Accelerator Tuning Question / Rejetting etc...

E

exoh_e

New Member
Hi.

I have a Seadoo Challenger 5672 with twin 720's. The accelerator pumps are all sorts of messed up; (Needle, Pump, Spring and pin) I removed the spring and pin and bought Residual Press valves, and even new Needles. It's just not right. I know the engines were designed for it by really smart engineers etc etc. I could buy knew carbs for 250 a pop but I'm curious right now.

But for... just a curiosity let's say. I could rejet slash change the float too the following?

(This is my challengers settings I'm assuming; It's a 2000 but all the 717's are like this.)
1999GTI717270500420N/ABN-40I-38MAIN-167.5 PILOT-752.0270500428 (Non Standard & Discontinued)36 - 40LOW- 1 HIGH- 0ACCELERATOR PUMP

I could go to the following settings right?
1997GTI717270500297N/ABN-40I (SB)MAIN-175 PILOT-67.51.5270500267 (80)38 psi (23 - 43 is manual spec)LOW- 1 HIGH- 1-1/2

Or does someone have a better idea? Let's just assume we have to rejet/float it. Thanks.


Source : Sea Doo PWC Carburetor Reference
 
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From what I can see from the chart it looks like your thinking of going smaller in the pilot jet, wait and see what the experts say but if your eliminating the accelerator pump I would think you would need to go larger for the pilot jet than you currently have
 
This is only a guess, but I’m betting that your current pilot jet is smaller than a 75, and that a 75 is what you would need if eliminating the accelerator pump. I have a 98 Challenger that also has the twin 717’s with accelerator pump. I may do a little research and see what I can find out what the current pilot jet is, I rebuilt my carbs but my eyes weren’t near good enough to see the size of it. A few good places to check would be Seadoo warehouse, they have parts fiche for almost every part, could also check OSD marine and I do have the shop manual.
 
62F41F1B-10E3-44D8-B956-A7FC38A545F6.png
This is from Seadoo warehouse for my 98 Challenger with twin 717’s it has the single carb with accelerator pump and has a size 70 pilot jet. There should be lots of information on this if you search google like this “ accelerator pump delete site:seadooforum.com. I would be more apt to rebuild the accelerator pump but if you do Eliminate it, I would go up to at least a 75 and start out with the low speed screw turned out 2 full turns, better to be to rich and bog/foul a plug than run lean. Good luck
 
burtshaver2021 said:
This is only a guess, but I’m betting that your current pilot jet is smaller than a 75, and that a 75 is what you would need if eliminating the accelerator pump. I have a 98 Challenger that also has the twin 717’s with accelerator pump. I may do a little research and see what I can find out what the current pilot jet is, I rebuilt my carbs but my eyes weren’t near good enough to see the size of it. A few good places to check would be Seadoo warehouse, they have parts fiche for almost every part, could also check OSD marine and I do have the shop manual.
Click to expand...
Get off that 20 bucks dude and assuage your worries. I do nothing on carbs without these. I verify every jet and needle. Good for inspection also. I had to tune my spectacles up recently and get the lights back bright. :D :D

Magiifying Spectacles
 
Ehh, It's running so off. I rebuilt it with all Mikuni parts and it's just not right. SO! I bought the two new carbs. Will report back just for fun.
 
That is the problem with twin engines and twin carbs. Gotta get everything working spot on. Good Luck !
 
No need to buy new carbs,, ever,,, really,, the problem with those accelerator pumps is finding a replacement for the umbrella check valve,
There is no mikuni part number for it,
You can bench test that pump
 
Well, I understand how they work sorta?

Depressing pump ----> Flow -----> Ball and spring retracts -----> Flow -----> Other ball and spring retracts ----> Squirt! ----> Both ball's close to keep fuel pressurized.

