www.tdiclub.com

Economy - Longevity - Performance
The #1 Source of TDI Information on the Web!
Forums TDIFAQ Articles Links Meets
Orders TDI Club Cards TDIFest 2014 Gone, but not forgotten VAG-Com List Unit Conversions TDIClub Chat Thank You



Go Back   TDIClub Forums > VW TDI Discussion Areas > General Automotive

General Automotive General automotive discussion. This is intended to be a discussion about other not VW and Diesel cars you may have or interested in.

Reply
 
Thread Tools
Old May 12th, 2008, 08:36   #1
PDJetta
Veteran Member
 
PDJetta's Avatar
 
Join Date: Nov 2003
Location: Northern Virginia
Default Carburetor Adjustment on 2-Stroke String Trimmers

Not exactly automotive, but I thought someone here will know the answer to get what I need:

Last year I bought a WeedEater 20 FL new and it has run poorley since I bought it. It is running too lean. It stalls, won't idle, bogs out when the throttle is opened with no load, and usually must be run on part choke.

I need to richen the mixture, but here's the kicker: The carburettor screws are not user adjustable. There is no slots in their heads and they are shrouded in dicast material and recessed to prevent "tampering". The owner's manual says to take it to a dealer for any running problems related to the carburettor and the only setting adjustable is the idle speed, the maual says.

Question: It appears that the screws were made to accept a plastic knob so they can be adjusted. Where can I get the knob to adjust the screws?

You can thank CARB (California Air Resources Board) for this mess. A few years back I worked for the Outdoor Power Equipment Association developing standards and I sat through many a meeting where it was revealed that the US EPA adopted CARB emissions standards for small power equipment and two requirements created more consumer disatisfaction with equipment in order to meet the regs: The equipment had to run so lean it ran poorley and the carburetor mixture could not be changed by the owner.

--Nate
__________________
2004 Jetta GLS TDI 5M Plat. Grey w/ Leather. RC Stage 2, G60/VR-6 clutch, steel skid plate, TDIHeater, CAT 2um fuel flter, Phat Noise, and VDO boost & volt guages.

Last edited by PDJetta; May 12th, 2008 at 11:19.
PDJetta is offline   Reply With Quote
Old May 12th, 2008, 09:51   #2
GoFaster
Moderator at Large
 
Join Date: Jun 1999
Location: Brampton, Ontario, Canada
Default

Can you post a photo of the "screw" in question? If you say that it looks like it was made to accept a plastic knob, that means you can get access to the end of the screw. Can you dremel a slot in the end of it and use a screwdriver on it? Can you get a needle-nose vice grip on it?

I've not had to deal with string trimmers and chain saws, closest thing I've worked on has been motorcycles (and only 4-stroke). They have the same anti-tampering garbage, but usually they've dealt with that requirement by pressing a sheet metal brass plug over the recess in which the idle screw adjustment resides. Stab those brass plugs with a punch, pry them off, and you are good to go.

In some cases, idle mixture adjustment isn't enough, you have to replace the slow jets in the carbs to get the engine to pull away from idle speed without leaving the choke on.
__________________
Brian P.
formerly ... 2006 Jetta TDI 5-sp, Spice Red, Unitronics stage 1, 0.681 5th gear.
and before that ... 1996 Passat TDI, Silk Blue
GoFaster is offline   Reply With Quote
Old May 12th, 2008, 13:46   #3
n1das
Veteran Member
 
n1das's Avatar
 
Join Date: Jun 2002
Location: Nashua, NH, USA
Fuel Economy: Who cares? It's a DIESEL! Great fuel economy comes as a bonus!
Exclamation

Quote:
Originally Posted by PDJetta
Question: It appears that the screws were made to accept a plastic knob so they can be adjusted. Where can I get the knob to adjust the screws?
Hi Nate, long time no chat!

I had to deal with this once with a weed wacker that belonged to my parents. Somebody doing yard work for them used it and it ran poorly just like you described. My dad set aside and had it waiting for me as a project to work on during one of my visits. They live in VA and I live in NH, so it had to wait until I was down for a visit during the Memorial Day weekend.

What I found with the carb was there were two adjustments...one for high speed (i.e., running at WOT) and one for low speed operation (i.e., idle mixture). The idle speed was adjusted by a stop screw for the throttle plate to keep it cracked open at just the right amount. There were a total of 3 adjustments. Anyhow, the two mixture adjust needle valve screws had a plastic cap on them to purposely limit the amount of adjustment that was possible. The most you were allowed to turn each screw was a tad more than a quarter turn. The caps appeared to be a CARB thing and I recall seeing a warning label saying something about the carb being non-adjustable by the end user. I found the high speed setting to be at the maximum (richest) position that the cap on the screw would allow but it was still too lean like you described. It had the exact same poor running symptoms like you described.

