rich/lean carbs on off on off ahghhh

[shack426]

Hi, I have replaced the spark plugs and did some rejetting. I am running the pods and a vance hines 4/1 pipe. The bike starts now really great. it runs up to about 4k really well and sounds awsome. At about 4k the bike falls on its face!!! no power at or after 4k, it spits supters and some backfiring. after driving around for a mile or two I come back and pulled the plugs, one is close to what I think it should look like darkish dry not real sooty, the other three look brand new, clean with just a signe of heat at the electrode. ( possible very lean??) they are all fireing, which way do I go now, hmmmmm. thanks for all the great imput, everyone is really a big help.

[shack426]

any help please. with 122.5 mains and 60 on the pilot it was way rich or seemed to be. with 112.5 main and 42.5 pilot it would not start. With 55 pilot and 112.5 main it would start and run but fall flat at about 3k. with 55 pilot and 120 main it ran better but still stumbled at about 4k. plugs have gone from being black sooty with one wet(these are the old plugs) to one looking good and 3 very clean ( these are new plugs) which way do I go now.????????????? would going back to the 122.5 but with the 55 pilot make it run that much better??? or just back to a rich problem??? would between a 120 and 122.5 be the answer on the main????

[chef1366]

What kind of bike do you have?

[BassCliff]

Patience, young motorcyclist

Hi Mr. shack426,

I see you waited almost 2 hours for a response. Sorry to keep you so long. I'm not sure what we're talking about but how about a shot in the dark? Here's a pretty good guide for jetting CV carbs. If you've got VM carbs then reverse the order.

Thank you for your indulgence,

BassCliff

[don_gibb6512]

Check out this recent thread:

http://www.thegsresources.com/_forum/showthread.php?t=124965

[shack426]

Thanks for the responses all. the bike is a 81 gs 750L. I have gone from to rich to what looks like to lean now????? before the plugs were black sooty and one wet, the bike was hard to start and could only be started with choke all way out. at that time the jets were (122.5 main and 60 on pilots)....... I went to 120 main and 55 on pilots and the bike starts good with good throttle response on low end up to 3.5k-4k. the plugs went to 1 looking good darkish but not sooty and the other 3 were very clean looking (brand new looking) with just a signe of heating at the electrode. All plugs are fireing and all cyl. heating up. the bike now bogs stumbles starting at 4k and can't get past that area of the rpm. I am using pods and a VH 4/1. I have been told once I get the bike starting then I have the correct pilot jet, now I need to keep bumping up the main to get the bike to run better past the 4k mark????? float hight is at .095 inches. do you think going back to the 122.5 is the way to go??? ( it was rich with the 122.5 but had the 60 pilots) As the bike builds rpm and acts great up to the 4k mark then starts to studer stumble back fire a little is this a signe of rich or lean??? and do I need to jack with the needle and clip now???? thanks to all, sorry for length.

[Mark M]

I have been told once I get the bike starting then I have the correct pilot jet, now I need to keep bumping up the main to get the bike to run better past the 4k mark????? float hight is at .095 inches. do you think going back to the 122.5 is the way to go???

All right, it sounds like you are changing more than one thing at a time. That will never work.

1) Get your pilot circuit sorted. Don't worry about the needle and mains yet.

2) sort your needle. Make sure you are running a big enough main jet to not be lean, but other than that, it is not critical yet.

3) Sort your main jets.

Put tape on your throttle grip and throttle housing. Mark 0 and full throttle, then divide it up into 1/8 increments. Use this as a guide to which circuit you are using. RPM is no guide as to which circuit, it is throttle position on CV carbs. Pilot is from idle to around 1/4-3/8 throttle, needle is from 1/4-3/8 to about 5/8 and main is 5/8 to WOT. There is some overlap, but these will get you in the ballpark.

Ride at steady speed and steady throttle position, then pull your choke on a bit and see what it does. If it gains rpm, you are lean. If it bogs badly, you are rich. If it bogs slightly, you are pretty close. Repeat for all throttle ranges and you will be pretty good. After that, it is fine tuning to suit you and how you ride.

If you are unsure of which way to go for intial changes, try rich first as it is safer than lean for your engine. To sort carbs you must be methodical and systematic. Only change one thing at a time and see what it does. Keep notes to know where you have been and how it worked. Always sort your pilot first, then the needle, then main jets on CV's, as the lower circuits affect the higher ones, but not the other way around.

Good Luck,
Mark

[srsupertrap]

Making several changes at once is usually problematic & difficult to diagnose. . . If your 750L was running correctly ??? before the jettings, pipe & filter mods you may want to consider the following course of action:

1) Look at the obvious & easy stuff first: Examine the Petcock, is it clogged or restricted?

