Carb Popping?

[Ingram84]

Hey guys, I have a 1992 marada ski boat with a 5.0 omc ford 302 in it. I believe the carb is a 2300 holley 300 cfm. Got the boat last summer ran it for 10-15 hours and it did fine. This year took it out with just me and my wife and cruised around and it did fine the first hour. Then when i went to accelerate it backfired through the carb.
I thought it was just bad gas as it had sit all winter ( i winterized it with 93 high octane and stabil in it.) So this past weekend i topped the gas tank off with more of the 93 gas and loaded the boat up with 6 people and was hoping i was good to go, but i was wrong. It wold pop 3 or 4 times back to back just trying to plane out. I couldn't pull a skier bc i couldnt get enough power quick enough. It never stalled or died just popped. If i slowly sped up it would plane out just fine and run nice. Since then i have changed the inline fuel filter to the carb and the water separating fuel filter.
When hooked up to the muffs in the driveway it will rev up just as fast as you would ever want. But under load it still pops. What am i looking at here?

 

[bjcsc]

Re: Carb Popping?

Lean under load..secondaries functioning?

 

[John_S]

Re: Carb Popping?

I don't know the specifics on your motor or carb, but the symptoms sound like the accell pump is not working correctly. With the engine off, flame arrester off, choke open, have someone advance the throttle from idle to full. You should see a steady stream of fuel into both barrels. If not or dribbling erratic, time for a carb rebuild.

 

[Ingram84]

Re: Carb Popping?

John, i was doing some research on past posts and i came up with either the accel valve or the power valve that may be the culprit.


Bjcsc, you'll have to excuse me i'm carb illiterate. What are my secondaries? Is that the accel valve or power valve?

 

[rplumbo]

Re: Carb Popping?

My Volvo 230 did the same thing. I checked timing and dwell and they were way out. Clean the carb, reset needles to factory settings, check timing and dwell and I bet you get back to normal. Timing light and dwell meters can be bought at Autozone for under $80 total. Good tools to have.

 

[fstncrnrs]

Re: Carb Popping?

I have mercruiser 260 did same thing it turned out being flat lobe on cam.

 

[Brenan]

Re: Carb Popping?

I just had the same problem, mine was a little light on the top speed, and accel. I could get on a plane, but it would stutter and hesitate, making me go back to idle for a minute. Top speed was 35

I timed it, replaced plugs, plug wires, clean bat terminals, and cleaned / lubed the centrifical advance in the distributer. (I think this was the main culprit). The tack is still bouncing around, but I'm working on that.... The pvc valve is broken i noticed tonight, but it didn't seem to make a difference.

Start with the basics and go from there...........

Engine is a 93' OMC cobra 302. Topped out on the lake today at 45! wahoo!

 

[6meter]

Re: Carb Popping?

John, i was doing some research on past posts and i came up with either the accel valve or the power valve that may be the culprit.


Bjcsc, you'll have to excuse me i'm carb illiterate. What are my secondaries? Is that the accel valve or power valve?

Neither. The secondaries are the 2 back holes, venturies, in the carb. The front ones are the primaries. The secondaries are not used , hence better gas mileage, until the throttle is pushed far enough to call for them. More gas is put into the engine so it also needs more air, hence the secondaries open up, and bad mileage it attained but also more power. 2 barrel carbs don't have secondaries.

 

[6meter]

Re: Carb Popping?

Sounds like my boat. It was the coil.

 

[John_S]

Re: Carb Popping?

Neither. The secondaries are the 2 back holes, venturies, in the carb. The front ones are the primaries. The secondaries are not used , hence better gas mileage, until the throttle is pushed far enough to call for them. More gas is put into the engine so it also needs more air, hence the secondaries open up, and bad mileage it attained but also more power. 2 barrel carbs don't have secondaries.

"I believe the carb is a 2300 holley 300 cfm."

Which is a 2brl.



As others have pointed out here, there can be many other causes outside of the carb. When was the last tune-up and what was performed?

 

[fossill]

Re: Carb Popping?

Start with the ignition system first including a compression check. The carb was the last thing on the troubleshooting tree during my days in the automotive world when dealing with a performance issue. As mentioned before start with the basics oand work from there. Usually there are lots of troubleshooting charts in service manuals that cover everything. And it helps to have proper diagnostic equipment instead of randomly replacing parts or adjusting things till the problem goes away.

 

[Ingram84]

Re: Carb Popping?

