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Discussion Starter #1
Hi guys. I have the carbs out of the my ZRX1200R currently as i had a missfire at partial throttle so decided to do a strip and clean of the carbs.

I have found two potential issues that i would appreciate your input on.

Diaphragm spring length. Before rebuilding i checked the carb Diaphragm spring free length.
Found a huge difference accross all four carbs. Please have a look at the attached pic. The bike pulled and rode fine with these different springs in but it really doesn't sit right with me.

Second is the main jet sizes. I found the jet sizes in the following order from cylinder 1 ... 92 - 95 - 92 95
Now i know plenty of bikes run a larger jet on the two inner cylinders to run cooler etc but have never seen it staggered like this.

All opinions welcome on this including if im being over cautious. Its just that these two things dont seem correct from my significant(ish) experience on working on 4 cylinder motorcycles.
 

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Looks like the same size wire and the same number of coils from here, somebody just got a little over-zealous with removal at some point in its life. If it makes a difference you won't be able to balance them.

104415
 

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Any opinions on the strange order of jet sizes?
[/QUOTE]
PO probably took the carbs apart to clean and didn't pay attention as to which was which.
 

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I've seen lots of CV carburetor banks that had a slightly different carburetor on #2 they sometimes put a little throttle actuated fuel pump on one carb to eliminate a hesitation in the thing wanting to run too lean at times.
Can't imagine you will be able to balance the carburetors with odd jet sizes like that on yours, it sounds like a mistake.
 

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Discussion Starter #8
I've seen lots of CV carburetor banks that had a slightly different carburetor on #2 they sometimes put a little throttle actuated fuel pump on one carb to eliminate a hesitation in the thing wanting to run too lean at times.
Can't imagine you will be able to balance the carburetors with odd jet sizes like that on yours, it sounds like a mistake.
Hi trials, yeah thats what i yhought.

Many foyr cylinder air cooled jap bikes have larger jets in the middle cylinders which is normal but having it big small big small seems wrong.

I will swap the jets so the larger are in the middle and see how she runs.

Its always pulled well before but i don't want to run one of the middle two cylinders too hot for obvious reasons
 

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Discussion Starter #10
Could the jetting have to do with the exhaust flow?
Im not sure to be honest.

The standard system is a four into one so is the new one.

Im not sure the difference in exhaust flow would require a staggered jet order.

All very strange.

For an update the bike still has a slight misfire at constant part throttle even though I cleaned and rebuilt the carbs along with renewing all carb rubbers and vacuum lines so I'm sure im air tight.

Its at nearly 100,000 miles on the clock so im just gonna live with it as is.

If it dies it has done me well over the years but it is my daily transport for everything including commutint and i would rather keep the miles off of my street triple.
 

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I would start with a compression test that would possibly lead to a valve adjustment.

If you can't replace the spark plug wires I would suggest spray them or cover them. Take a look at it when it's running in the dark of night and watch for sparks where they should not be, that would be the tell. Meter test your electrical ground and wire connections for resistance.

and check this out the parts diagram does indicate different jets for the middle cylinders
 

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Yeah - someone has f'd up your carbs. You need to get those springs replaced - that will more than likely be your misfire problem. The uneven springs will mess with partial and low end throttle.

Also - those jets are stock sizes (1 and 4 are #92, 2 and 3 are #95). Stock pilots are #35's. You might want to experiment with larger mains if you are running an aftermarket pipe.
 
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