Topic: Air/Fuel Ratio Sleuthing

[mlinder]

Let us assume, for a moment, that a bike has good timing, good plugs, good valve clearances, and reasonably acceptable electrical.
Let us also assume that, when ordering carbs form cyclex, we told them as much as we knew about the bike. 750, 4 into 1, about 50 to 100 ft above sea level.
And of course, I dont actually know the history of the bike....
It's obvious that Ken has put a lot of work and time into this carb system, and they work for him (and numerous other people), so I have to assume that the issue is with me.
So let's assume the issue is on my end...
What engine conditions would make an otherwise reasonably well set up engine run lean?
I have a few suspicions, the first being that perhaps this bike was big bored or cammed way back in the 70's from the two motorcycle hot rod guys who were brothers who owned it, but as it's appearance was for the most part, unmolested, outside of a (unidentified) 4 into 1 and lowering blocks, I just dunno. Paulages mentioned that a compression test may answer a question or two if the internals are not stock, but I don't know. (Many thanks to Paulages by the way, and Billy too, down at their workshop.)
Another possibility is Spark. A weak spark might cause it to need more fuel just to run, but not 100% sure.
I mean, I can't even really ride it unless the air screws are only 2/3 to 3/4 turns out. That's a pretty rich mixture. Also, tried the needles at second highest setting, and lost a lot of power above 4.5k, so going back to highest (richest) setting later today.

So what do you guys think? What are the possibilities of why my engine runs lean? I'm going to pull apart the old carbs and see if they are at different settings than stock tonight, which may give me some clues.

[mlinder]

Hullo engine gurus... I can see you are online now!

[Jerry Rxman Griffin aka MuthaF'er]

How do your plugs look at WFO? Needles affect mid up to high range. Needles at highest (richest)? If you put the clips in the top notch that effectively drops the needle lower into the needle jet closing off the opening even more. Leaner. Believe I'd put it in the middle position & see what happens. It is possible you could have a kitted engine. Not all 4 into 1's are made equal either. If your bike was kitted with a 12.5 to 1 kit then I would suspect you could tell a definite difference in higher compression if all the internals are in good shape. A standard kitting of 10.25 to 1 would not show as large a difference. May be hard to ascertain. The best way to tell is to take the head off, measure the pistons, and check out the cam.

[MRieck]

Having the air screws turned out that amount is fine. Big vacuum leaks can make it lean but than you'd be stalling coming to stop, erratic idle etc. A big bore kit doesn't change the jetting that much. I run CR-31's with a big cam, porting etc and the main jet is 123 I believe.  I said before you can try a richer needle, needle jet and main jet combination. It wants more fuel....give it to it.

[mlinder]

How do your plugs look at WFO? Needles affect mid up to high range. Needles at highest (richest)? If you put the clips in the top notch that effectively drops the needle lower into the needle jet closing off the opening even more. Leaner. Believe I'd put it in the middle position & see what happens. It is possible you could have a kitted engine. Not all 4 into 1's are made equal either. If your bike was kitted with a 12.5 to 1 kit then I would suspect you could tell a definite difference in higher compression if all the internals are in good shape. A standard kitting of 10.25 to 1 would not show as large a difference. May be hard to ascertain. The best way to tell is to take the head off, measure the pistons, and check out the cam.

When I said highest, I meant highest needle position (lowest clip position), meaning richest running. I have moved them one up, (slightly leaner) and doesn't run as well. I will try a plug chop later today, weather permitting, though my kill switch is no longer on the handle bars, so may be a bit tricky.
I wish I knew what this 4 into 1 was. Haven't seen another one, though I've seen ones that look similar, though don't they all?
If it is in fact kitted, am I right in assuming that a carb setup for a non kitted bike would run leaner, as it's pulling in more, without the needles and such being able to supply enough fuel?

[mlinder]

Having the air screws turned out that amount is fine. Big vacuum leaks can make it lean but than you'd be stalling coming to stop, erratic idle etc. A big bore kit doesn't change the jetting that much. I run CR-31's with a big cam, porting etc and the main jet is 123 I believe.  I said before you can try a richer needle, needle jet and main jet combination. It wants more fuel....give it to it.

