372xp 50 pulls on cold start

[DanAyo]

Fuel pump action from crankcase pulses has no affect at cranking speeds, it's all about the choke which must be COMPLETELY closed.

An old post with useful information. Old2Stroke taught me something, again! I was under the impression that aggressively turning the engine over was necessary to get the pulse to operate the fuel pump flaps in the carb.

I have learned from experience that the choke (not the throttle butterfly) must be closed to cause fuel to be sucked into the engine. A simple test is to block the throat of the carb completely while pulling the starter rope. If it fires it is likely the choke is the culprit.

 

[Old2stroke]

Update! Problem solved!
I finally got off my lazy arse, and pulled the fuel line at the carb, and sucked on it with the Mityvac, and saw air bubbles, so then switched it to pressure, and saw air squirting out of the line about a half inch from the carb end of the line. So for now, I just nipped off that bad end and she started up in five pulls from cold after sitting for a week.
Sorry all for wasting your time with my questions. When you want something done right; just go ahead and do it, simple, haha. Actually, I probably will change the fuel line too although it seems nice and supple.
Thanks to all who answered.

Good for you. Surprising part is that it ran "normal" with a leak in the fuel line.

 

[BrettS]

An old post with useful information. Old2Stroke taught me something, again! I was under the impression that aggressively turning the engine over was necessary to get the pulse to operate the fuel pump flaps in the carb.

I have learned from experience that the choke (not the throttle butterfly) must be closed to cause fuel to be sucked into the engine. A simple test is to block the throat of the carb completely while pulling the starter rope. If it fires it is likely the choke is the culprit.

Yep, choke closed.

 

[user 181829]

Update! Problem solved!
I finally got off my lazy arse, and pulled the fuel line at the carb, and sucked on it with the Mityvac, and saw air bubbles, so then switched it to pressure, and saw air squirting out of the line about a half inch from the carb end of the line. So for now, I just nipped off that bad end and she started up in five pulls from cold after sitting for a week.
Sorry all for wasting your time with my questions. When you want something done right; just go ahead and do it, simple, haha. Actually, I probably will change the fuel line too although it seems nice and supple.
Thanks to all who answered.

I really appreciate your final post here. We all have our experiences with things not being as we expect/assume and it is too easy to simply leave everyone else hanging *after* we figure it out. I've put my own 450/start-run problem down for the moment but if/when I pick it back up and resolve it, I expect it to be nearly as simple/silly as your problem and hope I have the presence of mind to update the list when I do!
- Steve

 

[user 181829]

Yep, choke closed.

this is a new realization for me, I always assumed the (primary) point of having the choke closed was to enrich the fuel mixture whilst starting from cold... I wasn't aware that it also increased the effective pulse-vacuum in priming the carb? That fits the way my own father taught me to start 2 cycle engines (close choke with ignition *Off* and pull 3-5 times before opening choke halfway and turning on ignition) which has in fact almost always gotten me a good easy cold start unless there is something deeply wrong with the fuel delivery system or compression.

 

[lostone]

How old is the saw? Lines break down and diaphragms get brittle over time. Do you run gas that has ethanol?

 

[fruitcakesa]

My Jonsy 2255 was an easy starter but had recently become more difficult.
I had never adjusted the carb in the years we have owned it so I thought I would...not!
The adjustment screws are limited to a total of a half turn and, after actually removing the carb, determined that the limiters are not removable short of damaging something.
During the carb removal, I discovered a slit in the fuel supply line about a 1/2 inch from the carb nipple.
I cut it off below the slit, reassembled the saw, refueled it , having drained the tank beforehand and after bulb priming it started it within 5 pulls from cold.
Easy fix, but found two small bolts left over afterwards...maybe look into it later. This is only a backup saw now.