Carb tuning
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=51157
Printed Date: November-24-2024 at 12:32pm
Topic: Carb tuning
Posted By: uncle-buck
Subject: Carb tuning
Date Posted: May-28-2023 at 12:42pm
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Recently did a partial rebuild of my boat's Holley 4160 carb. It starts with one turn of the key when cold as well as when warm, and it runs great. *But* the engine stumbles and cuts out under load - until it warms up. I adjusted the idle mixture screws for max vacuum (after the engine was warm) and it sounded great. But it would not start with a single turn of the key. Opened the screws a half turn (from 1 1/2 to 2 turns out) and it does again. Is the stumbling under load when the engine is cold an idle mixture issue, a choke setting issue, or something else? I can certainly live with waiting a couple of minutes for the engine to warm up. But it would be nice to be able to back off of the trailer when launching without waiting. ------------- 1990 Ski Nautique (original owner) PCM 351W with D.U.I. |
Replies:
Posted By: 75 Tique
Date Posted: May-28-2023 at 2:21pm
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I hate to sound like a Facebook responder who has no clue as to what I am talking about and offer a response that has nothing to do with the problem, but when I had similar symptoms (started fine, idled fine, ran fine) but stumbled upon pick-up, someone suggested timing. I checked that, tweaked it a bit and was good to go. ------------- _____________ “So, how was your weekend?” “Well, let me see…sun burn, stiff neck, screwed up back, assorted aches and pains….yup, my weekend was great, thanks for asking.” |
Posted By: KENO
Date Posted: May-28-2023 at 4:32pm
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How about a couple pictures showing your choke butterfly position when the engine is cold? One right before you touch the key at all and the other after it starts While you're at it, take a third one when it's warmed up and you don't have the hesitation.
If the problem is only with a cold engine, it's probably not ignition related. |
Posted By: uncle-buck
Date Posted: May-28-2023 at 10:09pm
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Appreciate your reply, Ken. It may be a week or two before I get those pics for you. ------------- 1990 Ski Nautique (original owner) PCM 351W with D.U.I. |
Posted By: KENO
Date Posted: May-29-2023 at 7:53am
If it's in the driveway, just take one picture of it cold, that'll tell quite a bit. 
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Posted By: uncle-buck
Date Posted: June-01-2023 at 5:56pm
Ken, here are pics of the choke plate when the engine is cold and after it has warmed up:  ------------- 1990 Ski Nautique (original owner) PCM 351W with D.U.I. |
Posted By: Wilhelm Hertzog
Date Posted: June-01-2023 at 6:34pm
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Shouldn't there be a bit more clearance between the choke plate and the choke tower when the choke is closed? Like 1/8"? ------------- 1982 Ski Nautique PCM351W RR II Velvet Drive 10-17-003 1:1 II PerfectPass Stargazer Do not go gentle into that good night. Rage, rage against the dying of the light. |
Posted By: samudj01
Date Posted: June-02-2023 at 2:32am
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Yes. That choke plate is too closed at cold start. There should be a small gap. You can adjust with the three screws around your elec choke (black round on outside of carb). The screws can just be loosened and rotate the choke an until your desired width. Measure with a drill bit if you want to be exact. With this gap you can get in, run blower, and then start. No need to have key on for. Time period. My 93 came just like this. Minor adj and it starts great. I bet the previous owner was always having issues first out unless he let the boat sit with the key on allowing the choke to warm up and open. ------------- 78 Ski Tique, 72 Skier w/302's, 93 SN w/351 & 17 GS22 w/zr409 Previous - 99 Sport Nautique w/GT40 and 87 Martinique w/351 |
Posted By: GottaSki
Date Posted: June-02-2023 at 8:21am
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Depends upon ambient temp how closed she choke should be and how preloaded, when cold a small gap can make it useless as the air volume is minimal getting around it is not substantial if its like 45 degrees out like its been overnight much of our spring, i would expect the see the choke closed full . 70, yeah a gap Idle mix set for max vacuum is not a good setting. Idle mix set for max vacuum is in gear is a much superior setting.
------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
Posted By: KENO
Date Posted: June-02-2023 at 9:27am
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Well Buck, it certainly not open too far Everybody has different opinions on choke adjustment and Holley videos aren't very good since they deal with car chokes with fast idle cams etc. that boats don't have. Some people around here on CCF wire it completely open and non operational and give a couple pumps of the throttle then start the engine and warm it up at about 1500 RPM or so for a minute or 2 before putting it in gear. Others have it adjusted like yours or somewhere in between. 1/16 to 1/8 of an inch air gap is mentioned in various different places. Like GottaSki says, max vacuum in gear gives the best off idle response. Being in Texas you could probably adjust the choke to be a little more open.............or if you're happy with how the carburetor responds, leave things as is A little warm up time is never a bad thing
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Posted By: uncle-buck
Date Posted: June-02-2023 at 6:51pm
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Ken, I will probably experiment with the amount of gap in the choke plate when the engine is cold and see what works best. The boat is running so well after it warms up, I really can't complain. So, of course, I had to order a new Quick Fuel M-600 to see if it will run even better. 😸 As always, thanks for your expert advice and guidance. ------------- 1990 Ski Nautique (original owner) PCM 351W with D.U.I. |