Carb Pop Off

[Jnz]

Should the carbs with an accelerator pump have the same pop off as ones without? Speedster twin 787 pop offs are first set 26, 31 w/ acc pump second set 28, 32 w/ acc pump. The manual calls for 38 +- 12 so i'm guessing ideal would be in the middle at 38. How is this achieved? I am using the springs that came with the new kits shiny silver and stock 1.5 ns

 

[Dr Honda]

You change the pop-off via the spring weight, and then bending the needle arm a little to fine tune things.

But personally... I'd put the factory springs back in. (Assuming they aren't rotten, or bent/stretched) They always seem to run the best.


If the new springs are from an aftermarket kit... the pressure won't be right. (The non OEM kits kind of suck)

 

[Sportster-2001-951C-Stock]

I recommend referencing the Mikuni chart for pop-off and make sure to use the factory specified seat orifice and spring weight accordingly. You CAN bend SLIGHTLY the metering arms to match pop of both carbs if there's a significant difference (+/- 1 psi is perfect), some gauges are more accurate (have less movement hysteresis) than others and tapping the gauge can help center the movement.

I would expect the result should closely match Mikuni's table within a few psi. Thus it appears this combination should pop near 32psi, I would be happy with anything between 25 to 32 b/c I prefer to fall SLIGHTLY on the low side of spec. but if they popped under 32, say 28, that would be okay by me.

 

[racerxxx]

Put the OEM spring back in.

 

[Sportster-2001-951C-Stock]

If your factory spec is 38psi, the black 80 gram spring should be the factory specified spring thus the spring from the kit is incorrect? I would confirm the black spring is correct and if yes then expect a pop higher than 32psi, within a few psi of 38.

The reason this is important is b/c if pop is too low you can have a bit too much fuel and have difficulty getting the fine idle mixture setup just right.

 

[jimmaki]

Take what I say with a grain of salt because I don't understand everything I know about this, but if your air intake system is stock, your low speed jet is stock and you're not trying to solve a problem, your best off with the original springs and making sure your low speed adjuster is tuned properly. Springs don't age and wear out like gaskets, rubber parts, etc. So unless you've changed associated fuel or air components, stick with the factory installed springs. Just because stuff is in a kit doesn't mean you will be better off using it all because it's there. On that I speak from experience. If you're not trying to solve a problem and your popoff is within that wide latitude within spec, there's little percentage benefit chasing after a nominal popoff reading by bending arms and changing springs.

 

[Jnz]

Trouble is when you get something used how can you tell the factory spring is in fact whats in there. I had a separate thread asking about the stock springs and it may be hard to tell if they're factory or not. These are the originals I pulled out, which I will give a shot at putting them back in.

q+t. If the manual calls for 38 +- 12, according to the chart above would the black springs come stock?

 

[Waterluvr]

Trouble is when you get something used how can you tell the factory spring is in fact whats in there. I had a separate thread asking about the stock springs and it may be hard to tell if they're factory or not. These are the originals I pulled out, which I will give a shot at putting them back in.

q+t. If the manual calls for 38 +- 12, according to the chart above would the black springs come stock?

Your target pop-off is 38 psi, so you'll need to install 80 gram black springs in conjunction with 1.5mm needle and seats to get there.

What you removed originally in your picture are 65 gram springs, which is likely what you used from the kit to replace them with the test results you got. It's not uncommon to see 65's in place of the original counter wound 95's that BRP shipped the boat with.

 

[Jnz]

OK so what does a higher vs lower pop do? If they start you at 38 and give you 12 leeway each direction? With the silvers and some tweaking I should be able to see 32, is it worth ordering black springs to get it to 38, the middle ground? Also is it just a matter of adjustment or do the carbs with accelerator pumps give off different readings?

 

[Waterluvr]

You don't have 12 psi leeway if you want it to idle and transition smoothly into range above the first 25% of throttle operation, a properly adjusted arm will pop at exactly 38 psi. I know the manual clearly states the deviation but if you want the boat to run right set your carbs up like this and go enjoy it:

1.5mm needle and seat both carbs
80 gram black spring both carbs
67.5 pilot jets both carbs
142.5 main jet Mag carb
145.0 main jet PTO carb

Make sure the one way check ball is moving freely against the spring on the accelerator pump diaphragm body inlet, and use carb cleaner with a straw to the AC pump injector inlet to make sure it's open and spraying into the throttle body in a uniform pattern.

 

[Jnz]

OK sounds good. Black springs it is

 

[Jnz]

Where is the best place to pick up 4 springs ?

 

[Waterluvr]

OK sounds good. Black springs it is

If your pop off is to low you'll be pig rich at 1.5 turns open on the low adjusters, you get a dribble of extra fuel in the first 25% of operation every time you touch the throttle from the accelerator pump and you'll get to much fuel in the chamber on those. 1.5 open on the low adjuster is perfect with the 80 gram spring so long as your accelerator pump is doing it's job you'll get a nice clean transition out of the regulated pilot circuit once enough air velocity is moving through the throttle body and the diaphragm holds the needle open the high circuit starts adding fuel through the bombsight.

It doesn't hurt to crack the high speed adjuster open just a little bit on the PTO carb, like 1/16 of a turn open from a gently seated position add's a bit more fuel to keep that cylinder temperature down.

