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318 engine tuning

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Brock69

Member
Hello - I have a 1973 31ft Trojan with twin 318's

The engines have been rebuilt along with new Carbs

The port engine runs real good in fact very good. The Stbd engine runs good but I have a sputtering sound coming out the exhaust at the back of the boat. The engine will speed up and go back down. (not alot) I have tried to adjust the carb but with no success.

I believe that this rough idle could be caused by more than one factor. My question is what would the starting point be in the process to correct this problem.

Thankyou
 
Brock69 said:
The engine will speed up and go back down. (not alot) I have tried to adjust the carb but with no success.

My question is what would the starting point be in the process to correct this problem.
Click to expand...
A good starting point would be to connect your standard strobe type timing light to #1 cylinder spark plug lead.
Aim this at your timing marks, and look for consistancy in the degress of advance while at idle.
Vary the RPM just slightly, and see if the advance remains constant witht the RPM.
If the advance is jumping around..... then there is an issue with the mechanism.
Also, we should see no change to the advance until after about 1k rpm.
IOW, it should remain in BASE advance mode up until about 1k rpm..... then we should see the progressive advance begin.... but no sooner.

The reason that I suggest this is.... if your mechanical advancing mechanism has lost a spring value, the advance may be irratic, causing a fluxuation in the amount of advance, and also in RPM.

While this may seem to be a low speed issue only, it may also be affecting your ignition advance curve for the higher RPM range where ignition advance is more critical.

Irratic spark lead..... and in particular a spark lead that is coming on too early, may damage your engine.

FYI... if original, your ignition distributors are old enough to warrant having them checked by a shop who owns an old school distributor machine.
They can be re-bushed and brought back to life and with a fresh curve calibration as well!

By 1973, these are very likely VR triggering (variable reluctor), so there is usually no issue with the VR system, but it would behoove you to have the advance curve checked and re-calibrated if need be.

DO NOT use automotive specs for this ..... be sure to use the recommended OEM Chrysler Marine specs for your engines.
 
BEHOOVE !!!

Rick, why is a Digital Timing light bad again?? I got this one that has the rpm on it ,pretty "effin" kewl if you ask me!! Bought it to set the timing on a 3.0 mercruiser,Talk about a pain in me bum! Where is 2 degrees after??

Somebody should design an engine where you have to crank it over by using the prop!!

Brock -pull the plug wires one at a time while running,screw in the mixture screws while running to hear a difference,then take em out blow it out with compressed air put em back ,lightly seat, back out 2 turns,start from there
 
Greasemonkey, I fully understand. Those who love their Digitally Advancing timing lights, really love them.
It's a personal choice, I suppose.
I actually like the idea of the Integral Tachometer timing light..... it's the advancing feature that I will not use.

For me, I want to see my ignition lead in REAL TIME and in REAL DEGREES...... hence an accurately "Marked Off'd Balancer" and "Std Strobe" style timing light.
If I were to rely on a Digitally Advancing timing light, I'm at the mercy of the electronics algorithm, etc.
One small user error.... one small equipment malfunction...... and you can see where this goes!
Since Marine Ignition TA is so important, I'm not willing to risk in this area.
Each to his own.
:cool:


Brock, your carburetor metering circuits will be separated..... I.E., the low speed circuit adjustment screws are for fuel/air mixture will cause a change to low speed metering ONLY. These will do nothing for high speed circuit operation.
The carburetor will need to be partially disassembled in order to make any changes to high speed fuel metering..... of which I would not advise!
Clean these circuits.... yes!
Change the metering.... No!


Brock, we can chase our tails until the cows come home, unless we use a methodical/systematic P of E (process of elimination)!
I'd get any potential ignition related issues completely out of the way first..... then, and only then, would I move on to other potentials, and one-at-a-time!

.
 
Thanks for your replies.

I dont know why I did not think of this early. As I said the Port engines runs very good - no problems

I believe that I can assume that the mechanical advance mechanism in the Distributor is working properly.
I am going to take the Distributor from the Port Engine and install it in the Stbd engine. They are the same.

If this does not work then I will swap Carburetors. If this does not work I will start the process of elimination.
(coil -Spark Plug wires)

Any thoughts on this will be appreciated
 
Brock..........
Brock69 said:
I believe that I can assume that the mechanical advance mechanism in the Distributor is working properly.
I'd not assume anything.
A simple check with your timing light, with the balancer marked off, will let you know what it's doing.
If it is not advancing to the OEM specs (of which you hopefully have by now) then this is very likely part of, if not all, of your problem.


I am going to take the Distributor from the Port Engine and install it in the Stbd engine. They are the same.
Do the above suggestion first. It may save you the trouble.

If this does not work I will start the process of elimination.
That is part of the P of E. :)
Click to expand...
 
Both distributors the same? Are you sure one of them isn't on a counter-rotating engine. I suspect it is and as such is not the same. The gear is cut in the opposite direction.
 
WoodieMan said:
Both distributors the same? Are you sure one of them isn't on a counter-rotating engine. I suspect it is and as such is not the same. The gear is cut in the opposite direction.
Click to expand...
Woodie, I believe that the Chrysler 318/360 distributor "driven" gear is separate from the distributor.
This would mean that either can be swapped, since the oil pump rotation remains the same for both Std LH and Rev RH engines.

MAL9-26305.jpg
 
..."This would mean that either can be swapped, since the oil pump rotation remains the same for both Std LH and Rev RH engines."

No, oh nomally wise one! The RR distributor requires a special collar to keep the oil pump gear down (due to reverse thrust loads).

Jeff
 
I remember the collar but for some reason thought the small blocks were gear drive unlike tang drive (Rick's pic) on big block distributors.
 
fastjeff said:
No, oh nomally wise one! The RR distributor requires a special collar to keep the oil pump gear down (due to reverse thrust loads).
Jeff
Click to expand...
Jeff, that's my short coming with the Chrysler engines. Good call!

The SBC has a similar issue when using the Std LH distributor with the gear change being made.
Mallory AV to a BV for example.
The thrust load changes, therefore the distributor housing technically needs to be different.


BTW, thanks for the "normally wise one" comment! I'm humbled!
(that, or you are good at being polically polite!) :D
 
Thanks I read that on the left under the head it should be. A 318 I don't have that I have. Like your pick 2536080. Do you know what that means
 
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