1994 Merc 25 HP 2 stroke carb jet?

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mtntop

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Hi, I have a 1990 2 stroke 25 HP merc with a .076 dia carb jet. I purchased this engine in Iowa and use it here in Colorado above 8000'. I rebuilt the carb, it starts but runs very rich at altitude. What do you guys think will happen if I run a .044 jet from a 20 HP merc in there? It will run leaner, which is what I want but how can I tell if it is too lean? I don't want to burn up the engine, it is like new w very few hours
Thanks for your insight!
 
That is going to be tremendously leaner, I am guessing it will starve at high speed.
 
nccatfisher said:
That is going to be tremendously leaner, I am guessing it will starve at high speed.

Thanks for the feedback NC Cat, after I posted this it occurred to me I should call a boat mechanic here in Denver and he told me to leave the jet alone, because going smaller would only improve my fuel burn rate without any improvement in performance and I would risk burning up a cylinder if I forgot to put the larger one back in at lower altitudes :) He did tell me to tweak the air/fuel mixture idle adjustment for better idling performance which changes with each change in altitude.
 
On a newer motor you can be sure that actual engineers have studied and will know about this issue. I'd check with the manufacturer and see what they recommend.
 
mtntop said:
nccatfisher said:
That is going to be tremendously leaner, I am guessing it will starve at high speed.

Thanks for the feedback NC Cat, after I posted this it occurred to me I should call a boat mechanic here in Denver and he told me to leave the jet alone, because going smaller would only improve my fuel burn rate without any improvement in performance and I would risk burning up a cylinder if I forgot to put the larger one back in at lower altitudes :) He did tell me to tweak the air/fuel mixture idle adjustment for better idling performance which changes with each change in altitude.
That is good advise because the motor actually runs on both jets at WOT. So your leaner setting at idle will effect it at WOT.

In the two cycle world, lean is a very bad situation as it not only doesn't perform well it isn't lubricating, and we all know the latter catches up to you sooner than later.
 
Mtntop, Looks like you and I have had a lot of the same issues running our old mercs here in Colorado at high altitudes.
I would love to talk to you in person about your motor and or meet up for some fly fishing for pike. The big lakes are about ready to go off
for pike in the next few days. Oh, a couple of beautiful gods you have there, just lost my golden in August :cry:
Carphunter 970-two seven 4- four four 08
 

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