1981 430CR Carb Tuning Question

I had my GoPro going at a hare scramble a couple of weeks back and I was able to record the issue I'm having.. First, I confess I don't know how to identify/name whats going on but I call it 'run on'. Basically, when I chop the throttle after a prolonged open-throttle section, the motor will continue with a pulsing rev for a short amount of time. Open the throttle and it goes away. I'm hoping there there is a way to fix this. Anyone know what this is called and what causes this?

Since the video I did change from a 2.0 slide to a 2.5 and also changed the pilot from a 35 (which was in the bike when I got it) to a 40. I rode it just a short while but in more technical conditions. I think it improved the run on but I didn't get to ride much WOT. Main jet is a 450 and the needle is the 6DH3 in the middle position.

The film is not attached but have you checked your spark arrestor, the mesh might be clogged up

check your inlet manifold, it may have a split underneath and can open up when you hit a bump jump wheelie etc and flash leans the bike so it pings and runs on for a short while. other wise you have an air leak somewhere. try the old wd 40 sprayed around gaskets and cyl head join while bike is idling. also do the engine seal behind the stator and see if it bubbles.

Yes, be a lean issue and could be even a slightly plug pilot jet, a sucked cylinder base gasket or all above things already posted.

Screw the mixture screw on the carb IN all the way and see if it goes away. If it does go up to a 45 pilot jet and re set the mixture screw to 1 and 3/4 turns out - then adjust the tick over to where you want it.

Andy.

good point. also if the mixture screw does nothing...you definitely have a leak, another test method.

All your jetting sounds very close... except the main. I typically need 500-540 on the 430's.

Thanks for all your replies. Was anyone able to see the video? I'll start with turning the mixture screw in and see if it goes away and then go from there.

Picklito, Going to a 500+ main from a 450 is a big jump (I believe stock is 440). I'll have to get some jets and experiment.

It's not a big deal. Go huge. Make it blubber on WOT. Then go down step by step till a loooong WOT pull gives a rare, isolated burble. Now you're controlling temp with the jet. You could hold it WOT forever at that point. Go down one step more. That's the correct main for an air cooled bike. You might be surprised what that motor wants.

Also make sure it's an R-4 needle jet. Some 81's came with a Q-8. I've seen stock bikes with 430 and 440 main... I wouldn't hold that wide open for more than a second or two... it's getting hot in there. Just sayin...

good sayin im thinkin..as an aside, for the last 4 years a mate drags his ol 430 out to ride the two day harrow event in july...inevitably he is always just buttoning up the top end the night before...a seizure every year for 3 years saw him rock up this year with the NEW main seal that was the problem all along...duh so if you cant make sense of the jetting, do a leak down test just to be sure its not gunna magically lean out somewhere

Picklito, is the needle jet pressed into the carb? I don't see a way to spin it out.

remove the main and the "holder" it screws into. the needle jet will press out the bottom with your finger.

I couldn't get any of the brass beyond the 'holder' to budge. Per the parts diagram there is the needle jet and the atomizer in there.

now that i think about it, i may have had to unscrew the holder partially and tap the carb slightly on some wood to lightly pop it free. the holder "pulls" the needle jet into the body lightly, so partially unscrewing it and giving it some light taps should unseat it.

I remove the main jet holder and use something soft like a wooden dowel or aluminum rod. Tap from bottom and it will pop out up top. They can get corroded in there around the dowel pin and be lil tough to get out.
One I had to heat with propane torch lil. I had two pilots that would budge so from now on before I remove a pilot, I heat the casting up opposite the pilot and they break loose real easy. I do the same if you need to replace a side carb vent as well.

Ok… It came out pretty easily when I tapped it from the bottom. The only other pilot jet I've removed screwed out through the bottom. What came out was a R-0. A R-4 would make it richer 1/4 to 3/4 throttle. Anyone else know what pilot jet their running?

Picklito has been a great resouce for info here on this site. Been never able to figure out his main jets
We have been getting down to 415 and 410 and still very rich. A moderator here is down even to 390 in his 430
and runs great. So temp, area, elevations, compression, desert different on Pic bikes ? All are factors for all.

Running a Q8 needle jet. As everyone knows I built more than a few 430s, always seen to end up around here even with a couple bikes with Mossbager reed blocks and others not. One bike we are running one step richer needle jet with a 2.5 slide. and running a 420 down from 430 , this is still rich

Also have a another bike with cut slide with UFO mounted on slide and half size pilot , so far so good on this
model , runs crisp and clean. Still rich up top a bit with that mod. Starting it is different

All the tracks i run dont have super big straights, even Unadilla or now at my age i have built in slowness on big straights.

And don't forget different fuels may need to have different jetting . Be consistent , use the same fuel when jetting .