float & throat sync - WOW!

[easyfinger]

New Guy Here from Knoxville

 

My buddy and I both have pre-owned royal stars his being a 1997 tour classic with some popping and occasional backfire on deceleration issues. His carbs had been monkeyed with previously; pilot screws, float settings and throat sync all over the spectrum. Mine is a 99 with the standard gurgling sound and slight popping while decelerating that you get with most factory tuned royal stars and has yet to be fine tuned.

Anyway, after learning what I could from you guys here at venture.org, I pulled my buddys carbs and cleaned all passages thouroughly, I set all float heights to 0.645 with calipers against base of float bowl, backed off throttle adjuster on carb #1 to close the throat and checked highest postion of throttle plate (closed) to bottom surface of throttle bore. I checked and rechecked measurement and kept getting conflicting measurements before I realized the hardend steel slide on my quality calipers would not measure the offset angle of throttle plate against the 90 degree angle of throttle bore. Remembering I had an old plastic caliper with a round pin slide I remeasured plate to bottom of bore facing with this tool and got consistent measurements every time and adjusted carb 2 exactly to carb 1, then #3, then #4. All throttle plates adjusted to 0.678. I adjusted pilot screws 2 1/4 turns out, put carbs , airbox, and tank on and... Whoops, I have a problem!

Carb #3 popping thru exhaust while throttling off and snuffing type sounds while idling when warm. Pilot screw adjustment had no effect and exhaust gas was cool compared to carb 1,2, and 4. All other carbs and cylinders sounding perfect. This indicated to me that #3 was running very rich.

 

After taking carbs off several times to see what the problem was and rechecking every measurement, my buddy and I devised a wooden jig to re-check float levels with clear plastic tubing with carbs fully assembled leveled and plumbed, and then mounted jig in my vice and set the carbs on top. Guess what, No 3 carb float level measured 1/8 high, while all the rest measured exactly at bottom circumference of main diaphram cover ( which is where I wanted them - high for quick low end throttle response). I took a wild guess and lowered float #3 by 0.035 and rechecked float level with plastic tube gage

and it came out exactly level with bottom of radius of diaphram bowl.

Now, can someone tell me why this one float would measure 0.035 lower than the rest but gage equally level with the other floats with tube gage?

Could it be that float seat is lower than the others? Could it be the float seat is turned in deeper in this one carb?

At any rate, we put carbs, airbox and tank back on bike and cranked her up. My God, It Sounds so Good and So In Tune - no backfire and no poping, and no snuffing, sound - Time for a little road check!

 

At constant throttle the bike seemed much quieter than before, but what was amazing was the smooth but powerful and instant throttle response and acceleration from closed throttle to open and every position inbetween. No lug, no lag or hesitation whatsoever. We hit a long stretch of sweepers and mild twistys where I could keep power up in third and fourth gears, while mainly using engine deceleration for braking and all we could hear, other than that wonderful throaty whumping sound, while accelerating out of curve, was a corresponding cooking sound, kind of like hot coffee percolating fast with an underlying boiling sound while decelerating into it.

And last but not least; Zero, pops, cracks, sniffles, or snuffles while riding for an hour and a half. We'll check the tuning with vacuum gage and tachometer next week but he and I agree, we'd be hard pressed to change a single thing.

[pegscraper]

Very nice work. Now you just need to swap the 32mm carbs onto the bikes.

[easyfinger]

Hello Pegscraper; I read alot of your posts before manually syncing carbs, thankyou very much. Now, how much moolah and work do I need to use the 32mm carbs? Will they slide in easily and fit under airbox, and is that extra power hard on the clutch? I might do a stage 1 or 2 modification on mine along with syncronizing carbs, just so I can keep up with my buddy after doing his. Hes got a red and white royal star tour classic with leatherlyke bags and it looks alot like yours. Classy!

[pegscraper]

Here's a link to the article I wrote about it. It's here in the 2nd gen technical library. A cam and valve spring swap is recommended too. I used V-Max cams myself. But the Venture intake cam would suffice. Royal Star exhaust cams are the same as the Venture cams. The clutch is fine. It's the same one as in the Ventures and V-Maxes. It can be beefed up if you want, but I haven't done it. Do this and I'll guarantee you will never see your buddy's taillights again. You'll think you bought a whole new bike.

 

http://www.venturerider.org/carbswap/

 

Last but not least, we have rules around here, fella. Ya gotta post pictures of your bike. Let's see some of your buddy's bike too.

 

You're from Knoxville, and that must be TN. We have a few members down there. I have a brother who lives right near Johnson City, so I get down there on the bike once in a while. Last year we went down over Labor Day weekend and hit the Dragon. (Check my gallery.)

[easyfinger]

Pegscraper, I'll keep my eyes open for those 32mm carbs. Your carb swap looks very professional and smart. I'll post a pic of my star soon. I'm very proud of the way she looks.

I hope you rode cheroholla hwy before or after you did the dragon. Give me a holler next time you come down - I'm close to cheroholla, blue ridge pkwy and many other fantastic roads and would love to take a spin with you.

[Tartan Terror]

You know it kind of makes me wonder if it is worth it to pull my carbs and check things like float height and spacings. It runs good but if this stuff is so off right from the factory how much better can it be?

[easyfinger]

Factory tolerances stack up on multi-carb applications and I suspect dealers wont give thier mechanics time to measure exactly, or maybe they dont know or dont care.

 

My buddies bike ran decent and so does mine, but now his runs GREAT!

I just pulled carbs off mine today and found the float settings from one extreme to the other when measured by tube and consequently, once I pulled the factory plugs out of the pilot bores I found the pilot screw turned out 4 turns on the low float carb while the high float screw was only turned out 3/4. The other two were 1 1/2 and 2 turns. Do you see the correspondence between float levels and the pilot circuit? The throttle plate sync was pretty good from factory (all within 0.008 in ). Now for those floats.

I measure and adjust float height to maintain the same fuel level in every bowl so that pilot circuit intakes and fuel levels maintain a consistent relationship in every carb, and sync those throttle plates so the main circuit pressures remain the same also. What you get is a correspondence between the two circuits that gives you a much smooter and more powerful response, and a much more enjoyable ride.

I measure float height at 0.320 in. for a high level in float bowl and float drop at .0.680 in, so I know floats wont bottom too far and bind the needle seat. I sync'ed both bikes (4-28mm mikuni carburetor throttle plates) at 0.685 in. from base of carb throat to uppermost part of throttle plate. I'll recheck tube measurements on float bowls tomorrow morning.

 

Its tedious work but well worth the effort and when youre done youll wonder why you ever spent money at the dealer for tune ups and carb syncs.