75 mercury 850 thunderbolt smoke from carb

[69ebkoskibee]

I recently purchased a used boat with a "running" 850 thunderbolt. When it arrived I couldn't get it to start for the life of me. Upon further inspection I found all the wiring needed to be replaced along with all fuel lines and carbs needed rebuilt. After I did all of that I still couldn't get it to start. Rechecked all timing which was dead on. I have spark on all 4 cylinders and compression is about 115 and within 5 psi hi to low. Now when I crank it it cranks half as fast and I have smoke or exhaust coming out of the bottom carburetor while cranking. Any ideas would be most appreciated!!!

 

[wired247]

reeds are shot or broken

 

[Chris1956]

Gee, You need to fix the "half speed" cranking. It will be real hard to start cranking slow. Not sure what is causing the smoke. Even if you have bad reeds (which is unusual), she should still start. Get that part fixed, an then we can investigate the reeds.

 

[69ebkoskibee]

Thanks for the input! I now have even more problems..... after she started cranking slow I went inside for the night, today when I went to fiddle on her I came to find that I no longer have consistent spark. It cuts in and out and seems like its firing mostly on cylinder one. Almost seems like every time it should fire it does but only on #1 even when it should be firing on a different cylinder. I'm no stranger to engines but this has me stumped and think this is why she's cranking slow? And have no idea where to go next on a 2 cycle? The rotor is spinning so I don't even know how it can send spa to one when the rotor isn't there.

 

[69ebkoskibee]

What would be making it crank so slow on a fully charged battery?

 

[Chris1956]

Cranking slow is usually caused by low amperage. Make sure all the battery cables are clean, tight and not rotted out. My old Merc had rotted cables under the insulation. Look for bulges and other defects.

 

[69ebkoskibee]

All wires and cables are new and all posts and contacts were cleaned when they were reinstalled. Could it be something with the starter itself? I read that you need to have near 300 rpm when cranking to achieve solid fire so maybe the starter is shot?

 

[Chris1956]

Well, You can disassemble the starter. Maybe there is some dirt on the commutator? Need to fix that slow cranking speed, or you not make any progress getting her to start.