Preparation for high altitude trip

[larry1167]

Heading to Lake Tahoe for a week. Taking my '87 Sanger with OMC Cobra 350. I have the special tool to adjust the jets on the carb and bought a Pro Pulse prop that is adjustable so I can play with the pitch. I called a shop in Tahoe and they suggested I advance the timing approximately 2 degrees along with adjusting the carb at idle. I am concerned about advancing the timing. I don't want to cause serious damage to the engine. Does advancing the timing sound like a good thing to do to get the boat to run better at 5,000 ft?

I am also going from a 3 blade 14.5x19 prop to a 4 blade 14.5 with the pitch set at 15 to start with.

 

[HT32BSX115]

Re: Preparation for high altitude trip

Heading to Lake Tahoe for a week. Taking my '87 Sanger with OMC Cobra 350. I have the special tool to adjust the jets on the carb and bought a Pro Pulse prop that is adjustable so I can play with the pitch. I called a shop in Tahoe and they suggested I advance the timing approximately 2 degrees along with adjusting the carb at idle. I am concerned about advancing the timing. I don't want to cause serious damage to the engine. Does advancing the timing sound like a good thing to do to get the boat to run better at 5,000 ft?

I am also going from a 3 blade 14.5x19 prop to a 4 blade 14.5 with the pitch set at 15 to start with.

Howdy,


I did the same thing a couple of years ago. I normally run 26p props on my Bravo III. I put 24p props on it for operation at Lake Tahoe. I didn't do anything to the engine at all and it ran fine.

It did about 4200 RPM at WOT(4600 at Sea Level) . I was surprised it even made it that high. Maybe 22p props would have been better. I didn't replace the jets.

I am not sure about a special tool for "adjusting the jets" You may only be able to adjust the idle mixture.

I don't think it will harm to advance the timing a little. At 6000 MSL, you can only make about 75% power even if the (running) mixture is correct for that alt. You'll be running fairly rich so detonation will probably be unlikely.

 

[larry1167]

Re: Preparation for high altitude trip

Thanks HT32. Yes, I can only adjust the idle mixture. Why does advancing the timing help at higher altitudes?

 

[fishrdan]

Re: Preparation for high altitude trip

On my trips to high elevation 6000-9000' I drop from a 19P to a 15P and swap out the carb's main jets. I don't remember off hand how much leaner, but 1 jet # per 2000' rings a bell. My engine idled well, so I didn't have to adjust the idle screws, this might be different for your engine though. I haven't bumped the timing yet, but going to do it on my next trip. The only other thing you can do for high altitude is swap to a lower gear ratio, but no one is going to do that unless the boat lives at high altitude. Oh yeah, I'm running a 4 cylinder I/O, so it needs all the help it can get at high altitude.

Something to remember, if you change the main jets or bump the timing, you need to reverse those changes before you run the boat at low altitude again, otherwise you could damage the engine. Same thing for the prop, but you won't damage anything unless you over-rev the engine,,, which is easy to do.

Have you checked Tahoe boat restrictions. I was going to take my boat up there this year, but decided the inspection hassle and fees weren't worth 1 day on the lake.

 

[HT32BSX115]

Re: Preparation for high altitude trip

Thanks HT32. Yes, I can only adjust the idle mixture. Why does advancing the timing help at higher altitudes?

Advancing the timing will always increase available power a little but you run the risk of detonation (pinging)

I don't know what carb that is but changing the jets might make it run a little better.....

Have you checked Tahoe boat restrictions. I was going to take my boat up there this year, but decided the inspection hassle and fees weren't worth 1 day on the lake.

YEAH! what a ROYAL PIA!!

I think it was something like $15 for the launch ramp and $35 for the Quagga Mussel inspection!!

 

[larry1167]

Re: Preparation for high altitude trip

My carb is a Quadrajet. I should still have plenty of power. It's 265 HP and my boat is low profile. Only weighs 2,500 lbs. If advancing the timing only gives you a little more power, I may leave it where it's at. I thought advancing the timing would make it run significantly better. Sounds like that may not be the case.

We will be up there for a week so the fees will be a little easier to swallow. We will be at Donner Lake so maybe they won't have the inspection there.

I am going from a 3 blade 14.5x19 prop to a 4 blade 14.5x15 prop. I can adjust the pitch on the 4 blade from 15-21. It's one of those Pro Pulse props. Thought it would be a good idea to be able to adjust the pitch if need be. The 4 blade should give me a little more torque too I would guess. We will be pulling skiers.

Fishrdan- thanks for the advice about changing the timing back to seal level spec if I advance it. I would have adjusted it when I got back home.

If I need to make some adjustments, should I adjust the idle mixture and then advance the timing, or the other way around?

 

[HT32BSX115]

Re: Preparation for high altitude trip

It probably doesn't make a lot of difference which one you do first. Just ensure that you get the idle set at around 600-650 or so. Any higher can damage your drive.