Makita 6401 BB Won't Start

[mstang1988]

A few years back I built a 6401 BB NWP kit. I had troubles getting it to start back then but finally got it started and "tuned" the best I could. I don't have much to cut around here so it sat for a while and went to start it up this week. I can't get the damn thing started. It ran fine before the swap. I also ended up pulling the carb and cleaning it up when I was having starting troubles last time.

Here is my original thread:
http://www.arboristsite.com/community/threads/6401-big-bore-wont-fire-over.212556/

It floods anytime I use the choke. I want to get to the root cause of this and get it running reliably.

Where do I start? I have spark, pulled the muffler and plug and the piston/cylinder look fine. Should I rebuild the carb? It was stored without fuel so unlikely gummed up. Could there be a leak in the crank case and could it cause this? When I was originally tuning the saw I didn't notice the break was on and the clutch got warm (and I'm replacing the drum as it is loose on the crank. Could I have heated up a seal and caused a leak?

Anybody in the Austin area with expertise that I can borrow? Anybody that runs a company in the community interested in taking shipped saw, repairing/tuning, and shipping back? I would pay but only reasonable amounts.

 

[Sapo_feo]

Have you checked the compression? The first BB I put on my 6401 gave me 110psi and was nearly impossible to start. Checked squish and with a gasket was .059. Some of the aftermarket kits are just not that great.

 

[mstang1988]

Have you checked the compression? The first BB I put on my 6401 gave me 110psi and was nearly impossible to start. Checked squish and with a gasket was .059. Some of the aftermarket kits are just not that great.

I did check the compression in the past but not on this run. It was low but the compression tester we were using was low as well. Squish on my BB kit with yamabond is .030. I can test it again.

 

[Sapo_feo]

I ended up blocking off the compression release with a plug included in one of the kits, it enables me to start the saw, but it was never on the first pull. Or the fifth.
I read your old thread, and saw I responded to that as well. I forgot about the NWP kits. The kits I tried later all had some issue or another. The only real success I had was my first NWP kit from Bailey's with a Tillotson HE18A. The last kit I tried was I think a Meteor and I blocked off the compression release. All the others were still using the Zama C3M carbs. Maybe that coupled with the low compression affected the impulse. I gave up on my tests and the saw is now in a bucket.

 

[mstang1988]

Well got it running today but only via starting after choking and pushing back in (i.e. high idle). It still won't run at low idle, even without the clutch/clutch drum etc. Will tune a bit more and see if I can't get it to run.

 

[Josh Long]

I was having trouble getting mine going after the swap as well... closer inspection revealed a crack in the fuel line, and a little one in the impulse line. I changed the line, cut the crack out of the impulse line so it is just shorter but not leaking, and shaved of the limiter tabs on the low side of the carb and set it to 1 1/4, same on the high, and it started without much drama tonight. It seems to me the low side of the carb with the limiter in place was set much lower.

I still need to tune it properly, but I'd like to learn a little bit more before I do because the saw will be used for milling, which means long runs and I really don't want to damage the new cylinder and piston.

I would start with the easy stuff, make sure the impulse line is clean and not cracked, fuel line, carb boot...

 

[Josh Long]

EDIT: I just realized you got it started, just wouldn't idle. My idle set screw had to be screwed in almost all the way to get it to idle without me playing with the throttle.

 

[mstang1988]

Wow, I'll have to mess a bit more. When you say idle set screw do you mean the "S" screw or the L. I can get it to start with fast idle but once I let the throttle off it dies. I can get the S as low as 2500RPM before it starts dying but that seems too high for the saw and it still won't idle. My 9000 idles in the 600-900RPM range.

 

[Josh Long]

Yes the "S" screw. Mine still needs much tuning, it really doesn't seem to like to idle until its warmed up.

On an unrelated note make sure you have re-tightened the bolts that hold the cylinder down after it runs for a minute (post swap) or else they will get loose, back themselves out, and shear off...Don't ask me how I know

 

[old guy]

That is too low idle speed, most saws idle from 2700 - 3000, what does the owners manual say?

John

 

[wde_1978]

Wow, I'll have to mess a bit more. When you say idle set screw do you mean the "S" screw or the L. I can get it to start with fast idle but once I let the throttle off it dies. I can get the S as low as 2500RPM before it starts dying but that seems too high for the saw and it still won't idle. My 9000 idles in the 600-900RPM range.

That is too low idle speed, most saws idle from 2700 - 3000, what does the owners manual say?
John

2500 - 2900 rpm should be a OK idle speed as long as the chain doesn't move.
600 - 900 rpm seems wrong/too low for a idle speed of a modern chainsaw.

Couldn't find a Dolmar PS-9000 manual , but I guess the PS-9010 should be similar enough.

 

[mstang1988]

I'll have to mess around with it. I thought the clutch engaged at 2400 rpm.

 

[smokey7]

I bring idle just under thr clutch engagement rpm. Make a few cuts and check again. I cant see and 2 stroke idling under 1000rpm. Hell my stock 2 cyl two strokes idle besy at 2000 but will roughbidle and shake badly between 1000-1500. Just remember adjust the high and the low and check the response the back to the high go back to the low adjust the idle speed set screw, back to the high back to the low It's not just the turn and forget type of
thing it requires going back and
forth between them then get a good 4 stroke and clean right up as soon as you touch wood.

 

[mstang1988]

I must be remembering wrong. Yep, will tune with clutch engagement etc. 4-stroking on these saws won't work because they have a limiter but should be easy enough to tune that H.

 

[wde_1978]

For what its worth, specs for Dolmar PS-6400/7300/7900 and Dolmar PS-7310/7910

 

[Chainsaw Jim]

http://www.arboristsite.com/community/threads/chainsaw-tuning-101.250802/#post-4660485