Ski Boat Forum

General Category => General American Skier Discussions => Topic started by: DanB on October 07, 2015, 05:09:40 AM

Title: Idle mixture
Post by: DanB on October 07, 2015, 05:09:40 AM
I have an '84 Skier with the Commander engine. I just put a new fuel pump and remanufactured carb on it. I was wanting to know what kind of max RPM I should be able to get just by adjusting idle mixture screws on carb? I heard there wasn't a good place to be able to get a vacuum reading off of this intake. I am trying to get max RPM running off of bucket on trailer? Once that is achieved I adjust "curb" idle on water in gear? So far I am only getting just over 750 RPM
Title: Re: Idle mixture
Post by: backfoot100 on October 08, 2015, 05:32:04 AM
Set the base timing and idle RPM on the trailer. Then take it down to the lake and put it in the water, warmed up and in gear, idling so the engine is loaded.

When setting the idle mixture, turn the screws all the way in until they seat (gently) and back out 1-1.5 turns as abase point. Turning each screw back in one at a time should kill the engine or almost kill it. Then back out to the highest RPM or highest vacuum. The specific RPM is irrelevant but it won't be much higher than the base idle RPM. Then do the other side the same way. Then readjust the base idle RPM screw on the throttle plate back to 600-650RPM. The end result should have both screws turned out the same amount at about 1-1.5 turns.
You might be going back and redoing the process over a few times before its dialed in but that's not unusual. That's how I've done it for years without issue. Make sure you take the timing light along just to verify everything is spot on.

The biggest problem that most have is that they do it with the engine unloaded and then wonder why they get an off idle stumble out on the water. Just like you're trying to do on the trailer. As long as it idles smoothly with the base timing set don't worry about the idle mixture until you get it on the water.

Title: Re: Idle mixture
Post by: Midskier on October 08, 2015, 12:56:42 PM
 Dan B - if you purchased a quality reman - your idle screws should be pretty close to set - you will just need to adjust the idle stop screw - in gear should be 600-650ish rpm - which might be 750-900 rpm in neutral - I think this is what your looking for

as Eddie already explained the idle mix screw adjustment - if correct there should be -0- stumble off idle - and restarts (warm or hot) should not require a throttle pump

also seating the screws GENTLY - because they are threaded through a cork bushing

I just did this on a commander today  :)

Dan T
Title: Re: Idle mixture
Post by: DanB on October 08, 2015, 06:21:25 PM
Had the boat out on the water today. Starting was consistent, but I had a bit of a stumble when I would accelerate. Thought it was good enough to try and ski behind. NOT. It would just stall everytime we tried to pull  a skier up. What it ends up being is the timing is all out of whack. It doesn't advance smoothly or return to base timing. Its a Pertronix distributor and there is some rust on and around the weights and springs. So my new question is what to use to clean and/or lubricate the weights and springs? How much do I need to disassemble?

Thanks so much for all the input
Title: Re: Idle mixture
Post by: backfoot100 on October 09, 2015, 05:41:31 AM
I'll give you kudo's for your troubleshooting abilities. Sounds like you have some engine mechanical aptitude. Nicely done.

That would be the stock distributor with a Pertronix conversion. You would just pull out the conversion plate to get at the weights and springs. Remove, clean, reinstall.
I've soaked in a carb cleaner solution to clean then up but brake cleaner or any other similar chemical would work fine. The biggest thing is getting the dizzy base cleaned out as well as the weights and springs. I've taken a shop rag and shrouded the top of the dizzy (to prevent overspray all over the place) and sprayed brake cleaner in there and then wipe it out good. Some compressed air if available is also handy (again shrouding with the shop rag). I've used a light oil like WD-40 or a light white lithium spray to lubricate. They should move nice and smooth when you're done. You'll obviously have to retime when done.

Just FYI, I would be very skeptical of that Pertronix unit. I've seen them fail on more than a few occasions from several friends of mine. I know of a few who even went back to points and never looked back again. I'm of the mindset that you either put in a complete electronic dizzy like an MSD or a DUI or leave the points in. I've just seen way too many issues with the conversion units, but that's just me. I also know of a lot of guys who have the Pertronix and love it. Just fair warning for future reference.

Another thing to verify is that the accelerator pump lever adjustment has no play in it. Standard Holley instructions say that there should be like a .015" gap between the pump lever and the pump diaphragm itself. This is BS. Snug it up just enough so there isn't any play at all. Even the very slightest touching of the throttle should start a pump shot from the pump nozzles. This can be done without removing the carb. Make sure that it doesn't get over tightened so the pump lever bottoms out the pump diaphragm on a full pump shot. As long as you adjust it just enough to take any slop out of it you'll be fine.

Keep us updated on the progress.
Title: Re: Idle mixture
Post by: Midskier on October 09, 2015, 08:53:10 AM
Dan B - I responded to your email b4 I read Eddies post .......... could have saved some typing :)

we both basically told you the same thing

Dan T
Title: Re: Idle mixture
Post by: DanB on October 09, 2015, 06:33:18 PM
I believe the Pertronix unit that is in my boat is a complete conversion. It is advertised as their Marine Billet Distributor. I bought a new set of weights w/ springs today. Instructions said remove springs then e -clips....of course the weights are different and my distributor doesn't even use e-clips. Cleaned up the old and will try the different springs to see what/if any of it works for me. Will be going back to Summit Racing for the third time trying to get the right plug wires. This time I will look at the wires before I get home.