I ended up prying the caps off the screws and adjusting them and got it running great. When I was finally done, I put each cap back on the screws with caps in the middle of their adjustment range.

If your trimmer was running good in the past and running poorly now, it might be due to clogged jet in the carb, bad fuel, or the wrong gas/oil mix ratio. Maybe try mixing in a little fuel injector cleaner into the gas/oil mix to help clean things out.

This is the adjustment procedure I used from what I remember (this was about 10 years ago):

1. Have the fuel tank about half full of fuel (almost said diesel, LOL) and the fuel must have the proper gas/oil mix ratio. The recommendations I've read from small engine repair books say the best adjustment is achieved with a tank half full of fuel.

2. The gas/oil mix ratio may affect how it runs, so make sure it's mixed exactly to spec (50:1, 40:1, 32:1, etc.). Also the gasoline used in the mix should be fresh 87 octane gas. Also make sure the air filter is clean/serviced.

3. Run the engine at WOT for a while to fully warm it to operating temp. Outdoor weather should be normal summer temperature and humidity.

4. Make sure the trimmer's string is at the proper length so it will be running with a load on the engine when running at WOT.

5. While running at WOT, adjust the main mixture screw to richen up the mixture. Turning CCW richens the mixture and CW will lean the mixture. Explore the adjustment range and find the "sweet spot" setting where it runs good and pefectly smooth at full RPM at WOT and without "4-stroking". 4-stroking is where the engine fires on every other compression stroke and does it with a distinct pop sound heard in the exhaust.

6. Richen the mixture about 1/8th of a turn from this sweet spot setting to set the mixture slightly on the rich side. This will help it accelerate smoothly from idle without hesitation and while under a heavy load. With no load on the engine, it is normal to run slightly rough (4-stroking) at WOT at this setting. You'll notice it will smooth out (begins fully 2-stroking) a soon as you start loading the engine. You'll have to experiment a little to find the best setting. In general the ideal setting will end up being slightly on the rich side of where it runs perfectly smooth at WOT with no load. Once properly adjusted, it may tend to 4-stroke at WOT with no load and will run smoothly without bogging down or hesitating while under load.

7. After setting the high speed adjustment, run the engine at idle and play with the low speed adjustment. This adjusts the mixture at idle and low speeds just above idle. If it won't stay running at idle, you'll need to give it a little throttle to keep the RPMs up just enough to keep it running while you play with the adjustment. As you get the adjustment close to where it needs to be, you'll notice it will stay running more easily at idle and will be able to idle on its own without having to give it any throttle. This assumes the idle speed hasn't been set too low to begin with.

8. Test acceleration from idle to WOT by quickly snapping the throttle to WOT and do this several times. It should accelerate smoothly and quickly without hesitation or stumbling during each snap acceleration. You may find you need to touch up the high speed mixture adjustment slightly in order to get it perfect.

9. Touch up the idle speed if needed by adjusting the stop screw for the throttle plate.

10. Go out in the yard and whack some weeds and tall grass with it and see how it performs.

You post brought back memories of me having to deal with the same thing about 10 years or so ago. One thing I also remember is the caps on the adjust screws were on VERY tight and I had to work to get them off. Adjustment was easy after I got them off. Got a dremel tool? Maybe try dremeling the caps enough to allow the screws to be turned so you can adjust things.

Good luck.
__________________
David Sterrett, N1DAS
2014 BMW (F10) 535d XDRIVE ///M-Sport, 255hp & 413 ft-lbs of AWD stomp 'n go fun!
2012 BMW (E70) X5 XDRIVE35d, 265hp & 425 ft-lbs of AWD stomp 'n go fun!

Last edited by n1das; May 13th, 2008 at 14:30.
n1das is offline   Reply With Quote
Old May 12th, 2008, 13:51   #4
DrewD
Veteran Member
 
Join Date: Mar 2004
Default

I have same problem with my weedeater. Mine is too rich due to my altitude 7200 feet. It won't idle either but runs well at higher speeds.

I think it will take a special security bit driver to turn the idle screws. I don't believe they are capped like older models.
DrewD is offline   Reply With Quote
Old May 12th, 2008, 14:01   #5
n1das
Veteran Member
 
n1das's Avatar
 
Join Date: Jun 2002
Location: Nashua, NH, USA
Fuel Economy: Who cares? It's a DIESEL! Great fuel economy comes as a bonus!
Exclamation

Quote:
Originally Posted by DrewD
I have same problem with my weedeater. Mine is too rich due to my altitude 7200 feet. It won't idle either but runs well at higher speeds.

