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Messed up my carb, HELP!

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Well I really did it this time. :bonk:I can't figure out what I did but the bike is running like crap at cruise. Idle is fine, WOT is fine but it stumbles and surges at mid range and my AFR meter is showing around 16. I have had the carb apart 4 times, completely stripped it and can find nothing wrong. The bike is almost unusable now :smirk: I have to pull the choke on to limp home.

It all started when I pulled the carb off Thursday Night to take measurements (planning an EFI project). While I had the carb off I decided to pop in a DJ 160 main (been running a 155) for a quick test. I didn't touch the needle. When I took it for a ride, the idle was good with AFR around hi 12's to low 13's. WOT looked good, with mid to high 12's. Any time accelerating moderate to hard it is fine. But WAY lean at cruise! And this with the exact same needle setting I have been running for weeks!:smirk: I have been running the DJ needle with the clip in the second slot. AFR readings have been mid 13's for 5th gear cruise.

The bike set up is, open air box (4 1" holes), ground headed weld, DJ needle, DJ 155 Main. Wideband O2 sensor and AFR meter.

So I went back to the original main and checked everything. No Change.

I dropped the needle clip to the 4th slot. Better but still too way too lean.

Tried 5th slot. Still a little lean at cruise and way too rich just above idle and low speed cruise. Like 10 to 11 on the meter.

Pulled apart again and remove the needle jet. Could not see any issues. Checked the float. OK. checked the manifold for possible leaks. Gave up and put all back together. Same problem. I sprayed WD-40 around the carb while it was running to try to detect leaks. Nothing.

So anyone have an ideas?

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Hey jaeger22, sorry to hear your bike's running bad. I can't help with all the AFR numbers and the re-jetting, (I was learning carb stuff from your earlier thread-still a newbie!), but maybe take a break, then retrace your steps? Ya think it would be something simple, but I know how changing just one little thing and not paying attention to it can throw a huge curve ball at you. Bet you get it figured out quick. Tinkering, learning and FRUSTRATION just seem to go together so very well - rember Murphy's law. It'll come to you.

rc

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Thanks for the encouraging words RC. Yes I keep thinking it will come down to something simple to but I sure haven't figured out yet. I am back to the exact set up I have been running for weeks. It only seems to affect the needle (1/4 to 3/4) but I didn't even change the needle when it started. I have checked the needle and needle jet.

I am hoping some of the real experts on this site will have an idea. Rob, Eddie, Jeff, others????

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Thanks for the encouraging words RC. Yes I keep thinking it will come down to something simple to but I sure haven't figured out yet. I am back to the exact set up I have been running for weeks. It only seems to affect the needle (1/4 to 3/4) but I didn't even change the needle when it started. I have checked the needle and needle jet.

I am hoping some of the real experts on this site will have an idea. Rob, Eddie, Jeff, others????

The description you are conveying points directly at the needle/needle jet. Have you removed the needle jet and checked the emulsifying holes? They need to be clean. Have you checked you main air jet port... this supplies emulsifying air to the needle jet. Have you double checked your fuel level in the float bowl? If it's too low your bike will run lean. Not sure how you were running the DJ needle in the second clip position unless you have the modded white plastic spacer under the clip (or the procycle kit) but the bottom line is the needle height needs to be the equivalent of the clip in the 4th position down with the clip sitting at the bottom of the slide. I'd run the 160 main.

Edited by mx_rob

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Rob, thanks for the help!:prof::worthy:

The description you are conveying point directly at the needle/needle jet.

Yes absolutely agree. That is why I was so confused to have this show after I changed the main jet. I didn't touch the needle or needle jet. In trouble shooting this problem, I went all the way to the 5th clip position and it was still too lean at cruise but started getting way rich just off idle.:smirk:

Have you removed the needle jet and checked the emulsifying holes?

Yes, with a magnifying glass I can see through the tiny emulsifying holes in one side clear through to the other. I also blew them out with compressed air.

Have you double checked your fuel level in the float bowl?

Yes, it is set slightly high but I did not adjust it given the nature of this problem. I even hooked up a clear tube to the drain so I could bend it up, open the drain and see the fuel level in the tube. Looked good.

Not sure how you were running the DJ needle in the second clip position unless you have the modded white plastic spacer under the clip (or the procycle kit) but the bottom line is the needle height needs to be the equivalent of the clip in the 4th position down with the clip sitting at the bottom of the slide. I'd run the 160 main.

I do seem to be running leaner jets than most others report. But I am just going by the AFR meter. So that makes me wonder if I original had some kind of issue in the carb that made it run rich for a given set of jets and I somehow accidentally "fixed" it when I was installing the 160 main. :smirk: I know that sounds a little crazy :lol: But . . .