Problem is my accelerator needles were messed up, non-salvageable. Stamped a similar Needle seems okay. My ball and springs are all sorts of messed up and I used the valves in this video "
"

Maybe I rebuilt the carbs wrong but I used OEM parts and the pop off was A.O.K. Still ran like crap (Both engines are 140 ish psi) and also they are single carbed. Maybe I'm impatient. I bought one new single carb just to see to tickle my fancy. All my other Ski's are fine; besides my 96 GTI 720 that thing runs okay but also has phantom spark issues(Many new things, but thats for another day)

I find it funny ya know, new Mikuni rebuild kit is 100 bucks (2 Carbs), a new carb was 200 all together 400 (Expensive for me consider my boat was 1800 in FAIR shape had to redo all seats, reverse/forward cable) but both engines had high psi and the engine bay was really clean. I bet the carbs need to be tinkered with and worse comes to worse I'll do it eventually and the new single carb I bought will be used for X future project because I'm addicted now, Three ski's in count... really wanna get into the 787's and 951's but I know the 657 and 720's "decently" now.



Edit: I should try a colder or hotter plug.... I will.. do that tommorrow and report.
 
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Still have alot of painting and detailing decaling to go but a work in progress!
 

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Anyone referencing this. I took off the accelerator turning lines completely and replaced them with regular throttle cables to the throttle assembly. (Throttle Levers ---> Carb; nothing else) I prefer the no turn acceleration because I am DEFEINTELY in more control and can perform different maneuvers.

Conceptually what they do is one motor gets "accelerated more" on the side your turning when you turn.. but lets say your trying to cut your wheel and youre docking the boat its a pain in the ass with it.
 
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exoh_e said:
Well, I understand how they work sorta?

Depressing pump ----> Flow -----> Ball and spring retracts -----> Flow -----> Other ball and spring retracts ----> Squirt! ----> Both ball's close to keep fuel pressurized.

Maybe I rebuilt the carbs wrong but I used OEM parts and the pop off was A.O.K. Still ran like crap (Both engines are 140 ish psi) and also they are single carbed. Maybe I'm impatient. I bought one new single carb just to see to tickle my fancy. All my other Ski's are fine; besides my 96 GTI 720 that thing runs okay but also has phantom spark issues(Many new things, but thats for another day)

I find it funny ya know, new Mikuni rebuild kit is 100 bucks (2 Carbs), a new carb was 200 all together 400 (Expensive for me consider my boat was 1800 in FAIR shape had to redo all seats, reverse/forward cable) but both engines had high psi and the engine bay was really clean. I bet the carbs need to be tinkered with and worse comes to worse I'll do it eventually and the new single carb I bought will be used for X future project because I'm addicted now, Three ski's in count... really wanna get into the 787's and 951's but I know the 657 and 720's "decently" now.



Edit: I should try a colder or hotter plug.... I will.. do that tommorrow and report.
Click to expand...

I never saw your video when you posted it but I've done a lot of tests on mikini carbs and I've never seen one crack at more than 3 pounds on my gauge. The only reason for the resistance and cracking pressure is to keep the line charged with fuel and it doesn't bleed down. Seems like a lot of pressure to me but good luck with it.
 
exoh_e said:
Anyone referencing this. I took off the accelerator turning lines completely and replaced them with regular with just throttle cables to the throttle assembly. (Throttle Levers ---> Carb nothing else) I prefer the no turn acceleration because I am DEFEINTELY in more control and can perform different maneuvers.
Click to expand...

I was curious about how that system works. My son's Speedster had those. The Speedster I recently restored did not have them and after reading this thread.... I'm sure glad it didn't have them. LOL Glad you got it sorted out. Gonna be really reliable now and that is never an accident or good luck.
 
etemplet said:
I never saw your video when you posted it but I've done a lot of tests on mikini carbs and I've never seen one crack at more than 3 pounds on my gauge. The only reason for the resistance and cracking pressure is to keep the line charged with fuel and it doesn't bleed down. Seems like a lot of pressure to me but good luck with it.
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They worked surprisingly fine, 5 psi would probably have the same result. I said before it wasn't working well I just had to configure it the right way.

Hypothetically if anyone else is trying to replace the accelerator pump nozzle; make sure its the right size. Anything under you'll get no performance and you'll have to cut it in half than it should be sorta better.

You have to keep the accelerator pumps unless you just get another carb set from like a 96 gti or... another 720'


cheers m8!!
 
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