Help..want to know more about popoff pressure

ISeeWetPeople

ISeeWetPeople

Location
Finland
I´ve read mikuni´s instructions about ten times now but still i dont fully undestand how different popoff settings effects to engine and is high pressure good or low for freestyle

can someone tell mee about that so i could understand what would be the best setting for me..


i have 701 yama, Loki head 185psi both, R&D M-16 reeds, dual novi maxflow 48, b-pipe and msd total loss

My settings for msd is

retard begining 4500
15@7500
28degrees from stator
max rev 8500

and please tell me if i need to change something
(i know that my pilot jet should be bigger)

my current setup

Brand = Mikuni/Novi
Model = Novi maxflow
Size = 48
Quantity = 2
Main Jet = 125 H
Pilot Jet = 115 L
Needle/Seat = 2.3
Spring = 65
Pilot screw = 2 1/2
Main Screw = 1 1/2
- - - - - -
Gas Octane = 93
Altitude = 0
Main type of riding = freestyle flatwater
Would it pass the 10 second WOT test = What is this??
Powerband = low mid
Motor type/setup = 701 , b-pipe, loki head 185psi, msd total loss, R&D m-16 valves. Dual novi maxflow 48,
 
CARBONX2

CARBONX2

Location
South Africa
You will need a low pop-off with 48's on a 701. You are going to struggle to set them right, not enough air velocity through the carbs for clean running. Your jetting needs to increase a lot, I would guess 140P/130M and work down from there.
 
schicks

schicks

Karma Enforcer
Location
West Michigan
flame arrestor...airbox. stock? how many screens? filters?

less restriction = higher pop off
more restriction (all 3 screens) = lower popoff

i think thats how it goes.
 
ISeeWetPeople

ISeeWetPeople

Location
Finland
i assume that it does because i read that on carburetor settings thread and there i saw that all race riders has very high pop-off

ok ill try bigger ones Thanks!!
 
speedysprocket

speedysprocket

Alex
Location
Chesapeake, VA
schicks said:
flame arrestor...airbox. stock? how many screens? filters?

less restriction = higher pop off
more restriction (all 3 screens) = lower popoff

i think thats how it goes.
Click to expand...
You're backwards. Less restrictive, lower popoff/larger jets. More restrictive, higher popoff/smaller jets. When you reduce the restrictions before the carbs, there will be less vacuum in the carb, so you need to make it easier for the engine to suck that fuel in.
 
schicks

schicks

Karma Enforcer
Location
West Michigan
this is from factory pipe: speedy is correct.

POP-OFF PRESSURE AND LOW SPEED JET
How do pop-off pressure and the low speed jet work together?
These two circuits overlap, although the low speed jet continues past 1/4 throttle where pop-off pressure has little to no effect. In general, if your pop-off is slightly too high, you can compensate by increasing the size of the low speed jet. The opposite is also true; if the low speed jet is slightly too small, you can compensate with less pop-off pressure. Once you get to the point where you think each is adjusted correctly, it's best to try varying the two to make certain you have the best combination. For example: If you have pop-off pressure of 30 psi and a 67.5 low speed jet, you should also try a pop-off of say 35 psi and a 70 low speed jet. To verify that you have the correct combination there are two things to test:

1. Throttle response should be crisp, with no hesitation.

2. Ride the boat at a constant 1/4 throttle opening for about 1 minute and then quickly open the throttle fully, there should be no hesitation and the engine should not show signs of being loaded up. If it hesitates, it's lean; if it's loaded up, it's rich. The first test is to check pop-off pressure, the second test is checking the correctness of the low speed jet size. Take the time to ride the boat slowly and thoroughly test your jetting changes. After a jet change, it takes the engine a few minutes of use to completely respond to the change.

When does it become necessary to adjust pop-off?
When personal watercraft come from the factory they have fairly high pop-off due to the fact that they also have somewhat restrictive air intake systems that cause the engine to generate very high manifold pressures; the higher the manifold pressures, the higher the pop-off pressure required to properly regulate the fuel delivery to the engine. As you modify or change your watercraft's flame arrestor to a less restrictive type you will most likely start to experience a lean hesitation caused by a decrease in manifold pressure. This change will require an adjustment in pop-off pressure to regain crisp throttle response. Because most aftermarket flame arrestors are less restrictive than stock, you will need to decrease pop-off to compensate.
 
ISeeWetPeople

ISeeWetPeople

Location
Finland
im sorry but dont uderstand term "all 3 screens"

do i have to lower my pop-off even more? current is 15psi (not measured but with 2.3g NV and 65g spring =15psi)
 
ISeeWetPeople

ISeeWetPeople

Location
Finland
when it starts to dribble fuel does the jetski feal restles and wont run smoothly.. two days ago i tried to adjust my carbs and for a short moment it run like stock,, smooth and quiet and stil had low end power.. i lost that spot and i did not get it again..
and now it has good low end but i think its bit too hard running.. so can it be that i should add more pop-off?
 
Vumad

Vumad

Super Hero, with a cape!
Location
St. Pete, FL
Quinc said:
From what I have read you want the lowest pop-off you can get before the jets starts to dribble fuel.
Click to expand...

No. The pop-off is a tunable component of the carb. It controls the mid-range transition. A popoff of 21 or 28 may be better for a particular setup than 18, even if it doesn't leak at an even lower number. I found the group K tuning guide to be most accurate to my limited experience, where it says that the popoff should be "Ideally, you want to run the highest possible pop off pressure that permits "hesitation free" mid range throttle response."

I'm no expert on the subject, but I have found that changing the popoff can make dramatic differences in mid-range response.

http://www.groupk.com/tec-carbs97.htm
 
ISeeWetPeople

ISeeWetPeople

Location
Finland
so what ive read here i should run 21-28 pop-off and go with 140P/130M and work down from there?
so i will try with 2.0 NV and 95gram spring

Sounds good??
 
Vumad

Vumad

Super Hero, with a cape!
Location
St. Pete, FL
ISeeWetPeople said:
so what ive read here i should run 21-28 pop-off and go with 140P/130M and work down from there?
so i will try with 2.0 NV and 95gram spring

Sounds good??
Click to expand...

Not sure on the specs for your setup, but remember higher popoff is leaner. So start high on your jets and work down. For your popoff, start low and work up. Always safest to start rich when you are not completely sure how to tune. Lower popoff is going to be richer.
 
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