1987 90HP carb jets

Distress_signal · Mar 9, 2004

Attempting to rebuild carbs on 1987 90HP Johnson. Spoke with local marine reapair shop and was told that the jet size is 56. When disassembled carbs, have two sets of jets in each. One is a 26 and other is a 34. Is this correct? Motor has a decelaration ping. Wanting to up the high speed jet size. Any recomendations? Distress

Joe Reeves · Mar 9, 2004

Re: 1987 90HP carb jets

It doesn't sound like you've removed the high speed jets, but are rather speaking of the low and intermediate speed jets. The high speed jets are located in the center portion of the float chamber (2 to a carb) which are about 1/2" long with a 1/4 x 20 thread.

Distress_signal · Mar 9, 2004

Re: 1987 90HP carb jets

Thank You Joe, I will check on that. But as far as low and intermediate, do these sizes sound about right? I am wanting to up the high speed jets, spark plugs are burning almost white, and I would like them just a little darker. Would the high speed jets happen to be the ones under the plugs in the bowl? Distress

OBJ · Mar 9, 2004

Re: 1987 90HP carb jets

On the sides of the float bowls you will see a drain plug. Behind these plugs are the high speed jets. They should be 56C and should be stamped on the jet. The jets you posted are the idle air jet (34) and the midrange jet (26). Make sure these jets are open and that the high speed jets are open. Use carb cleaner followed up by compressed air to clean the carbs. Make sure the floats are set correctly also. After rebuild, try the engine again before making any changes to the jet sizes. And also make sure the fuel system to the carbs is tight. If you have any hard hoses, replace them. Good Luck....keep us posted.

Distress_signal · Mar 9, 2004

Re: 1987 90HP carb jets

Thank You OBJ! You are right, they are in there. Well to make a long story short, Pulled them out of one carb so far, and to my surprise, one jet was a 56c and the other was a 57c. Would it be recommended that I correct this and make them both the same? Have not looked at the other carb yet, Can't wait!!!!!!!! Where is a good place to purchase new Jets? Also, who manufactures these carbs? Once again, Thanks to all. Distress

OBJ · Mar 9, 2004

Re: 1987 90HP carb jets

Yes...I would make them both the same. You can get them at any local Johnny/Rude dealer. Take your model number with you.

Distress_signal · Mar 9, 2004

Re: 1987 90HP carb jets

Once again, Thanks to all that have helped!!!!!!!!! Distress> Not so stressed Now!!!

walleyehed · Mar 9, 2004

Re: 1987 90HP carb jets

Timing advanced slightly too far will cause simular problems as well. Having all 4 plugs white with the correct jets, would lead me to #1, timing...#2, Float level, and I assume you have not removed the carb silencer cover and ran without it.

Dhadley · Mar 9, 2004

Re: 1987 90HP carb jets

What plugs are you using? What grade fuel? Have the heads been cut? And as Kenny asked -- whats the timing set at?

Distress_signal · Mar 10, 2004

Re: 1987 90HP carb jets

Ok, Gonna try to answer both of you here. The timing is set at 28 wot, no the heads are not cut, all stock engine. running 97 octane gas, spark plugs are new (L77JC4 Champions). No I have not ran it with the silencer of yet. What should I see when I do? The timing was just recently set at dock side, then run on lake for fine tuning. After effect was 28 deg wot 4900rpm with 19 pitch prop. Distress

walleyehed · Mar 10, 2004

Re: 1987 90HP carb jets

#1, your about 800RPM low of where you should be RPM wise....52-5300 would be as low as you would ever want to be propped for WOT...You're lugging the engine at 4900...#2, I assume you mean "87" octane, or do you use the "RON" scale?? I would highly recommend setting timing back to 26degs, as I don't know the method you have used to set it.

Distress_signal · Mar 10, 2004

Re: 1987 90HP carb jets

Walleyehed, Really not sure what the "RON" methode is, but Running Super Unleaded (93 octane I believe). I think I said 97 Octane earlier. As far as the 26 wot, I heard that somewhere once before. Book calls for 28, and someone had told me to set it at 26 for better performance or something like that. Can not remember for sure. But thanks for confirming that. As for the prop, Original prop was a 17, I just recently upped that to a 19. When I originally install the 19, rpms dropped down to about 4600. Since then, I have changed the setup of the engine and was able to gain the extra 300 rpms. I am going to attempt to run the 17 prop again with the new setup, and see what performance I acheive. But would really like to keep using the 19, but just can not seem to find the power to run it. Distress

Dhadley · Mar 10, 2004

Re: 1987 90HP carb jets

I would run it on 87 octane as long as its factory stock. Between the high test fuel and the lugging youre creating a bunch of combustion temp -- that may be causing your plugs to burn white.

1987 90HP carb jets

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