350 vs 383
08-26-2011 | 06:07 AM
#11
Gold Member
Joined: Oct 2002
Posts: 1,237
Likes: 165
From: SWFL
Interesting as many people with same combo (less compression) turn a 23" 5000rpm with same engine combo. Speeds in 62-65mph range. Exception would be a 21 Velocity that will gover 70mph with that package. Again, a large exception as those boats haul with their respective power.
Is your boat heavy ? Not a performance (quick) hull ?
Stock exhaust ? Too small flame arrestor ?
Have you tweaked your BG650 ? What spring do you have in the secondaries ? I've used same carb on just about same engine build and found stock jetting to be almost right on. 700ft above sea level. I, however, spent better part of a day tuning with secondary springs. Believe it or not, ended up accelerating the fastest and getting best top speed with the lightest spring in the kit. SHort/soft yellow one. I crapped (lol) with the difference. Yes, was armed with a GPS...no butt dyno stuff here.
So, if you haven't done atleast that, your carb has a quick change spring kit on it. It's the big red round thing with a slot in the middle. Just turn it counterclockwise with a decent size flat bladed screwdriver until it unthreads. Wallah, there's the spring.
Keep adding softer springs until your grin is the largest. If a softer one slows it down, go back to the last 'best' spring.
Is your boat heavy ? Not a performance (quick) hull ?
Stock exhaust ? Too small flame arrestor ?
Have you tweaked your BG650 ? What spring do you have in the secondaries ? I've used same carb on just about same engine build and found stock jetting to be almost right on. 700ft above sea level. I, however, spent better part of a day tuning with secondary springs. Believe it or not, ended up accelerating the fastest and getting best top speed with the lightest spring in the kit. SHort/soft yellow one. I crapped (lol) with the difference. Yes, was armed with a GPS...no butt dyno stuff here.
So, if you haven't done atleast that, your carb has a quick change spring kit on it. It's the big red round thing with a slot in the middle. Just turn it counterclockwise with a decent size flat bladed screwdriver until it unthreads. Wallah, there's the spring.
Keep adding softer springs until your grin is the largest. If a softer one slows it down, go back to the last 'best' spring.
08-26-2011 | 10:37 AM
#12
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Joined: Nov 2004
Posts: 14,177
Likes: 3,731
From: On A Dirt Floor
There will be charts included with the springs with cid vs opening point rpm and fully opening point rpm, however don't get carried away remembering those and don't sit down and crunch cid vs VE vs rpm vs carb airflow needed. Real world results is best. Keep putting in a softer spring at a time until you have a big grin on your face.
Once done you'll probably sit back and say "Oh, this is why some people recommend a mechanical secondary carb on even mild performance engines."
If your boat doesn't respond much , especially in terms of acceleration, then your boat will have a hard time responding to any mod or change.
Once done you'll probably sit back and say "Oh, this is why some people recommend a mechanical secondary carb on even mild performance engines."
If your boat doesn't respond much , especially in terms of acceleration, then your boat will have a hard time responding to any mod or change.
08-26-2011 | 10:45 PM
#13
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Registered
Joined: Apr 2010
Posts: 897
Likes: 10
From: Daniels, WV
There will be charts included with the springs with cid vs opening point rpm and fully opening point rpm, however don't get carried away remembering those and don't sit down and crunch cid vs VE vs rpm vs carb airflow needed. Real world results is best. Keep putting in a softer spring at a time until you have a big grin on your face.
Once done you'll probably sit back and say "Oh, this is why some people recommend a mechanical secondary carb on even mild performance engines."
If your boat doesn't respond much , especially in terms of acceleration, then your boat will have a hard time responding to any mod or change.
Once done you'll probably sit back and say "Oh, this is why some people recommend a mechanical secondary carb on even mild performance engines."
If your boat doesn't respond much , especially in terms of acceleration, then your boat will have a hard time responding to any mod or change.
Mine is a mechanical secondary so I'm good in that dept.
The exhaust is stock merc center risers and manifolds
The flame arrestor is a k and n that I think is 2 3/4 in tall and 9 in diameter
The stock jets in the carb are 72 in primary and 80 in the secondary
I'm yet to check a plug as I have been off the water for the last month but Is it possible I'm getting to much fuel and not enough air?
I've had a few folks mention that a 68 primary and 76 secondary might lean it up a bit and free up some ponys. I'm up for anything reasonable to try to gain a few mph
Here is a link to the boat:
http://www.concordboats.com/Magnum-II.html
Last edited by 87MagnumII; 08-26-2011 at 10:48 PM.
08-27-2011 | 11:16 AM
#14
Gold Member
Joined: Oct 2002
Posts: 1,237
Likes: 165
From: SWFL
There will be charts included with the springs with cid vs opening point rpm and fully opening point rpm, however don't get carried away remembering those and don't sit down and crunch cid vs VE vs rpm vs carb airflow needed. Real world results is best. Keep putting in a softer spring at a time until you have a big grin on your face.
Once done you'll probably sit back and say "Oh, this is why some people recommend a mechanical secondary carb on even mild performance engines."
If your boat doesn't respond much , especially in terms of acceleration, then your boat will have a hard time responding to any mod or change.
Once done you'll probably sit back and say "Oh, this is why some people recommend a mechanical secondary carb on even mild performance engines."
If your boat doesn't respond much , especially in terms of acceleration, then your boat will have a hard time responding to any mod or change.
