Makita 6401

[Chris-PA]

Chris, I found a Gulf gas station near me that sells non ethanol gas. Plus I use StarTron. Those two things helped immensely. Before that I had to fart around with my saws to coax them back to life after letting them sit for a couple minutes. Man, that got old fast.

Chris,
there was a station near the airport ( i think on either 'airport' or 'MacArthur' road) that sold ethanol free. It was there last year

Thanks guys, but there's a station 3/4 of a mile from my house and I decided some time ago I was just going to have to learn to use what fuel I can buy there.

These makita/dolmars have a rubber boot....

That's a good data point - the rigid manifolds are made of bakelite and are thermally insulating too, so I guess it isn't much different.

I was having this problem in hot weather with my MS361 (yes, you read that correctly). It helped to let it idle for a couple minutes after cutting to cool down a little.

That's a good point and I do that too.

Now I'm back to thinking about how to make a carb cooler, but it's not a trivial thing to design. Most saws don't have any room to mount a heat sink on the carb, and there is no air flow when you shut it off.

 

[timq585]

Having a similar issue with my dolmar 6400. It starts but my arm is pretty tired after it does. I bought a fuel line and impulse line but haven't done them yet.
Sounds like if fuel in the carb helps it start it's def a fuel issue.
Does choking it help?
Maybe a tank vent?
Has it always been this way?
I'm remembering someone told me of one that had problems and the impulse port wasn't drilled out completely in the cylinder. Fixed it and ran beautiful.

I have 2 of these saws, 1 runs and starts great no matter what. The other 1 runs like a scalded dog after you get it started. It will start right up when cold or on choke the first time, but after it is running and you shut it off, if it sits for 5 minutes it wont start. If you try and start it right after you shut it off it will fire right back up. WEIRD. It happens no mater what the temp is outside. I have run this saw in 0 degree weather, and 90 degree weather, still acts the same way. I have tried e-free gas too. Whats the deal with the tank vent? How can I test that? Thanks

 

[Andyshine77]

You may very well be having a fuel issue, but to me it sounds like you just need to set the low speed jet correctly. Did your dealer replaced the carb before trying to at least reset the carb?

Try setting the carb like this, it should improve things.

 

[pennsywoodburnr]

Thanks guys, but there's a station 3/4 of a mile from my house and I decided some time ago I was just going to have to learn to use what fuel I can buy there.

That's a good data point - the rigid manifolds are made of bakelite and are thermally insulating too, so I guess it isn't much different.

That's a good point and I do that too.

Now I'm back to thinking about how to make a carb cooler, but it's not a trivial thing to design. Most saws don't have any room to mount a heat sink on the carb, and there is no air flow when you shut it off.

Do you have an ethanol tester? Just to make sure you don't get a higher mix than the 10%?

 

[timq585]

You may very well be having a fuel issue, but to me it sounds like you just need to set the low speed jet correctly. Did your dealer replaced the carb before trying to at least reset the carb?

Try setting the carb like this, it should improve things.

Great video Andy, thanks. Before I took the saw in I was cutting up a log load. I tried tuning the saw up but it really didn't change the not starting after it got hot. I don't know if the dealer tried tuning it before he ordered a new carb. Today, I pulled the muffler to check the piston for scoring. It looked great, no scoring on piston and muffler not plugged up. Next I pulled the flywheel to check to see if maybe I had unknowingly sheared the key off and it was a little out of timing, That also checked out good too. I have one more thing to try, I have another 6401 that runs great and I thought maybe I might have a weak coil, so I could pull it from the good one and swap on to the other one. Any other thoughts, thanks again.

 

[heyduke]

i had the same problem on a makita 6401. it was the ignition module. i think once it got hot the rev limiter quit working and shut down the spark.

 

[Poleman]

I'm thinking a hole in the fuel line probably up close to the carb(where they usually are), posiblly loosing prime. I had one one do this, and act real weird...was hard to run down. These saws should never have a carb heating problem or any thing like the because of their design.
Heyduke, hit on something also with the coil....that's exactly the way they act if their starting to go out....usually quit cutting tho. If you run it again a quick way to check is to run it like usually then put a spark tester in and see if it has spark when it won't restart. If there's spart its probably not the coil....if it is just mod a Husky 272 coil and unlimit it. It will take you about an hour the first time.
Also pull the fuel line out of the tank and take out the filter and pressurize the system and look for a pressure drop or leak.

 

[Paragon Builder]

Hey Rich, I was wondering when you would show up?
Have you seen this thread?
http://www.arboristsite.com/community/index.php?threads/Dolmar-5105-trouble.281279/
I was wondering how the 272 coil acts compared to the stock one besides that it's unlimited????

