Could still be fuel. You could have a piece of dirt in one of the needle vlaves in the carb. Backfiring in the exhaust could be a sign of a too rich condition. Did you completely drain the fuel system over the winter or at least put a ton of fuel stabilizer in it? The fuel of today is junk!

Is it a consistant condition where it backfires every firing cycle?

What about your timing??

Checked timing- it is set @ 10 degrees advanced. Starts right up, runs good- just the backfire at idle. It is not consistant- or it doesn't seem to be. Cleaned the carb last night( thought it might be a vacuum leak, or plugged jet, no go.) Switched carb from other engine, ruled that out. I am going to buy a cap and rotor today, I will let you guys know what happens.

Thanks for all the input-

Scott

Is that the mark IV motor or the gen 6 motor:evilb: If it the mark IV then you might need to re-adjust the valves.

Sounds like you have a valve problem. I had the same symptoms when I was breaking rocker studs and also when I had a lifter gain lash and didn't pump up. Pull spark plug wires one at a time until it stops popping to narrow it down to which cylinder bank is having the problem. You might just need to redo the rocker arm adjustment. I forget if you have hydraulic flat tappet or hydraulic roller. If not broke in properly with high moly content additives, I have seen flat tappets wipe out a cam lobe.
Jason

Well- putting on the cap and rotor helped quite a bit- but it still does it very occasionally at a low idle.(800rpm) I guess it could be a valve but I have hydraulic rollers- and it runs really good at everything above 800 rpm. If I set the idle at 1000 it never pops- kind of weird. I'm kind of leaning towards 502's thinking, because the gas is old- so I am going to mix in some race gas when I fill it up. One more question- should you use throttle return springs, and if you do, is there a trick setup out there I should look at? Thanks guys for all your input-:ernaehrung004:

The Gen 5- its been so long I can't remember!!!

Sounds more like u have a flat spot on the cam ,,and the intake valve gets hung up @ idle and at higher RPM u can't feel it because it turns to fast !!!!:eek:

But if that was the case- wouldn't it happen all the time? I mean it pops once every 3 or 4 minutes-

Thats it...I thought you had a real problem:ernaehrung004:

I have return springs on mine...Nothing fancy...just in case.

Yes,,,could be , all depends on the valve seat ,push rods ,ect. !!

If the valve hangs up it doesn't need to be at every turn of the cam !!:party-smiley-004:

But hey ,,,that's what i think it is ,,,don't beat me to it !!!

And sorry ,because i know thats not what u want to hear !

I would not run like that anymore until u have it figured out . Faster then u think it gets hung up more ( if this is the problem ) and then u slam it on the piston ,valve break's off and ruins the complete block ?!
I would check it !!
Its not that much work !!!

Are your spark plug wires in good condition? How are they routed? It could be a cross fire between wires. But hey, I don't have a boat..............

Then it would do it all over the RPM range !!

Is this only at idle? Has the engine only been run at idle with only momentary lapses into 3-4K rpm?

Thats what he said !

I had the same thing happen with a 400 sbc. I did'nt break anything but I had a "pop" out of #6 cylinder. The pop at idle and also occurred higher up in the rpm range but was on decelleration after I got on it and let off. I readjusted the valves with the engine running and found more power out of #6 and #8 cylinder. The pop went away.

Its not the valves. I pulled the valve cover on the right side and then remembered Gen V are non adjustable. I am pulling the plugs next. I will keep you guys in the loop-

It was a bad plug on #6. Changed all the plugs just to be sure and its good to go!!! Thanks everyone for all the input. Hopefully if the weather cooperates water test this week- I will take pics and video:drink:

:ernaehrung004:

Glad to hear it was that simple. I look forward to test results. Scottie have you ever had this boat out? Before you started the rebuild?

Damn,,,did not think its that easy !!!!:eek:
Glad for you though.
:ernaehrung004:


HAVE FUN !!!!!!!!!!

