Robin Subaru EX17 6.5 HP Need more power

[Najuto9tail]

Hey guys I have a Robin Subaru Ex17 6.5 hp I want to modify my engine so that it gives more power. Where should I start?

Is it true that removing the muffler helps engine gain some power?

And what could happen if I remove the governor gear?

Suggestions are appreciated.

 

[Doc Sprocket]

Power improvements are pretty much standard no matter which engine you have. The first steps are usually a free-flowing exhaust (like a straight pipe instead of a muffler), a free-flowing aftermarket air intake, and a larger carburetor main jet usually goes with those to deliver more fuel to meet the additional engine demands.

Removing the governor allows the engine to rev higher, which will generally result in a greater maximum speed. I would encourage you to read the sticky here.

 

[Najuto9tail]

Thanks, is there any guide on how to remove the muffler and adding a straight pipe?

 

[Doc Sprocket]

No guide required. Unbolt the old one, and use it to keep papers from blowing off the workbench when running the ventilation fan. Bolt on the new one...

If you can weld, you could cut the flange off the old one and re-use it (what I usually do). If this is not an option, you'll have to source one. I have no idea who might have one.

 

[Najuto9tail]

I founded this in another thread in the forum, robertsons torque tube. It looks nice, will this work?

About the carb, some say it has to be replaced because the stock one is not adjustable because of a tamper or something like that. Changing Jet is an option ? Or should I get another carb like a honda clone carb for bigger engine?

My motor is stock at the moment I have not done anything to it yet.

 

[Doc Sprocket]

Absolutely! If it is available in your application, go for it!

 

[Najuto9tail]

Thanks for your help.

 

[fowler]

im sure the carb is adjustable
thye would have to adjust it from the factory

but some engines are fitted with stuff to stop u changing the settings
in some parts of the world (mainly the US) if these devices have been tampered with then they no longer conform to the enviromental laws

but u are breaching the laws by fitting a straight pipe so i wouldnt bother with saving the anti tamper stuff
they are usually stuff like unremoveable palstic or rubber peices that stop u accessing a place of the engine
but u can just cut them off

the laws may not even have effect on your state

 

[Doc Sprocket]

Sorry- I missed the carb question.

I have seen modern carbs that are just not adjustable, period. Never mind tamper caps, no adjustment at all...

For the most part, this just means you would buy a new, larger jet, or drill out your own.

 

[fowler]

well thats thick surely

sure the engine may pollute a bit more but what about all the pollution from makeing it and shipping all over the world every 3 years because u cant fix it up u can only replace it

i know my honda pushes a bit of smoke but its only been built once in the last 15 years
unlike our lawn mower thats just been replaced after 2 years in operation

 

[Doc Sprocket]

Yeah- it's a drag. I really miss the pre-EPA stuff. I have two spare series 1 Tec carbs because they are full adjustable, and I can use them on other projects.

As you know, I am ready, willing, and able to drill my own jest. But if I can do it by turning a screw- what could be better than that!

 

[Najuto9tail]

So if there is a tamper cap then you recommend not messing with it? I have not had time to take the engine apart since I have my last Final's exams tomorrow I have been studying hard ( I am studying Industrial engineering) Is not easy lol.

 

[Doc Sprocket]

Depends. If it's the type that pops off easily with a small flathead screwdriver, go for it. Otherwise forget it.

One of my clone carbs had the idle mix screw Loctite'd in place, with the head removed. I tired everything I had. No joy...

 

[Najuto9tail]

Ok now I get the point. That is my fear that the screw may not be adjustable but just like you said I have to take it apart and see for myself. Drilling the jet is complicated? What are recommended drilling measures?

 

[Doc Sprocket]

Well, hang on there a sec... There's not much chance that you'll have to mess with the idle mix screw. It will likely be fine as it is.

The main jet on the other hand, is accessible from under the carb. You would remove the bolt holding the bowl on (requiring no special tools) and unscrew the jet from inside.

Drilling the jet is easy if you have the tools. Required is a pin vise, and a set of numbered drills in the #60-#80 range. However- don't just drill it because you think you should. If the engine is running lean after doing a modification, then that's when you would enrich the mixture.

 

[Najuto9tail]

So you mean that after removing the muffler and adding the torque tube (or straight tube) if the engine seems to not work correctly then I should try out making the jet bigger?

Another question- If governor have a adjustable screw then by taking it out it will give better performance? This engine have a lever for governor is that what you meant in the sticky you gave me the link?

Sorry for asking to much is just that I have never done any of this stuff before on engines and want to be absolutely precise and know how to do things the correct way. And not messing things up. I have a friend with some knowledge on engines that with his help in our free time would be doing the suggestions given here. Thanks for all the help

 

[jamyers]

Changing carbs on Subaru's can be problematic, since their mounting bolts are horizontal and most Honda/Clone carbs have mounting bolts that aren't - assuming you want a stock-type carb.

If you're going to lose the governor and you don't mind re-routing fuel lines and throttle cables, then there are lots of options - slide-types like Keihin PE28, Walbro PZ, and their clones are just a few.

 

[jamyers]

Depends. If it's the type that pops off easily with a small flathead screwdriver, go for it. ...

Be VERY CAREFUL if you go to pry the cap off the end of an adjustment screw...don't do like I did and snap the screw off flush. Just pure dumb luck I was able to get the rest of it out.

 

[Doc Sprocket]

Changing carbs on Subaru's can be problematic, since their mounting bolts are horizontal and most Honda/Clone carbs have mounting bolts that aren't - assuming you want a stock-type carb.

Jammy- what do you mean? I just skimmed through this, and it looks pretty straightforward to me!?

 

[Najuto9tail]

Be VERY CAREFUL if you go to pry the cap off the end of an adjustment screw...don't do like I did and snap the screw off flush. Just pure dumb luck I was able to get the rest of it out.

Yeah I saw it on the other thread that you said something about that. From that I got the idea of not messing with the screw. The safest way is to pry it out with a flat head screw driver? What about pulling it with pliers?