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Discussion Starter · #1 ·
Hi.
INFO: Bought the bike cheap for a Bobber Project. Budget build. 15+k miles on the Clock. Last MOT done 2006.

Suzuki GZ 125cc - 2001
Original Carb Inner Diameter - 26mm

I want to change the CARB on it.
I am considering of going for a 28mm (Inner Diameter).

1. Is it worth upgrading the CARB to a bigger one ?

2. Would a 125cc engine have enough power to work properly with a higher diameter CARB?
- Would it have a
- If so. Which CARB would be better to use?
 

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If engine is otherwise stock and exhaust especially you are asking for tuning problems doing it. Unless you have the skills of course. It would be better to have a prejetted carb to that application but guessing no such thing will exist.

Yours and do as you will............
 

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Discussion Starter · #3 ·
If engine is otherwise stock and exhaust especially you are asking for tuning problems doing it. Unless you have the skills of course. It would be better to have a prejetted carb to that application but guessing no such thing will exist.

Yours and do as you will............
I will be changing the exhaust as well, The Stock stuff will be, frame engine and wheels. Apart from those items everything will be changing
 

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Ace Tuner
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Suzuki GZ 125cc - 2001
Original Carb Inner Diameter - 26mm
I want to change the CARB on it.
I am considering of going for a 28mm (Inner Diameter).
You should be able to go with a 2mm larger carburetor but...
Looking at the photos of the air box and air filter (that I can find) the main restriction of air entering the induction systems appears to be at the air filter inlet. To take full advantage of a larger carburetor you need to GREATLY reduce that restriction or even better eliminate it as much as possible. You may be able to open up the original air filter intake all the way to the edge of the element itself by cutting away and removing the original restrictive opening. There are other routes you could take to accomplish the same but most would be more complicated.
On the other hand if you do not know how to 'read' spark plugs and / or you don't want to spend a Bunch of Time learning how to or experimenting with adjusting and jetting your new carburetor... It ain't worth upgrading the CARB to a bigger one.

S F
 

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The bigger carb would theoretically provide you more top speed, if not for the fact your cylinder head is limited by only 2 valves. ... you have a performance bottleneck there. Stick all the carburetors on it you like, the poppet valves don't have big enough holes to let much more air and fuel through.
 

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Discussion Starter · #7 ·
The bigger carb would theoretically provide you more top speed, if not for the fact your cylinder head is limited by only 2 valves. ... you have a performance bottleneck there. Stick all the carburettors on it you like, the poppet valves don't have big enough holes to let much more air and fuel through.
In context its pointless to upgrade the carb, and better of just using Stock
 

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Unless your stock carburetor has a problem I honestly don't think you would see much difference in performance without a lot of expense and complications.
Bigger problem the GZ125 cruiser is going to have performing is weight, your bike weighs in at around 300 pounds and is fitted with small diameter steel rims. Since you plan to bobber it, that might address some of the weight problem, but basically nothing on that bike was ever made intentionally lightweight or to optimize performance. The bike came fitted with a CV carburetor, so if you are going to modify both the intake and exhaust system, you will be confronted with some major tuning issues. When that happens a non vacuum controlled carburetor would indeed be easier to tune, but the size of that carburetor would best not change significantly unless that change is accompanied by additional modifications to the engine.

At some point it just makes more sense to get a bigger engine, but as the bike sits wheels and suspension components are where you could see the most performance improvements for the least money spent.

Best luck with your project. Put it on the road before you modify the motorcycle and you will have a lot less problem with MOT inspections.
 
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