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AQ130C: bogs down under load

am_dew

Advanced Contributor
My up until now perfectly running AQ130C suddenly started acting up last weekend. While out of gear (in neutral), the engine sounds perfectly normal and revs to 3-4K RPM perfectly. If you put it in gear and accelerate, there is a noticeable loss of power compared to what it usually has and pretty quickly it starts to bog down and dies. If you back the throttle off when it starts to bog down to about 2000 RPM or less, it is fine. The highest RPM I was able to get yesterday was 4200 RPM (normally it will easily go to 5000) but it won't run at the RPM very long before it bogs down and dies on it's own, unless you back off the throttle. If you are in gear at idle speed or slightly above, everything is fine, but when you give it more gas, that's when things go quickly downhill.

The only variable since the previous outing where the boat ran perfectly to the very end of the trip (as it has every trip this year and in previous recent years) is that I put about 10 gallons of 91 octane gas in it along with about 3 oz. of marine Stabil in it. I did not touch the engine other than to check the oil level as do after every trip.

BTW, the engine oil is fine and both of the Solex carbs both seem to be operating fine...at least visually. I also pulled and checked the spark plugs -- they looked as good as any used spark plugs I've seen.

My first thought was fuel, so I checked the fuel filter (old glass bowl style) this weekend and while the filter was not clogged badly with it, there was some evidence of the Marine Formula Stabil (a light blue color). I'm not sure how old this Stabil was (maybe a couple years?) but I wonder if it did not mix with the fuel for some reason? Or perhaps I got some bad gas and/or have water in the gas tank? I'm thinking it can't hurt to put some HEET into the tank and take the boat out again on the river and give it a try. I thought I might also buy a portable gas tank and fill it with new gas and hook it up to the fuel pump and see how that goes if the HEET does not help.

This is very frustrating since the engine (a rebuild bought from Volvo by a V/P dealer who instaled it for me) has worked absolutely perfectly all season long and for the past several years if not longer since it was installed in about 2000. I can't help but think it's a fuel issue of some kind.

Any suggestions or advice?
 
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I'm tempted to drain my gas tank and re-fill, but siphoning off 15+ gallons of gas does not sound like a lot of fun, not to mention what do you do with the gas?
 
UPDATE:

I attached an external fuel tank filled with some fresh gas to the intake side of the fuel pump and took the boat out for a test run yesterday. No change in performance, so that rules out fuel tank issues or fuel quality issues.

I've uploaded a 2 minute video to YouTube which gives you a pretty good idea of what is happening: http://www.youtube.com/watch?v=-x9iCq06E-A

As you will clearly see and hear, it continued to bog down badly during acceleration and it never got beyond 4000 RPM (normally it will go to at least 5000) and it was hard to get it much past 3000 without it bogging down and shutting down. Notice that if I backed off the throttle when it started to bog down, it normally would not die. Numerous backfires and spitting from the carbs. I did not remove the flame arrestors while I was testing due to safety concerns. With the engine shut down, I did verify that each carb is getting a good shot of gas from the candy-cane tube in the top of each carb, so it does not seem like my accelerator pumps are to blame. It idles perfectly and while in idle I can increase the RPMs without any bogging down or hesitation.

Why this started happening all of the sudden is beyond me. No changes to anything between one perfect trip out and the next one when the problem started.

Will a bad fuel pump cause this sort of behavior? Or is it more likely to be caused by a problem with the carbs?
 
Watched vid, i recon 2 things.

Most carbs have a low and high needel , there could be a partial blockage in the high needel due to the marine stab which could of released dirt into the carb hence boging down with fuel restriction, but improving when fuel flow can match engine speed,

Secondly to me the engine timeing does not sound right, recheck you base timeing setting at TDC and make sure you have the advance showing when throttleing up, check distributor components, and the cams that advance engine, do a full check of plugs and leads, plug gaps and if need be check plugs outside of the engine, you may have a failing plug that fails on demand as revs/load increases.

Hope this may help
 
I'm not totally familiar with the AQ-130, but on my AQ 140 there is a screen in the fuel pump that should be cleaned now and again. On mine, you simply unscrew the pump cover and lift it off and you will see the screen. Be careful not to lose the spring that is under the cover. Have you checked that?

