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MercCruiser runs very, very rich 1989 4.3

M

me2633

New member
My 1989 boat has a 4.3LX,Alpha One,Thunderbolt ignition> it has a Rochester Quadrajet carb and ran perfectly for 20 years. The last two years have been nothing but trouble. At startup and through most/all of the RPM range it seems to be running way too rich. You can see the gasoline on the top of the water and smell it when it is running. The carburetor was replaced twice with a remanufactured carb, current one has serial number 17058213, and it seems unchanged. It has a remote choke which seems very slow to open but the engine still seems to have trouble even if I wire the choke open.

After three carbs (original plus two remanufactured), I am starting to think that either the supplied carburetor (both from the same source) is not correct for this engine or bad ignition is making it look like over-rich since it is not really burning correctly. I have changed the coil and the distributor and cap - no effect. I measure 12 volts at the coil when the ignition key is on but it drops to about 9.5 volts when I crank the starter. After it starts, the voltage is back up at 12 volts.

When we borrowed an original carburetor from a similar boat and installed it on my engine, the engine seemed to run fine.
 
Re: MercCruiser runs very, very rich

Be sure that your fuel pressure is not too high and blowing out the needle valve.
I have generally found that rebuilding a carb is never as good as a new one. The saving of a hundred or so dollars by buying a rebuild is usually lost on aggravation and time spent fooling around with the exact circumstances in which you now find yourself.
If you go to Jegs.com and enter marine carb in the search field it will pop up an edelbrock marine carb that has a special calibration kit for the 4.3. I urge you to buy this and install it and enjoy your boat instead of messing around. Sorry that you've had trouble with your rebuilds.
I doubt your issue is choke or ignition. Probably way overjetted.
 
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Re: MercCruiser runs very, very rich

" it has a Rochester Quadrajet carb and ran perfectly for 20 years." I agree it is time to replace it.
 
Re: MercCruiser runs very, very rich

Do a compression check. The engine may not be able to burn the same amount of fuel as it did when it was new. In it's later years my 1994 5.7 quadrajet blew black smoke at startup and sooted the transome while running. It was starting to get worn out and tired, compression consistent but down a bit. I replaced the long block and re-used everything I could including the same spark plugs (they only had a few hours on them), wires, ignition, and carb. I did not make any adjustments to the carb., just bolted it up. No more rich condition.
 
Re: MercCruiser runs very, very rich

I have no objection to spending money on a new carb but all the ones that I knew were an exact match were either rebuilt or remanufactured. I can't tell which of the Edelbrock carbs would be a match for my engine. I hate to change plumbing, etc. The Edelbrock are actually cheaper than the rebuilt units.

Although both rebuilt carbs (same model number on each carb) gave me a problem, I am wondering if the supplier just gave me the wrong carb initially and then the same wrong carb was reordered. All the data shows the original carb was a 17084516 R4/4MV. The two rebuilt carbs were 17058213 which I see means they were built in 1978, 11 years before my boat was built. I can't find any MercCruiser that used 17058213. An Internet search shows this carb was used on 1978-79 350 ci Chevy and GMC trucks.

My engine is only 262 cu. I wonder if the 17058213 is "jetted" for a much larger engine (350 ci or bigger) and might be giving me a very rich mixture.
 
Re: MercCruiser runs very, very rich

you didn't reply to the psi the fuel pump is giving you ? Why ? Cause you don't know? ?

Who sent you these carbs.

I know national carbs. They never fail.
 
Re: MercCruiser runs very, very rich

Once again, buying a pile of random jets and trying them until you hit on the proper combination is going to give you gray hair. Even after you do you are still stuck with a rebuilt carb that is at the very best questionable. You'll look pretty dopey to your girl/boy friend when the thing conks out in the middle of the bay and you try to convince them it ain't the old "ran out of gas" trick. Been there.
The carb I pointed you toward is the marine Edelbrock 1409, which you will need to change the jets for the 4.3 with calibration kit 1485, which is an extra $18. Both are at Jegs.com which has the best price on the web.
While you are at it replace the fuel pump and supply lines and fit up a new fuel filter (preferably a water separating canister type and not a lawnmower one)
 
Re: MercCruiser runs very, very rich

This Merc. number 3304-9354A2 is the correct carb for your engine. Call Jegs to see if the Edelbrock 1409 w/the calibration kit 1485 jets for the 4.3 is a direct replacement for it as o2batsea says. Buy it and try it out. If it has an electric choke you will need to tap into a purple wire for 12 vdc.
 