No big vacuum leaks here, idles perfectly. I will look at the plugs today after some running and see what they say. I do believe Ken sent me some different needles.

[Jerry Rxman Griffin aka MuthaF'er]

Sometimes with kits it is not necessary to change jetting. However, one could assume bigger displacement would suck in more air thus needing more gas to reach the correct air/fuel ratio. One question you could ask would the higher air volume/higher rpm increase the air flow speed thus sucking in more fuel without larger jets. Perhaps a bike was running a tad bit rich to start with and the larger cylinder volumes made the mixture correct. This would not be the case with your bike since you are not comparing the same carbs SO you have to start from scratch.
I'm curious as to what bike you have? Was your bike running perfect with the stock carbs? Or how was it running with the stock carbs? What jetting did you have your stock carbs set at? This might let us back up a bit and kinda start over without too many assumptions.

[mlinder]

Wasn't running at all with stock carbs. Well, had it running sorta once with stock carbs. I'm going to take them apart and take a look at them tonight, see how they were jetted, which should give me some clues.
It's a '69 die cast.

[mrbreeze]

I assume you had the old one cable to each carb set-up. What do you have now? If you have one cable branching into two cables,are both carbs opening together? As far as jet size and needle position,you just may have to start from scratch as rx suggests. I know what you mean about doing plug chops without a kill switch but even without doing the chops,you can tell if the bike runs sh!tty in between throttle settings. I'm not familiar with the twin Mikunis allthough I like them and do believe they will work just fine when dialed in. I would imagine they will be easier to work with than stock carbs....especially if you can change needle setting without removing carbs. Good luck with it and hope to see you post with the good ole "I finally nailed it!!!" statement real soon.

[mlinder]

I assume you had the old one cable to each carb set-up. What do you have now? If you have one cable branching into two cables,are both carbs opening together? As far as jet size and needle position,you just may have to start from scratch as rx suggests. I know what you mean about doing plug chops without a kill switch but even without doing the chops,you can tell if the bike runs sh!tty in between throttle settings. I'm not familiar with the twin Mikunis allthough I like them and do believe they will work just fine when dialed in. I would imagine they will be easier to work with than stock carbs....especially if you can change needle setting without removing carbs. Good luck with it and hope to see you post with the good ole "I finally nailed it!!!" statement real soon.

Yes, the old ones are one cable per carb. The new ones have a splitter in the cable to two cables, each one opening a slide on each carb. Paulages helped me bench synch them so they open simultaneously and at the same rate. The carbs ARE easy tow rok with. I can change needle position on both carbs in about 7 minutes without removing them.

[mrbreeze]

Bench synch is good enough to get er running but have you done a running synch yet? Thats where it really comes together although you will probably still have to fine tune your jetting and needle position. You'll get....I have faith in ya man!!!

[mlinder]

Bench synch is good enough to get er running but have you done a running synch yet? Thats where it really comes together although you will probably still have to fine tune your jetting and needle position. You'll get....I have faith in ya man!!!

No place to hook a manometer, my man.

[mrbreeze]

So what does Ken have to say about that? Maybe theres a way to tap into those manifolds but I suppose that would only seperate it to 2 cylinders? I would have to think about that one but I'm sure its do-able. They do it on multi-carbed cars so why not on our bikes? I would call Ken and see what he suggests.

[mlinder]

So what does Ken have to say about that? Maybe theres a way to tap into those manifolds but I suppose that would only seperate it to 2 cylinders? I would have to think about that one but I'm sure its do-able. They do it on multi-carbed cars so why not on our bikes? I would call Ken and see what he suggests.

I've emailed them a couple times in the last few months, haven't had a response. I do need to call them, I'm sure.

[paulages]

i'm skeptical of how he's gonna sync the carbs in the manner we are used to on the fours. if he taps a port into the manifold for a manometer, where would he do so? before the split to each cylinder? one carb feeding two cylinders that are pulling differently seems like it could yield an inconsistent reading, yet tapping vacuum ports into the individual manifolds seems useless, as one carb can't be tuned separately for each cylinder it feeds. i was suggesting that we try treating it like twin cylinder (like a cb350T for example, which also have no vacuum ports): run the bike on cylinders 1-2 @ a designated rpm (say, 1500K), adjust the mixture screw for the highest idle. pull the plugs wires from 1-2, and replace the ones for 3-4, and repeat the process on the other carb. then, with all cylinders firing, adjust both idle screws evenly for the correct idle RPM, and finally syncing the cables.

we started to do this on friday, but he hadn't done valve clearances, points, timing, etc., so it seemed pointless. sunday, we did these things, before he got back at the carbs again. he's got dyna components coming soon, and i'll feel much more comfortable helping with carb tuning once we know ignition isn't a problem.

mark--going to work. good luck with the gurus..hope you get some answers.

