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GT40 conversion to carb |
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macey 
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Joined: July-22-2018 Location: Ireland Status: Offline Points: 19 |
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 Topic: GT40 conversion to carbPosted: June-02-2023 at 7:43am |
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Hello from sunny Ireland. I have a 2001 196 GT40 EFI. I have been tinkering with this for a while and had various idling issues over my ownership period. My mechanic is a carb lover and is steering me towards removing the fuel injection system and fitting a carb. I understand the carb will not be as efficient as the EFI system and perhaps not as "nice" but my boat is now 22 years old and in great shape so I intend to keep it for some time. Carb stuff is much easier to get over here and mechanics who have the appetite or knowledge to work on my boat are few and far between. Carb set up is significantly more straightforwad.
I have a few questions:- Will there be any significant electrical implications with EFI removed (keypad start for example)? What are the options for getting back to the equivalent horsepower of the EFI system? Any advice on the best carb and intake to use. Any other relevant advice would be greatly appreciated. I understand this is quite a wide ranging question but any advice, especially from someone who has gone this route, would be greatly appreciated.
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 10637 |
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Posted: June-02-2023 at 9:03am |
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You should also be asking for advice on the best distributor, since the gt40 distributor has no mechanical advance and works in conjunction with the ECM to vary timing..
An electric fuel pump should be on the shopping list too.
Jonny Quest, who is pretty much a walking, talking advertisement for Quick Fuel carburetors and DUI distributors (and also dreams of "retroverting" his gt40) will be along to give you his thoughts
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Jonny Quest
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Joined: August-20-2013 Location: Utah--via Texas Status: Offline Points: 2840 |
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Posted: June-02-2023 at 9:16am |
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Damn, KENO! You know me too well.
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2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
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KENO
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Posted: June-02-2023 at 9:29am |
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Well spit those thoughts out
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Jonny Quest
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Posted: June-02-2023 at 3:16pm |
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Since you asked...
My little Ski Nautique with the GT40 engine is running very well. No complaints. As long as the EFI and ECM continue to perform reasonably, then everything remains in the OEM configuration. HOWEVER, if the EFI and ECM start giving me problems, then I'm just itching for a Winter Project. If that day ever comes, this is what I would likely do: - Block is "roller ready" so a roller camshaft is likely - New roller valve train with roller lifters/rockers, etc. - Aluminum heads (increase flow, compression ratio and drop weight) - Aluminum intake manifold (Edelbrock Performer RPM) - QuickFuel M-650 carb - Carter electric fuel pump (keep the FCC?) - DUI distributor with new plugs and wires - K&N fancy-schmancy air cleaner/flame arrestor - Audible horn with light for low oil pressure / high temp JQ |
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2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
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KENO
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Posted: June-02-2023 at 4:12pm |
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Well, I suppose you could both use the original gt40 low pressure fuel pump since PCM used that same pump on the carbureted Pro Tec engines, both Ford and Chevy.
It puts out a carburetor friendly 5 to 7 psi
For fire reasons you'll need to have a low oil pressure safety switch like what's in the link below from one outfit or another since the circuitry that does it on a gt40 will be gone Fuel leak, engine off but key still in Run, the pump would just keep on pumping and pumping without the safety switch It seems to me that only a really strange individual would want to keep his FCC though. |
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Gary S
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Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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Posted: June-02-2023 at 7:55pm |
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Better find out what kind of water he's running in over there as well some of your mods won't live long in some instances
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macey
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Joined: July-22-2018 Location: Ireland Status: Offline Points: 19 |
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Posted: June-03-2023 at 9:31am |
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Many thanks for all the input so far. Fresh water use and never left for long periods in the water.
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KENO
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Posted: June-03-2023 at 12:41pm |
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As far as your keypad question, I don't think there will be any issues there. The keypads are associated with the PME box under the dash and as long as you maintain power to the box you shouldn't have any issues.
