750 bogging issue

[Krashtestdustin]

hello all, so while waiting for parts to get in for my FR build, me and my brother decided to swap a 750 out of a 93 super sport xi into a 650sx hull, and well everything went just fine as far as the swap but he went to ride it for the first time the other day and ran into a issue, the ski idles just fine under a load but once you break 1/4 throttle with it it bogs down and wants to stall on you everytime, ive never delt with anything other than a 650sx as far as kawi stand ups go and not really sure where to start with this, i had my brother run a compression test for me since im in nc and hes in fl with the skis and it came out at just over 100psi on each cylinder, which is blatantly low considering by what i know around 165-170 is good so its obvious it needs a top end rebuild, my question is is there anything else that could cause this that i should check into

 

[Pro-pulsion]

My first concern would be to remove the flame arrestor and try to rev it up on the trailer. You do not need to hold it open, just try to get high rpms out of it for just a second or two. Watch for a backfire flame front to come up out of the carburetor, if not then it most likely will be carburetor kit related. If you do see flames however, time to look into into timing areas. The easiest is to test the coil resistance values first and see if the coil is failing under load. The most common failing point on the coil is the secondary winding which gets tested at the sparkplug boots. Sometimes the boots themselves are the culprit. If it tests out ok then move on to deeper areas. I have learned over the last year or so that the 750 Kawi engines have well known problem areas in the flywheel rivets. They wear and hammer around fracturing the flywheel. In addition, the worn out rivets allow the flywheel to be sloppy changing where the magnet positions are throwing off the timing and making the engine sluggish or not very responsive at all. If you are in that deep, it would be a good time to check the flywheel key too. Make sure it is clean with no wear lines or offset as this will also drastically interfere with proper timing. The list can go on from there but look to the simple things first. Oh, check the one way valve on the fuel tank, I have seen them seal shut and implode the fuel tank eventually starving the engine of fuel. Air should go in but not come out.

 

[Krashtestdustin]

i will send this exact message to my lil brother and have him get on it! thanks for the help

 

[Freakie]

assuming that it was running just fine in the original hull....I would ask what exhaust system are you using now in the SX hull....it might be that your pop off is now way too high for a less restrictive exhaust...that would lead to bogging.....else stick with what Pro-pulsion said.

 

[Krashtestdustin]

im using a westcoast 650sx exhaust from back in the day and aftermarket water box also from way back when when my dad raced, i never even considered that as a probable cause, im waiting to hear back from my brother on the flame arrestor test and my dads gonna try and find time to help him with the other stuff mentioned if need be

assuming that it was running just fine in the original hull....I would ask what exhaust system are you using now in the SX hull....it might be that your pop off is now way too high for a less restrictive exhaust...that would lead to bogging.....else stick with what Pro-pulsion said.

 

[Freakie]

That west coast pipe and water box is pretty good waking up the motor... I had a few of those in the day.......much better than any stock system...so I suspect you could have a pop off issue which shows up only on the water under load. Measure pop off on carbs and drop by 8 psi as a start to see if it revs better under load

 

[Krashtestdustin]

That west coast pipe and water box is pretty good waking up the motor... I had a few of those in the day.......much better than any stock system...so I suspect you could have a pop off issue which shows up only on the water under load. Measure pop off on carbs and drop by 8 psi as a start to see if it revs better under load

i will relay the word to my brother and dad, thanks man, one last question on that subject what is a good setting to start at with high and low screws on the carbs? my dad seems to think that could also be the problem that the high one may be to far out or in.

 

[JAKESPEED]

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[Vumad]

When I put a 750sp with stock dual 38s from a Xiss with a r&d pipe, into my x2 with a westcoast pipe and stock water box, it dumped fuel from the exhaust like the Exxon Valdez was sinking. I ended up going to a sbn 44 and tuning it.

 

[Krashtestdustin]

When I put a 750sp with stock dual 38s from a Xiss with a r&d pipe, into my x2 with a westcoast pipe and stock water box, it dumped fuel from the exhaust like the Exxon Valdez was sinking. I ended up going to a sbn 44 and tuning it.

its my brothers ski that hes building for his first ski ( he used to just ride my old 650sx ) and hes on a very low budget so we are hoping its just a carb related issue and not electrical but hes been busy with school and stuff so hes gonna try and check it out this weekend but he cant really afford to upgrade carbs atm and if he cant figure it out hes probably just gonna have to go back to the 650 we have sitting in the shop

 

[Vumad]

its my brothers ski that hes building for his first ski ( he used to just ride my old 650sx ) and hes on a very low budget so we are hoping its just a carb related issue and not electrical but hes been busy with school and stuff so hes gonna try and check it out this weekend but he cant really afford to upgrade carbs atm and if he cant figure it out hes probably just gonna have to go back to the 650 we have sitting in the shop

You don't have to necessarily upgrade the carbs. I would prefer dual 38s over a single 44. I run stock 38s on my Superjet.

The difference is that the Superjet comes with mikunis and the Kawasaki has keihens. When I asked where to get jets and how to tune the keihens, I was told buy a mikuni.

