gpx 110 high comp race engine jetting??

[AntNZ]

I convinced one of my mates to buy a second hand 2012 lxr.

the original 160ho has been taken out and been replaced with a gpx110 race engine to be able to compete in the 65cc 2smoke class national comp here in NZ.

The 110 has 6hrs on it and the original 160ho also came with the bike +an oko26 flatty.

The whole lot for $2200 which I thought was good buying.

The 110 has a mikuni 22 on it which I'm sure is genuine, the engine/carb combo was supposed to be tuned professionally...haha NOT!!

I took it for a spin yesterday and it started fine and idled good.

When riding there is a bit of hesitation about half throttle and simply will not rev out n the top end, just seems to go flat and do nothing more.

Even though it isn't running perfect I was surprised how powerfull these little 110's are.

I wouldn't have a clue what jets it has in it as I havn't checked.

Just a starting point for this engine/carb combo would be good please???

Would a oko26 be to big for the 110??
Also the oko is different from the 2 I already have, is it what you call a power jet??

 

[gottagetacheaperhobby]

Yep thats a power jet 26mm, and would definitely be 2 big for a 110. Got any pics of the engine? I have never heard of a hi comp 110, only new about the hi comp 125...
I would move the clip up and down, see which way it runs best and that will tell you if you need bigger or smaller main jet. If it runs best on the bottom clip go up a main jet or 2, if its better on the top clip then go leaner

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[AntNZ]

Yep thats a power jet 26mm, and would definitely be 2 big for a 110. Got any pics of the engine? I have never heard of a hi comp 110, only new about the hi comp 125...
I would move the clip up and down, see which way it runs best and that will tell you if you need bigger or smaller main jet. If it runs best on the bottom clip go up a main jet or 2, if its better on the top clip then go leaner

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I'll get a picture tomorrow but looks identical to the gpx125.

 

[AntNZ]

What does the powerjet do?? is it any better in any way than the standard oko26??

 

[AntNZ]

Pic of the engine and carb

 

[gottagetacheaperhobby]

The powerjet just adds extra fuel at high rpm, a lot of ppl close it off simply to make tuning easier. The 110 gpx engine would be a ripper i reckon, i had never even heard of it before lol.

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[AntNZ]

The powerjet just adds extra fuel at high rpm, a lot of ppl close it off simply to make tuning easier. The 110 gpx engine would be a ripper i reckon, i had never even heard of it before lol.

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Yeah, its supposed to to be a 13,000rpm engine just like the 125 so am very keen to get it jetted properly and experience them rev's
Still, I am impressed with it even though it's not quite right yet.....and it's in a LXR, even better!!!

 

[AntNZ]

So I got round to pulling carb of today ,the clip was on the bottom notch and had a plastic spacer under the clip aswell, I checked the plug and is definitely running lean.
The jets in it were 15 pilot and 95 main(mikuni 22).
Anyone got an idea roughly what jets a 110 would run with a mikuni 22??

Needs bigger jets obviously but don't know what to order?
I have a 22.5 pilot and 112.5,117.5main but am guessing these would be too big??
Thanks!

 

[gottagetacheaperhobby]

Try the 22.5 pilot, see how it reacts.. i reckon something around the 100/105 mark for the main jet...

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[headsmess]

usually if theyre running lean, theyll just conk out, so its either very close or youre misreading the plug. ie, the plug may simply be too cold, and then all youll ever get is a white plug. until the electrodes start melting

you didnt say what the plug is... if its a 5 or 6, go get an ngk 8 or 9... hi comp will also run hotter, which makes plug reading a tad harder, especially if its the wrong heat range. and a new plug is better for reading anyways.

easy way to see if it is running lean without resorting to drills, etc... pop the air filter, and put some tape over the intake, restrict airflow a bit. or use your hand but thats pretty hard to do when trying to pull full throttle (reminds me of the days on an old dt250, no cable, just pulling the slide with our fingers...)

if it gets better, stick the 112.5 in there, see what happens.

the needle being raised so high says the pilot is too small, and that can also affect the plug reading. plug chops only work when you hit the killswitch at the desired throttle setting, and thats after a few minutes of holding it there! if its lean down low, and you let it idle or arent holding full throttle when you kill it, forget it... go do another lap.

and then, of course, if the main jet ends up being to big...solder and drill it, or simply start sticking superfine wire in the hole, one strand at a time (headphone speaker wire is best. tack the bottom end to the base of the jet with solder. pretty easy to remove afterwards, as well)

personally, it sounds like its rich.... doesnt want to rev. but the mid range stumble will be the pilot/ low mixture screw being too lean. as i said before, if its too lean up top...it should just DIE when given full throttle.

always start with the main jet tuning first, full throttle, then work back to idle from there.

stupid effin power jets... too much hassle.

a bigger carb isnt necessarily better, either no point going bigger than the intake ports, if you get my drift... personally, on a 110, id be sticking with the 22...

you didnt mention your altitude either. it may have been jetted spot on for where it was to start with. though even that changes depending on the weather. there is no "standard" jetting. each engine, each day, each HOUR is different.