I put new spark plugs and wires on in april when i pulled it out to get ready for the summer. Other than changing the oil and filter I haven't done anything else. Except changing the water seperator and cleaning the inline fuel filter to the carb when this problem came up. I appreciate all the info you guys are giving me. What stinks is it wont do it in the driveway on muffs. I have to take it an hr away and put it under load.

 

[Brenan]

Re: Carb Popping?

Good luck. Mine ran like a champ on the muffs too. I am lucky and am 10 minutes from a lake. (and for a piece of red licorice my mechanic father in law took a listen) It backfired pretty good right after getting on a plane. Sometimes i couldnt make it plane and had to slow down.

Some of the things you may be able to do on the lake. You could put a cheap timing light to make sure you are getting advance (my plates were not moving much) when you accelerate. also, maybe check the ignition coil for voltage when it is acting up / running good to make sure there is no weird annomolies.

on mine there's a liittle vacuum canister behind the carb that i didn't notice on the first trip. Mine ran like crap when i tried plugging the pvc valve. Maybe one of those hoses came loose? it's worth the look even though it may not be the problem. If you pull the cap / rotor that might be worth an easy shot. I personally would replace them out on the water (Please don't hold up people at the dock though....... If it stays the same throw the old ones in the spare parts box for a rainy day. If it solves the problem, toss em. Clean the spark arrester, look down the carb (be careful) on the muffs and see how the spray looks.....

How was the condition of the fuel filters / fuel screens? If they were clean I'll bet you have an electrical problem. If they were full of crap, I'll bet it's a fuel system problem. Check the fuel inlet out of your tank? Hopefully if you do your compression test, it comes out okay. You could take a look at the plugs again too.

All that stuff is fast, easy and inexpensive to try....They have some really good info in the stickies too here. I have had lots of little issues I have been able to solve going through the checklists.

Please post how it goes!

 

[Ingram84]

Carb Popping/Timing issue?

Carb Popping/Timing issue?

Alright, so last night my brother-in-law comes over and starts messing with my timing. He gets it to backfire through the carb on the muffs in the driveway. He adjusts the timing by ear until he says its good.(He's a pretty reputable mechanic in town.) It runs good on the muffs and won't backfire anymore. We get a timing light a cpl hours later. ( he didn't know he was going to work until he got here. haha) Hook the light up and its showing its off by about a 1/2 inch from the marks.

Now my question is this? Will over adjusting the timing cover up my problem like a temporary fix? Or did that fix it and i'm just reading something wrong. I don't want a temp. fix. I want the problem gone. He tells me that usually if your timing is to advanced or retarded you would have like a "tick" that you would hear. Then tells me if its set to high I can burn up my valves.

Well i took her out today and she did perfect. Just like old times.Haha. But i want to hear from you guys on what you think. Is it a temp fix, am i guna burn my valves up? He told me he would bring his light next time he came down. Said the one we had may have been bad as it was blinking very slow.

 

[6meter]

Re: Carb Popping?

If the timing is to far advanced or retarded it will pop through the carb. The spark plug was firing while the intake valve is still open. Permenant fix.

 

[jeffw0038]

Re: Carb Popping?

My omc did that last time i had it out, took forever to get any speed carb was popping and it just ran like crap, so at night i fired it up in the drive and saw a light show for the engine, so i'm gonna replace plugs,wires and dist cap and should be good to go!

 

[fossill]

Re: Carb Popping?

Not sure about the marininized Ford engines, but the 302/351's (5.0L/5.7L) had a composite gear on the cam for the timing chain. It was prone to wear prematurely compared to ones with out, resulting in a worst case scenario of a jumped timing chain or more commonly late valve timing resulting in a "gutless" engine. We used to replace with the double roller variety.

 

[PitchFork]

Re: Carb Popping?

I was having the same problem with my 5.7L carb'd engine and have thrown $100 into it new plugs, checked timing many times, new coil, new cap and rotor and it was still doing it. I was about to buy a new Ignition Sensor $70 until last night I did some troubleshooting.

I took the flame arrestor off and went to WOT and noticed the secondary butterflies were not opening all the way. I had my sons push the butterflies all the way open and BAM 4,600 RPM from 4,000. So I will be loosen the windup spring on the secondaries today as it was dark and did not have the correct allen wrench onboard.

 

[daveabs]

Re: Carb Popping?

Backfire through the Intake is caused by lean AFR, timing off, worn cam lobe, or sticky valves. if you have a propane enrichment tool you can inject propane in the intake under load (when the problem occurs) to see if it goes away, meaning you have a lean problem. Since it was running fine before, you can probably eliminate worn lobes or sticky valves. Good Luck