Will check the accelerator pump tomorrow when I see if the advance is any better

Thanks
Title: Re: Idle mixture
Post by: DanB on October 09, 2015, 06:43:01 PM
One more thing... Base timing around 8 deg., I get that. As RPM increases so does the advance,I get that. But how high should my advance go at WOT? How much is too much My distributor has the Igniter II
Title: Re: Idle mixture
Post by: backfoot100 on October 10, 2015, 07:29:56 AM
Depends if you have a Chevy or Ford.
Chevy's like a little more advance. It's not unusual to run 14-16 degrees BTDC for initial timing. Fords go much past 8-10 degrees and they have a hard time starting.

Same on total advance. My SBC is running at 38 degrees total. Fords usually don't like much more than 30-32 degrees. Either way the total advance should be in somewhere in the 2600-3K RPM range.
Title: Re: Idle mixture
Post by: Midskier on October 10, 2015, 09:12:16 AM
Dan B go to and study the pertronix web site or call pertronix - typical distributors have 20-24 degrees of advance find out what yours can do and add that to your base timing = total advance so if you base timing is 8 and your distributor only provides an additional 20 degrees your total would be 28 .......... and that's it .

at this point leave it there for now and get everything else dialed in - then go back and add a little more timing around 10-12 base and fords don't like to start because the there is not enough momentum from just the starter speed to over come the piston being driven backwards by too much advance.......... too much advance at too low speed and the motor will be "confused" and the crank won't be high enough to keep swinging in the correct direction and may be driven backwards during a few cylinder cycles, so we have to find the best compromise - of easy starting and WOT performance.  Eddie check John's boat - I wrote the base timing on the cap in black sharpie I'm guessing it was 16ish........ Dan B you're safe @ least to 10 - but keep it at 8 for now, get your weights and springs and carb dialed in

Dan T
Title: Re: Idle mixture
Post by: DanB on October 10, 2015, 11:34:03 AM
All I can say today is that my timing does not react consistently. Started with the medium springs in distributor and depending how hard I accelerated I got different amounts of advance. If you just gradually increase RPM the timing would stay at 8 deg well above 2000, you could hear the engine smooth out when advance finally kicked in. Hard acceleration and advance was quicker. Tried the smaller springs and was pretty much the same story, except after advancing it took much longer to go back to base timing.

This was all done while on trailer.
Title: Re: Idle mixture
Post by: backfoot100 on October 10, 2015, 02:22:25 PM
Your advance weights are sticking. They aren't cleaned up as well as they should be. I also don't understand why you put different springs in. We're the old ones broken? The new weights and/or springs are not same as the originals. Something is definitely not right.
The weights need to be able to move very easily when reassembled.
Title: Re: Idle mixture
Post by: DanB on October 10, 2015, 03:08:52 PM
I bought a kit from Summit with new Pertronix weights and three sets of springs. I thought weights would be the same,,,just NO rust. The three diff sets of springs are so you can tune the advance curve. So yes I agree that they must still be sticking and I am very close to turning the Pertronix into an anchor. That being said, I started to look at my new carb vs the old one I just took off. Old accel. pump nozzle was a 25 with an orange cam. The new  carb has a 31 with a pink cam

I will keep trying
Title: Re: Idle mixture
Post by: DanB on October 11, 2015, 11:00:25 AM
Took Backfoot's advice and got slop out of accelerator pump lever which helped some. Took orange cam off of old carb and put it on the new and hesitation, stumble is gone. Ha d the boat out on the lake today w/o a skier and it ran great. I don't think the dizzy is working at 100% but you wouldn't know it from the way it ran

Thanks for the help
Title: Re: Idle mixture
Post by: backfoot100 on October 11, 2015, 03:03:29 PM
The cam and pump nozzle are that far off from the original???? The carb that you got was indeed a marine unit? They're the same CFM?
Something just doesn't sound right.
Title: Re: Idle mixture
Post by: DanB on October 11, 2015, 04:31:15 PM
Yes both are marine carbs. Reman is 80319 from National Carbs. I would say I am getting very close to having it right. Almost wish I had never looked at the timing. Now I have to debate whether to do dizzy now or wait until Spring.

You have to remember that the only thing I have ever done with a 4 bbl before last week was take the flame arrester off.
Title: Re: Idle mixture
Post by: Midskier on October 12, 2015, 08:49:31 AM
DAn B - you're fast becoming the the new carb expert - you ordered the right part # - 600cfm angled inlet (by the way the chevy carb is exactly the same except it has side inlet) I installed the same one last week on a commander ford - set base timing #8 - (did not power time) she ran 4480 rpm 44.8mph on gps with 2 men onboard , it was turn key only having to adjust the idle stop screw - 780-810 idle
in gear idle was 610-640, idle mix screws were one turn out - one pump when cold to start - all other starts were key only no throttle - up to a half an hour later -
Title: Re: Idle mixture
Post by: rickturl on April 25, 2020, 06:32:42 PM
I wanted to revive this thread from 2015 because the ideas have been incredibly helpful, and because I am hoping midskier or someone else can solve my problem. I've done everything suggested in this thread so far, plus a whole lot more. In spite of that, my max speed is 32 mph and max engine rpm is 3400.

Boat: 1990 Volante with Indmar/Ford 351 engine - lake is at 5000' elevation.

Data Collected:
Parts changed so far:

Based on the posts in this thread, it seems I should be able to expect a top speed closer to 42 mph and a top engine RPM of ~4200. Is this a realistic expectation? At 5000'? What else should I be looking at?

Thank you all for your help.
Rick