Author Topic: Finicky carb - Craftsman 3.3  (Read 220 times)

0 Members and 0 Guests are viewing this topic.

Offline Tony G

  • 3 cube
  • *
  • Posts: 10
  • Karma: 1
Finicky carb - Craftsman 3.3
« on: July 14, 2015, 01:11:45 pm »
Hey all,

I'm trying to revive an old Craftsman 3.3 and need some advice. I cleaned the fuel system out and put a new walbro kit in the carb and i thought I had it running pretty darn good. I made a few cuts and was pretty happy with where i had the screws set but now a few days later the thing is driving me nuts. I had it tuned nice when it was good and hot, and now it is sooo darn hard to start cold. I started messing with the low screw to see if I could improve that and now thing thing is running like garbage (should have left it alone). I've watched a few videos on chainsaw carb tuning but i am certainly an amateur. I can't find the sweet spot in this low speed screw. On my Echo it's so obvious, a quarter turn either way and you can hear each extreme, but not on this saw.

I've got the idle screw backed all the way out for now, and the low is about 1.5 turns out. It starts here but very fast idle, such that the chain is spinning pretty fast. So I slowly turned the low speed in and there is a point where engine speed comes down and the chain stops but then it instantly dies and wont start here. I tried turning in the idle screw a few turns but then no amount of low speed adjustment will bring the rpms down to a reasonable level.

If throttle response is lagging (bog) do i need to turn the low in or out? what about if it's hard to start?
Is it possible the high speed screw is out of whack? I had it it set just right before and haven't touched it. My understanding is that screw wouldn't affect its performance at idle.

Any advice here or rules of thumb would be greatly appreciated.

Share on Facebook Share on Twitter


Offline Cut4fun .

  • Administrator
  • Nitro Hotsaw
  • *******
  • Posts: 21952
  • Karma: 535
  • OHIO REDNECK Saw Repair Getter Done
    • Redneck Chainsaw Repair
Re: Finicky carb - Craftsman 3.3
« Reply #1 on: July 14, 2015, 01:24:07 pm »
Try opening your L up not screwing going in like you are makes leaner, try opening richer, then use Idle screw once you have it cold starting good again.  Some carbs on poulan redmax etc I have seen needing more then the normal 1 1.5 turns out.

Have you checked for air leaks. Intake boot, impulse line, carb nuts tight, cylinder, seals.




Madsen's  Saw Carb Tuning  http://www.madsens1.com/saw_carb_tune.htm


 Carburetor Adjustment On Pro Saws
Carburetor

All saws occasionally need to have their carburetor adjusted. A saw with a properly adjusted carburetor will produce maximum power, minimal smoke, run and idle smoothly, and give trouble free service. A saw that is too rich will produce excessive smoke and have insufficient power. A saw that is adjusted too lean will also have insufficient power, but this condition can quickly cause engine damage. The following information outlines the process of adjusting a carburetor on a pro saw.
Most Pro Saw Engines Have Three Carburetor Adjusting Screws:

    Idle Speed/Throttle Stop - This is the adjustment that controls how much the throttle valve (butterfly) stays open when the throttle trigger is released. If this adjustment is set too low, the engine will die when the throttle trigger is released. If this adjustment is set too high, the high idle speed will cause the centrifugal clutch to engage and the chain will run. This is a dangerous condition.
    Low Speed Fuel Adjustment - This is the adjustment that controls the proportion of fuel in the air/fuel mixture at idle speed. An adjustment that is too rich will cause the engine to load up and die at idle speed. A mixture that is too lean will starve the engine and cause it to race or surge. An extremely lean adjustment will cause the engine to die, too.
    High Speed Fuel Adjustment - This is the adjustment that controls the proportion of fuel in the air/fuel mixture at cutting speed. It would not be accurate to say this is the most important setting, because all of these adjustments need to be accurate for a saw to perform its best, but this is the adjustment that determines how the saw runs in the cut. An adjustment that is set too rich will not allow the saw to reach the RPM level necessary to build maximum power. Throttle response may also be sluggish and the engine will smoke and perform poorly. A mixture that is too lean will allow the engine to reach an RPM level where bearing failure and cylinder seizure are likely. It will also lack power in the cut and tend to run very hot.