Re: MercCruiser runs very, very rich

To Chiefalen,

I don't have anything to measure the fuel pump pressure. The supply lines/filters are clean and the pump supplies plenty of fuel (disconnect the supply line and crank the engine). This is a mechanical pump. What would be the cause of excessive fuel pressure?

The 17058213 carbs (both the same series) were sold to two different shops (one closed due to retirement) by some distributor. The second shop just ordered the same carb that was installed assuming it was the correct carburetor.

I am not saying that either carburetor failed. I think that both carbs are probably incorrect for my engine and might be causing the rich mixture problem. I know the original carb was 3304-9354A2 (Rochester 17084516 R4/4MV which is equivalent to Sierra 18-7604-1).

I can't find any reference to a Mercuiser using the installed carb, 17058213. Of course, they may have just used the 17058213 body in the remanufacturing and the rest might be correct but even the supplier is not sure what they actually sent.

I don't want to bother changing jets, etc when the boat ran fine for twenty years with the original setup. I just swapped an original carb off another boat (with the same engine) and put it on my engine and the engine runs fine with that carb.

I think I will order another rebuilt/remanufactured carb that I know is correct for this engine.
 
Re: MercCruiser runs very, very rich

The 170xxx casting number is usually only of value (in determining its configuration) when in the original shape. Once it has been to a rebuilder, all bets are off. Many rebuilders will use whatever castings are available and install a 'generic' calibration in them. You can always call and ask your source which jets/rods/springs/hanger went into the carb you have. If there is any hesitation on their part, I'd find somebody else to deal with.

As noted above, you need to make sure the rest of the engine is Ok before spending more money on carbs. Didn't see spark plugs in the posts above.

If you opt for the edelbrock, the 1409 is really your only option. It will run 'out-of-the-box' but best economy will come from leaning out the fuel delivery system.

Personally, I think you are better off with the q-jet and just need to get hooked up with someone who is really competent.
 
Re: MercCruiser runs very, very rich

Spark plugs are new (tried two different new sets, Champion and Autolite) , coil is new (tried two different new coils), distributor cap and guts of distributor are new. Ignition module is unchanged but I did swap modules with a similar engine and the performance was unchanged.

I have put a timing light on it and the timing is OK.

Since the engine runs fine with the other engine's carburetor, I think that the replacement carburetor that was supplied was incorrect. The same parts distributor supplied both rebuilt carbs.
 
Re: MercCruiser runs very, very rich

What are the carburetor floats made from...After a period of time, some of the composition floats became "gasoline logged" resulting in all kinds of flooding issues
 
Re: MercCruiser runs very, very rich

I have had the rich running problem from day one for each of the rebuilt/remanufactured carbs so the floats have not had a chance to deteriorate.

The original plugs were AC MR43T. I tried the Champions and Autolites just to see if there was a difference.

Chiefalen, do you know what the fuel pressure should be? Is there a simple gage that I can hook up to the fuel line that will have the correct fitting? If the lines and filter are clean and the pump is the original mechanical pump, what would be the cause of high pressure? I would expect low pressure as the pump wears and eventually fails.
 
Re: MercCruiser runs very, very rich

vacuum gauge is also the gauge to use for a fuel pressure test, look on the face of the gauge.

Or just mosy down to any auto parts store or plumbing store. They are cheap.

4-7 psi no less 8 maybe.

Leave the gauge hooked up after cranking the motor till it doesn't go any higher and it should hold pressure for more then a hour.

You wouldn't by chance be up in the mountains somewhere ? I'm not trying to be a smart@ss there is a reason i asked.
 
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Re: MercCruiser runs very, very rich

See how easy i changed it, i wrote it while waiting on the phone for the ins agent.

Me bad. My bad, oh chit however my kids say it.
 
Re: MercCruiser runs very, very rich

Maybe,could it be, a jet problem ? Are you telling the carb guy's how high up you are ?

I keep reading and re-reading this post, post #6 you said you borrowed a carb. Was original. Could the jet have too big a hole ?

I would like to know what the pump is giving.

The plugs show to rich a mixture HUH ? Just asking don;t get pissed i'm trying to wrap my head around this.
 
