All jets aren't created equal. Mikuni sizes their jets according to flow rate. The 175 is a rate of flow. DJ, references the size according to the hole they drill. If you look under the Tech Articles tab above, you can scroll down to the comparison chart for DJ and Mikuni. There's a big difference between what each calls a 175.

The big heads and little heads have the same spacing on the metering orifice when they are seated, and as so are interchangeable in theory. In SOME applications, the main jet is on a post with a spacer, and the larger head is required to hold the spacer and the emulsion tube correctly. I have big diameter jets in my SV650, just because I already had them, but it was born with small jets.

Let me start by saying I am by no means an expert here, but I have a few concerns about this issue:

1. I can't see how jetting could be the problem. If as you say the front jug is doing fine, the fuel flow is not the problem.
A slight air leak at the front jug manifold might allow the front to be a little leaner, but by the time there is enough air to
offset that much extra fuel should be obvious.

2. Other than the fact that the rear jug tends to run hotter due to limited air flow, the only other situation I can think of is misfire.
Based on your description, you don't have a DEAD no fire situation, but it sounds like the coil or wires are arcing to some degree.
I would suggest trying to look for arcing in the dark. (Note: I had that problem, and it was VERY hard to find it even in the dark)
I ended up changing my coils and wires and it fixed my misfire problems. Because of the cost, I wouldn't recommend a coil change just
to see what happens, but maybe someone here has a rear coil you buy or try?


Either way, I hope you get it figured out.

So I fired her up, turned out the lights, closed all the doors and got reallly sleepy all of a sudden lol j/k.

I'm thinking two steps:

a) compression test to see if there may be a valve issue
b) swap the coils to see if it may be coil/wire related

Thanks for all the input so far. The new jet should be in tomorrow, so hopefully have the carb back together and installed.

Not sure, but I thought you said you had stock coils? If so, you cant swap them (fixed wire length.)

Can you post a pic of 1 front and 1 rear plug color?

I think you are getting way off track with all the coil stuff. The rear fouling issue is common when jetted rich and you are jetted rich. When is your jet gonna be there?

davej wrote:
Can you post a pic of 1 front and 1 rear plug color?

I think you are getting way off track with all the coil stuff. The rear fouling issue is common when jetted rich and you are jetted rich. When is your jet gonna be there?

Not arguing, but I thought Tan was a correct plug color? What did I miss that would make you think rich?

davej wrote:
Can you post a pic of 1 front and 1 rear plug color?

I think you are getting way off track with all the coil stuff. The rear fouling issue is common when jetted rich and you are jetted rich. When is your jet gonna be there?

I'll snap some pics tonight. Reason I was thinking maybe coils was due to the big difference from front to rear. New jet will be in tomorrow.

DageonYar wrote:
davej wrote:
Can you post a pic of 1 front and 1 rear plug color?

I think you are getting way off track with all the coil stuff. The rear fouling issue is common when jetted rich and you are jetted rich. When is your jet gonna be there?

I'll snap some pics tonight. Reason I was thinking maybe coils was due to the big difference from front to rear. New jet will be in tomorrow.

You have describe exactly what many other have described in the past. It is usually cured with jetting and maybe a intake manifold re-seal. Mine was/did the same when I bought it.

davej wrote:
Can you post a pic of 1 front and 1 rear plug color?

I think you are getting way off track with all the coil stuff. The rear fouling issue is common when jetted rich and you are jetted rich. When is your jet gonna be there?

Well... here's the side-side pic of the set I just removed. Got a brand new set of iridiums in there now, jetted 172.5 mikuni jet, and set the pms to 2 turns out, needle on the 3rd groove (from the top), washer under clip. Here's to crossing my fingers, will be taking a test run in the morning.

I also dumped 6oz of Ring Free into the tank and filled her up with fresh fuel. Got an oil change kit on stand-by.

On a side note, can these plugs be cleaned with like DeepCreep and reused? Or are they junk? Getting expensive throwing $12 plugs in the trash.