97 gtx 780 wont start until I pour gas into carbs.

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Enforcer504

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I have a 97 gtx 780 I got used not running. To start I have 140 compression on both cylinders. I have rebuilt the carbs with Mikuni parts and also replaced the 1.5 needle and seat. Set pop off to 35 on both carbs. And I have set the low speed screw 1 turn out from seated. This ski will not start on its own unless I pour gas into the carbs. Then it will run and rev up but if I let the idle drop below 3,000 it will just bog and die. I assume now it has to be a gas problem. To add I have set the rotary valve timing just to make sure. The only thing I have not done is by pass the fuel tank and runs fuel line directly to a jug of gas to eliminate a fuel line problem. What do you guys think.
 
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Is that in or out of water. Idle should be at 3500 rpms out of water. 1500 in the water. Your issue could be the idle is just set to low.
 
Is that in or out of water. Idle should be at 3500 rpms out of water. 1500 in the water. Your issue could be the idle is just set to low.
Out of water. But I have to hold the throttle steady to get it up there and stay running. With no throttle input it will not run on its own.
 
I removed the carbs again and removed everything again and cleaned every hole. I’m hoping something was in stuck in there that went un seen. I will be installing them back in tomorrow morning
 
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Set the idle, reach down and turn the idle screw in until it holds about 3000 rpm on the hose. In the water it'll drop to about 1500. Double ck the oil pump alignment when you get it set.

By idle screw do you mean the one that can set the throttle. Or the low speed idle?
 
The idle adjustment screw is the one that contacts the throttle, not the low speed mixture screw.
The lever arms are the ones that contact the needle valve and spring inside the fuel chamber.
 
The idle adjustment screw is the one that contacts the throttle, not the low speed mixture screw.
The lever arms are the ones that contact the needle valve and spring inside the fuel chamber.

Yes lever arms are flush just like the manual says. I will get it running tomorrow and try and set the idle adjustment so it holds at 3,000on its own and see what happens. It is usually tricky to get it up that high in the rpms. I have to hold the throttle steady then slowly increase. If I do it to quick it bogs down and some times dies.
 
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I have to hold the throttle steady then slowly increase. If I do it to quick it bogs down and some times dies.

Somethings not right, it should be a quick response if it's sitting at 3000 or so and you jam it forward, especially on the hose. Did you use 'genuine' oem mikuni kits? it matters.. 35psi on pop off is good. what are your LS and HS needle settings?
 
Somethings not right, it should be a quick response if it's sitting at 3000 or so and you jam it forward, especially on the hose. Did you use 'genuine' oem mikuni kits? it matters.. 35psi on pop off is good. what are your LS and HS needle settings?

Yes I used genuine mikuni kit. Low speed is 1 turn out from seated. The main I do not remember. It runs great once I get it to 3,00 rpm very snappy on the throttle. Just getting it up to that rpm is a hard.
 
Just getting it up to that rpm is a hard.

It shouldn't be hard at all, this is where it should always be idling at when out the water, on the hose, on the trailer, etc. 3000 RPM.

With the throttle plates synced and completely flat or closed, with the idle screw barely touching, go 2 full turns in. This should get you in the ballpark, you may only need to tweak a 1/4" turn either way or not at all.
 
It shouldn't be hard at all, this is where it should always be idling at when out the water, on the hose, on the trailer, etc. 3000 RPM.

With the throttle plates synced and completely flat or closed, with the idle screw barely touching, go 2 full turns in. This should get you in the ballpark, you may only need to tweak a 1/4" turn either way or not at all.

I started it up today by adding gas in the carbs then held the idle at 3k and set the idle screw. Everything seemed great I stopped the engine fired it right back up. Then all all of a sudden the machine reeved very high and would not stop. I yanked the plug wires off and still kept going I then un screwed the battery terminals frantically while this thing is reeved up and still nothing. I then pulled the fuses in the mpem because I had it open all ready. And still nothing the only fuse I did not pull is the one right near the batter in the black. It eventually stopped on its own. And to add I pulled the dead key first thing. Any ideas on why and how it was running still?
 
Probably a big air leak. Likely the carb base gaskets. If it doesn't turn out to be the base gaskets, you might have to pressure test the engine.

Edit: how far did you turn the idle screw in? and, is there tension now on your throttle cable?
 
That's a runaway ski and it is caused by too lean of a fuel mixture typically from an air leak at the carb bases or intake manifold.
It is hot enough to keep running like a diesel so nothing that interrupts spark will do anything like you found.
The only way to stop it is to cool the combustion chambers so pulling the choke is the sure fire way to kill it.

If it stopped on it's own your cylinders are probably toasted and you will at least need a top end so you need to check compression first.

A runaway can also be caused b the idle being set too high and running too long without cooling water.
 
I started it up today by adding gas in the carbs then held the idle at 3k and set the idle screw. Everything seemed great I stopped the engine fired it right back up. Then all all of a sudden the machine reeved very high and would not stop.

Geez, scary, you either had the idle screw in too much and it ran away or it has a vacuum leak somewhere.
It must have really gotten hot to sustain running like that with all the stuff you disconnected. Let's hope it survived, may want to ck the compression. First reach down at the PTO flywheel and see if you can turn it by hand, it may have locked up.
 
Probably a big air leak. Likely the carb base gaskets. If it doesn't turn out to be the base gaskets, you might have to pressure test the engine.

Edit: how far did you turn the idle screw in? and, is there tension now on your throttle cable?

I screwed it in until it held at 3k.there was actually play in the throttle cable so it was not under tension.
 
I screwed it in until it held at 3k.there was actually play in the throttle cable so it was not under tension.

You didn't have the hose cooling it, so how long did you take doing this idle adjustment process? I'm asking for my own reference.. I know any longer than about 30 seconds or so off the hose or out the water it can get pretty hot.
 
I screwed it in until it held at 3k.there was actually play in the throttle cable so it was not under tension.

Hopefully the engine didn't get damaged. You'll have to check it now before trying to figure out why it wouldn't run right. Let us know if it will turn over by hand or if it is seized. Take spark plugs out and see if they are gray or if there are metal particles on them. Then compression check if you don't find obvious signs of damage.
If engine checks out ok, back off the idle speed screw until it no longer touches the throttle and count how many turns it took. Then you'll know how far in it was turned.
Another question...before adjusting the idle speed screw when you were manually holding the throttle lever to keep it running, how far did you have to pull the lever? 1/8, 1/4, etc.?
Question 2: when you rebuilt the carbs, did you turn the idle speed screw at all and did you turn the adjuster rod between the two carbs?
 
Geez, scary, you either had the idle screw in too much and it ran away or it has a vacuum leak somewhere.
It must have really gotten hot to sustain running like that with all the stuff you disconnected. Let's hope it survived, may want to ck the compression. First reach down at the PTO flywheel and see if you can turn it by hand, it may have locked up.
 
Just to add. The start just before the run away happens it did the same thing but on a very small scale. Like for 2 seconds then just does and quit. The thing I must add is that it blew two fuses during that run. The one back in the black box 20amp and the 5 amp in the mpem box. I have no idea why it did this. The carb gaskets are brand new I still think the carb is the starving it of gas and I have no idea where something is stuck
 
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