Monoblock

Flo · Post by **Flo** » Sun Jun 19, 2011 12:59 pm

Hello, first post here.
Just aquired a '52 G80s witha '51 Model 18 motor. It is fitted with a 28mm Concentric. Can't seem to get it running on very low revs. that well. Tonight, I shall clean points etc., but I want to replace the Concentric with a Monoblock. Tried a concentric on my old Super Rocket once, & ended going back to the clapped out Monoblock.
Anyway, the point is, would a 1-3/16" carb. work alright on it. They seem a lot more obtainable than a 1-5/32", it is only 1/32" bigger.

Samuel · Post by **Samuel** » Sun Jun 19, 2011 5:43 pm

Burlen Fuels Systems direct for any new carb to right specification for your engine

Flo · Post by **Flo** » Sun Jun 19, 2011 6:11 pm

I don't want really fork out for a new one. Think I might try the 1-3/16"

Duncan · Post by **Duncan** » Sun Jun 19, 2011 7:48 pm

It is an inch and 3/32" that you need, the 28mm concentric one you currently have is the equivalent size, the size went to one inch and 5/32" in 1954.

Flo · Post by **Flo** » Sun Jun 19, 2011 8:18 pm

The reason I was asking is because there is a nice one on Ebay at the moment. 1-5/32" might be more difficult to obtain. But it might be worth hanging on for, or a 1-1/8" monoblock.
Don,t believe there are any 1-3/32" monoblocks. If a 1-3/32" pre-monoblock came up, well could cost a lot.
The other reason to change from the concentric is that I don't like the looks of one on a fifties bike, it don't look right.
I don't want to spend a lot on this bike as it will never be worth it, as it is made up of parts from all through the fifties. It is just for riding & my obbsession of not being able to leave things alone.

wilko · Post by **wilko** » Mon Jun 20, 2011 12:12 am

Been using a 1 3/16 for years on my ironhead.

z1100r · Post by **z1100r** » Mon Jun 20, 2011 9:08 am

Any of the aformentioned carbs will work fine. Its all about jetting them correctly. To be honest your concentric should work better than a monoblock if it was jetted correctly. Just be careful you dont spend ages trying to get a 2-stroke carb to work. Alot of the cheap carbs about seem to have come off 2-strokes initially and they will run very rich if fitted to a 4-stroke.

I have a 1 1/8" 389 monoblock...on a 52 G80
Slide 3.5
needle 2nd notch down
needle jet 106 long with holes
main jet 200
primary jet 25
air screw 2 turns out
no airfilter

Its slightly on the rich side anywhere other than flat out but that makes life alot easier everywhere else, starting, tickover, mid-range cruising etc. I just spent the first week of ownership sorting out the carburation, its gone from dreadful to superb with just a main jet and a slide change. I cant stand badly carburating bikes, they are horible to ride.Edited by - z1100r on 20 Jun 2011 08:10:24 AMEdited by - z1100r on 20 Jun 2011 08:34:09 AMEdited by - z1100r on 23 Jun 2011 09:31:30 AM

Trefor · Post by **Trefor** » Thu Jun 23, 2011 1:00 am

I have a 1 1/8 monobloc on a 52 G80S
Slide 3.5
needle top notch
needle jet 106
main 250
primary 30
air screw 3 out
air filter
The description z1100r gives of how his bike runs would describe mine. I think wear in these old carbs would be a factor.

z1100r · Post by **z1100r** » Thu Jun 23, 2011 10:31 am

Trefor...climate and height above sea level will have a big effect aswell maybe - especially on the main jet. Ooops ..corrected my needle jet number. I might try dropping the needle and using a larger primary - when I can get one - but to be honest it runs very well now so i'm kinda not in a hurry to change it.

Trefor · Post by **Trefor** » Fri Jun 24, 2011 3:26 pm

I agree z1100r, if the bike's going well.. after all it's 59 years old can you make it go that much better? There's a tempation to spend time fiddling when you could be riding.