Carb Gaskets

[alfadave]

Just thinking about replacing my mech fuel pump........

And maybe taking the carbs off for access.

Got me wondering about spacer plates.

I've got these with Thakeray washers.

But it seems Misab plates are an alternative?

I understand these are something to do with prevention of vibration/frothing?

Are they really necessary?

Can I simply fit gaskets between my Webers and the manifold?

Probably lots of cans of worms on this.

But my daily runner Alfasud has the twin downdraught carbs fixed to the manifold using gaskets. Alfa Romeo

built a lot of these, seemingly without frothing problems

[MarkDa]

Guess a straight 4 vibrates more than a nice boxer 4?

[SENC]

I believe they require o-rings (preferably viton) or misab plates between the carb and manifold AND Thackeray or the rubber alternative washers.

[bitsobrits]

The spacers plates with O-rings really are necessary for proper carb function, at least on the Lotus twin cam.

Think about it: would the ever parsimonious Colin Chapman have spent money on these if they weren't required?

He would spend on true performance enhancers and occasionally on blingy bits that helped sell the cars, but pretty much never on functional items that no one would miss if they weren't there.

[elans3]

They are required, along with thackeray washers or the Cosworth type rubber bobbins and cup washers. The thackeray washers or Cosworth type mounting rubbers should be tightened until there is a gap of between 25 - 40 thou between the coils of the washer, or the cup washers. The instruction says 0.040", but I always thought that was a bit slack, and have set mine to 0.025" for the last 40 years or so..
Case in point. A friend of mine fitted 40 DCOE's to a Spitfire which had other mods to cylinder head and camshaft etc. When he first put it together he rang me to say that it went well, but at certain revs, he had a bad misfire. I went round and noticed that he had his thackeray washers tightened up solid. I slackened them off and told him to take it out again. He came back ten minutes later, beaming all over his face. "What did you do ?" he said.
He had the fuel frothing problem that occurs when there's no compliance in the joint between inlet manifold & carbs.
Seen it also on a friend's TR6 on triple DCOE's.
Spacer plates & O rings, or Misab plates, doesn't matter which. I've used Misab plates for years now, and prefer them , they're less fiddly.

[alfadave]

OK points taken!

Can I use misab plates along with Cosworth rubber bobbins and cup washers?

Seems the simplest solution?

[rgh0]

Rubber on top Thackerys on bottom. If Rubber all round the lower rubbers perish due to fuel attack. If Thackerys all round the upper Thackerys crack due to vibration and weight of the carbs. This is the wisdom according to Dave Bean Works for me



cheers
Rohan

[2cams70]

I prefer the thick aluminium spacers with machined grooves for proper "O" rings rather than Misab plates. You can get them from QED. With these plates you can use good quality Viton "O" rings rather than the usual Nitrile. Viton is what all the OEM's use for fuel injector "O" rings. I doubt Misab are using Viton as their "O" ring material.

https://qedmotorsport.co.uk/product/car ... ate-alloy/

[elans3]

OK points taken!

Can I use misab plates along with Cosworth rubber bobbins and cup washers?

Seems the simplest solution?

Yes, no problem, I have the Cosworth rubber type all round on my Alfa Twincam, been there for 4 years with no deterioration of the bottom rubbers, BUT my carbs don't leak or spit petrol. I spent endless hours getting them to be just right.
Probably safer to go with what Rohan says above, or change the bottom rubbers every so often.
Next time I have the carbs off the Elan, I'll change the thackerays, plates & O rings to the rubber bobbins and Misab plates.