Topic: Maduncle's brat style CB750F - now called "The carb eater"

[Syscrush]

Oh, and I'm just as curious as Cliff so I've just bought this on EBay, so Cliff and I will be able to compare modern carbs with 40 year old POSA injectors soon. Cheers, Terry.

NICE!!!

[jaguar]

size is not the only thing that governs what a carb can feed.

I missed out on a rack of 4 posa/lake "carbs" last year and still kicking myself


The posa carb for your single set up isnt that had to find or really that expensive

[jaguar]

But.....how are they to live with on the street?
cant imagine that they are civilized

[Syscrush]

But.....how are they to live with on the street?
cant imagine that they are civilized

I've never had one, seems there are more myths than first-hand experiences floating around.  I've heard different things from people who claim to have had them.  Some say that they're good for WFO drag-racing and nothing else, one guy said it was great for light-throttle and that he got 90mpg at highway speed on his Harley. 

It's just conjecture on my part, but I have a feeling that the fact that the tuning is so different from a regular carb means that it's more likely that the folks claiming that they're no good for the street had them set up wrong.

However, on the other hand I don't think that the complexity and all of the circuits & jets on a good carb are there for decoration.  I'd be surprised if a Posa/Lectron could be made as streetable & smooth as a good CV carb.

[maduncle]

But.....how are they to live with on the street?
cant imagine that they are civilized

I've never had one, seems there are more myths than first-hand experiences floating around.  I've heard different things from people who claim to have had them.  Some say that they're good for WFO drag-racing and nothing else, one guy said it was great for light-throttle and that he got 90mpg at highway speed on his Harley. 

It's just conjecture on my part, but I have a feeling that the fact that the tuning is so different from a regular carb means that it's more likely that the folks claiming that they're no good for the street had them set up wrong.

However, on the other hand I don't think that the complexity and all of the circuits & jets on a good carb are there for decoration.  I'd be surprised if a Posa/Lectron could be made as streetable & smooth as a good CV carb.

Well,

The great thing is that Terry and I will both be able to provide feedback on the POSA manifold set up - him with an original POSA carb and me with a brand new Mikuni carb.

[Psychonaut]

I never heard of a Posa until this thread. I did a search and found more complaints than praise. I just wanted to through this out there for a heads up to those looking at them. I know some Z car guys love SU carbs other hate them, maybe this is a similar thing I don't know.

http://www.shovelhead.us/forum/showthread.php?t=79431

[maduncle]

I never heard of a Posa until this thread. I did a search and found more complaints than praise. I just wanted to through this out there for a heads up to those looking at them. I know some Z car guys love SU carbs other hate them, maybe this is a similar thing I don't know.

http://www.shovelhead.us/forum/showthread.php?t=79431

Yep,

I found that colourful forum too when researching the POSA.

Like I said, Terry and I will be able to report back on the pro's and con's of log manifolds with Mikunis and log manifolds with POSA's.

The rate we are going - it could be a joint PhD!

[Retro Rocket]

The rate we are going - it could be a joint PhD!

P osa
H onda
D evelopment

 

[maduncle]

The rate we are going - it could be a joint PhD!

P osa
H onda
D evelopment

 

P osa ble
H onda
D isaster

 

[Syscrush]

The great thing is that Terry and I will both be able to provide feedback on the POSA manifold set up - him with an original POSA carb and me with a brand new Mikuni carb.

Agreed, can't wait to see some first-hand results!

[Retro Rocket]

The rate we are going - it could be a joint PhD!

P osa
H onda
D evelopment

 

P osa ble
H onda
D isaster

 

 

[Terry in Australia]

size is not the only thing that governs what a carb can feed.

I missed out on a rack of 4 posa/lake "carbs" last year and still kicking myself


The posa carb for your single set up isnt that had to find or really that expensive

G'Day Jag, what was the rack of 4 carbs for mate? I've seen a POSA twin carb setup (someone here posted the pic I think?) and I'd love to score one of them, but they're rarer than rocking horse schit! Cheers, Terry.

And for everyone else, yep, neither Cliff or myself are expecting huge horsepower gains or incredible fuel economy, we're just trying something out. For fun.

