351 running rough

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Ok so my engine is still running rough no improvement and I have narrowed it down a little. I think the timing/distributor is checking out, I have either replaced or checked everything I could and it says its in time. The only thing I havent checked is the coil as I am not sure what to look for.

I think the whole issue may have been and still is water in the carb. I ran about 4 gallons of clean gas with seafoam through it and no improvement. I took these pictures last night right after running. It looks like water is still condensated in the secondary throttle plates. What do you guys think I should do? Does that look like water to anyone else?

Also the jet by my thumb in the one picture is putting out a solid stream while at an idle and the jet on the other side is just dripping. Could water cause that issue? or has the water created other problems.

its just dirt. I have not been to the lake for over a month as the boat hasnt been running right. That was after idling in the garage for 10 minutes.

What do you think about the different amounts of fuel coming out of the sprayers? This carb was rebuilt 50 hours ago and ran fine.

I have been running out of a gas can straight into the fuel pump. I am trying to get it running right before I go through the trouble of draining the fuel tank etc.

What about the coil, if it was going bad would it run rough (miss) and backfire? I thought the ballast resistor was supposed to reduce voltage but I am getting 12 volts on either side of it.

Jllogan wrote: ... ...also the jet by my thumb in the one picture is putting out a solid stream while at an idle and the jet on the other side is just dripping. Could water cause that issue? or has the water created other problems.

I think it's possible to see condensation around your carb barrels because the vacuum around that area causes the air to cool and any moisture can get dropped out.

As far as one yet spurting a lot and the other just dripping. I don't think they're really supposed to be doing anything at all when at idle. The idle circuit, which discharges underneath the butterflies is supposed to take care of everything.

Dripping might be possible, but I'd say spurting is definitely wrong. Of course, your accelerator pump should spurt, but only as you are revving the throttle, not when idling.

Sounds like you could be due for a rebuild or replace on your carb. Not sure if water would cause the issue or not though.

Not sure on the coil thing.

maybe, Ill run it and take some videos/pics tonight and post for a diagnosis.

not the idle adjustment screws on the bowl but the throttle idle screw.

I have the new plastic floats which are supposed to be bulletproof so I never changed them.

There's a piece inside the bowl that's replaceable, right? The needle and seat I think.

Bri892001 wrote: There's a piece inside the bowl that's replaceable, right? The needle and seat I think.

You are right, I didnt replace that on the rebuild either.

kapla wrote: where´s 79nautique? he is the one for this tail chasing threads!

Yeah, he is missed

He had a lot of good knowledge. He may have insulted the heck out of you while he was explaining something to you, but at least he would explain it.

are the air/fuel screws working right? if you close them all the way the engine stumbles?

well it stumbles to start with. Ill screw them in all the way and see if there is a change.

I am thinking that by me adjusting the throttle linkage/idle is why its squirting in gas. By screwing it down its the equivalent of throttling up. There is no dripping after I shut it off thats what makes me think the floats are ok.

Who knows Ill test a few more things tonight and see what I come up with.

Ok so the tail chasing continues. I think there were and are a few things wrong with the engine. Tonight I tested the plug/plug wires with one of those inline spark testers and the spark on pistons 2,3,6 and 7 was very weak. The light was barely on and it was very bright on 1,4,5 and 8. Also I noticed that those are the first four and last four in the firing order (any correlation? what could cause that?). The cap is new but maybe it was weak or defective so it didnt last very long. I have had my hand on it quite a bit and never got shocked though.

So I thought the plugs might be fouled and I replaced them and the rough running improved. Now it was idleing much faster (600 before plugs and 1100 after new plugs), so I lowered the throttle/idle adjustment and then had to reset the timing. I checked the advance and it was reading 30 degrees at 2000 rpm which seems to be inline with what I understand it should be. So I am thinking the weak spark fouled the plugs. What could be causing weak spark on the 4 cylinders and good on the others? Could this be a bad coil or could that little light just be innacurate?

I agree to that the fact that it is strange but it definitely has weak spark on half on the rotation. I have had that cap on and off several times, you would think it would be fit sometimes. Maybe I should see if I could wiggle it while its running. There is no chance the coil could be weak and just cant keep up with the spark or something. The other thing is the cap is new as of a few months ago so you wouldnt think that would be the issue.

Maybe the dizzy is worn or something, I had it out and had some people look at it and it seemed fine but maybe its not.

I tested as soon as I started the engine and it still read weak. I suppose though that if the mix was bad in those cylinders you would never get good spark because of too much gas. The carb appears to functioning properly or at least acceptably now. Its hard to really tell how it is running now until I drop it in the water. It may be ok for a while but if it keeps fouling plugs thats an issue.

Is there anyway to really isolate and test the spark from the dist?


Right now I am torn between carb issue or dizzy issue and I need to eliminate one. (in the back of my mind there is still a possible valve issue, but since its both sides of the engine I am ruling that out right now.)

Summit Racing has a new points dizzy for 189 or a new electronic for 269, do I need RH or LH rotation I always forget. I know skidim has them but they are more expensive. I would probably throw on a new mallory coil too (so it matches). I need a way to pinpoint the dizzy though before I drop 300 bucks.

This all sounds so familiar. I went through the same thing for an entire season. Plugs, points, condenser, cap, rotor, wires, rebuilt carb,drained all old gas, fuel filter, fuel separator, finally decided it had to be carberation and took carb back into carb shop and had it gone through again. Still the same lag, wouldn't idle right, quit at low speeds. Talked to the guys at skidim about all the bad gas we have here in MN and decided to bite the bullet and buy a new carb. Bolted it on and the Nautique has never run better. I think the small orifices in low speed get corroded and if the rebuilder doesn't soak it long enough to get those cleaned out, it doesn't fix the issue. Good luck. It's pretty frustrating.