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OMC Cobra 4.3L will not get up on plane....please help!

brownja2

brownja2

Member
I am a second year boater and I bought a 1989 VIP Vantage with a 4.3L OMC Cobra in it last year. Sometimes it got up and going just fine, and sometimes it would just all of a sudden cut back to idle while going full speed...wouldn't stall, just cut back to idle with the throttle still wide open. I had plugs, wires replaced...points checked, carb. adjusted, etc. lately it will not even get up on plane and just goes along with the bow in the air at about 15 mph while wide open!:mad: I did notice that after I replaced the belts and tightened them up real good that it didn't do this (for a couple days) now it is back to not getting up on plane! I am going to try to re-tighten the belts and clean the carb. and flame arrestor. Any other ideas what this could be? The guy I bought it from said he gave up on trying to figure it out! I am guessing fuel delivery or something like ESA module???
 
In no particular order:
Clogged fuel line; pick up, filter, fuel pump or stuck needle valve in the carb.
Messed up linkage
bad fuel
blown coupler
blown prop hub
 
I have just replaced two tank pick up tubes in two different boats, the ethanol has made them so pliable that they collapse when going to full throttle. check your antisiphon valve at the tank also
 
Thanks for all the ideas, I will start trying them this weekend. I did have to have the gas tank pumped out when I first bought it because there was so much water in it from the ethanol, the marina where I get gas now claims that it is ethanol free, I have heard several stories of bad gas at some of the marinas around the lake.
 
I'm not sure, the RPM gauge and the gas gauge do not seem to be functioning properly. The RPM gauge jumps around erratically from 2K to 5K to 6K and back down to 2K....with no noticable souind or feel in the engine???
 
brownja2 said:
I'm not sure, the RPM gauge and the gas gauge do not seem to be functioning properly. The RPM gauge jumps around erratically from 2K to 5K to 6K and back down to 2K....with no noticable souind or feel in the engine???
Click to expand...

Ayuh,.... It's Best to fix yer Known Problems, then you can fix yer other problems...

Has the motor ever been serviced, 'n Tuned Up,..??
 
It had a full service and tune-up at the start of last season...it runs great, until you try to get up on plane...then either it sometimes does (finally) get up and goes fine for a while but then just cuts back to idle with the throttle wide open or it just wont get up on plane at all. I have noticed that usually it will get up and go when I first leave the canal and go with no problem as long as I want, but when I turn it off and float a while and then try again is when the problem starts....although last weekend it just wouldn't go at all, other than riding about 15 mph with it's nose in the air!
 
I do remember when I first bought it and it died in the canal because of the water in the gas that the machanic that came out and looked at the carb. said the choke was not open like it should be, but after they drained the tank and refilled it was fine for a while, so I will start with the choke...how do you disable it, or how do you adjust it so it stays open when it is supposed to? (sorry,....not mechanically inclined!...haha) As you can see, I am pretty new to this whole thing but do not really want to pay the marina $95/Hr. to do what I can probably do myself! I really appreciate everyone's help! Thank You!
 
kimcrwbr1 said:
Are you sure the choke is fully open when the condition occurs if it works fine and then it dont erratic problems are usually wiring related go through with a fine tooth comb. Clean ALL connectors good with electric cleaner and put back together with dielectric grease. Sand all grounds metal to metal. Look for burnt cracked bare wires and fix as necessary it has to be something simple. Are the controls in good condition and you confirm the throttle butterfly is wide open when the condition occurs.
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Thanks!....I am going to take it out saturday and confirm the butterfly is open when it should be....to be clear, it should be all the way open all the time once it is warmed up right? because that time the mechanic looked at it and commented about it not being open when it should be it was all warmed up. I will also go through all the connectors as well. If the butterfly is not open when it should be...how is this remedied?
 
There should be an adjustment on the side of the choke. If it's not opening or trying to open it's electrical. I put some Star Tron in my boat this spring, I have some gremlins in the tank. After I adjusted the points and timing along with the idle I put it in the water. Started right up idled out to the no wake zone and dropped the hammer. It spit and I couldn't get it over 3000 rpm it would bog down so I ran it about two miles, turned around and tried it again same results. Turned around and this time it spit then took off like it was shot out of a cannon. The last time I had it out I was going 40 mph on the gps at 4200 rpm. Seemed to fix the problem for now I'll know more next time I take it out, the Star Tron worked like a charm I had to use a bunch because I have a 80 gallon tank that was full, now I just have to burn the bad gas.
 
indybleck said:
There should be an adjustment on the side of the choke. If it's not opening or trying to open it's electrical. I put some Star Tron in my boat this spring, I have some gremlins in the tank. After I adjusted the points and timing along with the idle I put it in the water. Started right up idled out to the no wake zone and dropped the hammer. It spit and I couldn't get it over 3000 rpm it would bog down so I ran it about two miles, turned around and tried it again same results. Turned around and this time it spit then took off like it was shot out of a cannon. The last time I had it out I was going 40 mph on the gps at 4200 rpm. Seemed to fix the problem for now I'll know more next time I take it out, the Star Tron worked like a charm I had to use a bunch because I have a 80 gallon tank that was full, now I just have to burn the bad gas.
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Thanks!
 
