I Need The Carb Whisperer
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=35644
Printed Date: May-28-2024 at 6:52pm
Topic: I Need The Carb Whisperer
Posted By: Jonny Quest
Subject: I Need The Carb Whisperer
Date Posted: March-28-2015 at 1:43pm
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I'd like some carb advice from the gear-head experts. Engine is a 1994 351W that has been recently retro-fit back to carb & distributor. Carb is a Holley 4160 marine (600 cfm). (Pro Boss model with GT40 heads) The engine runs very strong and I'm quite pleased with the performance after the retro-fit. It makes me realize just how poorly the boat was running with the failing Pro-Tech TBI and ECM. I believe that my initial set-up is "spot-on" with proper timing, new plugs, wires, etc. I believe that the Carb is MOSTLY dialed-in. However, I'm getting a 1/2 to 1 second "bog" or "stumble" or hesitation when I go from idle to wide-open-throttle. After the initial hesitation, the boat takes off like a scolded dog. No problems with bogging or hesitating during RPM changes once the engine gets past the initial hesitation. Throttle response excellent and with current prop I can reach 4,500+ RPMs. My initial trouble-shooting thoughts to fix the "hesitation" are: "Accelerator Pump" circuit". The linkage is properly adjusted and I ran a 0.015" feeler gauge to ensure proper fitment. I pulled the squirter and it is a 31 standard by Holley. The accelerator pump cam on the linkage is orange with the screw in hole #2. I'm tempted to see what happens with the next size up squirter (35?) and see what happens. Perhaps even bump the screw from position 2 to position 1. Am I chasing the wrong solution? Thoughts? Advice? JQ ------------- Current 2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
Replies:
Posted By: JoeinNY
Date Posted: March-28-2015 at 4:13pm
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Just how did you use that feeler gauge to check the linkage? You need make sure it doesn't bottom out at full stroke - but there should be no play at idle. You shouldn't be able to perceptibly move the throttle before it starts squirting. If that doesn't work you should make sure your idle circuit is properly tuned. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: mamigacz
Date Posted: March-28-2015 at 9:25pm
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If you adjusted the lever like the below video, you should be in good shape. https://www.youtube.com/watch?v=k-Nx5HEzvlY" rel="nofollow - Accelerator pump arm adjusting Have you replaced the pump diaphragm recently? If not, it wouldn't hurt to replace it and see if your hesitation (lean spot) goes away. The squirters are not that expensive ($9.00), it wouldn't hurt to have a 35 or 31 in your back pocket if you still can't get this lean spot to go away. Is your current squirter a 25? What do you mean by position 1 and 2? |
Posted By: Jonny Quest
Date Posted: March-28-2015 at 10:50pm
I disconnected the throttle linkage and opened the carb up to full throttle, then I slid the feeler gauge between the linkage and the pump lever arm. The feeler gauge had a snug but not too tight fit. I believe that the idle circuit is properly tuned -- I used a vacuum gauge per Holley's recommendations. JQ ------------- Current 2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
JoeinNY wrote:Posted By: Jonny Quest
Date Posted: March-28-2015 at 10:58pm
1. Pump is new and appears to be working normally. 2. Accelerator Cam "inserts". Holley has different cams with different profiles (lift, duration, etc.). The various colors represent the different profiles. The cams have 1, 2 or 3 holes for the mounting screw to connect to the linkage assembly. The different mounting holes (labeled 1, 2 or 3) allow for additional tweaking of the cam profile. If memory serves, hole 1 is for low RPM idles (600-700) and hole 2 is for higher RPM idles (900-1,0000). It is my recollection that hole 1 gives the fuel squirt sooner and shorter. I may need to do a bit of refresher research. JQ ------------- Current 2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
Posted By: SNobsessed
Date Posted: March-29-2015 at 9:03am
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Even though idle mixture is optimum per vacuum, I would back them puppies out a turn to see if it solves the problem. You can always turn them back in. ------------- “Beer is proof that God loves us and wants us to be happy.” Ben Franklin |
Posted By: Bri892001
Date Posted: March-29-2015 at 12:51pm
Just want to highlight Joe's response here. They key to tuning out accelerator pump off idle hesitation, is when the throttle is in the idle position. If there is any kind of up and down play in the acc pump lever when the carb is at idle, then the pump squirt will be just the tiniest bit delayed on the squirt, and you'll get a hesitation. |
Posted By: Jonny Quest
Date Posted: April-06-2015 at 3:10pm
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Just got back from the lake. I changed out the 31 accelerator pump nozzle for a 35 nozzle. That did the trick. No hesitation from idle to W-O-T and acceleration is strong. Seems like the carb is dialed in. One final question for you carburetor gurus: I set the idle mixture screws using a vacuum gauge as follows: - I disconnected the PCV valve and used the PVC hose to hook up the vacuum gauge - Starting point for idle mixture screws was 1 1/2 turns open from lightly seated - Engine warmed up - Boat on trailer - in the water on the ramp - 650 RPM idling with transmission engaged In 1/2 turn increments, I tried 1, 2, 3, 4, 5 & 6 turns open (both screws) and watched the vacuum gauge. The best vacuum reading I got was 11 inches of mercury at the 1 1/2 turn setting. That seems a little lean to me, but the gauge didn't lie. Does that seem lean to anybody else? JQ ------------- Current 2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
Posted By: JoeinNY
Date Posted: April-06-2015 at 3:30pm
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Half turn increments are huge - the fact that it would be best in the ball park of 1.5 is not surprising based on my experience, but it might be better at 1.375 or 1.625. Get them equal and exactly where you get the highest reading in gear and go skiing. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: Bri892001
Date Posted: April-06-2015 at 3:30pm
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In this thread: http://www.correctcraftfan.com/forum/forum_posts.asp?TID=34309&title=how-to-adjust-holley-carb-srew-mixture" rel="nofollow - http://www.correctcraftfan.com/forum/forum_posts.asp?TID=34309&title=how-to-adjust-holley-carb-srew-mixture 3rd post down, mamigacz states that 1 1/2 turns is often the sweet spot. I've read that before. I'm honestly not sure where exactly mine is though. |
Posted By: Jonny Quest
Date Posted: April-06-2015 at 5:47pm
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To find the "ball park" I used the 1/2 turn increments. I did utilize 1/4 turn increments at 1, 1 1/4, 1 1/2, 1 3/4 and 2 turns to find the "sweet spot". Per the vacuum gauge, 1 1/2 was indeed the spot. I was just a little surprised to find my initial starting point to end up as the dialed-in point. JQ ------------- Current 2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |