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SRM-225 with an RB-K93 carb.

First question, doesn't Zama label their carbs "Zama?" Because all it has on it
K93
4Za
Then CHINA in the middle.
Then RB 37

That's it.

Also, the main question. It'll start and idle fair. Giving it throttle is a different story. When I get it to full idle, the RPM's seem about 3/4's. So I figured the screen was blocked, so I took the carb apart. And it was about 3/4 block. Diaphragms weren't too stiff, so I put everything back together. And couldn't get it to start.
Just a little bit of the gasket stayed on the carb.
So it not starting now, is that because there's too much of an air leak? The gasket didn't rip or tare. Just a little bit stayed on the carb.

BTW. Good spark and my gauge read 120lbs compression (cold)

Despite what 9,999 your tube experts say
Never reuse the diaphragms & gaskets from a cube carb.
The old ones will have compressed and your chances of getting a good seal are not particularly high.

Over the years I have learned not to jump in and rip a carb apart.
Very few problems end up being in the carb in any case.
But because they are there people feel obliged to rip them apart.
I suppose it makes them feel smart.
You can test most function of a cube carb without opening it up

To see if your carb is leaking, take it off .
Fit some hose to the two fuel spiggots then place the carb in a jar of water.
Block the return line off ( I use golf Tees ) and pump the carb to 10 psi
look for bubbles which will reveal where it is leaking from.
move the Tee to the other side and pressure test the purge bulb

I'm not a very good mind reader, but something made you mention a carb leaking. I could see how this would not allow the engine to run at full throttle. BTW, the spark plug didn't look like it was burning rich. it was a tan color and not coated. It the inside and out looked like it had been in there for a few years.

Unfortunately the big egos go to all sorts of efforts to make sure their videos come up top when you do a You tube or google search.
As THEY are what is important , not your problem the videos are really about them showing you how smart they think they are.

With a hand held that does not rev as high as you think it should , the usual culprit is the exhaust screen or exhaust being blocked and choking the engine.
A blocked inlet screen causes the engine to run lean which on two strokes makes them run too fast and lack power.

If the screen on the carb was partially blocked then the filter in the tank requires replacement or the carb screen will block again.
Cube carbs are a pressure vessel and run at around 7 psi so a really filthy looking carb screen will still pass sufficient fuel to reach full revs.

Nearly every donkey brain on You Tube will show you them blasting carb cleaner through every hole to "clean them out" with gay abandon.
Very few tell you which ones to spray and which ones not to.
Depending upon the exact carb there is from 1 to 3 check valves.
Carb cleaner will destroy many of them and cause them to become stuck in the closed position.
That is why Walbro went to the expense of making the very expensive carb cleaner that is check valve safe.

When blowing out a carb, you should , where ever possible blow the passages out backwards WITH LOW PRESSURE AIR , not a dust gun hooked up to your sand blasting compressor running 150, PSI that will force the crud so tight that you will never be able to shift it.

Like you, when I started out I watched all of the clots on U-toob and did what they did as cube carbs were totally new to me.
However since then I have learned better and never pull one apart unless the diagnosis is pointing to an internal carb problem .
And over time I have come across some of the better informed presenters and of course gotton my hands on some of the better service manuals.

In your post you mention a lump of the gasket stuck on.
This always happens and when it does you fit a new one that is nice & soft so can conform to the surface and make a proper seal.
If you run a cube carb on a wet stone you will see that the machined surfaces are not smooth but contain machining grooves.
This is intentional and is there to allow the gasket to fill in the grooves and thus make a pressure tight seal.
It also provide an escape path for air that gets trapped by the gasket.
It is also why the gaskets stick and break up when you are trying to take the carb apart and also the reason why you should never reuse them.

So now days the only time I jump right in & pull a carb apart is when a customer comes in with a tool that worked fine last season, has not been used for months and now won't start.
On those you can be fairly sure the carb will be gummed up, but only around 1/3 will be able to be cleaned properly.

