318 wonbt approach idle

"My second engine starts - roa

"My second engine starts - roars to life actually - when accelerator pumped.

Runs great above 1500 rpm.

Lower than that it runs for a bit but slowly seems to run out of steam.

Will go at 1200 for a minute or two, then quits.

Lower than 1200 it just dies.

The engine is a rebuild. The carb was rebuilt although I opened it up today and cleaned some gunk out of the fuel bowls and blew carb cleaner through all the jets and checked the needles and seats and floats. All seemed okay.

I also removed the idle mixture screws and blew carb cleaner through.

New fuel pump and I get lots of fuel. Clean filters etc. Lots of fuel in bowls. Accelerator pump works wonderfully.

I have managed to keep it running at 1500 so I could preliminarily set the timing although at fastest run it is harder to re-start.

The AFB Carb has the large idle screw on the front and it seems to run best screwed all the way in, although I can run it at about 2000 with the screw all the way out.

However, I don't think this has been a fair check of the idle screw.

I haven't been able to adjust the idle mixture screws but have them set at two turns out.

At about 1400 with the flame arrester off, I slightly closed the choke and the engine sped up maybe 200 rpm. Close the choke all the way and it dies.

Do I have a carb problem or should I be looking at electrical? (Points are new, condenser I believe is new, cap and rotor are new, coil is new I think)

Electrical checks that I have done show good spark from the coil, decent spark at the plugs but I noticed that below 2000, rpm wavers as much as 250 rpm.

Unable to tell if this is electrical or fuel-related and of course I am getting frustrated running from the helm station to the engine.

Anybody have any ideas?

Thanks

Mark"

"Mark:
Can you swap the carbs

"Mark:
Can you swap the carbs? If the problem persists, it's probably not caused by the carb. If it goes away when you swap carbs......."

"I experienced virtually the s

"I experienced virtually the same symptoms with my 67 318 which you describe and went through everything fuel related, including new pump, filters, carb rebuild, carb adjustments,etc. After nothing I did which was fuel related helped with the problem, I put the old coil back on(I had put a new coil on over the winter), fired it up and it ran perfectly. May not be your problem but might be worth checking out.

Good luck."

Bosco pointed you in the right

Bosco pointed you in the right direction. If you can swap I'd do so. If you blew gunk out while testing you proably have more since you could keep it running with the idle screw all the way out.

"Mark

If you have a four p

"Mark

If you have a four prong ceramic balast I would change that out, I had same problems with performace and the ballast was not regulating voltage. Also stalling at low idle could be a float adjustment in carb, if swaping them doesn,t work.

Art"

when you close the choke parti

when you close the choke partially and the RPM's picked up with a warm engine that means you are lean. there are two mixture screws on the front of the carb one at a time turn them out half turn at a time until highest engine rpme is achieved then an additional half turn. after you have done this to both a/f screws adjust the idle down on the idle screw (the one that moves the throttle arm). if this doesnt work.

You can also count the number of turns out of the same screws on the good running motor and try that.

"Did you ever solve the proble

"Did you ever solve the problem? I have an engine that is exhibiting the exact same symptoms... roars to life over 1500 RPM, will go down to about 1200, then starts to fade away. If I bring it down below 1200 it dies outright.

One other thing I've noticed, initially it starts relatively easily. The more it runs like this the harder it is to start. Eventually it won't start. Come back the next day is like starting all over again, easy start then no start."

"Hey; it simply needs an idle

"Hey; it simply needs an idle adjustment! The mixture screws need to come out a turn or so.

Warm the motor thoroughly and play with the smaller idle mixture screws--that big screw is an air control for idle SPEED. As the motor idles better, slow it down (turn in the big screw a bit) and try again. Eventually the motor will idle down okay.

Jeff"

"Like Jeff and Will said, it&#

"Like Jeff and Will said, it's most likely just getting the two mixture screws just right. They can be very very sensitive(at least mine was) to very minor adjustment(even less than 1/8th turn in my case)so just keep after it and you should get it right. Can be very frustrating so be patient. And, yes, mine was doing exactly what you seem to be experiencing but it runs great now."

