Runs great but low compression.

[Bobdoo]

Hi all. I'm new here, so excuse me for jumping right in with questions. But I have some. Here's the deal:

I'm looking at adding two used 2001 Sea-Doo GTX DIs. Both are physically in good condition for their age. I did a compression check on each one with cold engines. One boat had 98 psi each cylinder. The other had 120 psi each cylinder. The owner let me take them out for a run on the river to check them out. Both ran very good, the one with 120 psi really popping out of the hole and displaying noticeably better performance overall. But the one with the low compression was no dog, got up on plane easily, ran fine, idled fine, started fine, no overheating etc. I ran both of them for about 15 min each to make sure no problems appeared after they were warmed up and run for a while.no overheating etc. Couldn't check speed because speedo didn't work on either one but I'm pretty sure I got to about 40 mph on each one.

Question. 98 psi is very low but the boat ran very well. I'm concerned that even though it ran well, the engine is weak and who knows how long it will last? Owner wants $4500 for both including trailer, new spare battery, some tools, four gas cans, and bag anchors. Should I buy? Lower price? Pass? I certainly don't want to buy one only to have it die before the summer is out.

 

[smc0922]

the 120psi is even borderline, 135 is mint in the 951, unless the DI is different. Because they are DI is another factor as well, both are incredibly expensive to fix when they go, both with the fuel system and electronics- let alone the engine.

I doubt he would accept my offer of $2500, but he probably doesnt realize what it will take to make them 100% again which they certainly are not. If you want a project, then take them on. You will spend time and money on them in the very near future.

What do they have for hours?

 

[Coastiejoe]

As mentioned, the DI's are for whatever reason(s) temperamental machines.

Hard to diagnose when they need repair and cost more to fix them when you THINK you know what is wrong.

If you have your mind set in these skis, you need to steal them. It is an insult to the owner but it is what it is.

Did you check compression with both plugs out, wires grounded and full throttle?

 

[purple_people_eater]

you're gonna run about $395 for good parts on top-end kits and air compresser rings. 951's(di or not) NEED top end kits every 150 hours, IMO, or you risk throwing a rod right out of the cases. did you hear any abnormal tick or a "slapping" sound on the one with the low compression?

the di system is a very complex system that used an air compresser cyc. to inject fuel on the high pressure side of the piston stroke with bursts of high pressure air. they scream like a banshee when running and tuned correctly (getting pretty darn good eco. at it), but can be very pricey when things start to go wrong, even for the most experiacned seadoo guy (as mentioned above).

in good cosmetic shape, in my area, they go for about 3000-3500 per ski, plus 500-1000 for the trailer depending on condition. however you are looking at 1500-2500 in repair parts and labor to get them 100% again. if you could beat him down to about 3k, i'd do it, but that would be my number.

 

[Bobdoo]

What do they have for hours?

A little over 300 hours. The one with the best compression had a new short block installed 2 or 3 years ago.

 

[Bobdoo]

As mentioned, the DI's are for whatever reason(s) temperamental machines.

Hard to diagnose when they need repair and cost more to fix them when you THINK you know what is wrong.

If you have your mind set in these skis, you need to steal them. It is an insult to the owner but it is what it is.

Did you check compression with both plugs out, wires grounded and full throttle?

It was my understanding that since it's DI I didn't need to open throttle all the way to check compression. And, I left one plug in while checking compression--first one cylinder, then the other. But even if I did not do it quite correctly, it wouldn't make that much difference would it? I had thought about asking the guy to let me do another compression check though.

 

[Bobdoo]

"did you hear any abnormal tick or a "slapping" sound on the one with the low compression?
No. I listened very carefully for abnormal sounds. Didn't hear any. They both started right up when cold or warm.