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macey
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Posted: June-04-2023 at 4:55pm |
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KENO and Jonny Quest, thank you very much for your help. As a result of you help I am happy that the carb conversion is entirely possible for me. All parts appear to be available readily, even for someone over in Ireland. My initial post was prompted when I started the boat after a two year lay up during which I replaced all sensors, plugs, pumps, hoses and so on. It ran truly awfully. My remaining suspects for my initial problem were the injectors and/or the ECU. Idle and vibration was so bad I am quite hopeful the issue lies with the injectors.
My plan is to try a set of injectors this week and if that cures it great, if not the carb it is. I always had a carb and some form of performance tune in my head as a perfect project for the 196 but the tuning bit is probably not an option for this season. I am happy I can do the carb conversion at short notice if the injectors don't work out. KENO, I believe you recommended a set of injectors from Summit Racing in a previous post, is this still my best option? Many thanks again for all your help guys.
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KENO
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Posted: June-04-2023 at 7:45pm |
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Quite a few people have used the Ford Performance injectors like in the link below available from numerous places And here's a link to a thread talking about them and the adapters that come with them. You need the adapters because the later injectors have a different style plug on the injector. |
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Jonny Quest
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Posted: June-04-2023 at 11:28pm |
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The injectors and adapters KENO referenced are currently installed in my GT40. I’ve been pleased with the performance thus far.
JQ
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2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
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63 Skier
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Posted: June-05-2023 at 10:30am |
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Neil, in your first post you mentioned it has idle issues, then later said it ran truly awfully. Is this just at idle or also at mid range and high speeds? Before you tear the efi out, I'm wondering how much you've looked at the ignition side of things. You said plugs were replaced, how about plug wires? Distributor cap and rotor? These relatively cheap components can really make an engine run badly. You asked about getting back to efi HP once you have a carb on it. I'm curious what the answer to this is, I don't remember any discussion about it. I'm wondering if there is any HP loss with a well done carb setup over the efi, I don't really expect there would be. More fuel consumption yes, but loss of power no. Curious for anyone's thoughts on this.
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'63 American Skier - '98 Sport Nautique
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macey
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Posted: June-05-2023 at 10:50am |
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Hello 63 Skier. I stopped using the Nautique in September 2021. At that point in time it ran perfectly on throttle, pulled no problem, but would not idle.
I searched the forums and did many of the simple things like IAC, plugs, leads, distributor cap, fuel tank breathers etc. but none of the larger items like injectors. The original fault felt quite minor, most probably to my mind a sensor. I decided during the winter to do a fairly substantial refurbishment to the boat and hopefully at the same time replace the offending component. Engine removed, new carpet, lots of powder coating, all looks great but when I started it for the first time last week it sounded poorly, far worse than when I last ran it in 2021. Not off a cylinder but just very lumpy. A little rev will clean it up slightly but it does remind me of a fuel rather than ignition fault. Ordered injectors this morning, I really don't believe it is the ECU (perhaps that is more hope than belief lol). I also have a new distributor to fit. I am keeping the carb as my back up plan for next week but fingers crossed the injectors cure it. Jonny Quest and Keno have probably done enough to convince me carb is a good option but it has always been my understanding that fuel injection is more effecient therefore better performing than a carb. Over in Europe we have had very few carb engines for many years now, we just do not have cars with 5.8L engines. Very much enjoying the input from you guys and I will keep you posted once injectors arrive. Thanks again, Neil. |
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63 Skier
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Posted: June-05-2023 at 12:11pm |
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Sounds like a solid plan. I don't think many people will say that a carb setup is better than a GT-40 efi. Better than the earlier years Protec, yes, but the GT-40 is an amazingly good setup for easy starts, idle, skiing, etc. The general problems have been diagnosed and can be overcome. The lack of ECM replacements have led people to do a carb conversion and I've wondered if I would do that if/when mine fails, but seems like these days you can get a replacement ECM, though they are expensive. Like you, I'm doubting your problem is the ECM. I hope the injectors fix it for you.
