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1971 mercury 650 4 cyl thunderbolt

K

kevinbrian

New member
hi guys, I recently acquired this motor, first off, id like to ask the learned community their opinion of this motor as I would like to revive it. comp is 114 lbs all cylinders and ive isolated the first problem being a faulty trigger, pros and cons? thx guys..
 
An excellent design.----The last year for the 4 cylinder 650 as well.------Dropped simply to compete with the popular 3 cylinder competition.-----As is common today the electronic parts are expensive if available.----Stuff can be made for pennies but they want big $ as replacement parts.
 
thank you for your reply racerone, so, we had the motor running and the positive battery cable came off while running, the engine died and will only run in the "start " position... believe it is the trigger, any thoughts? thx
 
Triggers dead....finding a good used one without rotten wiring is hard but sometime you can find a good used one off blown motor.
 
There may be other options of 4 cylinder distributors / magneto units.-----They did build the 4 cylinder 50 / 80 / 85 HP models to 1977.----The earlier magnetos did not use 12 volts to make spark.
 
Some of them used the Lightning Energizer ignition, one of Merc's best. You'd need the front crankcase, the distributor and top bearing mount (along with a bunch of other parts) to use it, however.

Jeff
 
I found one online but you have to be careful there are 2 types one for the 800-850 models and one for the 650, it looks like the linkage holes are differently located.
Use the part Nr. cast into the top and your serial Nr.
 
i've found a new trigger unit thru CDI and dist shaft with the non removable rotor, does anyone have any thoughts about the compression being 114 lbs on all 4 cylinders? is that too low?
 
That comp. is slightly lower than ideal but it's within the 10 lb margin, I would use PowerTune to clean up the internals then run it 50:1 with synthetic oil. Knew a guy with 1 cyl low [90psi] who switched to Amsoil and the comp. came up to 140.
 
Are you still working with you're '71 Mercury 650? I have a '71 Merc 650 that I've owned since new, but I'm pretty sure it has 3 cylinders. I had very few hours on it when I put it "on the shelf" for several years. Then, in 2018, I took it to a shop in PA and had it completely overhauled. I'm now looking to sell the motor. Details of the work done on it are available. When I picked the motor up (in 2019) after its overhaul, I brought it home and it's stayed here, hasn't been used since. I'm sure the fellow in PA would give an honest appreciation of the motor. Interest?
 
racerone said:
A 71 model 650 is a 4 cylinder motor !!!----72 was the first year for blue stripes and the 3 cylinder models.
Click to expand...
Thanks. For some reason I've always thought of it as a 3-cyl. And, it's definitely not a blue stripe. What I'd really like to know is the weight of this motor (long shaft).
 
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