90hp Looper Carbs - What's the difference?

[McGR]

I've been chasing my tail for a couple of weeks now trying to figure out my low speed issues on my 1995 90hp 60 degree looper. My motor runs great at high speed but is a bit rough and feels like its dropping a cylinder at lower speeds. I've rebuilt the carbs (a couple of times now) paying close attention to all the pertinent details. Nonetheless, I'm still getting my low speed problem.

As a final act of desperation, I bought a couple of used carbs online today. I figure these units should help me confirm or eliminate the carbs as being the problem. Both of the carbs are the starboard carbs mounted on the common throttle plate (439008 437537).

Checking the part numbers it says that 439007 are port carbs and 49008 are starboard carbs. However, looking at the parts breakdown for the various carb components (body, bowl etc.) all components appear identical. I also pulled the carbs from my motor today and inspected them - both sides look the same to me. So I'm curious, what is the difference? Certainly there must be something if each side has different part numbers.

I'd like to be able swap carbs in and out on both sides until I figure out what is going on, but if each side is indeed different, I can only really swap out the starboard carbs. So... what's the difference???

 

[jakedaawg]

Did you service the throttle body assemblies? Most times poor idle issue is found there if it is indeed a fuel related issue.

 

[McGR]

I did remove the covers on the throttle bodies and clean the idle and mid speed jets. I didn't remove the idle adjustment screws, though I did thoroughly spray and blow out all adjacent passages etc. . I was hesitant to pull the adjusters because it idled so well in the past that I didn't want to mess up the calibration. Perhaps I should remove the idle mixture adjusters too?

 

[jakedaawg]

Have you verified that you're not losing spark intermittently at low rpm? Attach a timing light to each plug wire and run til you experience the issue. You may find the light flashes erratically when you feel the miss. It may be best to do at dusk or in the shade due to the optical

 

[McGR]

I haven't done the timing light test yet. It is on my list of things to check. Thanks.

 

[McGR]

OK... So I got my new to me couple of carbs. So I took them and rebuilt them and pulled off all the original carbs so I could clean the throttle bodies again - this time removing the mixture screws too. Overall things went well, as I'm getting real good at removing , taking apart and reinstalling these carbs. I didn't start the motor yet - maybe tomorrow evening.

However... after finishing the job I realized I put the new "starboard" carbs on the port side and I put the existing carbs previously from the port side on the starboard side. So now I'm sitting here contemplating if I should switch them out or not. All logic with the exception of the carb part numbers says all four are the same, as all individual components : carb bodies, float bowls, high speed jets, low speed air bleeds, floats, covers, gaskets etc. etc. are the same p/n. So what is the consensus out there - should I bother swapping port and starboard carbs, or does it not make any difference?

 

[jakedaawg]

Are there not passages that are on different sides on the mounting faces where it contacts the throttle bodies? Never payed attention because I always put em back where they go...

 

[McGR]

I'm not seeing that there's any difference in passages. How can there be?... Both sides use the same carb body (and same gasket).

This whole question has me very perplexed.

 

[Faztbullet]

Bodies look the same but venturi size and throttle plates make the HP differences between a 90 and 115 so be careful mixing carbs

 

[McGR]

All carbs are definitely the smaller throat 90hp type - checked part numbers. Just confused as to why parts listings show two different part numbers for port and starboard carbs yet show all identical individual components for both sides. Still running the original throttle bodies, so no change there.

 

[McGR]

So, I finally got the boat out this morning with the carbs installed on the "wrong" sides. It ran great! So... on my motor (1995 Evinrude E90ELEOC), I'm officially proclaiming the side (starboard/port) and position (top/bottom) does not matter.

In hindsight after this whole debacle, I'm fairly certain I know why I was having low/mid speed issues - the low speed emulsion tubes. I made the mistake of coming across a video of a guy who removed these tubes for cleaning during rebuilding. I decided to do the same. Unfortunately, the one detail missing was the correct position of the tubes upon re-installation. These tubes don't have any positive locating feature, they just simply press into holes in the plastic carb bodies. Long story short... I was pressing them in just a bit too far. My advise to the wise... Don't pull these things for cleaning, just run a thin wire and some carb cleaner into them during rebuilding.

I'm glad this episode is over, for a while there I had convinced myself that my block had cracked over the winter. Everything is good now... hooray.