[mlinder]

i'm skeptical of how he's gonna sync the carbs in the manner we are used to on the fours. if he taps a port into the manifold for a manometer, where would he do so? before the split to each cylinder? one carb feeding two cylinders that are pulling differently seems like it could yield an inconsistent reading, yet tapping vacuum ports into the individual manifolds seems useless, as one carb can't be tuned separately for each cylinder it feeds. i was suggesting that we try treating it like twin cylinder (like a cb350T for example, which also have no vacuum ports): run the bike on cylinders 1-2 @ a designated rpm (say, 1500K), adjust the mixture screw for the highest idle. pull the plugs wires from 1-2, and replace the ones for 3-4, and repeat the process on the other carb. then, with all cylinders firing, adjust both idle screws evenly for the correct idle RPM, and finally syncing the cables.

we started to do this on friday, but he hadn't done valve clearances, points, timing, etc., so it seemed pointless. sunday, we did these things, before he got back at the carbs again. he's got dyna components coming soon, and i'll feel much more comfortable helping with carb tuning once we know ignition isn't a problem.

mark--going to work. good luck with the gurus..hope you get some answers.

Thanks man, see ya soon. 

[mrbreeze]

Isn't it funny how you lay down all that cash to buy stuff from people and they can't take the time to help you figure out how to put it to work. It's not like you are asking them to come to your house and hook it all up,dial it in,etc.... I'm having the same problem right now with Mike's XS (Yamaha 650 site). I paid $120 for Yami hand controls that I knew might not have the same color wires to hook to my bike (they don't).But some of the wires go to different controls that our bikes don't posess so I Emailed them for a little help (maybe a simple wiring diagram that would enlighten me as to what goes where) Not only have they not replied to my email.....they don't even list a phone # to call them!! I didn't ask them to fly over to California and come wire up my bike for me. I now say F#@K them!!!! I'll figure it out on my own even if I have to go buy a book for a bike I will never use again.

[mrbreeze]

i'm skeptical of how he's gonna sync the carbs in the manner we are used to on the fours. if he taps a port into the manifold for a manometer, where would he do so? before the split to each cylinder? one carb feeding two cylinders that are pulling differently seems like it could yield an inconsistent reading, yet tapping vacuum ports into the individual manifolds seems useless, as one carb can't be tuned separately for each cylinder it feeds. i was suggesting that we try treating it like twin cylinder (like a cb350T for example, which also have no vacuum ports): run the bike on cylinders 1-2 @ a designated rpm (say, 1500K), adjust the mixture screw for the highest idle. pull the plugs wires from 1-2, and replace the ones for 3-4, and repeat the process on the other carb. then, with all cylinders firing, adjust both idle screws evenly for the correct idle RPM, and finally syncing the cables.

we started to do this on friday, but he hadn't done valve clearances, points, timing, etc., so it seemed pointless. sunday, we did these things, before he got back at the carbs again. he's got dyna components coming soon, and i'll feel much more comfortable helping with carb tuning once we know ignition isn't a problem.

mark--going to work. good luck with the gurus..hope you get some answers.

Right you are Paul...after thinking about it,I don't come up with an answer but I'm sure there is some kind of a way to do it. If you have a phone # to cycle-X,thats where I would start. You damn sure have to have all of your ignition,valve adjustments,etc. sorted out first (I assumed you did).If you are waiting on Dyna ignition, I would hold off till you have it and installed.In the meantime.....adjust the camchain & valves. Who knows??? Maybe your carbs are already set to run the way they are!!!

[Jerry Rxman Griffin aka MuthaF'er]

Why don't you mention this thread just in passing to CyclEx if you're not getting the results from them that you need.  Perhaps if they took a look they would decide they do not need the negative publicity in front of 3063 members/potential ex clients. I'm sure they have many other customers also that need their help too and only so much time to spread around. One has to choose how to best spend their time. 

