How do you know when your carb needs rebuilding...

[clinchscavalry]

or when it might be another problem?

Weekend before last I was cutting up a downed Red Oak using my Dolmar 3410TH for the smaller stuff and my 5105 for the bigger limbs. Both were running just fine although the 5105 seemed a little hard to get up to speed. In other words it bogged for a few seconds before it ran normally. Both were showing issues idling, sometimes cutting off, but I figured a little tweaking on the "L" screw would take care of that and just wanted to finish the job. For what it's worth, the 3410 has never run quite right even when new, but the 5105, other than hard starting at times, has been flawless and is my most used saw.

Fast forward to the next weekend and neither saw would run at all! The 3410 might fire once or twice and that's it, but the 5105 refused to do anything. Both showed a spark, but I did put new plugs on both just to be sure they were good.

I still get a couple pops with the little TH but nothing with the 5105. When a carb fails does it usually do it all at once? I ordered a kit for the Walbro carb on the small saw just because I wanted to try something inexpensive before hauling it to a shop.

I use non-ethanol gas in the saws and a little bit of Seafoam as well. These saws have had corn gas in them before but not lately.

Do these problems seem to indicate a carb rebuild or should I look at something else first?

 

[happysaws]

I would clean and rebuild both carbs and go from there.

 

[HarleyT]

It usually is cracked fuel lines, and or dirt/bad gas in the carb. You usually go through the carb, clean out the crud and fix the problems. You could re-use the old "kit" on most cases, but new diaphrams make the "rebuilt" carb
run better {like it should}.
It is usually the first thing to do when the saw starts running poorly, apart from checking the plug and air filter.

 

[clinchscavalry]

That's what I'll do, rebuild the carbs. Does anyone know what kit will work on the 5105? I ordered one for the Walbro WT series on the 3410, but the owner's manual doesn't say what's on the 5105.

I just looked at the 5105 carb but couldn't see a number without taking it off. However, there was a good bit of gas all around it, and the foam "breather" on top was saturated as well. Things don't look normal in there.

 

[Sportfury70]

It just seems a bit odd to me that both just suddenly won't start. Sounds like contaminated fuel to me, esp since they both sh!t the bed together. I've had carbs go from functional to paperweights quickly, but not without obvious signs a tankful or two beforehand. I've honestly rarely had to do a rebuild on any carb unless it sat for years and was gummed up and dried out.

Have you tried baselining the jet settings and attempting to start and tune from there? Sometimes thats all it takes to get one running again.

Another thing to think about is the weather is finally getting warm. I've had to re-tune all my equipment, mainly just back off on the H side a smidge and raise idle speed a hair.

 

[Kenskip1]

First thing would be to smell the gas.If the gas has been stored with a loose fitting cap the octane will evaporate and leave you in a situation that you described.There is gas in the saw but it does not have any octane to ignite it.You can put all the carb kits you want but if you have sour gas it will never run.Gas in a can left in the sun will add to the frustration.

 

[ken morgan]

First thing would be to smell the gas.If the gas has been stored with a loose fitting cap the octane will evaporate and leave you in a situation that you described.There is gas in the saw but it does not have any octane to ignite it.You can put all the carb kits you want but if you have sour gas it will never run.Gas in a can left in the sun will add to the frustration.

octane does not ignite...it does the exact opposite, the higher the octane the more the fuel resists pre-ignition. you are referring to the volatile's evaporating away..this is totally different from octane rating and what it refers to do a search on MON octane rating and RON octane rating. in the US its MON + RON/2 for the actual octane rating. also reference the entire cracking process it will help you understand the difference.

 

[CR888]

It always amazes me what some think of octane, what it does and what its there for.

 

[Kenskip1]

Ken,Your analysis is right on.However I will assume that you have been to a race track. You can smell the high octane gas they are running.When you smell gas, what is it that you smell? Octane. This is what made the smell back in the 60-70s when gasoline had octane in it. If you take the octane out of gas it has a very bland odor.This is what I was referring to.I do not have a very good way with words but stale mix is harder to ignite contributing to this persons situation.Thanks for the detailed forensic chemistry analysis ! Ken

 

[ken morgan]

Ken,Your .......

sorry if I came across as rude...the internet does not help with my style of speech. just preaching my shtick....I run a time attack car at fuji and ebisu for ***** and giggles and build my own engines etc. so i forget sometimes that others know as much if not more than I do .

 

[Kenskip1]

Ken, not a problem. Best of luck on the track.