 

[heyduke]

...that's exactly the way they act if their starting to go out....usually quit cutting tho. If you run it again a quick way to check is to run it like usually then put a spark tester in and see if it has spark when it won't restart. If there's spart its probably not the coil....if it is just mod a Husky 272 coil and unlimit it. It will take you about an hour the first time...

a spark tester doesn't always work. sometimes you'll see a spark when you pull on the string but the a defective rev limiter keeps the saw from starting. dolmar/makita modules are expensive but you need t find a way to try a known good one. i wish our brothers in china would start making a cheap unlimited ignition module for these saws.

 

[Poleman]

Hi Dan, as a matter of fact I have. I have two 200's that I've had to change the coils on and have worked on two others in the area with the same coil problems. Seems like they may have coil issues on the models in those years. I haven't had any problems since replacing them tho. I guess I'm speculating on the issue but it just seems a little odd that that many saws in this area would have the same issue.

The 272 unlimited coil on the 6400-7900 is pretty awesome to say the least. It give the saw room to rum and really works great on a ported saw. I have one at 13,8 and the other set at 14,4 because of different timing numbers and built slightly different. I have done a stock 7900 and 7300 which were good but now there better. The also have modded carbs to go along with being unlimited.
You may be thinking of the timing curve of the coil which I thought about when doing these but they all seem fine. Very quick throttle responce and pull strong on top. I still like to finish tuning in wood as you can feel the difference. I set to best performance in wood then check rpm unloaded to give me ideas of the different saws and how they respond.
I'm hoping to get my hands on a 7910 to see if the same trick would work on them as they have a slower rpm coil yet. I know the flywheel is different and wondering if the same mods will hold true. I feel the 7910 would really benifit from an unlimited coil to get the rpm's in a higher more usable range.....giving more power and making it more like a 7900. To me there's a lot more in the 7910 than what it's putting out.

 

[Poleman]

That's interesting the spark tester doesn't always work. I had the same issue on a stihl 500i cut off saw...I think that had 15 wires leading into the coil in 5 different plugs...pia.

 

[Andyshine77]

A coil getting hot and not working is certainly possible, I'd definitely try a different coil and see what happens. I've had a few 7900's that were sensitive on restarts, a bit of fine tuning normally cured the problem. I've also seen the impulse line expand and not seal properly when they get hot. Make sure to use proper impulse tubing, not Tygon.

 

[backhoelover]

did read all the thread did you vacuum test the tank vent i had the same problem was the tank vent

 

[backhoelover]

didnt

 

[Andyshine77]

did read all the thread did you vacuum test the tank vent i had the same problem was the tank vent

A bad tank vent normally shows up when you're running the saw. A vacuum will form, and the engine will starve for fuel.

 

[heyduke]

Hi Dan, as a matter of fact I have. I have two 200's that I've had to change the coils on and have worked on two others in the area with the same coil problems. Seems like they may have coil issues on the models in those years. I haven't had any problems since replacing them tho. I guess I'm speculating on the issue but it just seems a little odd that that many saws in this area would have the same issue.

The 272 unlimited coil on the 6400-7900 is pretty awesome to say the least. It give the saw room to rum and really works great on a ported saw. I have one at 13,8 and the other set at 14,4 because of different timing numbers and built slightly different. I have done a stock 7900 and 7300 which were good but now there better. The also have modded carbs to go along with being unlimited.
You may be thinking of the timing curve of the coil which I thought about when doing these but they all seem fine. Very quick throttle responce and pull strong on top. I still like to finish tuning in wood as you can feel the difference. I set to best performance in wood then check rpm unloaded to give me ideas of the different saws and how they respond.
I'm hoping to get my hands on a 7910 to see if the same trick would work on them as they have a slower rpm coil yet. I know the flywheel is different and wondering if the same mods will hold true. I feel the 7910 would really benifit from an unlimited coil to get the rpm's in a higher more usable range.....giving more power and making it more like a 7900. To me there's a lot more in the 7910 than what it's putting out.

poleman-

i would really like to see fotos of your dolmars with 272 coils. i know the iron core is the same but the spark plug lead on the 272 is on top of the module while the dolmar lead comes out of the bottom and is routed behind the flywheel. did you have to change the timing on your flywheel? if so, how did you go about it?

 

[Poleman]

I did a thread on this earlier. "Cheap Dolmar unlimited coil"
I used the same spark plug lead, and it is routed behind the coil. Also have to make sure the ground wire is pulled through and long enough.
Some modding to the mounting holes of the coil are required, then it's just finish fitting.

