Top End Performance issue/question

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mar-10s

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I picked up a 2001 GTI: I believe a 717 engine, sticker says 718cc engine? end of Nov.2015

Let me mention that the engine is grey, the exhaust manifold is white and the exhaust pipe is black.

I have gone through it since then doing the "many things" suggested in the threads posted by the great experienced people in this forum.

THINGS I HAVE DONE:
New Battery, grey fuel lines out, fuel selector cleaned out, fuel filter good, new plug wires and plugs, drained gas tank, oil injector gone went with block off plate (ethanol free gas from now on) mix 40:1 right now still in first tank of gas since block off installed, carb gone through/rebuild, new Needle n Seat, new jets both main and pilot, cleaned out bilge boxes, put in new bilge tubing, found a hood with working gauges MPH and fuel oil indicator.

ALL OF MY TESTING AND TUNING HAVE BEEN DONE IN THE LAKE UNDER LOAD
To my knowledge from manuals I have found online 717 engine with a Mikuni BN40I-38-48 have not verified that?

WHERE IT IS AT RIGHT NOW:
Starts right up no touch throttle or choke revs to steady idle cruises nice and smooth in no wake speeds
I have returned carb to OEM specs by going with a 75 Pilot 167.5 Main 2.0 N/S pop off is consistent 22psi tested 4x LOW speed out right at 1 3/4 HIGH speed out just a bit past 1. I have great low to mid range transition gets up on plane then no faster then 25mph, this is all with the black air box off,

HERE IS THE KICKER: Question ????
With the seat off and sitting on the right side and right hand on throttle I can gas it from idle (no hesitation) to a steady 25mph WOT, then I reach down and "cup" the airfilter/flame arrester with my left hand, this thing gets up like a rocket to about 52mph me hanging on with one hand,,,lol. Is it time to put the "air box" back on ?

I have NOT done anything to the accl pump assuming it is fine or that is the cause of my issue.

Has anyone experienced this, can anyone tell me what I have missed, can anyone tell me what to do to make it right.
 
well most of the post I have read say to leave air box at home while making adjustments, it is a PITA to reach the HIGH speed adjuster with air box on. I have only seen (1) post say to leave air box on ? so I went with majority vote on that. I know by now that there is a significant difference tuning on trailer with garden hose on it vs having it at the lake under load. If I put air box back on and it cures my issue I am golden. Going to lake this afternoon with air box on,, will see what happens ? and post the outcome this evening
 
Truefully the airbox on that ski cause a lot of restriction, that is the way it was set up to work, high restriction with high popoff, I see no way you could possibly adjust the carb out with the airbox off, as you have verified by cupping your hand over the carb you are running extremely lean, reinstall the airbox and the flame arrestor screen and give it another go, the high speed should be fully closed on that model ski.
 
thanks for the replies so soon on this.. I am not doubting anyone here, I just don't under stand a HIGH speed setting to be fully closed ? some articles say "maximum fuel flow for high speed adjuster is 3 turns out" that is why I am confused,,, to me that would make it super LEAN to have it closed
again I am new to this whole jet ski thing and that is why I am here. I have had it fully closed at one time and all it did was "bog" out at about 1/4 throttle
 
The high screw is closed on all seadoos because they account for this with the jetting and pop off. If the ski is stock go by the factory settings. All seadoos that are stock will run perfect with the screws set to factory spec. Don't go by what other forums say.

On another note, you did keep the oil tank and hoses connected to the cases for the rotary valve gear correct? Even with the injection system blocked off the rotary gear still needs oil.
 
mar-10s said:
thanks for the replies so soon on this.. I am not doubting anyone here, I just don't under stand a HIGH speed setting to be fully closed ? some articles say "maximum fuel flow for high speed adjuster is 3 turns out" that is why I am confused,,, to me that would make it super LEAN to have it closed
again I am new to this whole jet ski thing and that is why I am here. I have had it fully closed at one time and all it did was "bog" out at about 1/4 throttle
Click to expand...

Maximum fuel flow on a high speed screw is three turns out, that is correct, what this means is at two turns out you need to go to a bigger jet size, on Seadoos they are jetted with the screw closed , this way all a customer can do is richen the mixture and not lean it out and blow up the ski, if you continue to run that ski with no flame arrestor you will lean it out and it will seize up .My suggestion is pull the carb apart and check the screen on the fuel pumpp side , it's probably clogged up.
 
thank you makes sense now...lol i am home now,, i will set me LOW & HIGH back to specs LOW 1 turn out and HIGH closed.

yes i did leave the oil line on to the crank case.. i will bring the air box with me in a bit and put it on once adjustments are done...

be back later with results
 
hey guys,

back from the lake,, air box back on,, LOW & HIGH adjustments back to "stock" and suggested settings? I hate to give bad news but it ran like a big bag of s&*! rough idle, NO acceleration and a constant bog at every throttle position,, parked on beach I took the air box back off.. returned all adjustments back to where I had them yesterday,, started right up no touch anything,, idle and acceleration are back, right up to plane 25mph cup the airfilter with left and away we go to 52mph?

right back to where I started... ???? very stumped at this point
 
When you did the carb you replaced everything with all Mikuni parts? Your Popoff is total wrong. You didn't replace the factory spring did you? That is a special spring that gives you the 36-40 PSI Popoff its very hard to find that spring. I am pretty sure that is why your ski runs good without the flame arestor. I have the same ski that sat for 5 years and I just just cleaned up fuel system and replaced the oil and off I went. I got the ski for $325 with a trailer since I did an engine swap for a friend. I give my high screws a 1/4 turn from closed to make me feel better. The Accel pump could be clogged but that would just make you stumble when you hammer it and than it will catch up.
 
howie099 said:
When you did the carb you replaced everything with all Mikuni parts? Your Popoff is total wrong. You didn't replace the factory spring did you? That is a special spring that gives you the 36-40 PSI Popoff its very hard to find that spring. I am pretty sure that is why your ski runs good without the flame arestor. I have the same ski that sat for 5 years and I just just cleaned up fuel system and replaced the oil and off I went. I got the ski for $325 with a trailer since I did an engine swap for a friend. I give my high screws a 1/4 turn from closed to make me feel better. The Accel pump could be clogged but that would just make you stumble when you hammer it and than it will catch up.
Click to expand...

