November 13, 2014 at 7:12 pm #37041
I’m planning to make it to laguna seca by January, with my 99 stock Honda CR125 shifter kart.
Currently comes with the pump around fuel system, and I recently melted a piston by the exhaust side, destroying the jug.
Any recommendations on good jetting to the carburetor for this long track, and to keep it from happening again?
What is a good jet set up for that track?
Thank you all in advance. Fast Freddy. ;)
November 13, 2014 at 10:12 pm #37059Ray ChiappeParticipant
I used to run the pump around. Could not get it to work well. What I run might not work for your setup. You have to consider an Air Box in the equation, which is mandatory at Laguna. What jet were you using when you stuck it?
November 14, 2014 at 12:45 am #37061
55 and 170 when I stuck it
And yes, of course I’m planning to run an air box also.
Thank you in advance for all the help
November 14, 2014 at 7:27 am #37074Larry DobbsParticipant
Hey Freddy, you could always tune it up at our Sears Pointe Sonoma race on Saturday November 29th ;)
November 14, 2014 at 9:01 am #37076
I would love to, but I have a race here locally that falls on the 29th and 30th for our year end shootout KT100 YC Heavy Pipe.
Do you know what jet size is needed for Sonoma, also? Main and Pilot? Sprocket size/gear ratio
November 14, 2014 at 11:00 am #37084Ray ChiappeParticipant
I’m on the heavy side. Last time I ran the shifter at Sonoma I ran a 18/22. Prob would try a 17/21 next time. Both Laguna and Sonoma have good air. Not sure what to suggest because of that pump around. But I have run 55/175 at both tracks. With a 178 main in practice.
November 14, 2014 at 12:24 pm #37086
Thanks. Pump around should only affect fuel delivery, with out having fuel starvation, as it keeps the bowl full
As for the jetting goes I really don’t know what happened, but my piston got melted at the top edge by the exhaust port ( never stuck ) just lost compression, I opened it up and found a big chunk missing at the top down to the ring.
November 14, 2014 at 1:20 pm #37094Larry DobbsParticipant
I would recommend you talk to Jason at Swedetech. Joseph Hollinger runs stock moto. Email him off of our website http://www.nckroadracing.com for a second opinion. Your description makes me think that you have a problem more than just too lean of a main jet. Maybe an air leak.
November 14, 2014 at 1:47 pm #37096
I think you may be right
I think I’ll contact him
Thank you, so much.
November 14, 2014 at 5:20 pm #37107
Swedetech is closed till December, so I won’t be able to get any purchases or questions answered.
Thank you, every one who had inputs in trying to help me. Fast Freddy. ;)
November 20, 2014 at 1:17 am #37388Kerry MatthewsParticipant
18/22 is a good gear, I’ve been using it for the last several years there. Almost impossible to say what the jetting would be, as it’s going to be dependent on so many things. I use a SwedeTech fuel system, so my notes wouldn’t be accurate for you, but the weather at LS is the biggest determining factor.
November 20, 2014 at 11:05 am #37401
Thank you, Kerry.
Very good info, and yes, you’re right with weather conditions and elevation in Laguna Seca. It will still cold in January, and jetting may be a factor for me, but I’ll start fat, and then work my way down, and see what works best.
I just don’t wanna stuck the top end again, while the motor is screaming down the hill, or up hill. :)
November 27, 2014 at 11:39 am #37861
I will get to my jetting notes tonight – one comment about the fuel system, have used a pump around for several years at all of the road race tracks, and never had a problem. And Ryen grabbed a couple of club championships during that time. So it works. 170 does sound a little lean, but it is all about the air. I have a table built from all of the races, where I have noted the best jet (plug, EGT, and piston top inspection) for whatever the air reads, and now all I do is read the air gauge and go to my table and jet. Never an issue.
That said, one engine and driver is one jet, and another engine/driver at the same time, could be different. I know that several folks are usually a jet or 2 smaller than when we run. I know Ryen is a bit over the class weight, so that may be a factor heavier, needs more power, needs more fuel….
