my Friend got a new dolmar 7900 and is breaking it in. hes got about ten tanks through it . and today while we were cutting firewood with another one of our friends, and his idle speed seemed to raise up a bit. not like abnormally high or anything but higher then it had been the last ten tanks. Is this normal? i don't remember it ever happening with my 7900 but maybe it did and i didn't notice. Another thing. What have you guys been running for rpms with your 7900s? and where was it running before you set it after break in . i read somewhere that factory settings on the 7900 are pretty close to where they should be . is that true though ? or do they still need to be tuned in a bit once you get em loosened up ? i really wish i had a tac to see what its running at. i think ill just take it in either way. just would like to hear what you guys have found about this. Thanks
question about break in . 7900
- Thread starter arborman
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njforestfire
ArboristSite Operative
restricted air flow from a clogged air filter I believe will increase the idle speed...so check that first. Did you use different gas/oil ratio mixtures in those 10 tank fulls thru the saw?
Timothy
ArboristSite Member
was the gas tank about to empty?
Maybe the saw is finally starting to loosen up and because there is less resistance the idle has climbed a little.
no the gas tank was just filled a few min before. i was thinking also that maybe it was losening up and that is why it was doing it. my 7900 didnt do that though. maybe its just the difference in the two saws. who knows. the only thing i am not sure about is if his second tank was the exact same mix as his first becuae he filled up his can in the morning. could a richer mix bring up the idle ? if it was differnt i dont think it could of been that much different becuase i watched him mix it and it was about 3.5 oz of mobile mx 2t. and then one other thing i thought it might of been that may be a real shot in the dark. is he filled up with my bar oil which was winter weight and his was summer that he had been using which was very very thick. you could feel that the thinner oil was flowing much better in the cold weather. so is there a chance that the idle has always been a bit high and that the thin oil made it easier for the chain to spin and there for made it seem like the idle was coming up a bit since the chain was spinning slightly on idle?
njforestfire
ArboristSite Operative
I seriously doubt that the bar oil would have anything to do with the idle issue. For the idle to increase that much, it would (IMHO) have to be something with the air/fuel ratio going into the saw. i.e. different mix, not enough intake air. Did you try to change back to the other bar oil? That would give you the true answer regarding the bar oil issue.
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Crofter
Addicted to ArboristSite
arborman, If the temperature was considerably colder than previously it would cause the mixture to be effectively leaner and possibly make it a bit revvier. Sometimes a bit of dirt in a jet can cause temporary changes to mixture also.
