Normally it's just a small/jeweler's screwdriver. From the doc Rivets posted clockwise leaner, counter richer. Normally clockwise will hit a dead stop. It's a good idea to note where the setting is. Turn clockwise to stop, note how many turns, use that as starting point. I didn't see a recommended start point in the doc. I would remove and clean the needles as doc advises, and blow out with carb cleaner before putting them back in. The longer needle is the Low. Sometimes there are limiters on the screws, so you can't easily remove them, or adjust beyond a certain range.
TB90BC Bushcutter-Help
- Thread starter Boyde
- Start date
I am sorry, did you look at the picture? I see no where on that red thing or the white thing where a screw driver would, of any size would have any effect. Also, it appears that both these things have a locking mechanism to prevent them turning. I could be wrong, hope I am, but I don't see in that manual anything that deals with this situation.
Yes, I looked at the picture. From the angle, I couldn't clearly see the top, and whether there was a screw head. The lock may have been the travel limiter I referred to. I'd look for a better manual. I agree that they really had very little about adjusting mixture.
The red and white plastic is to restrict adjustment of the mixture screws. They are the black, under the red and white. I found https://www.manualslib.com/manual/183929/Troy-Bilt-Tb90bc.html?page=22#manual but it doesn't touch adjusting mixture screws. I searched, and found a couple of manuals, but none cover adjusting mixture, other than saying to take it to a dealer. It looks like you have to remove that white/red plastic junk to adjust. I circled the screw that it looks like you remove to pull the white limiter. Is there another like it? It looks like the red and white combo is what needs to come off, and the two black parts are the mixture screws.
Did you double check the diaphragm as Rivets suggested? I'd do that before disassembling into unknown territory.
Did you double check the diaphragm as Rivets suggested? I'd do that before disassembling into unknown territory.
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Page 1
Zama Newsletter
Volume 2, Issue 3 October 2022
Continue on page 2
I N S I D E T H I S I S S UE
1 Setting and Adjusting a Zama Carburetor
2 Technical Support Questions
In this edition of the Zama newsletter I will discuss how to set and adjust your Zama carburetor. All Zama carburetors are
set at the factory however when replacing your current Zama carburetor with an OEM factory replacement you may still
need some adjustments to be made to the replacement carburetor. This is due to the individual engines usage and
condition.
Also many times when a carburetor begins to have performance issues, the customer will try and make adjustments using
the L and H needle to correct the situation. A performance issue such as poor acceleration, rough idling, hard to start is a
sign the diaphragms need to be replaced and not always an adjustment issue. Customers who first try and adjust the
carburetor will later determine the diaphragms need to be replaced and find their carburetor is now out of adjustment
once new diaphragms are installed.
If you find yourself in one of the above situations please follow the below instructions on setting and adjusting your
carburetor. First find your L and H adjustment needles. The carburetor should have a letter L and H cast into the body of
the carburetor right above or below each adjustment needle. See below pictures for reference.
The L needle adjusts the fuel flow for the idle circuit and the H needle adjusts the fuel flow for the wide open circuit
(WOT). Normal adjustment of a Zama carburetor with two adjustment needles begins with the L needle.
If your carburetor will not start or run at its current settings, turn both the L and H needle clockwise to close both
needles. Once the needles are closed, open each needle two turns by turning the needles counter clockwise. Next turn
the throttle adjust screw (TAS) clockwise in all the way. When closing any adjustment needle or screw be careful not to
over tighten as this can cause damage to the carburetor.
Page 2
Continued from page 1
Now you are ready to start the engine. Once the engine starts allow the engine to warm up before beginning any
adjustments. Allow 2-3 minutes for the engine to warm up.
Once the engine is warmed up begin with the L needle. Turn the L needle clockwise while listening to the engine. The
engine will speed up to a point and then begin slowing down. The point of the highest speed is considered the optimum.
The optimum would be the most efficient point for running the engine.
Once the engine is set at optimum then adjust your throttle adjust screw(TAS). This screw only controls idle speed. The
TAS screw should be adjusted so that the clutch is not engaged. When a clutch is engaged the chain or string trimmer
head will be turning. There are some trimmers without a clutch so try and adjust these trimmers to a steady speed.
Once the throttle adjust screw (TAS) is set, you will need to recheck the L needle for the optimum point by performing
the previous instructions. This process of adjusting the L needle then the TAS screw may need to be repeated several
times to get the engine to run correctly. The L needle may be opened 1/8 to 1/4 turn from the optimum point to help with
acceleration at wide open throttle.
You are now ready to adjust your high speed or wide open throttle. Squeeze the trigger and accelerate the unit to full
speed. Once again search for optimum using the same technique you used for the L needle.
One thing to remember is to not let the carburetor drop much on the lean side of the optimum point (screw in) as you
want to find the highest speed when turning the needle. If you go too far past this point can result in engine damage. As
with the L adjustment the H needle may be increased (counterclockwise) no more than a 1/4 turn from the optimum
point.
If you have a Zama carburetor that has a single needle. The single needle will only adjust the H needle or wide open
throttle. The idle speed can only be adjusted by the TAS screw. The fuel flow for the idle circuit is normally controlled by
a fixed jet on these single needle carburetors. This information does not apply to Zama carburetors with a single needle
that are installed on Stihl units.
Zama carburetors installed on Stihl units are the property of Stihl. Zama after sales is not allowed to sell or provide
technical support for these carburetors. Please contact Stihl technical support at 1 888 326-9643 or [email protected] for
additional information.
