Carbs for a 378cc cb360

[Takeawaykitty]

Alright the police recovered my cb360 that was stolen a while back and well it was trashed. Busted fin, smashed tank, they dumped glitter on it and it had clear coat and over spray all over it My poor motor only had 3200 miles on it. But some how they managed to blow a hole clean through one of my pistons.

But anyway i took this as a sign that it was time to use the NOS GS850 pistons I have. the cylinders just got back from the machine shop and I can't help but wonder what people have had the best luck with carb wise with the 2mm over bore I'm using pods and a Mac 2 into 1 but what has everyone tried/using VM28s? VM30s? stock? And what are your thoughts?

 

[irk miller]

I used VM28's on mine. The stock carbs with PJ mods also work well.

 

[Takeawaykitty]

I used VM28's on mine. The stock carbs with PJ mods also work well.

Thanks for your input. I was leaning in the direction of buying some VM28s and giving them a shot. I just ordered a pair along with other the other bits. Do you have any recommendations on roughly what jet sizes I should start tuning with?

 

[irk miller]

Here is where I was on that bike:

Slides are 2.5 cutout
5F21 needle
P-0 Primary needle jet
130 main jet
30 slow jet

That's where my notes end on that carb setup. Can't remember if I went back to an O-8 Primary needle jet or went smaller on the idle. Regardless, that should be a decent baseline.

 

[teazer]

Irk,

By any chance did you try and bleed type needle jets on that bike? We had a pair of VM26s on a 240cc CB160 race motor and it made more power, was smoother and used less fuel with bleed type nozzles. On the dyno we had excess HC (fuel) even with the correct Co and CO2 levels with primary types and concluded that was excess fuel not burning but going straight down the pipe. Finding the correct nozzles wasn't too hard and may clean up midrange.

Our limited testing revealed, not surprisingly, that a Honda needs fine atomization. Primary types create larger fuel droplets than bleed (emulsion) designs. Fuel doesn't burn as a liquid. It's teh vapor on the surface of each droplet that burns and for thr same volume of fuel, smaller droplets have greater surface area and therefore burn faster giving a faster pressure rise and more complete combustion so more power and less fuel needed. At least that's my theory.

That's why more fuel injectors have more small holes to get even smaller droplets and more complete combustion. Higher feed pressure also helps with that process.

 

[irk miller]

Irk,

By any chance did you try and bleed type needle jets on that bike? We had a pair of VM26s on a 240cc CB160 race motor and it made more power, was smoother and used less fuel with bleed type nozzles. On the dyno we had excess HC (fuel) even with the correct Co and CO2 levels with primary types and concluded that was excess fuel not burning but going straight down the pipe. Finding the correct nozzles wasn't too hard and may clean up midrange.

Our limited testing revealed, not surprisingly, that a Honda needs fine atomization. Primary types create larger fuel droplets than bleed (emulsion) designs. Fuel doesn't burn as a liquid. It's teh vapor on the surface of each droplet that burns and for thr same volume of fuel, smaller droplets have greater surface area and therefore burn faster giving a faster pressure rise and more complete combustion so more power and less fuel needed. At least that's my theory.

That's why more fuel injectors have more small holes to get even smaller droplets and more complete combustion. Higher feed pressure also helps with that process.

After some replies in my build thread from you and PJ, I did in fact go to bleed type needle jets. Those size numbers, if I'm remembering correctly, are for the 175 series needle jets.

 

[teazer]

That makes sense. 175 series are swappable with 169 (primary) types. They are the same height and flange thickness and both take hex main jets.

 

[livingdead]

I have a set of stock 1973 cb360 carbs .. Very clean . Make mean offer