Sluggish sport jet 90

[k_hicks]

I have a 1994 Donzi with a Mercury Sport Jet 90, Force engine I am told, which cranks and idles good, just sluggish to plane out and not as much speed as it use to have. Would run 40 mph tow years ago now only about 30 mph. Change stator two years ago, changed switch box last year. Clearance on wear ring is .008 which I believe is good. I was told that the stator has a low side and a high side in it, is this correct. Just cleaned all carbs, good fuel supply, new plugs, all firing at low rpm, what about timing and how do I check it. Also would like to install a tach but dont know where to connect to. I would certainly would appreciate any help.


Ken

 

[maxum247]

Re: Sluggish sport jet 90

Look for air leaks in the fuel line or fuel pump, restricted fuel filter.
Check for a choke or throttle valve that operates improperly.
Check ignition timing adjustment.
Do a compression test on engine, see what the numbers are.
Look for loose bolts, defective gaskets or leaking mating surfaces on the cylinder head.

 

[k_hicks]

Re: Sluggish sport jet 90

120 to 130 psi on all three, new fuel lines, tank vent not clog, dont know how to check timing

 

[maxum247]

Re: Sluggish sport jet 90

120 to 130 psi on all three, new fuel lines, tank vent not clog, dont know how to check timing

If you don't have a manual , pick one up it's been well worth the $35 I paid for mine!
You can search here on the forum for topics on (engine timing.) Use the search button at the top of the page.

From what I know of compression numbers yours sound to be ok!
The main thing is for them to be within 10 -15# of each other and preferably over a 100# on each cylinder.

 

[k_hicks]

Re: Sluggish sport jet 90

Timing was way off, better pick up now, narrowed the skip down to no. 1 cylinder, good spark, runs good for a few min. then starts skipping, can hold my hand over carb intake when skipping and no change, believe i have a fuel shortage, guess i will clean that one again. Any tips anyone, thanks for the timing tip.


Ken

 

[maxum247]

Re: Sluggish sport jet 90

Timing was way off, better pick up now, narrowed the skip down to no. 1 cylinder, good spark, runs good for a few min. then starts skipping, can hold my hand over carb intake when skipping and no change, believe i have a fuel shortage, guess i will clean that one again. Any tips anyone, thanks for the timing tip.


Ken

Sounds like the coil on the number one cylinder may be getting hot and braking down once the engine warms up.

 

[k_hicks]

Re: Sluggish sport jet 90

swapped no. 1 and no. 2 coil and plug wire, still in no. 1

 

[maxum247]

Re: Sluggish sport jet 90

swapped no. 1 and no. 2 coil and plug wire, still in no. 1

Have you tried a different sparkplug on that cylinder, switch with another plug from a firing cylinder and see if the miss moves with the plug just for kicks, I know you said it fires at idle, but who knows.

 

[k_hicks]

Re: Sluggish sport jet 90

new plugs and have swapped them, going to take the carb now and clean it again. Let you know around lunch.

This thing is driving me crazy

 

[k_hicks]

Re: Sluggish sport jet 90

I give up, it going to the shop, then it will get a big FOR SALE sign.

 

[maxum247]

Re: Sluggish sport jet 90

I give up, it going to the shop, then it will get a big FOR SALE sign.

I have a few more simple checks you can try, if interested let me know!

 

[k_hicks]

Re: Sluggish sport jet 90

sure, ill try anything at this point, and i appreciate all the help

 

[maxum247]

Re: Sluggish sport jet 90

In the begining you said it was sluggish to plane and doesn't develope full speed.
Are the throttle valves in the carburetors in sync with each other and opening fully (Horizontal), anything less or more will cause the engine to either not reach full power, or bog.
When was the last time the fuel pump was rebuilt or was it?
Check the fuel system for air leaks again.
Check the idle adjustments on each carb and make sure there in sync with each other.
May be time to decarb the engine, get rid of the carbon deposits on the pistons.

 

[k_hicks]

Re: Sluggish sport jet 90

have narrowed it down to no. 1 piston, and it is intermittent, when it does skip i can choke out no 1 with my hand and nothing happens, choke no 2 or no3 and the engine dies.

 

[maxum247]

Re: Sluggish sport jet 90

have narrowed it down to no. 1 piston, and it is intermittent, when it does skip i can choke out no 1 with my hand and nothing happens, choke no 2 or no3 and the engine dies.

Carb may be out of adjustment, not sure.
Half of the CD module for that cylinder may be giving out.

I've heard that the metal connector in the rubber boot that plugs on to the sparkplug end can loose contact with the sparkplug causing the engine to miss on a cylinder.
Some people replace the sparkplug boots with screw on boots for motorcycles, instead of useing the type that came on the engine originally that peirce the wire end.

 

[k_hicks]

Re: Sluggish sport jet 90

is the cd and swithbox the same, im thinking that could be the problem, carbs all adjusted, and in sync, 5 psi on fuel pump, is that enough

 

[maxum247]

Re: Sluggish sport jet 90

is the cd and swithbox the same, im thinking that could be the problem, carbs all adjusted, and in sync, 5 psi on fuel pump, is that enough

Sounds ok on the fuel pump, usually somewhere between 4 and 6 psi I beleive.
If it doesn't have two blue or black CD modules it would be a (switchbox).
Sounds like (Thunderbolt Ignition). I'm not that familiar with that setup but the principal will be the same.

 

[k_hicks]

Re: Sluggish sport jet 90

Problem solved, bad trigger, back up to 40 mph and quick out of the gate, thanks guys

 

[maxum247]

Re: Sluggish sport jet 90

Problem solved, bad trigger, back up to 40 mph and quick out of the gate, thanks guys

I'm glad to hear that it is running well again!
Thanks for letting us know how things turned out!

 

[k_hicks]

Re: Sluggish sport jet 90

You are welcome, great site, lots of free information