Watch out for Mike's Needle Jets!!!

[johnnymac]

I have a great 1975xs650b that runs great but rich- I've had the carbs off many times and tried lots of things. I thought the richness might be from needle jets that may have been internally corroded from years of varnish and non use. So I ordered the needle jets that Mike said are for my year. They said z-6 and I looked at mine and they also said z-6. I got them today and I opened the box and the parts are not the same! Here is what i got. My needle jet is on the far right and mikes are on the left. The funky thing is that they all say z-6. Going back on Mikes website it now looks like the z-8 looks like mine but my model calls for z-6's. I also messed up my carb gasket in the process. Should I just order the z-8s and hope they work? I just want to ride.

 

[johnnymac]

Would this mean that Mikes needle jets are miss-stamped?

 

[cros36]

i have a 74. went through the same thing. i ordered the z-8's and they were the same as my stock z-6's. order some extra o-rings, i dont know if the z-8's are a hair smaller or what, but they seemed to have a little slop. i creased one oring putting it in, and that one came out, the other went in nice and is solid.

 

[johnnymac]

Thanks cros I thought I was going crazy- Did Mikes take the other jets back? I got lots of the o-rings from mcmaster carr. THANKS again for the reply.

 

[cros36]

well if i remember right there's two different z-6's or something, i dont remember correctly it was a little bit ago.

they didnt take the z-6's back, but.....

wait for it....



they gave me a refund!! mind you this was in the first week or so or the new ownership when the whole up roar was going on with that. so i dont know if that is still something that they would do, but they know about the problem, and so did mike. wouldnt hurt to write them an email to see what they say for at least a trade you know.

 

[Nine_Iron]

Same thing here.....I actually helped a guy in a post a few months back about this. Their Z-8's are the same as the Z-6's you need. I ordered the Z-8's and they worked perfect.....make sure to order two new o-rings!

 

[cros36]

i knew the other day when i was doing my weekly wishlist shopping cart that they only had one left. pry something that i can get at my local hardware store?

 

[5twins]

Mike's Z-6 needle jets are not mismarked, they're for the '70-'73 carb sets only. Those carbs had a raised floor in the main bore and require a longer jet. Mike and the new owners were/are aware of the incorrect product description but apparently choose not to correct it. Selling parts, that's what it's all about for these guys I guess. Who cares if they all don't fit, lol.

The needle jet o-ring is 4mm I.D. x 1mm thick. You can get a 25 pack of viton rubber ones from McMaster Carr for not much more than 2 from Mike's.

The Z-8 needle jet is the proper length but is slightly richer. It may work fine on a bike with some mods that needs it's carburetion richened up but might not be ideal in a totally stock machine. I touched on the difference in needle jet lengths in the chart I made up for the carb guide. Do some research before buying stuff and you may not get stuck next time .....

 

[XSLeo]

I have measured the length of the needles. All except the 4MI needle. The 4JN19 is 1.666 inches long, the 4N8 is 1.666 inches, the 502 is 2.039, the 5HX12 is 2.104 inches.
I think if you match the needles to the needle jets the mix should be ok. AS in use the Z-8 jet with the 4MI needle.
If your carbs have the long Z-6 then your carbs are not 75 carbs. more likely 72 -73 carbs.
When you look into the intake bell of the carbs does the hole where the slide set round or does it have a flat area just under the slide?
The 72-73 carbs have a raised floor, this means the area under the slide is rasised up to almost reach the slide. About 1/32 or 1/16 inch between the slide and the floor. The 74 -75 carbs will have a round area and be around 1/4 inch or so between the slide and floor. You may need to open the throttle plates to see better.
Putting the long Z-6 in the raised floor puts the top of the jet just above the floor, about 1/32 or so. The short Z-6 will be below the floor.
Putting the long Z-6 in the round floor carb will put the top of the jett a 1/4 above the floor. The short Z-6 will set just above the floor.
The jet should be just above the floor.
If your jet is worn a bit dropping the needle one slot, from slot 4 to slot 3 should compensate for the wear.
Hope this helps.
Leo

 

[5twins]

I've done some needle research as well but measure mine a bit differently, in MM (just like Mikuni does) and from the top clip slot to the point, not overall length. When comparing several needles of the same number, I found the overall length might vary by as much as a MM or so. Apparently, Mikuni isn't that critical about making the length above the clip slots the same on every needle. That section really doesn't matter much because it does no fuel metering. What they are critical about is the length from clip slots to point. That is important and must match exactly between needles of the same number. Here's what I found, top slot to tip .....

'70-'73 4JN19 40mm
'74-'75 4N8 46mm
'76-'77 4M1 45mm
'78-'79 5O2 50mm
'80-'84 5HX12 50mm (fixed clip)

'80-'84 5IX11 50mm (5 slot adjustments)
Canadian Needle

The Generics included in some rebuild kits :

Y-22 40mm
Y-31 45mm

You can draw a few conclusions by studying the lengths. The 4JN19 needle is 6mm shorter than the 4N8 because it mates with the longer version of the Z-6 needle jet. The 4N8 and the 4M1 actually run at the same height because the 4N8 is set 1mm higher in clip slot #4. The Y-22 generic needle included in some of the '74-'77 rebuild kits is too short (rich) for those short needle jet carb sets and might only work in the '70-'73 sets.

 

[XSLeo]

Very good info 5twins. Your method of measure is more usful than overall length.
The length of the needle needs to match the needle jets. My 76-77 carbs have the short Z-6 needle jets so I use the 4N8 needle.
They should have the Z-8's with the 4M1's.
I think after I get the new diaphrams I will get the Z-8 jets and 4M1 needles and see how they work.
Leo