Engine Bogging Down

[dr1979-340]

I have a 1979 340 Drifter that I fixed up this past fall and winter.  After putting it all back together I took it for a test run Superbowl Sunday to see that I put everything back together properly.  All seemed OK, however I did not open the throttle wide open at that time.

Yesterday we got a nice six inches of snow so I took it out again.  This time I opened it up all the way.  It seem to run good until I got past 3/4 throttle, then it would bog down.

I tried adjusting the air screw on the carburetor but this didn't seem to make any difference.  From what I read in the Service Manual, this air screw if primarily for idle adjustment and should be between 1/2 and 1 1/2 turns open.

Background on sled:  This sled sat for about 15 years without running.  I did not replace the crank seals.  When I took the heads off, one of the cylinders had quite a bit more carbon buildup than the other. 

QUESTIONS: 

1.  Would adjusting the needle valve clip be worth trying?
2.  Should I do a compression check on the cylinders? 
3.  Should I just go ahead and replace the crank seals?

[Dandb7]

15 years sitting.....Crank seals ...!!

[Tory944]

  Yep.

[dr1979-340]

Thanks guys.  That's what I'm planning on doing.

What should I see on a piston compression test? 

Is it a good idea to replace the rings at that point?

[dr1979-340]

I did a compression test last night and had 120 lbs. on both cylinders.  I'm guessing that I don't need to worry about replacing the rings or pistons at this point.

It only took me an hour to get the engine pulled again and stripped down.  I had to order a clutch puller today or I would have have the new seals in last night in about 2 hours.

It sure is easier taking it apart the second time.

[Gilson435]

120psi is good compression You probably already know this but make sure you seal the case halves! I use Yamabond or Permatex Motoseal 

[dr1979-340]

Thanks for the information!! 

I saw a U tube video of a guy replacing crank seals and he said to put the sealant on the outside edge of the seal also.  He said to put grease on the inside part of the seal.

Is this standard practice for those of you that have done this many times?

[Gilson435]

I do grease the inside of the seal. I don't use the bond on the outside of the seal but I suppose you could, I dont think it is necessary though.

[dr1979-340]

Thanks again for your input.  I feel confident now about finishing the job.

[dr1979-340]

Well the crank seal replacement went smooth and all is back together again.  I sounded like a different engine when I fired it up.  Thanks for all the input and information!!

[rminier]

 Great to hear! Now we just gotta wait 'til the snow flies next winter. I must admit, kinda nice walkin' around outside in a T shirt today...

[Gilson435]

Awesome! Glad it all worked out for ya