Around here I have become the "go to guy" for problem hand held tools and this is purely because I replace fuel lines, filters & grommets
So when I have adjusted a tool & sent it back, it works as it should for several years till it is time to replace the fuel lines again.

Now back to you and your problem
Pull the carb off the engine and leave the fuel lines attached.
Double check you have them on the right way round.
When you pump the primer bulb the line that blows out the fuel gets connected to the short fuel line that stops just inside the tank
Turn the carb sideways and blow air through the venturii and watch for atomised fuel mist coming out the engine side of the carb.
It should be a strong dense stream.
If not then you have probably wrecked the check valve, in which case it will be a lot easier & faster to replace the carb.
And Zama carbs have the work Zama casr into the body or pump cover depending upon where the pure bulb is located.
If it does not say Zama then it is not a Zama

Had one doing the same & I changed the tank fuel filter, & runs like new again..

Thanks for ALL of that information. I learned my first year, not to use carb cleaner on these carbs. Or compressed air within 6in from the carb. I blew a couple check valves out, and never found them. I do use seafoam spray, lightly. That may be too harsh. IDK. The small engine guy I worked for last year, used it. He was a 2 cycle wiz. Problem was, he wouldn't teach me much, because he was afraid I'd put in against him. LoL.


As far as the youtubers go, I do watch a lot of their video's. But I'm pretty good at filtering out the most of the ones you described. Do you have any youtube video's?

No.
I do not have a big enough ego to be bothered and do not see my job as educating the entire planet.
I do show customers what I do and explain why I do it because it should not be secret service mans business.
Most appreciate it .
I am here to learn just like every one else.

As you are setting up I hope you have a pressure / vacuum tester
Seek out the videos by Joe Pace- 2 stroke diagnostics or some thing like that.
That is where I learned the magic of pressure testing tanks, carbs & caps.
Quite honestly at least 75% of the problems are there and not inside the cube.

After that it is getting the EAR

Adjust an engine till it 8 strokes and stalls out rich a dozen or so times
Then do the same thing lean
You will hear the distinct different sound of a lean stall out & a rich stall out.
That makes diagnosing really easy once you have your ear in.

This applies particularly when adjusting the cross over between L & H jets on the older carbs.

When I was starting out I went to the effort of getting a smaller color tune ( Gunsens make them ) and setting up the video camera on the colortune while was adjusting the H jet.
On a few occasions when I have been really stumped I have resorted to doing that again.
I inherited a trimer clamp from the previous owner but found that a Triton Super Jaws works a lot better as it is a not more stable.
I can also clamp the bar of a chain saw in it so adjust the saw , chain on in the vice, really handy.

7394 said:

Had one doing the same & I changed the tank fuel filter, & runs like new again..

Click to expand...

Ironically, this one had no fuel filter at all. Not even just laying in the tank. Adding one made no difference.

PTmowerMech said:

Ironically, this one had no fuel filter at all. Not even just laying in the tank. Adding one made no difference.

Click to expand...

I'm thinking the dirt had already invaded.

Hello,

Check to make sure there is no blockage in the muffler. I had a mud dobber wasp build it's nest inside the muffler of a 25cc Homelite motor that caused it not to reach max RPM, a clogged muffler spark arrestor screen will do the same.

Just curious, why aren't you supposed to use carb cleaner on a diaphragm type carb?

Regards

Jeff

jp1961 said:

Hello,

Check to make sure there is no blockage in the muffler. I had a mud dobber wasp build it's nest inside the muffler of a 25cc Homelite motor that caused it not to reach max RPM, a clogged muffler spark arrestor screen will do the same.

Just curious, why aren't you supposed to use carb cleaner on a diaphragm type carb?

Regards

Jeff

Click to expand...

Muffler and screen were clear.

From what I understand, the check valves inside the block carbs won't take carb spray very well. I've heard that from too many decent small engine guys to chance it.

