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Old 06-28-2015, 10:07 AM   #1
Mike Britton
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Default I would like practical opinions on the Monoblock

So.... We all know how just when we get started on a project life seems to get in the way.
I'm at a point in my Bonnie rebuild where I need to spend some serious money, when the sunroom on my house decides to emulate the Titanic. Buckets, and even a trash can litter the floor in the room to hold back the monsoon that Texas is suffering.
Why am I wasting your time you say? Well here's the deal.
In addition to the 68 Bonnie, I have a 56 6T that was built into a flat track bike just at the cusp of the AMA ruling concerning brakes. Maybe 69 or so?
It's a sweet play bike, and more fun than monkeys.
.40 over, 11-1 hepolites, Connelly flat track cams, it's all there.
Since I have no money, I have decided to start on a "rebuild/repaint" of "Frankenstein" in conjunction with the Bonnie.
I had the carb off recently to clean and got to thinking.

OK, I'm finally getting to the point. What do you guys with practical knowledge think of the Monoblock as opposed to the later concentrics that are on my unit Bonnie?
My Monoblock is a 376/002 and shows wear on the slide, but still seems to run fine, and idles as well as the serious overlap on the cams allow.

What are the opinions on spending the money to rebuild the Monoblock as opposed to replacing it with a later Amal? I'm a bit concerned that the old carb is a bit worn out.
A trip to search on this subject is a lot like starting a political argument.
I would just like to hear from you guys that actually are dealing with customer's bikes that still have the early carb. Shall I just don't fix it since it ain't broke? Thanks, Mike
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Old 06-28-2015, 11:55 AM   #2
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Default Re: I would like practical opinions on the Monoblock

...I had a type 6 the I tried a monoblock in my old pre unit 500. I replaced main jet, needle, clip, float, needle of the float, gaskets and throttle slide. Then sleeved the carb (the type 6); then used an sleeved slide...then paid around 50 s pounds (16 years ago or so) and bought a new concentric from UK and forgot all the hassles.
Here is more expensive to buy these kits or bits due to international shipping and customs taxes so is wiser to get a new carb but in your case you can order locally so may be is good to try smaller changes and do not spend too much.
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Old 06-28-2015, 02:32 PM   #3
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Default Re: I would like practical opinions on the Monoblock

IMO,

forget about sleeving and replacing every other part in that old monoblock at about 80% of the cost of a brand new carb, ...a hassle free carb.... that will run fine for another 40 years.

about 50% of the re-sleeved carbs I see, never tune in right...just save up the money and buy a new one.

(and IMO...it will run stronger with a 389 monoblock anyway... The setup I like is an 1-1/8" 389 body with about a 300-320 main jet, 106 needle jet and a 3.5 slide, open up the manifold a bit if needed to match the carb)
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Old 06-28-2015, 02:55 PM   #4
Mike Britton
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Default Re: I would like practical opinions on the Monoblock

Thanks, Tony. I know that when we replaced the badly abused concentrics on my Bonneville it became a different motorcycle.
I was leaning toward another 930 for the pre-unit because they are such newer tech, and they work so well on the Bonnie.
I don't feel any need to be historically correct on the race bike, it's a bitsa after all.
But then I see you wanting me to source a decent 389? Better than the 930?
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Old 06-28-2015, 11:06 PM   #5
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Cool Re: I would like practical opinions on the Monoblock

Whether you decide on a 376 or a 389, you can get both new from Burlen ( AMAL ) for a decent cost and with Stay-Up floats and all the other modern goodies they provide. I run a 376/42 on my 1957 6T and it is an original carb and works fantastically. Not a race bike but nevertheless works flawlessly. You need to look at your port opening size on your head and see exactly which intake manifold you have fitted, whether E3304 or later and match your carb to the intake, etc., etc., or you can buy an intake to match what carb you get if you don't have it already. A few possibilities, variables.

http://amalcarb.co.uk/monobloc-series.html
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Old 06-29-2015, 08:51 AM   #6
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Default Re: I would like practical opinions on the Monoblock

Thanks, Jon! I do know that my manifold is an E3304. I have Burlen on my favorites, and looked at the new 376-389's. This bike won't make any full throttle runs any more, I really got tired of falling off of it!
You are talking about port matching, I worked in an automotive machine shop back in the Jurassic era so I'm familiar with port matching on automotive intakes. I'm assuming it's the same for Triumphs?
A new carb and a repaint is about all this old warrior needs to chase the kids in the neighborhood once in awhile, so it looks like a new 389 might be the thing.
I do know that single carb is a joy to tune compared to the twin carbs on my Bonnie!
I thought about one of the aftermarket twin manifolds for that head just because twin carbs on a pre-unit look so sexy, but then I thought about having to tune it. And since it's just a play bike, I really don't need all that carburation. With a 58 tooth sprocket the bike has plenty of grunt!
Should I go directly to Berlen, or is there someone in the U.S. I should go to?
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Old 07-01-2015, 01:12 PM   #7
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Cool Re: I would like practical opinions on the Monoblock

You are welcome Mike. There are a few outlets to get them here in North America but I would go through Burlen directly.

