Pods, Pipes, Panic! (Help! Your Bike has Pods)

[Ira]

Maybe this is more to the point: has anyone had actual, reproducible success getting a good idle with k&n pods and cv carbs?

An O2 sensor indicates my air/fuel mix is optimal at idle and throughout the first half of the throttle, but revs still fluctuate at idle and the bike stumbles if I whack the throttle open.

[tkent02]

Yes, I have ridden quite a few that idles perfectly.

[Ira]

Yes, I have ridden quite a few that idles perfectly.

At what rpm did these bikes idle, and how was throttle response?

[JTGS850GL]

Maybe this is more to the point: has anyone had actual, reproducible success getting a good idle with k&n pods and cv carbs?

An O2 sensor indicates my air/fuel mix is optimal at idle and throughout the first half of the throttle, but revs still fluctuate at idle and the bike stumbles if I whack the throttle open.

What exactly is your O2 sensor telling you is optimal? Another words, what A/F ratio is considered "optimal". Are you using a WB O2 sensor?

[Ira]

What exactly is your O2 sensor telling you is optimal? Another words, what A/F ratio is considered "optimal". Are you using a WB O2 sensor?

I don't know which O2 sensor was used. I brought the bike to a mechanic who tunes vintage race bikes, and he operated the dyno. By his assessment, the idle mix was in an acceptable range. "optimal" could be too strong of a word, but I recall the ratio was in the neighborhood of 14.7:1. I don't have the chart in front of me.

[GScaferacer]

I have a Kerker and K&N pods on my 550. VM 22 carburetors, which are just about identical to your VM26es except for the bore. Stock main jet is 80, I have 112.5 in there now, it runs well wide open. Smaller mains didn't quite do it. I'm also at 6,000 ft elevation, if I were in Chicago the mains would need to be bigger still.

You probably won't need that much of an increase, but one main jet size larger isn't even close to being enough.

So should I go with 140 main? What about slows?

[tkent02]

At what rpm did these bikes idle, and how was throttle response?

1,000 or so, perfect throttle response.

[tkent02]

So should I go with 140 main? What about slows?

140 would be way too big.

[JTGS850GL]

I don't know which O2 sensor was used. I brought the bike to a mechanic who tunes vintage race bikes, and he operated the dyno. By his assessment, the idle mix was in an acceptable range. "optimal" could be too strong of a word, but I recall the ratio was in the neighborhood of 14.7:1. I don't have the chart in front of me.

14.7:1 is Stoichiometric and would be lean for anything other then idle and very light load settings. Even then it would depend on many factors in the engines design. Under any load you should be seeing numbers more in the 12's. I've seen tunes well into the 10's under higher loads and higher RPM's.

The reason I asked about what type of sensor he used is, if he didn't use a Wide Band O2 sensor then any reading he gets other then 14.7 would be inaccurate. A narrow band O2 sensor's transfer curves are like a switch. Almost no output until it reaches 14.7 and then full on right after that. A very narrow range around 14.7 with very unpredictable readings in the unstable region between the floor and plateau.


Raw wide band output would look more like this:


Were 1.0 Lambda = 14.7 A/F or Stoichiometric.

As you can see there is much more linearity on a WB sensor and more predictable results of measurement. With linear corrected output you can achieve results like this:

[mmattockx]

Hate to beat a dead horse, but after reading this thread, I'm still left with a question since it seems we have mixed feelings on this. I have. 78 gs750. Kerker 4-1 and K&N pods. I want the most power I can from that by jetting the carbs. Now some have said the bike will run better with stock jetting and the exhaust. Some said only go up a size. Most of the threads are older as well. Just curious as to if all this info is still current and valid. Thank you.

So should I go with 140 main? What about slows?

This is your problem. You are looking for an exact answer from someone else on a different bike at a different elevation. The only way to get your jetting correct is to jet your bike yourself and work according to what it wants. It is extremely unlikely that you will find a perfect match turn key solution from people in a different zip code than you are. FWIW, the age of these threads has no bearing on the validity of the info. Nothing has changed with your bike since 1978 when it was manufactured.

Maybe this is more to the point: has anyone had actual, reproducible success getting a good idle with k&n pods and cv carbs?

I don't know if you are referring specifically to your 550 or any GS in general. My 82 1100E has pod filters, stock carbs and a Kerker 4-1 exhaust. It idles fine and has excellent throttle response off idle.