I think it will take a special security bit driver to turn the idle screws. I don't believe they are capped like older models.
A narrow pair of small Vise-Grips might work too.

Yours runs well at higher speeds so that says the high speed circuit is probably OK. The low speed mixture may need a tweak if it can be done. Some carb designs may only have a high speed mixture adjustment, if it has an adjustment at all. The idle speed adjustment is usually a stop screw for the throttle plate to keep it cracked open just enough for the engine to idle.

These kinds of headaches make me appreciate diesels all the more since diesels aren't fussy about air/fuel ratios and there are no air/fuel "mixture" adjustments to worry about.
__________________
David Sterrett, N1DAS
2014 BMW (F10) 535d XDRIVE ///M-Sport, 255hp & 413 ft-lbs of AWD stomp 'n go fun!
2012 BMW (E70) X5 XDRIVE35d, 265hp & 425 ft-lbs of AWD stomp 'n go fun!

Last edited by n1das; May 12th, 2008 at 15:44.
n1das is offline   Reply With Quote
Old May 12th, 2008, 16:02   #6
DrewD
Veteran Member
 
Join Date: Mar 2004
Default

I fixed mine and it took me 15 minutes to do it!

1:
I removed the carb. The bottom of the carb has a diaphram metal cover that is extended to form a guard for the mixture screws. I hacked sawed that extension/guard off.

Step 2:
The mixture screwed are recessed in small circular "tunnel enclosure" that prevent the use of pliers to rotate the screws. I used a grinder (a belt sander would also work) to grind the "tunnels" back so that they were level with the mixture screws. I would drain carb of fuel to prevent fire from sparks.

Step 3:
Use a hack saw across the "tunnels" and mixture screws to hacksaw a slot in both of the mixture screws simultaneously. Each was slotted deep enough to accept a small screw driver.

Step 4:
Blast carb with cleaner to remove metal debris and reinstall the carb

Step 5: Pat yourself on the back as you start your engine and adjust your mixture screws once it is warmed up.

My weedeater is now running great! My high speed needle was too lean and my low speed mixture was too rich. My idle is now 100% reliable.

Last edited by DrewD; May 12th, 2008 at 16:08.
DrewD is offline   Reply With Quote
Old May 12th, 2008, 18:33   #7
mohawk69
Veteran Member
 
Join Date: Apr 2005
Location: Richmond Hill, GA (Savannah)
Default

Take a look at the gas/oil mixture requirements. I've often used the same mixture for differing equipment to prevent having so many fuel cans around. It was never a problem and it would always run even if it smoked more then it should. that appears to no longer be the case. I had the same problems mentioned above and someone said to drain the fuel and put in the correct mixture. It started and ran fine.
mohawk69 is offline   Reply With Quote
Old May 12th, 2008, 20:44   #8
leicaman
Veteran Member
 
leicaman's Avatar
 
Join Date: Dec 2004
Location: Sheboygan, Wisconsin
Fuel Economy: Much better than the average car... :o)
Default

Mowawk69 is right about mixture on modern two-strokes being crucial. What I do with my two-strokers is to have a 1 gallon can dedicated to the fuel mix. I buy the small bottles in which all you need to do is to add it to a gallon of fuel. Walla, very few issues if ever. Years ago, older machines required some obnoxious oil rich mixture which of course smoked all over the place. Also if there is too much ethanol in the not quite so new two-strokes, it can can cause some issues such as degradation of carb parts. I believe most modern kits now have improved parts as a result. (I worked as a technician at a small engine place while in college and its a nice skill to have). Still have lots of cool tools.
__________________
2005 Passat GLS TDI, 160k miles, Now a daily driver Chainless and Gear Driven via the procedure by Oilhammer 06/17/2009, ngk hybrid glowplugs, Chainless and proud of it! Mileage?....adequate
leicaman is offline   Reply With Quote
Old May 12th, 2008, 20:52   #9
david_594
Veteran Member
 
david_594's Avatar
 
Join Date: Feb 2004
Location: Boston,MA
Fuel Economy: 51.7/48.2/40.7
Default

Are you sure its not just a vacuum leak? Its a pretty common cause of running too lean, especially in older equipment.
__________________
The Ohio State University College of Veterinary Medicine c/o 2013
2000 Jetta, 47mpg lifetime, 1968 Westy Weekender, 1979 Vespa p200
david_594 is offline   Reply With Quote
Old May 13th, 2008, 05:40   #10
PDJetta
Veteran Member
 
PDJetta's Avatar
 
Join Date: Nov 2003
Location: Northern Virginia
Default

Quote:
Originally Posted by n1das
Hi Nate, long time no chat!........
Good luck.
Thanks Dave. Hey, I missed you at the Impex Fest this year. I got chipped to RC 2

I appreciate the adjustment sequence. The weed trimer ran like crap from day 1. I read some of the on-line reviews and many buyers had the same problem!

