Hesitation at low rvpm...where to look?

[anteva2]

I have a 2005 Vmax with just over 7000 miles on it. It turns out that when I go in the city, leaving at low rvpm I notice a little hesitation before ascending, it is as if the fuel needed something richer in low. This "hesitation" goes away the moment you get above 2500 rvpm. Where to look first?
The bike has been parked in a garage for many years, but at least a couple of times a year it did about 30 miles. Logically, it has been tuned up by changing all the fluids, filters and spark plugs. It works very well except for that small "bump" at low revs.

 

[Fire-medic]

I suspect the pilot jet is plugged on 1 or more cylinders, a common occurrence for seldom-ridden bikes.



To fix this, you need to remove the carburetors, remove the float bowls, remove the jet blocks, then remove the rubber 'cork' in the jet block, and remove the pilot jets to see which one's plugged (or more than one). It's a good idea to already have on hand the jet block gaskets. Buy them OEM or the K & L set pictured. Don't waste your $ on the off-brand aftermarket rebuild kits from ebay! They're trouble personified!



A pilot jet with a stainless steel wire used to poke-out hardened deposits.



How to solve the pilot jet issue if yours has a broken slot:
I've purchased used VMaxes where the pilot jet was just sitting in the jet block, not screwed-in. Each carb body has a pilot jet, so you are dealing with 4 of them.

I suspect the 'mechanic' who did the work didn't bother to tighten them sufficiently, it doesn't take much torque to do that (snug the pilot jet properly so it doesn't back-off out of its threaded hole). If you're not careful, you can break-off one side of the slot brass. Be sure to use a tight-fitting screwdriver so its tip 'fills' the pilot jet slot, and is as-wide as you can fit into the jet block passageway.

If you discover you have a damaged pilot jet, where one side of the screwdriver slot is missing, you can probably remove it using a left-handed drill bit. The action of the left-hand threaded bit biting into the brass will probably unscrew the pilot jet. If that doesn't work take it to a machine shop before you make things worse, or contact members dannymax, one2dmax (Sean Morley), or Captain Kyle.

Why have the jet block gaskets (#35, below) on-hand? They often tear when you attempt to remove the jet block.





Do not confuse the pilot jet with the pilot screw!



That is below the CV diaphragm cap. Yours may have an aluminum plug in it, to prevent tampering. Behind that aluminum plug, you can see the pilot screw head. It's #22, below.

https://www.ronayers.com/oemparts/a/yam/50045c0ef8700209bc7942f3/carburetor

 

[anteva2]

Thank you very much for your advice Fire Doctor. As you well know, I'm not good at using a screwdriver. Do you think a little sea foam will solve the problem? Thank you very much again

 

[Fire-medic]

Sea Foam probably won't hurt, if you use it as-directed. However, when those small jets become blocked, often the chemicals won't fix the problem.

 

[joksi]

I am having a similar problem, maybe a bit worse even. Below 2000U/Min my Max shoots and has less than zero power. Carb has been properly cleaned (sodablasted, ultrasound plus mechanically).
Since my Max runs too rich on low rpm, we suspect the rubbers (#43 and #45 on the spare parts drawing) to be too hard to seal properly.

Ordered them yesterday, report will follow.

 

[Fire-medic]

I'm guessing you're referring to #3 & 42, the rubber donuts?





https://www.ronayers.com/oemparts/a/yam/50045c0ef8700209bc7942f2/intake
I am only a hobbyist not a mechanic, but I think a poorly-sealing donut would create a lean condition, and not a rich one?

 

[MaxMidnight]

Agree with Mr Medic - if the rubbers were air to be drawn in then that would result in a lean condition.
A starter fluid test described elsewhere would confirm the diagnosis.

Are we dealing with stock bikes or have any modifications been done?
What leads you to believe the mixture is rich?

At low engine revs it is the idle circuit that controls the mixture.
Can we assume that the air filter is clean and has been changed within living memory?

Are the Primary air jets (PAJ's) standard i.e. PAJ1 90 (except California 100 & Europe 95); PAJ2 170. Are they in the correct hole if they have been removed (if this is possible??)

What happens when you adjust the idle mixture screws i.e. do the revs or engine note change when you turn them? If not the idle circuit is plugged.
Are the float levels correct?

 

[Shawn Dupuis]

Ethanol gas plugging jets my bike gets it all the time in south Florida