jet sizes on 70 bbk

[ThaiGyro]

Sooo much good advice here. When I raced two strokes 125',250's and OMG; I did many, many plug "chops". Since those days, I have learned that street bikes should be attended to at their operating range. Do you run down the street wide open? Yes, but every moment?

In my opinion, you should "tune" for you intended range of flow. Maybe a bit tough, if you like sudden throttle response, but not all that hard. You can actually get a plug read at ANY rpm...and know what your systems are doing together. Top end reading is easy, but best for racing, I think.

Some like EGT indicators, while others tune for O2 reading. On a 2 stroke, either one is a challenge, due to unburned oil residues, but both indicators of combustion. The trick is to get your tuning without fancy and expensive gadgets. Experience, properly applied.

[Lucass2T]

I never do plug chops...there's too much involved to get a good reading (rpms, throttle position, load, temperature etc). Variables just change too much. Rough tuning is just guessing main jet and finetuning is purely on feeling, which you only can develop over time by doing alot of testing and making lots of mistakes (pushing limits and going over them).

EGT and CHT readings are a good way to make certain engine conditions visible and help you not going over the limits.

[motoxracer98]

Thanks for the info ill try that on my next one. How long (or how many miles) should i drive it before running it at w.o.t for a plug chop

[motoxracer98]

Well guys it happen again i ran the bike twice last night for about 10 mins riding around at 1/4 throttle everything seemed fine tonight i took it out again waited for it warm up fully drove it about a half mile alternating between 1/4-1/2 throttle and i tried a couple quick 3/4 throttle "burps" let the bike idle back down each time them as im riding along between 1/4 & 1/2 about 20 mph- Soft sieze it shut the motor off fired back up and kept rolling and it done it again so i fired it back up and babied it back to the house less than a half mile away . got home checked the plug it was a light blackish greyish color.
I figured it wasnt enough fuel(although it had 115 main in it).that was the biggest jet i had i got a drill bit that was about the size of a 125 jet 1.24mm i drilled out a old jet an i made it a little bigger by wallowing it out a bit. I figured noway will it be lean now
Well took it out again and it siezed again ! What now?? Im so aggrivated.i havent done the leakdown test yet i guess ill have to pick up the stuff tomorrow and try that. The pic below is after the last run and soft sieze half throttle with 2 quick bursts of 3/4 throttle

[motoxracer98]

Also the bike have no power it was very lagging and it just seemed like something was wayy off could this all be because the absence of a base gasket

[gsx600racer]

That sucks. I don't think your squish or compression were culprits.
Plus I think your plug looks lean although it probably does not have much run time on it.

Any air leaks, even if the carb was jetted correctly will cause a lean condition.

Mapping your port timing will determine if you needed the base gasket/s or not.

You can make your own degree wheel here for free. Thanks Brent

How to use the degree wheel is here.

Once you get your numbers, post them here. There are a few good tuners here what guide you in the right direction.

Here is the info for a DIY leak down tester.

I wish you reconsider investing in some larger jets both main(a few larger) and pilot (at least one larger)
Not sure what you needle height is, but it wouldn't hurt to raise the needle or lower the clip to make things richer. A few jets are cheaper then a new piston/rings and maybe a cylinder.

Not not sound like a *ick, but I'v never seen a rich engine seize. Foul plugs, yeah. Carbon up faster, yup.
Running rich is cheap insurance.

If there are any RC/real pilots here, im sure have heard the phase "altitude is insurance". Because the higher you are, the more time you have to recover before you meet the ground.

Lastly, wait till you get it all set up(temp gauge sensor). Patience is your friend.

[motoxracer98]

Thanks. Im going to try to locate some hets today and get them overnighted here 120main - 140 at least as far as the pilot i would live to order some of those but i dont know what size it is it doesnt have anything wrote on it ?? . i do have delorto carb here ive never installed the jets i have for it go to 135 i think . if i tried that would i have to go even higher since its more air or where would my jetting numbers fall with the dellorto on there ?

[eclark5483]

Don't know if it's been asked or not, but HOW are you lubricating? Pump or premix or both? If it's pump/both, have you checked to make sure it is functioning correctly?

[motoxracer98]

Premix 32:1 maxima racing castor oil

[motoxracer98]

I need some more info on carb sizes for my bike i think im going to end up buying a new carb or using this delorto i have im using my factory one now(16mm Leader brand). Its seems the delorto jets are hard to find thats whybi was thinking of going with a different more common carb a genuine Mikuni or Khein what do you guys suggest ?

[pinkscoot]

Treat land has all sorts of Dellorto jets and they ship fast Treatland. They also have needles and anything else you need.

[motoxracer98]

Could you tell me what cable i need in order to switch over to the delorto i was told i need to change throttle cables? Also i need a range of jets to order 110-130 ? Or higher

[190mech]

From what Ive read,the soft seize you had is at part throttle,that would mostly controlled by the jet needle not the main jet..A thinner(richer)taper needle will give you a richer part throttle(thats where most cylinders are fried),if you switch to a Dell,find out what needle it comes with and get a thinner one also...

[gsx600racer]

As I mentioned in other conversations, I am not that knowledgeable with Delorto carbs. I would recommend taking some time to read this. Although its for OKO carbs, the tuning fundamentals are the same for the majority carb out there. I found this very helpful.

[motoxracer98]

Your right 190 mech its never actually happend at w.o.t. its always siezed after riding it for a bit once the engine gets good and warmed up around half throttle crusing . it also runs like crap when it warms up when the motor is cold it actually runs decent .