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Posted by: North Coast Jim May 22 2020, 04:12 PM

Engine is out and I'm doing some investigations. Bought a set of Redline 40 IDFs for the engine build. They've run OK but not great. Couldn't keep lean idle set properly. drivability an issue, pops and backfires at times. Jetting changes made no difference. Suspected gasket air leaks. Should have done the starting fluid check but didn't.

While the engine is out took the manifolds off from the heads. The gasket as supplied from Redline is a thick phenolic (?) spacer with paper adhered to both sides. Found a defect in each one at both ports. Near the top of each port the phenolic has a defect - a void. The paper on each side covers the defect but does not seal the intake. Found evidence of a leak path at this area

Question - do I need the phenolic spacers ?? Can't find them on line as single replacement parts. Read of a need to keep the carbs from heat soaking but the manifolds are aluminum and are 5" tall. Don't see a need for them. Am I correct in this analysis ??

Was thinking of using .060" gaskets with Permatex red (min film deposit ) at this interface instead. What wisdom can you all impart.

Thanks for any and all input

Posted by: MikeM May 23 2020, 11:08 AM

Here's my 2 cents...
I had a terrible problem with fuel percolating in the carbs. After shut down the heat from the engine would be soaked up by the intake manifolds and boil the gas in the carbs. I'd say you definately need the phenolic spacers. I also used a spacer between the carbs and intakes which helped alot, along with proper float adjustment.
Good luck...
Mike

Posted by: Mark Henry May 23 2020, 11:20 AM

Use them.

Posted by: Al Meredith May 23 2020, 11:31 AM

I have had problems like yours, Found the manifolds (probably made in China or Mexico ) are not flat on the head side. If you have access to a belt sander , level the manifolds that should allow them to use a thin gasket if you want. AL

Posted by: cpavlenko May 23 2020, 11:37 AM

I had the same problem with percolation after a drive after installing Weber dual 40's. Installed the phenolic spacers between head and manifold. This helped, but now I'll give it a good drive in the heat. It's only been mid 70's here. I should have my car running by next week, temps going up to low 90's, will see how it does then. (Note) if I would've put them between carb and manifold, raintray would have to come out. Not enough clearance.

Posted by: North Coast Jim May 24 2020, 05:43 AM

Thanks Mark, always value your opinion. Where does one go to purchase these items. all I find are the standard gaskets not the spacers gaskets. Can you supply a source name or two for me. Thanks again.

Posted by: GregAmy May 24 2020, 06:09 AM

2 liter?

https://www.pelicanparts.com/More_Info/039129707M17.htm?pn=039-129-707-M17&bt=Y&fs=0&SVSVSI=978

Posted by: 80cap May 24 2020, 06:24 AM

I just had the same problem
I bought new gaskets from Pelican and noticed that the AA Performance head on #2 cylinder was not machined correctly. I carefully resurfaced the manifolds and installed them, torqued them to 15 Lbs. Next time I pull the engine down I will have the port welded , rebored and machined flat. I found the leak by spraying starter fluid at the base of the manifold.

Posted by: HAM Inc May 24 2020, 07:59 AM

Al, this issue with poorly finished manifolds has been a problem for the past few years.

CB manifolds used to be very nicely finished. No more. The castings stink and the machine work looks like it was done with a hatchet. They flow good, but that's about all I can say good about them.

There are only two manufactures currently making high quality T4 manifolds that I'm aware of. Both perform great on the flowbench.

Pierce makes some damn fine manifolds, and on the flow bench they have superior swirl characteristics to the CB.

I am not a paid spokesman and I am not friends or even know anyone at either company.

https://www.piercemanifolds.com/product_p/99004.822.html

https://www.csp-shop.com/en/brand-shops/intake-manifolds-csp-type-4-129-711-440k3-21127b.html

Posted by: porschetub May 24 2020, 03:50 PM

I have a new set of Empi ones and the casting are truly horrible,very poor runner/port alignment and would require some time to clean up the casting flash's...it's like they were never really finished.
I fitted the short ones (like CSP ) to a motor recently and they required very little work.