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View Full Version : Intake Manifold = Bad Design


ed_in_az
2nd September 2006, 07:21
With Carb Cleaner I found a slight leak on the bottom rear manifold seal. After taking the flanges off and checking for fit that bugger does not sit flush. It depends on the rubber seals to fill slight gaps on the bottom where both the front and rear hit the heads. I used Preachers old cylinders to do my conversion so I don't know if the manifold did a perfect fit on my old cylinders, but I doubt it. The only way to get a proper metal to metal fit would be to grind the intake manifold to match up with the heads. So with new gaskets installed I'll find out tomorrrow if the leak is gone. But with minor variations in cylinders / heads these intake manifolds aren't perfect fits.

Has anyone else noticed this?

To me it looks like a design just begging to leak.

But, I sure hope it doesn't.:o

sportysrock
2nd September 2006, 16:00
Install the manifold, seals, flanges, and bolts just snug. Center the carb and manifold with the carb support or hamcan and snug up the bolts the best you can. Then to finish tighten the bolts you remove the carb so you can get at 'em. Then button it all up and you should be good.

t.c. Johnson
2nd September 2006, 16:20
It's a piss poor design. It's almost criminal that these bikes don't have twin carbs by now. But if they insist on only one carb, then they could certainly have come up with a better design.

ed_in_az
2nd September 2006, 16:43
Install the manifold, seals, flanges, and bolts just snug. Center the carb and manifold with the carb support or hamcan and snug up the bolts the best you can. Then to finish tighten the bolts you remove the carb so you can get at 'em. Then button it all up and you should be good.

Yep that's just what I did last night. I'll check for leaks today. I think they could have still used a compression design gasket, but maybe one that overlapped like the one at the base of the Carb. I would think that would seal any gaps better.

I guess I now have one minor complaint at my bike.:p

chrishajer
2nd September 2006, 17:24
The manifold does not fit perfectly in between the intake ports. That's why they have the rubber gasket and the flanges, to take up the gap. The problem with them leaking is not the design so much as the gaskets gets out of position on installation, or they just get dried out and leak.

On the Iron Heads and Shovel Heads, you need to align the heads with a drafting triangle to get them close enough to seal. If you think the Evo style XL intake design is bad, you should take a good look at the Iron or Shovel intake manifold.

FYI, they changed the intake on the '07 EFI models :D

--Chris

ted
2nd September 2006, 17:25
I usually put a thin coat of silicone grease on the gasket. That way it will move a bit while being tightened and fill any gaps better. The silicone grease you use on spark plug boots works real good for this.
Ted

ed_in_az
2nd September 2006, 18:35
Good info on the grease.

I suppose the new manifold isn't backward compatible.

Anyway it appears mine doesn't leak. It idles and runs better when cold now. I'll bet the engine will run a little cooler overall too.

Off to ride now!:tour

Holiday traffic is awful though.:frownthre

sportysrock
2nd September 2006, 19:11
If it was sucking air, then it should run cooler now (richer - as designed, rather than leaner - and leaking)

IronMick
2nd September 2006, 20:51
On the ironheads the trick is to FULLY install the manifold BEFORE tightening down the rocker cover/cylinder head assembly; this brings the cyl heads to the manifold. Then you get a perfect seal, especially with the o-ring seals.

This is the technique in the FM. Unfortunately many mechanics do not do it this way and you get leaks.

Shu
2nd September 2006, 21:49
I use spray white lithium grease on my intake seals too. Then you can tighten the intake down and still rotate it to install the carb correctly. The key is to check the back of the carb (the flange into the intake seal) and make sure it is perfectly installed in the intake when the support bracket (or a/c back plate) is in the correct position. Once everything is lined up perfectly the gap you described is still there, but minimal and yes the seals and flanges will seal it up.

hdsporty
3rd September 2006, 16:16
last night i noticed on my bike that when i let off and the RPMS are high my pipes crackle just fine...but when the rpms drop and im still coasting, my bike pops out the exhaust almost like a backfire. And now im gettin alot more carb farts at low rpm when cruising too. It never used to till i had to take the head off my bike for some repair work, and now i think i might have an intake leak....will that cause all the weird popping and farting????

Shu
3rd September 2006, 16:35
last night i noticed on my bike that when i let off and the RPMS are high my pipes crackle just fine...but when the rpms drop and im still coasting, my bike pops out the exhaust almost like a backfire. And now im gettin alot more carb farts at low rpm when cruising too. It never used to till i had to take the head off my bike for some repair work, and now i think i might have an intake leak....will that cause all the weird popping and farting????
If nothing else changed...then it does sound like you have an intake leak or a carb to intake leak.

What carb are you running though?

Colona? Been there a time or two. Use to race the car at Cordova (and 23rd Avenue;))

hdsporty
3rd September 2006, 17:11
just a stock cv carb.

yep good ol' colona. was actually on 23rd avenue last night when i noticed the problem! just recently at cordova too for the world series.

Shu
5th September 2006, 22:46
hdsporty,

check for an intake leak or exhaust leak.

So do they still call it the Pepsi World Series of Drag Racing? I spent a lot of time up there racing my old Poncho, Chevelle and Camaro. Loved the sand pits, but the racing more than made up for it. Do a lot of bikes cruise 23rd? I remember the cars used to be backed up bumper to bumper on Friday and Saturday nights. Then they put their foot down on cruising and it died....man I wish my daughter could have had that experience.