Help re-jetting 1989 Johnson 175

[crashkaloop]

Hope I can get some help on this one?

I have a 1989 Johnson GT 175 and I want to re-jet the high speed orifice. The current jets are 61C, which is one of the standard jets listed in the parts diagram, listed as part # 0320661. They also list a 56C as part # 0325019. These appear to be the only high speed orifices available.

I operate at lakes at 6,000 to 8,000 feet in altitude, and my plugs are fairly wet most of the time (running too rich).
I measured the actual opening size of my jets and they are 61 thousands, so I now know what the 61C stands for in the part number. And that now tells me with some confidence that the other jet in the parts list (56C) would be 56 thousands orifice.

1) Are these the only two options available for my engine?

2) Is the 56C jet likely to be the correct jet for my altitude?

I know that some will tell me to change my prop, but I truly want to re-jet because I know the engine is running rich.

Thanks for the help!

 

[emdsapmgr]

Re: Help re-jetting 1989 Johnson 175

The factory makes all sizes of "C" jets, from .026 to .076 thousandths. They come in 1 thousandths increments, per the factory service manual from that year. [I believe a few of the really large sizes have been discontinued based on low sales volume.] You are misreading the parts listing. The 150 model takes the .056, your 175 takes the .061 jet. That's a sea level jet size. There is not a lot of information in the factory service manual regarding rejetting for higher altitudes. There is no doubt some logic to reduce the size of the main jet, based on some altitude formula. The factory customer service guys may be able to give you specifics-give them a call in Illinois: 847-689-7090. Those engines do run rich at idle.

 

[crashkaloop]

Re: Help re-jetting 1989 Johnson 175

Yep, I was afraid that that other orifice was for a 150 hp, so thanks for confirming that. I have the Johnson service manual, but I can not find anywhere that indicates much about the correct jets for high altitude. At least that I can find.

It is good to know that the jets are sized in 1 thousandths increments though. That should allow me to dial this thing in just right.

I called the phone number given, but it says it is disconnected.

Any other suggestions on where I might find a chart that can indicate the correct size jet for high altitude?

 

[boobie]

Re: Help re-jetting 1989 Johnson 175

Call BRP customer service at 1-262-884-5993. They may be able to help you out.

 

[crashkaloop]

Re: Help re-jetting 1989 Johnson 175

I got in touch with a mechanic who says there were no options for the high speed orifice on this year engine. Can this be true? Do I just have to live with an engine that runs this rich?

I hope maybe one of you folks can answer this for me, as I just can't believe there is no way to make this engine perform better at high altitude. :blue:

 

[boobie]

Re: Help re-jetting 1989 Johnson 175

I have a box full of different size jets . As said above, call BRP.

 

[crashkaloop]

Re: Help re-jetting 1989 Johnson 175

Problem partially solved.

My manual does indeed show all, or many, of the C series jets, and gives the part numbers. I was looking through the carb section, and the info on jets in the tune-up section.

So now, I was left to try to figure out which jets to order for my altitude. The mechanic I mentioned, sent me a chart for 1982 engines which shows the proper jets for certain elevation ranges. They show a 175 HP engine at sea level to 3,000 feet to have the exact same jet I have now. Then, they show that same engine at 3-6,000 feet has a main jet of 56C. However, since I am almost always above 6,000 feet, I lowered it one more size and ordered the 55C jets. Nice surprise were that they were ? the price of the 56C’s.

I will try them out and monitor my spark plugs carefully for the first few times I run the boat. I usually check them after every use anyway. If they show I am too lean, I will step the jets back up accordingly.

Again, thanks to all for the great suggestions.

 

[boobie]

Re: Help re-jetting 1989 Johnson 175

I guess it pays to read the manual.:joyous:

 

[crashkaloop]

Re: Help re-jetting 1989 Johnson 175

I guess it pays to read the manual.:joyous:

Yep. Cover to cover if needed. Shame it doesn't give any elevation recommendations though. But I use to have to guess at jet size for dirt bikes in the old days, and I managed.

I still plan to take your advice and try BRP tomorrow.