You may find that a special adjustment tool is needed to adjust your carburetor. These tools are only available to
licensed repair shops or technicians from the manufacturer of the unit. Zama does not sell these tools.
TECHNICAL SUPPORT Q & A
Q: Can you provide the turns open for a specific carburetor if given the model number?
A: I should be able provide that information for most carburetors. Some carburetors will not have specific turns open
and with these carburetors you will need to set the turns open at 2 turns for both the L and H.
Q: What is the best way to contact Zama aftersales for technical support questions?
A: The quickest way to receive an answer is by emailing [email protected] with your question. I usually will
respond the same day. On weekends I will normally respond the following Monday.
Q: Is the service manual still available and where can it be purchased?
A: A new service manual will be available in January 2023. The part number will be Z000-400-Z000-A and the list price
is $25.00 each. The service manual may be purchased from any Zama distributor and will include over 50 additional
carburetor models. Also over 100 part number have been updated and this manual will also include a quick to kit
reference guide.
Zama Newsletter
Volume 2, Issue 3 October 2022
Continue on page 2
I N S I D E T H I S I S S UE
1 Setting and Adjusting a Zama Carburetor
2 Technical Support Questions
In this edition of the Zama newsletter I will discuss how to set and adjust your Zama carburetor. All Zama carburetors are
set at the factory however when replacing your current Zama carburetor with an OEM factory replacement you may still
need some adjustments to be made to the replacement carburetor. This is due to the individual engines usage and
condition.
Also many times when a carburetor begins to have performance issues, the customer will try and make adjustments using
the L and H needle to correct the situation. A performance issue such as poor acceleration, rough idling, hard to start is a
sign the diaphragms need to be replaced and not always an adjustment issue. Customers who first try and adjust the
carburetor will later determine the diaphragms need to be replaced and find their carburetor is now out of adjustment
once new diaphragms are installed.
If you find yourself in one of the above situations please follow the below instructions on setting and adjusting your
carburetor. First find your L and H adjustment needles. The carburetor should have a letter L and H cast into the body of
the carburetor right above or below each adjustment needle. See below pictures for reference.
The L needle adjusts the fuel flow for the idle circuit and the H needle adjusts the fuel flow for the wide open circuit
(WOT). Normal adjustment of a Zama carburetor with two adjustment needles begins with the L needle.
If your carburetor will not start or run at its current settings, turn both the L and H needle clockwise to close both
needles. Once the needles are closed, open each needle two turns by turning the needles counter clockwise. Next turn
the throttle adjust screw (TAS) clockwise in all the way. When closing any adjustment needle or screw be careful not to
over tighten as this can cause damage to the carburetor.
Page 2
Continued from page 1
Now you are ready to start the engine. Once the engine starts allow the engine to warm up before beginning any
adjustments. Allow 2-3 minutes for the engine to warm up.
Once the engine is warmed up begin with the L needle. Turn the L needle clockwise while listening to the engine. The
engine will speed up to a point and then begin slowing down. The point of the highest speed is considered the optimum.
The optimum would be the most efficient point for running the engine.
Once the engine is set at optimum then adjust your throttle adjust screw(TAS). This screw only controls idle speed. The
TAS screw should be adjusted so that the clutch is not engaged. When a clutch is engaged the chain or string trimmer
head will be turning. There are some trimmers without a clutch so try and adjust these trimmers to a steady speed.
Once the throttle adjust screw (TAS) is set, you will need to recheck the L needle for the optimum point by performing
the previous instructions. This process of adjusting the L needle then the TAS screw may need to be repeated several
times to get the engine to run correctly. The L needle may be opened 1/8 to 1/4 turn from the optimum point to help with
acceleration at wide open throttle.
You are now ready to adjust your high speed or wide open throttle. Squeeze the trigger and accelerate the unit to full
speed. Once again search for optimum using the same technique you used for the L needle.
One thing to remember is to not let the carburetor drop much on the lean side of the optimum point (screw in) as you
want to find the highest speed when turning the needle. If you go too far past this point can result in engine damage. As
with the L adjustment the H needle may be increased (counterclockwise) no more than a 1/4 turn from the optimum
point.
If you have a Zama carburetor that has a single needle. The single needle will only adjust the H needle or wide open
throttle. The idle speed can only be adjusted by the TAS screw. The fuel flow for the idle circuit is normally controlled by
a fixed jet on these single needle carburetors. This information does not apply to Zama carburetors with a single needle
that are installed on Stihl units.
Zama carburetors installed on Stihl units are the property of Stihl. Zama after sales is not allowed to sell or provide
technical support for these carburetors. Please contact Stihl technical support at 1 888 326-9643 or [email protected] for
additional information.
You may find that a special adjustment tool is needed to adjust your carburetor. These tools are only available to
licensed repair shops or technicians from the manufacturer of the unit. Zama does not sell these tools.
TECHNICAL SUPPORT Q & A
Q: Can you provide the turns open for a specific carburetor if given the model number?
A: I should be able provide that information for most carburetors. Some carburetors will not have specific turns open
and with these carburetors you will need to set the turns open at 2 turns for both the L and H.
Q: What is the best way to contact Zama aftersales for technical support questions?
A: The quickest way to receive an answer is by emailing [email protected] with your question. I usually will
respond the same day. On weekends I will normally respond the following Monday.
Q: Is the service manual still available and where can it be purchased?
A: A new service manual will be available in January 2023. The part number will be Z000-400-Z000-A and the list price
is $25.00 each. The service manual may be purchased from any Zama distributor and will include over 50 additional
carburetor models. Also over 100 part number have been updated and this manual will also include a quick to kit
reference guide.
