omc 4.3 cobra skipping

[Ski-King]

help guys, got a 89 sunbird 4.3 v6 chevy. she just won't run good backfires when turning up the speed. at idle runs from 600 rpm to 900rpms.i did it all i think,check compression staying at 140 to 150 all cylinders,gap plugs at .035. cleaned points set them to .019 set timing 6 btdc. pulled dist.cap looked good, made sure rotor was looking at #1 plug when #1 was at tdc on compression stroke. took carb off broke it down soaked it over night in carb cleaner.rebuilt carb put it back on,set idle at 600rpm balance both air screws for highest rpms three different times while setting rpms back to 600 each time as well.pumped old gas out added new 93ron gas back. when i start it up cold she idles good till it warms up then it runs from 600rpms to 900rpms up & down. on the river backfires though out throttle range

 

[P.V.]

Re: omc 4.3 cobra skipping

Ok. If I read you correctly, you gap'd your existing plugs (rather than install'd new ones), clean'd up your old points (rather than replace'd them), still have an old dist. cap and rotor, and you still have the firing order wrong (I believe).BTW, is the timing advancing? Still have the old condensor? I also suggest using a dwell meter rather than just a feeler guage!

 

[Ski-King]

Re: omc 4.3 cobra skipping

ok p v timing on a 4.3 v6 is 6 btdc with 93 ron gas 1 btdc with 90 ron gas.why replace plugs points ,cap ,rotor , condensor if they all check out ?<br /><br /><br /> thanks

 

[cjflanagan]

Re: omc 4.3 cobra skipping

How do you mean they check out, like there there so their ok? The boat still runs poorly. These parts are not that expensive...

 

[Bondo]

Re: omc 4.3 cobra skipping

Your problem is Fuel related.........<br />Either the carb isn't Getting fuel,<br />Or it's Junk,+ needs to be Replaced...........<br /><br />The surge at idle Sounds like a Vacuum leak......

 

[Ski-King]

Re: omc 4.3 cobra skipping

thanks ya'll i will try all the above this week . let you know soon .<br /><br /><br /> THANKS AGAIN

 

[P.V.]

Re: omc 4.3 cobra skipping

My point is this: Do the EZ'iest things (and often the cheapest also) first! NEW points, plugs, condensor, etc.... Then it's not a question of if it's good or not (yes, it IS possible to buy "new" parts that are defective, but that's another story) but that you've eliminated those items as the source of your problems , so your problem must be another system on the motor! ie: fuel, coil, mechanical problems,etc......

 

[Ski-King]

Re: omc 4.3 cobra skipping

ok guys replace the coil, plugs,condensor,rotor,points,fuel filter,set points with dell at idle 600 rpms looking at about 39 on meter.600rpms idle set time to 6deg.btdc compression still 150,140 balance the carb, after a rebuild. even tied coke open when motor reached running temp. still it idles all day great, go to speed up a little starts to skip will only run about 1/4 throttle.

 

[rattana]

Re: omc 4.3 cobra skipping

I agree with Bondo, it sounds fuel related. If you didn't use new gaskets you could have a leak.

 

[Ski-King]

Re: omc 4.3 cobra skipping

rebuilt carb with new kit.no vacuum leak took a piece of hose in ear went around carb .i think it's fuel too , just hate to buy new carb and still have same prob.

 

[rattana]

Re: omc 4.3 cobra skipping

When you open up the throttle is there a good stream of fuel squirting in each barrel of the carb?

 

[rattana]

Re: omc 4.3 cobra skipping

When you pump the throttle is there a good stream of fuel squirting in each barrel of the carb? It sounds like it is starving for fuel. Did you double check the float setting? Have you checked the fuel pressure going to the carb?

