Dolmar 7900 issue

[ffchewy17]

I do get a good amount of use out of my saws. I run a personnally owned (3 man) arborist company, I'm a class C faller for the FD, and I have 40 acres of hardwood select timber in western NC that I cut furniture grade timber off of. I do all the above because it's fun for me, I'm trying to get better every day at cutting and climbing. I would still consider myself and intermediate climber and faller. All of the above jobs are in addition to my full time profession that pays the bills. I work on all my own saws, I have learned the majority of the saw repairs from the help of everyone on this site and originally arboristsite.

I usually check compression on all my saws once a year, that determines my ring replacement and the condition of the piston skirt/crown. When I re-ring I will hit the inside of the jug with some scotchbrite 200 on a drill to help break in the new rings.

You guys on here help teach me something new everyday, thanks again.

 

[Khntr85]

I do get a good amount of use out of my saws. I run a personnally owned (3 man) arborist company, I'm a class C faller for the FD, and I have 40 acres of hardwood select timber in western NC that I cut furniture grade timber off of. I do all the above because it's fun for me, I'm trying to get better every day at cutting and climbing. I would still consider myself and intermediate climber and faller. All of the above jobs are in addition to my full time profession that pays the bills. I work on all my own saws, I have learned the majority of the saw repairs from the help of everyone on this site and originally arboristsite.

I usually check compression on all my saws once a year, that determines my ring replacement and the condition of the piston skirt/crown. When I re-ring I will hit the inside of the jug with some scotchbrite 200 on a drill to help break in the new rings.

You guys on here help teach me something new everyday, thanks again.

Damn man, you must have a damn good job to have the 40 acres lol....

I tell ya I bought a comp gauge and I used it one time when I first got it....I thought it was a tool I needed, but it just collects dust....

 

[Poleman]

The Dolmar carbs do have a tendency to accumulate fines like Brian said. Have found quite a few like this. I would also check the filter....I don't like the felt filters myself. They have a tendency to get schlacky inside and won't draw....and you can't tell it.

 

[ffchewy17]

The 40 acre where bought in 1971 by my grandfather with no road access, cheapest way to do it

Small update ... decided to go ahead and just do a bunch of preventitive maintenance instead of hunting for the one broken thing. Put in new impulse line, fuel line, fuel filter and rebuilt carb. Waiting on a new tank vent to come in the mail. I think the main issue was I forgot to replace the winter cylinder door on the airbox. Saw started and ran great , richened up the high side a bit due to the heat to try and cool the cylinder a bit more.

What was the part of the carburetor that was clogged up? I'm not very experienced rebuilding carbs.

Poleman, what filter do you prefer to run?

 

[ffchewy17]

Any updates on someone running a 7910 non-window piston in the 7900? Worth it? The cheapest I could find the 7910 piston for was $98.00.... just curious before I pull the trigger on the purchase

Thanks again everyone

 

[ffchewy17]

Damn man, you must have a damn good job to have the 40 acres lol....

I tell ya I bought a comp gauge and I used it one time when I first got it....I thought it was a tool I needed, but it just collects dust....

I actually use the gauge more than I thought.

The FD down here pays really good, but the trade off is the *s-wordbags we have to deal with on daily bases

 

[Rob Stafari]

I recall that happening to me once with my Echo 3900 that had a bar tip give up from heat and stop the saw dead. The engine would start and run but the chain was frozen. I greased and oiled the tip and the saw was back in business.

Yeah I was in a hurry and was able to just switch bars to get it done. Have yet to try to mess with the seized tip, but should prolly get it soaking in some oil to see.

 

[backhoelover]

Any updates on someone running a 7910 non-window piston in the 7900? Worth it? The cheapest I could find the 7910 piston for was $98.00.... just curious before I pull the trigger on the purchase

Thanks again everyone

@fordf150 is a dolmar dealer check him out. hes a damn good guy tool has treated me like his own son no lie and i havent really bought that much from him like some guys on here

 

[backhoelover]

tool- too

 

[Khntr85]

Hell man you may as well wait to do any engine work if your saw is running good agian....you could always do that when you have some down time...

