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loeweb
10-24-2007, 03:19 PM
Quick question for anyone who can answer. I took the boat out a couple of weeks ago and skied a couple of sets and barefooted at the end. Boat ran great when skiing, but stalled out when barefooting. At full throttle it would almost "cut out" and I had to let up on the throttle just to keep it going. I think I need to replace the needle and seat in the secondary. So the question is How hard is this to do? Do I need to take out the float to get to it, or will it come out of the top? Thanks in advance for any help given.

TRBenj
10-24-2007, 03:53 PM
Not sure I agree with your diagnosis, but Im far from a carb expert. Sounds more like a fuel starvation issue to me. Id inspect the fuel screen(s) at the inlet of the carb and at the tank pickup, as well as the check valve on the tank.

From what I understand, needle/seat issues usually result in fuel dripping down into the intake after shutting down.

loeweb
10-24-2007, 04:01 PM
Yes, but wouldn't that be the issue the whole time? It only chokes out when I am running full throttle or close to and after about a minute or so. I think that it is a starvation issue it would be happening all the time. I know the fuel filters are good and the carb inlet screen is good, but how do I check the check valve and teh tank pickup screen? Couldn't get the pickup out of the tank, and don't know how to do it.

whitedog
10-25-2007, 12:16 AM
I ran into this same problem late this summer. Turned out the fuel filter was getting plugged, but the main problem was a weak mechanical fuel pump. would only hold about 2 psi not the 4-6 required for a sustained WOT run.

kvalve
10-25-2007, 12:25 AM
Take it to you local MC dealer, they'll be able to help you out ASAP !
[how's that Jim?]

88 PS190
10-25-2007, 12:26 AM
what does it do when you go to full throttle during accel?

Does it cut out then? or just when it reaches top speed at WOT?

TRBenj
10-25-2007, 10:38 AM
Yes, but wouldn't that be the issue the whole time? It only chokes out when I am running full throttle or close to and after about a minute or so. I think that it is a starvation issue it would be happening all the time.
No. A fuel starvation issue would be most likely to occur at WOT or high RPM's since thats when you use the most fuel. If its happening after a delay, that would indicate that your bowls are emptying and the fuel supply cant keep up with the demand. Could be a fuel pump issue or a blockage in the line. Check the screens and check valve first.

loeweb
10-25-2007, 01:38 PM
No. A fuel starvation issue would be most likely to occur at WOT or high RPM's since thats when you use the most fuel. If its happening after a delay, that would indicate that your bowls are emptying and the fuel supply cant keep up with the demand. Could be a fuel pump issue or a blockage in the line. Check the screens and check valve first.

I see. How do I check the Check valve? I know how to get it off the tank, but how do I test it. I had it off this summer, and was able to blow through the line into the tank pickup. How Do I check the fuel pump. I think the next time out I'm going to hook up to an auxillary tank. Any other suggestions?

clevan
10-25-2007, 10:51 PM
To answer your original question, if I were going to replace the needle and seat I would just go ahead and overhaul the carb. It is not difficult if you have a source of clean compressed air and a few basic tools. Make sure you get the correct kit from a marine distributor MC or Skidim. Remember the kit may cover several variants of the same carb so you may have extra parts. Make sure you match up the parts in the kit with the parts you remove. Start with a clean work area and try and do it all in the same day. And most important, read the instructions. It is possible that your secondary float or needle are stuck closed. I check my fuel pump by inserting a tee fitting at the outlet to the pump and attaching a fuel pressure gauge and running it at the lake. A couple summers back mine was cutting out at high rpm, local MC dealer suggested I change points and condenser. I changed points, condensor, rotor, cap, wires and plugs, fixed the problem.

KHall
10-26-2007, 08:01 AM
Fuel Starvation, full throttle is when you need most fuel. I would check pump for pressure and flow,and ckeck for blockage upto and in carb.

loeweb
10-26-2007, 12:52 PM
thanks again everyone. I need to find time to get it out now and check the pump pressure, and go from there.

loeweb
11-01-2007, 01:39 PM
what does it do when you go to full throttle during accel?

Does it cut out then? or just when it reaches top speed at WOT?

Accelerates fine, and holds speed fine. After a minute or so at WOT it cuts out, or hesitates?

Jayc
11-01-2007, 02:13 PM
I had a very similar problem the other week. We normall wakeboard and ski so not much full thottle use.

I had a barefoot and after a 30 sec or so run the boat cut out. Lifted the hood and there was loads of fuel pouring out the back of the carb. It looked as if it was just flooding out the secondaries. I guessed it was the float stuck on the secondary bowl and proceeded to give it some sharp taps with a screw driver tor elease the float. Anyhow after soaking up the fuel we restarted and has been fine ever since.

JLeuck64
11-01-2007, 02:59 PM
The next time you take your boat out for a run try this. Remove the engine cover and the flame arrestor from the top of the carb. Have a buddy run the boat to duplicate the same symtoms as before. When the symptoms return look at what is happening down the throat of the carb. To much fuel choking out the engine or not enough fuel which causes the engine to lean out. Tell us what's happening.

loeweb
11-01-2007, 03:02 PM
Will do thanks again.

loeweb
11-24-2007, 04:32 PM
still haven't had the boat back out yet. Really cold here all of a sudden.

mc79
11-24-2007, 08:26 PM
Your gas flow is restricted but clearly it is not severe if you can still ski. The cleaning and rebuild recommendations are good. Here's a low risk trial and a good excuse to just get out and ride. Put a can of Sea Foam Marine gas treatment (from Autozone) in a half tank of gas. I bought a '79 MC that had not been run in 5 years. The tank, lines, filter and carb were full of gunk. All of the components were manually cleaned several times and the carb jets still clogged. It took several Sea Foam treatments but this stuff finally disolved all of the crud.

Later, I had a fuel pump that went bad. My fuel pump is a double diaphragm model which I think is required for marine applications. Best I can tell, a hole is the diaphragm is the only way it can fail. When this happened, excess fuel flowed through the sight tube up into the flame arrester. The sight tube is required to keep fuel out of the bilge when the diaphragm ruptures. This caused excessive smoke and rough idle at low speeds. After running at low speeds, it would blow a lot of carbon into the water when you came out of the hole. Replacing the fuel pump was a 30 minute task.

cartoon head
12-06-2007, 09:05 AM
Sounds like fuel pump to me,but could be a blocked tank vent, causing a partial vacumm in the tank.
I would overhaul the carb as last resort.

hydro-therapy
12-06-2007, 02:39 PM
Remove old fuel filter, install new in-line if not already present, check fuel pressure at idle and at WOT. look for and listen to possible air leak at the base of the carb.

Wes
12-16-2007, 01:54 AM
Not sure what year of your boat or engine, but my first boat did exactly the same thing. Turned out to be the check valve at the fuel tank was being blocked with junk at high demand. Simply cleaned it and problem over. Too bad I rebuilt the carb, replaced the fuel pump and all filters before I checked the simple things.