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olds 455 running poorly need help (long)

J

josh_2562

Well-known member
I just got this boat 3 days ago. The boat had been sitting for around 5 years with out running. This is every thing that I have done to it

changed the carb to a new Qjet that had been sitting in the shed for a year
New plugs cap rotor
new fuel filter oil and filter
cleaned gas tank out the guy said he had drained gas before parking it and he had put new gas in it. I drained that gas out (looked like tea) and put new gas in it.

I got the engine running good would start right and idle and spin a 67" prop up to 2900rpms at 1/4 throttle (he had a 80"x 34 pith wood prop on it but it was bad from sitting)
I went to take the boat for a ride but it was to wind so I didn't put the boat in the water, on the way back home it started raining really hard.I didn't have the air breather on the carb. when I got home I covered the carb.
The next day I tryed to start it and took awhile to get it running and now it only running on 3 cylinders. 2 on one side and 1 on the other. I checked this by putting water on the header while it was running.
I have changed the plugs again.Made sure that there was no water in the cap. I"m running off a different gas tank now also. It running rich and back fireing out the exhaust. I don't know what else to check. also It seems to run a little better if I take the vacuum line off the distributor and plug the hose. Thanks for any help Josh
 
Well honestly ALL of your description doesn't add up to me, but I think I have a few ideas why. But before we get into that, entertain me if you don't mind.

Is this problem at idle only, or does it run better as the RPM come up? Second; Look at your intake manifold. Are 4 of the cylinders that aren't firing one level of the intake manifold? If you don't know what I mean....The intake I'm assuming is a dual plane. It has an upper-level 4 runners and a lower level 4 runners that all snake amongst themselves sporadically from side to side. If the pipes that are cold coincide with let's say all the tall runners or all the low runners.

My first instinct is that the problem is mainly at idle and is 4 runners all of one level of the dual plane. If so, one side of the carburetor is plugged internally from crap it got in it.

Not saying that's the problem, but that's what my gut's tellin me.

Felber
 
It does not backfire at idle just when I give it gas.it does not get any better as I give it gas. I think the cylinder that have the cold pipes are geting gas. When I pull the plug they smell like gas and are wet.But I will check to see if they are all on the same plane.

I even took the valve covers off to see it it has some stuck valves. there all good. I have a good 750 edelbrock carb that I'm going to put on and try it.with the qjet it was running a little rich even before it start running like crap. Thanks for the help Josh
 
Well obviously it's just killing the plugs. It's either because the carb is dumping raw fuel or you have an ignition problem. I seriously doubt the ignition would pick 3 and not the other 5 though. I'd check all 8 wires for spark, then tackle the carburetor issue. I'd also let the cylinders air out before putin new plugs in it. If there's a lot of fuel in those holes, they're just gonna kill another set of plugs.

Felber
 
I think you right about ignition. I changed the plug wire around to see if the problem went with them. I check to see if the one not fire are on the same plan and I think they are. Do you think one side of the carb could be dumping to much fuel on that side. I didn't let it air out before I put the new plugs so they may be fouled to.Thanks for the help
 
could also be a vacuum leak on one side of the manifold. It would be a big one to cause all the cyl's to not fire on one side of the carb but you could also check that out.
Tim
 
Thanks for the help but I have check for vacuum leaks. It get gas to the 4 cylinder but I think its getting to much. I pulled the plugs out and sat them on top of the engine and turned it over and the all had fire. I think the qjet use metering rod could some thing got in there not letting one close like it should? I have never messed with the q jet carbs.I'm going to let the cylinder air out and clean the plugs up and try that. if that don't work .I will be changing the carb tomorrow, after I put a new starter on it :evil: Its a good thing I only paid $800 for this boat. Thanks for all the help Josh
 
You have good thinking on the metering rods but Q-Jets have both pairs (primary and secondary) metering rods linked together. So the only way one side could have an issue is if a metering rod broke. But it could be a case of a leaky well plug under the base or a plugged airbleed. But the hard part there, is the fact that it ran great, then ran like crap when you started it the next morning, which throws away the metering rod or airbleed theory. It really just kinda points to a flooding situation (needle and seat) or possibly the well plug I mentioned (I always JB weld them when I rebuild QJets for this reason).

Keep us updated as to what ya find...You may just want to pull the carb and look down into the manifold plenum to confirm the amount of fuel being dumped and where....And if you change carbs, I'd overdesign my fuel filters so it doesn't trash another one.

Felber
 
well I really don't know how I fixed it but I got it running good again.I put new plugs and changed the carb. put some sea foam in with a vacuum line.It now has no blow by and runs great. thanks for the help FELBER632, bravo1218
 
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