Dolmar/makita/Solo won't start after hot. Please help

[Logger4Life]

I have like 4 built 7900s and 681s and thay all suffer from the same problem . They all run awesome until I shut them off then they will not start up again. I have tried all kinds of different things to figure out what the problem is but nothing will fix them on all of them it seems as though they are building to much pressure inside the tank. I was felling with my 681 and the hotter it got the worst the problem got it was even pushing fuel back out of the vent. Now this tells me that I should drill a second vent hole in the tank some where close to thes top of the tank to release the pressure but then gas will spill at some angles and also dirt could also get into the tank. Gas costs to much to just be dumping it out all day long. I fell for a large company that whole tree skids everything except for the veneer quality Hardwood and trees that are just to big to skid with a Timberjack 460 so my saw is running pretty much non stop except to fill up when you got to keep 3 460's moving you got to keep moving you know what I mean And it sucks that my favorite felling saws just won't stay running or sorry won't start back up after fill up. I have alot of $ in theses saws and they all do the same thing. Even the newest one. It is almost like they are boiling the fuel. If anyone out there can help please I am not to proud to take advice. you live and you learn. Is anyone having the same problems

 

[sefh3]

Have you tried replacing the tank vents?

 

[loganj01]

My Dolmar 7900 does the same thing, but not all the time. There is some kind of hot air damper that sends hot air into the airbox for cutting in super cold weather...mine was in the correct position though. It hasn't given me a problem yet this year, but I haven't really used it a lot lately because everything I've been cutting has been really small so the 028 has been the go to. Mine seemed to cause the most trouble if I ran it out of fuel...absolutely refused to start until it cooled off. I posted about it on here last year, but we never came to any concrete solution.

 

[benp]

Sometimes both of mine hiss when shut off and pushes fuel out of the vent after being run and hot. It seems the fuel tank pressurizes for some reason.

I have never had a no start problem though.

I just lay them on their side and unscrew the cap for a bit and all seems ok. Unfortunatly in a production setting that convenience is not there.

I reminds me of the gas boiling issues that the old Yamaha Grizzlies used to have.

 

[Logger4Life]

Thanks for the feed back. But here is the kicker as of 2008 all 6400-7900's come with a one way vent I had 2 2007 Makita 7901's that where ported also and I didn't have as much trouble with them . So I just don't know what to do besides putting a second vent in the tank that works as a two way vent. But as much as gas costs I just hate the fact that I will be dumping my hard earned $ on the ground. I love the saws for felling but if they won't start I can't use them. I actually have been running a Brand new 365xt with a 20" bar & chain. But the carbs on them suck and the clutch side bearing and crank seal and unfortunately the 372xt's bearings go out even faster plus they won't idle consistantly. I just blew up a 365xt the other day that is why I have a new one. the cylinder plating flaked offright above the exhaust port and hit the piston and rings and Ka-Boom.


Come on you Dolmar guys what is going on with my saws? 4 saws same problem. You run them hard for a tankof fuel shut it off to refuel and then they will not start again until they are cooled down.

 

[sugarbush]

Thanks for the feed back. But here is the kicker as of 2008 all 6400-7900's come with a one way vent I had 2 2007 Makita 7901's that where ported also and I didn't have as much trouble with them . So I just don't know what to do besides putting a second vent in the tank that works as a two way vent. But as much as gas costs I just hate the fact that I will be dumping my hard earned $ on the ground. I love the saws for felling but if they won't start I can't use them. I actually have been running a Brand new 365xt with a 20" bar & chain. But the carbs on them suck and the clutch side bearing and crank seal and unfortunately the 372xt's bearings go out even faster plus they won't idle consistantly. I just blew up a 365xt the other day that is why I have a new one. the cylinder plating flaked offright above the exhaust port and hit the piston and rings and Ka-Boom.


Come on you Dolmar guys what is going on with my saws? 4 saws same problem. You run them hard for a tankof fuel shut it off to refuel and then they will not start again until they are cooled down.

the change in 08 was from a foam to sinter filter with same type duck bill valve. have you checked spark before refueling when engine is still hot?

 

[parrisw]

Have you tried adjusting your L needle richer?

 

[PLAYINWOOD]

I sometimes have had this problem when the saw sits for weeks and then I drive it hard, but after a few tanks it seems to loosen up.Never had the gas boil but it can be a bugger to start.
I've always thought the diaphragms were dry.Do stock 7900 's do this?

I've also seen "too hot" worksaws boil gas when they are worked hard.

Not what I want to hear on the 365, I've got one in the mail as we speak.

Good luck

 

[LegDeLimber]

Sort of sounds like a place to try that ghetto idea I had about using those 4, dollar store meat thermometers to look at hot spots.

 

[rmh3481]

Fill it back up while its idling? You sure its not the ignition?

Only other thing I can think of is if its pressure and the carb needle is up and its flooding. Echo makes a couple of vents that may work for you. The first is plugged into a fuel line added to the tank, you just plug the check valve vent into the line and your done. The part number is A356000031

The other vent is used on the older 8000 and would need to have a 1/4 inch hole drilled, but once you add it, it sits just about flush and has a one way check valve built into it. Part number is 13131406320.

 

[ncfarmboy]

I sometimes have had this problem when the saw sits for weeks and then I drive it hard, but after a few tanks it seems to loosen up.Never had the gas boil but it can be a bugger to start.
I've always thought the diaphragms were dry.Do stock 7900 's do this?

I've also seen "too hot" worksaws boil gas when they are worked hard.

Not what I want to hear on the 365, I've got one in the mail as we speak.Good luck

Me either mine arrived yesterday.
I can't help the OP I haven't had any problems out of mine.
Shep

 

[nstueve]

I think we need more info...

