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Merc 3.0 Carb(TKS) problem?

E

Ed Dickenson

New member
I recently bought a 06 Mariah with a Mercruiser 3.0 with TKS Carb. The engine and everything runs great when it is cold. When it gets hot it WILL NOT operate at idle speed. It will run at 50% + throttle but it will not run well or at all below 2000 rpms.
I checked the spark, compression, I cleaned the fuel system, changed plugs, distibutor cap and rotor, I pulled the carberator and cleaned it very well and everything apperared to be working well. Someone suggested I cut the shroud over the the Idle Air mixture screw so I could adjust it as they said it might be causing my problems. I ran it neutral at home and adjusted the idle and air mixture screw. It ran great both cold and hot and at low RPMS. I thought I had solved the problem whatever it was.
I took it out today and it ran great after I fine tuned the idle and idle air mixture screw in Drive. It ran like a champ for about an hour and a half. I turned it off several times and it started and idled perfect. Later I went to slow down and the engine stalled. After that, no matter what I did I could not get the engine to run below 1700 rpms. It would not start unless I immediately throttled it when starting. I would have to throttle it about about 75% to start it and it would not run below 50% throttle.
No matter what I adjust the boat will not idle. I assume it is a carb issue and maybe something to do with the TKS system and "enrichment module. At this point I would buy a new carb if I thought it would solve the problem. I am afraid I am missing something else though. Anyone have any advice?
 
We have seen this before with the tks system. I am going to go out on a limb here and post this. I hate... yes hate the tks carb. I know guys that is a very strong word but again i hate that freekin carb. Wow now i feel better.45 years wrenching on everything from prop. driven planes to jet engines, and every kind of small engines and this freekin tks system stinks.

There are a ton of good used old fashioned electric choke mc-carbs for sale on flea bay. Want to save headaches now and in the future get one. Throw in on the engine set it up, and just go boating and have fun instead of fooling with the tks system forever.

Yea i know alot of guys gonna flame me for this post.
 
I was thinking about replacing the carb and I was wondering how easy it would be to put an old fashioned electric choke carb on.
I went out this morning and now the boat won't even start cold. It is not getting a very good supply of fuel. I keep thinking CARB but could my problem be the mechanical fuel pump? I have researched and cant figure out how to tell if the mechanical fuel pump is working properly. I suppose it could be something in the carb gunked up and this problem is a combination of the fuel issue and the TKS "enrichment" module.

It is very aggrevating because the engine runs great(well it did), until it gets warm.
 
I would love to get rid of it but I don't have the know how to convert it to a regular style carb. I talked to several carb sellers and the bases dont match up and I have no idea how to wire the electric choke. Even worse I would hate to think that I am missing something else and doing all that work to find out it did not solve the problem. The boat started and ran great today in the driveway. The TKS system appears to be working fine. The plunger activates when warm and the engine purrs nice. I don't know what gives with this thing. I am going to drain the fuel and see if maybe something in the fuel system is causing this. I changed the filter and there was quite a bit of grit.
 
Ok run it on a external tank of clean fuel... clean the filter that that is in the fitting that enters the carb.

Copied and pasted here from another website i wrote this .
I pumped all the fuel out of my onboard fuel tank when i got it.

You can do one of 2 things, pump the water out of the bottom, or all the fuel out and here is how.

If you just wish to pump just the water out of the bottom of the fuel, you will need to purchase a cheap electric fuel pump from any auto store dc powered.
You will also need about 15 foot of cheap fuel hose from the auto store and clamps to fit the fuel pump.

Install the hose on the fuel pump both ends and cut about five feet on the sucking side of the pump just look for the arrow on the pump.

Remove the fuel pickup tube it's the one where the fuel hose hooks to the tank a 90 degree angel fitting, it's a anti-siphon valve. Unscrew it.

Crank the bow of the boat all the way up, and stick the hose connected to the electric fuel pump 5 feet into the bottom and back of the tank.

Into a clear container pump the water out till you see clean fresh fuel and stop the pump.

Or into a large container pump all the fuel out.

Now check the valve by blowing thru it, check the screen thats its clear.

Install the valve and pickup tube your done.
 
I changed the filter and there was quite a bit of grit.
Click to expand...
If the grit was tan and looked like fine sand it is most likely dried fuel varnish granules. That crap is inside the carb...you need to dissaemble it and do a good cleaning and blowout of the idle circuits because the problem is never going away on its own. Install a 10-20 micron fuel/water separator filter between the tank and fuel pump. You must have read a post from Chiefalan for fuel tank cleaning.
 