The latest is that I pulled the carb off again (for the 5th time) and completely dissembled every part. Checked every jet and "O" ring, cleaned the body with carb cleaner and blew out every passage and jet with compressed air. I also put a dab of silicon grease on the slide. I put it all back together with the jetting I have been running with (155 DJ and needle in 2nd clip position) and when for a ride. Better!:lol: Still not the same as before but at least I can run without the choke on. The AFR readings at 50-60 MPH cruise were just like the stock set up, around 14.7. So I move the clip to the 3rd slot and it got about half a point richer. (around 14 at 55 MPH cruise, 13 WFO and 12.8 at idle) Runs good now but I may go the the 4th slot to make a tad richer. Then try the DJ 160 again but I am still getting AFR readings around 13 WFO with the 155, so I am in no hurry.

It seems I am now at a state where I am needing jetting closer to what many others are running. So is it still a little broken or was it "broken" before? I don't know, but I don't know any way to "fix" it from here so I am just going to continue adjusting to the current state. I just hope it stays in one state!

Thanks again for the help!

John

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Have you messed with the fuel screw? Also is this a dirt model or S model carb. i.e. pumper or vacuum?

Also is it popping on decel?

I went rounds with my old 350 some years back:banghead:

I had the S model carb, and I ended up replacing both the jets(14, 23)(they appeared clean) and went with an extended fuel screw(25), and replaced the diaphragm(6). Worked great until a blew the bike last fall.

Added: you might also take a look at numbers 31 32, these are your air jets. I think 32 is the main if I remember correctly? make sure they're not clogged. should be a 1.3 and .6

1910_9B.gif

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Emulsifying holes??:smirk: Man, a tid-bit of info here and there..YIKES! I don't think the BST bible covers them. O-well, great opportunity for me (and other's as well) to LEARN more stuff.:smirk: I've got a spare BST40,

now it's time to take it apart and study it. I'm a stickin' with the stock carb for now.

Keep hammerin' away at it jaeger, it's got to be something simple.

rc

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Emulsifying holes??:smirk: Man, a tid-bit of info here and there..YIKES! I don't think the BST bible covers them.

You can see them in this pic.

They're the tiny holes in the needle jet.

I run a thin piece of wire through them and then spray them with Berrymans B-12 carb cleaner (the only brand I'll use) to be certain they're clean :smirk:

2537293189_3024a62fab.jpg

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Snipage.....

put a dab of silicon grease on the slide. I put it all back together with the jetting I have been running with (155 DJ and needle in 2nd clip position) and when for a ride. Better!:smirk: Still not the same as before but at least I can run without the choke on. The AFR readings at 50-60 MPH cruise were just like the stock set up, around 14.7. So I move the clip to the 3rd slot and it got about half a point richer. (around 14 at 55 MPH cruise, 13 WFO and 12.8 at idle) Runs good now but I may go the the 4th slot to make a tad richer. Then try the DJ 160 again but I am still getting AFR readings around 13 WFO with the 155, so I am in no hurry.

Unfortunately without an accelerator pump it's tough to set AFR's at optimum and still expect to get good response to faster throttle movement. At WFO 13 is too lean for a safety factor IMO.... 12.5-12.8 is what I shoot for. 13-13.2 is good for mid-range torque (roll-on) but at full load WFO I steer clear of the 13's.

It seems I am now at a state where I am needing jetting closer to what many others are running. So is it still a little broken or was it "broken" before? I don't know, but I don't know any way to "fix" it from here so I am just going to continue adjusting to the current state. I just hope it stays in one state!

Thanks again for the help!

John

Hard to say... it was certainly "out of the norm" running as it was.

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Unfortunately without an accelerator pump it's tough to set AFR's at optimum and still expect to get good response to faster throttle movement. At WFO 13 is too lean for a safety factor IMO.... 12.5-12.8 is what I shoot for. 13-13.2 is good for mid-range torque (roll-on) but at full load WFO I steer clear of the 13's

Sounds exactly right to me. I put in the 160 main and went to the 4th clip position on the needle. WFO is now in the range you list.:smirk: But above idle to 1/4 throttle was very rich in the mid 12's. Then it leaned out as I increased cruise speed to around 14 at 65. At around 70 and above got richer again as it came on to the main jet. Snapping the throttle open almost anytime pushes it into the 12's.

So I dropped the clip down one slot to the third position. This seems to be the best compromise I can get with the current set up. Nice mid 13 at slow cruse and 14 to 14.5 at 60-65. A tad leaner than I would like but no worse than the stock set up. MPG seems to be great. I filled up this morning after a 50 mile ride across town and back and got 55.7 MPG. Best ever. I will need more samples to know for sure but this is very encouraging. And the bike feels great. I think this is as good as I will get it with the BST. My goal here was not to get the absolute max power, my racing years have long passed, but to get the best compromise between increased performance and MPG.

Thanks again for taking the time to help me sort this out.:smirk:

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Glad it's sorted out and running acceptable. Carbs are always a compromise.. they can not vary AFR based on engine load and speed.... not that they don't do a pretty amazing job of what they do... but it is not possible to perfect for every situation. With a wide band 02 sensor you will always see things you don't like at certain parts of the throttle. The best set-up is the best compromise for the type of riding you do. :smirk:

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