 

[Ski-King]

Re: omc 4.3 cobra skipping

yes when i open the throttle it gets two good steady long blast .when i rebuilt the carb i was very careful to make sure the settings where at the right specs, did it three or four times to make sure.i went ahead and bought a new carb today, i called my local napa store and they where lucky to cross the marine #s and get one . paid 327.00 i hope thats not to bad? flint river marine wanted 948.00 , i almost sh-t a brick.i'll try this new carb tomorrow and let you guys know what the outcome is .i did not see what the fuel pressure was, whats the best to tell?<br /><br /> thanks ya'll for all the help!!!!!!!!!

 

[edfresh]

Re: omc 4.3 cobra skipping

Ski-King: Just adding some other possibilities... Could be an intake manifold leak that shows under larger intake volume (could use propane, starter fluid or something to locate it). Could be centrifigual advance within distributor (timing light should show change when idle speed is raised). Also, are you sure you set the timing to 6deg BTDC? My 4.3L engine's timing plate that has the timing marks is very rusty and hard to read. Also, what about fuel filter? Could be a little clogged. Is flame arrestor clean? May be starved for air. etc. etc.<br /><br />By the way, this is a GREAT forum. These "case studies" augment the dry service manuals!!

 

[rattana]

Re: omc 4.3 cobra skipping

You could buy a fuel pressure/vacuum gauge from almost any automotive shop for under $20 dollars. Connect it to your discharge fuel line from your pump. No need to connect the fuel line to the carb just to check the pressure of the pump, unless you think the pressure of the pump is failing after it warms up. Ed has some good ideas, what does the timing do as you bring up the RPMs?

 

[Ski-King]

Re: omc 4.3 cobra skipping

ok ya'll thanks for all the help , you guys are great.today i put a new carb on her cost me 350.00 still ran the same maybe a little better but not much.funny you guys said look at the centrifgual because today at the river on my test run i did look at it and they where stuck , a little oil and moved them back and forth they came lose. i thought guys we had it for sure this time. nope still did the same thing, now iam a little sad load the boat and go home.later in my shop iam sitting in my boat looking at the motor trying to think what it could be , started looking in the manual and was reading about the interupter switch.guess what someone had the screws to tight and the switch was stuck all the way in making my motor run half rpms at full throttle . so in the morning i'll try again i'll let you guys something sunday night

 

[edfresh]

Re: omc 4.3 cobra skipping

Ski-King: A weekend has passed. Did fixing the interupter switch fix the problem? Bet it did!

 

[Boatin Bob]

Re: omc 4.3 cobra skipping

Even if the interupt switch was stuck in as soon as you put it into gear the overstroke switch should have opened up the circuit to kill the ESA and if it was a newer ESA the internal timer would have kicked in within 6 to 9 seconds.

 

[Ski-King]

Re: omc 4.3 cobra skipping

edfresh don't really know, fixed the switch prob. then took the boat to huggins outboard to get it looked over, you know make sure the cables were adjusted right.while we had the motor running (not in gear) we could hear a nocking sound. couldn't tell if it was top or bottom nocking. they said they wouldn't work on the boat because it had been in before (before i bought it ) with the same sound and it's been rebuilt.so i said fine i'll do it.i'am going to fix this boat all the way through, can't stop now lol.so i pulled the motor monday night,broke it down to the block last night.did a bore gauge on it and it was .040 at the bottom about .050 at the top. could go to .060 with it but i think it's getting to thin.and it would cost about 550.00 to get a cyl. bore and line bore, heads built, then about the same money to get a master rebuild kit.can go to napa and get a rebuilt 4.3 for around 1400.00.i found a 4.3 bored to .040 the guys said they would build that block new everything (with my crank) for 850.00 with pop up pistons. motor should be ready this monday night.so if all goes well i sould have to motor back in the boat tuesday night and go for a test run on the river wed.(end of month)...........pray for me guys<br /> THANKS YA'LL<br /> (BONDO <br /><br /> A BUNCH OF GREASE IS STILL BETTER,,,<br /> THAN NO GREASE AT ALL. ) LMFAO!!!!