THunderbolt 500 50hp motor has spark, fuel , comp but wont start

[snake91876]

Have a early 70s thunderbolt 500 50hp 4 cylinder engine. The motor spins, has fire, comp, and fuel, just rebuilt carbs today. Motor spins and chugs a couple of times and
sounds like its going to bust off but never does. Any suggestions on what could be, motor was running and just quit and wouldnt start again. This is the belt driven distributor model and looks complicated.

 

[mrallen007]

Re: THunderbolt 500 50hp motor has spark, fuel , comp but wont start

I have a much different engine (94 3 Cyl 2 Stroke), but I'm working through an issue with similar symptoms. Motor ran fine when I bought it of course, but choked out and died the first time I had it on the lake. Since then I can kill a battery from a full charge trying to get her to fire. Once I get her running, she dies before I can get off the trailer. I've been beating my head on a wall so long the wall's getting tired of it.

But today a guy at West Marine put me on to a viable lead. Turns out my fuel pump croaked. Just that quick, it stopped working. To test it I pulled the fuel line from the carbs and turned the key. Running the engine off the starter should pump fuel through the lines. Be sure so have something to catch the fuel in case the pump works though. When I did this I got no fuel.

I stripped down the pump tonight and it is clogged pretty bad. Ran just fine for years before I got it. It clogged and died on me in just a few runs. Now it does the same as yours. So, I have a rebuild kit on the way now.

This may be a shot in the dark, but worth a shot at least. Happy hunting. Let me know how it goes.

Billy

 

[MacDaddy21]

Re: THunderbolt 500 50hp motor has spark, fuel , comp but wont start

Have a early 70s thunderbolt 500 50hp 4 cylinder engine. The motor spins, has fire, comp, and fuel, just rebuilt carbs today. Motor spins and chugs a couple of times and
sounds like its going to bust off but never does. Any suggestions on what could be, motor was running and just quit and wouldnt start again. This is the belt driven distributor model and looks complicated.

I just got done rebuilding a 1979 mercury 402 (40 hp). I had just rewired everything, and when i tried starting it, it would try and try but would not kick over. I pulled the fuel pump off and pumped the primer bulb and made sure it was pumping fuel through. then i checked for spark, which i had. then i got a buddy to come over and spray starter fluid in the carb while i held the key on start. after a few seconds it fired off and ran like crazy. it just took that extra little bit to get it going. now, my motor hadnt run since 2002. so its been awhile, but it is pushing water out of the teller like a brand new motor. might try some starter fluid if you havent. if you are getting spark, fuel, and compresion, you should be almost there.