My Homelite 25 is on EI and runs really well. The only trouble I have with it is this: When I bring it up to full throttle, It will reach max RPM at about 3/4 throttle. When I push the stick past 3/4, it tends to slow down a bit. The EI system is RCexl with auto advance. Could this be a timing problem or a carb problem, ie high speed needle? I have not checked max RPM's, but will do that now. It has a 16 x 8 MA prop. What kind of max rpm should I be getting? It is totally stock except for EI and a Zenoah G26 carb.

Okay, I put a tach on her. She tops out between 7600 to 7700 rpm. At an ATV setting on my radio at 100%, it idles at 2400 to 2500 rpm. I set my radio ATV on the throttle to 120% and I couldn't shut the engine off. The idle was 1500 to 1600 rpm. Does 7600 to 7700 top end sound good for a homie 25 on a 16 x 8 prop? No mods, just free flow muffler, bigger carb and EI. What d'ya think?

that sounds reasonable, is the carb you put on there a 1/2" venturi? if so, that's probably the cause of your over 3/4 throttle issue, just limit the throttle to peak rpm in your radio and call it good.

Yes, it is the WT-645 with 12.7 mm venturi (1/2"). I had a wt-540, but couldn't get it to run properly.

Make sure the butterfly is parallel to the air flow at wide open. If you go over center that will do it. Second, is the high needle set properly? Open it up a little and see if the problem goes away, might it be leaning out? Be sure your gaskets on the intake are good. Although an air leak sould not mess with the top end as much as the idle it is worth confirming. Ignition, set it for 28 DBTDC. Be sure you are finding TDC accurately by either the dead stop method or a dial indicator methods. Since it is runnig you could play with the timing as see what the tach has to say about it. Could your spark plug gap be too wide? IF it is missing over a certain RPM close the gap a bit. Your batteries are fully charged?

Only after it is running right mess with the radio. You will have to set the end points and throws. You will be loosing the idle screw, it serves no purpose in a model installation. Keep the return spring. If it is to powerfull weaken it. You want it though. It acts to give you zero linkage play. It does not have anyting to do with whether the engines runs properly or not.

My homie 25 runs fine with the larger carb and the smaller one too. It runs smoother with the 11 mm carb.

Your carb is too big

You need a 11.11mm carb like a Walbro WA-167-1 or a WT499

Also the engine's torque sweet spot when not all ported is around 7400 rpm. This means a 16 X 10 or maybe a 18 X 8 depending on your flying style.

Cool, thanks. I'll try a 16 x 10 and see how that works. I think I'll stay with the carb as it is and just set the throttle to be max rpm when the stick is all the way forward.

if you are happy with the idle speed and reliability along with the throttle response the carb should be ok as those are the reasons to go with a smaller carb.

EBAY has carbs all the time. Look for NOS ( new old stock), or just plain old "new". Search for lowest price first. There are several guys who have EBAY stores. They will have a bunch of them for about $10 each. The ones you want are on this list. I take no credit is was posted here by someone else.

... here is the list of Wt carbs with accelorator pumps, and hi and low needles and no primers.

6.5 mm with fuel pump return spring (4 stroke)
WT 366-1
WT 456-1

7.95mm
WT 37-1
WT 424-1

9.53mm

WT 35-1
WT 38-1
WT 204-1
WT 357-1
WT 367-1
WT 381-1
WT 385-1
WT 417-1
WT 449-1
WT 450-1

11.11 mm
WT 29-1
WT 356-1
WT 358-1
WT 464-1
WT 516-1
WT 517-1
WT 527-1
WT 613-1

12.7 mm
Wt 513-1
Wt 537-1

13.49mm
Wt 171-1
Wt 172-1
Wt 228-1
Wt 285-1
WT 529-1
Wt 451-1
Wt 480-1
Wt 540-1
Wt 542-1
Wt 555-1
Wt 610-1

Well, first flight of this engine on a new airframe didn't go so well, dead stick shortly after take off. I did not have the velocity stack in place and it is in a coweled engine, not sure if this is the reason, it ran fine on the ground. May need to adjust the high end a bit. My exhaust tubes broke off in the landing, so they had to be put back on with JB Weld. Hope it holds.