carb adjustment for altitude?

[iaonbb]

Hey all, here’s my dilemma…I have the 310 carb engine. 10 hours thus far. Followed the break-in schedule religiously. Here are the symptoms I’m experiencing:

1. Won’t idle at start-up. Must run in neutral at 1k rpm’s for a couple minutes before I can do anything.
2. Acts like it wants to die when shifted into gear and/or trying to idle out of the no-wake zone
3. Runs very inconsistent overall, e.g., rough, surges, grinding noise? etc..
4. Idles perfectly after running 3-4k rpm’s for a few minutes and then returning it to idle, e.g, stopping to pick up a rider, etc… then, starts acting like it wants to die again after another few minutes.

History: It’s an ’04 that I just bought new. Guessing it had gas sitting in it for extended periods of time. I’ve ran 2 tanks of premium through it, the second with a bottle of dri-heet to try and absorb any moisture in the tank/fuel that might be causing any issues. No change whatsoever. Going to run a 3rd tank through tomorrow with a can of seafoam to see if that helps. At this point, I’m thinking it may need some minor carb adjustments. I’ve spoken with my dealer who said it sounds like it might be running rich, which makes sense at this altitude. I’m scheduled to have it in the shop at the end of the month for the 20 hr service and winterization. I planned on having him adjust the carbs then, including drilling out the caps to access the bleed screws if necessary. Sounds like carsondoc’s post from ’03 best matches my situation.

“YellowMoomba,
I was having all kinds of engine problems at slow speeds and idle until I adjusted mine. Now you can barely tell the difference between this boat and an EFI engine. Runs great. I live at 4700 feet and often operate the boat at 6200 feet."

However, I was hoping I might be able to make a few adjustments to the idle, air/fuel ratio, etc. myself first, without resorting to drilling. We’re heading out tomorrow for the first day of riding after the break-in and I would like to try and tweak it a little while we’re out. I know very little about engines but I’m sure I could turn a few screws here and there. Anyone care to help out a newbie with some “carb 101” advice. Step-by-step inst’s would be most appreciated! Need to know by tomorrow a.m. if possible…many thanks in advance!!!
MDB

[carsondoc]

Hi ia. It does sound like you are having the same problems I encountered. The first thing I did was have my dealer try to fix it in the shop. He increased the idle speed a little and advanced the timing a little. Unfortunately, these changes made only little difference. The problem with just increasing the idle to fix this is that you will start putting more stress on the transmission when going from idle to "in-gear". That's why it's not recommended to increase your idle rpm above 1100 (actually, it shifts smoother when your idle is about 6-700 rpm and is probably better on your tranny).

With that said, you can try to increase your idle rpm a little (you said you were already idling at 1000 rpm?). The screw is on the port side of your carb. You can figure out which one it is by taking the air filter off your carb and looking at your accelerator linkage on that part of your carb. With your boat off (in the garage maybe) just look at your carb while someone accelerates/decelerates a couple times. It should be fairly obvious--it's a big screw that stops the accelerator mechanism on the carb. Then, when you are in the water idling, take off the air filter and turn the screw a little while you watch your tachometer. Obviously, be very careful around the front of your engine where the parts are moving.

I would not increase it above 1100 idle rpms. When you shift into gear you will drop a couple hundred rpms. If this does not fix it, adjust the idle air-bleed screws and get your idle back down to 700 or so.

Good luck and I'm sure with some tweeking you can get your boat running great.

[iaonbb]

Thanks buddy...never guessed you'd still be on, lol! I should be more clear...I normally idle around 700'ish or so I think. Right after startup, I run it in neutral (using the tranny disengare at the bottom of the throttle) at 1k until it will idle decent.

So, my only two options are either the idle speed or drilling out the caps to get to the bleed screws? I was hoping there was some sort of air/fuel mixure screw or something that I could adjust as well (or is that what the bleed screws are)? I know I can't adjust the timing, right?. Many thanks for the quick reply!
MDB

[rbc_racing]

I had the exact same problem on my 04 that I bought this year. It just needed a slight adjustment of the idle mixture screws under the caps. There was another thread about this posted not to long ago where the indmar rep said it was ok to adjust them as long as you don't live in cali. I started out by screwing them in all the way and backing them out 1 and 1/2 turns, then fine tuning the adjustment on the lake after that. It runs great now, It acts just like and EFI engine now.

[carsondoc]

Ia, the air/fuel mixture screws are the idle air bleed screws--same difference. It's actually a very simple process. It's just a matter of popping the brass caps off so you can get at them. Everyone on this board talks about drilling them out but I have to admit that I was skiing with my dealer when we did mine and all we had was a rock and a screwdriver! What ever gets 'em out! As RBC can attest, it makes a world of difference. You'll be a happy camper.

Go ahead and try the idle adjustment first but if that doesn't cut it, just fix the idle air-bleed adjustment and you should be good to go.

[YellowMoomba0]

You and I are at much different altitudes. Me about 360. The idle screw did nothing more than raise the rpm and make the tranny plates slam into gear. As well, idle speed was too fast. I kept this setting all of 10 minutes. I know of no other way than to adjust the bleed screws. Then again, Im not sure how the altitude difference will affect you. All you can do is try it with the idle screw first. If I had to guess now, then Id say you will have to adjust the bleed screws to get happy about the performance. I would be interested to learn though if the idle screw adjustment alone would fix your problem.

[iaonbb]

Ok, so I printed the older post on how-to remove the brass caps...I'm out in my garage as I type, cover and filter off, trying to figure out exactly which caps we're talking about. I see two diferent sets of brass screws on the top of the carb (small and smaller), and four larger brass "leather tack" looking ones on the side. None of them look right?Where the heck are these things? Afraid to start drilling unless I'm 101% sure. Sorry guys, but engines are not my forte'

[YellowMoomba0]

Whats your email address, I will send pictures of the Carb

[iaonbb]

Found 'em! Wil report back later on how it worked out..thanks

[iaonbb]

Well, I'd have to say it was a success...Most noticeable diference was in the idle smoothness and puttering out of the marina. Also starts much better after being turned off for 5-10 minutes, e.g., switching riders, drifting, having a beer, etc. I did not touch the idle speed as it was around 8k and I though that was plenty high. Still needs a little tweaking though I think. I turned the bleed screws about a 1/2 turn out (counterclockwise) from their original position and noticed it smoothed out almost immediately. Didn't have to use the tranny disengage and pump the throttle and get it to re-start once!

So....here's my next question...what is actually happeing when I back the screws out (counterclockwise)or turn them tighter (clockwise)? Does one direction equal more fuel and less O2 and vice versa? I'd assume that backing them out (counterclockwise) increases the O2 and decreases the fuel? Does one screw control the air and one the fuel, or do they both do the same thing? Figure I could probably have her dialed-in by the end of day tomorrow if I knew exactly what was happening when I turn the screws one way or the other...any techies out there know?

In summary...this board rocks!!! Solved most of my probs and saved me the $95/hr labor!! woohoo...now what else can I buy for the boat with my savings
MDB

thanks guys!