It was the spark plug wires!!!! I knew it!:party-smiley-048:

No, it has never seen water since I have owned it- which is coming up on 5 years now. I have spent all day working on the wiring- as with everything else I end up redoing 98% of the work(its hard to get quality work anymore) getting really close.

Jaxx- it was a bad plug- not a wire! I have never seen a bad spark plug before- but that is what it was:ernaehrung004:

Scott- How was Havasu?? I couldn't afford to come this year:(

I was joking!!!!!!! What type of ignition are you running?

Havasu was outstanding!! Thursday night's street party was the place to be- a lot of new boats to check out. Some standouts were the new Z044 MTI and Skater/DCB and Eliminator all had huge presence.Got to hang out in the channel most of Friday in a killer Nordic Thor(Thanks Nordic!!) and by the look of things you would never know a depression was going on. In my opinion the coolest boat there was the Black and silver M35 widebody by DCB- as soon as I rob a bank I'm getting one!! Missed you this year Eddie!! Maybe next year-:evilb::evilb:

I never know when you Law Enforcement guys are joking and when you are serious- I mean just the other day I had one tell me I was way over the speed limit and I thought he was joking- man was I wrong:drink:

I am just running a Pertronix Flame thrower coil and a Mallory Unilite for my ignition- nothing special.

If you were in the peoples republic of kalifornia I could help you with your speed issues, but you're in WA so you are on your own!!!!:evilb:

I asked about the ignition because "back in the day" with old points style ignitions fouled plugs could be common on performance motors, but with modern high energy stuff not so much so. I'm glad it was just a plug. I hope it didnt delay you much in trying to get that boat in the water.:ernaehrung004:

Scottie -- Glad to hear it was something simple, I also thought valves at one point but I just couldn't bring myself to actually suggesting it. Let's get that thing in the water! I want to see what she can do! Good luck man! :ernaehrung004:

Well- got her in the water tonight- engines run perfect, got the shifter backwards(it was a 50/50 shot) and discovered I have a leak from the rear of the starboard engine:mad: I'm thinking it might be the bellows- or the blocks for the hydraulic lines. Its definately coming from the inner bellow area. Ideas anyone??

At least its fresh water!! Boat looks great in the water. Check your exhaust clamps...mine were leaking when I launched mine the first time. If its real low then it could be the things you suggested. Hopefully it isin't the transom assembly.

Thanks Eddie- it does look a lot better in the water. I could see where it was coming in from- it was definately the shaft- so I will reseal the hydraulic block(real good possibility) and check out the bellows. Hopefully it isn't the transom assembly:eek:

Thats what they make bilge pumps for! :evilb: JK

The boat looks awesome scott. In regards to the leak, definetly check the shaft bellow. I just replaced mine and twice almost tightned the clamp down with the lip in the bellow not fully into the groove. Did you actully get to bring her on plane or did you keep it close to the dock?

No- I never took it off the trailer- it was getting late and all I wanted to do was see if it was going to leak. Hopefully I will be able to get it out and play with it later this week, its not leaking that bad:drink:

Still ,,any water in the bellow will cause the bearing to rust !!!!

FIX IT !!!!!!
Not that hard !:ernaehrung004:

It's becasue she's been out of the water so long she needs to swell up! :D

Looks good!

LOL:ernaehrung004:

100000 starving comedians in the world and you guys are trying to be one:drink:

I pulled the hydraulic blocks out- the gasket was good but there was a lot of water in there- so I am going to reseal it. Should I run a bid of RTV around the transom for good measure? I RTV's the sh*t out of the corks and transom plates when I put them back together. I also checked the bellows and they look good- so if resealing the blocks doesn't cure the leak it must be in the transom plate.

I also worked on the rear hatch cover- got it cut, just need to figure out hinges and measure for the ram- hopefully tonight I will have some more photos.:food-smiley-007:

[QUOTE=scottie150;2864455]100000 starving comedians in the world and you guys are trying to be one:drink:

I attempt to mask my ignorance with poor comedic skills :lolhit:

I Just Read This Hole Post And I Think You Are Crazy But The Boat Looks Awesome And Your Really Close So Stick With It