Hitachi jets fit Nikki carbs! Confirmed.
06-27-15, 10:19 PM
#1
Hitachi jets fit Nikki carbs! Confirmed.
Pilot jets
HITACHI main jet 4H7-14984-40-00 4X7-14984-41-00
In my quest for tuned Nikki perfection, I recently found a website selling Hitachi jets for motorcycle carbs. I was actually looking for Mikuni B42/55 "air jets" to use as a replacement for my dwindling supply of slow air bleeds in Nikkis and happened to notice the word Hitachi a little further down the page. Having had some experience with old school Hitachi carbs for early 13Bs, I was curious.
I looked up the specs and compared them to a couple of my Nikki and Hitachi jets and low and behold they were close enough that I decided to order a couple sets of pilot jets advertised at 40.
I didn't know why they were called pilot jets or what 40 represented but I assumed the hole is small enough to be a pilot hole for drilling out to larger sizes. Or it must be a motorcycle carb thing. lol
They arrived today and yes they are basically right at .40mm or .39mm. Close enough. And the pilot hole is perfect for drilling out larger.
Now I can experiment with sizes smaller than the stock 91 Nikki jets as secondary air bleeds to get rid of an annoying and common problem with boosted Nikkis: the dreaded secondary delay or hiccup, bog, what have you.
So far I tried a previous set of solder filled Nikki jets drilled to .73mm but it lead to glitches while the secondaries were open similar to when the primaries have 60 air bleeds. So yes folks your air bleeds can be too small.
My next test is to drill the soldered ones out to the next size up which was .79mm but the next step above that is .81mm. Well, 81 is pretty much right in the middle between 73 and 91, more or less. I guess 82 would be closer. Anyway it's worth a shot. If it works in that it doesn't lead to glitches and the AFR is good, I can drill the pilot jet out the same amount and not have to worry about solder bloom.
However the slow bleeds are solder filled and drilled to .35mm, so solder bloom is something I'll need to deal with unless I can find some B42/55 blanks. Maybe I'll look for those next.
By the way, jetsrus sells other popular sizes of Hitachi jets that are perfect for your hogged out Nikki ranging from 110 to 134. They skip over 114 for some reason. 114 was more or less perfect for 22.3mm venturis. Oh well, can't win them all.
Main jets.
HITACHI main jet 4H7-14984-40-00 4X7-14984-41-00
HITACHI main jet 4H7-14984-40-00 4X7-14984-41-00
In my quest for tuned Nikki perfection, I recently found a website selling Hitachi jets for motorcycle carbs. I was actually looking for Mikuni B42/55 "air jets" to use as a replacement for my dwindling supply of slow air bleeds in Nikkis and happened to notice the word Hitachi a little further down the page. Having had some experience with old school Hitachi carbs for early 13Bs, I was curious.
I looked up the specs and compared them to a couple of my Nikki and Hitachi jets and low and behold they were close enough that I decided to order a couple sets of pilot jets advertised at 40.
I didn't know why they were called pilot jets or what 40 represented but I assumed the hole is small enough to be a pilot hole for drilling out to larger sizes. Or it must be a motorcycle carb thing. lol
They arrived today and yes they are basically right at .40mm or .39mm. Close enough. And the pilot hole is perfect for drilling out larger.
Now I can experiment with sizes smaller than the stock 91 Nikki jets as secondary air bleeds to get rid of an annoying and common problem with boosted Nikkis: the dreaded secondary delay or hiccup, bog, what have you.
So far I tried a previous set of solder filled Nikki jets drilled to .73mm but it lead to glitches while the secondaries were open similar to when the primaries have 60 air bleeds. So yes folks your air bleeds can be too small.
My next test is to drill the soldered ones out to the next size up which was .79mm but the next step above that is .81mm. Well, 81 is pretty much right in the middle between 73 and 91, more or less. I guess 82 would be closer. Anyway it's worth a shot. If it works in that it doesn't lead to glitches and the AFR is good, I can drill the pilot jet out the same amount and not have to worry about solder bloom.
However the slow bleeds are solder filled and drilled to .35mm, so solder bloom is something I'll need to deal with unless I can find some B42/55 blanks. Maybe I'll look for those next.
By the way, jetsrus sells other popular sizes of Hitachi jets that are perfect for your hogged out Nikki ranging from 110 to 134. They skip over 114 for some reason. 114 was more or less perfect for 22.3mm venturis. Oh well, can't win them all.
Main jets.
HITACHI main jet 4H7-14984-40-00 4X7-14984-41-00
06-27-15, 10:28 PM
#2
Mikuni B42/55 air jets
GENUINE MIKUNI AIR JET B42/55
I'm not sure how Mikuni sizes their jets but I'm pretty sure if you get a set of 110s they will either be at 1.10mm or 1.18mm. I've confirmed that 118 is fine for stock 20mm venturis up to at least 25.4mm but after that you want to start making them smaller.
Get yourself a .0465" drill bit if 118 is your goal. Works for me!
I'm still looking for blanks of this part to drill my own for secondary slow air bleeds of a smaller size than the stock nickle plated 60s but no luck so far.
Note I found these for sale on eBay for cheaper and I even found them in the 50 size, but they are currently out of stock. Here is a link to the 70s.
http://www.ebay.com/itm/Mikuni-B42-55-Air-Jet-OEM-CV-70-B42-55-70/161130727756?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D31966%26meid%3Dc07393fd05fc43f2aa8a51a8e55477c1%26pid%3D100011%26rk%3D1%26rkt%3D10%26sd%3D171166435849
One last thing. The aftermarket 50s arrived and I tested the drilled hole. It is really pretty accurate. Methinks the 115 might be pretty close to 118 without going over. Anyone care to try it? Or the 120 maybe?
GENUINE MIKUNI AIR JET B42/55
I'm not sure how Mikuni sizes their jets but I'm pretty sure if you get a set of 110s they will either be at 1.10mm or 1.18mm. I've confirmed that 118 is fine for stock 20mm venturis up to at least 25.4mm but after that you want to start making them smaller.
Get yourself a .0465" drill bit if 118 is your goal. Works for me!
I'm still looking for blanks of this part to drill my own for secondary slow air bleeds of a smaller size than the stock nickle plated 60s but no luck so far.
Note I found these for sale on eBay for cheaper and I even found them in the 50 size, but they are currently out of stock. Here is a link to the 70s.
http://www.ebay.com/itm/Mikuni-B42-55-Air-Jet-OEM-CV-70-B42-55-70/161130727756?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D31966%26meid%3Dc07393fd05fc43f2aa8a51a8e55477c1%26pid%3D100011%26rk%3D1%26rkt%3D10%26sd%3D171166435849
One last thing. The aftermarket 50s arrived and I tested the drilled hole. It is really pretty accurate. Methinks the 115 might be pretty close to 118 without going over. Anyone care to try it? Or the 120 maybe?
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