Merc 260 Won't Idle Below 1000 RPM After Hydrolock

[Showtime22]

1980 21 Ft Four Winds
Mercruiser 260 (Chev 350) Pertronix Ignition Alpha 1 Carter Thermoquad Carb

My engine will no longer idle below 1000 RPM.

On the 4th of July the motor Hydrolocked. (Water entered the cylinders thru the exhaust) I was able to remove the plugs and turn the water out. After reinstalling the plugs on the lake it started right up but wouldn't idle below 1000, and would die when I tried to plane out. I plowed home at slow speed.

I have drained the oil and changed the plugs, oil and filter. Oil was not milky but seemed thin and the dipstick showed it was slightly over filled.
I have checked the plug wiring and firing order.
I have removed the fuel line to the carb and it had good flow.
The engine has run solid all season and I assume compression is good.

I have tried timing the motor at the lowest RPM I can keep it running.
The best I can adjust it to is 0 Degrees before it dies. I need 8 BTDC

Does anyone have any ideas of what I need to look at after Hydrolock?

Currently I think it may be a fuel delivery issue. The Carter Thermoquad Carb was recently rebuilt but I when I look down into it - The right accelerator jet has a whisp of fuel sucking into the motor, and the left one is dry. Could this whisp of fuel be an issue?

I have included a picture.

 

[bruceb58]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

First off, it should idle slower at 0 than at 8. Usually as you advance the spark you r idle will creep up. maybe I don't understand what you mean here.

Second, you should probably check your compression to see if anything got damaged.

I would also double and triple check your firing order again. I chased a problem for 3 days until I checked the order for the third time before I found it to be wrong.

 

[Showtime22]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

Yeah that reads weird.

I put the timing light on it at the lowest RPM possible while still running
(1000 RPM). It showed around 20 degrees ATDC and I could only turn the distributor until it showed 0 Degrees before the engine dies.

I will check the compression as soon as I can get a tester.

 

[bruceb58]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

I really doubt it could possibly run at 20 ATDC. You on the right spark plug? If you are facing the engine, it is the first one on the right.

If it is ATDC, that would mean the timing mark is to the right of the timing tab. Is that what you see?

 

[Showtime22]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

I did check that I was on the #1 cylinder earlier today. (The front passenger side of a boat) The timing light lit the line about 2 inches down from the tab. So it was saying around 20 Degrees ATDC .

I will triple check my wiring.

 

[towman818181]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

yep i think its time for a compression check also

 

[gadget73]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

Whats the passenger side of the boat, port or starboard? The Donzi we used to have was a port helm, starboard passenger. The Rinker is starboard helm, port passenger.

Agreeing with the others though, time for a compression test. I've seen sucked valves before after a hydrolock. Basically the valves had been shoved in so hard that they looked like an inside-out umbrella. One motor that a customer locked shot the spark plug insulator right out of the metal, flipped 3 valves inside out, and broke the piston rings on one cylinder. believe it or not, the thing still ran. Horribly, but it did run.

also cant say I've ever seen a TQ on a boat. I like them, but I've never come across one in the wild. Did you install that, or was it original?

 

[Bondo]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

also cant say I've ever seen a TQ on a boat. I like them, but I've never come across one in the wild. Did you install that, or was it original?

Ayuh,... Definitely Not stock...

With the capped vacuum ports, it's probably automotive....

 

[Showtime22]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

I checked the compression today - seems healthy for a 1980

8)163 7)160
6)154 5)160
4)155 3)162
2)160 1)162

FRONT > PORT SIDE

The carb is not stock. My dad got it for me cheap when the Rochester 4 barrel was not rebuildable. It came to me shiny and rebuilt, but its hard to find a wealth of literature for a Carter Thermoquad.

The boat runs and shifts into gear nicely in the drive way, but the motor only runs well at 20 degrees ATDC.

Would removing the distributor and installing it one cog over help?
I don't think it would. The boat used to allow the correct timing before the Hydrolock.