Also, I agree with checking the timing and advance. I assume this engine has an exposed timing belt? Not all that likely, but a backfire can cause a worn or loose belt to jump time. Keep up the faith. Mike
 
I'm not totally familiar with the AQ-130, but on my AQ 140 there is a screen in the fuel pump that should be cleaned now and again. On mine, you simply unscrew the pump cover and lift it off and you will see the screen. Be careful not to lose the spring that is under the cover. Have you checked that?

Also, I agree with checking the timing and advance. I assume this engine has an exposed timing belt? Not all that likely, but a backfire can cause a worn or loose belt to jump time. Keep up the faith. Mike

One of the first things I did was check the small fuel filter which screws into the side of my pump and it was fine.

I checked the advanced timing and it was spot on. No exposed timing belt on this engine.
 
start with a compression test. get some basic checks out of the way.
does sound fuel related though.
I'd also look at advance weights/springs in the distributor.
 
I watched the video, good job! I'm now thinking vacuum loss or an air leak (could be one in the same). Have you had the carbs off? Check the carb mounting bolts and manifold gaskets, mine loosened over time and created a similar problem (twin solex). Any air leak in the fuel system or one that robs vacuum, can cause this type of issue.

Have you been able to check fuel pressure on the output side of the pump?
 
I watched the video, good job! I'm now thinking vacuum loss or an air leak (could be one in the same). Have you had the carbs off? Check the carb mounting bolts and manifold gaskets, mine loosened over time and created a similar problem (twin solex). Any air leak in the fuel system or one that robs vacuum, can cause this type of issue.

Have you been able to check fuel pressure on the output side of the pump?

I have not taken the carbs off, but I did check their mounting bolts and they were tight.

How do I check the fuel pressure?
 
You have to use a fuel pressure gauge that you connect to the output line of the pump. Some places such as Auto Zone will rent or loan you one with a deposit. If you want to continue to work on the boat and other engines, you may want to buy some of these tools and eBay is a good place to look for deals!

Also, you can do a vacuum test and this video shows you how. http://www.youtube.com/watch?v=5hAgHDSOpMs

Fuel is delivered with fuel pump pressure from the tank to the carbs and via vacuum ONLY beyond the carbs...low vacuum, low fuel flow.

Keep pluggin', you'll get it. Mike
 
Thanks Mike. I get the feeling this is going to be a slow process of elimination, especially since in order to test something I do or change, I have to take the boat out on to the water to test it, and with the season just about over and with weekends being the only time I can work on it and test, the boat will likely just sit until next spring. :(
 
I use a cutoff plastic barrel to test my boat at home, especially for the type of tests that you need perform. Neither test will require much running and it would be nice to have it out of the way so that when spring comes...you're on the water. Mike
 
I use a cutoff plastic barrel to test my boat at home, especially for the type of tests that you need perform. Neither test will require much running and it would be nice to have it out of the way so that when spring comes...you're on the water. Mike

Agreed on all counts about being able to perform the tests at home. However, since the problem I'm having only happens while under load (idles perfectly and engine sounds perfect when in neutral and revved up), I have to take it out on the water in order to test any changes I may make. Luckily, I have a ramp very close by, but even then to launch, test and unlaunch, we're talking a minimum of a couple hours, not to mention the launch fee. Not complaining, just sayin' it's gonna take some time to do this. :)
 
Both tests that I suggested will work regardless of the engine being loaded and will either prove of eliminate those possibilities. The reason that it bogs down under power and is that it takes more fuel under load (prop loading) than it does under static conditions (drive in neutral). Therefore, if you have a vacuum leak or low fuel pressure, you may well be experiencing a lack the fuel to provide for a loaded scenario. Let me know how it turns out.

I know from experience that these things are terribly frustrating, but in the end there's nothing to it but to do it. If you get into the carbs, let me know as I just rebuild my twin Solex's. Mike
 
Both tests that I suggested will work regardless of the engine being loaded and will either prove of eliminate those possibilities. The reason that it bogs down under power and is that it takes more fuel under load (prop loading) than it does under static conditions (drive in neutral). Therefore, if you have a vacuum leak or low fuel pressure, you may well be experiencing a lack the fuel to provide for a loaded scenario. Let me know how it turns out.