My leaf blower is as exactly as you say (with the set screw limit caps) and that is kind of how I adjusted the carb on it, I pulled the plastic limiter caps up over their stops.

The weed trimmer has no caps and the stubs for the screws (slow mixture and hi-speed mixture) are really recessed in the carb housing and not marked as to function(which is "Hi" or "Lo"). I will remove the mixture limit screw caps from the leaf blower and see if they fit on the ends of the weed trimmer carb set screws.

I refuse to pay ANY shop any money to repair ANYHING of mine with a piston(s) in it!

--Nate
__________________
2004 Jetta GLS TDI 5M Plat. Grey w/ Leather. RC Stage 2, G60/VR-6 clutch, steel skid plate, TDIHeater, CAT 2um fuel flter, Phat Noise, and VDO boost & volt guages.
PDJetta is offline   Reply With Quote
Old May 13th, 2008, 05:44   #11
PDJetta
Veteran Member
 
PDJetta's Avatar
 
Join Date: Nov 2003
Location: Northern Virginia
Default

Quote:
Originally Posted by DrewD
I fixed mine and it took me 15 minutes to do it!

1:
I removed the carb. The bottom of the carb has a diaphram metal cover that is extended to form a guard for the mixture screws. I hacked sawed that extension/guard off.

......
That is exactly the way mine is designed too. If the plastic caps from the leaf blower do not fit, I will preform a carb set screw "gaurdectomy"

Thanks.

--Nate
__________________
2004 Jetta GLS TDI 5M Plat. Grey w/ Leather. RC Stage 2, G60/VR-6 clutch, steel skid plate, TDIHeater, CAT 2um fuel flter, Phat Noise, and VDO boost & volt guages.
PDJetta is offline   Reply With Quote
Old May 17th, 2008, 14:58   #12
PDJetta
Veteran Member
 
PDJetta's Avatar
 
Join Date: Nov 2003
Location: Northern Virginia
Default

Quote:
Originally Posted by DrewD
I fixed mine and it took me 15 minutes to do it!

1:
I removed the carb. The bottom of the carb has a diaphram metal cover that is extended to form a guard for the mixture screws. I hacked sawed that extension/guard off.

Step 2:
The mixture screwed are recessed in small circular "tunnel enclosure" that prevent the use of pliers to rotate the screws. I used a grinder (a belt sander would also work) to grind the "tunnels" back so that they were level with the mixture screws. I would drain carb of fuel to prevent fire from sparks.

Step 3:
Use a hack saw across the "tunnels" and mixture screws to hacksaw a slot in both of the mixture screws simultaneously. Each was slotted deep enough to accept a small screw driver.

Step 4:
Blast carb with cleaner to remove metal debris and reinstall the carb

Step 5: Pat yourself on the back as you start your engine and adjust your mixture screws once it is warmed up.

My weedeater is now running great! My high speed needle was too lean and my low speed mixture was too rich. My idle is now 100% reliable.
Did it today and it runs GREAT! The "low speed" screw had to be unscrewed about 1/2 turn and the "High speed" screw unscrewed about a quarter of a turn.

The owner's manual states the idle speed is the only user adjustment and to take the trimmer to the dealer for poor running related to the carburettor

--Nate
__________________
2004 Jetta GLS TDI 5M Plat. Grey w/ Leather. RC Stage 2, G60/VR-6 clutch, steel skid plate, TDIHeater, CAT 2um fuel flter, Phat Noise, and VDO boost & volt guages.
PDJetta is offline   Reply With Quote
Old June 3rd, 2008, 12:54   #13
santiagoq
Newbie
 
Join Date: Jun 2008
Location: Mexico
Default

In reading what you have written, it appears that you know what you are talking about, so I decided to write and see if you could help me with my problem.

I have a Homelite TrimLite string trimmer that's three years old. It worked without any problem for more than a year, and, believe me, I put it to the test! However, after letting it sit without using it for maybe six months, I could not get it started again. There was a cracked fuel line from the fuel tank, and on further checking, I noticed what looked like taffy in the fuel tank and fuel filter. At the same time, I attempted to clean the carburetor, because it was also pretty gummed up, but I still could not get it started. So, in desperation several months ago, I replaced the carburetor, gas tank, fuel filter and fuel lines. After doing that, it worked fine for several weeks, but since then, it has refused to start again.