[mlinder]

Kens a nice guy, very knowledgeable, and far as I could tell, cared about issues people may have with his products. I imagine that the emails are just not being mentioned to him by whoever is reading them. When I call him, I'll mention that my emails were not answered. Since I haven't gone through any great lengths to contact him so far, I won't say anything against him. As much my fault as anyones.

[MRieck]

i'm skeptical of how he's gonna sync the carbs in the manner we are used to on the fours. if he taps a port into the manifold for a manometer, where would he do so? before the split to each cylinder? one carb feeding two cylinders that are pulling differently seems like it could yield an inconsistent reading, yet tapping vacuum ports into the individual manifolds seems useless, as one carb can't be tuned separately for each cylinder it feeds. i was suggesting that we try treating it like twin cylinder (like a cb350T for example, which also have no vacuum ports): run the bike on cylinders 1-2 @ a designated rpm (say, 1500K), adjust the mixture screw for the highest idle. pull the plugs wires from 1-2, and replace the ones for 3-4, and repeat the process on the other carb. then, with all cylinders firing, adjust both idle screws evenly for the correct idle RPM, and finally syncing the cables.

we started to do this on friday, but he hadn't done valve clearances, points, timing, etc., so it seemed pointless. sunday, we did these things, before he got back at the carbs again. he's got dyna components coming soon, and i'll feel much more comfortable helping with carb tuning once we know ignition isn't a problem.

mark--going to work. good luck with the gurus..hope you get some answers.

You would need to take the vacuum measurement from the carb itself (like the earlier CB750's)

[mlinder]

I just pulled a plug and looked at it. Only has a few miles on it, but its tan and metal on the side electrode, still metal on the center electrode, but for a little darkness close to the insulator/tip seal, and a bit of dark on the casing. Gonna ride it a bit harder on the way home and see what I get.

[Sam Green Racing]

I have a few suspicions, the first being that perhaps this bike was big bored or cammed way back in the 70's from the two motorcycle hot rod guys who were brothers who owned it, but as it's appearance was for the most part, unmolested, outside of a (unidentified) 4 into 1 and lowering blocks, I just dunno.

Mark, I'm not to sure how much a modded cam would affect the carburation but it's not much of a job to check the cam.
Set number 1 cylinder at TDC on the power stroke (you will have clearence on both tappets).
Fit a degree wheel to the end of your crank with a wire pointer conected to a fixed point on the motor and pointing at zero on the wheel.
Rotate the crank and note the degrees at which the valves open and close, you can find Hondas stock timing figures in your workshop manual.
If you get figures like, inlet opens 37 BTC and closes 68 ABC...exhaust opens 67 BBC and closes 37ATC,...then you'll know you have a very hot cam.

Sam.

[paulages]

thought about while at work, and came up with an answer to my own questions...but of course MReick had already posted it. seems like if you tap a port at the manifold before it splits to the two cylinders it will read the ame is it would at the carb, and get at least a good enough reading to set both carbs to the same idle. i still think the reading will probably jump up and down if there is any variance in the vacuums of the paired cylinders. only one way to find out, i guess..

[mlinder]

I have a few suspicions, the first being that perhaps this bike was big bored or cammed way back in the 70's from the two motorcycle hot rod guys who were brothers who owned it, but as it's appearance was for the most part, unmolested, outside of a (unidentified) 4 into 1 and lowering blocks, I just dunno.

Mark, I'm not to sure how much a modded cam would affect the carburation but it's not much of a job to check the cam.
Set number 1 cylinder at TDC on the power stroke (you will have clearence on both tappets).
Fit a degree wheel to the end of your crank with a wire pointer conected to a fixed point on the motor and pointing at zero on the wheel.
Rotate the crank and note the degrees at which the valves open and close, you can find Hondas stock timing figures in your workshop manual.
If you get figures like, inlet opens 37 BTC and closes 68 ABC...exhaust opens 67 BBC and closes 37ATC,...then you'll know you have a very hot cam.

Sam.

This makes sense. I will try to mickey mouse something up like that the next week or so. Thanks for the idea.