R1 carbs - mid conversion questions

[chappers1.3]

Been reading alot about this on various sites so decided to try it myself. I got a set of carbs, with airbox and fuel pump all off an R1 for 130quid which i didnt think was too bad.. decided that Bogg Brothers can stick their 190quid+vat manifold and have opted to make my own one......... so started....

Engine is a 2ltr 8v with a 1.8 big valve head, i remembered i had the original manifold (1.8) to hand so i destroyed it with an angle grinder.... ended up with quite a nice face plate that is ready to bolt onto the head with all holes in correct place so that has saved me time making templates etc. all i need now is 4 tubes welding onto the face plate at the correct angles to suit the carbs. ports on manifold are 90 - 90 - 90mm centre to centre where as carbs are spaced 75 - 85 -75. this means middle 2 will be near enuf straight and outside 2 will have to be angled in by about 20mm each. ideally i would like carbs about 90mm away from head - dont knwo where i read it but thats what i am going to try n make them to.

Now my questions?

The ports on my inlet are 37mm.... R1 carbs have a 40mm port. so i will have to make the tubes with a slight cone if i want to match them up using the R1 adaptors? this will give the manifold a slight venturi effect speeding up Airflow into the engine... can anybody think of a problem with this?

or my 2nd idea was.......

get some pipe as close to 37mm I/D cut to length (will be abit shorter than 1st idea by maybe 40mm or so) and and just use some silicon hose to connect the manifold to the carbs. i know that this 2nd idea could possibly reduce flow - again anybody any ideas???

also - brake servo vacuum pipe....... of course i will need one of these adding the the manifold, i am quite stuck about how to add this, and where to put it.. thinking that i can just take a feed off one of the manifold tubes??? is this how its done on your normal weber manifold for carbs/throttleboddies?

thanks.....

[Adam]

For the brake servo, just fit a union to one of the manifold runners.

Make sure the tubes match the head ports for size, as you dont want the head/inlet flange "presenting" itself to the incoming air fuel.

You can use samco hose to fit the carbs, but you would probably need a stepped reducer hose to fit a 40mm carb, and a 37mm tube, unless you took up the extra 3mil on the tube somehow.

[chappers1.3]

does samco hose collapse if used on inlet, because its creating a vacuum? coz isnt it normally used for boost pressure?

I dont think i should have too much of a problem as its only going to be 50mm worth of hose i should imagine, going to find some pipe today that will suit the ports on my flange.. thinking a 40mm O/D with wall thickness of 1.5mm should do. then going to flare out the ends nearest the carbs to try and reduce the step from 40-37 so is nearer 40-40.....

will let you knwo how it goes...:eek:

[Adam]

Vacuum hose has to be thick walled to stop it collapsing on itself.

[Welsh Dan]

How difficult would it be to port the head and flange out to 40mm?

If you did that, you could then use 40mm ID tubing, use trigonometry to get the spacing right then weld away :).

[chappers1.3]

think porting the head to 40mm is abit too much 4 my machining skills. wud b gud tho. still looking for piping, no joy at moment!!

been reading the vaux tech guide about the carbs - it says you have to drill the jets to 1.8mm? but also mentions some weber jets that would suit - anybody used these - if so what size jets are u using?

[Welsh Dan]

Could you countersink the flange to make up the 3mm gap like so?


----------\ /---------- Flange carb side
-----------\ /----------- Flange head side
------------| |----------- Head

[chappers1.3]

maybe - its an idea....
will see what sort of pipe i can get hold of, if i need to blend/countersink i'll give it a go....

will keep u informed how it progresses, thanks for your help.

[craig green]

Opening out the head to 400mm (if poss) would drop gas speeds & lose power & torque.

You could use short lengths of rubber/silicone pipe to mount carbs to the inlet, my Dads Mikuni carb conversion is done the same way. However again if there is a step against the wall of the carb or inlet than it will sap power too.

I say get someone who can TIG weld alloy to create a pukka bolt on inlet manifold for the carbs.