mercruiser 350 260hp missing

[dremmick]

I have a 1991 ski supreme. The carb has been rebuilt and the idle/air screws are set at 2.5 turns out. IT really bogs and you have to feather the throttle to get to higher speeds. Also alot of times when its idling, I pop it into to gear and it dies. A few years ago i replaced the points with a petronix igniter. But it seems like its really missing. I tried checking timing and it read about 30 degress. But it should read 8. Once i set timing to about 10 the engine wont stay running. Any help would be greatly appreciated.

 

[achris]

Re: mercruiser 350 260hp missing

When you set the timing to 8* did you adjust the idle speed and mixtures too?

 

[6meter]

Re: mercruiser 350 260hp missing

A question I've wondered about while reading here. A '91 350/260 with points? My '86 350/260 has the thunderbolt IV electronic ignition from the factory. When did they put points back in?
Isn't there a procedure to check the "base" timing? Not "advanced" timing? Need the instructions from the aftermarket kit to check timing correctly.
Idle air screws need to be fine tuned while the motor in idling. They do nothing above idle speed. MANY different adjustments on the carb that need to be correct. Water in the gas or bad old gas from last year?
If you have a skip or miss and it boggs down taking off, you could have more than one problem
Lots of other things it could be. Hows the plugs and wires? Coil?

 

[achris]

Re: mercruiser 350 260hp missing

A question I've wondered about while reading here. A '91 350/260 with points? My '86 350/260 has the thunderbolt IV electronic ignition from the factory. When did they put points back in?

Yours is a stern drive, his is an inboard.

Isn't there a procedure to check the "base" timing? Not "advanced" timing?

Not on Thunderbolt IV, only with EST, DDIS and TB-V. Set initial timing on TB-IV same as you would with points.

Need the instructions from the aftermarket kit to check timing correctly.
Idle air screws need to be fine tuned while the motor in idling. They do nothing above idle speed. MANY different adjustments on the carb that need to be correct. Water in the gas or bad old gas from last year?
If you have a skip or miss and it boggs down taking off, you could have more than one problem
Lots of other things it could be. Hows the plugs and wires? Coil?

 

[6meter]

Re: mercruiser 350 260hp missing

Thanks achris! Still strange to me on the inboard thing. I didn't mean to hijack dremmick's thread. Seems my questions got answered, now how about the OP's.

 

[jtmarten]

Re: mercruiser 350 260hp missing

Set your timing, then re-adjust the carb settings. If it is still missing, pull 1 plug wire at a time, see if there is any change. Sounds like it could be a bad plug wire, cap, or rotor.
You should pull the plugs and read them as well.

 

[dremmick]

Re: mercruiser 350 260hp missing

To check timing do i have to ground out the purple/white wire? So how can i set the timing when I cant get the timing degress close to 8 degress. It kills the engine around 10-12.

 

[achris]

Re: mercruiser 350 260hp missing

Have you checked that the vibration damper on the pulley hasn't spun? If it has, then your timing marks are not in the right place. Take spark plug #1 out and CAREFULLY with a screw driver in the hole, turn the engine until that piston is at the very top of travel. Look at the timing marks on the pulley and make sure that they line up with TDC.

If that's ok, then check you have the spark plug leads on the right plugs and the right connection on the dissy cap. (I know that sounds odd, but on a V8 you can get a couple of leads wrong and not notice. A 30* advance at idle is just wrong! And sounds like you're picking up a different cylinder).

Now, when you say it 'dies' at 10-12?. What do you mean? It just stops at that point or it runs slower and slower and finally dies? If all else is right, then as you back the timing off, increase the idle speed screw. As the timing is retarded and engine will run slower, that's normal and you correct that by opening the carb butterflies a little...

Chris........

 

[dremmick]

Re: mercruiser 350 260hp missing

When retarding timing down to about 10 or 12 it slowly idle lower and lower the more you turn and will kill the engine. To adjust the screws do I close them? Do they make a tool to turn them? Since they are in a crappy spot.

 

[jtmarten]

Re: mercruiser 350 260hp missing

The idle adjust screw is very easy to access. It should be on a bracket on in front of the main linkage (where cable attaches), and simply acts as a variable 'stop' for the throttle linkage.
I'd leave the idle mixture screws at 2.5 TO until you get the timing and idle stabilized. Then you can fine-tune the idle mix.

 

[dremmick]

Re: mercruiser 350 260hp missing

Sorry I meant idle mixture screws. I'm going to have to adjust them since I tried to adjust idle screw to get it to stay running when around 10 to 12 to keep it running but did not work. So when retarding timing do I turn idle mixture screws in or out?

 

[jtmarten]

Re: mercruiser 350 260hp missing

They're usually 2-2.5 turns out. If your idle is set high enough to where the butterflies are opening, adjusting the idle mixture screws won't change anything since you'll be off-idle into the main circuit.

 

[dremmick]

Re: mercruiser 350 260hp missing

So im heading to the lake this weekend to work on the boat. The timing is set around 30 degree right now. Do i need to ground purple and white wire? Also what should i do first? Thanks for your help guys

 

[skipdow]

Re: mercruiser 350 260hp missing

forget about what the timing mark says if its not computer controlled then get a vacuum guage plugged into manifold vacuum and dial the distributor to get the highest vacuum reading then back it down about 1-1 1/2 " of vacuum and tighten the distributor readjust the carb idle speed and you should be good. doing it that way will adjust the timing to suit your engines condition and cam timing best for each engine. you can follow it up by checking for pinging but that usually works great for me.

 

[jtmarten]

Re: mercruiser 350 260hp missing

Never heard of such a method for adjusting timing. So, using that method, what is your total advance?? How do you know you're not exceeding 36* and are about to blow a piston??

Timing should be 34-36* (36* max) at full advance for highest performance. The base timing will be that minus the advance the dizzy provides.

 

[dremmick]

Re: mercruiser 350 260hp missing

Well I have not tried the method of grounding the purple and white wire. A mechanic told me to ground that wire. Anyways I don't know musy about timing. When I timed at idle the gun was set a 0. So I turned the knob on gun until I could see line appear on timing marks. Which when gun was at 32 degress. Timing mark was at zero

 

[jtmarten]

Re: mercruiser 350 260hp missing

Well I have not tried the method of grounding the purple and white wire. A mechanic told me to ground that wire. Anyways I don't know musy about timing. When I timed at idle the gun was set a 0. So I turned the knob on gun until I could see line appear on timing marks. Which when gun was at 32 degress. Timing mark was at zero

Make sure you had the pickup on cyl #1.
32* at idle is wayyyy too much, it'd put you around 54-56* total assuming 22-24* advance from the dizzy. Depending on your ign system, you may have to ground or connect wires to put the ECU in base timing mode.

 

[jtmarten]

Re: mercruiser 350 260hp missing

3. Double and tripple check that you have the plug wires routed properly. It is very easy to get them mixed up. Firing order - 1-8-4-3-6-5-7-2. As an FYI the number 1 plug wire should be at about the 6:30 position. (Almost straight forward of the engine.)

4. Set your timing light to zero (or use a standard timing light without the advanced controls) and visually see where the timing really is.

#1 can be in ANY position as long as the firing order is correct.

If you've ever used a digital advance timing light, you'd never use a standard light again. Most balancers show up to 20*, how do you measure total advance? Just assume its OK if you set the base timing? That works, but only if you know exactly how much advance is provided by the dizzy.

 

[dremmick]

Re: mercruiser 350 260hp missing

Thanks guys I will try those few things. I don't have the petronix flamethrower dist, I have the petronics electronic points