SRM-225

[PTmowerMech]

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

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.

 

[PTmowerMech]

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.

 

[PTmowerMech]

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.

 

[bertsmobile1]

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

 

[PTmowerMech]

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

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.

 

[bertsmobile1]

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.

 

[PTmowerMech]

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.

 

[bertsmobile1]

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

 

[jp1961]

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

 

[PTmowerMech]

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

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.