1.) I would start by getting a inline spark tester so you can run the saw and watch the spark at the same time. this will show you if the spark is there when it's hot. Although I can't imagine 4 saws all having problems with ignitions at the same time. Especially since I haven't heard of any wide spread 6400/7900 ign problems.

2.) Go back to basics... Check your compression right away when it won't start. You might be loosing compression when your hot and if you're dipping close to 100-120psi the saw may not want to start for ya... just a thought... who tuned the saws? have you run to lean and torched a piston or two? only takes a min to pop a muffler and check the pistons condition...

3.) if it's not spark or compression its going to be fuel system related. I would knock off the first two and then come back to fuel as it could be vent, delivery, carb, tuning, air leaks etc... fuel and delivery are more extensive to weed through...

BTW: what are you running for gas? how old is it? does it have ethanol? what 2cycle mix? Curiosity more than anything, but even the best of us get fooled by bad gas sometimes :bang:

 

[zogger]

All your saws have the same over heating symptoms...not an expert here at all, but perhaps you are just asking too much of them. If you are doing trees so large it is maxing out skidders, maybe you need to bump up to 90 cc saws.

 

[nstueve]

All your saws have the same over heating symptoms...not an expert here at all, but perhaps you are just asking too much of them. If you are doing trees so large it is maxing out skidders, maybe you need to bump up to 90 cc saws.

well if that's not a good seg-way to talk him into a 9010 I don't know what is! LOL...

 

[Logger4Life]

Hi thanks again for the advice. And I do have 3 390xp's all built by ECsaws I like them very much it is just as many trees that I have to cut to feed the Skidder's for 9hours a day weight matter's a 7900 with a Sugi Hara 24" bar full is 3lbs lighter than a full 390xp that is alot at the end of the day.

First I have checked that compression on the saws they are all in between 190psi and 210psi the race 681 is up at 240psi cold but that one doesn't count. I'am talking about the work saws.I have tried richening the L speed and a bunch of other things with the carb I even changed out the needle vavle. doesn't change what happens.

Second I thought the same thing about the ignition systems 4 saws same problem and the Dolmar has a red coil and the Solo's run the black coil.

I just don't get it do the stock ones do the same thing?

 

[MCW]

I doubt that fuel vapourisation is the issue. I've run 3 different 7900/7901's hard over the years all day in summer temperatures as high as 111°f and never had an issue starting. The only issue I've had with the 7900's starting is either from blocked pre filters on the HD filter kit (I don't run the pre filters anymore) or with certain mineral oils. The Husqvarna Low Smoke was a nightmare. Switched to semi synthetic/full synthetic and solved that problem immediately with no other changes to the saws. Funnily enough I have also heard of issues with pro Stihl saws running certain dino oils as well and this was from a dealer.
I highly doubt you could have a number of these saws exhibiting the same problem without it being a common issue with filtration, tuning, or fuel/oil. They are a pretty solid design with few mechanical issues (unless you're a one eyed Stihl fan ). If you had one 7900 with an issue like this it could be a whole number of things but to have a few of them with the same problem makes me think it is something else as mentioned.

My first 7900 actually split the fuel tank after suffering from the early series bad breather. I had to get it plastic welded back up and has been fine after updating the breather however poor starting or fuel leakage wasn't one of the issues I had.

All your saws have the same over heating symptoms...not an expert here at all, but perhaps you are just asking too much of them. If you are doing trees so large it is maxing out skidders, maybe you need to bump up to 90 cc saws.

Sure they are smaller from a cc point of view but that doesn't mean they can't take a beating. If they are tuned correctly they'll run the same temps as the bigger saws in the same wood. The only thing really holding these saws back from bars over 32" is their oiler and with a decent oiler they could consistently run bars well over that.

 

[loganj01]

Hmm...I had some of that Husky Low Smoke oil at one time, but I can't remember if it was when I was having a lot of trouble with my 7900 starting. I've been using Stihl synthetic for a while and haven't had a problem. I would never have thought the oil would have made a difference...

 

[MCW]

Hmm...I had some of that Husky Low Smoke oil at one time, but I can't remember if it was when I was having a lot of trouble with my 7900 starting. I've been using Stihl synthetic for a while and haven't had a problem. I would never have thought the oil would have made a difference...

I honestly wouldn't have thought that either but after about 10-12 tanks and bingo, hard starting. Have found out since that it's not just me and also not just limited to Dolmar saws either. Plug fouling was the issue and this was with properly tuned saws at 50:1 as well.

 

[heyduke]

Come on you Dolmar guys what is going on with my saws? 4 saws same problem. You run them hard for a tankof fuel shut it off to refuel and then they will not start again until they are cooled down.[/QUOTE]

I have two 6400's with 84cc top ends from baileys. one is fine but the other will die and refuse to start if you push it too hard, sounds like the same issue. i love the saws, plenty of power, can really throw chips but if i bury the bar in a big piece of wood and cut hard, it just dies and won't start again until it cools down. there have been a few other threads on the forum that addressed this issue but i haven't seen any that found the root cause. My gut feeling is that the ignition module/rev limiter screws up when it gets too hot. i'll keep looking. when i get time i'll switch modules between the two saws and see if the problem follows. Will post what i find.

Good luck

 

[JustinM]

I have several dolmars but never consistently have the problem the OP is describing.

One thing I do know about the Dollys - especially the 70cc and up - is that they are super hard to get started once flooded. I can flood a stihl or a husky and usually 8 pulls with the plug out & a new plug & its good to go. When Ive flooded out my 7300 or 7900 I have found I need to just put it away for the day & get a different saw. And of course its easy enough to do if you're used to the reverse on/off switch of a stihl. Do it at least once a year when i havent run dolmars for a bit. lol.