Jetting suggestions
 

G'day guys.

I am after a couple of suggestions in regards to my carb settings, based on your experiences. I have just done a full rebuild so cannot do any proper tuning until it is run in, so I am after a base setting until I can open the throttle up and test it properly. As the main jets effect the idle on a CV carb these will only be a guess until I can open it up.

I have 10:1 compression, long billet velocity stacks (intake runners), Unifilter (larger than K&N), Moriwaki Ti headers and Staintune mufflers with the baffles in. I have 50 pilots and DJ needles. I am running 180/182 mains due to the velocity stacks, as advised by the manufacturer. I have used a Colortune spark plug to adjust the mixtures at idle so these are now right. No way it would run with 48 pilots at all, it was too lean. 50 pilots and mixture screws are set at 1.5 turns out. Feels good up to 4000rpm which is my rev limit until the engine is run in.

It is idling a bit erratically, fluctuating a few hundred RPM. I know air leaks could do this but I cannot find any. Could the main jets be causing this at such low RPM?

Obviously a proper tune will be the answer, but until I can do that I am after a "best guess", and would appreciate your thoughts before I pull the carbs off another 17 times. Approximately of course...... LOL

You didn't mention a sync. Have you?

G'day Bling. Yeah I forgot to mention that. After I shut off my computer I started to think about it a bit more. I have done it by ear, which I found with the intake pulses of the twin to be more difficult than I have found in the past with other engines. So that is an unknown quantity until I get a good quality vacuum tool for the job. I have a cheap one, but is no better than my ear and a piece of hose on the twin.

Would that be the most likely cause do you think?

I have noticed that even though we are in the middle of winter here (Aussie winter of course so not real cold, about 10 degrees celcius), it will start without the choke, so it is getting plenty of fuel. Lean it off though and it will backfire and carry on. Is it normal to start without choke in mild conditions?

Shayne - Before you can judge much else about your carb setup you really need to get a 'good' sync done. Especially after a major tear down as you've done.
Try to get your hands on a good gauge setup to get it right.

Side note: I was running long runners on both carbs for a short time and had a problem getting the carb-sync to stay well balanced through the range. I suspected a problem shortly after adding the long to the front so I setup my sync gauges on a tank bag and took it out on the road. http://www.3457.com/images/gauge3.jpg
I'd be able to balance them well at idle but it was way off at 3K or 4K under load ... if balanced at 4K it would be far off elsewhere. etc.
After messing around for a while I put the short runner back on the front and it stays balanced much better through the range ... Obviously the long runner isn't your current rough idle problem but may be something to consider later.

I suggest trying the 48 pilots again. I tried the #50s and had the exact same symptoms as you do. Do the carb sync first though before you start tuning. I've no experience with the longer intake stacks. I imagine they keep intake velocity high at higher rpm but suck at lower rpm. At least this is what I've heard.

Thanks guys. The velocity stacks are significantly larger than the stock runners, and were designed on a flow bench. Dyno tests and real world running shows them to be a good thing by all reports. Designed by a guy who works for Honda and had a VTR race bike as his toy. The ones I have are long, and for reasonably stock engines to assist in low to mid range airflow. Other runners are available (similar to Moriwaki ones) that are shorter, and are for race-type performance as you suggest Greg.

I think I will ensure the carb balancing is right before I go looking at anything else. Can anyone recommend a good internet tool seller where I could get a good carb synch tool?

Consider making your own. If you have a source for commercial gauges in your area you can put together something like this setup that's very sensitive and accurate.

https://www.superhawkforum.com/forum...read.php?t=651

Thanks John, I remember seeing that when you first posted it. Good job. Fits well on the tank bag too I see!

I have got a lot of jobs on the list at the moment, and to be honest I think I would just rather buy one if I can get one for a reasonable price

If you need a source for commercial gauges I can help. I'm in the process of making a sync set-up, of course stealing the idea from 99Hawk. The only difference is that I'm using Ametek gauges over WIKA (Ametek is a better product). I have not decided whether I should use glycerine filled gauges or dry. Anyhow, if anyone would like the other two gauges taking space in my garage, I will gladly do a random act of kindness and send them to you assuming someone pays the postage.


I do have a question for 99Hawk.....how do you attach your gauges to the bike? Is there a fitting that you attached to the gauge hose?


Karl

I'd love to take those off your hands, but I might as well let someone get them who will be using them very shortly. I won't need them for a while (the time it takes to save up the cash for slipons and a jet kit). Very generous offer 3D02.

Dibs. PM sent.

Karl,
The two vac lines run to the left side of the frame, both lines have a small section of steel brake line inserted in the end and then capped with standard vacuum line caps.
http://www.3457.com/images/3.jpg
( both lines tied back )

http://www.3457.com/images/4.jpg
(lines with caps in place)

http://www.3457.com/images/5.jpg
(the red marked line is for the rear cyl)

So basically connecting both gauges up to the bike is quick and easy.....

Sometime ago I put up this web page with more details:

http://www.3457.com/files/vtr-sync/


.

I went to have a look at your link John, but it doesn't work. I take it you have a T-piece to run another line to the petcock from the rear line. Do you leave this hooked up when using the gauges?

One thing I forgot to mention Greg, is that with the 48 pilots, it was very hard to start, idled more roughly than now, and when you blipped the throttle, backfired badly. When you rode it it surged badly and just generally ran like a pig no matter where I put the mixture screws. When I went to the 50 pilots it improved out of sight, only the fluctuating idle of 200-300 rpm remains. It is heaps better.

I will keep it in mind though to try the 48's again as you suggest when I know the balance is right. I had another go at doing it by ear this arvo. Hopeless!! I must be losing my touch, or the twin is just too hard to pick.

I am hoping it is the latter. LOL

Yes, maybe I wasn't clear but you put a 'T' in the line to the petcock then run a short line off the 'T' to someplace where you can access it for the rear cylinder vac gauge. Leave that line in place, capped off, the rest of the time.

edit: ps: the link above is now fixed...

Righto, thanks. Now I just need to look at some gauges.

Most industrial supply houses should carry vacuum gauges. Here are some part numbers.

Marsh Instrument Company
P/N J7605P (Glycerine Filled)
63MM SEVB 1/4 NPT
0/30 "Hg&KpA


The one's Vincent will be getting.
U.S. Gauge (Ametek)
P/N 656201AA4CD3A00
30 In Hg/0 PSI
Size 63MM Connection: 1/4 NPT