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Old 08-22-2010, 11:55 PM   #1
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Default 95 Maxum 1800SR 4.3 hesitating bad at half throttle to full throttle after warmed up

Been having an issue with my boat, after the boat is warmed up (runs fine for first 30 mins or so) it seems to be stalling out or badly hesitating at half throttle to full throttle but never dies. back off the throttle its fine its seems as if its not getting fuel from the 4 barrel meetering jets when the 4 barrel opens up. Spark is good new distributer, new coil, new plugs and wires, fuel pump is working good, checked the fuel pickup check valve in the fuel tank its good checked and replaced fuel filters. No choke on my carb so I know its not the choke closing when it shouldnt. I am baffled Not sure what to look for anymore. any help would be greatly appreciated.
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Old 08-23-2010, 10:25 AM   #2
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did you turned your fuel filter upside down to look foor water in to it. if there is to much water in the engine takes fuel and water in at a certain moment....and believe me.......it does'nt run on water......check the tank if there's water in it (that was the problem i had with my bayliner a few years ago)

greatz, ed
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Old 08-23-2010, 12:17 PM   #3
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Yea I have already cleaned the fuel tank out and checked my fuel filter. That was my first guess on what the cause was but it didn't fix it.
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Old 08-23-2010, 01:07 PM   #4
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then it gets too less fuel or something wrong with the ignition mechanism, look if carb. works fine, needles in the carb. open fully, take it of and clean it, check al the holes in the carb. if they ar clean so that al the fuel needed can go true....look if there's no old fuel (that's rubbered) in the holes (here in holland in the harbours during the summer you buy other fuel then in the winter.......the summer fuel has additives that change to very, very, very little rubber balls when it gets to old, and they can constipate the little holes were fuel has to go true)

these ar just some ideas to check......clean your whole fuel system from the beginning till the end......

succes, ed
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Old 08-23-2010, 01:18 PM   #5
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What kind of carb is it Soldier?

Dan
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Old 08-23-2010, 01:18 PM   #6
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I have replaced fuel lines fuel pump fuel filter checked the tank and pickup tube and check valve replaced distributer cab rotor coil plugs and wires the only thing left to do is rebuild the carb (I hate rebuilding carbs lol)
I was wondering though if a intake leak would cause the engine to do what its doing?
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Old 08-23-2010, 01:19 PM   #7
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Its the weber 4 barrel carb I think, I know its a 4 barrel
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Old 08-23-2010, 03:25 PM   #8
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Would be good to know which carb it is Soldier, kind of surprised it's a 4BBL on a 4.3. Are the secondaries huge compared to the primaries?

1) Engine
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Old 08-23-2010, 03:46 PM   #9
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Would be good to know whic carb it is Soldier - are the secondaries huge compared to the primaries?

Nevertheless:

1) Engine starts fine?
2) In the 1st 30 minutes engine runs fine and will accept 1/2 to WOT without hesitation?
3) After 30 or so minutes engine will not accept 1/2 to WOT without hesitation?
4) After 30 minutes engine and starting at idle, engine will accept 1/2 throttle without hesitation?
5) After 30 minutes when you go to 1/2 to WOT and the engine hesitates, you can reduce throttle and it will then run fine, up until you try to go to more than 1/2 throttle?
6) When the symptom occurs, is there any back firing/popping through the carb or exhaust?
7) After warm up can you ever get the thing to run past 1/2 throttle at all? Can you coax it up to WOT?

When this symptom occurs, have you tried to very gradually open the throttle all the way? In other words, with the engine warmed up and starting at idle, slowly open the throttle over the course of, say, 15 -20 seconds.

First off, the engine should be up to normal operating temp within 5 or 10 minutes, unless you are not running a thermostat, so I don't think it really has anything to do with the engine temp. It could possibly be a vacume leak, but at this moment I'm more inclined to think the fuel tank vent is clogged/obstructed. A quick test you can do for that; when the symptom appears bring the engine back to idle then go unscrew the fuel tank filler cap - no need to take it all the way off, and re-tighten - then try to run it to WOT again.

