Midrange issue

[grimmie]

Hey,
Question for you carb nutz out there.

I'm having a midrange issue. Runs fine 'til 4100 RPM's, then it starts to break up a little. Doesn't really matter what gear it's in, just when it hits 4100 it breaks up. Really see it when I'm cruising at like 65-70 mph.

2000 VMAX 17000 miles
Kerker 4-1 w/comp baffle
Morley's carb kit
Stock needles w/one shim
I'm almost sure it's the 160 jets, I'll check to be sure
PAJ2 is the 177.5
Mixture Screws are 3.5 turns out

Plugs and wires are new. Carbs are clean. Runs great otherwise. Throttle response is really good.

Suggestions?

Thanks, Shane

 

[[email protected]]

II would try another shim on the needle first.

 

[davidon]

Agree needles need to be adjusted

 

[tugla]

you dont have stg 7 or adjustable needles do ya? not sure whats in seans kit. does that issue only happen if your slow thru the rpm? if your wide open thru the gears do you still get that stumble?

 

[SpecOps13]

I had this exact same problem with my 89. I'm gonna look at the thread I have under the General VMax Questions and will link it here if I can come up with something...

This is from my 89's thread:

Added 12/21/2010: I picked up a fuel relay at CaptainKyle's this morning and a Real Fuel Filter at the dealer. I didn't think Kyle would be stocking fuel filters.. Wrong. When I got home, I installed the filter and the relay. The relay didn't help my condition and the hose I bought for the filter to the fuel pump was so stiff (USCG B-15 Ethanol Proof) I had to double clamp to get the leaks stopped...I charged the battery and ran the bike. It started and ran good until I tried a 4th and 5th gear roll on. It still breaks up at about 4,000 rpm. If I back off the throttle just a touch it will keep picking up speed without breaking up. Stage 1 with the needles dropped all the way and it's still running rich... Could be the drilled slides. I may have to JB Weld and re drill...


I decided to go after the overly rich conditions of the DJ Stage 1, as it sets. Since I don't have any jets or needles to swap in right now, I had to come up with an alternative. The plugs were running dark enough that I went one heat range hotter on them. The carbs all seemed to have cleared up with the cleaner I've been running and are all working with each other. My mercury manometer is as old as the hills. Impossible to clean the tubes. So when I use it I have to swap the tubes / hoses that are closest to reading the same from cylinder to cylinder and side to side. I ended up rechecking myself 4 or 5 times over today.

When I took it out for a ride, I was shocked and left in Awe. It's a smooth as glass and holds a steady speed without any fuss at all. I grabbed a hand full of 2nd gear on one of the less traveled roads and had to throw all my weight forward to keep the wheelie under control.. It's a good thing I didn't try that in first. This things purrin like a kitten (Of The Cheetah Variety)..

Note, the Dyno Jet Kit turned out to be a Stage 7 that had been partially but not completely uninstalled... Once I got the whole thing out and stock needles installed, My main jet went to 147.5 at Sea Level and standard plugs..... It now runs great....

BTW: I have a Kerker 4-1 with my own design core....It's over 2", probably 2 1/4"


Hope this helps you somehow.....

 

[grimmie]

Hey, thanks for the replies. BTW, I'm at sea level too. I tried adding another shim last fall and it made things worse. I'm pretty sure the plugs are running dark. I'll check that again and try the hotter plugs.

Thanks, Shane

 

[gamorg02]

mine did the same until i went with stg7 needles, i'd recommend that.

 

[RaWarrior]

I've got like the exact same issue...just a faint "break up" in the 4-5000RPM range. Nail the gas and it's fine, but at steady cruise it just doesn't want to hold a constant speed.

The plugs would say it's running a bit on the rich side, but when it's "breaking up", setting the v-boost open, it instantly makes it better, so too lean? Tried adjusting the needles to no avail. Gonna put 147.5 mains (unknown what I have now, I'd assume a DJ170~ roughly equal to a Mik 160 since that's the suggestion for the stage 1 kit), and a stock 170 Mik PAJ2....I currently have a 190 Mik PAJ2, so the kit wasn't installed completely, or was fiddled with afterward.