 

[JustJason]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

eagh... doesn't happen often but your timing chain may have jumped a tooth. if it 1 just 1 or 2 teeth you'd still get good compression but your timing would be all over the place.
I'm with BruceB on this one... no way that is going to run at 20ATDC... if it SEEMS to then something is lying to you/trying to tell you its broken.

 

[Showtime22]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

Yikes - Today I threw the kitchen sink at this and I'm still unable to set timing to 8 BTDC.

I've gotten the motor to idle at 800 RPM by adjusting the idle screw.
So now its running good on muffs but still dies when I adjust the timing away from 20 degrees ATDC.

I removed the electronic ignition and went back to points,
I tried a different coil,
I cleaned up the distributor points,
Checked firing order again,
Checked compression again,
Looked for vacuum leaks....same results.

I am wondering if the timing chain has indeed skipped a tooth.
Is there a way to check if the timing chain is aligned without opening the cover?

Would looking at where the timing mark on the pulley is at TDC on the firing stroke of cylinder 1 tell me?

 

[JustJason]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

are you using a timing light with advance? or just a basic light.

Are you absolutely sure your at ATDC and not BTDC?

After you've checked your firing order. Pull the number 1 plug out, bump it with a remote starter until your on the comression stroke. Then, using a screwdriver to feel the top of the piston manually with a wrench on a pully bring the #1 to TDC (it may be easier to pull all the plugs so your not fighting any compression) If the line on the balancer is at 0 on the timing tab then there is still something wrong with the ignition system. If the line is not pefectly on the 0 on the timing tab then you have a spun balancer/missing or broken key.

 

[Showtime22]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

Thanks JJ -

I'm using a basic timing light from Sears with no advance setting. Recently bought.

I will test 2mrw and post.

 

[JustJason]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

let us all know how you make out.

 

[Maclin]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

The Carter TQ has well plugs like a Rochester that can start leaking and fuel dumps right into the manifold, they will NOT idle below 1k rpm and will be very hard to start and with the engine off the fuel bowl will drain completely until there is no fuel pressure. This dumps a lot of fuel into the cylinders which gets past the rings and thins the oil and can change the oil level if it is severe. The only fix it to take it all apart and epoxy them back in.

Having typed all that, this should be changed out to a Marine carb in my opinion. I love TQ's performance, but this is not a Marine safe carb.

 

[Showtime22]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

Thanks for the info - I'll keep an eye on the oil and consider a different carb in the off season. I knew I was in for an adventure with the TQ but I thought I may gain some hp.

 

[soaringhiggy]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

if it hydroed that hard, bending a rod is a possibility, did you feel any vibration when it runs?

As stated above, a spun ballancer could give this indication as well. Finding TDC will show this. Good luck.

 

[fabrimacator21]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

if it hydroed that hard, bending a rod is a possibility, did you feel any vibration when it runs?

As stated above, a spun ballancer could give this indication as well. Finding TDC will show this. Good luck.

This is what I was gonna say... very common for a hydro locked motor to tweak a rod which=not fun.

Jumping a tooth on the timing chanin would be the first thing to check if you can't get it figured out. Not hard to pop the timing cover off and check it out.

What rpm were you at when it sucked water?

 

[Showtime22]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

I was at idle around 800 RPM in neutral when the motor stopped and hydro locked. The alternator died taking the battery down and killed the motor. Luckily I had a spare battery and tools to get the water out.

Today I checked TDC and the balancer mark was about 3 inches past the timing tab. I'm hoping the key shred and moved the balancer.

Time to remove the pulleys then the cover if needed.
How do I lock the motor to get the middle bolt out of the pulley/crank?

THX

 

[JustJason]

Re: Merc 260 Won't Idle Below 1000 RPM After Hydrolock

if your going to do try it by hand you can buy a couple of piston stops.

I always break out my ingersoll rand for the big bolts though.