2) I am inclined to believe the pipe wouldn't cause this grief but the pods could. If the Pods are not K&N's and you oiled them this may explain a lot. But you stated the 3 of 4 spark plugs are clean which contradicts the falling on it's face symptom.

3) Keep the pipe & filters On & Restore the original jetting for diagnostic purposes only. If the fall on it's face symptom disappears focus on the jetting changes you made. The addition of the VH pipe to stock motor will normally only requires the main jet to be bumped by a couple of sizes.

[shack426]

hey thanks to all, I will try the advice tommorow as I am on duty now. (firefighter) You guys really know your way around these bikes, keep up the good advice giving.

[shack426]

also as for the pods being K&N I don't know they came with the bike. I don't see any markings saying K&N. so if there not should I run them dry with no oil in them?? I got the bike with the pods and VH on it. the bike would not run, it had 112.5 mains and 42.5 pilots, the only way to make it start and attempt to run was to pull the choke out all the way and crank, crank until it fired at which time it would barley run. The dealership here suggested putting 122.5 mains and pilot of 60 at which time it started right up and idled and could actually drive around the block, but it was running way rich, (3 plugs black and sooty, one wet with its cyl. not firing and not getting hot.) back to dealership, they said now to put a 120 main and 55 pilot, the bike started great, great sounding throttle response sitting it garage. took bike out and it ran great until I got up to about 4k, where it stumbled and falls, spit, sputter, backfire. all cyl. are hot and firing, pulled the plugs and thats where 3 are clean and 1 looks darker (not fouled or sooty, just like its been running.) so since it starts now with the 55 pilot, should I go back to the 112.5 main or bump back up to the 122.5 main??? I will try Mark M and srsupertraps suggestions in the am. Thanks to all.

[Tony]

Hey shack, looks like we have a similar problem (post: a girl wants a ride this weekend). I will be just beginning my jetting experiments and have greatly benefited from your post.

As for the pods, K&N will be marked on the chrome end caps very clearly. These are the only filters I have come across that need oiling, except for some cheaper mock offs from a website: http://www.mikesxs.net/. These filters are the same as the K&Ns but cost a total of about $65 w/ shipping as opposed to $180+ w/out. DO NOT OIL THE PODS IF THEY DO NOT LOOK LIKE THESE FILTERS.

Good luck

[BassCliff]

Hi Mr. shack426,

Before you go too much farther with the carbs, I just wanted to remind you that the valves should be properly adjusted in order for the carb configurations to remain stable. How many miles on the bike? Do you know much about the history? When was the late time the valves were adjusted?


Thank you for your indulgence,

BassCliff

[Tony]

Shack, if the Factory Pro website (graciously offered up by the kind BassCliff) is at all confusing, you should give them a call. I just got off the phone with them and spoke with guy that was super helpful. He offered up some tips that weren't on the site. With thanks to all the knowledgeable GSers and Factory Pro, I feel confident diving into my first carb experiment.

[greg78gs750]

Hi Mr. shack426,

Before you go too much farther with the carbs, I just wanted to remind you that the valved should be properly adjusted in order for the carb configurations to remain stable. How many miles on the bike? Do you know much about the history? When was the late time the valves were adjusted?


Thank you for your indulgence,

BassCliff

i was just gonna say this. how are your valves? cause, if they arent in spec, the cold pipe could not be carb related at all. i also agree with the others, you gotta tackle one thing at a time. the mains will have nothing to do with starting, the pilots have little influence on wot, etc. sounds like you arent afraid to dive right in, just be systematic about it.

[shack426]

hi all, as for the valves no I have not checked them. as for the milage it has 18k per the odometer and the word of the previous owner. I do think something has been done to the top end due to seeing red/orange gasket sealer between the head and cyl. as for the pods mine are pyramid shape with a fiberish cloth with wire mesh filter but no indication of them being k/n. Do I oil them?? could oiling them cause the stumbling??? as for the cold pipe, its not cold any longer, it now runs hot like the rest I belive due to my installing new plugs and bringing the main and starter jets down to 120/55 from the 122.5/60 Its cyl. plug is brownish clean where the others are new looking clean. does this make a difference?? and yes lets all stay in touch on these issues hopefully we can get them worked out. the bike just sounds so good in the garage while reveing the throttle, its just when I go out when I get up to 4k it stumbles spits etc..... could this be in the needles???? or should I just stay with the main jets as the issue??? thanks.