200T carburetor accel pump block off.

[ptjeep]

From my personal experience and what others have said, there is no loss in throttle acceleration. They still rip after doing this mod.

 

[TonyRumore]

In my experience you really have no choice, but to either block it off or replace the carb altogether. Once the piston/o-ring get worn, the piston tends to score up the bore that it slides in. Once the bore is scored, you're screwed. Replacing the piston and o-ring will be a temporary fix that will start leaking again shortly.

Tony

 

[MCW]

I've swapped accelerator pump carbies back to older 020T models (no accelerator pump) with no loss in throttle response. I really don't think the 200T's needed it.

 

[LowVolt]

Well I lucked out. I do not have carb discussed and a new filter fixed my 200t.

 

[dl5205]

bumped

 

[Chris-PA]

Can someone explain what problems the pumps are causing? Are they just wearing out?

The fuel for acceleration has to come from somewhere. Without an accelerator pump you make the L richer than it needs to be, and that provides the fuel for acceleration. With a pump you set the idle for the correct mixture and the pump shot provides the extra fuel. I'd rather be able to set the idle mixture correctly compared to having to set it rich.

My GZ4000-based saws all have pumps, and looking through spare carbs recently I saw that even some old Craftsman/Poulan carbs had them. I have not had an issue with them and was curious what happened on these.

 

[Duane(Pa)]

Can someone explain what problems the pumps are causing? Are they just wearing out?

The fuel for acceleration has to come from somewhere. Without an accelerator pump you make the L richer than it needs to be, and that provides the fuel for acceleration. With a pump you set the idle for the correct mixture and the pump shot provides the extra fuel. I'd rather be able to set the idle mixture correctly compared to having to set it rich.

My GZ4000-based saws all have pumps, and looking through spare carbs recently I saw that even some old Craftsman/Poulan carbs had them. I have not had an issue with them and was curious what happened on these.

I would bet ten bucks this is all related to ETHANOL enhanced? fuel. Think about the friction protection that mix affords in the cylinder/combustion chamber and the high temps etc. that fast moving pistons and rings are subjected to. So, I would think that mix would be slick enough to handle lubing the dang accelerator pump bore/o ring. Freakin' corn.....

 

[komatsuvarna]

The accelerator pump piston is a brass piston with a rubber O-ring. It rides in the aluminum carb housing. After time and wear, the O-ring wears, the tiny brass piston gets some wear and what looks like light scoring marks from rubbing the aluminum housing, which is more or less the pump cylinder. In my mind, when that piston and bore gets some wear, it allows tiny air bubbles to enter the carburetor fuel metering system...making the carbs act like they do.

On the one's I've done, I remove the welch plug on the back of the carb first. I remove the accelerator pump piston and spring. I put a small amount of epoxy in the accelerator pump bore then put just the brass piston back in the bore and mash it down. That will squirt the excess epoxy out the welch plug you removed filing the whole passage as well. Then just epoxy up the welch plug hole and let it set up good. Just like Preston done.

I noticed no difference in acceleration at all.

 

[Chris-PA]

The accelerator pump piston is a brass piston with a rubber O-ring. It rides in the aluminum carb housing. After time and wear, the O-ring wears, the tiny brass piston gets some wear and what looks like light scoring marks from rubbing the aluminum housing, which is more or less the pump cylinder. In my mind, when that piston and bore gets some wear, it allows tiny air bubbles to enter the carburetor fuel metering system...making the carbs act like they do.

On the one's I've done, I remove the welch plug on the back of the carb first. I remove the accelerator pump piston and spring. I put a small amount of epoxy in the accelerator pump bore then put just the brass piston back in the bore and mash it down. That will squirt the excess epoxy out the welch plug you removed filing the whole passage as well. Then just epoxy up the welch plug hole and let it set up good. Just like Preston done.

I noticed no difference in acceleration at all.

Thanks - I never really liked the design that both Walbro and ZAMA use. The cheap soft metal of the casting makes a poor wear surface, and the cut-back throttle shaft probably puts a fair amount of side thrust on the piston. Some of the ones I have do not have a brass cover over the throttle shaft/linkage portion, and I oil them regularly.

I have to say though that I have several that are pretty old and work fine, so I wonder if these have some problem. Or they may just get a lot more hours on them.

 

[Thommo]

Finally found this old thread again and thought i should post the results of what i did with the carb on my little Echo. After i blocked off the accelerator pump i had a flat spot on acceleration when the idle mixture was set for best idle. If i adjusted the low speed so it accelerated smoothly, it would be too rich at idle so i removed the welsh plug and drilled out one of the idle progression holes to the next size. i drilled out the hole closest to the main fuel nozzle. It now runs perfectly.

 

[griffonks]

I think the really old 200T's were pre- EPA and did not have acceleration pumps.

 

[jeffbecky1]

Thank you for this fix. It works great!

 

[ZeroJunk]

Been a couple years since I went through a 200T carb and replaced the pump. In the meantime the aftermarket carbs have shown up on eBay for $15 or less shipped. I have used a lot of these carbs on various models of saws, blowers, and weed eaters and they work fine. So, I don't know that there is much reason to mess with one anymore.

 

[Definitive Dave]

there are several models of the aftermarket carbs by different builders, unmarked for easy resale, beware of the ones that wont tune or keep a tune, I see them being "closed out" by ebay merchants very cheaply, they might work or they might suck as bad as the one you re trying to replace
We have had a lot better luck with the Zama sourced carbs than the Hunai model
Dave

 

[lone wolf]

there are several models of the aftermarket carbs by different builders, unmarked for easy resale, beware of the ones that wont tune or keep a tune, I see them being "closed out" by ebay merchants very cheaply, they might work or they might suck as bad as the one you re trying to replace
We have had a lot better luck with the Zama sourced carbs than the Hunai model
Dave

True story!

 

[Definitive Dave]

Also Lone Wolf measured up the aftermarket main bearings with fancy tools and his brain and figured out they have more slop than the OEM bearings.
these bearings are not like standard bearings we use in most chainsaws at all
I have a handful of guys who rebuild with the AM bearings all the time, but I am worried that failure will occur more quickly than on new OEM bearings.
For a difference of about $25 per saw I would prefer OEM crankcase bearings in my saws to use or sell since these are typically high use saws, coveted by arborists and climbers.
Dave

 

[lone wolf]

BTW the carbs that Dave is selling now all seem to work quite well. I have run about 15 of them so far and they are good.

 

[lone wolf]

MS 200T aftermarket bearing one side measured almost 4 thou play.

 

[lone wolf]

MS 200T OEM bearing measured at 1.5 thou

 

[Definitive Dave]

SCIENCE!!!!!!