Carb rejetting rant / questions.....

[NMShooter]

(Not really a repair question, but close. Sorry if mis-posted)

Been shopping for a used ski / runabout I/O. I think I have settled on the drive being Volvo Penta, as it sounds as though the reliability, performance, and repairability is good.

My target price is to stay below $10k. I've been finding good deals, but here is my dilemma.....

I am going to operate this thing at significantly different elevations, ranging from about 1000ft to as high as 8500ft.

Initially, I was hunting for an EFI boat, but pretty quickly found that in my price range they just don't exist. So it looks as though I will be going with a carb'd boat.

Here are my questions.....

1) how difficult is it to re-jet the carbs? If this is a two hour job, I may not be interested. If I can do it myself in 30 minutes or so, I might consider it.

2) How much carb tear down to get to the jets? Other than the primaries, do I need to worry about others?

3) Do I need to swap out any needles to get the different jets to run right?

I'd appreciate your comments. Thanks!

 

[Bondo]

Re: Carb rejetting rant / questions.....

Here are my questions.....

Ayuh,.... Welcome Aboard,... It depends on Which carb,....

Mine is a Merc- Weber/ Edlebrock performer/ Carter clone....
It's 2 screws, change the needles 'n or the springs, back in with the screws, 'n done...
10 minutes, Tops....

Volvo has used a few carbs, So,.......

 

[Don S]

Re: Carb rejetting rant / questions.....

Volvo has pretty much stuck with Holley carbs since the mid 90's. A prop change usually does more good that jets anyway. Find a prop that works for your altitude, and adjust the idle mixture and go for it.

 

[NMShooter]

Re: Carb rejetting rant / questions.....

I have heard that before (from boat shops here too) as "change the prop and be done with it". This sort of surprises me.... having ridden carb'd dual sport motorcycles at a wide range of elevations, I can't imagine not fiddling with the jets on my bikes. If I don't do this, they sputter and run rough, especially through acceleration. They tend to run really hot when rich too.

When going to higher elevation, I could re-gear my bike, but this only masks the issue. Seems to me that a comparable thing to say for old carb'd cars would be to put smaller wheels on the thing.

Is this really not a problem with boats? Do they not run better with proper rejetting for the altitude you are at? Or is it just too much of a hassle and folks just don't care?

 

[Silvertip]

Re: Carb rejetting rant / questions.....

5% power loss for each 1000 foot change in elevation (at least that's the number I remember). You don't gain back any power by rejetting. You "compensate" for that lost power by regearing (bikes, cars, trucks, whatever). You can't regear a boat except by changing the prop (or the outdrive but that's a bit over the top). Adjust the idle mixture if needed, as suggested and go boating. If there really is an issue - THEN it may be prudent to rejet. I live on the midwest flatland but spent lots of time in the mountains for many decades and never had a carbed car perform badly due to the atitude. Less power to be sure. But certainly not bad in any other aspect.

 

[Tahorover]

Re: Carb rejetting rant / questions.....

I just drop 2" of propeller pitch when going from the Delta (70' above sea level)to Lake Tahoe (6200').