Installed new carb and checked the screen and muffler, which were not clogged at all. Still at about 3/4 RPM's.
Note: It doesn't bog down at full throttle. When I squeeze the trigger, It rev's up ok. (a little slow on the response). The throttle plate goes to full throttle. Same as the old carb.

To add to the above, I found the adjustment screw and turned it til it was running lean, then to rich then back close to the middle. But can't really get any more RPM's out of it.
Btw, thanks to Bert, I can now here the difference in sounds. Thanks Bert.

As inaccurate as compression testers are, I put both of these side by side (customer brought me two exact SRM 225). My gauge reads almost exact on both. Right at 100lbs.

You are getting into very esoteric type things to check now.
If the mixture is fine and the butterfly opens fully and the timing is correct then it can only be a gas flow problem or a faulty ignition module.
Some of the module have a clipping circuit in them to limit the upper revs.
These are gnerally only found on the 4 stroke engines .
I do not have the experience or specific knowledge of Echos to know if the coils have limiters on them.
However being a top shelf model they could have them fitted.
The other thing is a damaged transfer port(s).
To check them you have to pull the barrel and that is a PIA job.
With the barrel off then there are the piston spacers either side of the conrod can cause grief


Have you pressure tested the crankcase & tank as suggested earlier ?
A leaky cylinder base gasket will also show up more at high speeds than at idle.
Same story for the crankcase oil seals, if leaking out they effectively reduce the fuel getting into the cylinder thus cap the top speed.
A mal functioning fuel tank breather is another high speed problem

bertsmobile1 said:

You are getting into very esoteric type things to check now.
If the mixture is fine and the butterfly opens fully and the timing is correct then it can only be a gas flow problem or a faulty ignition module.
Some of the module have a clipping circuit in them to limit the upper revs.
These are gnerally only found on the 4 stroke engines .
I do not have the experience or specific knowledge of Echos to know if the coils have limiters on them.
However being a top shelf model they could have them fitted.
The other thing is a damaged transfer port(s).
To check them you have to pull the barrel and that is a PIA job.
With the barrel off then there are the piston spacers either side of the conrod can cause grief


Have you pressure tested the crankcase & tank as suggested earlier ?
A leaky cylinder base gasket will also show up more at high speeds than at idle.
Same story for the crankcase oil seals, if leaking out they effectively reduce the fuel getting into the cylinder thus cap the top speed.
A mal functioning fuel tank breather is another high speed problem

Click to expand...

I have a gut feeling it's not a fuel problem because the same thing was going on with the old carb. New carb came with new lines, grommet and breather.

I have not checked the seals. I don't have a pressure tester. Maybe I could crank it and spray soap and water around the places you mentioned. Or WD 40.
Will the bubble out or suckered in?

About the transfer port. You're talking about where the shaft and engine connects? As in something causing the engine to bog or bind it up some? The head spins free-er than the one that runs fine.

At full throttle it sounds exactly like it's running fine, only with the throttle pulled 3/4 of the way. The throttle goes as far as it can go on the throttle plate.




P.S. why can't I get anything easy? Dayum it, man. Well, the ither one was easy. So I shouldn't complain too much.

There are 3 cut outs in the bottom of the piston.
One opens the inlet port to the carburettor so the new charge can get into the crankcase

There are two more, one either side of the piston to allow the fresh charge to enter the cylinder
These can get blocked or damaged.
Usually the port that gets blocked is the exhaust port because people run fuelil ratios that are way too oil rich.

On some engines there is a plastic plug that sits in the side of the engine . to make the transfer ports and these can get damaged, melt, drop down, get out of place etc.
I do not have an IPL for your exact engine so do not know if it has port stuffers or not.
Also the piston itself can get damaged which prevents the ports working as they should.
To check that you need to poke a mirror down the induction port and of course , know what the piston cut aways should look like.
This gets confusing as some engines have different ports either side , one favouring idle & the other high speed running or other times just to control the swirl of the fresh charge entering the cylinder.

