d17 motor stumbles

[bob from ill]

freshly built motor runs descent. but it stumbles at all throttle possitions. rebuilt carb, new itake gaskets. new coil points wires and plugs(autolite 64 with 3/4" reach gapped 25 thous.) timed with light @ 25 deg btdc. When fist got running, it ran really smooth. the rain cap on the muffler didnt even bounce around at low idle. hooked tractor up to haybine and mowed about 5acres hay and when done it was running as mentioned(stumbled). The only thing that was done during this was I filled up with fresh gas. the gas i use is nolead with 10% ethanal.

 

[Will Herring]

Is it a vintage of tractor that requires some aftermarket lead additive? Is one of the plugs bad?

 

[bob from ill]

Ive read on here that lead additive is nothing but a gimick. ive also changed to a differant set of plugs with no change.

 

[Texas Denny]

It most likely is carburetion. There are so many things that could cause this. Plugged main jet, plugged tube from the main jet to the venturi, holes in the tube from the main jet to the venturi, missing venturi, venturi installed upside down. You simply have to get every single channel open to original dimension and insure that the tube from the main jet to the venturi is Perfect.

 

[Anonymous-0]

you might recheck the valve lash.

 

[Sid]

25 degrees BTDC?

 

[DickL]

I didn't read where you removed the sediment bowl and disassembled it. A quick way to make sure it is clear for a check is to blow air from the carburetor back thru the tank. With the gas cap off that is.

 

[Anonymous-0]

I have rebuilt several 226 cubic inch alliS engines over the years and yes, fuel can be a problem, but If you have good flow and the engine is stumbling when you give IT throttle I would suggest a plug or pionts. I just went thru the same thing with a 45 engine I CURED IT WITH A SET OF CHAMPION J-8 PLUGS. tHEY HAVE A LONG DESIGNATION BUT THEY STILL ARE J-8. The autolite plug I had installed were new and they broke down after about three hours on dyno at break in of engine.

 

[Texas Denny]

Bob, how did you come up with 25 degrees before TDC? I thought correct timing was at TDC and that the distributor automatically advanced as much as 25 or 30 when running (according to my manuals). I would expect hard starting and no power at 25 TDC. Typically Allis were timed statically at zero.

If you used a timing light at full rpm, 25 should be OK. I"ve never set one other than by ear. I usually adjust distributor for fastest rpm and then retard slightly. All, I"m afraid, a matter of feel.

 

[Flat47]

Most D series gas motors are indeed timed 25 degrees BTDC at spec rpms per service manuals. There is a "F 25" marked on the flywheel at the fire point which is 25 degrees btdc. When timing with a light, that should be seen in the flywheel timing hole. There are no weight or vacuum advance systems on these delco distributors like in automobiles.

Check the simple stuff first: plugs and wires, carb, sediment bowl.

 

[bob from ill]

I have a 170 and it runs smooth so wednesday im gonna swap plugs wires and even the carb and see if it changes the way the d17 runs. When I say it stumbles I mean when at a set rpm itruns smooth for about 3 to 5 seconds then it just pops a small pop out of the exhaust pipe. i have a rain cap on and at low idle it opens the flapper about a 1/3 then suddenly it snaps open and closed and then back to 1/3 again. when at wot it does the same but only it is openall the way. When it was almost dark i started the trator and used a screwdriver blade to arc the plugwires at the plug on the head to see if it was intermittant spark but found nothing wrong. Im really frustrated. i got all the books and have used them to rebuild this thing and its been in the family for 40 years so i want to get it running right for my dad,(its his tractor).