Time for a carb rebuild?

[High Altitude]

First of all - thanks to all the members of this site who help people with their technical problems. I have been lurking on this site for quite awhile and I am amazed with all the good maintenance tips. Second of all, I apologize because I don’t own a Malibu, but I still use your site. Luckily, the Gekko GTS-20 that I own uses the same powerplant as some of the older Malibu’s. The power plant is a 1995 Mercruiser Magnum Tournament Ski, 265 HP, carb (weber 4 bbl), perfect pass, 301 hrs.

Okay, here is what’s going on. Boat was running perfect at the end of last season right up to the very last day. On the day I went to go run it for the last time (so I could change oil, winterize, etc.) it wouldn’t hold idle. I had to run it to about 2000 RPM to keep the engine running. Anything less and it would die. I put her to bed and told myself I would fix the problem at the beginning of this season.

In early May, I got the boat and did a full tune-up. (rotor, cap, plugs, plug wires, new coil, compression test on each cylinder, timing, impeller, fuel stabilizer) I also needed to re-align the engine, replace the strut and bushings plus change out the steering cable. I also padded the motorbox. At the end of a many hours of work, I turned the key and it started right up. There seemed to be a noticeable vibration at idle despite all my work (not in gear). I ran a can of sea foam in the gas and added half a can to the oil. The engine seemed to settle down and I enjoyed a few days of pleasant running. The starts were a little harder than the previous year, but overall I was happy. Since then, I seem to have a recurring problem with the engine idle. First, when I start the engine cold, I need to hold about 2500 RPM until the temp reaches 160 degrees or it will die. It will restart but I need to keep the RPMs up. Next, as I engage the throttle in forward or reverse, the RPMs begin to drop. Even when I bring it back into neutral, the RPMs are at about 450 (or it might just die). If I try and accelerate sometimes it will sputter and then take off or sometimes sputter and die. Finally, after a half hour of starts and stops, towing skiers etc. it goes away and runs like a champ. The idle also reverts back to the proper setting which is 650 and holds it perfectly. At speed, the boat works every time with no problems. I’m usually at 28-32 MPH in the course but the RPMs are higher then average because I use an ACME 911 prop for the altitude (13x10.5). What the heck is going on?

Here is what I have tried and the results:

Are there weeds on the prop? No

Are fuel levels too low? No, it does it with a half tank just as much as an empty tank.

Is it a sticky choke? The choke appears to be fully open when it is warmed up. The low idle continues with the choke fully open.

Are the plugs gapped correctly? Yes they are (.035) and the plugs look like they are burning really nicely. (light brown color with no buildup)

Coil? I replaced it, but I haven’t actually put the voltmeter to the new one.

Filter? The Weber carb is squirlly when it comes to filters (you have to actually take part of the carb apart to change). Because of this, I have not checked it yet, but why would it run solid at high speed and resolve itself after some use? I still need to replace the water separating filter.

Timing? Set at 12 degrees per Malibu dealer in Denver. I used the proper technique for the Thunderbolt V ignition.

Oxygen deprivation due to a dirty filter or the new motorbox padding? Same problem with the flame arrestor on or off, motorbox cover open or closed.

Idle screw is loose? No, checked it many times.

Vacuum leak? Have not checked.

Faulty mechanical fuel pump? The sight tube is empty. It runs perfect at speed.

Bad fuel lines? Have not checked but it seems like that would effect high end performance.

Carb rebuild? Have not rebuilt since I owned it (4 years) and I don’t know if it was done before that. I generally have run stabilized fuel and did proper winterization. It does stay winterized for a long time because I live in Colorado. I don’t feel like doing a carb rebuild if it is not needed but my gut tells me this is the problem. The thing that vexes me is, why does it only do it some of the time? From my days of flying military aircraft, intermittent problems always seemed electrical.

Sorry for the long post, but it saves a bunch of follow up questions. Any ideas? Thanks in advance! -Marc

[nuttyskier2002]

First of all - thanks to all the members of this site who help people with their technical problems. I have been lurking on this site for quite awhile and I am amazed with all the good maintenance tips. Second of all, I apologize because I don’t own a Malibu, but I still use your site. Luckily, the Gekko GTS-20 that I own uses the same powerplant as some of the older Malibu’s. The power plant is a 1995 Mercruiser Magnum Tournament Ski, 265 HP, carb (weber 4 bbl), perfect pass, 301 hrs.

Okay, here is what’s going on. Boat was running perfect at the end of last season right up to the very last day. On the day I went to go run it for the last time (so I could change oil, winterize, etc.) it wouldn’t hold idle. I had to run it to about 2000 RPM to keep the engine running. Anything less and it would die. I put her to bed and told myself I would fix the problem at the beginning of this season.

