Ignition Timing and carb set-up

[CheckmateFever]

Ok engine guru's, as i've been whining about for over a month now, i lost speed and RPM's this year after an exhuast conversion was done. I was talking to a freind of mine tonight, fellow land hotrodder, about timing. I remembered that last year i had my boat tuned up and the guy told me the timing was off and he set the timing back to the "by the book" setting of 8 degrees BTD, it was at 11 or 12 degrees before. It did seem to hurt my performance slightly last year, but not really that noticable. My buddy said that advancing the timing could help my RPM situation big time, as much as 300-500 rpms. What do you guy's think, should i bump the timing back up 12 degrees or is it to much advance? My buddy also said i have to adjust the fuel mixture settings and maybe even go up a jet size to make up for the increase exhuast flow, will adjusting the mixtures alone help and or fix my RPM loss?? What jets should i run in the carb if i do have to change out the jets?? I know from being a car guy that timing makes a big diff in how an engine runs and factory settings are usaully very conservative for economy, is true for my 350? Thanks for any help!

 

[Big Dave]

I would go back to 12 and try it..... make sure it is not getting hot or pinging.
I always run premium in mine so I can have the timing a little higher..
old school way was to advance until it pings or the starter drags and back it off until those things go away
your module only has 24 or 26 deg total advance, and there is not any in the distributor like a car would be...
I think the v6 module is the 26 degree,

 

[Big Dave]

I think more of your drop in rpm is due to increased prop diameter, but the timing will make a lot of difference too
combine all of those things at one time, WOW major change and no way to tell what caused it
The glm aluminum manifolds are supposed to flow more air than stock merc in addition to being lighter
thru hull should flow more than thru prop, with no other changes, you should have seen an increase in top end
If you are still running the factory carb, It should have been rich enough to compensate for the exh changes.
if that is not the oem carb, (ie...rebuilt or one off of a car)there is a good possibility it is jetted wrong.

 

[vinny p.]

Dont get to engulfed on what your base timing is. Other than idle quality, it is not important. Your concern should be total timing advance. What is the total timing after the advance has kicked in? Dont rely on what your module is supposed to give you, check the timing with a good quality advance light. It should be between 32* and 36*. As for you mixture, how are the plugs? After you are sure of your timing setting, do a high speed plug check.

 

[kct11]

vinny beat me to it. check your timing at about 3500 rpm, all the advace should be in by then. set it 36 degrees and give it a try. you can check base timing after that for referance.

 

[Big Dave]

you guys are up way too early for me to compete with.....

 

[Taz]

My 92 454 Mag book is 8 BTDC but runs best at 12 before or 36 full advance. I found this sweet spot like Big Dave said advance till there is a slight ping at WOT then turn back till it goes away. Then check starter if it soins free then your good.

Hey does anyone know why the starter gets tight when the advance is to High?

Checking plugs is the best way to check carb, but a quicker spot check is to look for carbon stains on transum. Clean the transum and then do a high speed run or two then check for carbon on the transom. I like to run a little fat so a little carbon on the transom is what I look for. Try it.

 

[bigsbetter]

The starter gets "tight" as you're calling it because the timing is advance so much that it is actually fireing too early and trying to push the pistons back down the cylinder before they reach TDC. The combustion is happening too early and the engine can't turn it over if the starters trying to spin it one way but the pistons are being forced the other way.

 

[Big Dave]

easiest way to tell if it is the timing or other issue, just pull the coil wire out of the cap and try again to start..... if it turns over easy with no drag, it is ignition