As stated above and as I stated in my post before this one that the restrictive airbox is specifically designed to run with high popoff, I don't know exactly what you have going on there but something inside the carb is not right.
 
hey guys, back from round 2 at the lake today,,everything put away eating mcdonalds with a side of two stroke on my fingers,

howie099... the carb rebuild kit I got came with 4 springs, I have had pop off's from 18, 23, 34, 43. tested each time in those increments, in my situation the higher the pop off I go the more it stumbles through the throttle transition and still never reaches the higher rpm range and no faster then 25mph all with pretty much the same L/H settings.

on my 2nd trip out today a took a pc of flat thin plexiglass with me about half the size of an index card, with the seat off and the BOTTOM portion of the air box ON and the flame arrester ON, I gas it right up and get going to plane and 25 I began to lay the plastic pc down over the filter (does not cover the whole filter), just about half with round portion of the carb intake not obstructed at all, takes right off to the higher rpm range 44-47mph with all responsive throttle positions. great low end through mid range to WOT. no stumbling or bog at any throttle transition. So this lil restrictor mod (temporary) seems to have this ski operating at it's best since I have had it, with a pop off of 22-23.

to me it seems I have a vacuum to fuel ratio issue through the throttle transition.

speedracer.. you mention check screen on fuel pump side, ? inside the carb it has been replaced with new one from rebuild kit. Or are you talking about the accelerator pump. That is one thing I have not got into, if that is the root cause of my issue then yes I will check it out.

that is where I am at with it right now. Thanks for all the help and input guys, I know I am new to this and everything I have done is mostly from this forum to get me where I am at. Thank you
 
Ok a couple of things here , what needle and seat did you put in it, I ask because the size of the needle and seat affects the popoff pressure, were any of the jets changed, was the high speed check valve changed, were these OEM Mikuni parts or aftermarket, if they were aftermarket especially the main diaphragm it can and will cause running issues.

What you are doing by cupping your hand or putting plexiglass over the screen is artificially creating high vacuum and richening the fuel mixture, some way some how you are now seriously lean on the main jet, this can either be a carb issue. a vacuum leak issue such as the carb base gasket or a fuel flow issue.

Personally it sounds to me like it may be lean in the midrange and you are getting it through that spot by hand choking it to richen the mixture, is the accel pump working, here is a quick test without pulling anything off, warm up the ski, cut it off, now work the throttle about twenty or thirty times, try to restart it, if it fires right up the accel pump isn't working, if you have to hold the throttle wide open to start it and clear it out the accel pump is working normally.
 
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I have returned carb to OEM specs by going with a 75 Pilot 167.5 Main 2.0 N/S

this is based on what I believe I have as for the carb
 
the high speed check valve that came with kit ( very small clear plastic thing ) was a heck of a lot stiffer than the one that was on before I rebuild the carb.
 
your popoff should be between 36-40 with a 2.0 needle and seat in that carb if the correct spring is in it. like I said high popoff 22 ain't gonna get it.
 
speedracer...

I will check the accl pump theory like you suggested and see what happens. Then I will get the pop off back to where you suggest.
thank you for your help.
 
speedracer..

I want to touch base with you on something you said about the

were these OEM Mikuni parts or aftermarket, if they were aftermarket especially the main diaphragm it can and will cause running issues.

the main diaphragm I got in the carb kit was a bit more 'thicker' stiffer not as plyable or 'flemsy' as the one that was on it when I got it and does not have little red end nub pc. there is a nub, but not exactly like the one that was on it. The carb does not leak any fuel and the new diaphragm fit right in it's place, so I just thought the original was worn. It wasn't brittle or anything very thin and had some creases in it.
 
To be honest every time I have been into a carb that was built with aftermarket diaphragms it had running issues, I would toss them and put OEM Mikuni ones in it
 
Stop chasing your tail. We have been there too and are trying to get you through this quickly.

Buy a genuine Mikuni Carb kit, the correct spring if you tossed the original one and a new carb base gasket. Replace all the carb parts with the ones in the Mikuni kit, install the correct spring and your pop off should check out at the exact factory spec. Verify Acc pump function and install carb with new base gasket and complete air cleaner. She should run spot on.
 
I appreciate all the input here guys,,

I will test speedracer theory on the accl pump when I get home this evening, if it is not functioning as it should, I will fix it, then get the carb back to it's specs.

results to follow later.
 
UPDATE ::

last night I was prepping for todays suggested work from speedracer, before I tried the accl pump test.

I was looking at the 'housing arrester' #273 000 131 and noticed 4 holes at the base of the plate ( up to this point I thought it was the way it was supposed to be ) looking a little closer I saw that they were threaded for something. A threaded plate of sorts #270 000 393 screwed in with 4 #207 351 660

like I said, up to this point I did not know anything went there, nothing was there when I got the ski and I didn't know any better, I am using ref #'s so ppl know what exactly I am talking about.

So with that find last night, what purpose does the threaded plate serve ( it looks like it does cover about an 1/8" portion of the round intake opening when installed ) and I am PRETTY SURE that the 4 holes right there at the base of the plate are NOT helping my current situation. I am not sure about that plate, but I would have to say that those 4 holes need to have screws in them.

thoughts. suggestions ?
 
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