Makita EA6100 Surging

[rta01]

Need some help/ideas/advise on a Makita EA6100 that is surging at high throttle. Surges under load and no load. Same machine I posted a thread on about a year ago (https://www.arboristsite.com/threads/new-makita-ea6100-questions.345738/). Haven't used it any since then. To summarize that posting, bought as a used HD saw. Replaced several worn items. Saw ran pretty good but stalled is the the 20" bar was totally in a log or stump. At that time it did not have the surging issue. I had bought a carb kit but have not yet put it in.

Again, not surging at idle, only when revved. Was only cutting 4 tp 6 inch logs, so should not be an over capacity issue.

Here is the list of items I've come up with to go through:
1. Clean and rebuild card. That would be too easy, but definitely need to do it regardless.
2. Air leak from fuel lines or intake boot. Have ordered a boot just in case. Cursory inspection without teardown: Fuel lines may be a bit on the hard side so .... Intake boot looks good and still pliant for what I can see.
3. Gas tank vent clogged. That one has got me thinking. When I removed the gas cap to fill, the tank was pressurized. Did the gas spew thing. It had been sitting a year. Would a clogged vent cause that, or is the vent on this saw like a check valve to just let air in as it runs?
4. Bad seals. I hope not, I don't want to deal with that.

So, anything else? Am I on the right track?

 

[fordf150]

tank vent holds pressure in the tank. it will let air in but not out so what you experienced is normal for basically every new saw.

fuel lines are pretty stiff and not real sticky??? when new so be sure they are bad before ordering new ones


my experience working on these is very limited...we have had very, very few issues over the years with them.

check compression! that is the one major issue we have found on the 6114/6101 concrete saws which is based on the 6100 chainsaw. anything under 140-145...replace the piston ring. low compression causes some funny running issues and hard starting(that is a relative term because these saws should start on 3 pulls at most)

have replaced a couple coils and sold a couple strato intake boots(strato boot and intake boot are seperate...strato boot comes with the aluminum plate and reeds).

have heard of a couple people having carb issues but never saw one myself so cant confirm if they were actual carb issues or something else.

 

[Franny K]

My Dolmar 6100 was behaving strange, like a cheap flat head lawn mower type engine on governor higher and then lower rpm. I got a double D screw driver. It must have been like 4 turns out. Don't feel real confident about ending up somewhere around 1 1/2 turns out, less than that seems to have a hanging high idle when coming off full speed. Could the high speed screw slowly unscrew itself? It does not turn real easy. Seemed to get worse until I had to order a tuning screwdriver. Not real sure this is the same as your surging. Seemed pretty down on power as well, no compression problem. Might also check and make sure the tubes are pushed all the way onto the back of the purge or prime flexible button thing. Perhaps I caused that issue. I also seem to recall the fuel line came off inside the tank, took kind of special bent wire thing to be able to get it back on. It was frustrating there for a while I think it is back to normal now.

Point 3) reading on here fuel tank vents in modern stuff only let air in. A little squirt when opening them seems to go with the territory. The vapor pressure of the gasoline will increase with temperature.

Fran

 

[sevensandeights]

In my experience with a Makita 6421 with a BB kit and then an OEM 79cc piston and cylinder is that surging is caused by an air leak. Check the carb bolts and cylinder bolts.

 

[rta01]

My Dolmar 6100 was behaving strange, like a cheap flat head lawn mower type engine on governor higher and then lower rpm. I got a double D screw driver. It must have been like 4 turns out. Don't feel real confident about ending up somewhere around 1 1/2 turns out, less than that seems to have a hanging high idle when coming off full speed. Could the high speed screw slowly unscrew itself? It does not turn real easy. Seemed to get worse until I had to order a tuning screwdriver. Not real sure this is the same as your surging. Seemed pretty down on power as well, no compression problem. Might also check and make sure the tubes are pushed all the way onto the back of the purge or prime flexible button thing. Perhaps I caused that issue. I also seem to recall the fuel line came off inside the tank, took kind of special bent wire thing to be able to get it back on. It was frustrating there for a while I think it is back to normal now.

Point 3) reading on here fuel tank vents in modern stuff only let air in. A little squirt when opening them seems to go with the territory. The vapor pressure of the gasoline will increase with temperature.

Fran

Just finished the carb clean and replacing all the internals. Fuel lines were good when I took it out. Haven't been inside the tank yet - that's next.

 

[rta01]

In my experience with a Makita 6421 with a BB kit and then an OEM 79cc piston and cylinder is that surging is caused by an air leak. Check the carb bolts and cylinder bolts.

Yeah, air leak is what I'm afraid of. Piston and cylinder are in great shape, so don't want it leaning out on me. the carb bolts (nuts really) were tight when I pulled it off. I'll give the cylinder bolts a tweak.

 

[sevensandeights]

I bought my saw with a newly installed BB kit. The impulse nipple was loose at the base of the cylinder. Unlikely in your case being that it is all stock. After I swapped in an OEM 79cc p&c I also found a small tear in the intake boot. This might have been self inflicted though from taking it on and off a bunch while fiddling with the BB kit and then OEM 79cc p&c.

 

[rta01]

I bought my saw with a newly installed BB kit. The impulse nipple was loose at the base of the cylinder. Unlikely in your case being that it is all stock. After I swapped in an OEM 79cc p&c I also found a small tear in the intake boot. This might have been self inflicted though from taking it on and off a bunch while fiddling with the BB kit and then OEM 79cc p&c.

Well got the carb back on and fired it up. Seems to run fine, but didn't try cutting with it or let it run very long. I did replace the fuel filter and the line inside the tank looked OK. Wasn't soft or anything. Sprayed carb cleaner around the fuel lines and intake boot while running at half throttle. It bogged down. Especially when I sprayed behind the carb. Suspecting the intake boot now.