November 27, 2014 at 1:19 pm #37864
Thank you, Roger
I appreciate this very much
I have always respected a gentleman and his notes/book keeping
November 28, 2014 at 11:44 am #37932
So looking through my notes – Laguna air is often between 500′ and 1000′ relative air density. And we have run 182, 180 and 178 – 182 for around 500 and 178 at 1000 and higher. Again – I am always checking plug color and EGT behavior and adjusting around that. Laguna is also not very much on long straightaways. For same air, at places like Thunderhill and Sonoma, I stay on the richer side as the long WFO sections need the fuel.
I don’t have access to the kart to verify the pilot, but I believe we have a 60 in there and the needle I don’t remember either – but there is pretty much just one needle all the road racers use. This is all on a PWM, without airbox.
December 2, 2014 at 7:35 pm #38181josh martinParticipant
For what its worth, i use the cr125 jetting app regularly. I find it to be highly accurate for sprint track racing, but have discovered (the hard way) that its suggested jettings are way too lean for big road-race circuits. It is still useful, as long as you understand its limitations. For large road-race tracks, i have found you need to add nearly 20 jet sizes (if it says 178, you need about a 198), otherwise a 100 mph piston stick is in your future. That being said, it is dead-on for about any size sprint track.
December 3, 2014 at 8:16 am #38211Chris HegarParticipant
If your needing near a 200 main your probably a little lean in another part of the carb.
December 6, 2014 at 11:42 pm #38503
I think you are on to something there Chris – sprinters use a leaner pilot – and a bit leaner needle as well to get it to pop out of corners, and they rarely rev out.
Josh – as I said, in my post above we are not anywhere near a 200 (195 even) at the RAD for LS and Sonoma for usual air. Over the next week or two I will get out there and verify my pilot and needle and report back. Like I also said, I have run successfully with the engine, never cooking the piston or anything, and, so have a reliable set of data up to 6000′ like at Miller Motorsports down to sea level. And about every 400′ is the next size. But still one engine is not the same as another, so plug color, egt, and piston have been my guide and now more folks are using o2 sensors and that will be even more accurate as to how “right” the jetting is.
December 8, 2014 at 10:20 am #38582Chris HegarParticipant
Fuel type/oil and plug heat range are also variables to consider.
December 8, 2014 at 10:27 am #38585
Yup, fuel, pre mix, plug, tires, radiator type, pipe, etc. I agree.
Hey guys, thank you for all your help
Unfortunately I’m not gonna be able to make it, as I sold the kart in broken condition. Sad
A buddy of mine came over to my shop, saw the kart and fell in live with it, made me an offer and bought it.
He will be seeing you guys up north in January at Laguna Seca, and Willow Springs, Button Willow, and Infenion.
Thanks so much for all your input. God bless you all. Fast Freddy. :)
December 13, 2014 at 10:03 am #38817Mark MorrisonParticipant
The Winter Classis at Laguna Jan 24 2015 is approaching fast. Registration will open on Jan 1 2015. This will be a rain or shine event. Due to restrictions the field is 35 karts per run group. Noise is 92 db you get one warning. This year’s format is a practice session, qualify session and the Main you must use the same set of tires from qualifying in the main. Stay tuned for more info here as will at our website nckroadracing.com
Mark Morrison, President NCK
December 26, 2014 at 5:12 pm #39410
Finally got out to the trailer and got into the carb – pilot we use is a 60 and the needle is a DGH
And we have never messed with either at any track from sea level to Miller Motorsports park. Not to say that is always golden, but it has been reliable and given me good tuning indications on the main jet. Perhaps more extended time at higher altitude, I might try a leaner needle, or try a 58 pilot and see what changes. At most though, maybe moving the clip up one slot might all that is needed to correct a mid richness or something.
- You must be logged in to reply to this topic.