Carb Experts Help! (Seadoo Challenger accelerator pump issues)

[treetopflyer737]

I freshly rebuilt two carbs on my motor and am having issues with the accelerator pump on my PTO carb. I have a challenger 1800 with the twin 787 motors with the Mikuni 40i-38 Carbs. I have checked all check valves and made sure none of the small nipples are obstructed. Accelerator Pump Diaphram is new and pop off pressures (40 psi), along with diaphragm holding pressures (4psi) check out OK.

Motors start fine and run from (1/8-1/4) throttle fine. Motor accelerates properly to high rpms but about 5-10 seconds at (1/2)-(Full) throttle falls on its face and dies (starving for fuel that the accel pump should be supplying). After taking air filter cover offf and inspecting the carb lines, I noticed when revving the motors, there is no fuel coming out of the outlet nipple on the accelerator pump (Blue lines) to feed both of the carbs when throttle is opened. Inlet line (Red Line) also seems to have very little fuel going through it to the inlet nipple on the accel. pump.


I took accelerator pump and accelerator pump carb apart and found that one of the plastic check valve on the same side of the pump was not correctly lined up and corrected and tested that. Now I am Stumped. Why am I not getting any fuel out of the outlet nipple of the Accel Pump on the PTO carb? Does anyone have any tests to perform other then ones in manual?

 

[XP 787]

Disconnect hoses to nipples in carb throat and manually move accelerator pump. If fuel squirts from hoses then the nipples are clogged. Just went thru this same issue.

 

[snikwad003]

Accel pump only squirts on throttle up, as you move throttle forward, does not spray fuel when throttle is not moving

 

[treetopflyer737]

So I tried the manually moving the lever with my hand and it no longer is pulling fuel through the red line to the inlet fitting and is NOT squirting fuel. Diaphragm does hold 4psi and check valve in the inlet nipple tests ok by mouth (blow air in however cannot vacuum air out).

I have found a few things in the Challenger 1800 manual to be misguided. Manual states you can check the injector nipples (see picture red line attached) check valve in the same fashion (by blowing through a rubber hose by mouth) however none of the injector nipples on all 4 carbs (even on the two carbs with the working accel pump) will work by blowing into them but I can tell they are unclogged because you can spray carb cleaner or compressed air through them.



So if diaphram is holding pressure and all valves seem unclogged, can the fuel pump not be supplying enough pressure for the accel pump to be working? EDITED** I have checked the two circular check valves in the fuel pump Mag carb and those are new and in working order as well.

 

[treetopflyer737]

I have noticed while blowing and sucking into the accel pump fuel feed nipple (Blue line attached) that it blows/sucks both ways. However I see no mention about this being a check valve in the manual. Should this nipple only suck in vacuum?

 

[treetopflyer737]

I changed out the old lines that were installed and read on a few posts I researched on here about a small part in the old fuel line (seems like an inline pressure regulator) I may be missing... It is called a Recharge Jet Accelerator Pump part # 270500348. I did not see this part in the manual though however it also fails to show the spring!

http://www.ebay.com/itm/NIB-Sea-Doo...-Jet-Accelerator-Pump-270500348-/291351024514

You guys think this could be my problem and does anyone know if they came equipped on the 97 challenger 1800? I rebuilt the other two carbs in the same fashions with all new lines and the accel. pump on that carb is working fine.

http://www.seadooforum.com/showthread.php?4785-Accelerator-pump-problem

 

[treetopflyer737]

**Update** Swapped Diaphragm from working accel pump PTO carb to other PTO carb and found that its the diaphragm thats the problem. Although my diaphragm shows no tears or serious wear and also PASSES the 4psi manual check, it seems to be bad. Man o man this cost me a lot of thinking hours.

 

[snikwad003]

Did you confirm your bad diaphragm to be bad in the other carb? Sounds like you may be on the right track but the accelerator pump isnt doing any thing 5-10 seconds after it has reved up and falls on its face makes me wonder if you have a compound problem

 

[treetopflyer737]

Yes however the bad diaphragm shows no tears and still passes 4 psi pressure check.... I replaced it with the diaphragm from the working carb and the accel pump operation corrected leading me to the conclusion that even though it looks OK it is still a bad diaphragm.

I rebuilt these motors/carbs from the bottom end up with new cranks pistons and cylinders including replacing ALL fuel lines and fuel/oil filters. I'm hoping that this was the main issue with the stalling, it seemed like a fuel starvation issue to me and to know that the accel pump was not working whatsoever on that motor leads me to believe it. I will be back in the water this weekend and retestand report results. Thanks for the help so far.

 

[howie099]

Those accel pumps just give you a shot of gas when you hammer the throttle so you just don't get a stumble. That is all it does you can usually get them to squirt even when the boat is not running once since the lines re charge as your drive or it idles. The recharge jet is there to keep the system from pulling to much gas from the primary fuel system. Bunch of people removed them with no issues. When doing the crabs I replace all rubbers and needle/seat. Do it once is my motto boat season is short don't want to fix stuff in the season. Glad you got it

 

[Dr Honda]

Throw them in the trash, and re-jet to the 96 specs. (Can't tall you how many I did that to in my shop)

 

[treetopflyer737]

The bad accel pump diaphragm (that tested OK at 4psi) was definitely my problem in this particular case!!! I ordered the recharge jets however have not installed them yet and boat ran great. Motor has not fallen on its face after 5-10 seconds at 1/2-full throttle once since replacing it with a new one. Boat finally produced two great days on the water, I couldn't be happier- been working on this damn thing for the last year! :cheers:

Also after experiencing this change directly, I have a hard time believing people can just eliminate the accel pump all together without making some serious jetting changes or at the very least blocking it off completely so that it doesn't effect fuel supply and vacuum in other parts of these carbs.

Dr. Honda.. Interesting about jetting and running the 96 specs. I'm assuming it was the same carb setup BN40i-38 without accel pump installed?

 

[treetopflyer737]

Thanks for the feedback everyone!