Jd 70 missing

[JDSkyski]

I have a 70 allfuel that has 90 psi compression on both cylnders. The idle passages in carb are clean, both plugs are getting good fire. I put a straight chrome stack on it and it seems to be missing at every thing but full throttle. Can pull either plug wire at lower speeds and will stay running. My question is this I"ve checked tempature on head at start of exhaust and they checked within a few degrees of each other at all speeds so it must be firing ok but why does it sound terrible? Thanks all

 

[Anonymous-0]

maybe you its your hearing from the fancy exhaust pipe i would suggest spending 16 hours a day plowing for a week and see if you still notice the strange sounds ????? HELLO

 

[BushogPapa]

It is just an illusion,,,the "Lead Cylinder" gets the crank back up to speed and the "Trailing Cylinder" seems to be doing nothing...but it actually is..

I wonder, why does my "B" always fire on the left cylinder (Lead Cylinder) and miss on the Rt almost never fires..??
SAME Deal...just not as pronounced in the twin carb layout..

 

[JDSkyski]

Bushhog, my 44A allfuel sounds sweet compared to this when I have it tuned good. Also never been around dual carb tractor until this one Just use it to launch the boat at the lake house but has to pull a steep hill will talk a sweet song under load so all must be ok right? Some old 2 clyinders get a nice retirement too unfortunatly not me yet.

 

[gtx1967jewison]

just fyi, i've proven on the dyno twice now, one a B & the other an R diesel, both lost several hp with the straight pipe, & we spent an hour tuning the B to get even that. its only 27hp to begin with so a 6 hp drop was huge. keep the muffler. we even started with a 5 ft tall straight pipe & cut it 1ft at a time looking for gold. no dice.

 

[2cylinder]

If its to far advanced at idle they tend to miss fire and carry on, check the timing and make sure your springs for your timing advance weights aren't broke, try retarding the timing and see what that does for ya. 2cylinder

 

[BushogPapa]

You know, maybe it would be a good idea to check the valve lift with a Dial Indiator to see if there is a problem...
Valve adjustment or worn Cam Bearings could cause it be weak on one cylinder at idle or light load..

I ran across one JD 50 that had that same problem..bad Cam Bearing..sounded like it had a very weak cylinder.and I had just put that head on and ground the valves myself..!!
When I grind them, the valves do not leak..!!

Ron..