Author Topic: Drilled out jets.....WOW, what a difference! (Read 4431 times)

BlackMax · « **on:** July 31, 2009, 06:43:47 PM »

I was having some trouble with low power/dogging and exhaust popping at 1/2 or more throttle, for the LOOOOOONGEST TIME. After going through the electrical, which made things somewhat better, it was still dogging a good bit, and popping out the exhaust under heavy throttle. I decided (with your help) that the 105 jets were probably too small for my setup (ported head, cam, 4-1, pods). Today, I looked all around for jets, but couldn't find any; and didn't want to wait for an internet order. So, I drilled mine out with a 1.34mm bit, using a hand drill and vice-grips. Yea, I'm all about precision

.

Well............Now the bike is smooooooooth as silk, at full throttle all the way to the redline in all gears. What a great sound!!! Especially after all these weeks dealing with a bike that just wasn't right, despite buckets of cash having been thrown at it.

I'm pretty stoked.

Zaipai · « **Reply #1 on:** July 31, 2009, 06:47:13 PM »

Wow very cool. Glad it worked for you. What would that make you jets now, 120's?

BlackMax · « **Reply #2 on:** July 31, 2009, 06:48:23 PM »

134s

For jet size, just move the decimal to the left by 2 spots. So, 105s are 1.05 diameter hole. 127s are 1.27mm diameter hole.....etc.

TwoTired · « **Reply #3 on:** July 31, 2009, 07:09:19 PM »

Twist drills make a larger hole than their shank size. They have too, or you would never get them out of the hole they drilled.
You probably have at least 140's now, if not larger. Check the spark plug deposits. Check all the plugs. Twist drills aren't known to make precision holes even if fixtured correctly.

BlackMax · « **Reply #4 on:** July 31, 2009, 07:21:18 PM »

good point. I'll watch for carbon. If so, I'll just drill them to a smaller size....oh, wait.

127 was my intent. Just went out and re-measured. The calipers say 1.37mm. Hmmm, might be a little rich; but, time will tell.

Soos · « **Reply #5 on:** July 31, 2009, 07:35:11 PM »

Quote from: TwoTired on July 31, 2009, 07:09:19 PM

Twist drills make a larger hole than their shank size. They have too, or you would never get them out of the hole they drilled.
You probably have at least 140's now, if not larger. Check the spark plug deposits. Check all the plugs. Twist drills aren't known to make precision holes even if fixtured correctly.

+1000

The RIGHT drill in brass can do good, but your average drill you can buy will make a tri-lobed hole.
I would guess you are in the 140-145 range as well.

l8r

Soos · « **Reply #6 on:** July 31, 2009, 07:37:03 PM »

You do know that you can get a SET of jets for like 5.00 ... right?

http://www.z1enterprises.com/detail.aspx?ID=1926

ok... 1.44 *4... = 5.76....

l8r

BlackMax · « **Reply #7 on:** July 31, 2009, 07:41:39 PM »

Quote from: Soos on July 31, 2009, 07:37:03 PM

You do know that you can get a SET of jets for like 5.00 ... right?

http://www.z1enterprises.com/detail.aspx?ID=1926

ok... 1.44 *4... = 5.76....

Just didn't feel like waiting to see if this was my problem. It was an impatience thing. No worries. I'll buy some 130s and keep them around if the plugs get carbon'd up. The carbs were already apart, and the objective was accomplished. That being, I now know the 105s were simply too small to allow the engine to even operate under any type of load.

l8r

razor02097 · « **Reply #8 on:** July 31, 2009, 07:44:58 PM »

Quote from: BlackMax on July 31, 2009, 07:41:39 PM

Quote from: Soos on July 31, 2009, 07:37:03 PM
You do know that you can get a SET of jets for like 5.00 ... right?

http://www.z1enterprises.com/detail.aspx?ID=1926

ok... 1.44 *4... = 5.76....

l8r

Just didn't feel like waiting to see if this was my problem. It was an impatience thing. No worries. I'll buy some 130s and keep them around if the plugs get carbon'd up. The carbs were already apart, and the objective was accomplished. That being, I now know the 105s were simply too small to allow the engine to even operate under any type of load.

As long as it works

Achmed · « **Reply #9 on:** July 31, 2009, 08:16:17 PM »

Man, I would be surprised that a 78 Supersport (by the way supersports are the best!) could go up about 8 or 10 sizes and still be anywhere in the realm of operability. Just a testament to these bikes' awesomeness! For now, I guess. What's the air intake and exhaust situation? I wonder if you're going to be getting 20 mpg? Or fouling plugs above 1/2 throttle?

Hey, if it works, it works.

Spanner 1 · « **Reply #10 on:** July 31, 2009, 08:22:47 PM »

Yeah, sounds great...but ( hate to be the damper !) stock=105's, now 140's (+,-) Wow !
Will it actually run at highway speed for a prolonged time with these jets ? Quick runs around town/hood wont get the bike to op. temp.......

Johnny5 · « **Reply #11 on:** July 31, 2009, 08:30:41 PM »

Quote from: Spanner 1 on July 31, 2009, 08:22:47 PM

Yeah, sounds great...but ( hate to be the damper !) stock=105's, now 140's (+,-) Wow !
Will it actually run at highway speed for a prolonged time with these jets ? Quick runs around town/hood wont get the bike to op. temp.......

