2700-3200 rpm flat spot

[BIGMO]

Hey guys.

1994 Vmax. UFO 4-2 exhaust - Morley Muscle kit installed. Carbs rebuilt professionally 2 years ago, all diaphrams replaced, Carbs synced.

At 2700-3200 rpm i am getting a flat sound. kinda like running out of gas but not near as severe and a little bit of popping, kinda like bub bub bub. This is only when i am slowly revving but mainly when i hold it at 3000rpm is where its most noticeable. This is all kinda subtle.

air fuel screw is like 4 or 5 turns out (cant remember) and the stage 7 needles are rich, like 2 from the end. So basically im covering up the problem with my fat needles and alot of air fuel. My fuel mileage isnt great. i get around 28 - 33 in town, which is standard for some but ive heard of alot better mileage.

So any ideas on what jet affects that range of RPMs? Or what i might do to to help it.

I doubt anyone who just rides my bike would notice it but I ride at that 3000 rpm at 25mph and 35mph which is most of my trip to work. Its just something I want to work out.

Thanks for any advice guys/gals.

 

[gamorg02]

it *sounds* lean to me. but u said ur needle is already way rich eh? when its having th eproblem does putting the choke on make it better or worse?

 

[one2dmax]

2nd clip from which end?

 

[BIGMO]

Found this on my Carb rebuild: Mikuni 155 mains, PAJ2. Mikuni 170's

Im at 783 ft elevation

I beleive second clip from the point end, it might be 3rd, I havent been in the carbs for a year. basically i got the stage 7 needles pulled way out to let more gas in. and the A/F screws turned way out to let more air and fuel in.
At the 3000 rpm is there a certain jet that works at that rpm? Do you think upping the main jet (i think its stock) would get me more gas and i can lean out the A/F screws and move my clip 2 from the blunt end instead of the opposite side? Im going to be doing some work this winter and fine tuning that 3000 rpm is on my top of list. Wish Wichita wasn't 5 hours away. You ever work on Saturdays Sean?

O.T. - btw sean i still gotta take pics of those braces for chroming.

 

[BIGMO]

What does the PAJ2 do? at what point does it come into effect? Air jet right?

 

[maleko89]

It supplements pilot air along with PAJ1 to the PFJ. It has an affect up to 5K rpms or so. It is closed off during high vacuum deceleration.

 

[BIGMO]

Thanks Mark. Im going to swap mine out to those bigger ones you sent a long time back. It looks real easy to do, so If it doesnt help I can swap em back out. Take of side covers and there they are. Per your awesome tutorial, you musta known i was gonna need crayons bro. thanks! I think I might have some time to actually work on my own bike for once. Maybe I can lower the needles into the throat a little more and screw the AF screws in some to get better mileage. Something isnt quite right.

 

[maleko89]

Before swapping PAJ2's I'd turn your mixture screws in a bit to see if that helps. Make sure air filters are clean too. Dirty ones will cause you to run rich.

 

[BIGMO]

Thanks Mark. I turned em in a couple turns which made em about 2 - 2 1/2 turns out. It kinda lessened my vboost a bit. Didnt seem to kick in as hard. made the flat spot more noticeable. Any other advise as I go into the weekend?
My V45 project is on hold as the owner (My brother in law) bought a HD Super Glide. I cant say that Im disappointed to not have to work on that Honda for a while. I got Vmax stuff to work on! lol.

 

[BIGMO]

BTW filter is almost new. Its from the Morley Kit I just installed at the end of last season. This isnt a new problem, Its been like this since the rebuild. I just pulled the needles out rich and turned the AF screws out rich to cover it up.

 

[maleko89]

Put screws back where they were and then see what needle clip is at. Does the midrange cut out or does it feel "wet"?

 

[BIGMO]

midrange (between 2500-3300) kinda cuts out. Needles are 2 clips up from the point end, not sure from blunt end. If im throttling I dont notice it at all. its just when i hold it at 3grand it kinda cuts out a bit and seems to lose a bit of power. jsut kinda goes flat till it hits 3300 or more. between 0 - 2700rpms it runs good, then at around 2700 it start sputtering a bit till 33oopms, 4 grand it runs well. Really it runs very well except at this one spot. I know Ive got it close but cant seem to figure out what affects the 2700-3300rpms. Thanks AGAIN.

 

[maleko89]

Are the carbs sync'd? Try this. Unplug vboost so that it's open all the time and re-test.

 

[BIGMO]

Y

 

[BIGMO]

Yes sir carbs are synced. Ill unplug it this weekend and see if it makes a difference. Which Vweeep is it that its wide open? The 2nd Vweep? I cant remember.
Sounds like you are thinking changing the PAJ2 one size up would NOT do any good? Obviously im guessing at this. lol.

 

[maleko89]

Let it veep once and then turn key off. Unplug round connector under left scoop. Since it's cutting out at small throttle angles and your rpm range is fine if under load I'm thinking something is up with your pilot circuit. 2nd clip from the point on your needles seems rich to me. Perhaps the transition from pilot to needle is off. I don't think one size difference in PAJ2 will make much of a difference.

 

[BIGMO]

Cool. Ill give it a go and unplug the Vboost this weekend and let ya know how it goes.

What is the pilot circuit? "the transition from pilot to needle is off" what affects that?

Thanks for the advise as always man.

 

[maleko89]

Pilot circuit has an effect up to 5K rpms. transition to needle is 4-4500 or so. Have you checked your plugs?

 

[BIGMO]

Mark,
I unplugged the Vboost last monday. Ive rode it about a week. I forgot how much fun it was to ride with Vboost open. It seemed to lessen the dead spot some, its still there, just not as noticable. There was alot more crackling and sputtering (like a small block at the track) at the lower RPMS when i set the Vboost to wide open. Once it was warmed up that seems to go away some. This may be such fine tuning that I need to take it to seans and have him Dyno tune it? Im sure its kinda hard for you to diagnose carbs porblems liek this over the net. lol. thanks for your help though. its much appreciated.

I havent pulled the Spark plugs for a while but this has been consistent through all my spark plug changes (i usually change em once a year or so). Its gotta be some kinda adjustment im missing.