Logo
FULL SITE MENU

1970s mercury 650 thunderbolt timing? help!!

J

jjc4209

New member
Hi I have a 1970 mercury 650 thunderbolt 4 cylinder. I can't seem to get the timing right on this thing. If some can point me in the right direction I'd appreciate it. I bought it about a year ago.. idled great. As soon as I got it in the water and go into forward it would stall. Found out my ignition coil was burned up. I recently rebuilt the carbs.new fuel lines.ignition coil. Before I did all of this I would idle great. We re did the timing after the work we have done. And won't stay running for more than 5 min like it loads up or something. Please help me hahaha. I'm a rookie
 
You have the trigger and not points I put it as a 1971 model 650 you will need to get a better manual the ones I just gave you are for the points type magneto you have the switchbox with a trigger.
 
A 1970 model would be a 4 cylinder.----Timing rarely goes out of adjustment.-----What is your motor doing / not doing ?
 
I’m having difficulty figuring out which specifications to use to time it. What started this was breaking the distributor belt. I did not know my timing points before this happened, so I’ve been forced to start from scratch. The procedure is relatively the same no matter which procedure I use. 1. Crank to distributor timing procedure is identical, so I’m not worried about that. 2. Is the idle then WOT procedure. 3. Finally set primary and secondary carb(s) pickup. For the carbs, I set them to engage primary as the distributor begins advancing. I set the secondary with the power lever at full throttle so that the carbs are just barely not hitting their max stops... The problem is the distributor timing. I tried 4-6 btdc idle and 21 btdc WOT. Hole shot was completely gutless. I then learned about cross flow, so I tried 3 btdc idle and 32.5 btdc WOT. Hole shot was very weak but after about 6 seconds it got on step. My third attempt was in response to the timing sticker on the machine. I tried 3 btdc idle and 25 btdc WOT. This produced the best results thus far. About 3 seconds to on step. Still.. I’m doubting that I’m all the way there. Should I try 26 or 27 WOT? I’m pushing a Lund 16 if that helps any. Thank you in advance.
 
Auuurrgh... Another automotive guy trying to time an outboard like it was a car engine!

Forget about idle timing. Remove the top carb's throttle cam (one screw) so you can safely hold the motor wide open 3,000 rpm). Time it at 21 degrees, and leave everything else alone!

Jeff
 
So the consensus is 21° BTDC.., OK. It’s just frustrating that there are multiple procedures for the same year/make/model. Last night I found a procedure (Seloc manual, I think) For a 1970–71 mercury 650 W timing at 38°. I still can’t explain why it won’t climb out of the hole. I’ve change the diaphragms in the fuel pump, my hoses are good, rebuilt the carburetor’s, I’ve got bright blue spark on all cylinders. Thoughts?
 
1. Time it as specified

2. Add 1/2 turn OUT on the idle mixture screws

3. Try a prop with a lot less pitch

Jeff
 
Back
Top