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'63 American Skier - '98 Sport Nautique
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Jonny Quest
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Posted: June-05-2023 at 7:29pm |
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I don't think that Macey feels that carb is better than EFI, but simply an option for consideration if the EFI and associated systems become too troublesome. My feeling as well. I'll keep my GT40 in the factory configuration until such time as EFI / ECM problems and parts availability push me toward old school carb / distributor.
JQ
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2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
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KENO
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Posted: June-05-2023 at 7:54pm |
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Since Moates closed the doors and went out of biz in Nov 22, finding a chip to work in place of their F3V2 chip which is used to copy the ECM tune onto and then put it into an old 4 cylinder Mustang ECM to make your spare or maybe desperately needed gt40 ECM is rather tough.
I haven't seen a reasonable solution come up yet
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macey
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Posted: June-08-2023 at 4:21pm |
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Hi guys. New injectors arrived today very promptly from Summit Racing. Hopefully get a chance to fit tomorrow or Saturday morning. First time fitting injectors but doesn't look too scary. Any tips or advice?
One item that I have not found a reference to is a little white unit connected to breather pipe under plenum chamber. What is this and does it require maintenance or replacement? Thanks again, Neil.
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KENO
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Posted: June-08-2023 at 8:24pm |
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Jonny Quest would probably tell you that it's a lot easier if you remove the upper half of the manifold.
If that little white thing has an arrow on it and the line runs to the MAP sensor, some people call it a filter and others say it's a check valve that doesn't seat real tight and it acts to dampen or smooth out the signal to the MAP sensor I don't think they get much of any maintenance
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Gary S
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Posted: June-08-2023 at 11:07pm |
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Hope you got the harness ev1 to ev6 adapters
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Jonny Quest
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Posted: June-08-2023 at 11:53pm |
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Before attempting to remove and replace the fuel rail, pressure regulator and injectors, REMOVE THE INTAKE MANIFOLD (upper half). It’s waaaay easier. The voice of experience…
JQ
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2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
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macey
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Posted: June-09-2023 at 2:03am |
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Keno, that is a perfect description, exactly the part I am talking about. Does it require attention?
Gary, yes got adapters thanks to the links provided. Jonny, by intake manifold, do you mean the big silver thing? I had referred to this as the plenum chamber but I’m no expert? Thanks again gentlemen. |
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KENO
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Posted: June-09-2023 at 6:50am |
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I call it a filter, never replaced it though
I think car guys may have a check valve associated with the vacuum lines in that area since there's a lot more vacuum plumbing on a car. PCM has a part number for it and they call it a MAP fuel vapor filter. Part number is R077008 I think what you call the plenum and the upper intake are the same thing.
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macey
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Posted: June-10-2023 at 11:13am |
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OK, the problem persists.
Idle is much worse than when I last ran the boat 2 years ago and obvious even when cold. 2 years ago idle issue did not cause a problem until engine had warmed up.
Injectors fitted but this has not solved my issue. I will give a summary of what I have done up to now and I would very much appreciate any input if there has been something obvious I may have missed. I have removed and clenaed out fuel tank filled with fresh fuel. Replaced fuel pick up pipe. Replaced fuel lines to and from tank. Checked tank breather. Replaced check valve (it was quite noisy when drawing fuel) Replaced both fuel pumps. New FCC filter, seal and pipe. Replaced both relays. Replaced injectors. I have removed and refitted all connections to check for disturbed cables and lubricated with contact oil. Cleaned flame arrestor. New engine battery, alternator was replaced a couple of years ago. Replaced distributor cap and leads. Replaced Ecoil, Map sensor, TPS sensor, IAC valve, air intake temperature sensor, TFI module. Replaced water and oil sensors. New distributor cap and plug leads. I have not replaced the knock sensor or the distributor itself and not the ECU. Fuel pressure is just under 40psi when I first start up but drops when engine starts loping. Some form of vacuum/air leak is possible but some direction on how to check this would be great. I did check and clean the wire filter at the IAC valve. As I have said already assume nothing, it is entirely possible I have missed something simple. For the guys who have been helping me up to now, if there is any way to link this post to anyone else you are aware of who has come through this and is also knowledgable that would be super helpful. I am probably at the end of my ability with this and I must now consider removing everything (at least for the remainder of this season) and try a carb. I get the feeling even if I do that I may refit everything during winter just to finally get an answer. Many thanks again everyone. |
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63 Skier
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Posted: June-10-2023 at 5:23pm |
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2 items come to mind, both obvious but figured I'd mention them. You replaced the distributor cap, how about the rotor? And did you verify the firing order when you replaced the plug wires?
