Bonneville America Forums Forums Technical Forums Performance Mods balancing

I know some of you guys have seen enough carb balancing questions but I tried to balancing mine today with a homemade balancer and I got the atf in the hoses to finally match within 1/2 inch even after switching the hoses but when I turned the idle back down to 1100 to 1150 the oil in the balancer showed a 8 inch difference. I never noticed anyone else complain about that particular problem yet. Is that to be expected or should I investigate a little more? I did come up with some serious backfiring from the mufflers on decel recently too.

mike

first you shouldn't have the 1/2" difference and it is possible that at the slower RPM the difference is magnified but I don't know about the 8" part that is a HUGE difference. I would rebalance and if you can't get it closer investigate farther.

thanks dog, I seemed to struggle to get it that close. One little tweak and it would overshoot the mark. will attempt it again.


mike

Could be caused by an imbalance in the idle mixture. Since there can be differences between the carbs and the cylinders they feed, turn count alone will not assure equal idle mixture.

I used a yard stick, with about 20' of clear tubing as my balancer. I filled it with the same oil I use in the bike. I was lucky if I could get it within 1". I would switch and it might be 1" off in the other direction. One thing you have to remember using a home made balancer like mine (the yard stick) is that it will probably be 5 to 10 times more sensitive than store bought balancer. So I figure my 1" is probably more like 1/8" to 1/4", which is more than good.

I also run a hose between the carbs to help compensate for any balance error. I use the home made balancer to get it close and then install the cross over hose to help make sure it stays close.

Tom

I know you mean this but just to be clear don't use the crossover hose during the balancing process.

I have heard that about the homemade balancer too. That's what I used and was concerned about whether there was anything deeper wrong with my carbs or worse. and yes, I took my equalizer hose out during the process. I know Pat explained another way of balancing with the mix screws like I had to do to my 1960 and hope I won't have to try that process yet.

mike

I've had the same problem trying to sync with the homemade balancer. Getting them matched at one idle speed yeilds huge variations at other idle speeds or throttle positions.

Also, adjusting the idle mixture screws seemed to have almost no effect on idle speed.

Could these be symptomatic of a vacuum leak?

No, I remember someone say that the mixture screws don't contribute much to idle variations. they are not the same as car carbs so to speak. With a car, 2 turns of the screw could change the rpm's 400 rpm's or more and that doesn't happen with these. If vacuum leaks are a concern, make sure the hose clamps are snug and you have tight fitting vacuum caps.

lctrc, there ars some carb tuning tips on Dinqua's carb site tunuing mikuni hsr carbs regarding air leaks http://www.mikuni.com/pdf/hsr_tuningmanual_021003.pdf

it's basically the same reasoning but for mikuni carbs. It should apply in theory.

mike

I am not convinced that using the homemade (HM) carb tuners are accurate. I know, I know, fluid in a tube and all that....

My premise is the sensitivity of the HM tuners is the problem. They are too sensitive even with typical dampening. Hook up some regular vacuum gauges without dampening (humor me) and notice how wildly the gauges fluctuate. Now dampen them with some sort of restriction and notice that they still fluctuate wildly, just not as much.

To accurately balance these carbs, I've found that you need to severely restrict the input to whatever metering device you are you using. Steel rods/mercury/fluid all work as long as you restrict them appropriately!

I'll give that a try Phil.I know before I made my balancer I bought a pair of vacuum gauges and boy did they bounce. tiny vise grips on the hoses they slowed down some but I wasn't happy until I was convinced of the HM accuracy here.

mike

I have balanced literally thousands of carbs with a homemade balancer and it is extremely accurate and in my opinion there is no such thing as too accurate just an experienced lighter touch on the adjustment.

Also, is it an issue (with the homemade balancer) that one side bounces way more than the other?

I only had a couple do that and in those cases it was carb wear.

I wouldn't think it is wear then. Haven't done enough of the CVK carbs yet. Only done 4 of them and all went smoothly.