Maybe the rich plugs are from a rich low end, and the motor always runs slowly for probably a minute or two before I actually park in the garage. Guess I'd have to do the "plug chop" on the side of the road to actually get anything from the plugs.

 

[grimmie]

I have a set of DNT 426 needles-brand new. Do you think I should should try the needles first? If so, what clip position do you recommend I start with?

Thanks, Shane

 

[SpecOps13]

Are you set up with separate air filters and the stage 7 air correctors in the top of the carbs? If not, you'd be better using shimmed stock needles and re jetting leaner... I hope you don't have the problems I had with a partial installation. My plugs did run very brown and stock plugs were close to fouling, that's when I tried the 7's in place of the 8's...

PS: My current carbs are stock except the 147.5 main jet (Mikuni Number) It started out with 155.0's.... A/F Screws are 3 to 3 1/4 turns out... Needle is shimmed 0.034...

 

[grimmie]

Are you set up with separate air filters and the stage 7 air correctors in the top of the carbs? If not, you'd be better using shimmed stock needles and re jetting leaner... I hope you don't have the problems I had with a partial installation. My plugs did run very brown and stock plugs were close to fouling, that's when I tried the 7's in place of the 8's...

PS: My current carbs are stock except the 147.5 main jet (Mikuni Number) It started out with 155.0's.... A/F Screws are 3 to 3 1/4 turns out... Needle is shimmed 0.034...

I'm running the air correctors and air filter that come with Seans kit.

 

[tugla]

and you got a new set of std 7 needles?

try it on 3 or 4 from the point, easy enough to chg if its wrong, takes a few mins to do.

 

[SpecOps13]

Others can guide you better with the combo you have. Our set up is too different for me to be guessing....:biglaugh:

 

[overzat]

i am in the same boat same set up as grimmie going to try a 165 main if that dont do it stage 7 needle i guess

 

[tugla]

which jets DJ or mikuni's? id try 160 dj or 150 mikunies if not down to 147.5Mik. what are you running now?

 

[grimmie]

I ended up trying a couple things with the needles. I had added a second shim on the stock needles a while back but the problem was worse. Yesterday I ran it with no shims and the problems got worse. I ended up trying the DNT426 needles that I got when I got the carb kit. I started on the third clip from the pointed end. I ran it for about 10 minutes and the midrange is really strong. The break up is gone. It sounds good and feels good. A bad thunderstorm just rolled in here so I had to put it up. I'll run it again tonight if I get the chance and advise.
Thanks, Shane

 

[tugla]

glad your moving in the right direction keep us posted

 

[RaWarrior]

Here's what finally solved my issue, which sounds pretty similar to yours.

Switching the 155 mains to 147.5
Switching the 150 PAJ2 to 170

Stage 1 needles still at 5th clip, a/f screws still 4 turns. Midrange is smoother, torquier, beefier. Lag is completely gone, cruises at 80 up a hill smooth as can be. The top end feels stronger as well.

 

[grimmie]

Thought I would give an update.

I ended up switching from 160 to 155 mains. Running the Stage 7 needles on the 2 notch from the blount end. Mixture screws are 4 turns out. Bike ran really good. I'll be riding a while tomorrow so I'll advise after that, but it's definitely getting close.

 

[grimmie]

I ended up with the 155 mains, stage 7 needles on the 3rd notch from the blount end, and mixture screws are 4 turns out. I'm trying the v boost open. I was never a fan of having the v boost open but it has a little more umph down low and it sounds really good to me. I shot a quick video, not great.

The throttle response is really good and it cruises like a dream. I'm gonna take it out this evening for a while.

http://www.youtube.com/watch?v=L1ln7G0yRQg