Should I rejet the carb?

[Gareth123]

Should I rejet the carb? I just changed the engine from 145cc to 200cc. The bike is stuttering at speeds over 80km/h. I've put a colder plug in (It helped, I was then able to reach 70km/h without it stuttering) and have adjusted the mixture screw to richen up the gas (that got me to 80km/h, any further adjustment made no difference)

I'm not sure how to check the timing so I thought I'd rejet the carb first to see if that helped.

[Voltaire]

The idle circuit is really only adjustable for idling...
Then its a combination of the slide cutaway, needle and main jet
The needle controls from about 1/3 to 3/4 then its just the main jet.

Google the 200 engines carb, it might be larger or just have different jets.
Running lean at 80 kmph ....when you release the throttle if the revs are slow to come down.....lean.
Engine may also run hot and plug white looking.
timing should not need changing.
What sort of bike is it?
4 stroke?????
Big bore kit or a different motor?
Thats my 2 cents worth.

[Gareth123]

Its a XL 185 barrel thats been bored out to a 200. The carb is a GL145 carb. Yip its a 4 stroke. Will google it now. The revs aren't slow to come down at 80km/h and the plug is looking white, thats why I changed the plug and adjusted the mix

[CookMySock]

After those mods, definitly. Or at least get the gas analyser or EGT guage over it to check it.

Steve

[Sidewinder]

no reject the brakes

[Voltaire]

Its a XL 185 barrel thats been bored out to a 200. The carb is a GL145 carb. Yip its a 4 stroke. Will google it now. The revs aren't slow to come down at 80km/h and the plug is looking white, thats why I changed the plug and adjusted the mix

Just compare the XL 200 carb to the GL145...probably a larger bore carb.

[KiwiGs]

You will need to re jet I would think.
That is a just under 9% rise in cc.
The easiest way to know for sure is do some plug chops at a couple of different throttle positions
Cheers

[Gareth123]

You will need to re jet I would think.
That is a just under 9% rise in cc.
The easiest way to know for sure is do some plug chops at a couple of different throttle positions
Cheers

Plug chop? Thats where I ride at a certain rev range and just kill the bike right? Do I have to wait for the bike to cool down before I remove the plug? Or will I get the same reading no matter what?

[F5 Dave]

You will need to re jet I would think.
That is a just under 9% rise in cc. . .

What? Where did you study math? it's at least another 25% bigger, that is huge.

ok chances are your jetting requirements have changed. Start with getting the main right. Obviously you aren't too far out if it will get to 80, so I'd go up two sizes on the main & keep throwing one size bigger until the improvement stops.

Many will jump several sizes at once & go too far losing performance & consumption. make sure you do this with a clean air filter.

[KiwiGs]

What? Where did you study math? it's at least another 25% bigger, that is huge.

ok chances are your jetting requirements have changed. Start with getting the main right. Obviously you aren't too far out if it will get to 80, so I'd go up two sizes on the main & keep throwing one size bigger until the improvement stops.

Many will jump several sizes at once & go too far losing performance & consumption. make sure you do this with a clean air filter.

10% of 185 is 18.5, 18.5+185=203.5 which is just a bit bigger than 200 so I said about a 9% rise in cc.

[KiwiGs]

Plug chop? Thats where I ride at a certain rev range and just kill the bike right? Do I have to wait for the bike to cool down before I remove the plug? Or will I get the same reading no matter what?

Yeah thats right
You dont have to do it hot, it shouldnt make any difference to the colour of the plug. You might not notice if the plug is too wet but I dont think that will be a problem to begin with.
Cheers

[Gareth123]

10% of 185 is 18.5, 18.5+185=203.5 which is just a bit bigger than 200 so I said about a 9% rise in cc.

Yeah but the original engine was a 145 not a 185

[KiwiGs]

Its a XL 185 barrel thats been bored out to a 200. The carb is a GL145 carb. Yip its a 4 stroke. Will google it now. The revs aren't slow to come down at 80km/h and the plug is looking white, thats why I changed the plug and adjusted the mix

Whoops, that what I get for not starting at the start

[Gareth123]

LOL I can see why you got confused.

Anyway I did the plug chops and the colour always came back as a slight tan colour.

So I just pulled apart the carb and gave that a clean. One small hole on the main needle (it had small pin holes up the side) was blocked so I cleaned that out. Put it back together and test rode it and it still had the same problem.

So anyway I had to go to my mates place and on the way home the problem got even worse. Now it does it under gentle accelleration, albeit not so bad as hard accelleration. Could it be a problem with the electical system? I had a quick check over the outside of it and nothing seems obviously worn out. What if the inside of a cable is dying a slow, painful death? How would I check that?

[Gareth123]

Oh and I just had a thought, When I first got the bike back from the bike shop I did give it a quick squirt up to 100km/h just to see how the bike went. It didn't stutter then at all. it would have stuttered straight away wouldn't it? Thats why I thought it may be the electrical system.