Chevy 383 Stroker Timing Issue?

I just installed a fresh 383 stroker into my 21' Cruisers Inc. Got her running but been dealing with what we beleive to be a timing issue? The engine was built at a local very reliable shop and all parts are new. Chevy 350 block checked over, machined and set up for Marine crank, mild cam, stainless valves, roller rockers, rollered timing set, brand new cylinder heads etc etc.

I was told compression is 10:1 and a cylinder compression test shows 197psi on all eight holes.

Under load she seems to be stumbling and missing, initial timing was set at about 10' and total about 30'........she sounded good on land with just the hose hooked up but when put on the water she stumbled getting up on a plane and then the starboard exhaust rubber extension tube melted a hole in itself where it joins to the riser???

I have gone through the basics, double checked for TDC on the compression stroke, double checked firing order, triple checked plug wire routing, plug wires are a brand new MSD set, checked dist cap for cracks or carbon trails, dist is also brand new MSD marine pro-billet plug and play with MSD coil, no external module, it is built into the dist.

Tried changing the timing and all that happens is the stumbling appears at slightly different RPMs and there is some mis-fire knocking....

The dist came with two heavy advance springs, should I change them? If so, to what? Should I lock out the advance completely? There is no vacuum advance. I am running out of ideas and summer is coming!!! lol

Thanks for any help and/or suggestions. Jeremy

 

Sorry forgot, engine is carburated with a newer Holley 780cfm electric choke, new mechanical fuel pump so fuel supply does not seem to be an issue..........

 

If I read you correctly you said that it is stumbling under load and perhaps you have a cooling problem on the starboard side. It sounds like you are chasing ignition gremlins.

A few thoughts:
Running hot because of over advanced ignition, cooling water problem, too lean, or all of the above?

Do the plugs on the starboard side look different from the port? Do they look like they are running hot?

I have a 454 with lower compression than you. I run a 650 Holley Spreadbore. Maybe you are overcarbed and underjetted.

Good luck, let us know what the cure is when you find it.

 

Thanks for the response, I agree with you now that I have looked in detail at the burnt exhaust rubber hose, it is not getting water, or enough water through the riser on that side, I will check the water port/passeges........now to the timing, all plugs are good with an even tan burn colour, I am going to try an advance curve kit for the dist. Right now there are two heavy springs and a medium advance bushing (21') I will try two medium weight springs and a red advance bushing (25') and see where that takes me.

This engine has six hours running time with no problems, same carb and everything else except the wiring set-up, so this is why I am leaning towards timing issue, having said that, I could valve a stuck/lazy lifter that is bleeding down....???? Ya gotta love boat motors!!!

 

By no means am I trying to imply I know whats wrong! A few thoughts occur to me.

Plugs look good

Cooling water problem coupled with plug condition diminshes chances that your actual motor is running too hot because of tuning.

10:1 compression is not radical but it is pointing in the direction of making motor run too hot.

Unless I misunderstand the details it sounds like you are moving in the direction of more advance and quicker too. It seems like that coupled with your remarks of "misfire knocking" sounds a little bit like too much advance already.

Would a stuck valve show up on the compression test?

You've changed a bunch of stuff, I keep coming back to the carb. It was set up for one situation and now you are in another.

I keep a big block chevy tuned up and play around with the variables but I am no expert. I am just sort of thinking out loud here, acting as a sounding board. LOL, that's why I am interested in your results, more knowledge for me!

 

So I have learned some info about the engine from the actual builder.

The compression is NOT 10:1 it is more like 8 1/2 or 9:1.

The cam is a Melling Marine mild cam, I thought perhaps the engine was over camed, but that is obviously not the issue.

I have checked and replaced the intake gasket, thinking perhaps a vaccum leak in combination with timing and fuel issues.

I have replaced the carb with a brand new Holley marine 750cfm as well as changing the weight springs in the MSD dist from two heavy silver to one light silver and one light blue, this should help the advance to speed up a little. I agree that there might be to much advance but I do think the engine is not advancing fast enough, so if I lower the total advance a little and speed the advance curve up a little it might help. Today I will put everything back together and set up the total advance timing at about 28' or perhaps slightly lower, with initial timing at about 8' and see what happens......

 

try here:
http://www.performanceboats.com/html/forums/forumdisplay.php?f=37

There are some really knowledgeble folks there. Present your problem and then read a few other threads and get a feel for who really knows what. These guys breath this stuff.

 

Awesome, thanks............

 

So, it boils down to a timing set up as well as a fuel/carb issue and on top of that, a cooling issue with the aftermarket exhaust system. BTW. If anybody is thinking of using Eddie Marine for an exhaust system, DON'T...... they have poor customer service and the product for the money is not that good.......

I ended up having to make my own cooling system for the risers, the set-up supplied by Eddie Marine was not enough to keep the system cool. On top of that, I had to set the MSD dist to the lightest springs and have the advanced curve very sharp.

The fuel issue was solved by installing a brand new Holley 750cfm marine carb, no problems there..........

Bottom line, runs like a top, 65mph at 4500rpm and doesn't miss a beat.... thanks for all the input......

TollyWally, thanks for your two bits.........

 

Sounds like it's running fine!

Explain your home made riser set up and what you mean by a sharp advance curve? It sounds like I was wrong and you needed your advance in quicker.

Where do you have it set now and how many degrees does it advance etc. I have just started to play with mine. I'm all in at 31 or so.

 

The risers and exhausts supplied by Eddie Marine had the exhaust manifold's water fed straight into the risers externally, unlike Mercruiser set-ups where the exhaust water is fed through the risers. For my engine, and I would suspect many others that are not stock, this would be an issue...........? The exhausts manifolds are cool but the risers and rubber exhaust tubes get hot, hence the burnt exhaust pipes that I had..........not enough water. And before anybody says. " You need a low water pick-up or an external water pick-up....or a raw water pump." There is more than enough water supply/flow from my Alpha leg impeller..........it works just fine, the problem was the distribution of that water.......all I did was to take the outlet just in front of the thermostat housing that normally fed the old Mercruiser risers, and spliced that line into the existing line from the exhaust manifolds to the risers in order to add additional water.........are you with me?

I then put a brass tap "stop cock" in the top of the fitting that use to feed the risers, which now does the same thing, and if needed I can add more or less cold water to the system. If I did not have the "tap" the water would just flow straight through the system without cooling anythig.........lol


The sharp advance curve just means that when I hit the throttle the peak advance is reached quickly, there is no drag or stumble, at least in my application.


My total advance curve is 28' with a 21' advance bushing and a 7' to 8' initial timing.

Now I just hope the crap weather up here gets better.......