 

[Bobdoo]

Here's the rest of the story. The owner had the two Sea-Doos with trailer and other stuff I previously mentioned listed for $5500.00. He said he'd go down to $4500 after I did the compression check. After the test on the river, I asked him to consider going lower because of the low compression in the one boat. He said he really couldn't because he thought $2000 for each one plus $500 for the trailer (this is the way he factored the price out) was about as low as he could go. To be honest, when I saw the low compression I thought hmmmm, price should be more like $2500. But I never offered him that after he said he couldn't go any lower than $4500. BTW, he's a real pleasant guy to deal with and he's let me check everything out to the extent that I want to.

Anyways, if you guys think I might get a significantly different compression reading with wide-open throttle, wires grounded and both plugs removed, then I'll do another compression test. I don't think the guy would have a problem with me doing that.

 

[purple_people_eater]

hmmm.... like i said 3k would be my number.

 

[kicker]

These are 2 skis that are on thier way out mechanically. Plus they are hard to trouble shoot without the proper diagnostic equipment, especially if you are not familiar with them.

If you want to buy something in that price range, grab a couple 787 carbed (or even RFI is better then DI) skis in good shape and good compression. Much easier to trouble shoot, more reliable, and cheaper to rebuild when needed.

Here is a couple, one is a 947 the other is a 787.

http://phoenix.craigslist.org/evl/boa/3829458170.html

 

[Coastiejoe]

It was my understanding that since it's DI I didn't need to open throttle all the way to check compression. And, I left one plug in while checking compression--first one cylinder, then the other. But even if I did not do it quite correctly, it wouldn't make that much difference would it? I had thought about asking the guy to let me do another compression check though.

You could be correct about the DI's as far as the throttle goes, I don't know enough about them to know what the standard is. That said, I would think all plugs would still be removed.. I could be wrong,, DI's are a different beast.

 

[- BiRkS_]

It wouldnt hurt to have the throttle open. Also, With compressions that low on both skis, I would question that tester. I'd try it on something i know that has good compression. Because at 90 PSI, i would expect very hard starting, lots of smoke, very poor idle, regardless of DI and it would just fall on its face while accelerating. So i think you may have an inacurate gauge.

Lol I used to have a gauge that read 10 PSI lower. Used to pack that one when picking up sleds back in the day. Worked great until one guy pulled out his snap on beside me and proved my gauge wrong. So much for that bargening chip haha.

 

[Bobdoo]

Birks, my tester is good and it's accurate. I've also tested compression on my motorcycles, and vehicles. The gauge works correctly. But I still want to run another compression test on them. BTW, I read on a boating website that running a dynamic compression test is better than a static or "differential" compression test like I did. Oh, another BTW-as I said I did the compression test when the engines were cold. But during the first test I accidentally forgot to disconnect one of the plug wires and the motor started. PSI went right up to 150. Waddya make of that?

 

[AdamXP800]

Personally, I would walk away. High hour, 951, and DI on top of that. You can easily get in over your head and end up spending a huge amount of cheddar on diagnosing and "repairing" if you can even figure out what needs repairing.

 

[- BiRkS_]

If you can get them for 3500 then thats a deal. 1500 per ski, you could sell them any day like that. and get 1000 for the trailer (depending on quality) With the 951, I would strongly disagree with just a top end, unless you were going to turn around and flip the ski. Reason being, you're putting all that new power, on a 14 year old crank and bearings. Recipe for disaster.

I got a 951 carbed GTX 2 months ago. Swapping a motor from a '98 to 2000, i bought it running, running rough, but running. When i pulled the engine, I decided, hey why not pull the carbs and reed valves out and get a peak at the bottom end. As soon as i did that, the MAG side was full of oily rusty water! but the thing is this ski ran. 132/128. Had I have ran that engine, it would have blown itself to pieces on the first ride.

So basically, if you want the ski to last, tear it appart and rebuild it once. rebuild it right. If you want to flip one of them and recoup some money, throw a top end on it, break the engine in gently (thats the key) and sell it. Thats my $0.02

 

[Bobdoo]

Personally, I would walk away.

I think that's what I'm going to do. They are very old after all and the guy was honest about their use--they used them a lot.

Thanks everyone for your input.