Trojan Boat Forum

Anyone have any ideas on why my port engine stalls when in idle and in gear once the engine is warmed up. At 500-550 RPM with no load the engine throbs. This is a '73 400 Chrysler Marine. It's been like this for several years and I figured it's time to try to do something about it. I did check dwell - perfect 29 degrees. Timing was perfect at 5deg BTC. Engine timing advance seems to work well. Carb was rebuilt 6 years ago. Tried adjusting idle jet screws but saw no improvement.

Also a little strange is when it does stall one has to keep throttle at idle to get it to start. Off idle and it just cranks endlessly.

I have the idle up to around 700 rpm to keep from stalling, but it's not great for the drive when shifting into gear. Runs great otherwise.

Any suggestions?

Not sure if it is just idle speed being too low... Don't have my manuals etc here, but I think target for my 1979 Chrysler 360's is 650 or 700 rpm in gear at idle... 500-550 with no load (assuming out of gear) seems low to me.

captainmaniac wrote:Not sure if it is just idle speed being too low... Don't have my manuals etc here, but I think target for my 1979 Chrysler 360's is 650 or 700 rpm in gear at idle... 500-550 with no load (assuming out of gear) seems low to me.

I agree. Would have to look it up but I think the 500 may be the rpm to set timing only.

I agree with the above and add..

Two things jump out from your explanation...real low idle speed and the stalling after the choke kicks off( warmed up)....sounds to me the engine has a lean idle condition, causing it to stall under load......adjust the idle mix screws to out 3 turns each from lightly bottomed out( turn screws in to stop then counter clockwise out 3 turns) ......set your idle at 650 lets say no load then put it in gear and see how much the idle speed drops , if there is enough fuel( rich enough) the goal is the engine should not lose much rpm.....clockwise on screws is lean,ccw is rich.....I am assuming these are the original afb's in good shape.....play with the mixture from there to get the best lean idle.....sounds like the timing etc is just fine, most settings are 1.5 to 2 turns out ideal but with old stuff I find the circuits need more fuel...if none of this has any effect then you may have a restricted idle circuit in carb or a vacuum leak...

Makes sense about the idle being too low. I assumed the specs on the engine dwell and timing at idle applied. I will also recheck with the idle mix screws too.

Thanks guys

As per my 440 manual, idle speed at no load is approximately 650 rpm. I am pretty sure yours would be the same.

You might drop yours back to 650 rpm and see if that works. If not, I would not get too upset about 700 rpm.

In gear, you should be seeing 500-550 rpm.

Ok, I'll check it out.

Thx