Hi There! (Older Merc Question)

[bp207]

Hi, I am new to this site. Have been reading stuff for a while, just registered though. From Southern Maine and finally getting a chance to enjoy summer after a somewhat long winter.
I just picked up an older Merc model 200 20 hp ser no. 4152571, according to my research it is a 1975. I'm actually trying to fix it for an older lady whose husband just died.
I determined that the switch box (332-4911) was bad because of britle and broken wires, also the trigger was bad, (338-34996), it had no resistance, so I replaced both. Now there is plenty of spark on both coils, but the engine only runs on one cyl. Am I missing something? Have already taken it apart again to make sure that all was correct and it seems alright. It almost seems like the timing of the second Cyl. is off? Are these the right parts? I researched this and all seems right but can't figure out wtf is going on.
Any suggestions or advice would be welcome. Thanks in advance.

 

[iggyw1]

Hi, I am new to this site. Have been reading stuff for a while, just registered though. From Southern Maine and finally getting a chance to enjoy summer after a somewhat long winter.
I just picked up an older Merc model 200 20 hp ser no. 4152571, according to my research it is a 1975. I'm actually trying to fix it for an older lady whose husband just died.
I determined that the switch box (332-4911) was bad because of britle and broken wires, also the trigger was bad, (338-34996), it had no resistance, so I replaced both. Now there is plenty of spark on both coils, but the engine only runs on one cyl. Am I missing something? Have already taken it apart again to make sure that all was correct and it seems alright. It almost seems like the timing of the second Cyl. is off? Are these the right parts? I researched this and all seems right but can't figure out wtf is going on.
Any suggestions or advice would be welcome. Thanks in advance.

Did you perform a compression test? If that is ok, check each plug for a good spark. If the compression and spark out of the plugs are good, you are having a fuel problem. No fuel getting to the cylinder that is not firing. If so, it could be the carb or reed valve that is faulty.

 

[bp207]

The compression is equal in both cylinders and I removed the carb and cleaned it, (checked the reed valves , visually, while I was in there). the engine still has the same symptoms, it starts and runs but only on the top cyl. . When the bottom plug wire is removed it does not change the way it runs but it will spark to ground. I even switched coils to see if it had any effect but it did not.
By the way, what is the compression supposed to be on that particular engine? Or what is acceptable? Thanks.
Bob P.

 

[bp207]

Does anyone know if 75 psi is too low for the compression in that 1975 20 hp? Both cylinders are pretty much the same, 75 seems a bit low though to me. The engine will start and run on one cyl, just can't get the bottom cyl to fire!

 

[bp207]

ttt