GT 150 jet sizes not listed...

[crbenny]

My factory service manual lists available orifice sizes and ID #s but doesn't stipulate what the factory jet size is for my '91 Johnson. What is the correct # for idle, intermediate, and hi speed orifices?

 

[Dhadley]

Re: GT 150 jet sizes not listed...

Thats in the parts catalogs. What the exact model number?

 

[crbenny]

Re: GT 150 jet sizes not listed...

It's a J150STL FSB but the model # is no longer legible...

 

[Dhadley]

Re: GT 150 jet sizes not listed...

The letters after STL should be EI if its a 1991. If youre sure it has 1991 GT carbs the idles should be 35's, the mid 30's and the hi speeds 65C.

 

[crbenny]

Re: GT 150 jet sizes not listed...

The guy I bought the boat and engine from said it was a '91 but there doesn't seem to be a way to tell for sure without the model #. I've been buying parts for '88 to '91 and so far the part #s correspond to what I've removed. Also I don't know if these are the original carbs. I'm having an ongoing problem with operation between 1200 rpms and 4000 rpms where I assume the hi speed jets take over. Then it tears up to 5500 rpms like no 150 I've ever seen! I had found that the timer base had 2 bad sensor coils and I replaced that. Compression is between 88 and 95 psi on all six. New powerpack, wires and QL77JC4s. Timing is set, carbs syncronized, and I had pulled the carbs to check for fouling but found them to be freshly rebuilt like the previous owner had told me. Midrange still bad. What I didn't do was pull the jets because I don't have the orifice tool. They're way smaller than the jets in a Holley so I left them in. I understand it's common for the not so competent to get the idle and intermediate jets all mixed up. Gotta go back in I guess... The jets you list sound aggressive. What should the carb #s be? If you were me, how would you set them up with so many unknowns? The boat is a 1200 lb early (70s) '19 Whaler and the engine pushes it effortlessly up to near 50 mph. Much appreciated for the input guys...

 

[crbenny]

Re: GT 150 jet sizes not listed...

As best as I can see, they're 08989599. Not sure what you can extrapolate from that...

 

[OBJ]

Re: GT 150 jet sizes not listed...

I checked also crbenny and Mr. D is right on.<br /><br />Bogging down at midrange could mean that one of the intermediate jets are plugged or at least partially plugged. Have you checked the sync and link? If the throttle plates are not coming open at the right time, this would cause the problem also.<br /><br />The orifice openings can be checked with wire drills of the correct size...ie...a 30 intermediate jet can be check with a wire drill of .030. The letters denote the thread size of the orifice.<br /><br />In my early dazes, I made a orifice remover from and old screw driver of near the correct size. Just filed it down till it fit.<br /><br />From another angle, have you checked the primer solenoid is not dumping fuel into the carb throats when it's not supposed to? You can check by pulling a primer hose off one of the carbs with the engine running. If it's spitting fuel, chech the primer solenoid red lever is pointing down to the bottom of the solenoid and that it is not energized.<br /><br />Also check for any recirc hose that may have pulled lose from a nipple or borken hoses. Fuel lines in good shape? None that are hard and need replaced, all connections tight?

 

[crbenny]

Re: GT 150 jet sizes not listed...

I checked the sync and link and also pulled the hoses from the priming solenoid and all is well. The recirc hoses are intact and I've replaced all fuel lines and filters under cowling. Also replaced the water separator. Decarbed twice, changed plugs twice, checked coil resistances and they're all 255 to 265 ohms and fire while running. I've gone thru the factory service manual 20 times and NO ONE I TALK TO CAN GET THIS ONE. That's why I'm gonna open the carbs again and check the jets... Any input is still greatly appreciated..

 

[crbenny]

Re: GT 150 jet sizes not listed...

Just pulled the carbs apart. Jets are correct and clean. Carbs are spotlessly clean. HELP!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[seahorse5]

Re: GT 150 jet sizes not listed...

What is the carb pickup timing set at?<br /><br />Does the timer base advance smoothly when the throttle is opened?<br /><br />What is WOT rpm?<br /><br />Where is the waterline in relation to the idle relief holes in the back of the exhaust midsection?

 

[Dhadley]

Re: GT 150 jet sizes not listed...

I know the carbs look clean. Have they been soaked in cleaner with new OE kits installed?

 

[crbenny]

Re: GT 150 jet sizes not listed...

Carb pickup timing is 7 BTDC and the timer base, which I just replaced and greased, advances smoothly. WOT is 5600 RPM and very strong. The boat sits nice and high. Water level is not causing back pressure as it breaks up on plane. Carbs haven't been soaked however the hi and midrange jets and passages are in the plastic bottom and everyone agrees they shouldn't be submerged. I can blow thru the midrange holes with the jets out and feel the air out the sides where the hi speed jets plug in. I have used OE kits..

 

[crbenny]

Re: GT 150 jet sizes not listed...

Carbs torn down again and this time I soaked the metal bodies and removed the knockout plugs for the midrange orifices. Spotless inside. I bought a 3 gal. tempo gas can and hose with bulb to eliminate anything outside the cowling. Good idle, strong top end, lousy midrange...