Dlomar 7900

[Logrover]

I have one i bought second hand, i have put a new exhaust on it as it was cracked. Its starts first pull, easiest saw to start i ve ever had but it wont idle for long, initially it idles fine the then speeds up and stops. Piston seems ok, minor scoring from use.All the plastic stops are still in place on the carb adjustment screws. Both screws are wound out anticlockwise as far as the plastic stop allows, any adjustments and it wont start.

 

Could it be an air leak somewhere?? I would also possibly like to port it etc

[wisecobandit]

Hmm initial thoughts are possibly set a bit to rich? Maybe worth idling it til it stalls and pulling the plug out to see if it looks excessively wet or black.

The carb settings "ideally" tend to be half way between there movement with stops fitted so it could be loading up with fuel and causing the stalling. The L screw will affect it more obviously on tickover.

Also the fact you say it starts easy usually means the carbs set a tadge rich but not always the case.

[computeruser]

Good suggestions above.

 

Speeding up from idle on its own, to me, suggests too much air or too little fuel. Start with the easy stuff - check intake for cracks, replace fuel/impulse lines, replace fuel filter. Any changes?

 

Then pressure/vac test if it is still acting up.

 

As for the adjustments, cut off the tabs on the limiters so you can actually screw them in/out as needed. They are an annoyance that serves no purpose to the end user.

[spudulike]

That rise in revs before it dies sounds ike lack of fuel like a saw does when it runs out of fuel or too muh air from an air leak.

 

The usual thing to do is strip and clean he carb plus check the fuel line, filter and tank breather.

 

If all this is OK then pressure/vac test would be next on the cards.

 

You need to sort this before any tuning work is completed on the saw.

[shavey]

i have read somewhere on the internet last year that some of the 7900's had idling and running problems and it was owing to a sloppy throttle shaft in the housing on the zama c3m carb maybe worth a check

[Logrover]

Right i had another play with this saw, removed the silly plastic stops on the carb screws, wound them all the way in and set them back to factory setting, L one turn out, H 1 1/8 turn out, adjusted the idle and its starts, idles and revs perfectly so well happy. still a superb starter, going to give it a good hammering tomorrow

[wisecobandit]

Right i had another play with this saw, removed the silly plastic stops on the carb screws, wound them all the way in and set them back to factory setting, L one turn out, H 1 1/8 turn out, adjusted the idle and its starts, idles and revs perfectly so well happy. still a superb starter, going to give it a good hammering tomorrow

 

:thumbup: Great news. Always pays to check the basics first.

[Logrover]

put 9 litres through it today felling big pine, going ok but it did go out of tune and i had to mess with it. it will do!

[peatff]

put 9 litres through it today felling big pine, going ok but it did go out of tune and i had to mess with it. it will do!

 

You might need stronger springs under the mixture screws if the caps were spacing them a bit. Try stretching them a bit.

[wisecobandit]

Or a dab of clear nail varnish on the thread of the mixture screw against the carb body normally works.