Idle question
 

Current Setup: 540 ci Naturally aspired 9.2:1 comp.. Aluminum Heads.
Cam duration is 233in 237ex lift is 600in and 580ex. 112ls.
850 Sea Daemon worked over by Nickerson
Ignition is MSN Distributor p/n 83606 ready to run hooked into an MSD digital 6 plus box p/n 6520.
The ignition timing is locked out at 34*

Boat runs great..
The boat idles at 900 to 950, and in gear drops to 600-650.
Is this normal? Seems like a large drop to me???
I have tried over and over to adjust the idle mixture screws, ect.
The shifting seems a little “rough”.. nothing major.. and no “issues” have arisen.. however, I am not a fan of the banging into gear.. (even though this is a slight bang)

Any thoughts? Is this normal??

One thing I have thought of; The MSD pn 6520 has a pink wire. When juiced with 12V, this wire will tell the box to “pull” timing out of the motor. I can pull as much as 10*.
So, in neutral, I would have 12v going to the box, making the timing 24* instead of 34*. Once shifted, cut the voltage, jumping the timing back to the locked out 34*.
This should, in effect, lower my neutral RPM’s by 100 (maybe??? Perhaps??) and also raise my RPM’s once shifted into gear???

Thoughts?? Other options?

John

Re: Idle question
 

MINE DOES THE SAME THING -THE BANGING WHEN I SHIFT. I IDLE AT 1000 AND WHEN IN GEAR DROPS TO 600 AND ACTS LIKE IT WANTS TO DIE. I HAVE NOT BEEN ABLE TO FIX THE PROBLEM WITH THE IDLE SCREWS ON A HOLLEY 750

Re: Idle question
 

If you can idle the engine down to 800-850 out of gear and keep it at 550 or so in gear would help. Very normal what your experiencing though. Do not pull timing out, this will hurt you. I run most of my engines locked out. They idle cleaner and shift into gear better with more timing in them.

Re: Idle question
 

My 540s act the same when when I first start them. They are really cold blooded, but after they are run for awhile, they are will shift at 600 without dying.

Re: Idle question
 

Do you run a start retard as well??? I have turned on the start retard feature of the digital 6 box..so.. anything below 500 rpm would trigger the box to pull 20* out… have to keep that in mind as well.. maybe I should turn it off??

Also, can/do you adjust any carb settings for this? Should I continue to play with the idle mixture screws???
Sounds like this issue is normal for performance motors

Re: Idle question
 

When tiring to get the best idle, do you adjust the idle mixture screws with a vacuum gauge? Do this at idle, or, in gear tied to a dock?
What about adjusting the rear butterflies? This should allow air into the mixture, but no fuel right? This would increase the idle, and also allow me to close up the front butterflies?
Is there a trick to getting the “best” idle in and out of gear??

I guess what I am trying to figure out is: Why do I have almost 350 to 400 RPM drop when I put the boat in gear???? And how can I fix that???

Re: Idle question
 

Start with both the primary and secondary throttle plates open the same amount. The idle mixture screws start @ 1 1/2 turns out from seated. Get your idle speed @ 850-900 with engine warmed up. I do have set boats up with them tied tight to dock. This is a very good way of dialing in the idle mixture screws. Most of the tuning is done by experience, a vacuum gauge is not needed and will not help you.I get the boat to idle in gear tired to the dock without stalling.

Re: Idle question
 

I thought the start retard on the MSD box was wierd to the starter and only pulls 20 out what activated by the starter.As soon as the started is released it advances, not related to rpm???????

As Dean I lock out all my high perf motors, the idle is
a lot better

Re: Idle question
 

Rob,
This is correct about the retard. I don't even use that on 15.1:1 compression engines. And locking the timing sure makes em' sound good !

Re: Idle question
 

The MSD Digital 6+ does offer a start retard feature.
When set and during cranking, the timing will be retarded 20 degrees until the engine reaches 800 RPM when it returns to the mechanical setting (in your case, 34 degrees).
When the engine speed drops below 500 RPM, the start retard feature is reactivated.
I have this box and do not use the start retard. I also run 33-34 degrees locked.

Re: Idle question
 

Ran a very similar setup to yours last year and yes, that was normal for me. The idle drop is hard to get out but as stated earlier, is quite normal for that cam. If you are getting a bang at shift it won't hurt, mine has done it for years and years. It is part of the equation when you build over stock and especially with any kind of cam. I'm getting a 600-800 RPM drop now that I've added a blower, that's even harder to deal with. PS- don't take timing away. Add it if you can, it will help a bit.

Re: Idle question
 

Thanks for the advice.. Just got done, tuning yet again..
double checked the timing. it was closer to 38.. I never did check it last week after I added the 6+ box.. Got it at 34 now.
Also, got the carb as best as I can get it.. idle is 650 in gear, 950-1000 out.. Sounds like this is normal, and the best it will get.

RLW, why do you not use the start retard? Seems to me like a win-win situation??? I have had it turned on for a week now, no issues with it.. Curious

Thanks again

John

Re: Idle question
 

John,
I have experimented with the start retard and without it. It doesn't seem to make any difference, most of the time. There has been a couple times where I would get that slow "over the hump" like start but, it has been far and few between. I actually played with it today. I just got done installing a new harmonic damper and wanted to run it in the driveway before tomorrows boating excursion. I initially started with the -20 degree feature.
I started the engine about four times using it. It started fine and idled fine.
I deactivated the start retard and it also started and idled fine.
I always thought the Start Retard was to provide easier starting of high compression engines.
Russ

Re: Idle question
 

John just FYI, I run a very similar cam duration (@.050") numbers just like you although @.050" duration numbers don't tell you everything about a cam. These cams are used in my 565cid engines, 9.5 cr, aluminun 315cc heads, HP950 Holley w/4 corner idling, Crane HI-6M ignition box, MSD crank trigger, Autolite AR3934 spark plugs, 34* locked in timing and the engines will idle down as low as 550rpm in neutral if I want....but I usually keep them around 700rpm or so. Dropping them in gear is a nice, easy event at that RPM and will see 500rpm in gear if I choose. Cranking compression will show about 185-190 lbs on the gauge. I use a jig that retards the timing down from 34* to about 16* or so when starters are cranking. I have run at idle speeds in "no wake" zones on several occasions for over an hour at a time without any load-up---no load-up ever!