Hi Guys: Just modified a 26CC Homelite engine. A CDI ignition was installed and stock muffler is being used for testing. The problem I get is Low RPM's....just around 5,000 using a 17X8 propeller. Timing seems to be right...no kickbacks and easy starting. Is the stock muffler the cause for this low RPM?...any suggestions will be greatly appreciated!!!

Could be-open the muffler to flow, maybe a 1/2" hole to let gasses out. Carb is a big thing. Try a #24 and maybe a #28 venturi size carb. Should fix your problem. Maybe go down to a 16x8 prop.
Set your timing for 30 deg BTDC.

Is this a new motor? Might need to break it in some. what oil you running?

Hi...Thanks for all your help on this topic. Yes, this is a new motor...oil used is the one that came with the trimmer. Will drill a 1/2" hole at the muffler as recommended. Should I leave the engine running at idle for beak-in? How many tanks? Thanks

Vary the RPM often at first, and when its good and warm...shut off and let cool. Heat cycles gets break-in done faster. I have read that 99% of engine wear occures while a engine is warming up. I would also later on....try a bigger carb! Capt,n

I agree with Capt'n, Maybe go with a smaller prop to start with since it is a new engine. Follow the MFG. fuel mix for break in and run several 10 -12 oz tanks-then let her rip.

If the Carb. does not have two fully adjustable jets drilling out the muffler will cause it to go lean on top end.

OK Gentlemen: I drilled a 1/2 inch at the stock muffler and RpM's went up to 6,500 with same 17X8 prop. I have ran 3 tanks for breaking
and next step is to test with a larger carb. The plane I'm planning to put this engine on is a heavy Katana and I believe a smaller prop will not do a good job, so I need at least 7,800 rpm. Will see what is achieved. Thanks to all of you that gave ideas and suggestions.

Too much prop for a new engine, go down to a 16/6 or 16/8 for break in. Too much prop on that new engine is making lots of heat.

Before you try the bigger carb, you need to take the muffler apart and gut it. Take out any baffles, screens, etc., and leave only the bolt tubes or whatever is in there to keep the muffler from crushing when you tighten the bolts.

Then, you will need TWO outlets of 1/2" i.d. After trying it with the modified muffler, then try it with the larger carb too.

I recently put an aftermarket muffler on one of mine, and in place of my two normal 1/2" outlets, it had two slightly smaller exit tubes. The engine lost 200 rpms...

AV8TOR