97 seadoo challenger 787 hard start when hot

[jsheinrichs]

97 challenger 787 single engine I did the compression test and it is 150psi on both mag/pto I cleaned the carbs set the pop of presure to 42psi with 1.5 needle and pilot jet 65 high speed jet mag 142.5 / pto 145 it starts up great and runs great but when hot in the watter parked for about 5 min it starts up very hard only in full trothel and once it starts it runs great again , it has ben doing this before I cleaned the carbs and even after cleaning and adjusting , please help

 

[Dr Honda]

When you had the carbs apart... do you remember if the regulator diaphragms had a red nipple?

Here's the deal. Almost all the aftermarket diaphragms have issues. Either the bellows is too stiff, or the nipple is too long. This causes the needle and seat to leak a little. SO... on a hot engine, after you shut it off... it will drip the fuel out of the carb. This becomes a 2 fold issue.

1) The engine is lightly flooded
2) There is no fuel in the carbs.

About 3 years ago... It was a real issue, and I changed about 10 sets of diaphragms showing this same exact issue.


If you have Mikuni diaphragms (with a red nipple) then it's you needle and seat that are just leaking, and warn. (The needle needs replaced)

 

[jsheinrichs]

Yes I have the diaphragm with the red nipple but I am going to shop for a new carb kit and needle valves , do you recommend to get 1.5 needle valves again?
And I was thinking of changing the pilot yets, right mow I have the 65 but I have sometimes a weak spot in about 3000 to 4000 rpm so would it help to but # 70 in it?

 

[Chester]

Also, you can check the rotary valve clearance. A worn out RV cover will make it very hard to start when hot.

Chester

 

[jsheinrichs]

Yes Chester if it was the rotary valve clearance that created the hard start when worm it would start hard each time even right after stoping it, but I only have the broblem about 5min after stoping it. correct me if I am wrong.

 

[Dr Honda]

I can't answer for Chester... but as far as the carb parts... replace the N/S with the recommended OE size. (it should be a 1.5) And, verify your pop-off, and after you put the cover back on... make sure the needle isn't leaking.

 

[jsheinrichs]

Ok I got the new needle valves and the carp kits in the carbs now and the boat works better than ever before but the hard start when hot is not solved, next I will take of the rotary valve cover and check the clearance. will keep you updated.

 

[jsheinrichs]

Hi I am still having problem with starting when hot after parking for about 10 min or so , I have rebuilt the carbs and did the rv valve clearance test today and it measures .27mm . What is next that I can check please help.

 

[Dr Honda]

Have you checked the compression? Also... just for giggles... put in a fresh set of spark plugs.


If the RV is in spec, and the carbs are verified to not be leaking... it should be starting up without an issue.

 

[jsheinrichs]

Yes the compression is 150psi and the carbs I pulled of the gas line in and put 15psi on it for 5min (closed the return gas line at the same time) and there is no pressure loss , is there a chance that the accelerator pump could leak?

 

[Dr Honda]

Not really. It feeds up from the regulator side, and enters the top of the carb. I know the 800 carbs are sideways... but I think the hose is still above the diaphragm.


When it finally starts.... does it sputter, and clear out before running smooth again?

 

[jsheinrichs]

Yes that is the case, starts hard sputters then works great , is an idea to lower the arms by the needle valve? To get them further away from the diaphragm, right now they are flush with the body of the carb

 

[Dr Honda]

You can try. But if you have Mikuni diaphragms... it won't mater. BUT... bending the arm down about 1mm... that will raise the pop-off about 3 psi.

 

[Albysure]

I have a 98 sportster 1800...same thing is on going with me...Tryed all the things you have done...nothing works....have you solved this issue or found any more solutions?

 

[Guest_User]

same weird gig here on a 98 challenger, but only does it on the Starboard engine...
new engines, all carbs rebuilt with Mikuni kits and all in spec with all new needles and seats. and replaced the plugs after engine break in. Also 2 new accel pump diaphrams installed.
I thought it was just a learning curve. being used to EFI ski`s.

if I shut the boat down, it will refire right up. if the boat sits for more than 10 minutes or so, the starboard engine will take a bit of intermittent cranking to fire over. What I learned> when I shut the boat off for more than 10 minutes, I have to push the throttle lever 2x no choke and it will turn over, no stumble, good idle right away and it will continue to run good...
just weird. really don`t know other than maybe fuel evaporating in the hot engine.
14 year old seadoo fuel pumps (2) were replaced with 2 HV Mikuni dual outlet pumps and each carb has it`s own fuel supply.
So I`m still learning and watching on what`s going on...


what I did notice before the repowering the boat was that the throttle cables were improperly adjusted and the starboard cable did not fully return, resulting in a hard start. Both Mag carb throttle shafts were hanging, and both were disassembled and fixed.

 

[jsheinrichs]

One more thing I just found that the acc. Pump has only one check valve by the inlet but no check valve by the outlet, I will get a inline check valve and install it right after the acc. Pump and see if it makes a different .

 

[Guest_User]

One more thing I just found that the acc. Pump has only one check valve by the inlet but no check valve by the outlet, I will get a inline check valve and install it right after the acc. Pump and see if it makes a different .

I`m pretty sure the check valve on ours is after the accel pump and inbetween pump and discharge nozzle.
I`ll have a better look when I`m down in the hatch next time...