I first find TDC at standard timing and make a mark to index. I've made a template from a timing wheel for making timing marks on the case.
I mod the holes in the coil and get it close, then mark the case from TDC to 35 degrees without the flywheel on. I then mound the coil, I have left the spark plug wire in place just unscrewed it from original coil. A little patience and possibly a couple small washers super glued to the mounting holes on the case to help clearance. Fit the flywheel.to set air gap of .10 and tighten coil down. Index crank to TDC then find the 30 degree make made on case (33 if ported) tighten flywheel in place and recheck timing index and marks. Put on ground wire and possibly need to bend tab to clear case. Reassemble starter, start and run and enjoy.

Here's some photos I've taken..kinda in order that shows how things were layer out and fitted. I need to photo my next one better to make it easier to follow along and better detail.

Hop this answers your questions, or gives you the idea. Let me know if you are looking for spacific.

 

[heyduke]

View attachment 431890 View attachment 431891 View attachment 431892 View attachment 431893 View attachment 431894 View attachment 431895 I did a thread on this earlier. "Cheap Dolmar unlimited coil"
I used the same spark plug lead, and it is routed behind the coil. Also have to make sure the ground wire is pulled through and long enough.
Some modding to the mounting holes of the coil are required, then it's just finish fitting.

I first find TDC at standard timing and make a mark to index. I've made a template from a timing wheel for making timing marks on the case.
I mod the holes in the coil and get it close, then mark the case from TDC to 35 degrees without the flywheel on. I then mound the coil, I have left the spark plug wire in place just unscrewed it from original coil. A little patience and possibly a couple small washers super glued to the mounting holes on the case to help clearance. Fit the flywheel.to set air gap of .10 and tighten coil down. Index crank to TDC then find the 30 degree make made on case (33 if ported) tighten flywheel in place and recheck timing index and marks. Put on ground wire and possibly need to bend tab to clear case. Reassemble starter, start and run and enjoy.

Here's some photos I've taken..kinda in order that shows how things were layer out and fitted. I need to photo my next one better to make it easier to follow along and better detail.

Hop this answers your questions, or gives you the idea. Let me know if you are looking for spacific.

poleman-

i'm a bit unclear. "I first find TDC at standard timing and make a mark to index." what do you mark? the flywheel? the case? both? you mark the case from tdc (or 25btdc to 35btdc.

"Index crank to TDC then find the 30 degree make (mark?) made on case (33 if ported) tighten flywheel in place and recheck timing index and marks." i don't follow you. i think you mean, "set the crank to top dead center" when you say "index" but i don't have a clue what you aligned to 30btdc. was it a mark on the flywheel that used to be tdc? are you saying that with the 272 coil i need to advance timing 30 degrees from the dolmar timing? also, how did you remove the flywheel. did you use the impact to the crank method or a special puller?

sorry to axe dumb questions...

 

[Poleman]

Lol....not dumb questions....I just can't say all I want the easy I want.
I find tdc and mark crank and flywheel with punch.(incase one wants to revert back to stock). I then mark the case where the tdc line points at the case. I then choose a fine and area to put degree marks. I use the fin that points at the bend above the coil.(see in picture), from there I put timing marks every 5 degrees up to 30 then every dergtree after that.(see pic again).
After removing key from flywheel and masking sure crank is at tdc I place the marked flywheel fit on the 30 degree mark and not moving the flywheel. Tighten flywheel and recheck marks are where you want them. Crank at tdc and marked fin at 30( if stock) ported like a little more. Reassemble and make sure ground wie I'd not touching anything. Everything should go back together like usual. Saw should start and run but now with unlimited coil and easier to tune.

Hope that helps....

 

[heyduke]

Lol....not dumb questions....I just can't say all I want the easy I want.
I find tdc and mark crank and flywheel with punch.(incase one wants to revert back to stock). I then mark the case where the tdc line points at the case. I then choose a fine and area to put degree marks. I use the fin that points at the bend above the coil.(see in picture), from there I put timing marks every 5 degrees up to 30 then every dergtree after that.(see pic again).
After removing key from flywheel and masking sure crank is at tdc I place the marked flywheel fit on the 30 degree mark and not moving the flywheel. Tighten flywheel and recheck marks are where you want them. Crank at tdc and marked fin at 30( if stock) ported like a little more. Reassemble and make sure ground wie I'd not touching anything. Everything should go back together like usual. Saw should start and run but now with unlimited coil and easier to tune.

Hope that helps....

rich-

thanks, i'll go thru this again. i hope you won't mind if i bother you again. i have a brand new 272 module (unlimited) and an 84cc 6401 with a flakey module. at first, on hot days it would die after the first cut then wouldn't restart for maybe a half hour, typical module failure. i found that the moduele was severely packed with bar oil and chips and after cleaning all that out it would do a day's work but didn't seem to have any limiting and also seemed to be less powerful than my other 6401. so i'm seriously thinking about using my 272 module. thanks for the help.