Runs and Starts Perfect Until under load

[rickthebodyman]

I was just wondering if anyone might have the answers for the worst nightmare I have ever owned. I have a 70HP 1970 Chrysler engine on my boat. Had lots of ignition problems in the past finally over came that obstacle. boat will run and start perfect every time in the driveway while in water. revs flawlessly all day log until you put in under a load in the water. it has no power once it is in the water it will idle all day but no top end. I did play with the timing some when I was working with the ignition problems and wonder if that could be it. I just have not been able to find anyone to show me how to acuratly set the timing and the seloc book wasnt very clear either. alot of people keep telling me to rebuild the carbs which I did clean before I ever tried to start the engine. I find it hard to believe that is where the problem is being it starts and runs so good out of water. I have also heard the gasoline could be the problem being we have 15 percent alcohol in the fuel here. any help woul be greatly appreciated I am tired of spending money on this engine. you get to where you ask yourself is it an engine or an anchor that is the question!

 

[Frank Acampora]

Re: Runs and Starts Perfect Until under load

It is an engine, but you just don't understand it. Look at your chevy in your avatar. How much pedal and fuel does it take to rev it in neutral? How much fuel does it take to run the course or 1/4 mile?

Just like your car engine, the outboard will rev in neutral or in the driveway with no load and run perfectly. This requires very little fuel. However, an outboard is always under maximum load in the water. So when running in the water in gear, it requires a LOT more fuel.

So, before you go messing around with the carbs or ignition, check the fuel supply from the strainer in the tank to the carb float bowls. Check for clogs and check the screen on the fuel pump. Remove the fuel pump top and replace the diaphragm and gasket--about 5 bucks.
Check that the main jet, the brass screw in one on the bottom of the carb inside the bowl, is not clogged. And, check that the float and inlet needle are set correctly and the needle seat is not clogged either.

15% alcohol in the fuel will not cause any problems other than fuel lines will eventually start to deteriorate and need to be replaced.

Timing should be set at 32 degrees before top dead center at wide open throttle. Top plug is #1 and firing order is 1, 2, 3.

You can remove all three plugs and ground them then static time the engine. Remove the prop. With the ignition key on and the engine in foward gear and at wide open throttle, turn the flywheel slowly by hand. You will see the plug spark at a specific spot on the flywheel. If you have the timing pointer with 6 marks, the long center mark is 36 degrees and 32 is 4 marks to the left.

At the top of the forum page click on Force/Chrysler FAQs. search and click on the post Synchronizing timing and carbs.

 

[steveclv]

Re: Runs and Starts Perfect Until under load

You don't NEED to remove the prop (especially if static timing cos the engine can never start) but just beware that it will spin when you turn over the engine so make sure that no-one is standing near it. It's a safety thing!

I used a simple automotive inductive timing light and ran a 12V wire to the yellow wire on the starter solenoid to spin the engine over to check it dynamically.

 

[SwampThing]

Re: Runs and Starts Perfect Until under load

I used a simple automotive inductive timing light and ran a 12V wire to the yellow wire on the starter solenoid to spin the engine over to check it dynamically.

Do you still have to jump the NSS switch or does this bypass the NSS function?

 

[Frank Acampora]

Re: Runs and Starts Perfect Until under load

On that year engine, you do not need to jump the solenoid. Spinning the flywheel by hand will still fire the plugs with the ignition key on AND because it is slow, when you see or hear the spark, you can then look at where the timing marks are located in relation to each other. You can slowly rock the flywheel back and forth a couple of degrees to double check and make sure you are accurate. NO timing light is needed and distributor timing does not change when the engine is running like the newer Prestolite ignition.

 

[steveclv]

Re: Runs and Starts Perfect Until under load

Do you still have to jump the NSS switch or does this bypass the NSS function?

That bypasses the NSS switch.

Frank - yes I realize that you can do that engine statically - but I was always taught that checking it dynamically would be more accurate as it took into account backlash and play in the internals of the engine/distributor etc - is that not the case with the OP's motor?

 

[Frank Acampora]

Re: Runs and Starts Perfect Until under load

In the prestolite system, there are two sets of magnets under the flywheel (one to charge the CD boxes and one to energise the trigger coils) and these do change dynamic timing.