I know from experience that these things are terribly frustrating, but in the end there's nothing to it but to do it. If you get into the carbs, let me know as I just rebuild my twin Solex's. Mike

I watched the video about checking for a vacuum leak. I could be wrong but I don't think the AQ130C has any ports on the intake manifold that I can attach a vacuum gauge.
 
Since you don't have any vacuum ports, the gage method is going to be dificult. You can try a can of carb cleaner. Spray at suspected leaking spots (base of carb, intake manifold, ect.). Engine idle will change if carb cleaner is sucked in. Of course, you'll want to use some common sense when spraying flammable liquid on a hot engine!

I'm still wondering about your fuel supply and am not convinced that you've ruled that out. You can put a fuel pressure gage between the fuel pump and carb. It appears that you have rubber tubing instead of a metal line from the fuel pump to the carbs so a "t" in the line for a gage can be easily installed. Harbor freight has several fuel pressure gage sets at a decent price and Auto Zone MAY have one as a loaner.

Take a good look at the carb and check for loose screws. Some possible leaks include the venturi hold down screws, and the high speed jet holders. I know for a fact that those can be an embarassing cause of failure to reach WOT!

It sounds like you have the older glass bowl type of fuel filter. I don't get a warm fuzzy feeling with those and would recommend you switch to the screw on water/sediment filter type of canister filter. I realize that you've allready tested with a clean fuel source but that's something that you may want to do over the winter.
 
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Thanks Joe. I will check the fuel pressure. Also, I found this document about how to rebuild the Solex PA441 carb, which is what I have.

http://www.panix.com/~am_dew/44pa1_rebuild_instructions.pdf

I have a question though about this and your advice regarding the carbs. When you say "high speed jet holders" is that what is also referred to as the "main jet holder" referenced in step 4 and on the first pic on page 2 of the above document? Short of doing a complete rebuild of the carbs, I thought I would remove these jets, then clean them and also spray carb cleaner into the holes they come out of to be sure they are not clogged.

An yes, I have been meaning to replace that glass bowl fuel filter for some time, but I keep putting it off since it has served the boat well for the past 39+ years, so it has not been a high priority. I did replace the filter in it very recently (after this problem started) so I know that is not part of the problem.
 
When you say "high speed jet holders" is that what is also referred to as the "main jet holder" referenced in step 4 and on the first pic on page 2 of the above document? Short of doing a complete rebuild of the carbs, I thought I would remove these jets, then clean them and also spray carb cleaner into the holes they come out of to be sure they are not clogged.

Yes, that is what I was calling the high speed jet. I was thinking that it may have wiggled loose and was causing a vacuum leak. I had that happen to one of mine. Don't know how much good it'll do to just clean the jets. There are also passages inside the carb that need to be cleaned and that's really what a rebuild is all about. Just removing them and cleaning probably would't hurt, especially if it works. My concern would be that if that helped the engine run better, then it indicates there is indeed crud and varnish in the rest of the carb. If it doesn't help, it really doesn't tell you much of anything since interior passages could still be clogged or dirty.

Have you checked the timing advance yet? Manual says it should be 12 degrees BTDC at idle and 27-29 degrees at 2000 RPM.
 
Yes, that is what I was calling the high speed jet. I was thinking that it may have wiggled loose and was causing a vacuum leak. I had that happen to one of mine. Don't know how much good it'll do to just clean the jets. There are also passages inside the carb that need to be cleaned and that's really what a rebuild is all about. Just removing them and cleaning probably would't hurt, especially if it works. My concern would be that if that helped the engine run better, then it indicates there is indeed crud and varnish in the rest of the carb. If it doesn't help, it really doesn't tell you much of anything since interior passages could still be clogged or dirty.

Have you checked the timing advance yet? Manual says it should be 12 degrees BTDC at idle and 27-29 degrees at 2000 RPM.

I will be checking these jets tomorrow and yea, I understand that even if that ends up working, it's very possible that the rest of the carb could have crud in it.

I have checked the advanced timing and it was spot on. I have never been able to get a good timing reading at idle and because the engine performed flawlessly up until now, I never worried about that and instead focused on making sure the advanced timing was set properly.
 
Strange as it may be, after trying to help you with your problem, I went out last week and could not maintain 5,000 RPM without fuel starvation. I could run 3500 RPM without any issue. I've tested literally everything and I'm down to the fuel pump not providing enough fuel for high speed running. I'm going to replace the pump.