Rich Running Conditions

An over rich carburetor adjustment is when the proportion of fuel in the air/fuel mixture is too high. When this occurs,  the fuel does not burn well. What does burn, does not produce much heat, so the power stroke is weak. The partially burned mixture is expelled into the muffler and exits the saw as smoke. An over rich condition also causes carbon buildup.
Lean Running Conditions

A lean carburetor adjustment is when the proportion of fuel in the combustible air/fuel mixture is so low that there is not enough fuel to burn. This also makes a weak power stroke and causes the saw to have insufficient power. In addition to low power, a lean condition causes the cylinder temperature to rise, which can  lead to a seizure. A lean condition also allows for excessive RPM, causing rod bearing failure.
Blocked exhaust port

It is best to use a digital tachometer when adjusting the carburetor on a pro saw. These tachs are easy to use and require no wires. When the tach is placed near the spark plug, it picks up an electrical signal when the plug fires. On a two-cycle engine, this occurs every engine rotation, so the tachometer simply counts the pulses and displays the results.
Carburetor Adjustment Procedure

    Before you start the saw, locate a small flat-bladed screwdriver. The screwdriver needs to be small enough to fit through any adjustment hole. Make sure the holes are free from debris and the ends of the adjustment screws are visible. On some saws, these areas can pack with chips, making adjustment difficult or impossible.

    You're also going to need a tachometer. It is difficult (for even a trained ear) to adjust today's saws as accurately as is necessary without a tach. We have adjusted thousands of saws and we use a tachometer religiously.
    Begin by checking the saw's air filter. Clean it if necessary. Adjusting the carburetor with the air filter partially clogged is like adjusting the carburetor with the choke partially on. If you adjust your saw with a dirty air filter, the saw will run too lean when the filter is cleaned.
    Check the fuel level. The tank should be over half full. If the carburetor is adjusted when the fuel tank is nearly empty, the carburetor may be adjusted too rich when the fuel tank is filled.
    Start the engine and warm it up. Carburetor adjustments made on a cold engine will be too rich when it reaches normal operating temperature.
    Begin by setting the idle speed. Try to set the speed at about 2700 RPM. If you don't have a tachometer, try to set the speed so the saw will idle with the chain stopped. Never set the idle so the chain runs when the throttle is released. If the saw will not idle, go to the next step.
     Set the low speed fuel adjustment. Slowly turn in the screw until the engine surges or starves for fuel (lean). Make a mental note of the position of the screwdriver slot. Now slowly turn the adjustment screw out and the engine should run better. Keep turning the screw until the engine starts to load up (rich). Make a note of the position of the screwdriver slot and compare it to the position of the lean adjustment. Now slowly turn in the screw to a position where it idles the best. It should be about midway between the rich and lean positions.

    Click on the link below and a WAV sound clip will be loaded into your browser. What you'll hear is an idling saw. Slowly we lean the low speed adjuster until the idle climbs and it then starts to die. Then we go rich and the engine starts to blubber, the RPM's drop, and the engine almost dies. The optimum setting is between these two extremes.

    These are approximately. 25 seconds long, but require time to load. Those of you with slow systems or connections may not want to wait! Click here for Saw Idle Adjustment Sound WAV
    Go back to step (4) and reset the idle speed. Chances are that the RPM setting has changed since you optimized the fuel mixture adjustment.
    Set the high speed fuel adjustment. Hold the trigger wide open and check the RPM with the tachometer. The listing below identifies the maximum RPM setting for popular pro saws with bar & chain and no load:
        STIHL 044, MS440, 046, MS460 - 13,500 RPM
        STIHL 066, MS660 - 13,000 RPM
        STIHL 084, 088, MS880 - 11,500 RPM
        HUSQVARNA 272, 372 - 13,500 RPM
        HUSQVARNA 288, 385, 390, 394, 395 - 13,000 RPM
        HUSQVARNA 3120 - 11,500 RPM
    NOTE: If you do not have a tachometer, set the RPM level so that the saw "four cycles" or "blubbers" at wide open throttle. Do not attempt to set at maximum RPM levels without a tachometer. Setting the adjustment slightly rich will diminish performance, but reduce the possibility of damage to the saw engine.
    Click on the link below and a WAV sound clip will be loaded into your browser. What you'll hear this time is a saw being adjusted for full speed. After revving it up to max RPM and holding the trigger, we adjust the high speed rich, causing it to slow down and blubber. Then we adjust it lean, causing it to sound smoother, but then it starts to starve for fuel. As we back it off from lean to rich again, the sound becomes slightly rougher. This slightly rough sound (or 4-cycle sound, as it's sometimes referred to) is where you want it to be. We like to say, as "close" to the smooth as you can get it, but still just slightly into the rough.

