timing advance 86 350 with thunderbolt IV ignition

[lime4x4]

Having some power issues on a 1986 searay with a 350 4bbl carb engine. Tonight i was checking timing. Base timing is set to 8 deg when running the engine at 2000 rpm's i aimed the timing light and i had to adjust the dial to 30 to get the mark lined up with 0 deg on the timing tab. According to the mercruiser manual at 2000 rpm it should be around 12 deg advance. To me it seems to be going to full advance way to early.I didn't check what the advance was thou at high rpm's

 

[sprink56]

Having some power issues on a 1986 searay with a 350 4bbl carb engine. Tonight i was checking timing. Base timing is set to 8 deg when running the engine at 2000 rpm's i aimed the timing light and i had to adjust the dial to 30 to get the mark lined up with 0 deg on the timing tab. According to the mercruiser manual at 2000 rpm it should be around 12 deg advance. To me it seems to be going to full advance way to early.I didn't check what the advance was thou at high rpm's

Here are a couple of thoughts. Is this an original marine centrifugal advance distributor or has it been replaced with a vacuum advace automotive version? If it's a vacuum advance you have your answer.

If it is an original style distributor, the weight springs may be old and streched or may be lighter springs than spec. allowing for a faster advance than spec. calls for.

BTW...what does MerCruiser call for as a base timing at idle? Is it 8...just wondering.

 

[lime4x4]

marine dist. The dist has no weights or springs

 

[SCORPIO]

marine dist. The dist has no weights or springs

Are you sure? I'm not that familiar with these distributors (I'm going to be as I have two on my boat I need to time and tune this spring) but all other dists. I've wored on have weights under the plate that holds the hall effect sensor.

 

[sprink56]

marine dist. The dist has no weights or springs

It must have springs or weights or it can't advance. The newer crank fired rigs don't have a distributor...the computer controls the advance. Some of the MPI rigs have computer controled advance but 1986 Mercruiser...you have weights and springs beneath the breaker plate.:thumbsup:

A suggestion...take the distributor out and take it to a performance shop with a Sun distributor machine. They will spin it up and tell you exactly whats happening. NASCAR guys have been using these things for years. They are still around in a few shops...you're probably going to need to find an "old school" hot rod shop to get this done. Once you know what is going on you can customize that distributor to do anything you want.

 

[lime4x4]

the ignition system is electronic. There is only a hall a effect switch in the dist housing

 

[fc3]

The 1987 Factory Service Manual does not show advance weights or springs for the thunderbolt distributor, only for the points distributors. The advance curves are calculated by the ignition module.

The procedure for setting base timing is very simple. It's just

1. Connect the timing light to #1. Make sure you have #1!
2. Connect a accurate tach
3. Run the engine at normal idle speed
4. Aim the light at the timing marks
5. Adjust timing by rotating the distributor
6. Remove timing light and tach

You might want to check the advance curve. Could be that the module is hosed up, but I really doubt that. You might not have #1. Looking at the engine from the front, which means the distributor is at the back, #1 is the first plug on the right.

Best regards,
Frank

 

[SCORPIO]

WOW I learned something new today. I would have expected to see advance wieghts. I've never had one of these setups before and my previous boat had points converted to electronic. Sounds simple and more reliable without the weigts and springs, fewer parts K.I.S. keep it simple.

 

[sprink56]

My '86 260 Mercruiser had weights and springs....I put a spring kit in it and re-curved the distributor. My '86 EFI 320's had the ECM with it controling the advance.

If the distributor in question is electronic then I suspect there is a resistance problem in the module. A total ignition analysis is needed....check for trouble codes.

Try to find a Mercruiser mechanic with the tools to scope this out. Hope it works out.