Just need somoene to point in me in the right direction.

[Crazy Damian]

Cleaned and synched carbs, everything idles good, revs good, get it out on the road and WOT 0-110 no problems at all fast as hell.

Try to cruise at anything inbetween 45 and 75 and I get backfiring and missing on the right side.
the bad, no mufflers installed thats why I know it's on the right side.
I checked, and double checked the floats, everything appears to be right.
Anyone have any ideas.

Damian

[BA80]

I had that problem once. It was the pilot jets for me. I had the wrong style in there.

Also manifested as a stumble at light accelleration.

[Crazy Damian]

had to check what I bought.

I had to go back and check what I bought because when I purchased jets I purchased a selection so I could play around.
I didn't realize till now that I had gotten the wrong size pilot jets.

I put new 137.5 mains and installed 45 Pilots.

I also purchased 142.5 mains but havent installed them.

[TopCatGr58]

Hey there Damian,

He said the wrong STYLE...not the wrong size. There are 2 styles of pilot jet, the VM series=Wrong and the BS series=correct.

I'm surprised Greg didn't say anything about putting on some mufflers, something with a little backpressure.

Also, check the pickup coil wires, the timing plate, the vac. adv. pot, the cent. adv. parts, ensuring that they are all moving easily and smoothly, not hanging up on worn edges and such.

Backfiring could indicate a lean condition, with those pipes you could probably put in the larger mains and see how it behaves. What do the plugs look like???

T.C.

[BA80]

It's not so much the size, 45s should be fine, it's the number of bleed holes in the side. Genuine Mikunis have 6 holes 2-1-2-1. A lot of the aftermarket pilots will have 8 holes 2-2-2-2. That is where it causes the stumble and uneven power at part throttle cruise.

[BA80]

Yeah, I don't think that would cause what he's describing TC. Sounds like the wrong style pilots to me.

BTDT.

[TopCatGr58]

Hey Greg,

I have to politely disagree!

Have you seen this diagram from MikesXS?

Note: BS 30/96 type Pilot Jets WITH Side bleed holes
holes and those without side bleed holes are
completely interchangeable.**Per MikesXS**

The pilot jets that folks have found in the K&L kits have been reported as the VM series, and that's why they won't meter properly, not necessarily because of the side holes.

I know that the pilot jet provides fuel well into the mains portion of throttle operation, and I've had a broken float post that caused mild flooding that really interfered with the low rpm throttle response on my bike.

He only stated the SPEED he was running at but not the RPM or gear he was cruising at at those speeds...4th or 5th? At 45 mph if he's in 5th he's running it at almost lugging rpm.....IMHO, and at 75 mph he should be around 4,500-5,000 or more, well into the mains by then!?

T.C.

[BA80]

Speed doesn't control the where the fuel comes from on these carbs TC. Throttle position does.

But, I'm not here to argue. Just offer up experience.

[Crazy Damian]

picture of the spark plugs.

I'm going to double check those pilot jets in a few min when I get the carbs apart. More info, When trying to cruise in 4th or 5th at around 5k rpm is when it seems to happen the most. But I guess I need to check my measuring calipers because looking at the park plugs is telling me that has to be wrong.
The pic shows the plugs from left to right Cyl1,2,3,4

[BA80]

Does it change with throttle position or not. When Mine was doing that it would go away if I opened or closed the throttle a little and if I held it steady it would be uneven. That's the way my plugs looked too because I always opened the throttle a little

[TopCatGr58]

Greg,

I'm not trying to argue either, just having a discussion about the problem. I totally agree that throttle position applies, but depending on the engine rpm the throttle position and the transition position of the carbs, butterflies and such can be different, from just off idle to well into the throttle. He only provided the vehicle speed, not the engine speed(s) that he was experiencing the stutter, and it might be occuring at many throttle positions and not just the off idle or low/transition positions. Yes he said cruising, and that usually implies very little throttle input and points to the low speed circuit as being the primary fuel supply place, but at 75 mph I would think he would be into a bit more throttle than just the low speed circuit!?

Would still like to hear what his plugs look like, black and sooty or bleach white, or somewhere in between? Black/sooty would point more to the wrong pilot jet style as has been often reported to cause the overly rich condition and poor low speed throttle response. But if they are very white, then that would point more towards it running too lean...with those open pipes and very little backpressure. Just some thoughts for him to ponder, investigate and hopefully figure out to correct the peformance flaw.

T.C.

PS, that was fast, yep, black sooty plugs...so probably the wrong pilot jets! CUDOS Greg!

[DGXSER]

There are actually three types of pilot jets I have seen. The VM style which will have the eight holes mentioned, the BS type (correct) which have the six holes, and also the N151 type with no holes in the sides. There was a member on here from Indy a while ago that was ready to give up on his bike all due to the wrong style of pilot jets.

By the time your up at 5k RPM your into the mains almost exclusively. By the look of those plugs, your way rich. But, did you chop the engine at the high RPM, or run it up there and then finish in low RPM and idling. The end running condition will show most on the plugs. I would start with making sure you have the float height correct, and the right style of pilot jets. Let us know what you see there, and we can move forward after that.

[BA80]

Smdh..........

[DGXSER]

But wait....According to a recent thread I recall, no one should look at jetting until they are sure they have looke dinto all of their electrical issues.

[BA80]

Ain't bitin' Don. Throw your bait elswhere.