Mikuni CV Jets - Bore sizes

[salty_monk]

Does anyone have a list of how the numbers relate to the actual bore sizes of the main jets? I haven't been able to find one.

The reason I ask is I have some 122.5 Jets & some spare 115 Jets that I removed from a set of Canadian GS1000G carbs.

In theory the 122.5 jets should be bigger by 3 stages but when I measured them up today the bore size on the 115's is bigger by 0.1mm. Very strange.

I'm wondering if these 115's have been drilled out at some stage (strange as the rest of the carb set was completely stock) or if my 122.5 is from a different kit (Dynojet or something that's measured differently)

Anyway info appreciated as always - see pic, markings are very similar on both (markings on my two sets of 115's are identical by the way, the ones I have in mine now are stock from Kent's GS1100GL 8V



Dan

[tone]

I only have a little info on this but here it is anyway :-D

some jets are measured by actual hole size (mikuni.s i think) & some are measured by the flow rate (DJ ?) i dont know about any other makes of jets but suspect something similar :?

This could account for some differance in actual hole sizes, but the jets in your pic look to be from the same maker by the markings, some of the differance could be wear i suppose but it is quite a bit of a differance considering the marked sizes i suggest starting with a new set of jets to give an acurate pointer on any running problems

hope that made some sort of sense & helps a bit :-D

[chef1366]

If they are both Mikuni jets someone drilled out the 115s.

[salty_monk]

Well they look like Mikuni's to me as the markings the same... Very strange.

They could be anything though as I don't know the history of either...

I'm going to pull #1 Float bowl in a moment & take a look at the size of that one.

[salty_monk]

Well as usual you're right Bill

They are Mikuni's & they are drilled out to 1.3. Just about got a 1.1 down the 115's I've got.

Strange as the needles etc were all set to stock. Wonder what setup that bike was running. I guess they are probably 130 or 132.5 equivalent now so maybe he had a 4:1 & pods or something... strange with no changes to the needles.

Dan

[chef1366]

Just curious but how did you measure the bore size?

[salty_monk]

It's a secret

One of the other things I learnt today, getting the main jets out with the carbs fitted is a royal PITA!

I took the first two to a shop & gently tried the back end of various size drills down them till I found the one that fit. Then I measured it precisely with a set of digital vernier.

The one I pulled tonight... I used 3 pcs of wire (actually two paper clips & a straightened torch spring) that measured 1.1, 1.2 & 1.3mm diameter.

Pretty impossible to measure them any other way, the vernier don't fit down the needle recess or down the back from the slot side.

Dan

[Jd Powell]

The square within a square symbol identifies your jets as mikuni. To my knowledge all the round mikuni jets are sized dimensionaly. Mikuni hex head jets, and dynojet jets are flow rated.

[chef1366]

The square within a square symbol identifies your jets as mikuni. To my knowledge all the round mikuni jets are sized dimensionaly. Mikuni hex head jets, and dynojet jets are flow rated.

Other way around. Mikuni are flow rated and Dynojets are size rated.

[TheCafeKid]

Actually, 49er i believe mentioned that MiC measured their jets two different ways. The round head jets (commonly found in the VMs for sure) are bore measured, while the hex heads were flow measured i think he said. Dunno if that is in fact the case, but something to investigate for sure.

[salty_monk]

These round ones of mine seem to match the size of the bore... The 115 will allow a 1.1 mm wire through & the 122.5 will allow a 1.2mm wire through. That's as close as I can get.... 0.05 of a mm is only 2.5 thou

[RASNDAS]

All the information I have says that Dynojets are rated by hole diameter and Mikunis by flowrate ( CC per minute flow at some pressure). Most of the mikunis I have measured however seem to follow hole size also as a 122.5 would be 1.225 MM in diameter. I have compareed a number of Mikuni jets and fluid mechanics would show an increase in flow rate as a squared function of the hole diameter. In other words a .2 MM hole will flow 4 times as much as a .1MM hole. Measuring Mikuni jet holes as compared to there stamped size does not bear this out. your 115's are deffinatley drilled out.