SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: Brad @ SCJB on March 24, 2015, 07:29:05 PM
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Working on a friends boat.....ran great last year. He put a new cap/rotor/wires on it....and it is now backfiring out of the exhaust on both sides at idle. Put the old cap/wires back on and it's still happening. Triple checked firing order....swapped the coil......we are stumped. Only thing hes changed since last year is the cap, rotor and wires.
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Maybe carb gummed up? From sitting in the off season?
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Just had the carbs rebuilt.
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Forgot to mention that.
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The backfire is rhythmic going from one side to the other...which point to ignition in my book.
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Check plugs
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When ever I get back firing like that . I pull the # 1 plug and and get it to blow.
It sounds like 180 out.
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Could also be a stuck valve. If all else fails pull the valves covers and make sure all the valves go up and down.
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Pulled the distributor... Checked the teeth on both sides. Set it at TDC....same thing.
I would say stuck valve as well but its back firing on both sides.
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Well you did say it has been sitting for a year??? Stranger things have happened!
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Could be 2 valves one on each head
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Re check plug wires / firing order, maybe some crossed plug wires
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I would run the valves real quick like. If you have to, back them all off a turn and see if it still pops.
Try the damp towel trick too, take a couple of damp shop towels and start to block off the carbs creating a rich condition.
Do you have the right carburetor base gaskets? Are the floats set right ?
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Is it possible that you guys didn't put the wires on right???
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Checked the firing order a million times...put in a brand new battery....been on the phone with Glenn (gt jets) and hes even stumped.
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Almost has to be a broken ground wire or something just wrong enough to allow it to run.
Have you tried removing the alternator belt?
I am grasping at everything I can on the way down.
GT
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What happens when you rev it up???
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Carbon build up on the heads??? Try a little water down the carb when reving it up. Like a tea spoon!
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Compression test and or leak down could verify or weed out a sticky valve.
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Compression test is 120 across the board
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Carbon build up on the heads??? Try a little water down the carb when reving it up. Like a tea spoon!
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LOL we used to pour like a liter down em....LOL :thumbup:
Ensure the pick up wires are not backwards......
Green from the 6A to the black/purple and purple to the black/orange... Also too grounding the box is muy importante...
Just out loud for the listeners...
GT
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Maybe pulled the plug wires away from the boot?! Bad connection? Cap on right? Lol I'm just fishing here
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Are you guys running a 6al box???? If so try to disconnect it. I have herd of them going batty and doing shit ilike that.
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Check exhaust temps to see if you have a cooler cylinder. Will at least help you identify what cylinders are the problems.
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Are you guys running a 6al box???? If so try to disconnect it. I have herd of them going batty and doing shit ilike that.
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Maybe change the rpm chip as a test.
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Perhaps a few lazy lifters since she's been sittin?
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Brad does it clean up at higher rpm's?
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Brad does it clean up at higher rpm's?
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Nope.
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Nope.
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. Just having the carb rebuilt sounds kind of fishy.
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. Just having the carb rebuilt sounds kind of fishy.
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Sort of kept trying to go down that road. ...
I think so too.
I'm thinking stupid lean somewhere.
GT
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Sort of kept trying to go down that road. ...
I think so too.
I'm thinking stupid lean somewhere.
GT
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. That's what it sounds like I would have the carb rebuilder have another go at it or find a new one.
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. That's what it sounds like I would have the carb rebuilder have another go at it or find a new one.
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There are two on a tunnel ram. Twice the opportunity for a slight boo boo.
GT
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The thing is that the backfire isn't a lean pop. It's a loud bang with 6" of flame shooting out. To me thats unburnt fuel getting into the header and burning.
The other thing is that its rhythmic. If I wasn't standing in front of it and checked the firing order maybe 5-6 times myself, I would bet it was a crossed plug wire, but its not.
Hal is bringing over a ready-to-run distributor today and they are gunna give it a go. If it still does it after that, I'm starting to wonder if the timing chain went bad.
Also, its a MSD 6a box, no rev chip in it.
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The thing is that the backfire isn't a lean pop. It's a loud bang with 6" of flame shooting out. To me thats unburnt fuel getting into the header and burning.
The other thing is that its rhythmic. If I wasn't standing in front of it and checked the firing order maybe 5-6 times myself, I would bet it was a crossed plug wire, but its not.
Hal is bringing over a ready-to-run distributor today and they are gunna give it a go. If it still does it after that, I'm starting to wonder if the timing chain went bad.
Also, its a MSD 6a box, no rev chip in it.
So the grounds were good and the pickup wires didn't get reversed?
I was sure that was a possibility.
It could be cross talking, but with two different caps, rotors and wires. It sort of all but eliminates it.
I would eliminate fuel stuff first. But trying the distributor cannot hurt.
GT
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Is an hei distributor make sure the metal ground strap is in the cap, I've seen those get left out.
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Is it possibly the swapped firing order? I forget what cylinders they swap but maybe thats it. Or is it jumping spark. In the wires?
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The swap is 4 & 7
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Thanks for the help but as stated the firing order has been checked a dozen times.
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Ok wasnt sure if maybe it was forgotten that it was swapped
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This Fukker running yet? Lol
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I got my money on some bent pushrods 👍
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Not yet we will be working on it again tonite so fingers crossed
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Popping out exhaust, cyl is firing with exhaust valve partially open. Pull one plug wire at a time when the popping stops you will know what cylinders are causing the problem. Sounds like incorrect firing order.
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Popping out exhaust, cyl is firing with exhaust valve partially open. Pull one plug wire at a time when the popping stops you will know what cylinders are causing the problem. Sounds like incorrect firing order.
not trying to be rude, but we checked the firing order a million times as stated above.
If I had not even checked it myself several times, I would agree with you.
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could there be moister in the distributor or a cross feed between wires?
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Still doing it with a new distributer. Checking float levels now
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I got my money on some bent pushrods 👍
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I have to agree or a couple stuck valves. Seen this a couple times. Has there been valve covers pulled yet??
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X2 on pulling the valve covers.
Could you put a timing light on each wire to verify each cylinder is consistently firing?
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Did the plugs get checked?
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I think we got it :)
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I think we got it :)
spill the fukkin beans! this is killing me!
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Dizzy a tooth off and adjusted floats.
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You heading to the lake for some evening testing?
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Dizzy a tooth off and adjusted floats.
I call BS on the dizzy being a tooth off. That doesn't even make a difference - no such thing lol - and even if it was, the dizzy never came out between last October (when it ran great) until last night after it was already popping.
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Hmm didn't you stab it in there last night there b-rad????
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Hmm didn't you stab it in there last night there b-rad????
There is no such thing about the dizzy being a tooth off. It just changes the position of #1. Even then, when I checked the timing, after I stabbed it, it was dead on. Your theory is invalid. :screwy: ;)
and like I said, it was popping before then. and that 'stab' was the same one that it was running on back in October.
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Lol. We're not sure could have been the floats but whatever it was it's better now
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Hmm didn't you stab it in there last night there b-rad????
. Good to see you all picking on the Ford guy.
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Hmm didn't you stab it in there last night there b-rad????
Anyone else see it? Lol
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Hmmmm.
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. Good to see you all picking on the Ford guy.
He must have as stabbed it in the front of the engine.
Just kidding brotherman.
Peace
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#1 is on the other side of the engine?
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Okay, I'll shut up now
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Okay, I'll shut up now
No, please, go on.
;D
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Hmm didn't you stab it in there last night there b-rad????
That right there looks like someones new quote to add to their profile! lol
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That right there looks like someones new quote to add to their profile! lol
I knew I was not the only one lmao.
GT
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