Is there a way to check/unclog the pickup tube or anti-siphon valve without having to tear things apart and get inside the gas tank?
 
there should be an axcess plate on top of tank, your delivery line is threaded into the tank, remove the antisiphon, which is threaded into the pickup, and then take out the pickup tube, with that much ethonal in it i would bet there as floppy as a wet noodle and colapsing on themselves.
 
roscoelab said:
there should be an axcess plate on top of tank, your delivery line is threaded into the tank, remove the antisiphon, which is threaded into the pickup, and then take out the pickup tube, with that much ethonal in it i would bet there as floppy as a wet noodle and colapsing on themselves.
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thanks, now i just have to figure out where the gas tank is and how to access it!
 
Usually in the floor, trace the line back from your fuel pump to the tank. My pick up tube is welded to the tank so I just back flushed it with low air pressure. If it's in the floor you'll see the screws for access to the tank.
 
kimcrwbr1 said:
The choke thermostat is adjustable I believe you just loosen the screws and twist it open. It could also be a bad connection clean it with electrical cleaner and use dielectric grease to put it together. You should have voltage to the choke thermostat when the engine is running. Maybe it is just sticky clean it with carb cleaner make sure it moves free the spring will close it cold and after you start it you should be able to see it open after a few minutes you just rotate the thermostat to adjust spring pressure and clean the linkage good also.
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so....I am sure you will love this question..........what is a choke thermostat??
 
Soooo, pulled the fuel pickup line-not clogged, screen intact no debris. Changed the fuel filter/water separator. Replaced the anti-siphon valve. When I dumped out the gas from the fuel filter/water separator into a bowl...it had phase separation, top was clear, bottom was an orange "gel" like subatnce! Added Star Tron treatment and filled tank with non-ethanol gas. When I took it out after doing these things, it ran great and got right up on plane.....but....the next day when I tried....same problem....will not get up on plane....nose in air...about 15 mph. I am wondering, the first day there was just my wife and I in the boat, the second day I had 7 people in there....plus coolers. I am sure I was under the max weight limit....shouldn't it still get up on plane with more weight in it? or am I asking to much of her to do that with such a load? I had phase separation in the fuel last year too and had to have tank pumped out....only use non-ethanol gas now!
 
Sounds like a awful big load for your boat. I don't know how heavy your boat is but 7 people plus coolers is a bunch, my 260 hp would strain with that load. Did it miss or spit and sputter like it did before? Take it out with the wife again and see how it runs with a smaller load.
 
indybleck said:
Sounds like a awful big load for your boat. I don't know how heavy your boat is but 7 people plus coolers is a bunch, my 260 hp would strain with that load. Did it miss or spit and sputter like it did before? Take it out with the wife again and see how it runs with a smaller load.
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No spitting and sputtering....maybe just too many people! 2 of the 5 people were only about 90 lbs. each though. I am estimating about 1,000 pounds all together with people and gear...it says max. load is 1200 pounds. I do remember once I had even more weight on there and it DID plane out....I am going to see how she acts with just me in it next weekend.
 
kimcrwbr1 said:
Was the weight evenly distributed next time start moving bodys around or if you know your gonna load it up try trimming different it sounds like the weight was all in the stern trim the enging down a notch and see if she planes. Trial and error will get you there but when you load it up your gonna lose mph.
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Yes, I actually had the heaviest people go into the cuddy at the bow...still no plane...I am beginning to think it is just too much weight for her to handle!
 
of course....it has acted this way with just 2 people in the boat before as well..........the gas being phase separated can't be helping either! Anyone had that issue due to ethanol gas? What is a good solution? I have tried some additives like star tron and stabil....no luck.
 
kimcrwbr1 said:
Was the weight evenly distributed next time start moving bodys around or if you know your gonna load it up try trimming different it sounds like the weight was all in the stern trim the enging down a notch and see if she planes. Trial and error will get you there but when you load it up your gonna lose mph.
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...also, engine was trimmed all the way down (I always start out like that)....
 
brownja2 said:
something like ESA module???
Click to expand...

start with that - takes only a few seconds to unplug the esa and try planing again
start with the easy things


ever clean the flame arrester?
ever remove the points plate from the distributor to check/clean/lube the advance weights and springs?
also easy things
 
hystat said:
start with that - takes only a few seconds to unplug the esa and try planing again
start with the easy things


ever clean the flame arrester?
ever remove the points plate from the distributor to check/clean/lube the advance weights and springs?
also easy things
Click to expand...

Cleaned / blew out flame arrestor, have not checked points, what do you lube the weights and springs with? There should be a certain gap for the points as well right? I have the Seloc manual for this engine.
 
any light lubricant - 3 in 1 oil or engine oil
cleaning the old gummy residue off them is more important than what new lube is used.
small toothbrush and a can of brake clean
 
brownja2 said:
I am a second year boater and I bought a 1989 VIP Vantage with a 4.3L OMC Cobra in it last year. Sometimes it got up and going just fine, and sometimes it would just all of a sudden cut back to idle while going full speed...wouldn't stall, just cut back to idle with the throttle still wide open. I had plugs, wires replaced...points checked, carb. adjusted, etc. lately it will not even get up on plane and just goes along with the bow in the air at about 15 mph while wide open!:mad: I did notice that after I replaced the belts and tightened them up real good that it didn't do this (for a couple days) now it is back to not getting up on plane! I am going to try to re-tighten the belts and clean the carb. and flame arrestor. Any other ideas what this could be? The guy I bought it from said he gave up on trying to figure it out! I am guessing fuel delivery or something like ESA module???
Click to expand...

My Buick V6 did the same thing....FUEL PUMP !!!
 
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