Also, looks like you have a 5 fin iron head on there ?
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Old 07-01-2015, 01:34 PM   #8
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Default Re: I would like practical opinions on the Monoblock

like your man says Burlen direct.
Twin carbs are fairly simple to set up.
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Old 07-01-2015, 02:40 PM   #9
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Default Re: I would like practical opinions on the Monoblock

"Also, looks like you have a 5 fin iron head on there ?"

Yes sir. You know more about the motor than I do. 1956 6T, all numbers match.
The story I got when my late wife dragged it home from an out of business Triumph dealership in 1969 was that the bike was being pieced together to run AMA short track/half mile. Even though 650 OHV's weren't allowed in Grand National at the time.????
I suspect it was going to be a desert sled, but really don't know much except the lowdown on the engine.
I do know that the beast pulls like a tractor, and idles like a top fuel car! Lots of overlap in the cams.
Has an Airheart disc on the back, state of the art in 1969, Betor front, from I'm guessing by the 2 piece bars, a Montessa.
Barnes quickchange wheel in the back, Boranni spool up front.
I've been looking at used 389's, and I'm thinking, for the money involved buying a decent core and rebuilding it, I'm better off just buying a new one. Looks like about $100 difference between a new 389 and a new 930.
Tony, if I order direct from Burlen, can I get them to install the jet sizes you recommend? Thanks, guys. I was convinced the 930 was going to be the carb you guys would recommended, wrong again!! Mike
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Old 07-02-2015, 01:23 AM   #10
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Default Re: I would like practical opinions on the Monoblock

monoblock is a far better carb than a concentric

believe they are being remanufactured and are available new

this has to be the best option
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Old 07-02-2015, 08:17 AM   #11
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Default Re: I would like practical opinions on the Monoblock

Having been inside both, it seems to me the Monoblock is easier to work on. I'm not sure why, they are very much alike. Just seems that way to me.
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Old 07-02-2015, 02:14 PM   #12
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Default Re: I would like practical opinions on the Monoblock

I just went through the same thought process and opted for the 930 souly on the fact of finding a air cleaner for the monoblock was non existent and where I live the dirt does blow so I went with the 930 and a slinky cleaner . But you can't count out the cool factor of the monoblock
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Old 07-02-2015, 03:20 PM   #13
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Default Re: I would like practical opinions on the Monoblock

If you look closely at the picture of my bike you will see I worked a little magic on a K&N style filter for a concentric to fit my 376. Didn't take much, and stays tight.
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Old 07-02-2015, 04:53 PM   #14
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Default Re: I would like practical opinions on the Monoblock

...my previous comment is a report from a real rider (me) not a Sunday biker or a racer; so I suggested like other members to buy a new one; a concentric in this case; due to cost not so much an comply with what s intended for; also works with all the Triumph twins.
Of course you have the monobloc cool factor, but if it s not for that you do not really need a monobloc to do the job.
Again, my motorcycle is not a toy or a Sunday bike. I put thousands of kms in a year on it; I do not have a car I m motorcyclist and with an older Triumph than you with a 16 years old concentric performing just right.
If you are not into period correct or like that, you can put a concentric for 170 Dollars an forget all the hassles and keep some money in your pocket.
With the 2 older carbs I had 11-13 kms/liter; when I put the new one I had/have obtained 25 kms/liter.
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Old 07-02-2015, 05:06 PM   #15
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Default Re: I would like practical opinions on the Monoblock

Your real rider and the toy thing is getting old.
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Old 07-02-2015, 10:13 PM   #16
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Default Re: I would like practical opinions on the Monoblock

Settle down girls, you're all pretty.
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Old 07-02-2015, 10:21 PM   #17
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Default Re: I would like practical opinions on the Monoblock

...possibly, but I did not found other way to remark that I tested a lot this concentric carb and not guessing how good could be...
-I had 50% of the engine dismantled last week and now in service again.
Always on the road; the toys are not on the road due it not even have a place to put a bag or like that.
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