Bike Carb Manifold Question

[agent_zed]

Hi,

so just thinking about finally getting round to putting the bike carbs on my old pinto to hopefully give it a bit more life.

 

Need to make a manifold so am getting a flange cut so i can weld it up to suit my carbs etc.

 

My first question is do i go stainless or mild (prob a dumb question but just checking stainless is the best option)

 

Second what size holes should the flange have? my carbs are 38mm OD outlets which luckily is a standard stainless tube that i happen to have. Is that ok for the holes to be that size into the engine or do they need to be flared to match to the head (don't know what size that is to be honest iam assuming bigger).

 

will be adding vacuum take off into a plenum for brakes and dizzy.

 

I'm hoping bike carbs will get me a bit more ooomph as it doesn't seem to want to get past 4.5k at the moment on the 28/30 weber and i can only think its not getting enough fuel, timing checked and advance is set correctly. Running 2ltr camshaft in 1.6 and just fitted 4-1 exhaust.

 

Thanks

[blue]

The holes in flange shoud be same size as head (best) or smaller never bigger as the air will hit "the head" and you will lose anything you might gain

also if your taking a vac from them it needs to be from all four carbs not just one as you will cause that cylinder to run leaner then the rest

[Guest 2b cruising]

It's not to bad going from small diameter to larger diameter.

Have you investigated the reason for low reving. It could be something very simple like furred up main jets. Or week mixture. The jets fur up a little every time they dry out. Just try running aw elders nozzle cleaner through them. They are not expensive and work wanders.

It is not the wrong carb because that is the standard for your engine. Hence it should run to max revs.

Has someone fitted smaller jets than standard.

Are there any leaks from the manifold drawing air after the carb. ie, it is common that the base of carb warps through people over tightening.

The gasket between head and manifold can leak.

If you have servo, it or the vac tube can leak. The one way valve can leak.

If you fit bike carbs you will need to drill out the jets to the correct size. On 2 ltr it is 1.3 mm. Sorry I don't know the correct size for the 1600.

Whatever you decide, I would persist in getting it to run properly first. This could save you scratching your head after the conversion if it doesn't cure the fault. You could then be taking off the bike carbs in case it is them.

Finally you will have to make a plenum and join all vac pipes to it to run your servo otherwise you could possibly set the mixture wrong on one cylinder, causing valve or piston burn out.

Also you will need to improve you exhaust from standard manifold to 4-1 to get optimum benefit from bike carbs.

I hope some of this information is helpful to you. Regards, Ken.

[agent_zed]

thanks guys. yeah i've taken the carb apart a fair few times over the years. occasionally it seems to run better so i think it gets crap in them. Need to fit a fuel filter as priority either way. I'm kind of convinced its the carb thats restricting it. At the moment it's surging a bit on tickover so i think its getting fuel and then not.

 

I think i'll get it made at 38mm holes then so i can just use standard pipe and it's equal from the carbs to the head.

 

yep exhaust is now a 4-1 manifold with a 2inch main pipe straight through exhaust can

 

not expecting 0-60 in 5 secs from a 23yr old 1.6 pinto but if i can get it a bit better if would be nice and all part of the fun. Manifold should be around £35 for me to knock up at a rough estimate as i have left over stainless welding wire and bits of pipe from the exhaust.

 

Once its on and running i'll prob rolling road it/have it checked to make sure its not over or under fueling. Does the colourtune equipment allow you to see if its burning correct at various revs? or is it just basic tickover?

[Guest 2b cruising]

 

They are just a basic running set up. Good if you can see the flame clearly. With carbs, if the mixture good on tick over it should remain good throughout the Rev range. Throttle bodies can be controlled differently through the management system.

[Dave R]

i have a stainless pinto inlet flange laying here doing nothing, surplus to requirements

[agent_zed]

oh cool drop me a PM with a price if you are looking to part ways with it.

[Stewart]

It's not to bad going from small diameter to larger diameter.

Have you investigated the reason for low reving. It could be something very simple like furred up main jets. Or week mixture. The jets fur up a little every time they dry out. Just try running aw elders nozzle cleaner through them. They are not expensive and work wanders.

It is not the wrong carb because that is the standard for your engine. Hence it should run to max revs.

Has someone fitted smaller jets than standard.

Are there any leaks from the manifold drawing air after the carb. ie, it is common that the base of carb warps through people over tightening.

The gasket between head and manifold can leak.

If you have servo, it or the vac tube can leak. The one way valve can leak.

If you fit bike carbs you will need to drill out the jets to the correct size. On 2 ltr it is 1.3 mm. Sorry I don't know the correct size for the 1600.

Whatever you decide, I would persist in getting it to run properly first. This could save you scratching your head after the conversion if it doesn't cure the fault. You could then be taking off the bike carbs in case it is them.

Finally you will have to make a plenum and join all vac pipes to it to run your servo otherwise you could possibly set the mixture wrong on one cylinder, causing valve or piston burn out.

Also you will need to improve you exhaust from standard manifold to 4-1 to get optimum benefit from bike carbs.

I hope some of this information is helpful to you. Regards, Ken.

what is aw elders nozzle cleaner ?????

[Dave R]

a welders nozzle cleaner.....

[Guest 2b cruising]

Fankyew.

[Dave R]

agent_zed .. clear your in box if you want an email!!!

[agent_zed]

oops sorry cleared now. didn't realise that if you press delete and it puts a red 'delete' next to the message then you have to tick the box and delete again to actually remove it. doh.

[agent_zed]

next question is there a optimum length for the tubes on the manifold? longer better or shorter? should they be the same length as the carb?

 

Iam not too worried as they won't be equal length anyway but might as well be somewhere nearer right