why...

The holes in the stepped washers are barely larger than the studs that the washers fit over, and I'm starting to think that maybe those holes need to be a little larger, to allow those washers to tilt a little bit when thermal expansion or contraction of the manifolds is taking place.

I've noticed the (flat) washers Volvo used on the B18's seem to have a generous amount of slop in those holes; I've also observed one surface of the factory washers is domed quite a bit. Is this something I should be focusing on, as something my stepped washers should have?

The only other issues I can think of would be a crappy gasket, or a problem with the split intake port sealing rings.

I checked the intake manifold mounting flange on the granite block at work, and it looked nice and level.

If their is an air leak, it has to be on the underside of the intake manifold, BTW; I did the bit with spraying WD40 on the manifold to head area from the topside already, and it had no effect.

Any thoughts would be appreciated.

Bill

Are you sure it isn't the carb? You mention the "crappy intake gasket" - you did use a new one didn't you? Instead of the WD-40...try propane from a small torch, it is easier to get into places while the engine is running, doesn't get all over everything like carb cleaner or WD and works for finding leaks. If the intake was checked for flatness, then was the head? I'd start with the carb as the problem and go from there.

Craig

Propane is a really good idea; I don't care to use carb cleaner around my polished and clear-coated intake manifold.

I didn't check the inlet/exhaust side of the head for flatness; I did have it completely rebuilt, and the underside of the head was checked and surfaced by the machine shop.

The Mikunis are new, as were all engine gaskets at the time of the rebuild. I used permatex on the gaskets in front of and behind the heat shield, and on the backside of the adapter pieces that go from the Mikunis to the face of the heat shield.

I tried dismantling, cleaning, regasketing and repermatexing everything from the backside of the carbs to the inlets of the intake manifold, new PCV valve and hose, with clamps now on every part of the PCV valve setup.

The block is a B20, the PCV valve plumbing is B18 style, with an unrestricted nipple on the intake manifold.

I've already found and repaired two vacuum leaks, one was a split rubber cap on the vacuum takeoff on one the Mikunis; the other was an unclamped hose going from the breather box to the PCV valve. Fixing the last leak made a substantial improvement, but the car still isn't running right.

I'm going to remove the breather box and permatex around the o-ring next, and if that doesn't fix things then the intake manifold is going to come off for inspection and a new gasket.

Did Volvo use the same split sealing rings for the FI and carbed manifolds?
I'm not sure which type of engine the one's on the car came off of; I had assumed they were all the same dimensions.

Bill

AFAIK Volvo used the rings on all manifolds for the B18/B20, but I've never had the FI manifold off a car, so can't really comment.

Try using a stethoscope or just a piece of tube stuck in your ear to locate the leak. That works way better than spraying stuff on your engine, its just a little hard to do in the hot areas of the engine. I have had good success with home made stepped washers. I cut some stainless washers in half, sanded them down to the proper thickness and lightly tack welded them to whole washers. You have to retighten the hardware after some hot cool cycles a few times to ensure the seal.

If you don't already have a mechanic's stethoscope, get one. They are like ten bucks for cheap ones and they work great. Use just the open end of the tube to hear for air leaks. With the metal probe attached to the stethoscope you can have hours of fun listening to the different parts of your engine.

You can probably run without the split rings if you are worried about those. I don't think my setup even has them.

Bill,

The problem is probably not in your nicely machined washers, but to eliminate that possibility, just use a regular hardware store washer of the thickest kind you can find plus a washer of the same sort cut in half. I've dealt with the intake and exhaust manifold flange thickness difference successfully that way. If the problem persists, you'll know that wasn't the cause and you can go back to the washers you were using. Of course you can also enlarge the holes in the washers you are using with a drill or a rat-tail file.

Bob S.
--
'62 PV544 (B20, M41), '71 142E, '93 240 Classic Wagon.

I'm battling an factory intake that keeps loosening.

You mentioned the WD-40 trick. Try it with carb cleaner. For some reason, I have had better luck with carb cleaner sprayed onto the mating surface. The area on mine that has been a source of frustration is the gap between the intake and exhaust on the #1 cylinder at the top. Just can't get that to stay tight.

I have a SS bolt in there instead of a stud. Perhaps that is my problem. Also that hole has a helicoil. Again, maybe that contributes.

I am amazed how little it takes to tighten up that gap. Sometimes as little as a 1/2 flat on the bolt will do. As a matter of fact, I just had tighten it again 2 nights ago. It brought the idle down from 1100 to around 800 and also got rid of the chugging problem I had on the road at 2200 rpm.

Anyway, try the carb cleaner around the gaps. Sometimes you'll get better results if you remove the fan belt so the spray doesn't get blown all over the place - don't run the car for more than a few minutes like that though because the waterpump will not be turning. Then also snug all the manifold fasteners.
--
Tom - '60 544, '68 220S, '70 145S, '86 745T, '06 Mazda MPV

Howdy Bill,

You told us everything except the known condition of the throttle shaft bushings. Are they relatively new or known go be airtight?

My experience with the manifolds, limited as it may be, is that once tightened on, they stay that way. Unless there was something wrong with the gasket or the mounting surface at install, I don't think it an issue.

Let us know about the throttle shaft bushings.

sd

I'm not logged in so I can't edit my message. If I actually read your post, I would have seen in "Mikuni".

DUH.

sd