Holley 4160 running rough after rebuild

Hi,

I have a '89 Ski Nautique, and the last time I ran the boat (about a year ago) it would stall if I rev'ed it (hit the throttle hard). When I started prepping the boat for the new season, I noticed that if I pumped the throttle, I wasn't getting any fuel from the squirter.

So I believe that the accelerator pump had failed (which is probably why it stalled when I hit the throttle). So I bought a marine renew kit (specific for my list number), and rebuilt the carb.

After refitting the carb, I set up the idle mixture. At first I tried the standard 1.5 turns out, but it wouldn't idle. Those first few starts took quite a lot of pumping the throttle and revving. It made a few small puffs out of the top of the carb while I was trying to get it started. Not sure if that can be considered a back fire? Is backfire just small puffs or a loud bang?

It idled better after turning the idle screws out to 2 turns in total - so I think that made the mixture richer.

First time out on the water, the boat fired up, and I idled out of the dock. When I accelerate and put the engine under load, is feels very under-powered, and is not very smooth. Even if I give it full throttle, if surges and feels weak. It does build up speed eventually, but is really down on power, and doesn't runs very smoothly.

The engine also stalled twice near the end of the day just while idling. Once when it stalled, I noticed a few bubbles in the inline glass fuel filter (between pump and carb). I do plan to remove this, as I understand it is not safe - was installed by previous owner). However, after re-starting, the bubbles were gone.

Any recommendations on what to look at?
- Vacuum leak - wouldn't that mostly affect idle?
- Blown power valve - could I have damaged the new power valve with the backfire when I initially started it?
- Could it be related to the secondaries? Maybe the vacuum diaphragm isn't actuating properly?
- Could something else have gone wrong with the rebuild of the carb?
- Could there be another problem - maybe fuel starvation somehow?

Any advise would be great

Thanks,
Greg

Thanks for the help :)

Yep, I just used the gasket in the kit. I'll check for vacuum leaks tomorrow.

Won't the vacuum leak mostly affect the idle? Or could I compensate for the vacuum leak at idle my adjusting the mixture screws, then at partial throttle, they no longer have effect?

I'll test both screws responsiveness...

I'm also going to check for any air leaks on the fuel lines from the tank all the way to the carb.

Greg_SA wrote: ... I still only starts properly at WOT.

One simple check here is to make sure your choke is opening as expected. Make sure you plugged the choke wiring back when you re-installed the carb.

The reason I mention that is that WOT will mechanically force the choke open, so, if that's the only way it starts, maybe the choke is too far closed the rest of the time.

Greg,
If a warm start requires opening the throttle up, then the common issue is a dripping carb when the engine is shut down. The gas is flooding the engine so when the throttle is opened, more air is delivered to the engine overcoming the flooding. How did you set the float levels when you rebuilt the carb?

Thanks for the feedback.

I don't see any fuel dripping into the carb when shut down. When I rebuilt the carb (about a month ago), I did check the float levels and they were fine.

I did also check the timing - it was way too advanced. So I set it back to 10 BTC, and set the idle to ~ 750 rpm, and set the idle mixture for maximum vacuum.

I took it out on the water this last weekend, and as soon as I engage drive, the revs drop significantly and it cuts. I had to increase idle to about 1000 rpm so that I could get it off the trailer.

Then when I gave throttle, it would bog down badly. I advanced the timing back to where it was previously (which is quite a bit more than factory spec), and it was a bit more stable, but still bogged and spluttered when taking off. If I give a lot more throttle, it overcomes the spluttering and then runs fine.

In neutral, it revs fine, and picks up instantly when I hit the throttle, and I can see the accelerator pump is doing its job.

The distributor cap looks fine, and it has Pertronix ignition module. Things look pretty dirty/rusty under the "points plate" though So I suspect you are correct, and the advance springs are probably stuck. I'll strip this and rebuild. Maybe that is why the boat only really runs when the timing is too advanced at idle? It is compensating for the lack of advance from the springs?

I was starting to wonder if the power valve that came with my kit was the wrong one? The old one was a 6.5. I didn;t check what was in the kit when I installed it. The kits seems to vary (could but 5.0 or even as low as 2.5). If it is a 2.5, could this also be causing issues?

Thanks,
Greg

Greg,
Get that mechanical advance moving free. Does your timing light have the advance feature?

I'll check the timing later today... I think the timing was somewhere around 20 BTC, but that was at around 1000 rpm.

I'll also check for vacuum leaks - I have a stethoscope or could use butane gas or some starter/carb spray.

I opened up the distributor, and the advance mechanism had some surface rust and was pretty dirty, but it was definitely not stuck. The weights move freely. I lubed it up anyway. The springs do provide resistance, but they are quite rusty. I think I'll replace them soon anyway, as they'll probably break one day. As far as I understand, it is quite difficult to source these springs?





Regarding the Pertronix - the timing looks stable with the timing light.

I have heard that the exact power valve is not that important, but I have also read other forum posts online about power valves causing the engine to run very rough off idle and stumbling/coughing, etc due to a very lean condition.

Greg_SA wrote: ...As far as I understand, it is quite difficult to source these springs? ...

Nautiqueparts still lists them:
http://www.nautiqueparts.com/distributorsprings.aspx

Greg_SA wrote: I just find it strange that once the stumbling passes, the boat runs fine.

Not that strange actually

Did you ever answer my inquiry about the idle mix screws being effective?

Either should be able to stall the boat out when closed.