650/X-2 Help

[msutherland]

I am a newbie. I used to ride sit downs back in the early to mid 90's. My 16 year old son is wanting to purchase a stand up and has found a 1990 650 sx for $500. I have only seen pictures and it looks good cosmetically. The owner stated the carb needs a vacuum pump. He said it had a larger 44mm carb on it but would bog down at high rpm's so he put the original cqrb back on it. He said he could put the larger carb back on it if I wanted to show me it runs but that it would need a new pipe on it if I wanted the larger carb. Does this sound correct? Is there much of a performance difference between the two carbs? Im not mechanically inclined and I dont want my son to waste hios money on something he has to sink more money into to get it running. Its about a 3 hour drive to go look at the ski but Im skeptical of buying anything I cant see running. My gut feeling is to have him install the larger carb back on it so I can see it start and run. The owner claims that it has 165 psi on each cylinder but from what Ive read this seems kind of high for a non modified engine. He said it has a primer kit installed and the oil block plate so its now pre-mix. Any ideas or suggestions on things I should look for or at when considering this purchase. If I do buy it should I put the larger carb on it and if so do I need an aftermarket pipe or should I buy a vacuum pump for the original smaller carb?

 

[GrantWarden]

It should be OK. The carb will lose a little bit of low end but overall will be better. Just make sure that the engine spins freely and pull out the spark plugs to check the pistons, so bring a flashlight.

 

[Wilke]

Couple thoughts:

- Seller sounds like he has no idea how to tune a two stroke, and only knows enough about the mechanics to get himself in trouble.

- the larger carb is probably just jetted/adjusted incorrectly - you don't NEED an aftermarket pipe to run a bigger carb, but just a bigger carb on its own doesn't give you much. And either carb probably needs a rebuild, and the vacuum pump he's referring to is probably the external fuel pump for the original keihin 28mm which is probably missing.

- 165psi is high for a stock engine, should be in the 150 range. Could have an aftermarket or shaved head, or more likely just a cheap gauge giving poor readings (or he's just pulling a number out of thin air that he heard one time regarding jetski motors).

- $500 is a decent price for a 650 thats in ok condition and has a good motor. Have him put the other carb on to hear it start and run, and bring a compression gauge and do the test yourself. If its starts up and runs and passes a compression test and looks good otherwise(no excesssive corrosion, impeller looks in good shape, ect.) I'd say have at it.

 

[msutherland]

We are on the way to look at the jet ski. We spoke with the owner again and he stated that with the larger carb the jet ski bogs down when idling and in lower RPM's. He thinks it is overloading due to the smaller/stock pipe. Does this make sense or does he not know how to tune the carb? Is there any advantage to running the larger carb or should we just go back to a 28 mm carb?

 

[Vumad]

We are on the way to look at the jet ski. We spoke with the owner again and he stated that with the larger carb the jet ski bogs down when idling and in lower RPM's. He thinks it is overloading due to the smaller/stock pipe. Does this make sense or does he not know how to tune the carb? Is there any advantage to running the larger carb or should we just go back to a 28 mm carb?

The seller doesn't know anything about his ski. Do not take anything he says as true. He has absolutely no idea what he is talking about. It is a good price for the ski, but his word is completely worthless. Don't trust him.

It's like when I look at quads. People just tell you the only thing they know about the thing. They know it has a carb, so that must be the problem. "Battery is just dead", because they don't know it has a flywheel, stator, cdi, ignition, start/stop componets, they just assume it's the battery, they don't know, but some sucker will buy it thinking "it just needs a battery". My favorite has been, "the carb needs to be cleaned" on efi... it doesn't have a carb jackass. Why lie. This guy has no idea. He's making up.

The 28mm carb that comes on the 650sx is a joke. You should not spend a penny on the 28mm carb. It chokes the motor and it's junk. The 44mm mikuni carb is a great carb for the ski. The carb works just fine with a stock pipe. The ski runs poorly with the 44mm carb because something is wrong. It is most likely carb tuning, but it could be a number of other things. It doesn't run with the 28mm carb either, so the issue may not be the carb.

