Tuning Carburetor

[DEREKD]

I have a 1991 Ski Nautique and am having problems with the carburetor. when I try to give it gas it boggs down on me and sometimes backfires and dies, if im lucky enough to get it to run it constantly makes a popping noise. My question is how do I adjust the carb to get it to run right. I see that there are two smaller screws that you can adjust on both sides of the carb, and then the bigger screw that looks like it adjust the throttle. Any help would be appreciated. Thanks

[TRBenj]

RE: Tunning Carburetor

Are you sure the timing is OK? You may not be able to adjust it if you have the Protech, but you should make sure the timing is correct before messing with the carb.

[coloradonautique]

Derek,
I rebuilt the carb on my old 91 several winters ago and I think I had a cheat sheet from the Holley rebuild kit. I will take a look for it tonight.

Otherwise, there is some good information online directly from Holley.

http://www.holley.com/data/TechServi...ech%20Info.pdf
http://www.holley.com/data/TechServi...ded%20View.pdf

For reference, my '91 SN had a Holley 4160 four barrell on top. I would imagine you have the same if you have the 351W (5.8L HO) engine and protec ignition.

There are a couple of things I would check first before playing with the carb, especially if the engine was fine before and you have not changed anything since then.

I agree with TRBenj, definitely check the ignition and timing as well as the spark plugs and ignition wires (make sure they are in the right order). You may also want to check the accelerator pump attached to the carb. It injects gas when you first move the throttle and smooths out the transition between idle and accelerating. It is a mechanically actuated plastic lever that gets pushed by the throttle assembly. If I remember correctly, you should be able to give it a push with the engine off and get a stream of gas injected into the primary barrels.

After that, the initial carb adjustments can be found in the link I provided. I believe it is 1.5 turns out on both screws from completely closed/seated. You want to keep both sides balanced. After that, the engine will need to be tuned while running, ideally with a vacuum gauge. If you don't have one, I think you can do the poor mans version of turning clockwise (from the above initial setting) till the engines bogs, then counter-clockwise till it bogs, and then pick the spot halfway in between. Obviously the vacuum gauge is much better.

Good luck,

Lorin

[DEREKD]

All, Thanks for the reply's and the advice. I believe the spark plug wires may not be in the correct order, but do not know what order they go in. Any advice?

[TRBenj]

I believe the spark plug wires may not be in the correct order

Thats also a very good possibility based on your description of the problem.

The firing order for your LH 351w is as follows:



Im not familiar with the way the Protech coilpacks are arranged, so hopefully someone else can chime in.

FYI, I dont think the HO option (ProBoss) became available until 1992.

[ccskier16]

[DEREKD]

Thank You All, those diagrams were a huge help. I'm gonna go work on it and hope that was the problem. Thanks again.

[pj]

Trace those wire diagrams carefully. Some nucklehead had the wires mixed up on my '91 and I just had the joy of spending $2k to get the engine rebuilt.

[TRBenj]

ccskier, great diagram.

Derek, remember that you have a LH Ford, so follow the wiring diagram on the lower left.

[Hydrofoilmaniac]

Also, look at the engine nameplate. It should include the firing order.

[knowscc]

Once you have confirmed all the basics, accelerator pump, firing order (on the PCM engine ID plate), base timing, fuel condition, etc, check the following. If engine backfires through the carburetor continuously at speed, remove and inspect all eight spark plugs. Note if any have the center electrode burned off and identify which cylinder it came from. Typically, water leaking from riser gaskets into the middle two cylinders can produce this problem. R&R risers and replace the gaskets, making sure hole in front of gasket faces forward.

[efox]

If the engine backfires through the carb, it is also highly likely that the power valve will be toast. How do I know that...been exactly where you are right now. I turned the idle set screws all the way in with the engine off, backed each out 2 turns. I then ran the boat and adjusted 1/4 turn in until bog and then backed out that 1/4 turn that made it bog.

[Stevo1989]

I have a 1990 ski nautique 351 pcm I changed the fuel water separater and plugs and the boat ran great for a few trips out . On about the 4th time taking it out it began to pop really frequently from the carb when going any faster than maybe 10mph then it stopped and ran fine for most of the next time we took it out then the same issue

[Stevo1989]

Now anytime I go above 10mph it pops and looses power any recommendations?