The difference in our problems is that I can throttle up and have excellent throttle response and it runs fine for a couple of minutes before starving for fuel. Were you ever able to test your fuel pump?

Mike
 
No, I have not tested my fuel pump. The day I was going to do that, I managed to puncture my gas tank (which was almost full of gas) with a large flat head screwdriver. With no other viable options available to stop the leak (I sat there with my thumb pressed hard against the rupture to stop if from leaking gas into the boat) or remove the gas from the tank, my girlfriend called the fire dept. They came and put some sort of putty on the rupture, then I pumped the vast majority of gas out of the tank, and that's where I stand right now until next spring when I decide the best way to repair the gas tank. A real bummer.
 
You reminded me of story from my past...I was in the Yukon Territory at 20 degrees below zero and having carburetor problems. I leaned over the front of the truck with the engine running to try and adjust the carb when I knocked a screwdriver off and it went through the radiator! Not all that many radiator shops on the Alaska Highway. Two days and a few hundred dollars later I was on my way.

I put my boat away and will also wait for spring, maybe we can pick this back up and fix both of them. I do have to say that I wish I had a U.S. made engine and this boat is now FOR SALE!.
 
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That does not sound like fun either.

Not sure what I will do with the gas tank. I know removing it and having it welded/soldered is the best but getting the tank out and back in will be nothing short of a big pain due to the tight space it's in. So, I'm not sure what I will do at this point but I have all winter to decide.
 
Where is the hole located? There are a lot of GOOD adhesives that will allow you to put a metal patch on a small hole.

I feel the same way, I have all winter to decide what I'm going to do.
 
The hole is maybe an inch from the bottom of the tank -- the size of a large flat blade screwdriver. This tank was repaired in the 70's by my dad when it leaked along the bottom seam. He does not exactly remember what he used but he seems to recall a United airlines mechanic neighbor of ours giving him something that was used to repair airline gas tanks. That repair has lasted 35+ years. I'm thinking that I may try sanding down the putty the fire dept. stuck on it so it's just above flush with the tank and then using some JB Weld or some other metal expoxy or other stuff made for gas tank repair over and around that.
 
Take a look at JB Marine Weld. This is an aluminum tank is it not? Now, if the tank is getting questionable in general, you may want to consider that in your scenario. as gas pouring into an I/O boat isn't for the faint of heart.
 
Not sure what the tank is made out of. Defintely will be considering all options with safety being at the front of my mind, but replacing the tank I think would be pretty costly due to the fact that it would probably have to be custom made to fit the space. I have not seen any replacement tanks online that even come close to what this one looks like. It's about 2 feet tall x 18 inches wide x 1 foot deep but is not perfectly rectangle either and one of the sides as I recall is angled. It fits right behind the rear jump seat on the port side, between the back of the seat and the transom.
 
I'm back online here after taking a break during the off-season.

Here is an update on my situation where the engine was bogging down/surging under load:

  1. Removed and cleaned high speed carb jets; no obvious blockage.
  2. Checked cylinder compressio. Results: 165-185 in all 4 cylinders
  3. Check fuel pump pressure. Result: almost 3 PSI (speci s 3.2)
  4. Sprayed some carb cleaner and Deep Creep into each carb and ran engine. Repeated 3 times.
Took the boat out for a test on the river with fingers crossed and everything was perfect! I ran it 17 miles without any signs of what was happening last Fall. Go figure. All I can figure is that either one of the high speed jets was in fact clogged and/or something got cleaned out by the carb cleaner and Deep Creep I sprayed into the carbs.

Now I need to focus on fixing the small puncture in the gas tank.

Welcome back El Pescador!!

Bob
 
Gas tank has been fixed for a while now and we took the boat out again today after a couple of successful outings so far this season. Right off the bat, It would not throttle up past about 2000 RPM without stalling out. Idled it back to the dock at the launch ramp and removed each carb's high speed jet and blew it out and then reinstalled. Ran perfect after that...go figure. Quite a bit of gas came out of each jet port after removing the jet...not sure how much is normal but it seemed like quite a bit...maybe a tablespoon or so? It did not seem either jet was clogged when I blew into it. No starting issues and the engine also revved up just fine in neutral before I removed each jet. Any ideas on what may be happening here?
 
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