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After multiple jetting attempts, we are still suffering from delayed starts. Any suggestions with what other issues we might need to address with our new motor.
Thank you in advanced
 

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Are you saying it lags or bogs as you accelerate? What is the basic engine, how much ignition timing do you have in it? What is the carburetor, and while we are at it, what ignition system are you running?
 

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Barry has decades of experience building ill try to add a little here, To get off idle you need to transition and there are several other things that lead to that transition, Position of your throttle blades at idle, accelerator pump adjusted correctly, accelerator pump cam, how about power valve how much vacuum are you pulling is it the correct valve etc, Don't get too hung up on just jetting, as mentioned above where is timing at and is advance working etc...
 

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Are you saying it lags or bogs as you accelerate? What is the basic engine, how much ignition timing do you have in it? What is the carburetor, and while we are at it, what ignition system are you running?
Hello, and thank you so much for getting back to us... ok question #1- At the start of the race it has a major hesitation at the hit of the throttle. #2 Engine is 490 Dart Chevy #3 Ignition timing is 38 #4 Carb is twin 10-50 dominators #5 Ignition is MSD Al 7 crank trigger.
This is super helpful, we retired our last year motor and really like what it can do once it gets going but it's killing us at the start. We are having a competition carb shop go through them and considering putting the motor on a DYNO.
Half the fun of all this is fixing and working on the motor ourselves but we are seriously stumped, we did move the timing up to 40, it helped but its not even close to what it should be performing at.
Thank you again:)
 

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Barry has decades of experience building ill try to add a little here, To get off idle you need to transition and there are several other things that lead to that transition, Position of your throttle blades at idle, accelerator pump adjusted correctly, accelerator pump cam, how about power valve how much vacuum are you pulling is it the correct valve etc, Don't get too hung up on just jetting, as mentioned above where is timing at and is advance working etc...
Barry, thank you as well for getting back to us! We are feeling good about the throttle blade, and accelerator pump is properly adjusted. They are 50cc accelerator pump and the pump cam is (white) 643's. The power valve is plugged off. We don't know how much the vacuum are pulling... is it worth drilling a hole in the manifold and put the gauge on it? The only reason we are sensitive to jetting is that we live at very high altitude and race at very low. So we are always changing them. Thank you for these great questions, I added some other comments above as well too Obnoxious001. I know we are all very busy and I can't express enough how grateful we are that both of you took the time to engage and help out with great questions and inquiry. Looking forward to hearing for back. Have a nice rest of the weekend!
Lori DeCarlo-Thurston
 

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Dang, thought this was gonna be an old small block :) this is big stuff and way above my paygrade,,, good luck chasing these gremlins.
 

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Hello, and thank you so much for getting back to us... ok question #1- At the start of the race it has a major hesitation at the hit of the throttle. #2 Engine is 490 Dart Chevy #3 Ignition timing is 38 #4 Carb is twin 10-50 dominators #5 Ignition is MSD Al 7 crank trigger.
This is super helpful, we retired our last year motor and really like what it can do once it gets going but it's killing us at the start. We are having a competition carb shop go through them and considering putting the motor on a DYNO.
Half the fun of all this is fixing and working on the motor ourselves but we are seriously stumped, we did move the timing up to 40, it helped but its not even close to what it should be performing at.
Thank you again:)
MSD boxes are very voltage sensitive, less than 12.3 volts and you may have issues. They instruct users to connect the large black and red leads directly to the battery.

What sort of racing are you doing?

There is a formula for how many jet sizes to change based on elevation, and if you are racing seriously you probably should have an air density gauge in your pits. Lets start with race elevation vs "home", how many feet for each? One time many years ago I went to a circle boat race at high altitude and the guy I went with to help crew had no spare jets for carb, so we tuned it strictly by ignition timing, had 44" degrees in it, had it running good, but had to remember to back down timing at the next race at Long Beach (sea level). The size of the accelerator pump diaphragm is perhaps not as important as the accelerator pump nozzle size. Check the number on them, look up what "stock" is for that carb to make sure they have not been changed drastically. You can be getting a "bog" from too little or too much fuel on the hit.
 

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Sounds like she's going lean at the hit..Turn the air screw's out 1/4 - 1/2 turn more on all of them.. I would replace stock # 37 squirters with #42 or maybe even larger squirters and see if that helps.. I also found if the carbs are set up with progressive type throttle linkages you need to have the carbs idling just off the primaries - Back Off the idle set screws off on the secondaries - If your linkage is progressive the secondaries should just start to open when you hit the throttle, no sooner...
 

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Discussion Starter #10
MSD boxes are very voltage sensitive, less than 12.3 volts and you may have issues. They instruct users to connect the large black and red leads directly to the battery.

What sort of racing are you doing?

There is a formula for how many jet sizes to change based on elevation, and if you are racing seriously you probably should have an air density gauge in your pits. Lets start with race elevation vs "home", how many feet for each? One time many years ago I went to a circle boat race at high altitude and the guy I went with to help crew had no spare jets for carb, so we tuned it strictly by ignition timing, had 44" degrees in it, had it running good, but had to remember to back down timing at the next race at Long Beach (sea level). The size of the accelerator pump diaphragm is perhaps not as important as the accelerator pump nozzle size. Check the number on them, look up what "stock" is for that carb to make sure they have not been changed drastically. You can be getting a "bog" from too little or too much fuel on the hit.
OK, CHECK LIST: So our MSD boxes are at 12.7. And its connected as recommended above. So good so far:) We so drag boat racing, when they have the races:)
We are interested in purchasing a air density gauge too. Do you have one you like, and ease of use? So we are at 5000 ft and we race at 400. We understand what you saying about the ignition timing, we went from 34 to 40. It helped but not race ready for sure.
The accelerator pump size nozzle came with 48 and we went to a 59. Currently we sent the carburetors to a reputable competition carb shop. We are waiting on that now, pretty far down the list, but hopeful!!
We are so appreciative for all the input, it has brought up lots of questions and things to look at. Thank you so much
 

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Sounds like she's going lean at the hit..Turn the air screw's out 1/4 - 1/2 turn more on all of them.. I would replace stock # 37 squirters with #42 or maybe even larger squirters and see if that helps.. I also found if the carbs are set up with progressive type throttle linkages you need to have the carbs idling just off the primaries - Back Off the idle set screws off on the secondaries - If your linkage is progressive the secondaries should just start to open when you hit the throttle, no sooner...
Gosh, thank you so much, we will need every bit of this. We are doing one thing at a time so we actually know what worked and what didn't. As we progress, we will post. Thank you again, Lori
 
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