At what rpm did these bikes idle, and how was throttle response?

My 1100 idles at ~1100rpm and response is excellent.


Mark

[Ira]

JTGS850GL - Based on the two charts you posted, the output resembled the wide-band sensor.

Before I elaborate, let me get my hands on the actual numbers. Thanks for the thoughtful response.

[Rob S.]

At what rpm did these bikes idle, and how was throttle response?

My 1100EZ idles beautifully at 1300 rpm, response is great, pulls to redline with nary a cough or sputter. V&H exhaust, APE (K&N style) pods, DJ stage three kit. Next time I see my tuner, I'll ask what specifically he needed in addition to the DJ stage three kit; I know there were some other parts.

Having access to a dynamometer is a big help.

[GScaferacer]

So should I start with a dynajet stage 3 kit and go from there?

[duaneage]

I would start with plug readings at speed and see what you get. Before you spend money on a kit determine a few things first.

Are the carbs synced? Valves adjusted? Air filters properly oiled? Any intake leaks on the boots?

I would start with new plugs since old ones can be hard to read. If you foul them up they can be cleaned (I use Hoppes 9) but new ones are best and they are not too expensive. Later you can use them when it's time to replace.

[Crankthat]

While I am here and have this copied, another user posted this chart a while back.
I think this is a good place for it.

Keihin, Dynojet, Mikuni Jet Size Cross Reference

All Hole Diameters Are in Inches

Hole Dia”---Keihin # -- DynoJet # -- Mikuni #
0.0350---- 92.5--------- 92----------- 86.3
0.0360---- 95----------- 94----------- 88.1
0.0370---- 97.5--------- 96----------- 90
0.0380---- 100---------- 98----------- 91.9
0.0390---- 102.5------- 100---------- 93.8
0.0400---- 105--------- 102---------- 95.6
0.0410---- 107.5------- 104---------- 97.5
0.0420---- 110--------- 106---------- 99.4
0.0430---- 112.5------- 108--------- 101.3
0.0440---- 115--------- 110--------- 103.1
0.0450---- 117.5------- 112--------- 105
0.0460---- 120--------- 114--------- 106.9
0.0470---- 122.5------- 116--------- 108.8
0.0480---- 125--------- 118--------- 110.6
0.0490---- 127.5------- 120--------- 112.5
0.0500---- 130--------- 122--------- 114.4
0.0510---- 132.5------- 124--------- 116.3
0.0520---- 135--------- 126--------- 118.1
0.0530---- 137.5------- 128--------- 120
0.0540---- 140--------- 130--------- 121.9
0.0550---- 142.5------- 132--------- 123.8
0.0560---- 145--------- 134--------- 125.6
0.0570---- 147.5------- 136--------- 127.5
0.0580---- 150--------- 138--------- 129.4
0.0590---- 152.5------- 140--------- 131.3
0.0600---- 155--------- 142--------- 133.1
0.0610---- 157.5------- 144--------- 135
0.0620---- 160--------- 146--------- 136.9
0.0630---- 162.5------- 148--------- 138.8
0.0640---- 165--------- 150--------- 140.6
0.0650---- 167.5------- 152--------- 142.5
0.0660---- 170--------- 154--------- 144.4
0.0670---- 172.5------- 156--------- 146.3
0.0680---- 175--------- 158--------- 148.1
0.0690---- 177.5------- 160--------- 150
0.0700---- 180--------- 162--------- 151.9
0.0710---- 182.5------- 164--------- 153.8
0.0720---- 185--------- 166--------- 155.6
0.0730---- 187.5------- 168--------- 1575
0.0740---- 190--------- 170--------- 159.4
0.0750---- 192.5------- 172--------- 161.3
0.0760---- 195--------- 174--------- 163.1
0.0770---- 197.5------- 176--------- 165
0.0780---- 200--------- 178--------- 166.9
0.0790---- 202.5------- 180--------- 168.8
0.0800---- 205--------- 182--------- 170.6
0.0810---- 207.5------- 184--------- 172.5
0.0820---- 210--------- 186--------- 174.4
0.0830---- 212.5------- 188--------- 176.3
0.0840---- 215--------- 190--------- 178.1
0.0850---- 217.5------- 192--------- 180