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'63 American Skier - '98 Sport Nautique
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Jonny Quest
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Posted: June-10-2023 at 11:26pm |
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Fuel pressure regulator?
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2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
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macey
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Posted: June-11-2023 at 6:42am |
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63 Skier, yes replaced the rotor. I was careful to replace plug leads one at a time so I would be fairly sure they are correct. (will actually do a check just in case) but it does run for a very short time correctly so I think they are ok.
Jonny, I did a leak test on fuel system and it started at 40 psi and remained above 38 after 5 minutes. I took the vacuum pipe off the FPR and there was good suction from it. Fuel pressure increased by about 5 psi when off, no sign of any fuel leaking past. I will probably change the regulator if I can pick one up locally but doesn't feel like the issue. Fuel pressure does fluctuate when the idle starts to wander. I think this is more a result than a cause but obviously not sure. One final point for this post. When I did my list of what I had done up to now I did replace the alternator 3 years ago. Actually writing this down reminded me that I had not actually checked for charge. As it turns out the alternator is not charging! Can a faulty alternator cause poor engine running? I do have a new distributor but I have never fitted one before. I believe the distributor gives the crankshaft position information to the ECU. Is this correct? If the distributor is an easy fit does anyone have a link to a good step by step guide? Yet again, many thanks.
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63 Skier
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Posted: June-11-2023 at 11:18am |
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The electronics want to see steady voltage. Without a charging alternator, that is just over 12 volts when the battery is charged, but dropping with discharge and maybe general battery health. With a functioning alternator you are seeing 14 plus volts steady all the time. I'd absolutely make sure you have a working alternator and a battery in decent condition as your next steps.
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'63 American Skier - '98 Sport Nautique
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macey
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Posted: June-14-2023 at 5:21pm |
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So the alternator did not cure the issue. New one fitted and no change to idle.
Distributor also fitted today with no solution. I did buy an Inova 3145 fault reader but it did not communicate with the diagnostic port. Perhaps it was not the correct choice. I am going to proceed with a complete strip out and carburetor installation now. I may return to the fuel injected set up if I feel dissatisfied with the result but I do crave the simplicity and the greater availability of knowledge. Part of me would be quite determined to actually resolve the issue, it does feel like it should be quite simple but summer is short so carb it is. Jonny and Keno, as already mentioned I am over in Ireland so sometimes parts can be little slow for me. Summit were excellent with international shipping on the injectors so I will probably use them for the carb stuff. It would be great to organise everything I need in one order (gaskets, flame arrestor, etc) so would be much appreciated if you would take a little time to ponder a complete carb fitment. I will obviously keep you guys posted on the results and my "feelings" on the performance and general difference after the change. Yet again many thanks.
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bwinn
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Posted: June-14-2023 at 8:28pm |
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https://correctcraftfan.com/forum/forum_posts.asp?TID=25584&OB=DESC
Read if you’re not familiar with yet. You can fix this. Hang in there. There’s a YouTube video of a dude checking all the sensors on one of these makes checking alot of them simple. I feel like you will be better off in the long run to fix rather than swap. Good luck Burton |
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