 

[AntNZ]

usually if theyre running lean, theyll just conk out, so its either very close or youre misreading the plug. ie, the plug may simply be too cold, and then all youll ever get is a white plug. until the electrodes start melting

you didnt say what the plug is... if its a 5 or 6, go get an ngk 8 or 9... hi comp will also run hotter, which makes plug reading a tad harder, especially if its the wrong heat range. and a new plug is better for reading anyways.

easy way to see if it is running lean without resorting to drills, etc... pop the air filter, and put some tape over the intake, restrict airflow a bit. or use your hand but thats pretty hard to do when trying to pull full throttle (reminds me of the days on an old dt250, no cable, just pulling the slide with our fingers...)

if it gets better, stick the 112.5 in there, see what happens.

the needle being raised so high says the pilot is too small, and that can also affect the plug reading. plug chops only work when you hit the killswitch at the desired throttle setting, and thats after a few minutes of holding it there! if its lean down low, and you let it idle or arent holding full throttle when you kill it, forget it... go do another lap.

and then, of course, if the main jet ends up being to big...solder and drill it, or simply start sticking superfine wire in the hole, one strand at a time (headphone speaker wire is best. tack the bottom end to the base of the jet with solder. pretty easy to remove afterwards, as well)

personally, it sounds like its rich.... doesnt want to rev. but the mid range stumble will be the pilot/ low mixture screw being too lean. as i said before, if its too lean up top...it should just DIE when given full throttle.

always start with the main jet tuning first, full throttle, then work back to idle from there.

stupid effin power jets... too much hassle.

a bigger carb isnt necessarily better, either no point going bigger than the intake ports, if you get my drift... personally, on a 110, id be sticking with the 22...

you didnt mention your altitude either. it may have been jetted spot on for where it was to start with. though even that changes depending on the weather. there is no "standard" jetting. each engine, each day, each HOUR is different.

The plug is a c7hsa ngk, altitude is pretty much sea level(35ft) above and the bike came from a place that is the same altitude.
Yeah, I prob didn't do a really good chop only got into 3rd for only a second on wot before i hit the kill switch.
I will do as you suggested and try tune the main first, just have to get more jets.
Forgot to mention that for it to idle the screw has to be in a fair way, The slide is about 20mm or more from bottoming out so guessing it definitely needs a bigger pilot.....correct me if im wrong????

 

[AntNZ]

How would a keihin pe24 go with a 110cc, is it still a bit big???

 

[gottagetacheaperhobby]

If the slide is so far up then the pilot jet is pretty much not even being used, so yeah its definitely lean, i only said stick with what you had in the pilot circuit as you said it started easy, i didnt know the slide was so far up. If thats the case then you really need to start there, find a pilot jet that will allow it to idle with only 2 to 5mm of a gap under the slide.
I did get a 24mm oko power jet working on a 110, but it was not easy lol, lots of trial and error with the jetting....
Another easy way to see if its to lean is turn the choke half on and see how it runs...only works with the butterfly choke though..

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[AntNZ]

O.k, so as you can tell from the date on the previous post.......it has been a while since I even attempted to get this engine running!
its such a pain in the ass having to unbolt the mikuni when I wanna change jets or even adjust air/fuel screw so the bike has just been sitting there looking sad for a long time!!
I love the OKO's for ease of tuning and performance gains.....

for those in the know.....what size OKO would be best suited to a high-comp 110cc??

oko21 or oko24???, and a good starting point with jetting would also help...?

I have found both carbs on e-bay for $60nzd with free shipping and x5 main jet kit, just gotta choose the right sizes??

Thanks in advance...

 

[gottagetacheaperhobby]

I managed to get a 24 running on a lo comp 110 so it would suit a hi comp 110 fine IMO. Can remember jetting though, it was a long time ago lol.

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[AntNZ]

cheers stu, I'll go for the 24 then!

 

[rotn50]

cheers stu, I'll go for the 24 then!

Have you tried the Chinese 19mm mikuni (vm16) carby? I had a really hi comp 125 I built and this particular carby suited it like chalk and cheese. Obviously it all comes down to air and fuel where most people think bigger carb is better. Oko 24 might be the answer for sure. But if not try the bikini copy 19mm.

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[AntNZ]

Have you tried the Chinese 19mm mikuni (vm16) carby? I had a really hi comp 125 I built and this particular carby suited it like chalk and cheese. Obviously it all comes down to air and fuel where most people think bigger carb is better. Oko 24 might be the answer for sure. But if not try the bikini copy 19mm.

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cheers mate, I havn't ordered the carb yet....do you think the oko21 would suit the 110 bit better than a 24mm??

 

[rotn50]

cheers mate, I havn't ordered the carb yet....do you think the oko21 would suit the 110 bit better than a 24mm??

What's the jetting in the 21 OKO Mate?

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[user 20441]

if you want high revs over torque then go for the 24 ,eventough it's going to be hard to set up correct.
21mm will be better overall if you ask me, easier to jet, and more rideable...
if i had a 140cc i'd choose between 24 and 26mm. my 125cc has a 22mm carb and feels nice overall