Advice needed on Jet Sizes please.

Hi All. I'm in need of your kind assistance again please.

I have a kind of new to me 1991 200hp mariner. Serial number 0D068540 While getting to know the motor I have come across a few things that tell me that it might have been fiddled with before i got it, so i am nervous that certain things may not be as they should.

i have recently moved house where i was operating the boat at around 5700 to 6000 ft above sea level. I will now be operating between sea level and 2000 ft and believe that a change of jets may be needed to prevent me from frying the motor.

i recently rebuilt the carbs at my previous elevation. They appear to be wmc 1,2 or 3 carbs. The main jets were 0.68. Across all three carbs. I cannot recall what the idle, air and intermediate jets were.

can anyone please tell me what the correct jet sizes are for this motor at the altitude i will be operating at?

thank you kindly

The poster is from South Africa and should be able to find some local help.

Thanks Guys. I will call the local Merc dealer and ask them. If they can't give the details i will call the guys at Seaway marine.

I currently have a 19p laser II that topped out at 5400 at around 53 MPH, was looking at changing it to get a bit more top end at the higher altitude. Was thinking of going to around 21, but perhaps a 23 at the new altitude would be better. I'll ask the Merc guys at the same time.
Thanks again.

Hi guys.

I called Merc locally and Seaway marine in Seattle. Both say they can only tell me what Jets the motor was supplied with and not confirm which i need to use at sea level.

They both confirm: Jet Bowl vent at 0.076, Progression jet at 0.034, main fuel jet idle air bleed at 0.046 and Main jets at 0.064. These are the jets currently in the motor. This agrees with this site. Can anyone confirm what altitude the jet sizes on this site are for?

Hi Just in case any one was following this thread. It turns out the Main Jet which should be 0.064 at sea level is 0.066 and the Jet Bowl Ven which should be 0.076 is actually 0.082, so both the Air and Main Jets are larger than they should be..... I have ordered the correct jets and will let you know what happens when they're in.

So finally got hold of someone who regularly works on these motors down here. Turns out the jets i have are 100% correct as confirmed by the manual. There is a slight anomaly as the motor is 1991, but the carbs are WMH 1 which show up on the systems as being fitted only until 1990. The jetting on the later carbs is different with smaller fuel and air jets....

took it to a local famers lake today set the idle mixture screws and it takes off like a stabbed rat!!!!

Tachometer also screamed straight to the 5400 plus and sounds like it has more to give. i'm going to get an aluminum 21 pitch and will see if that gives me more top end. If it works i will buy a stainless and keep the aluminum as a spare.

Thanks Kimcrbwr1.

i'm currently running a 19P laser II. It's a vented prop. When trimmed up at WOT i was getting around 5400 to 5600 at the 5000 meter altitude. There is plenty power out of whole and top end is around 53mph. I have the 1.87 gear ratio

Yesterday was the first time i ran at sea level and i could tell straight away that there was more power, but also got the impression that the prop may have been slipping. It shoots out of the hole and straight to around 5400, 5500 without even trimming up and if i take off on anything other than fully trimmed down it acts like i'm taking off with it trimmed halfway out of the water.

i normally run the boat with myself an adult passenger and 2 - 3 kids with a full to half tank of gas. The boat is a 18.5 foot bowrider and is mostly used for cruising/blasting around and towing skiers, wakeboarders and tubes

in speaking to the guy who set up the motor he said if i want all round good performance i should go to a 21p, and preferably a laser II as i have now, because they seem to be popular well made props. I can get my hands on a 23p at a reasonable price but the 21's are around $700....

should i go with the 21 and just wait till i find one at a better price?