I've got a set of 33mm Mikuni smoorthbore carbs set up for a CB750 head for my 1060cc engine, another set of 32mm CV's and a set of 31mm CR's for my 836cc engine, so it's not like I'm starved for choices, I just think this 70's era setup is kinda cool, and will be really cool if the bike actually runs and is rideable!

At least I'll have something new to post in the "What did you do to your bike today?" thread! Cheers, Terry.

[Retro Rocket]

Build a chopper Terry, and wack the posa on that. You know you want too.....

[jaguar]

Yeah it was a rack of 4 posa(actually i think they were lake) injectors that went right onto a cb750 head.
cool set up, sold on ebay for about $350.  ill dig around and see if i saved a picture

i have seen posa cast log manifolds with a single or dual injector.

[Terry in Australia]

Build a chopper Terry, and wack the posa on that. You know you want too.....

Ha ha, I'd love a CB750 chop Mick, I bought a Santee frame and springer front end many years ago, but gave them away (yep, for free, boohoo) when I was getting posted and the army wouldn't pay to ship them for me. Have you seen the CB750 trike frames from CycleX? I'd love a trike more than a chop, but the shipping would probably kill the deal. Cheers, Terry.

http://www.ebay.com/itm/Honda-cb750-Trike-frame-and-rear-end-Custom-chopper-/200655963600?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item2eb80705d0

Yeah it was a rack of 4 posa(actually i think they were lake) injectors that went right onto a cb750 head.
cool set up, sold on ebay for about $350.  ill dig around and see if i saved a picture

i have seen posa cast log manifolds with a single or dual injector.

Thanks mate, and if you see any more, I want one!

[maduncle]

Yay - on the bike for a ride tomorrow morning, give it a goos spurt before pulling it off the road to do the single carb project.

I need to actually buy the carb first, either here in Australia via a Mikuni dealer or off eBay.

This should make a good Christmas project.

[maduncle]

After yesterday's ride to work and back I just have one small question -

... how hot should a CB750 oil tank get?

It gets hot enough to almost burn my skin through my jeans, not so hot that the oil bubbles or the paint softens on the oil tank, but still pretty darn hot.

I will get an oil temp gauge to mount off the engine, that way I can see what is happenning - other than that, I will start to look at cooling and tank relocation options.

One possibility is a cylindrical tank slung under the frame below the fuel tank and above the POSA log manifold, there might be room between the carb and the head. Could get a little messy with plumbing but I could then run a cooler off the tank too.

Fun.

[Terry in Australia]

G'Day Cliff, the answer is.......... (drumroll)........... fcuking hot!

Water boils at 212 deg F, but engine oil often runs at 270 deg F or higher. On a hot day in a Melbourne summer, (like today, for instance) the oil tank will get so hot that you can't touch it, and the OEM sidecover has a dual purpose: 1, to hide the oil tank, and 2, to provide a heat shield so you don't burn your leg.

You don't want to run a hot oil tank too close to your carb or fuel tank mate, you want your fuel and the air around your intake to be as cool as possible. Make yourself another seat with an oil tank incorporated into the hump, just make sure you leave an air gap so you don't burn your bum! Cheers, Terry.

[maduncle]

Thanks Terry!

I might use the right hand leather pannier I have spare and see if I can't convert it to an oil tank cover...

(Six hours later)...

So - it works like this now.



Oil tank side - now you see it.



Now you don't.

I used the right hand side leather pannier I had made months ago when I got the left hand side one done. I just cut the back out of it and mounted it using the two top oil tank mount bolts. Now it hangs over the oil tank and gives me a bit more insulation from the hot oil - and it matches the pannier on the left hand side.

[Syscrush]

That's beautiful.  I generally dislike 750's due to the oil tank alone (I'm funny that way), but damn if that doesn't look great.

[seanbarney41]

now you stick a potatoe in there, go for a ride...an hour later, fresh baked potato!

[hapakev]

Very slick!

[Flying J]

Well done and very original. I bet you will see people start copying that idea. I too do not care for 750s because of the oil tank. But my taste is a little off. Looking good

[maduncle]

Thanks guys,

There could almost be a market for leather "pannier look" side covers for 750's - I might try making another pair.

I really want this bike to have that 50's "big Brit" look, so the panniers help to achieve that (IMHO).

Just imagine what the single carb will give to the look!

[CBGhia]

I love this bike.  The seat is exactly what I was wanting to do this winter so that I can finally 2 up my bike.