Interesting. I think though even prolonged highway speeds, if keeping the throttle in the same position for a while) the needle should be doing the most work. If the jets are around 140, I dont see a lot of power at WOT. It's probably a little soggy.

Zaipai · « **Reply #12 on:** July 31, 2009, 08:35:56 PM »

Quote from: BlackMax on July 31, 2009, 06:48:23 PM

134s

For jet size, just move the decimal to the left by 2 spots. So, 105s are 1.05 diameter hole. 127s are 1.27mm diameter hole.....etc.

Sweet, see I learn some thing every day.. I love this site!

BlackMax · « **Reply #13 on:** July 31, 2009, 10:16:10 PM »

Quote from: Johnny5 on July 31, 2009, 08:30:41 PM

Quote from: Spanner 1 on July 31, 2009, 08:22:47 PM
Yeah, sounds great...but ( hate to be the damper !) stock=105's, now 140's (+,-) Wow !
Will it actually run at highway speed for a prolonged time with these jets ? Quick runs around town/hood wont get the bike to op. temp.......

Interesting. I think though even prolonged highway speeds, if keeping the throttle in the same position for a while) the needle should be doing the most work. If the jets are around 140, I dont see a lot of power at WOT. It's probably a little soggy.

Well, at WOT is sure seemed like an ape, from 3k-10k. But then, I'm comparing it to 105s that were making all the cylinders cut out, and "crackle pop" out the exhaust. I'll take the bike out in the AM, and hammer it to see if it smokes black. For the drill bit, I had to guess, as they weren't actually labeled with shaft diameters. They were just labeled #53, #54, #55, etc. I tried to go significantly smaller than a 1/16", which I new was too big. 3/64" was exactly what I was looking for.....but alas, I had to use my eye, and hope I could visually gauge to within .05mm. I got close.

Man is it nice for now..... to hear it rev with the new head/cam. If I have to re-jet, small price to pay

jx25 · « **Reply #14 on:** August 01, 2009, 12:22:36 AM »

thats what I would of done, just drill em out, you can always buy another set of jets like you said this way you didnt have to wait

Hush · « **Reply #15 on:** August 01, 2009, 01:25:12 AM »

Hey you are mobile and having fun, probably if you keep the revs to very high you will be OK

I wouldn't piddle around town too much as the plugs are bound to carbon foul, but don't let our disussions on the rights and wrongs of jetting get you down, we can debate that forever (been 40 years so far) so enjoy and put some miles under your saddle.

mystic_1 · « **Reply #16 on:** August 01, 2009, 07:50:14 PM »

Quote from: Soos on July 31, 2009, 07:35:11 PM

but your average drill you can buy will make a tri-lobed hole.

OK, can anyone explain to me exactly why this happens? It absolutely drives me nuts, not only the accuracy thing but it offends my sense of aesthetics.

mystic_1

BlackMax · « **Reply #17 on:** August 01, 2009, 08:27:44 PM »

Quote from: billybob on August 01, 2009, 08:20:23 PM

No... But it pisses me off too.

If you don't want to wait for jets just go to your local dirtbike hotrod shop and get mikuni small jets, that's what I did $3.50

I went to a bunch of places. From Honda dealerships to hard-core bike service/parts places....nothing. I was kinda surprised. They said the CB jets "from the old days" were unique??

I went for a 40 mile ride today in the canyons......all perfect. Man, what a nice ride and sound. I mean, it's no Ducati with desmo valves...but it's still pretty sweet. Anyway, when I got back, I pulled the plugs. They were tan to dark tan with no fluffy buildup. So far, so good. Still got 127s on the way.

Flying J · « **Reply #18 on:** August 01, 2009, 08:34:32 PM »

did you move the needle up? I would imagine with that much change you would need to.

BlackMax · « **Reply #19 on:** August 01, 2009, 09:14:31 PM »

Quote from: ffjmoore on August 01, 2009, 08:34:32 PM

did you move the needle up? I would imagine with that much change you would need to.

uh, no...can this be done without removing the carbs? If so.......how? (never really worked on carbs before, sorry)

Hush · « **Reply #20 on:** August 01, 2009, 09:14:31 PM »

Jezz I'd leave them in then, sounds like you lucked out big time, bet you couldn't repeat that.

Achmed · « **Reply #21 on:** August 01, 2009, 09:22:26 PM »

You've never worked on carbs before but you drilled out your jets? Yeah you are lucky so far. Them jets don't get into the carbs by themselves. Ride it all night long, dude!

754 · « **Reply #22 on:** August 02, 2009, 08:19:28 AM »

Raise the needles and you will be good with 120,s, like the rest of the world.
I dont agree with the tri shaped hole everytime, on redrilling something already drilled.

However it is common on thin plate, use spliy points to avoid that.

tomsweb1 · « **Reply #23 on:** August 02, 2009, 08:41:37 AM »

I don't believe the needles in the 78 are adjustable, if the ss is anything like my A

754 · « **Reply #24 on:** August 02, 2009, 08:48:40 AM »

They could be if you use 77 ones.
I think the 78s can be shimmed.

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Author Topic: Drilled out jets.....WOW, what a difference! (Read 4431 times)