Motorcycle carbs on 2.0 S

[Cone8v]

Hello, its my first time posting here. 

I bought a 1979 manta b 2.0s a couple of years ago. Im doing the body work and its coming along nicely, the engine runs but it has a small carb making around 80-90hp and i want to change that. There are no used weber 40 mm's in my country for some reason, the new ones are around 500eu a piece from a neigbhouring country.

Im 19 and i dont have a thousand euros to drop just on the carbs. My dad owns a car body shop so im doing all the body work/welding myself, only paying for materials. Im also working as a mechanic so im doing everything by myself. Dad has owned his manta since he was 18 so i have a ton of spare parts and his knowledge. Without that id never get to where i am right now with the project. 

I thought of getting motorcycle carbs, for example the yamaha r1 carbs. I would separate them, weld the separate intake pipes and make a throttle linkage, weld the vaccum line for the brakes and connect them to the intake pipes . The brake servo pump is on the left side where the steering wheel is so i wont have problems with fitment of the carbs.

Ill be changing the valve seats in the future because these ones are made for an old type of fuel that had lead in it, might fit bigger valves if i find them, all the parts for this engine are insanely expensive or not available. Thats why i want to build the carb system with bike carbs. 

I dont know which jets i need to feed this engine. Does anyone have specs for the idle jet, main jet etc?

The stock jets feeding the 1000c bike engine are surely not enough for the 2.0 right? 

[Jonathan Pounsett]

Welcome @Cone8v.

 

I can’t advise you about whether bike carbs are a good combination with the Manta cih engine, but what I would say is proper investment in developing car carburettors stopped years ago, unlike bike carbs that are still being improved every day.

Post some photos as soon as you get the chance - we all love a project and you’ll get loads of comments and helpful advice.

[611]

Im sure there must be a tread somewhere on the site as i remember someone having fitted as set of R1 carbs on a manta engine (might have been the Vauxhall lump) 

and from memory i think they had lots of problems getting the fuelling right as the bike ones were never design for an engine that big in capacity.

I might be wrong but im sure that was the main issue.

Don't know how easy/hard it is to search for an old thread on this topic?

 

Andy

[Cone8v]

15 hours ago, Jonathan Pounsett said:

Welcome @Cone8v.

 

I can’t advise you about whether bike carbs are a good combination with the Manta cih engine, but what I would say is proper investment in developing car carburettors stopped years ago, unlike bike carbs that are still being improved every day.

Post some photos as soon as you get the chance - we all love a project and you’ll get loads of comments and helpful advice.

Here are some older pics, ill take new ones soon. 

 https://postimg.cc/gallery/Yvft2Yj

13 hours ago, 611 said:

Im sure there must be a tread somewhere on the site as i remember someone having fitted as set of R1 carbs on a manta engine (might have been the Vauxhall lump) 

and from memory i think they had lots of problems getting the fuelling right as the bike ones were never design for an engine that big in capacity.

I might be wrong but im sure that was the main issue.

Don't know how easy/hard it is to search for an old thread on this topic?

 

Andy

I tried hard to find the forum post but to no avail, the person did mention his bike carb build and even sent a pic of them installed on the engine but i cant find his original post, if he ever made one. The users name was Shug that posted the pic, i think. 

[Moonmonkey]

I don’t think there is an issue putting bike carbs on a larger cc engine, a lot of the autograss guys run bike carbs on red top C20XEs so I would think a CIH would be ok in theory

Agree they would need to be well balanced, but they’re a cheap way to 4 x 38 mm carbs.

If you think about it, the power is coming from the chemical energy in the fuel, so with the right pumps I would think they are ok. . I remember reading Dave Walker in CCC saying chemically you needed 1/2 pint of petrol per bhp per hour (assuming 14.8:1 ratio). After reading this I disconnected my fuel line from the facet red top and ran the pump and timed it into a measuring jug from my Mums kitchen. Didn’t go down well, but I was getting enough fuel for 360bhp on a 240bhp engine.