There is nothing wrong with the keihens, but a pipe is a major tuning change. The 650 pipes are much smaller and more restrictive than the 750 pipes. You are probably running very rich.

You only need to locate parts for the keihens and tune them. You don't need to replace them.

Besides, I now have a set of dual 44 mikunis, which I bought for $50 less than I sold my keihens for.

 

[Krashtestdustin]

You don't have to necessarily upgrade the carbs. I would prefer dual 38s over a single 44. I run stock 38s on my Superjet.

The difference is that the Superjet comes with mikunis and the Kawasaki has keihens. When I asked where to get jets and how to tune the keihens, I was told buy a mikuni.

There is nothing wrong with the keihens, but a pipe is a major tuning change. The 650 pipes are much smaller and more restrictive than the 750 pipes. You are probably running very rich.

You only need to locate parts for the keihens and tune them. You don't need to replace them.

Besides, I now have a set of dual 44 mikunis, which I bought for $50 less than I sold my keihens for.

ahh ok my dad was saying its probably really rich also but he doesnt have the time to go look so i told my brother to count how many turns out the screws are and to get back to me

 

[Vumad]

If it idles fine and bogs at 1/4, (if it works anything like the mikuni) you will need to change the low speed jet or needle. I've never tuned a keihen.

But turning screws is free so you can start there.

 

[Krashtestdustin]

If it idles fine and bogs at 1/4, (if it works anything like the mikuni) you will need to change the low speed jet or needle. I've never tuned a keihen.

But turning screws is free so you can start there.

exactly my thoughts

 

[Krashtestdustin]

another question pertaining to my brothers ski, we currently ride on a private lake/pond but the hull we did the 750 swap into we dont have paper work for since the ski was bought as a parts ski way back when, would there be any issues registering it as a homebuilt or would it be possible to track down the original owner to get paper work to register it? the ski was bought roughly in like 94

 

[Vumad]

another question pertaining to my brothers ski, we currently ride on a private lake/pond but the hull we did the 750 swap into we dont have paper work for since the ski was bought as a parts ski way back when, would there be any issues registering it as a homebuilt or would it be possible to track down the original owner to get paper work to register it? the ski was bought roughly in like 94

You can not register an oem hull as home built.

Buy a hull that is legal, track down the original title. Any other potential "solutions" will not be discussed here.

 

[Krashtestdustin]

You can not register an oem hull as home built.

Buy a hull that is legal, track down the original title. Any other potential "solutions" will not be discussed here.

thats why i asked, im not real particular with the rules for registering stuff since ive only really bought stuff with paperwork

has anyone had any experience with the spark? i know its a new ski so i dont know what the kinks are with it

 

[Vumad]

thats why i asked, im not real particular with the rules for registering stuff since ive only really bought stuff with paperwork

has anyone had any experience with the spark? i know its a new ski so i dont know what the kinks are with it

My experience is limited, but they are great. Lots of pep and light. Friend at the lake was getting almost a full 180 off a 2-3 ft boat wake which is pretty impressive given the size. There are videos of people throwing some big 180s on them in the surf. The local riders also say they are pretty much bone dry inside after riding.

The extras can kill you making a nice priced entry ski into a monster budget breaker. I think all the bells and whistles run like 9k out the door.

However, the 50 and 90hp models are exactly the same. It's all programming. It doesn't matter if you buy the 50 or the 90, if you buy the 110 programming lot, it's the same ski in the end. The extras like the 3-seat upgrade etc still cost what it costs.

It really has no competition. It's the smallest available, the cheapest available, the lightest available, possibly the most fuel economical, even if the hull is junk plastic you can buy 2 whole skis for only a little more than a base vx110.

 

[Krashtestdustin]

My experience is limited, but they are great. Lots of pep and light. Friend at the lake was getting almost a full 180 off a 2-3 ft boat wake which is pretty impressive given the size. There are videos of people throwing some big 180s on them in the surf. The local riders also say they are pretty much bone dry inside after riding.

The extras can kill you making a nice priced entry ski into a monster budget breaker. I think all the bells and whistles run like 9k out the door.

However, the 50 and 90hp models are exactly the same. It's all programming. It doesn't matter if you buy the 50 or the 90, if you buy the 110 programming lot, it's the same ski in the end. The extras like the 3-seat upgrade etc still cost what it costs.

It really has no competition. It's the smallest available, the cheapest available, the lightest available, possibly the most fuel economical, even if the hull is junk plastic you can buy 2 whole skis for only a little more than a base vx110.

cool, i just picked up a x2 for my next project once my FR is done and now wife wants me to get her and my little one a ski and if i cant find the floats for a x2 then its a base model spark next on the list

 

[Vumad]

cool, i just picked up a x2 for my next project once my FR is done and now wife wants me to get her and my little one a ski and if i cant find the floats for a x2 then its a base model spark next on the list

Old hulls can be found free and shuttle crafts do not need registrations. I've considered finding an old hull for free and converting them into a shuttlecraft. Something like a Seadoo xp could be real sporty, but I had also considered something big like a vx1100 hull and flat decking the nose like a bay boat.