Is my Dolmar 5100S worth the trouble ?

[Doorguru]

I just picked it up locally. I initially got it to run with a lot of tricks/coaxing, but soon realized it had serious problems. Hard to pull (from compression) and although it was firing and getting fuel, it would not even try to do a normal start. After minimal, partial disassembly, I discovered, what I think, is excessive rod play. My question, is it worth repairing it? I have done similar repairs on more common brands with no problems, but due to this not so common (but great!) saw, it might be more difficult and costly getting the parts. Also I noticed a piece of one fin is missing on the flywheel... I always wanted to add this model to my collection.

If there is any interest, I will post some pictures.

 

[huskihl]

Are you certain it’s not flooded? The metering needle had a habit of bypassing fuel when they sat for awhile.

 

[Doorguru]

Are you certain it’s not flooded? The metering needle had a habit of bypassing fuel when they sat for awhile.

Yes sir, I am quite certain it is not flooded.

 

[ballisticdoughnut]

Post pictures. The big end of the rod will move a bit on the crank side to side but should have little to no movement up and down.

 

[Sidecarflip]

Just about to take one apart for a customer, same issue hard to start excessive compression but his has a comp release so I'll look at that first

 

[Doorguru]

Post pictures. The big end of the rod will move a bit on the crank side to side but should have little to no movement up and down.

I don't have it fully taken apart, but when holding the piston stable with a stick, I can rock/turn the crankshaft back and forth slightly without the piston moving and hear some light clicking noise. Maybe this is normal? I was able to start it once by priming the cylinder, but it stalled at low RPM's.

I tried cleaning the carb with no results. I equated the almost impossible starting issue and hard to pull as a timing issue due to the play, but I could be completely wrong.

Here is the saw when I first got it.



Also I am concerned with half of a fin broken off the flywheel affecting the balance.

 

[ballisticdoughnut]

That saw is in good shape, I’d be surprised if the crank was bad. I’ve got a 510 with a 5100 top end, it’s not the easiest saw to start when cold. They’ve got pretty good compression. If you’ve got the tools do a pressure vac test. If it’s got an air leak it isn’t gonna run right no matter how many times you clean the carb.

 

[Doorguru]

That saw is in good shape, I’d be surprised if the crank was bad. I’ve got a 510 with a 5100 top end, it’s not the easiest saw to start when cold. They’ve got pretty good compression. If you’ve got the tools do a pressure vac test. If it’s got an air leak it isn’t gonna run right no matter how many times you clean the carb.

I pulled off the cylinder and can feel no up and down play. The piston looks great as does everything else. It's pointing to a possible a seal leak (?)



Here is the flywheel with the broken fin:

 

[Doorguru]

Here is the saw running right after I got home with it. I had to manually prime the cylinder, but even then it was hard to start. Would it still run like this with a leaking seal?

 

[ballisticdoughnut]

Did you try adjusting the carb? It sounds lean on the low speed. That could indicate an air leak or it could just need some adjustment.

 

[huskihl]

Lean on both high and low. Carb could have some junk in it. Or diaphragms are hard. Or air leak

 

[huskihl]

Any chance the impulse hose is unhooked?

 

[ballisticdoughnut]

Lean on both high and low. Carb could have some junk in it. Or diaphragms are hard. Or air leak

Sounded a bit lean on high to me as well.

 

[Doorguru]

Carb was properly connected and, as mentioned, was cleaned. The gaskets and diaphragm appeared fine. I might go ahead and order a rebuild kit though.

I had planned on adjusting the jets after I made that video, but could never get it to restart. It is getting good spark, but the rope must be pulled fast. For the heck of it it, since the seller gave me a new aftermarket coil, I replaced it. It reacted the same, so I put the factory one back in. He even gave me a new can of store bought premix, and a new chain. It came with the case and tool kit also. If all else fails, I am sure I can sell the parts to get my 75 dollars back.

While I have the cylinder off, I will remove the piston and check the wrist pin/bearing and double check the lower end for play. I will then re-assemble and find a way to do a suction/pressure test. I am confident that I will get this right in a little while and will keep you informed on my progress.

 

[jack-the-ripper]

Just buy this & save yourself some time instead of rebuilding the carb, if everything else checks out ok. https://www.ebay.com/itm/114125326359

 

[Doorguru]

Just buy this & save yourself some time instead of rebuilding the carb, if everything else checks out ok. https://www.ebay.com/itm/114125326359

Funny.. I was just getting ready to post this update below the same time you wrote yours:
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So I put it back together, but left the carb off. I primed the cylinder, pulled the cord once and it fired and ran. Tried it again and same results. Another time.. same results. I put the carb back on, primed the cylinder and it ran as in the video. Shut it off and tried to start it.. no go. Would not even fire. Primed the cylinder, pulled the cord numerous times, no go.. would not even try to start. It acts as though it is getting flooded anytime the carb is on. Does this make sense ?

Something is going on with the carb. Maybe order a rebuilt kit ??

I also found a used $20 flywheel to replace the one with the broken fin. The old one might have been okay, but it bothered me.
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The carb you showed looks the same other than where the throttle cable connects. Maybe I am suppose take something off of my old one?

 

[sean donato]

Just break the opposite fingers off the flywheel and move on with getting it to run right. Something is definatly up with your carb.

 

[Doorguru]

Just break the opposite fingers off the flywheel and move on with getting it to run right. Something is definatly up with your carb.

Yes, I was thinking of doing something like that, even putting it between centers, but for about 20 shipped I went for it. Got the carb coming too.

 

[Doorguru]

Installed the new carb and the used flywheel. Runs with the air filter off, but as soon as I put the air filter on the engine dies. Even if I put the air filter on while it is running with the top half off, it stalls. So just slightly reducing the air intake at all causes it to stall. Also I noticed when I rev the engine and look at the opening of the carb I see a very fine mist of gas spraying out. Exhaust screen is clean.

Never noticed the mist before, but this is exactly what it was doing before I changed the carb. Must be the seals. What else could it be??

 

[ballisticdoughnut]

Does the carb have that round foam doughnut on the metering diaphragm cover?