Re: MercCruiser runs very, very rich

Here is the complete history.

I bought the 1989 Thundercraft as a brand new boat in 1989. I had no troubles with the boat for almost 20 years until part of the engine compartment filled with rainwater (automatic bilge pump failed to turn on) and the starter was immersed in water for a couple of weeks and froze up at the end of the season. A new mechanic replaced the starter and some steering cables at the end of the year; the next spring the engine started having a high speed stumble/bog. After replacing just about everything electrical, he said we needed to replace the carburetor.

After putting in the rebuilt carburetor, it ran way too rich; I was no longer worried about the high speed miss; the boat was almost unusable.

The following year, I took the boat to a new boat shop to get it ready for the spring. When he was trying to get it ready, he called me saying the engine was running way too rich and he was getting gas in the oil and it looked like it was getting dumped in from the carburetor. He said we could either take it apart or buy another rebuilt unit; he said it looked like the previous mechanic had been "fooling around" with the rebuilt carb. To get the boat usable quicker, I told him to just get another unit. Both mechanics use the same supplier and I am afraid that in both cases the supplier may have sent the wrong carb, a Rochester but perhaps set up for a bigger motor.

We no longer got any gas in the oil but it was still running way too rich. You can smell it at all speeds, particularly idle, and you can see the gasoline "slick" from the unburnt gas in the exhaust. The plugs are black (no oil). Usually, the engine will not even start unless you hold the throttle at WOT when starting.

To the best of my knowledge, no jets or metering rods or any internal components were changed on either rebuilt carburetor and certainly not on the last rebuilt.

There is another 1989 Thunderbolt on the lake with its original carburetor. I borrowed it and installed it on my engine with no adjustments. The engine runs fines, no idle issues, no high speed miss.

Obviously, this certainly points to the rebuilt carburetor being the source of the problem. I have ordered a Mallory 9-34009 remanufactured unit which is equivalent to the original carb. Hopefully, it will arrive in time for me to install and test this weekend.
 
Re: MercCruiser runs very, very rich

I did some digging in the 'old printed stuff'. If the rebuilder gave you a "generic" part, it is highly likely to have been jetted really rich for your application. I compared the effective primary fuel flow area for your OEM number and compared it with one of the last carb equipped SBC - 15% larger.

If the 'just ordered' part winds up running too rich, I'd seriously consider starting with the original merc specified rods, jets, springs, and hanger, and proceeding from there. Those parts and a few air horn gaskets and you should be dialed in before the 4th worst case.
 
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Re: MercCruiser runs very, very rich

I assumed that if the Mallory 9-34009 was the rebuilt/remanufactured version of 3304-9354A2 then it would have the same jets, rods, etc. Are you saying that the internal hardware of 3304-9354A2 was revised over the years?

I am not sure what "and compared it with one of the last carb equipped SBC - 15% larger" means. What is SBC? Please explain.

I never expected to have to rejet a carb that is supposed to be equivalent to the OEM carb supplied with the engine.
 
Re: MercCruiser runs very, very rich

Just to complete the loop, installed a Mallory 9-34009 remanufactured carburetor today. If you see the history, this is the third rebuilt/remanufactured carburetor in the last three years. Put the new rebuilt on and the engine runs perfect. Starts easily, idles nicely, no high speed miss, no gasoline slick, no gas smell.

I am fairly sure that the carb that I took off as well as the previous one were rebuilt by the same company. Same internal part number on the rebuild sticker and both of the prior rebuilds were done in early 2007 (based on the paper sticker on each carb). The latest rebuild that I installed has a rebuild date of late 2009 and has the same part number and the rebuild sticker in the same spot. Perhaps, someone was having a bad year in 2007. As they say, S*** happens.

After a huge number of man-hours, it appears that I had two rebuilt carbs that were set up in such a way that the engine would barely run.
 
Re: MercCruiser runs very, very rich

SBC = small block chevy - a v-8 that has more displacement so will require more fuel than the v-6. the 15% refers to the cross sectional area of the primary fuel passages during the cruise condition. That means 15% more fuel available -> it will run rich.

I'd say not to spend anymore with the outfit that produced your first two rebuilds.

Glad you are running right now.
 
Re: MercCruiser runs very, very rich

Listen it's a lost art really rebuilding carbs. I would say 50 percent can't be rebuilt.

Glad your back on the water.
 
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