If you want to use the boat this weekend the 65's in the kit will work, just dial the low side down to 1 ~ 1 1/4 turns open and see how that runs the boat for you, you may like it enough to not want to mess with the 80 gram springs but that's how I send all of them back out.

 

[Waterluvr]

Where is the best place to pick up 4 springs ?

SBT or their partner vendor Watercraft Superstore sell them individually, check prices even though they ship from the same place I think SBT is going to have the best price.
http://www.shopsbt.com/jet-skis/low_speed_main_jets_springs.html

 

[FinnExplorer]

I borrow your thread,

Maybe a stupid question but would overboring of cylinders affect pop-off? I've replaced n/s(1.2 oem) on both carbs, used the original springs and the levers/arms should be set the way the shop manual tells you to do. Bad hesitation if I hammer it when idling. Takes a second or two to pick up and then seems to run perfect. I tried fine tuning with the low speed mixture screws without much success.

 

[Sportster-2001-951C-Stock]

There isn't a 12psi window on pop, the pop should be very close to Mikuni's results, within a few psi. Adjsut the lever arms as described level with bottom of chamber if someone has bent them and then try to match pop of both carbs by SLIGHT adjustment of lever arms.

Sure, you can make a 65 gram spring pop at 38psi but you'll have to mangle the metering arm to accomplish this, and an arm that's mashed down low into the chamber won't allow the needle off the seat far enough to supply high speed fuel no matter what the pop is.

Finnexplorer, if your carbs aren't running the factory air box, springs and jets, you need to get that back to spec then go from there. If your cabrs are fitted with accelerator pump and nozzles, make sure the fuel shot is a nice squirt, not a small dribble.

BTW, I run an 80gram instead of 95 gram spring and #80 pilot jet instead of #75 in my 951, it was too lean part throttle so I installed these and now runs great.

 

[FinnExplorer]

Sorry for messing another guys thread.

My boat is bone stock except the overbore(1mm over stock). N/s size is per parts catalog and carb adjustments are also stock by shop manual. No accelerator pumps in this one. Carbs been worked through late last summer due to leaking needles/seats. With leaky needles was ofcourse pain to get started but when cleared didn't hesitate when hammering it from idle

 

[Jnz]

When doing the pressure hold test of 10psi, is the needle and seat the only spot it could leak from? I cover the area in Wd and pressurize it, but get no bubbles. Yet it still won't hold solid it slowly drops to about 5psi. Also is it common for the oring on the bottom side leak or something I should look at. Fresh kits and it doesn't look any different than the other 3 orings that seal fine.

 

[jimmaki]

How are you blocking off the return? Check gaskets under inlet cover. If you're flooding the needle valve area and don't see bubbles from either the needle/seat or the oring then the leak is probably somewhere else. Also define "slowly drops" ... how long does it take to drop from 10 psi to 5 psi?

 

[Waterluvr]

You can have a leak anywhere in the carb before the needle and seat in that scenario, good example of why it's so important to test them.

A little dish soap and water will show you where the leak is, I find people have more trouble getting the 1/4" fuel transfer and return line barbs sealed up than say the pump cover.

 

[jimmaki]

You didn't say how much you overbored but increasing the total displacement changes the fuel demand, plus a top end rebuild and proper break-in will change (probably improve) the manifold pressure. An improper break in and poor compression could give you a lean condition. Check for leaks in the fuel system, clogged check valves in the fuel tank vent lines and blockages in the carb low speed circuit, especially the bypass ports. Also make sure the check valves in the carb are flat and aren't leaking.

 

[FinnExplorer]

You didn't say how much you overbored but increasing the total displacement changes the fuel demand, plus a top end rebuild and proper break-in will change (probably improve) the manifold pressure. An improper break in and poor compression could give you a lean condition. Check for leaks in the fuel system, clogged check valves in the fuel tank vent lines and blockages in the carb low speed circuit, especially the bypass ports. Also make sure the check valves in the carb are flat and aren't leaking.

Sorry I edited it in there too late, 1mm overbore. I'm not even sure if it's hesitation or bogging anymore. Gotta try to pull some choke next time I test. See if it stumbles even worse.

 

[Jnz]

How are you blocking off the return? Check gaskets under inlet cover. If you're flooding the needle valve area and don't see bubbles from either the needle/seat or the oring then the leak is probably somewhere else. Also define "slowly drops" ... how long does it take to drop from 10 psi to 5 psi?

The return I have a spare hose with a bolt in the end of it zip tied. It held for the others. As far as pressure drop its loosing 5psi over about 20 seconds starting at 10psi. Im thinking I have a bad oring on the bottom where the filter is, I had a carb from the second motor where when I pressurized it you could here it coming out, so I swapped the oring and that fixed the problem, and I thought it sealed up when I put that oring in this carb. Maybe just a bad new seal, although it looks perfect and like the rest.

 

[Sportster-2001-951C-Stock]

You can dunk the entire carb in liquid such as water or diesel fuel, pump the pop tester and look for air bubbles escaping then blow the liquid out once you find the leak, it won't hurt anything if liquid's in there a short while (couple days).

 

[Jnz]

That's a good idea, it can't be but two things right, either bottom oring and the needle and seat. Isn't that all that seals this circuit? I will give that a shot tomorrow and hopefully find out what I need to order. Its a bummer waiting a week and needing more parts to wait longer.