Need a little help with timming marks.

[capthook]

Ok. My marks are very worn and I know they go in 2 degree increments I can see the lines but want to make sure that I am actually 8 degrees BTDC. Here is a picture hopefully. I think that BTDC is on the left when looking straight on at the engine and ATDC is on the right am I correct?

 

[Reel Poor]

Re: Need a little help with timming marks.

I think that BTDC is on the left when looking straight on at the engine and ATDC is on the right am I correct?

Your correct.

 

[capthook]

Re: Need a little help with timming marks.

Thanks. Now for another question or 2. I run cheap gas like 87 or 89 pump. Should I add any octane boost or lead additive, or should I change my timing a little like to 6 or 4 degrees? Also when timing I know that your engine is supposed to be in good running order. By good running order this means with Idle set at 500-600 rpms and running good correct. But when you are timing you are advancing the time and engine rpms go up. Then what? Go back and adjust the carb so that it is back at idle again? I find this challenging and a little confusing. How do I know I am set up correctly? Timing right on at idle. Never mind I think I just answered my own question. Thanks.

 

[BIGLICKER]

Re: Need a little help with timming marks.

Hi Capthook,
You need additive if you run on unleaded petrol as you will burn the valve seats out if you don't. You could always get the valve seats changed if you want to run on unleaded petrol.
Cheers Roy.

 

[Haut Medoc]

Re: Need a little help with timming marks.

You do not need an octane booster or anything above 87 unless your engine is from the early seventies or before, it will usually say what requirement are needed right on the valve cover....​

 

[BIGLICKER]

Re: Need a little help with timming marks.

You do not need an octane booster or anything above 87 unless your engine is from the early seventies or before, it will usually say what requirement are needed right on the valve cover....​

I read this in the posting "1973 Reinell 140 Mercruiser GM 4 cylinder; Merc 1 Drive" SO, I think the engine is OLD.
Therefore I personally WOULD USE AN ADDITIVE IN THE FUEL.