yet another carb spring/popoff psi question

[PatinMD]

Thanks for the many thoughts and suggestions.

I'm going to order the seadoo spring later today. That will remove any question about the correct spring. I'll change out the spring and go with the 2.0 seat and test popoff then. If it's a 130 g spring, well that will answer a lot of questions.

I know the 115 g spring with the 2.0 seat gave a 25 psi pop off. Perhaps going with the lower popoff would lessen the chance of running lean than the 1.5 with 65 g spring at 36 psi. Either way, I can't get to factory spec's with the available parts. Hopefully the choice won't matter with the new seadoo spring.

The lever is set to the max height, as it was on the original carb. I didn't adjust it on the new carb, that's the way it came. I tested it for leakage, with the popoff tester and it was holding.

The jets are as spec'd 167.5 and 75. I don't want to open that can of worms, as Sportster said.

I expect to work on the carb setting this weekend, so I'll know how the idle mixture screw responds after that.

 

[PatinMD]

I ordered the spring from the one and only place that offered it for deliver in 7 - 10 days. Then I found out it was out of stock, but they still expect to deliver it in the 7-10 day time frame. I didn't mind paying the 10$ for it as much as I hated paying the 9.99 shipping price. I ordered some other parts with it just to spread out the shipping $ pain.

OSD had the spring cheaper and probably ship cheaper too, but they're oos for sales right now.

I was looking in the manual for the spec'd compression when I came across the spring spec. Darn. I didn't think to look there. But the 02 GTI is listed as having a 130 g spring. So that's the answer of how a 2.0 N&S can have a popoff of 36-40.
No sense doing anything else with the carb until the right spring comes in.
Thanks to everyone for their help.

 

[Mickirig1]

You rebuild it yet? My 2000 GTI spec's say 36 pop off. I used the original spring and arm. Replaced the 2.0 seat and valve. Popped at 36 pounds all day long. I ended up buying a used Carb to cure my Problem child Ski's ill's. You have to make sure the carb is CLEAN! If the transitions ports are not clear, it will never run right! The jets may be worn or stuff is built up behind them.

 

[Sportster-2001-951C-Stock]

I guess you have the link for Mikuni's manual but I wanna make sure, maybe someone else reading your thread in the future could use the link as well:

http://www.mikuni.com/pdf/sbn_manual.pdf

 

[PatinMD]

I guess you have the link for Mikuni's manual but I wanna make sure, maybe someone else reading your thread in the future could use the link as well:

http://www.mikuni.com/pdf/sbn_manual.pdf

I saw that manual but stopped reading when it referred to being for Super BN carbs. None of the documentation I had seen referred to the BN-40i carb as a Super BN 40i. I just took a second look and they appear to be the same carb.
Are all the modern BN carbs Super BN carbs?

Thanks for the link.

 

[PatinMD]

You rebuild it yet? My 2000 GTI spec's say 36 pop off. I used the original spring and arm. Replaced the 2.0 seat and valve. Popped at 36 pounds all day long. I ended up buying a used Carb to cure my Problem child Ski's ill's. You have to make sure the carb is CLEAN! If the transitions ports are not clear, it will never run right! The jets may be worn or stuff is built up behind them.

I had to give up on the rebuild for now. I couldn't clean the accelerator pump ports. The output side wouldn't allow flow in pressure or vacuum. Also, the entire interior of the carb showed corrosion (pitting) so I wasn't sure if it would have sealed once reassembled.
I'm battling the calendar on this one. Any day now and I'll get a freeze warning that'll force the ski's into winter hibernation. Quickest and least risk of failure was to go w a new carb.
Thanks

 

[Sportster-2001-951C-Stock]

I expect yours are Super BNi's, and the "i" denotes the new style improved fuel pump, which was the latest revision so my understanding is you need parts for SBN40i, as opposed to SBN40 or BN40i, assuming there were such animals. A kit for an non "i" will have the wrong fuel pump gaskets and diaphragms, the "i" has that rounded hump on two of the fuel pump sides.

My 2001 Seadoo factory service manual calls the 2001 951 carbs BN46i but they're definitely SBN46i carbs.

 

[Sportster-2001-951C-Stock]

I couldn't clean the accelerator pump ports. The output side wouldn't allow flow in pressure or vacuum. Quickest and least risk of failure was to go w a new carb.
Thanks

Maybe the new carb also came with an accelerator pump. Those a-pumps seem to be somewhat delicate, there's a rubber (silicone I think) mushroom check valve inside that's easily torn so be gentle with that. And carb cleaner (acetone) will eat the diaphragm, I'm pretty sure.

 

[PatinMD]

I expect yours are Super BNi's, and the "i" denotes the new style improved fuel pump, which was the latest revision so my understanding is you need parts for SBN40i, as opposed to SBN40 or BN40i, assuming there were such animals. A kit for an non "i" will have the wrong fuel pump gaskets and diaphragms, the "i" has that rounded hump on two of the fuel pump sides.

My 2001 Seadoo factory service manual calls the 2001 951 carbs BN46i but they're definitely SBN46i carbs.