With Motorola system, you do not have these magnets and forces. Flywheel magnets act only upon the stator which is immovable. Additionally, since two cycle engines are loaded only one way on the bearings and since the timing is being checked at 32 degrees BTDC There is no internal backlash for which to account. Indeed, the reason for setting the pointer at 36 degrees to find TDC is to eliminate the backlash at TDC. The distributor belt has no backlash (if correctly adjusted) as demonstrated by the fact that if you are close to time, within a degree or so--I never measured, and depress the belt with your finger, it will advance very slightly and spark. Points will not change while running unless they have a weak spring and start to bounce, while the electric eye distributor is rock solid.

So, all things considered, you can set those old Motorola/distributor systems very accurately by hand, statically, in the driveway. Double check them while running and you will see no variation in timing from static. 'Course, no one is saying that you should not set them dynamically--the choice is always yours to make. BUT: They make it very simple if you don't have a timing light or don't have one handy.

I have a couple of engines with each system and for all practicality, I see no difference. Indeed, I have no particular preference. I do like that Prestolite is self energising but don't like that you need to short it to stop the engine. I don't like that Motorola systems require input voltage to run and don't like that you can not pull start them with a dead battery--however, how often does your battery surprise you by dying while you are on the water? Again, all things considered, the Prestolite type systems are a little simpler and probably a little better.

 

[rickthebodyman]

Re: Runs and Starts Perfect Until under load

Have replaced the diaphram on the fuel pump already last summer. replaced all the fuel hoses and the tank as well I dont believe there is a strainer in the tank as it is just a 5 gal tank like you purchase at walmart. I have not actually moved the flywheel in refernce to the timing but I did mess with the adjusting screw on the advance that is what I was wondering if could be off. also this engine will rev in gear in a drum of water. I also have tried adjusting out the mixture screws while on the lake but that did not seem to help. Do you think my timing could still be off by messing with the advance or does that set differently?

 

[steveclv]

Re: Runs and Starts Perfect Until under load

Definitely - if you are too far retarded then you kill the engine performance - it needs advance to generate the power - too much advance will cause pre-ignition (detonation). Do a timing check asap.

 

[rickthebodyman]

Re: Runs and Starts Perfect Until under load

please excuse my ignorence but is that screw on the distributer where I adjust the timing on the engine. I know thats a stupid question but im not real sure how to adjust it if its off. if it were a car of any kind I can fix it but this baby is a breed of its own. if I am getting this right at 32 degrees it should fire. if not adjust that screw until it does. again im sorry if the questions seem juvinile I just want to make sure I am doing it right. this thing runs and starts to good to have very much wrong with it but I am at my witts end I have messed with this for two years. thanks for any advice I can get I do appreciate it!

 

[Frank Acampora]

Re: Runs and Starts Perfect Until under load

The double threaded screw held between two plastic blocks does indeed set or adjust timing. You loosen the nut and move the screw. one direction closes the gap between the two plastic blocks and advances? timing, the other direction opens the gap and retards? I forget, it has been so long since I have timed my engines. Can you spell Alzheimers? Rotating the distributor body against flywheel direction advances timing.

Anyway, when correctly set and if all other sync steps have been performed correctly, the distance between the two plastic blocks should be between 3/16 and 1/2 inch.

If for some reasen you remove the distributor belt, be certain to set tension correctly. Too tight and the engine will have trouble shifting into and out of gear. Too loose and timing will wander. Check it with a feeler gauge as explained below.

To set belt tension, loosen the distributor mounting bolts. One is in a slotted hole. Turn the mount to tighten the belt. Tension is correct when a .010 steel feeler gauge when pointed like a finger in the center of the belt deflects the belt 1/8 to 3/16 inch before bending.

Carb adjustments are a fast way to destroy an engine. Please go to the FAQ sticky at the top of the forum page and read synchronizing timing and carbs.

 

[bravogolf]

Re: Runs and Starts Perfect Until under load

Rick. I had THE SAME issue. I fixed the idle adjustment screw. I moved the bolt so it put more pressure on the engine block, which increased the idle. I made sure the idle wasn't too high for when I placed it into gear.

Check out my own forum post...
http://forums.iboats.com/showthread.php?t=468883&p=3181664#post3181664

 

[mike zerr]

Re: Runs and Starts Perfect Until under load

had the same problem with my 85hp force whent thrue the carbs and rebuilt the carbs the problem turned out to be a tube in the bowl of the top carb cutting off fuel and to needle and seats sticking the 33 dollars for carb kits is well worth the hassles the carbs are easy to work on just pay attention to the link and sink info when putting back together