I should clarify that it never would just idle. It never accelerated smoothly, and I always had to give it some throttle, but if I would give it too much or not enough, it would die.

I have changed the spark plug, replaced the fuel mixture, making sure it is the exact mix (50:1, with fresh 87 octane gasoline, per specs). The air filter, fuel tank, filter and carburetor are all clean. The spark plug is getting spark, but I don't know how to tell if it is getting enough, and I have cleaned what appears to be a type of magneto for generating the spark, which was dirty with dust, but even then it will only occasionally even try to start. I have turned the main mixture and low speed adjustment screws back and forth, hoping that this would let it start, but I can't even get it started in order to adjust them. Also, how do I know which is which, and which direction to turn each of them?

I live in southern Mexico, and although we occasionally see a string trimmer, they are still a novelty here. So, unfortunately, finding someone to work on it is going to be a little difficult. As a result, I am pretty much on my own to figure out the problem. What would you suggest that I do?
santiagoq is offline   Reply With Quote
Old June 10th, 2008, 06:23   #14
streeker02
Veteran Member
 
Join Date: May 2008
Location: Acton, Ontario
Default

Quote:
Originally Posted by santiagoq
In reading what you have written, it appears that you know what you are talking about, so I decided to write and see if you could help me with my problem.

I have a Homelite TrimLite string trimmer that's three years old. It worked without any problem for more than a year, and, believe me, I put it to the test! However, after letting it sit without using it for maybe six months, I could not get it started again. There was a cracked fuel line from the fuel tank, and on further checking, I noticed what looked like taffy in the fuel tank and fuel filter. At the same time, I attempted to clean the carburetor, because it was also pretty gummed up, but I still could not get it started. So, in desperation several months ago, I replaced the carburetor, gas tank, fuel filter and fuel lines. After doing that, it worked fine for several weeks, but since then, it has refused to start again.

I should clarify that it never would just idle. It never accelerated smoothly, and I always had to give it some throttle, but if I would give it too much or not enough, it would die.

I have changed the spark plug, replaced the fuel mixture, making sure it is the exact mix (50:1, with fresh 87 octane gasoline, per specs). The air filter, fuel tank, filter and carburetor are all clean. The spark plug is getting spark, but I don't know how to tell if it is getting enough, and I have cleaned what appears to be a type of magneto for generating the spark, which was dirty with dust, but even then it will only occasionally even try to start. I have turned the main mixture and low speed adjustment screws back and forth, hoping that this would let it start, but I can't even get it started in order to adjust them. Also, how do I know which is which, and which direction to turn each of them?

I live in southern Mexico, and although we occasionally see a string trimmer, they are still a novelty here. So, unfortunately, finding someone to work on it is going to be a little difficult. As a result, I am pretty much on my own to figure out the problem. What would you suggest that I do?
Yours most certainly sounds like trash in the carb/float, not uncommon when leaving fuel in the tank/carb without stabilizer for extended periods of time. That carb needs to be pulled and cleaned. Once it's running, worry about low/high speed circuit adjustment.
streeker02 is offline   Reply With Quote
Old June 10th, 2008, 07:16   #15
DrewD
Veteran Member
 
Join Date: Mar 2004
Default

Santiagoq,
If you are sure that the fuel system is not clogged or compromised (fuel lines, fuel pickup filter, carb, no fuel in primer bulb etc) and your ignition system is up to par with new plug, good wire, good gap etc.. than here is a tip that many don't know about:

EXHAUST: Many small engines have a mesh screen in the exhaust outlet. This fine mesh screen is designed to act as a spark arrester. Often, there is residual oil in the muffler that pools on the mesh when the engine is stored in the winter. It hardens and completely blocks exhaust flow. This happened to an Echo leaf shredder and had me stumped for weeks until I tried starting it with exhaust off. I don't either bother replacing the mesh and haven't had any problem with "sparks".
DrewD is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -7. The time now is 01:47.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright - TDIClub Online LTD - 2014
Contact Us | Privacy Statement | Forum Rules | Disclaimer
TDIClub Online Ltd (TDIClub.com) is not affiliated with the VWoA or VWAG and is supported by contributions from viewers like you.
1996 - 2013, All Rights Reserved
Page generated in 0.16410 seconds with 11 queries
[Output: 139.37 Kb. compressed to 117.41 Kb. by saving 21.96 Kb. (15.76%)]