"?? Vacuum leak ??
Could a pv

"?? Vacuum leak ??
Could a pvc valve have gone bad, or a split hose.

Fred 156-M"

"I was checking the idle adjus

"I was checking the idle adjustment section in the service manual. It said to run the engine for 10 minutes to warm it up, but the engine will only run for a minute or two before it dies.

If I turn the screws out a turn before starting it, should I expect to see it run a bit longer?

Thanks for all the advice. I'm heading back down to the boat tomorrow for more troubleshooting.

Carl"

"..."If I turn the screws

"..."If I turn the screws out a turn before starting it, should I expect to see it run a bit longer? "

Could be, but try this instead: Carefully note how many turns it takes to bottom (lightly!) each idle adjustment. Then turn them out 2 full turns.


Jeff

PS: Let us know how far they were out before, okay?"

"I think we're on to somet

"I think we're on to something!

The engine did respond to adjustments. It still isn't running, but I did get it to run a little longer and at a little lower RPM. The problem is that after a few tries it doesn't want to start anymore, until it sits for awhile.

Here's how the screws were set before I started;

Outboard screw - 3 1/4 turn
Inboard screw - 2 1/4 turn

Question... why does the engine stop starting after a few tries? Also, the problem seemed to start rather suddenly. One day the engine ran fine, the next it wouldn't. What would cause this? Do the screws just work themselves out over time? Or is there some other factor at work?

Thanks,
Carl"

Question... why does the engin

Question... why does the engine stop starting after a few tries?

Sounds like dirt. Do you have a holly or an Edelbrock?
If you don't want to take it apart again. Try this
Remove both idle screws. put finger over both holes. start engine bring down to idle speed.
do it 2x. reinstall screws. set at 2 and 1/2
turns. Let me know if it works.
I'm sending you a carb manual that is very helpfull PDF.

Carl... If your engine is elec

Carl... If your engine is electronic ignition it could possibly be the Electronic Control Unit - some call it Module - My '81 318 exhibited the exact symptoms & finally would not start... as a last resort I changed the ECU & VOILA! Problem solved. Experienced the same prob. on a '79 Jeep CJ7 & Voila! Problem solved as well... Hope this info helps... Mike... '81 PENN YAN w/RWC 318...

"File is to big go here.
EDEL

"File is to big go here.
EDELBROCK http://www.edelbrock.com/automotive_new/mc/carbs_acc/marine.shtml"

"Mike has a point, and since t

"Mike has a point, and since the module is dirt cheap--about 30 bucks at NAPA--why not change it?

Jeff

PS: Those idle adjustments were out WAY too far."

"Hey Carl

I had similiar is

"Hey Carl

I had similiar issues with my lm318s' I did the following to correct the problems regarding performance.

1) remove the manual choke assemblies from my carter afb carburators (I had to many problems with them)
2) cleaned and rebuilt carbs and set mixture screws 2.5 turns out on each.
3) complete tune-up (ECU,coil,balast,wires,plugs,cap,rotor,fuel filters)
4) oiled distributor springs, weights etc.

Started engines with clean fuel, I disconnected fuel hose from tank and used a small 2.5 jug to eliminate any bad fuel problems.

I had to adjust my mixture screws to 1.5 turns each because engines were running to rich for my climate (Fort lauderdale)

I suspect clogged fuel filters or something with the electronic ignition components mentioned above. Also when setting timing I found distributors were not advancing (oiling components freed up problem)

Spent a few bucks on everything,and my performance @ full throttle is 4300rmp each with a boat speed of 38mph on smooth water per my GPS.

I performed all the work last summer and stored boat for 7months. I dropped in this past May and everything is still Good. I use the STARON additive,starting is easier, no smoke and keeps fuel fresh.

Hope this helps!

Take Care
Art Kane"

Looking back I realize I never closed the loop on this one.

I finally broke down and called a mechanic. His diagnosis was bad carb, rebuild or replace. So I went with a new carburetor.

After he had the new carb in we discovered that there was water in the fuel. His comment was, "that could have been your problem all along." $500 bucks later. Oh well, it runs now.

Welcome to a rather LARGE club!

Jeff