Question about Air intake and setup

[D-Max2012]

Hi Guys,
I've been trying to get my 91 running right since I purchased it 2 years ago.
The PO just modified **** for just for doing it.. He told me that he used the bike around town. To me, why do performance mods, if your going to just putt around town. Leave the Beast Max alone and get a scooter.

Anyway, I've been trying to care for the Max the way it should have been.

I've been trying to knock out this stumble around 4-5K. I already changed the wrong 147 main jets the PO had in there with 152.5 all around. Replaced the diaphragms, broke down and cleaned out the carbs more times than I can remember - Ultra Sonic cleaned them twice. Coated my tank, Carbs are 100% spotless. Set my Air Mix screws to 2 turns out after trying multiple setting. Set Float levels as per manual. Carb synched, (All other Jets, are stock). Compression test within specs. Stock Muffler with Baffles.
Battery Charged. Charging system 100% in spec with manual.

Anyway, I've tried that little test (on this fourm), to see if your running rich or lean by placing a little duct tape over 1/2 of the air intake (Left/Right on the air box). I noticed that the bike pulls strong when the tape is there. That would suggest I was getting too much Air to fuel mixture (Lean). So I upped the Main Jets to 152.5 and it still does it, but I have to cover only 1/4 of the intake get the same results. So it looks like I'm on the right path to running without any tape at all

Here's the strange part. Yesterday I figure, bring the needle jets from center clip position, (3rd from blunt end) to (4th from blunt end) to see if more fuel around 4.5K would allow the bike to pull correctly without any tape. It was terrible and it stumbled on take off. So today, for the 1st time, I decided to go the other direction and place the clips, 2nd from the blunt end, to allow less fuel around 4.5 K. The bike rolled off SMOOTH from 1st to 2nd and 3rd perfectly, but again, when I got to around 4.5K it had a little hesitation. Past that point it would accelerate OK. So I placed the tape back on, covering about 1/4 air. Now the bike rolls off SMOOTH in 1st, transitions from 2 to 3rd, SMOOTH. Around 4.5K I feel a slight hesitation, but when I roll the throttle, it pulls like a beast . Took it to 114MPH to test if tightening the spanner nuts helps with the wiggle at high speed.. It was SMOOTH as glass .

Now I know there are many factors to consider with carbs and individual setups, but I'm wondering if going larger on the mains would be the next step.

 

[Traumahawk]

Ok.....usually around 4K-5K is where the needles really start kicking in. Stock needles arent adjustable. Is this a canadian bike (the stock needles are adjustable) or I'm wondering if there are stage 1 or stage 7 needles in there. Can you take a pic of the needles?

 

[MaxMidnight]

Further to Mt Traumahawk's post this shows what does what in the rev range.

As going leaner on the needles has helped perhaps a shim to give a half clip adjustment would help? Alternatively a tweak on the idle mixture screw might help.

One other thought, whilst I can understand that you probably want to fix the issue yourself it can become very frustrating/ time consuming/ expensive.
A dyno session would tell you exactly how the bike is fuelling at a particular rpm thus allowing your changes to be made based on facts.
It will also allow you to understand better the effects of any adjustments you make.
IMHO it would be money well spent

 

[thor_eyerdhal]

The above board is not accurate for the Vmax, the needle affect full throttle too

 

[tugla]

is it all stock air box....and or is the "Y" part of it been shimmed up...if so remove the shims.

 

[D-Max2012]

Since this 91 had a PO. I cannot swear that its not a Canadian bike but since he modded damn near everything, I'm sure he swapped the needles also. This is the needle type that's in the bike when I got it.
.

Tugla - The Air Box it stock not shimmed.
Changed out all new Carb boots and V-Boost Boots.
Multiple checks for air leaks, used starter fluid, and propane test. no engine change, during any of the tests.

I forgot to mention, I have a .5mm shim on each needle right now.. removing them would cause the needles to sit .5mm leaner. I wonder if it would make that big of a difference?

 

[MaxMidnight]

The above board is not accurate for the Vmax, the needle affect full throttle too

Whilst I don't doubt you where do you get this info from?

 

[D-Max2012]

So looking at that chart, the Pilot Air screw has an effect across the entire throttle band.
Going by Thor's comment, the needle jet effects the entire throttle band also?
I can see where this can be confusing.. Depending on the needle itself (some are sharp pointed, some are more blunted), and how far it sits in the housing when it is at full throttle, it can have an effect, I would think.

 

[Rollie]

You might want to pull and check your plugs . I had a cracked plug once that gave similar symptoms. Something to do and rule out anyway.

 

[D-Max2012]

even though I can check it, I doubt if its the plugs.. I just put them in there 2 weeks ago.

 

[sdt354]

You might want to pull and check your plugs . I had a cracked plug once that gave similar symptoms. Something to do and rule out anyway.

+1, and very common. Using some tall automotive plug sockets, it's easy to crack a plug porcelain taking the socket off after tightening. The socket in the OEM toolkit works good. I always ask a customer, with an issue, if they changed plugs.

 

[sdt354]

Put stock needles in, make sure there aren't air correctors installed.

 

[tugla]

ya Steve's idea might be good. especially if stock exhaust.
if you need I have set stock needles and wouldnt mimd those ones you have.

 

[tugla]

and yes try it without the shim and clip 2