Ok. I have cleaned out the entire fuel system. A little bit of water in the tank and a little more in my new Fuel Filter(i replaced it again). I changed the filter inside of the mechanical fuel pump. That was a near impossible task with the fuel pump installed. Probably would have been easier if the fuel pump was removed but I didnt have a replacement gasket. Who ever designed that fuel pump bowl contraption needs to be shot... The filter was completely shot and disintegrating . All of the tank valves and screens were good.
It still is not running in idle when the engine gets hot(normal operating temp). Next step is to rebuild the carb. I am paying someone since I don't have the experience or time to get it done quickly. I would like to do the electric choke option but I can't find a shop or online dealer to help me through the process of putting in the eltric choke carb. So I guess I will go with a rebuilt carb and a new TKS module.

I noticed talk about vapor lock, and I wonder if that is what mine could be doing. Also something similiar to vapor lock and might be a potential problem is the overflow tube from the fuel pump to the carberator sits on the engine. If this hose were to get hot could it "push" air into my carb? Just a thought...
 
I did everything possible. I changed the plugs and wires. Completely cleaned the fuel system. Took apart the fuel pump and changed the filters. Cleaned the Carberator. Checked Engine compression and timing. I then sent the carberator to a shop to have it rebuilt. They sent it back and I still had the same problem. The engine was acting like the choke was wide open. It doesnt have a choke but has the TKS thing attached the carberator. I took the TKS module off and it appeared to work fine when I tested it. After that I was ready to give up when I had a huge stroke of luck. Where the plunger on the TKS enters the carberator, the was a tiny metal burr preventing the plunger from retracting. 1 minute with a file and the burr was gone. Started the engine up and I have not had the problem since. I was kind of aggrevated that I spent so much time and effort, and it turned out to be a simple thing. On the plus side, I gave the thing a complete tune-up and it runs like a champ now.

I would check out the TKS module. One of the mercruiser manuals tells how to test it. It wasn't very hard. Worse case, even if you had to replace it to find out if that is the problem, it doesn't cost too much. Good luck, it's no good to have a boat that doesn't run right.
 
I thought I was the only one having problems with the Mercruiser TKS carb. I had similar issues with my Mercruiser 5.0 TKS over the past 2 weeks. I had an unsteady idle and surging at the 1800 - 2000 rpm range during my last boat trip. In addition, I had to crank my engine multiple times to start up the engine. I changed my fuel filter, plugs, and anti-siphon valve and rebuilt my carb. I even took my old fuel out and put new fuel in the tank, I still winded-up with the same problems. I decided to change my fuel enrichment module and to my amazement, my unsteady idle and surging at midrange was corrected during a test run on the water today. I also thought it was a mechanical fuel pump issue. I'm glad I went with changing my enrichment module instead. My engine runs great now. Thanks to this forum, I was able to get some good pointers on correcting my TKS carb. problems.

I am also glad that your TKS carb. problems were finally corrected by shaving the burr on your brass plunger. Frustrating but rewarding once you are able to correct the problem. Now we can all have fun boating!
 
I've been running a 5.7MIE w/ a TKS carb for 7 seasons. I've come to terms with it and within its limitations, it works very well. BUT!!!

1) any claims by MERC that you can just turn the key and start it are BS! This is true ONLY if the fuel bowl is filled up, and even then a single pump of the throttle to have the accelerator pump give an initial squirt to the engine helps a lot. IF the engine has sat for a few days, then things get... interesting. It's no better than any other type of carb setup. You will need to crank the engine (in bursts) until the fuel pump fills the carb bowl. I have an electric fuel pump and am going to install a push button switch to simplify things. As it stands now ( sans switch), I crank the engine in bursts of a few seconds until I see the oil pressure gauge indicate some oil pressure during cranks. At this point, the electric fuel pump will start to operate. I crank it one more time, briefly, and then pump the throttle once. I return the throttle to the idle position and then the engine usually starts on either the first or second crank. It will then run, regardless of the weather, hands off thru its "cycle", i.e. idle at about 1100 to 1300 until the water temp comes up (you will hear the typical TKS hiss at this time). AS the engine warms up, the hiss will start to fade, and then, fairly abruptly, the engine revs will drop to 650. Once the engine is warm and the hiss stops, the TKS is "out of the system", and whatever issues you may have are the same issue you will ever have with any other carbed engine. When the change over to ethanol "enriched" ( adulterated!) fuel happened, I had a massive gunk issue since the ethanol "cleaned out" my almost 40 year old gas tank and dumped it in the carb (past a 10 micron filter!).