In early May, I got the boat and did a full tune-up. (rotor, cap, plugs, plug wires, new coil, compression test on each cylinder, timing, impeller, fuel stabilizer) I also needed to re-align the engine, replace the strut and bushings plus change out the steering cable. I also padded the motorbox. At the end of a many hours of work, I turned the key and it started right up. There seemed to be a noticeable vibration at idle despite all my work (not in gear). I ran a can of sea foam in the gas and added half a can to the oil. The engine seemed to settle down and I enjoyed a few days of pleasant running. The starts were a little harder than the previous year, but overall I was happy. Since then, I seem to have a recurring problem with the engine idle. First, when I start the engine cold, I need to hold about 2500 RPM until the temp reaches 160 degrees or it will die. It will restart but I need to keep the RPMs up. Next, as I engage the throttle in forward or reverse, the RPMs begin to drop. Even when I bring it back into neutral, the RPMs are at about 450 (or it might just die). If I try and accelerate sometimes it will sputter and then take off or sometimes sputter and die. Finally, after a half hour of starts and stops, towing skiers etc. it goes away and runs like a champ. The idle also reverts back to the proper setting which is 650 and holds it perfectly. At speed, the boat works every time with no problems. I’m usually at 28-32 MPH in the course but the RPMs are higher then average because I use an ACME 911 prop for the altitude (13x10.5). What the heck is going on?

Here is what I have tried and the results:

Are there weeds on the prop? No

Are fuel levels too low? No, it does it with a half tank just as much as an empty tank.

Is it a sticky choke? The choke appears to be fully open when it is warmed up. The low idle continues with the choke fully open.

Are the plugs gapped correctly? Yes they are (.035) and the plugs look like they are burning really nicely. (light brown color with no buildup)

Coil? I replaced it, but I haven’t actually put the voltmeter to the new one.

Filter? The Weber carb is squirlly when it comes to filters (you have to actually take part of the carb apart to change). Because of this, I have not checked it yet, but why would it run solid at high speed and resolve itself after some use? I still need to replace the water separating filter.

Timing? Set at 12 degrees per Malibu dealer in Denver. I used the proper technique for the Thunderbolt V ignition.

Oxygen deprivation due to a dirty filter or the new motorbox padding? Same problem with the flame arrestor on or off, motorbox cover open or closed.

Idle screw is loose? No, checked it many times.

Vacuum leak? Have not checked.

Faulty mechanical fuel pump? The sight tube is empty. It runs perfect at speed.

Bad fuel lines? Have not checked but it seems like that would effect high end performance.

Carb rebuild? Have not rebuilt since I owned it (4 years) and I don’t know if it was done before that. I generally have run stabilized fuel and did proper winterization. It does stay winterized for a long time because I live in Colorado. I don’t feel like doing a carb rebuild if it is not needed but my gut tells me this is the problem. The thing that vexes me is, why does it only do it some of the time? From my days of flying military aircraft, intermittent problems always seemed electrical.

Sorry for the long post, but it saves a bunch of follow up questions. Any ideas? Thanks in advance! -Marc

High, I've rebuilt theses carbs before and they are pretty easy,.... especially if you have any mechanical experience. Do replace all filters first. Also,... do you have a timing light with varible strobe delay? If so check that your timing is advancing and that it is staying consistant (vs. just quickly checking and calling it good). Also check your spark. It should be a good fat blue spark at 1/4" gap.

If all is good,... I have a Weber 4 Bbl that I pulled off of mine. I replaced it with a Holley 4150 mechanical secondary. This Weber was running perfectly when I pulled it last Spring. By the way my motor is the same model and year as yours. I just wanted the Holley for added performance. If you want this carb I'll sell if very cheep.

[Surfin247]

Sounds like carb. I have the same engine in the Echelon and had same problem. Since the carb was the original and a full rebuild kit was around $125, I found a stomping good deal for a Edelbrock Marine series 600cfm #1409 for $299 shipped to my home. It was a quick and simple take old off and bolt on the new carb. Took less than 30 mins. If your carb is relatively new you might go with rebuild. If it looks like the original you might consider replacing it. The whole bottom of my old carb was completely rusted and probably some of the lower passage ways. I would have hated to buy a rebuild kit and have no real improvement. The new Edelbrock has been running like a champ for over 18 months now with no problems. The idle underway stays right around 645 rpm and only occasionally moves 1 or 2 rpms from there. Also, the Ededlbrock is super easy to rebuild if it ever needs it and the kit is much cheaper than the original Carter/AFB.

[High Altitude]

Thanks for the advice. Interesting to see that carb rebuild seems to be the concensus among two other owners of the engine. Obviously, I will change out the filter first. I could rebuild my current one, buy the spare from Nutty and rejet using my old jets, go to flyingfishcarbs and get one remanufactured for $248 with the correct jets, or purchase an Edelbrock 1409. Does anyone know if it is a simple procedure to rejet these Edelbrock carbs for altitude. My lake is at about 7000 MSL. It looks like Edelbrock has made this a pretty tuneable carb but I just want to make sure.

[High Altitude]

UPDATE:

I ordered the Edelbrock 409 yesterday. Hopefully, I will get it within a week and get it on right away. After spending quite a bit of time researching carbs, I can say I am impressed with the Edelbrock's ability to be changed. I bought one of the carb kits with extra jets and rods, so I can set it up for altitude in no time at all. I'll give another update when the install is done to share my thoughts. Also, I went up and skied this morning. There was too much wind so the skiing was poor. Strangely enough though, the engine ran fine. Very frustrating. Hopefully the $350 I just spent is worth it.

Question: Do I need an adapter plate for the 409 if I had a Weber sitting on a stock manifold? I did do some research on this site but most people had the Rochester 4bbl and I'm not sure if it is a different setup. Thanks for any help you can give me!