My truck runs greatwith no load but at 1/4 or so throttle t as I tryto accellerate it stumbles, misses bad, i have good compression , timing is correct , new fuel filter, just removed the pre cat put on a header, checked rear cat took it into a mechanic (not a Mazda guy) He spent 2 or more hours on it, confirmed the basics are all ok . he said it's acts like a clogged cat but isn't. carb blows fuel spray out ? like somthings out of wack. could it be the carb?

 

Have you checked the spark plugs to make sure they are not fouling? Make sure there is no oil or other build up on them. The way to test for a clogged exhaust is with a vacuum gauge. First find a good vac port that is manifold vacuum. Then hook the gauge up to that port with a long vac hose and let it hang inside the driver window. The reason for the long hose is so you can drive down the highway. Next monitor the vac reading at idle for reference. Then start driving about 45-55 MPH and keep the throttle steady and see what the reading is. It should read about 17-20 Hg and about the same at idle. If it is low like about 10 and keeps going towards zero the exhaust is restricted. If it keeps good vac the exhaust is good and flowing properly. The vac reading will be low when accelerating.

 

Truck is now running about 95%, I had to advance timing way off but it runs, I am going to check the crankshaft key/ timing gear to see if something moved there, dosn't make scence that timing it right with the pully mark and the #1 is in position but it won't run there. could also be the upper timing gear pin has sheared . Would help if I had a history of the truck but I don't.

 

pulled the timing gears off & crank timing srocket was loose result of mashed key now the crank has the keyway ruined wondered if I could weld in the bad part of the groove and try to keep the gear from slipping again.

 

filled in the damaged keyway with weld and reworked it extended the keyway to good crank metal with a dremel used t stock keyway and put it back together runs perfect hope it holds for a good long time. any body ever done this?

 

Rather ingenious! Sure beats having to replace the crank.

 

I've heard of it done that way and a couple other ways. I think you can also get an insert where you grind a big groove in the crank then press in the insert which allows you to put the key in just like new.