If you are going to work on these engines you need a pressure & vacuum gauge.
There is no two ways around it.
Either two gauges or a single gauge that works both ways and the latter is a big time saver.
Usually I pump 30 PSI into a crankcase to test the seals.
Even then it is hard to find the leak using bubble blowing liquid ( pinch it from the kids/grandkids ) so much better than 20% dishwashing liquid in water.

I've got a worn out Weed Eater blower, I'm gonna take apart tomorrow and just look at everything.

In the parts diagram, I'm seeing small ports in the gasket I think you're talking about.

You're right, I do need a pressure tester. They look to be about $40 online.

FWIW
I battled on with what came with the business for several years
YNext I went cheap & Bought the pressure pump you originally linked to , a good bit og gear but requires a lot of pumping to do crankcases
Following that I bought the cheap plastic Mightyvac which was good till the very first time it got fuel in it cause I was too lazy / stupid to empty the fuel tank first.
After that , despite fitting a full rebuild kit it always had a lot of drag, so much I ended up breaking 2 handles.
Finally fitted a metal handle & persisted with that for around another year, but the slow piston movement cause the pin to continually fall off.
Last year when just about all I did was weed line trimers & chain saws I bit the bullet & bought the full metal one.
I have been kicking myself ever since for not buying the good gear to start with.
Cuts down the diagnosis time on these engines in 1/2

The mob who make the Tiny Tach also do a range of diagnosis tools worth looking at.
They do blanking plates for cabs & mufflers.
I then got a couple of 14mm x 1.25 bolts and drilled a hole in them so I can block off the muffler & carb then pressure test via the spark plug hole.
If you want to spend big money, Stihl , Husky & Echo at least do a full pressure testing kit that has the input in the carb blanking plug.

Eventually I will make some of them as on a lot of engines you do not get clean enough access to the carb manifold to slip the blanking plate ( thick rubber sheet ) in

Hello,

Just thought of one more item to check. Is the carb gasket on the engine side partially blocking the pulse port?
Is there any blockage in the pulse port itself?

I doubt this is it, but you've already covered all the bases. Do you have another carb that's known to be good to see if that solves it?

Regards

Jeff

jp1961 said:

Hello,

Just thought of one more item to check. Is the carb gasket on the engine side partially blocking the pulse port?
Is there any blockage in the pulse port itself?

I doubt this is it, but you've already covered all the bases. Do you have another carb that's known to be good to see if that solves it?

Regards

Jeff

Click to expand...

I haven't messed with this in a couple of weeks. Gonna do some more checking today. Checking on the pressure testers that Bert mentioned at the moment. But, IIRC, I've switched carbs already on this. This is one reason I got a new carb for it. But that didn't change anything. The port I'm thinking you're talking about is through the carb, gasket an into the intake, then into the cylinder, correct?
My memory being what it is, I'll have to probably rechecks a lot of the same things I've already checked.

Note to add.

Turning it upside down, makes it rev higher. Turn it back over and the RPM's come back down slowly. But turn it upside down and it's almost immediate increase in RPMs.

And the inside of the muffler is wet.

Hello,

Yep,,,not sure if the hole goes into the cylinder or crankcase.

I was thinking a poorly made gasket might be partially blocking it. Or even installed upside down,,,been there done that.

Regards

Jeff

jp1961 said:

Hello,

Yep,,,not sure if the hole goes into the cylinder or crankcase.

I was thinking a poorly made gasket might be partially blocking it. Or even installed upside down,,,been there done that.

Regards

Jeff

Click to expand...

I'll double check that. But a note to add, it was doing this when I was brought in. The carb, you could tell had been on it for a pretty long time. The air filter was shot. I guess it could've been using it that way. But I won't think so. Not this guy. Some folks, I wouldn't put it past them to use a weed eater at 3/4 rpm's. But since the man has two identical ones, I can't see it.