Issues could be a long number of them...
the 44mm carb could need a rebuild
there could eb a problem with the ignition
the reeds could be bad
the jetting may be wrong
there could be a leak or gasket problem
blah blah blah
many cause with not enough information to know
probably just jetting, but could be something else

$500 is a very fair price for a running 650. It is a bad price for a non-running 650. Do not buy a 650sx unless it has a minimum of the following 3 things
1) a title. Do NOT buy a ski without a title. It doesn't matter what line of crap they feed you. no title, no sale.
2) runs. If it doesn't run, it will cost money to fix. a 650sx is not worth spending very much money on
3) has good compression. Numbers should be around 150 and no lower than 140. Anything lower is damaged and will need a rebuild. Anything higher has had something done with the motor (assuming a good gauge)

Sounds like you need to do some more research before you buy. A 650sx is a money pit. I bought my 1st 650sx for $800 and it was a money pit. I wish I would have bought a newer ski for more money. My 650sx ran great, but the parts were worn out. A battery cable breaks. Then the rusted bed plate starts getting loose. Then the ignition stops working right. Then the carb spring breaks. Then the missing air hose drops water into the carb after a sub and blows apart your crank bearings, and you never even knew the hose was missing because it didn't come with one and you don't know anything about your ski. It will cost you more than $500.

 

[feartheride]

My first stand up was a 650 and lasted for ever with few issues..

 

[Vumad]

That was very pecimistic of me. I think you should buy the ski if it has those 3 important things I listed...

$500 is a very fair price for a running 650. It is a bad price for a non-running 650. Do not buy a 650sx unless it has a minimum of the following 3 things
1) a title. Do NOT buy a ski without a title. It doesn't matter what line of crap they feed you. no title, no sale.
2) runs. If it doesn't run, it will cost money to fix. a 650sx is not worth spending very much money on
3) has good compression. Numbers should be around 150 and no lower than 140. Anything lower is damaged and will need a rebuild. Anything higher has had something done with the motor (assuming a good gauge)

If you are riding at a lake, you will have a lot less problem. Ocean water is a death sentence for an old ski.

My ski broke, and so was I. I constantly had to figure out ways to keep the thing running. Old connections and a piece of speaker wire kept it in the water. etc etc. The ski will cost money, and he will ride it less than a nicer ski. I patched that thing together until my motor came apart. I wish I had more time on the water, so I am very negitive about my experience.

However, I learned a LOT about these motors in the process. I bought 3 to 5 old broken skis at a time, kept the parts I needed and sold the ones I didn't. I had to manage my money and engineer things to the level I could afford. I was forced to come onto these forums, read a lot, and network out to the people around me. I had lots of issues, got towed a lot, and could never ride alone (shouldn't anyway).

Now, I've finished college. I'm a firefighter and a paramedic. I have a full time job and a clean strong running stock 2004 superjet, in addition to a number of other things. I've decided to take what I have learned to the next level, enrolled in USF, am going to start working on a bachelor's degree in mechanical engineering, and am joing the SAE club to learn to build race cars (USFracing.com).

While it may cost your son some money, and be a complete pain in the ass, he may learn a lot in the process. He will have a project he can work on with his dad. You could front the money and buy him a ski that runs perfect, and he could ride it all the time, but he wont learn anything. Make him find the information, he will probably need your help some, but he will learn a LOT in the process. Keep an eye open for a cheap sit down ski with a 750 motor in it (I found a 750xi ss for $450, sold the hull and title, carbs, trailer and etc, kept the motor and was $50 ahead). I smoked my 750 motor with a tuning issue (didn't know what I was doing), costs me $80 in a bore, $100 in parts, and now I know how to rebuild a 2-stroke, and everything about how it works.

Buy it (if it meets those 3 things), just budget extra money to fix it. He'll learn a lot.

 

[msutherland]

Thank you so much for this detailed advice! The jet ski will run if you pour gas directly into the 28mm carb and will continue to run if you keep pouring more gas into it but it's missing the fuel pump that attaches to it. I'm thinking it's probably just a jetting problem with the 44mm.

 

[Vumad]

Thank you so much for this detailed advice! The jet ski will run if you pour gas directly into the 28mm carb and will continue to run if you keep pouring more gas into it but it's missing the fuel pump that attaches to it. I'm thinking it's probably just a jetting problem with the 44mm.

So you bought it then? Don't waste any time or money on the 28mm carb. Use the 44mm carb. It's one of the best carbs you can use on the motor.

Save the 28mm carb and manifold. The 44mm carb could be used on a 750 motor. If you ever upgrade to a 750 motor, you could put the 28mm carb on the 650 motor and sell it as a running motor, keeping the 44mm carb for your new 750.

 

[msutherland]

Yes, we bought it. it cranked and started right up with the smaller carb if we pured gas into the carb. The larger carb he gave me isnt a mikuni (sp?) but is a keihin like the smaller 28 mm one currently on it. The engine was immacuatley clean, I was shocked. The compression was 150 on both cylinders. We are going to attempt top put the larger carb back on it and see what it does. The guy told me it would run but would (load up) as he put it at idiling speeds and then flood out with the larger carb.