6-71 Heavy Smoke

[JohnVickrey]

Someone school me please.  When under heavy acceleration or when pulling a pretty good hill I have severe black smoke.  If I take my foot out of it the smoke will go down to a wisp.  I can pretty much control the severity of the smoke with the throttle.  I have N65 injectors and normal timing with a Limiting Speed governor.  I get from 8 to 9.9 miles per gallon towing a GMC Sonoma. 

Question: If I drop down to N60 injectors will it smoke less and still maintain performance?  Embarassing in the toll gate when I don't remember to keep my foot out of it.

[bevans6]

 You can have N65's and normal cam timing but the injectors need to be timed fairly advanced, around 1.470", I don't have the specification handy.  But that is likely part of the issue.  You can also look at intake and exhaust restrictions, clogged air cleaner and muffler.  But it's possible that running the rack and getting the injector timing more advanced can help with the smoke.  Going to N60 injectors will reduce potential power by around 20 hp, 318 down to around 300 (if it was an 8V-71).  I couldn't find data on the change in a 6-71

Brian

[Dave5Cs]

John Brian's right about the N-60's I have them in my 6V-71 and I tow my 95 S-10. Sometime it unhooks itself and passes me up rolling her headlight hoods as she passes me, and that's down hill.

Dave

[luvrbus]

It may not be the injectors did it just start or has worsen over time ? the old girls when they start smoking heavy usually means it is getting tired you can try injectors or different setting but not much you can do with a N65 with std timing.

I am not a huge fan of the N injectors myself, run a compression check if it checks out ok I would have Don @209-863-8810 build a set of 7G60'S with a calibration of 60 you won't lose any power only the smoke if the engine is in good shape.

Give Don a call Friday he may have other ideas to help you, he is the sharpest in the US on old DD injectors and will talk to you tell him I said call   

good luck

[chessie4905]

   Before we turbo'd our 4104, it had n65's, 4 valve head, advance timing. It would smoke a little at lower rpm but not great amount. It would run almost clean wound up even going up a grade. Yours is most likely either being lugged or air filter is restricted, or needs a  tuneup with proper injector setting with your standard timing.

[bevans6]

Just looked it up, brown tag N65's with standard timing calls for 1.460" and "correct to advanced timing at 1.484" at first opportunity".  So there you go.

Brian

[chessie4905]

   Oh, and make sure your emergency shut down flap isn't slightly closed. It should be latched open, but I'd check it.

[luvrbus]

Not enough info on the condition of his engine,check the easy things first as mention the air supply then if you think the engine is great shape pull all 6 injectors and have them tested only takes 1 bad one to smoke like a train.

If you own a set of gap gauges for the governor check the gap it is probably set on 200 change it to 170 you can control the smoke with the gap it just makes one sluggish then there is always the fuel modulator you can install

[chessie4905]

    You can also change the fuel restriction orifice size some. BTW, how many miles to a quart of oil? How much blue or white smoke upon starting? How long till it clears up?

[JohnVickrey]

Thanks for all the replies.  Bus runs good just have to keep my foot out of it.  When I get home I will go through it again. 
I think the smoke has very slowly gotten worse since I put the the N65's in about two years ago.  Probably ready for a tune-up.  The emergency shut down flap is tie wrapped open, it was hanging out in the airway.  I run from St. Cloud, FL to St Ignace, Mi and have to put a gallon of oil in to bring it back to just above the add mark.  Just a puff of white/grey smoke on cold start up.  Air filters are paper filters, I pulled one out and took it for a short run, still smoked.  Also forgot to mention, it's a two valve head.  Smoke clears up when it tachs out. 
   
We are in Elkhart, IN for a couple of days to check out all the RV Surplus stores. 

[John Z]

Hey John, would like to read a write-up on your surplus shopping. Have heard others say they were there, but no other info.