The cut and paste from the manual probably won't come out as well as I'd like but it calls for a Mikuni BN-40i diaphragm, fuel accelerator pump. I have the GTI.

CARBURETION
GTI GTI LE
Carburetor Type Mikuni BN-40i diaphragm, fuel accelerator pump Quantity 1
Main jet 167.5
Pilot jet 75
Spring 130 g (4.6 oz) 115 g (4.1 oz)
Adjustment
Low-speed screw 1 turn ± 1/4
High-speed screw 0
Idle speed (in water) 1500 ± 100 RPM
Idle speed (out of water) 3000 RPM
Fuel
Type Regular unleaded gasoline
Minimum octane no. 87
Fuel return line orifice 0.8 mm (.031 in)

thanks

 

[PatinMD]

Maybe the new carb also came with an accelerator pump. Those a-pumps seem to be somewhat delicate, there's a rubber (silicone I think) mushroom check valve inside that's easily torn so be gentle with that. And carb cleaner (acetone) will eat the diaphragm, I'm pretty sure.

You're on the money. It was the a-pump that I couldn't get clean. The diaphragm inside of it wasn't in too bad of shape. It holds pressure. It was the exhaust side of the a-pump that I couldn't get open. I had it apart and soaked it in carb cleaner, then in CRL a mineral deposit cleaner. The CRL worked wonders on other parts, taking the white deposits right off. (it's a mild acid) But it didn't open up that port.
Kicker is, SeaDoo wanted 325$ for that part alone. And they were the only ones that had it.

The new carb did come with the a-pump. It came with everything I needed except, the #428 spring (130 g) and the carb to oil pump cable (I reused the old one). Oh, and I had to change the 70 jet to 75.

thanks

 

[PatinMD]

Arrrggghhhhhh. I received the package with spring in it this evening. The spring that had to be ordered as an OEM SeaDoo part 270500428. The one that is listed in the SeaDoo manual as a 130 g spring. In the box was a part marked 730-03030. A quick check of the parts catalogs shows it to be a 65 g spring. Almost two weeks waiting for this 'special' spring that they didn't have in stock and needed to wait to get it from SeaDoo, and I get the wrong part.
Thanks for listening to the vent.
The next three days are 70 degree plus, then on Saturday we drop to highs of 50's for the foreseeable future. I already took tomorrow and Friday off since I knew the parts were coming in this evening.
So to plan B. I'm going to pull the 115 g spring from the old carb, install it and a 2.0 N&S in the new carb which gave me a 25 psi pop off. That will provide enough of a fuel flow, although it might be at a lower kick in with the lower pop off. It should be a 36-40 pop off.
Wish me luck.

 

[Sportster-2001-951C-Stock]

If pop comes out too low, I'd expect the idle mixture screw probably won't be able to control idle mixture. So if the low end isn't too rich and you actually have decent control over idle mixture then you should be good to go.

It'll be interesting to see how this works.

 

[mikidymac]

So Benji and I have had the same carb issues on our 2003 GTI's as you and I have done a ton of these carbs with no issues but my GTI carb finally got me and nothing I did fixed the hesitation. I finally bit the bullet and bought an entire new carb from OSD and Benji did the same. I can say our skis have never run stronger. Best money I spent on the GTI.

 

[Strizzo]

I had a similar issue with my accel pump, I ended up taking the housing apart and poking an Allen wrench in to break the blockage. Before that I had put 90+psi of compressed air into it and couldn't get it loose.

 

[PatinMD]

I spoke with the vendor. The 130 g spring is no longer available. They're going to send a 115 spring as it's the closest I can get (I asked them to do so).

I also looked closer and the spring from the old carb is a 95 g spring not the 115 that I thought. I installed it in the new carb with the 2.0 N&S. Popoff was 26 psi. I installed the carb and I'm having some trouble with the idle speed. I've got to think it thru, but first impression is that it's running too rich as it doesn't want to drop rpm's. Seems like it wants to stay closer to 4,000 than dropping to 3,000 (out of water idle). I need to get it in the water tomorrow or Fr.

What's the max rpm I should see on the engine? It's a 720 in a 2002 GTI. Stock.

thanks

 

[Strizzo]

usually an idle that won't come down is lean, if the idle drops right down where its set and then is sluggish after idling a while, its probably too rich.

 

[Sportster-2001-951C-Stock]

Could be the throttle cable is adjusted too tight, not allowing the butterfly to close. Dual carbs could also be the butterflies aren't syncrhonized.

If the throttle cable isn't holding the butterfly open and it's still idling high, then too lean so try adding some fuel with idle mix screw and see if that tames it down.

If you put it in the water and idle is too lean it's liable to refuse to idle, just stop running.

Since carb is new, should be just a matter of getting the pop pressure up high enough it doesn't fuel-flood and the jets you already confirmed are correct.

 

[Sportster-2001-951C-Stock]

Rev limiter I think is 7,100RPM and that shouldn't bounce off the limiter so you might be able to turn near 7,000 If your pump is good and tight, probably more like 6,800 is my guess.

