sport jet 120

[ranman6]

I have a mecury sport jet 120 hp, I just rebuilt the engine from ground up.

I have problems with it starting that I can't figure out , when I have it hooked up to water hose in my driveway it fires up just fine, but when I get it in the water, I have to prime it with starter fluid to get it to fire.

Can't figure this one out, once it fires it ones fine and then I shut it down out at the lake and wait awhile there I go again, have to prime it .

What gives, where do I start to troubleshoot this one???

 

[kend301]

Re: sport jet 120

Start by verifying that it will still start on the hose out of the water. Sounds like a fuel restriction or a bad fuel pump , did you rebuild the fuel pump and the carbs ? the float angle could be changing from the boat on the trailer vs the boat in the water .

 

[ranman6]

Re: sport jet 120

didn't rebuild the fuel pump, I did the carbs though. It could be the float levels I guess, how would you compensate for that. Whats strange is that it runs fine after its primed.

 

[kend301]

Re: sport jet 120

No way to compensate , PULL THE CARBS and check the floats , if they are low you are running lean and your new motor will go BOOM !! (not a good sound)
Forget checking fuel pump flow , rebuild it just sitting off the motor will stretch the diaphragm to the point of low fuel pressure .. again lean mixture and melted pistons will result .
Stop using starting fluid as scored cylinder walls will result .

Solve the problem , trying to compensate for it will really **** you off in the future !!

 

[ranman6]

Re: sport jet 120

Thanks for the advice, what I meant on the compensation was from the trailer to the water, I did set the floats according to the manual.

You don't think I need to check gas flow? I did put a inline fuel filter in it but don't think that is the problem.

If you are thinking its running lean, then can't that adjustment be made in the carb mixture screws?

 

[Oode]

Re: sport jet 120

Your carb mixture screws are to adjust the mixture at certain operating points, usually idle, or just above. Once you open that butterfly, there are a series of jets and port that correct the mixture at other operating points. Once you are at WOT, the float height and the main jet are about all that is left, the flow through the throat of the carb creates enough of a vacuum to suck gas through the main jet from the float bowl. If that is lean, your engine will run hot and likely sieze and/or score the cylinder walls. Then you will be truly unhappy...

Check the flow if you want, but I think the advice is to just assume it is not up to snuff and rebuild. It's all of $10 worth of parts, and seems to be a sensitive part of this particular design..... I've done my 3 times in 2 months, still don't know if it's right or not, but time will tell...

 

[kend301]

Re: sport jet 120

Your idle mixture screw is located on the left (port) side of the carb at the top right behind the intake mounting flange . To adjust them , turn them all the way in and then out 1 1/2 turns and forget about them . you can tweek the adjustment but you run the risk of running lean just because lean does sound better and picks up some RPM's at idle but will hurt the motor .

 

[ranman6]

Re: sport jet 120

Going back to begining of this you stated that it sounded like a fuel restriction, and or carb problems like the float levels.

So whats first, and if it is the floats, again how do you think I should adjust these if there is a difference from the trailer versus the water?

A little more background on this, is I have rebuilt the carbs, set the floats to specs. and has a hard time starting without prime (which I won't use starter fluid any more) but seems to run fine while its running.

Thanks for all the input, just trying to figure this out before I have to put this thing away for another season.

 

[Oode]

Re: sport jet 120

I guess I have to admit I'm a bit stumped, but lets start with a few ???

- When it is on land, is it level or bow up/down???

- When you "hook it up to the hose" are you unscrewing at the intake can connecting, or are you using the "consumer" flush kit??

- What temperature is it when you crank in the driveway vs. at the lake???

- Do you have much water in the bilge when trailering/launching??

- Is your tank all the way full???

- How many times has it exhibited this behavior???

just a start, because as you say, there is no good reason for it to start one place and not the other....

 

[ranman6]

Re: sport jet 120

OK to answer all these,

- It is usually bow down, because my driveway is sloped a little.

- I am unscrewing at the intake and have an adapter to go to water hose, I don't give it any pressure, just enough to keep it cool while it is running.

- The temperature is the same, because I will start it before I drive it to the lake which is only about 45 min. away.

- No water at all in the bilge, I have the hardest time just as I put it in first time, or when it sits for awhile after we bring it back in.

- Tank is usually 1/2 full most of the time.


-It does it most of time while starting, I have rebuilt the whole engine and it runs fine on the water. Just doesn't like to start, unless its in my driveway.....I guess it does'nt like the water!

 

[ranman6]

Re: sport jet 120

Well I'm going to be working on it tommorrow, so any other suggestions would be taken in consideration.

I guess the first place to start would be the carbs/ float levels.

Sure has me stumped, but I will post up anything I find out.

 

[kend301]

Re: sport jet 120

Check the floats , bow down will let more gas in , bow up will reduce the amount of gas in the bowl if the floats are set incorrectly .

 

[ranman6]

Re: sport jet 120

Well now I really need help, I have a whole different problem

So I pulled the carbs and adjusted the floats that were not too far off, I did see that maybe the float needles were sticking a little so i cleaned them and reinstalled the carbs.

Put the hose on a little water to it and water is coming out of the 2 lower cylinders now, pulled the spark plugs and water was in the bottom 2 cylinders.........why??

So now I have pulled the head doesn't really look like that could be the problem, head gasket looks fine, I don't know what to do now ??

Should I put it back together and try to restart it and see if I can get the water out?

Do I have to pull the engine and rebuild it again, and the big question is what in the h##% went wrong it was running fine last week-end !!

 

[kend301]

Re: sport jet 120

See my reply in "to much water "