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Old 08-23-2010, 08:24 PM   #10
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you i always forget something.....

oke Dan, that can be the problem also......
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at this moment I'm more inclined to think the fuel tank vent is clogged/obstructed. A quick test you can do for that; when the symptom appears bring the engine back to idle then go unscrew the fuel tank filler cap - no need to take it all the way off, then try to run it to WOT again.
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greatz, ed
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Old 08-23-2010, 08:32 PM   #11
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It is a 4 barrel carb I have a vortec 4.3 in the boat the lx motor
Just checked the carb it has the W stamped on top for webber and has 2 small primarys and 2 larger 2ndarys
1) Engine starts fine? Yes engine starts fine
2) In the 1st 30 minutes engine runs fine and will accept 1/2 to WOT without hesitation? Yes correct
3) After 30 or so minutes engine will not accept 1/2 to WOT without hesitation? correct
4) After 30 minutes engine and starting at idle, engine will accept 1/2 throttle without hesitation? about half throttle yes it runs fine
5) After 30 minutes when you go to 1/2 to WOT and the engine hesitates, you can reduce throttle and it will then run fine, up until you try to go to more than 1/2 throttle? no anything after half throttle it will start hesitating
6) When the symptom occurs, is there any back firing/popping through the carb or exhaust? no backfireing or poping from exhaust
7) After warm up can you ever get the thing to run past 1/2 throttle at all? Can you coax it up to WOT? it seems to not want to go wot without hessitating it will go wot for maybe a second then start hesitating

The carb has smaller primarys and the secondarys are a bit bigger (wish I had a camera to show you but it is deffinitly a 4 barrel carb

I was able to pump all 30 gallons of fuel out of my tank through 50 foot of hose into my truck tank watching the flow it never slowed or seemed to have trouble pumping untill the tank was empty (electric fuel pump) thats why i didnt think it was a fuel tank issue could be wrong

Thanks for the input guys this has really got me stumped lol
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Old 08-23-2010, 08:55 PM   #12
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A little unclear how you pumped it from the boat to your truck. If you stuck a hose into the boat tank through the boats' fuel filler opening and used an external pump then that test would not be valid.


When the engine is running it is drawing gas from the tank. If the vent is clogged/partially clogged there will be a vacume created because "make up" air cannot enter the tank.

Because it will run fine during the 1st 30 or so minutes I don't see this as being a carb issue, or ignition related.

Dan
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Old 08-23-2010, 09:53 PM   #13
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No I hardwired the electric fuel pump and disconected it from the fuel water seperator and used a long hose with hose clamp and pumped it to my truck using the regular fuel pickup tube from the fuel tank as if it were feeding a really big carb haha Oh and when im pumping gas into my boat tank you can hear the vent hissing and then it will overflow with fuel out the vent when the tank is full so i dont think the vent is cloged
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Old 08-24-2010, 08:24 AM   #14
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Quote:
Originally Posted by ss3964spd View Post

Because it will run fine during the 1st 30 or so minutes I don't see this as being a carb issue, or ignition related.

Dan
as i understand it runs fine untill a specific rpm, and not to full speed...so maybe it runs oke whole time untill lets say 2500 rpm......and when you press the throttle more down it runs bad????????

if this is correct i cant see why it would'nt be an issue like that...

lets hear it.....greatz, ed
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Old 08-24-2010, 01:55 PM   #15
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Quote:
Originally Posted by ed & inge View Post
as i understand it runs fine untill a specific rpm, and not to full speed...so maybe it runs oke whole time untill lets say 2500 rpm......and when you press the throttle more down it runs bad????????

if this is correct i cant see why it would'nt be an issue like that...

lets hear it.....greatz, ed
It will run fine all the way to wot for about 30 mins then after 30 min or so half throttle to wot it wants to break up hesitate on me
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Old 08-24-2010, 05:19 PM   #16
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try checking the coil at that point and see if the voltage is dropping causing this hesitation...also check after it's thoroughly warmed up to see if the carb is properly torqued onto the intake manifold...as well as the top of the carb..sometimes the screws on the top plate will back out causing a slight vacuum leak....

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Old 08-24-2010, 06:09 PM   #17
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What kind of ignition system? Electronic module inside the dist? If yes, was that replaced?

Still think it's a fuel issue though......
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Old 08-24-2010, 08:31 PM   #18
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take a tank of an outboard motor fill it up with fuel and conect it to the engine (cut the original tank off) lets see what happens.........if it still runs **** original tank is oke....if it runs oke....original tank problem......

lets give it a try.....

greatz, ed
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Old 08-24-2010, 08:38 PM   #19
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I pulled the carb off today figured it couldnt hurt to rebuild it when I get it back on ill have to try the external tank idea and while im at it im going to replace the electronic module inside the distributer (I dont think its bad but couldnt hurt. Going home to texas on the 1st of september so probably wont have the boat in the water again untill I get back. Thanks everyone for the help Ill let you know how it turns out when i put the carb back on
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Old 08-24-2010, 09:21 PM   #20
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I know you said the distributor is new but you didn't mention anything about the module inside it - which is why I asked about it. I've heard about them getting wacky when they get hot but they usually stop working all together, not just at higher RPM's.

Let us know what you find out.

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