    This one is larger than the first, and requires more time to load. Those of you with slow systems or connections may not want to wait! Click here for Saw Full Rev Adjustment Sound WAV
    Go back to step (4) and fine tune the idle speed adjustment and low speed fuel adjustment. Movement of one adjusting screw often causes the other two to need readjustment.
    Your saw is properly adjusted and ready for work.

Why A Carburetor Has To Be Readjusted

If a carb is set right when a saw is new, why does it have to be readjusted? Some people wonder why their saw needs occasional tuning. They don't understand why saws can't be set at the factory and stay correctly adjusted for the life of the saw. The reason is there are many operational changes a user makes without realizing it. These changes include working at different elevations, changes in fuel, and a host of other factors cause saws to need periodic carburetor adjustment.

Today, sophisticated electronics can monitor and meter air/fuel needs. With this technology, saws will be able to "self adjust." This technology is well developed for automobiles and trucks. The process of miniaturizing an economical and durable system that will work on a saw engine is being developed. Until then, keep your tachometer and screwdriver handy.
Our Advice

The preceding information briefly explains rich and lean running conditions. It also identifies the three adjustment screws and their function. It should be noted that on today's pro saws, most of these adjustments have "limiters" that limit the range of carburetor adjustment. In most cases, proper adjustment is within this range, but not always. If proper adjustment for your saw is outside the limited range, take your saw into a shop. Sometimes this is caused by a problem with your saw, and sometimes the range on the limiters just needs to be reset.
REDNECK Saw Repair Getter Done

Offline Tony G

  • 3 cube
  • *
  • Posts: 10
  • Karma: 1
Re: Finicky carb - Craftsman 3.3
« Reply #2 on: July 14, 2015, 01:48:47 pm »
That madsens link is what i followed when i first got it up and running after the rebuild. It ran really nice. But because it was hard starting i messed with that low screw and she's running like garbage. I suppose there could be an airleak from the cylinder side, but the impulse and boot and everything else is fine. I think you're right, I need to be richer than I am now because of the racing rpms. I'll open it up, and then bring the idle screw in to keep it running. I'll start over and see what I can figure, maybe I just need more time with it.

I'll let you know how i made out!

Offline dannyupsolate

  • Piped Saw
  • *****
  • Posts: 328
  • Karma: 28
Re: Finicky carb - Craftsman 3.3
« Reply #3 on: July 14, 2015, 03:29:15 pm »
one of the things I have had a hard time getting through my head is how sensitive these chainsaws are to the most tiny air leak. A tiny leak at a seal, the intake, the gasket where the carb screws on ,impulse line if so equipped is all the difference in a saw that runs like crap and a good running saw. no amount of screw adjusting will make it stop sucking air. sometimes even reseating the carb on its gasket can make all the difference.

Offline Tony G

  • 3 cube
  • *
  • Posts: 10
  • Karma: 1
Re: Finicky carb - Craftsman 3.3
« Reply #4 on: July 14, 2015, 03:39:15 pm »
sometimes even reseating the carb on its gasket can make all the difference.

Actually, as sure as i was before there was no leak, it's entirely possible that i rattled something lose during my first test run! If i can't get it to run right i'll go through everything again.

How can one check for a bad seal?


Offline dannyupsolate

  • Piped Saw
  • *****
  • Posts: 328
  • Karma: 28
Re: Finicky carb - Craftsman 3.3
« Reply #5 on: July 20, 2015, 01:19:39 am »

 

Related Topics

  Subject / Started by Replies Last post
2 Replies
1175 Views
Last post July 18, 2012, 01:40:02 pm
by Cut4fun .
5 Replies
242 Views
Last post February 11, 2014, 03:36:38 pm
by Cut4fun
35 Replies
1080 Views
Last post November 11, 2016, 11:28:35 pm
by pete
3 Replies
775 Views
Last post July 13, 2015, 12:41:04 am
by Eccentric
17 Replies
664 Views
Last post September 15, 2014, 12:30:02 pm
by 660magnum
2 Replies
383 Views
Last post September 23, 2014, 07:29:34 pm
by Cut4fun .
27 Replies
476 Views
Last post January 29, 2015, 10:17:58 am
by Spike60
14 Replies
346 Views
Last post December 01, 2014, 10:59:27 am
by 3000 FPS
4 Replies
150 Views
Last post December 21, 2014, 08:08:43 pm
by AmericanPsycho
3 Replies
272 Views
Last post June 30, 2015, 07:11:44 pm
by Jason K