2) The only effective fuel filter system IMHO, is one with a 10 micron filter w/water separator. If you have a filter attached to a mechanical fuel pump, it is likely only effective against quite larger particle size. Spend a few bucks and get a remote mounted RAYCOR filter with a metal bowl and drain for water removal. Check bowl for water ( by draining a small amount into a can) every time you run thru a tank. Keep a good fuel additive in you tank, added just before you refill the tank.

3) Sometimes the fine passages on the TKS will plug up badly so that the only way to clean them is with a very fine wire.

4) MAke sure the TKS piston ( as posted previously) moves freely. With a cold engine, this can be done (ignition off) by removing the screws that retain the piston assembly and make sure that the whole module slides in and out easily. Run your finger into the bore to check for burrs. As engine warms up, and a thermostatic switch in the water jacket sends electricity to a heater coil in the TKS module that causes the piston to slide and block off the enrichment port, thereby stopping the "hiss" and allowing the idle to drop to normal.

The reason for the previously mentioned push button switch is to allow me to get the electric fuel pump to run and fill the carb bowl without cranking the engine on those cold fall Saturdays when the engine has not been started in 2 weeks, and the battery is getting a little low.

5) I found out that ( 2 attempts 2 years apart) that removing the top of the carb destroys the inordinately expensive gasket between the carb top and the bowl. I once had a VOLVO 1800 cc engine with dual carbs that had graphite impregnated bowl gaskets, that allowed me to remove the bowl and reuse the gasket numerous times. With this in mind, the last time I replaced the gasket, I smeared a very thin film of marine grease on both sides of the gasket, taking care to work it into the "fabric" of the gasket. I have since removed and replaced the bowl top and not damaged the gasket twice.

6) Turning your engine off and walking away for a few days, will result eventually, with deposits in the bottom of the carb bowl ( and metering jets). To avoid this, shut off the fuel valve, and allow the engine to run until it runs out of gas. Attempt one restart ( about 1 in 3 times mine will run and start for a few seconds) to make sure bowl is really empty.

7) If the fuel lines on the boat are "pre ethanol", replace them as the inner lining of some pre-ethanol hoses will slowly dissolve in ethanol and end up as deposits in your carb.

8) The innards on pre-ethanol red plastic gas tanks are also solvent (slowly) in ethanol laced fuel. This I learned the hard way with my 4 stroke 7.5 HONDA.
 
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I have a 2008 Maxxum with the 3.0 engine and TKS. I'm having some of the same problems you all are talking about. I just rebuilt my carb, installed a water/gas separator, and an inline fuel filter. My engine really won't run below 2,000RPMs and surges above that. I'm going to try and check the TKS mechanism next week. What a pain in the ass this thing has been. Almost got stuck out in Tampa Bay yesterday!
 
Ed Dickenson said:
I recently bought a 06 Mariah with a Mercruiser 3.0 with TKS Carb. The engine and everything runs great when it is cold. When it gets hot it WILL NOT operate at idle speed. It will run at 50% + throttle but it will not run well or at all below 2000 rpms.
I checked the spark, compression, I cleaned the fuel system, changed plugs, distibutor cap and rotor, I pulled the carberator and cleaned it very well and everything apperared to be working well. Someone suggested I cut the shroud over the the Idle Air mixture screw so I could adjust it as they said it might be causing my problems. I ran it neutral at home and adjusted the idle and air mixture screw. It ran great both cold and hot and at low RPMS. I thought I had solved the problem whatever it was.
I took it out today and it ran great after I fine tuned the idle and idle air mixture screw in Drive. It ran like a champ for about an hour and a half. I turned it off several times and it started and idled perfect. Later I went to slow down and the engine stalled. After that, no matter what I did I could not get the engine to run below 1700 rpms. It would not start unless I immediately throttled it when starting. I would have to throttle it about about 75% to start it and it would not run below 50% throttle.
No matter what I adjust the boat will not idle. I assume it is a carb issue and maybe something to do with the TKS system and "enrichment module. At this point I would buy a new carb if I thought it would solve the problem. I am afraid I am missing something else though. Anyone have any advice?
Click to expand...
Throw the TKS in the garbage! Replace it with a Rochester two barrel with electric choke. It's called pleasure boating, not irritation boating!
 
1) TKS works well IF you keep the emulsion tubes clear. Carb cleaner won't do it but an correct size number series drill bit will...
2) Your response is to a NINE year old post!
 
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