CV carb Air/Mixture adjustment question - Harley Davidson Forums: Harley Davidson Motorcycle Forum
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post #1 of 10 (permalink) Old 07-18-2019, 10:03 AM Thread Starter
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CV carb Air/Mixture adjustment question

Hello all,
I decided to adjust the air/gas screw on my 98 Sportster 1200. The screw turned 4 1/4 turns clockwise before seating. I read online that if it turns more than 3 out, the pilot jet is too small. (Im new with these CV carbs please forgive ignorance....lol) So if the pilot jet is too small, is this an adjustment that has to be made or does that mean I have to get a larger number pilot jet? I took the Carb apart and cleaned it when I first purchased the bike and I thought the jets were stock, so how could stock pilot jet be too small?

The air gas screw turned 4 1/4 turns clockwise before stopping, so I turned it 4 1/2 turns back. The bike runs pretty good, idols fine once warmed up and throttle response seems to be good, choke works fine. It does not back fire too much, maybe very slightly when coming to stop after riding for a while (but its minor). The only indication of running rich is the strong smell of gas when running.

Should I not worry about this or do I need to do something with pilot jet?
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post #2 of 10 (permalink) Old 07-18-2019, 11:55 AM
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CV carb Air/Mixture adjustment question

Did you look to see what size jet was in the carb? What kind of engine modifications have been done to the bike? Its should run fine around 2-2.5 turns out....


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post #3 of 10 (permalink) Old 07-18-2019, 12:48 PM Thread Starter
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I am going to have to go back in the carb to get the number, but I thought everything was stock. There have been no modifications to the bike, nothing noticeable. The air gas screw was exposed and the cover had already been drilled out so someone probably adjusted it in the past. After watching vids on how to adjust it, I was surprised that mine turned so much.
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post #4 of 10 (permalink) Old 07-18-2019, 02:42 PM Thread Starter
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I checked the jets, I have a 42 Pilot and a 170 Main Jet.
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post #5 of 10 (permalink) Old 07-18-2019, 02:51 PM
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CV carb Air/Mixture adjustment question

If the bike is completely stock the air screw plug should still be there. Since its been drilled out, you have a pretty good idea someone has done something to the carb. I would take the carb off the bike give it a very thorough cleaning, see what jets I had in it, get a good rebuild kit and any jets that I might need, then put it all back together and start with the air screw set at 2.5 turns out. Something is not right if its turned that far out on a completely stock bike!!

Stock pilot jet size is 42.

Just seen your post about jet size. Those are the stock jets. You did say that it runs fine, so you could dig further to find the problem or just ride the hell out of it until it gives you some more problems....

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post #6 of 10 (permalink) Old 07-18-2019, 03:15 PM Thread Starter
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Thanks so much for reply. I rebuilt the carb when I first got the bike with rebuild kit. I also put in a new vacuum piston at top with diaphragm. About an hour ago I went ahead and turned the air mixture screw clockwise until it stopped. Basically I reset it and going to start from there. I opened it 2 1/2 and started it. Bike idled descent once warmed up; however, it "pops" now when I rev the engine when I release the throttle, so I may have it to lean. I may open it a 1/4 more and see if that improves it. On a positive note, I did not get the strong smell of gasoline like I did before. Also, dont know if this makes a difference, but the previous owner put slipons and removed baffles.

Thanks again!!
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post #7 of 10 (permalink) Old 07-18-2019, 03:45 PM
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An extra 1/4 turn should be ok. The free flowing pipes will make a small difference and if you have a high flow air cleaner, you will probably need to go up one size on the pilot jet.


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post #8 of 10 (permalink) Old 07-18-2019, 04:16 PM Thread Starter
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Just to note, when I purchased the bike the bike was in great condition. Its a 98 anniversary with only 27,000 miles on it; however, the bike had a bad gas leak which appeared that it was not addressed for a long time. I suspected that it was coming from the carb at first (accelerator pump or stuck float). After rebuilding and cleaning the carb, I discovered the gas leak was from a punctured gas line. It was a perfect sized pin hole on the back of line just up from the carb. I replaced the line and no leaks now. I am curious if the screw was turned out so far due to the fact that the carb was not getting enough fuel when it was leaking. I have no idea why they didn't see or fix the leak. (I purchased the bike from the dealership, so I never saw owner. I feel stupid because I failed to see the leak at dealership...lol). But since I have fixed the bike and leak, the bike always smelled like it was running rich. So maybe thats the case. All in all the bike has run good.

I have regular stock air cleaner on it, which I put a new one in. I also put in new plugs and full oil service.
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post #9 of 10 (permalink) Old 07-18-2019, 07:34 PM
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sounds like air screw was just out too far. bring her out 2 1/2 turns if it idles good leave it. the backfiring you describe is only decel pop if not excessive it's normal. if its a little rich cool, most run too lean anyway. check plugs, if not wet or sooty, ride on. have fun and be happy!
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post #10 of 10 (permalink) Old 07-18-2019, 09:07 PM Thread Starter
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Thank yall so much for the input and help. I have it out a little little over 2 1/2. I just took her for a ride and it sounds and rides great. idles really nice. I am not touching a thing
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