One issue maybe how close the CIH inlet ports are and how good a flow you can get through the manifold in the space, as 4 x R1 carbs might be an awkward width unless you can separate into pairs.

If you only want a 2 choke carb a Weber 38DGAS (3.0 litre Capri/Granda) is a good compromise and fits with a bit of machining on the standard 1900/2000 inlet manifold. Used to use on on a Road Rally spec 2.0 CIH running 130/135bhp. 

 

 

 

[Cone8v]

10 hours ago, Moonmonkey said:

I don’t think there is an issue putting bike carbs on a larger cc engine, a lot of the autograss guys run bike carbs on red top C20XEs so I would think a CIH would be ok in theory

Agree they would need to be well balanced, but they’re a cheap way to 4 x 38 mm carbs.

If you think about it, the power is coming from the chemical energy in the fuel, so with the right pumps I would think they are ok. . I remember reading Dave Walker in CCC saying chemically you needed 1/2 pint of petrol per bhp per hour (assuming 14.8:1 ratio). After reading this I disconnected my fuel line from the facet red top and ran the pump and timed it into a measuring jug from my Mums kitchen. Didn’t go down well, but I was getting enough fuel for 360bhp on a 240bhp engine.

One issue maybe how close the CIH inlet ports are and how good a flow you can get through the manifold in the space, as 4 x R1 carbs might be an awkward width unless you can separate into pairs.

If you only want a 2 choke carb a Weber 38DGAS (3.0 litre Capri/Granda) is a good compromise and fits with a bit of machining on the standard 1900/2000 inlet manifold. Used to use on on a Road Rally spec 2.0 CIH running 130/135bhp. 

 

 

 

Getting any proper weber carb is not an option, cant find them used here, only new ones in a neigbhouring country. The oldtimer scene is not that popular here, people are into hatches and fwd cars powered by dohc 16v (c20let, z20let 1.8t vw, 2.0 tfsi etc. ) 

I found a set of yamaha r1 year 2000 carbs (40mm each) for 130 eu, i would make two intake manifolds and split the carbs in sets of two. Then id draw the intake plate and get it machined so that its perfectly flat. Id weld the pipes to the plate and ill probably make metal flanges with those intercooler pipe rubbers to tighten the carbs to the intake manifold. I dont know what the length of the pipe + plate should be and i dont know if the jets in those yamaha carbs are enough to feed the engine. 

Ill get the yamaha r1 fuel pump and a presure regulator. Thank you for the info about how much fuel it needs to pump, thats one check off of the list. 

I gotta find what jet size for each carb, and the length of the intake manifold. 

 

[Moonmonkey]

R1 carbs are made by Mikuni. There are some Mikuni performance companies on the net who may be able to help:

http://mikunipower.com/RS01.htm - USA

http://www.motocarb.com-UK

[Jessopia74]

Perhaps give https://www.boggbros.com a call, they are really helpful and have been doing carb mods/kits for years so they will even probably be able to help with the jets needed.

But the carbs will be fine, they are plentiful large enough for 2.0 but will need jets changing and the tweaking of air needles etc . 

[Cone8v]

3 hours ago, Jessopia74 said:

Perhaps give https://www.boggbros.com a call, they are really helpful and have been doing carb mods/kits for years so they will even probably be able to help with the jets needed.

But the carbs will be fine, they are plentiful large enough for 2.0 but will need jets changing and the tweaking of air needles etc . 

 

5 hours ago, Moonmonkey said:

R1 carbs are made by Mikuni. There are some Mikuni performance companies on the net who may be able to help:

http://mikunipower.com/RS01.htm - USA

http://www.motocarb.com-UK

Thanks guys, ill ask about the stuff i need, ill do all the work myself because im far away from UK and because of my budget. Ill post updates as soon as i start building.