final carb tuning

cpt137 · Full Member Joined: Jan 10, 2009 Posts: 97

After working all summer getting the beast running right there is one little tweek to do. It starts fist kick or button push with the choke. Idles fine with the choke for about 15 seconds then gets running to rich. Take the choke off and idle fine. But if I try and ride it before it is completely warmed up, lets say 5 minutes, it will back fire and pop out the exhaust and carbs as I try to accelerate. Not a whole lot, but it does. Once it gets warmed up it runs perfect. Timing is on and plugs look perfect. Just that little time just before it's fully warmed up. I know I should do a full warm up but I'm not sitting around for 5 minutes. Any thoughts? Pods and 2/1 and stock jetting. Seems to work good other wise.

acbanks · Posted: October 24, 2009, 9:02 pm Post subject: Re: final carb tuning

I'm no expert by any means, but it sounds like it's a bit lean. Most guys change the main jets one or two sizes larger when running the pods, which also richens the midrange to some extent. If you don't want to buy new jets you can raise the needles(lower the clips) a notch instead(assuming you have a 1970-79) That should richen things up right above idle. You'd still have to watch out for detonation at wide open throttle if you keep the stock main jets.

I've got a '78, running 140 mains, 35 pilots with the needles in the middle. Pods and straight pipes.

xsjohn · Posted: October 24, 2009, 9:08 pm Post subject: Re: final carb tuning

CR to much for the long run.............tune all you want........it's only a 650.....ah what would I know.......... more than you think..........and jayel would say a pouch while he grind his to death with 17/32.........have to be easy on the exptress now ....could get a ticket........... rid of the vibes makes a big difference..........ah what the fucrk..........

gordo · Posted: October 24, 2009, 9:14 pm Post subject: Re: final carb tuning

CPT137, give xs john a P.M. His needle kit is what you'll need to solve all that, plus your engine will run even better. As ac stated, sound's like your a little lean on the transition from pilot jet to slide movement. the taper John has engineered into his needle's fixes that problem. They come with a complete set of instruction's for all set-up's. And, he e-mail's you constantly for guidence until your happy. Their a bit pricey, $40, but well worth it. I have the same set-up as you do, & My girl run's really well. When you talk with him, he will tell you all you need to get. The right main size, pilot size, ect.

xsjohn · Posted: October 24, 2009, 9:27 pm Post subject: Re: final carb tuning

Been running a 47 pilots lately and love it.....(screw that epa log needle for sure ) .......hard to find a .0185 wire to do that for good pilots but I have one ....a 47.5 should be good also....if you are careful with the turns on the mix screws.... .....god the wings and the carbs and the 8-1...........a freeway flyer......when is the last time anyone enjoyed their car at 250 degrees plus....... slap hand on e forhead .....ah WTF......... vibes about none to boot.....have to gear it right though........230 degrees is all I saw this summer and it was higher than I liked....cars 195 ......but better that 280 from square one 10 years ago........ :lol:...............74,677 miles............

You know if you want to turn this thing to redline and have it run long.....it won't last.....turn mine to to 3500-4000...8-1 and shift and settle back for a good ride...maybe 5k when I am a liberal ....18/28........set the timing retarded so it will run right at lower rpms....duh.....3k at 55....and 3700 at 70..and good temps.......good luck with all that....may take some extra study......sorry I am so stupid............

Final carb runing has lot to do with ignition timing,,,,,,,,advanced from the factory for sure.......for any decent gears...........good luck with all the 8.7-1 cr anyway......

Have to laugh at both sites for .....well I'll leave that for another post....stock TCI has never missed a lick either.... Laughing

xsjohn

cpt137 · Full Member Joined: Jan 10, 2009 Posts: 97

It's a 78. I tried the next larger jets and it was to rich. I had Johns needles on my b34's on my 1983 and worked great, but these are b38 and I don't think there is a needle kit for them. I did lower the needle 1 notch but not much help. It doesn't stumble at all once it gets pat 2500 rpm, that's why I don't think I'll mess with the mains. Fuel levels have been set correctly. I am trying to figure out a way that I can have an "adjustable " choke like the later models instead of the on/off currently.

acbanks · Posted: October 25, 2009, 11:21 am Post subject: Re: final carb tuning

Yeah, that enricher choke sucks. When it works...great. When it doesn't you just end up flooding it.

cpt137 · Full Member Joined: Jan 10, 2009 Posts: 97

I think I have a solution for my choke. I took off the bent metal thing below the lever that positions it full open or closed, and took out the bushing from the back of the choke lever. I put a couple of small lock washers behind the lever to provide some tension. I think I may have to locktite the screw in to keep it from turning, but allows me to vary the amount of choke I have. Doing just what I want now.

jayel · Posted: October 26, 2009, 6:08 pm Post subject: Re: final carb tuning

cpt137 wrote:

but these are b38 and I don't think there is a needle kit for them. I did lower the needle 1 notch but not much help..

john does have needles for the BS38's and you should have raised the needles (lowered the clips)

cpt137 · Full Member Joined: Jan 10, 2009 Posts: 97

I meant to say lower the needle 1 notch. I'll check on the xs needles.

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