 

[PatinMD]

Took the ski out yesterday. Ran fine at the dock. Untied it and it ran a little hi on the rpm - 2400 at idle as it went thru the little harbor. It was idling at 3,000 on the hose when the carb was adjusted. There was the light smell of unburned gas while going thru the harbor, so it seemed to me to be running rich. But it wasn't emitting smoke in the exhaust.

Takes about 5 minutes to get thru the harbor. Once out of harbor and past no wake zone, brought it up gradually to a higher rpm, maybe 15 - 30 seconds and approaching 5000 rmp. Then it died. Wouldn't restart after multiple tries. Waited about 5 minutes and it would start with the throttle partially depressed, would rev up high, go fast and shut down in 5 - 8 seconds. Did that two or three times then I finally gave up and towed it back into the harbor. Would not start on the trailer (in the water). Choked, partial throttle, no throttle, no matter, it would not start. Got it home and it started hard, but started and ran fine, on the hose.
It still has the 95 g spring with the popoff of 26. The 115 spring hasn't arrived yet. I'll wait till the 115 spring gets installed before working on it again. But what else might be causing it to run fine on hose and for a small time on water, then die and not want to restart?

thanks for all the help I've received so far.

 

[racerxxx]

I didn't go back and check the thread, but did you check the compression?

 

[PatinMD]

Compression was 140/145.
thanks

 

[Sportster-2001-951C-Stock]

Did you unscrew the gas cap to make sure the tank vent isn't causing a vacuum as fuel is being consumed? If makeup air can't enter tank, the pump can't overcome the vacuum.

But it's unclear if you're running too rich, was it 4-stroking (rich burble)? 5,000 RPM only, can't get more? If pig rich, maybe you fouled plugs? Black with fuel soot, grey too lean, brown just right.

If lean hesitating, you might roast a piston so monitor compression afterward just to make sure no harm done.

If you were running out of fuel (weren't fuel-fowling plugs), confirm no air leaks in fuel lines. Connecting a bulb pump and siphoning into a can underneath the ski should reveal air leaks.

Fuel valve clogged, or low fuel in tank?

If trailer idle was 3,000 then water idle should be less than or around 1,500 unless your pump is super lose (toasted wear ring?). The pump loads them that much...

Trailer running won't tell you much more than "yes, it runs", sorry. You can get an idea by starting on trailer if a cylinder is misfiring or something like that.

If you had said your idle was extremely low in water and you had to open the throttle to clear it out, I'd suspect too rich (loading up with fuel).

I'm sure I'll think of something else to ask in a minute, lol...

 

[PatinMD]

I checked the gas cap, although I hadn't burnt enough fuel to cause much of a loss of volume.
Not sure of a better way of describing the engine as the rpm's rose from idle to it's top out of about 5,000. It didn't top out at 5K. It died at 5K. There was still a lot of throttle left.
I'll check the plugs, but I'd expect they're brown now, after running on the trailer while flushing the engine.
I checked the fuel lines from carb to tank before putting the carb back on.
Fuel valve was pulled and cleaned (it wasn't dirty) while I was waiting for carb parts.
The pump and wear ring look pretty good. I've not measured the gap, but the ring looks shiny and there's much less than a dime of space.

That idle speed not dropping has me puzzled. I'm thinking it's back to the spring. I should have the spring installed this week. But - and it's one of those weeks - I tore up the wear ring in the other ski. So I can't take this one out until that one gets repaired so I can have a tow boat on hand. Probably be next week before I can do anything besides run this one on the trailer.

thanks!

 

[Mickirig1]

You have to make sure you have no air leaks. It is much easier to suck air then gas. You have a pop off tester check, the whole system. The procedure is in the repair manual. Check all the connections, if you can turn it on the nipple it's too loose! Take the water separator / fuel filter out of system. Bridge it with a piece of 1/4 inch brake tubing. They cause many problems. Gaskets go bad, or not tight enough to seal. You cleaned the tank selector, but did you check it's air tightness? If you have a plastic fuel filter check for creaks in it. There are other connections that can leak air. Like the oil and gas tanks necks. Caps and lines. That's why pressure checks are so important. I chased a leak for a whole season till I found it!

 

[PatinMD]

Finally had time to work on the ski today.

Pressure tested the system, the gas cap leaked (cracked ) but stopped leaking if I tightened it really hard. There was another small leak somewhere else, but tightening every clamp stopped it. The vent (out) worked when I took off the hose pincher to release pressure.

I didn't like the looks of the gasket when I pulled the carb, so I put a new one on there.

The spring that was so hard to find - came out of a sealed Sea Doo package with the correct part number, which should have made it a 130 g spring. It looked exactly like the 115 g spring. Same in every way. Put it in the carb and the pop off was exactly the same as well - 26 psi. So, I took the old 115 spring and stretched it. Then stretched it a bit more until it was about an eighth inch longer than the other spring. Installed it and got a 32 psi pop off. The manual calls for 36 - 40, but 32 is close enough for me for now. The new spring pushed the lever up high enough that I had to adjust it down a bit. So the new carb with the new parts is ready to go.

Now I wait for a day to put it in the water.

thanks for all the help that I've received.