 

[huskihl]

Any updates on someone running a 7910 non-window piston in the 7900? Worth it? The cheapest I could find the 7910 piston for was $98.00.... just curious before I pull the trigger on the purchase

Thanks again everyone

The 7910 slab sided piston is a slight upgrade for a 7900. I'd say it's noticeable

 

[Wilhelm]

Any updates on someone running a 7910 non-window piston in the 7900? Worth it? The cheapest I could find the 7910 piston for was $98.00.... just curious before I pull the trigger on the purchase

Thanks again everyone

I've got a windowed AM piston in my Dolmar PS-6400, don't know the manufacturer though - got it off eBay UK.
Looked great out of the box, runs flawless.
I did use OEM circlips and a Caber piston ring.
Been using it for ower a year, checked for damage at the beginning of the year and the piston has no scoring.

AM is definitely worth considering.

 

[Khntr85]

@fordf150 is a dolmar dealer check him out. hes a damn good guy tool has treated me like his own son no lie and i havent really bought that much from him like some guys on here

I will second this, dude is a flat out good dealer, honest, and very knowledgeable.....the type that once you buy from, you will continue to buy from....

It takes a lot to be competitive on the internet with so many options....when you find a guy that is honest to his word, willing to help, and competitive prices, they become your only dealer!!!!

 

[Wilhelm]

3x for @fordf150 , great guy!

https://performanceoutdoorequipment.com

 

[Wilhelm]

AM if You like:
https://www.hlsproparts.com/mobile/Product.aspx?ProductCode=H31790

 

[Wilhelm]

Note:
I never bother switching the carb boot door to winter on my saws (PS-6400 & PS-7900).
The lowest temperature I used my saws in was about -15 to -20°C, never had my saws carbs freeze and the saws actually run much better sucking freezing cold air.

If You run Your saws at much lower temperatures, You might still want to allow the carb to suck warm air from the cylinder though.

In regards to "vapor lock" it affects only starting the saw, not how it runs once she's come to life - at least that is my humble experience with my Dolmar PS-7900 which has become very prone to vapor lock during the last year.

 

[ffchewy17]

I have purchased a couple bar mount spacers from fordf150.... great customer service. I actually talked to him last week about a echo 355t or the new dolmar top handle, tons of great info. We also spent considerable time talking about FD vent saws and carbide chains.

I probably hit him up about the piston , it seems like the consensus is it makes a big difference.

Just contacted mastermind about porting a MS461

 

[Poleman]

I usually use the Stihl type filters or Husky with the screen instead of the felt.

The picture is of the screen in the carb before it goes through the needle. Also seen them with like a jelly type blob....I call them slugs cuz that's what it reminds me of....a slug trail.

Windowed or slab piston.......I think it's a toss up. I run both and really can't tell a difference....but....most all my saws are modified in one way or the other whether ported, carb mod or unlimited could.....they just all run GOOD!!!

 

[huskihl]

Note:
I never bother switching the carb boot door to winter on my saws (PS-6400 & PS-7900).
The lowest temperature I used my saws in was about -15 to -20°C, never had my saws carbs freeze and the saws actually run much better sucking freezing cold air.

If You run Your saws at much lower temperatures, You might still want to allow the carb to suck warm air from the cylinder though.

In regards to "vapor lock" it affects only starting the saw, not how it runs once she's come to life - at least that is my humble experience with my Dolmar PS-7900 which has become very prone to vapor lock during the last year.

I don't think your 7900 is vapor locking. It's flooding. Easiest way to start them is hold the throttle wide open and start pulling. I think the needle in the Zama leaks fuel by resulting in a flood condition. Mine hasn't done it since I swapped an HD12 in from a 372xp.

 

[Wilhelm]

I don't think your 7900 is vapor locking. It's flooding. Easiest way to start them is hold the throttle wide open and start pulling. I think the needle in the Zama leaks fuel by resulting in a flood condition. Mine hasn't done it since I swapped an HD12 in from a 372xp.

I used to think that my PS-7900 is flooding, pulled the plug a dozen times just to find it to be bone dry.
I no longer pull the plug, just engage throttle lock and start yanking till she comes to life - takes easily 15-20 pulls.

I'm no 2-stroke engine expert, maybe it isn't vapor lock what bothers my PS-7900.
All I know she didn't have this issue before, and with time passing it is getting worse.

I am at a point where I am considering a carb rebuild.

This issue is non-existent during winter operation.