Author Topic: 550 rear sprocket question (Read 5522 times)

Scott S · « **on:** April 09, 2012, 06:40:25 PM »

I swapped a 550 engine into my CB500 and somewhere along the way I read that I needed to change the rear sprocket to match the transmission ratios in the 550 engine.

I have a 17/37 set up now. Runs great and pulls strong, but the gas mileage is down compared to the 500.
Tuned correctly (lowered the needles one clip, timing set, valves adjusted, spark plugs look nice, no flat spots, etc., etc.), I'm getting a BEST of 33 mpg. Average is 29-30 MPG.

At an indicated 60mph, it's running 5K rpm. That just seems high to me.

Did I get the correct rear sprocket? Is there a better combo to use to lower the RPM and raise the mileage a little without completely losing the performance I gained?

TwoTired · « **Reply #1 on:** April 09, 2012, 06:48:33 PM »

17/37 is stock and what my 550's have that get 45-50MPG on good gas. (I haven't measured with the ethanol contamination. I'd expect 3% down for that.)

CoachDoc · « **Reply #2 on:** April 09, 2012, 09:59:50 PM »

My '74 550 shows an indicated 71 mph at 5K rpm's in 5th gear. The 60 mph you're getting at 5k is a bout what 4th gear should be. Somethin's not right, but you do have the correct sprocket ratio. Speedo off? Try running with a GPS to verify it.

dave500 · « **Reply #3 on:** April 10, 2012, 12:17:28 AM »

my 550 geared 17/37 runs 100 kays/5000 rpm,(going by both the stock wobbly speedo/tacho and a bicycle speedo,so that sounds right,although they do feel like they are revving a fair bit,,ill get two hundred/two hundred twenty kays on the main tank,two tired gets good economy because he probably tries to,has yours been carb synced lately?

TwoTired · « **Reply #4 on:** April 10, 2012, 01:39:48 AM »

Quote from: dave500 on April 10, 2012, 12:17:28 AM

two tired gets good economy because he probably tries to

Not sure what you mean by this. I'm not making any concerted effort for fuel economy beside keeping it in tune. It's a combination of city and highway driving and I flog them when driving, keeping the engine in the power RPM band, except for highway cruise and stopped. 70 and 80MPH is routine on the highway. (It's true that my last few years of driving have been a bit tamer, as with warfarin in the system a let off from the bike will bring a likelihood of bleeding to death. But, my mileage reports are from the era prior to that.)

The mileage reported applies to my 74 550K, 76 Cb550F, and my 77 Cb550F. The 78 CB550K actually gets better mileage than the others, probably due to its factory lean burn tuning.
I had a 75 Cb550K that got about 35-40 MPG, but that had a 16T front sprocket, and didn't see much highway use because of it (and the noisy Mac 4 into 1). Sold that bike a few years ago.
The other bikes have the stock pipes, and air box. All but the 78 CB550K got a UNI NU-4055 air filter installed.

With the stock sprockets and tire sizes on the CB550, the MPH per 1000 RPM is 12.24 in 5th gear. 5000RPM would be 61 MPH
The CB500 is 12.65 MPH per 1000 RPM in top gear. 5000RPM would be 63 MPH.

However, look at the speedometer errors reported when these were new. And remember, tire height changes will also effect indications.

I should add that the 74 Cb550 has a Windjammer fairing on it.
The 76 CB550F has a Quicksilver fairing on it.
The 77 CB550F has a National cycle fairing on it.

The now sold 75 CB550K did not and neither does the 78 CB550K (which I will sell next).

It wouldn't surprise me that the faired bikes get better mileage at least in part because of the fairings. But, I certainly rode them the most because they had fairings. I much prefer a more upright position on the bike rather than laying on the tank. So, perhaps a riding position that creates more wind drag on an unfaired bike has a toll in the mileage department?

Cheers,

dave500 · « **Reply #5 on:** April 10, 2012, 02:25:38 AM »

i fiqure i do about 5 litres per hundred kays,,using an online converter i get 47 miles per us gallon,not bad i think considering i dont spare this bike especially on accelleration and i live in a hilly twisty area,i guess if i tried to save fuel itll go easy 50 + miles per gallon?you might be a little rich scott?i have a 4-1 pipe,decent electronic ignition and 38 slow/100 mains,i forget where the clip ended up,,i actually dropped from the 40 slow to the 38 during my fettling of this engine leaving the main alone.

Scott S · « **Reply #6 on:** April 10, 2012, 05:26:56 AM »

Well, I did a tune-up on the engine stand and some more tweaking once it was in the bike. It was really rich and had a flat spot, so I lowered the needles and tweaked the carbs.
Last time I checked the plugs, they looked good. This also improved mileage slightly.

It's been in the bike long enough now that I could do another tune-up; valve and cam chain adjustment, re-check timing and synch the carbs. (It runs fine, but this was an engine that I bought from Craigslist. Did an initial tune-up and now just want to re-check everything.)
However, that won't lower the RPM's at 60 mph.

According to TwoTired's calculations, the 500 and 550 should turn similar RPM's at 60 mph, but I swear I don't remember the 500 revving that high and I could get mid to high 30's withought trying and over 40 on long trips.

Scott S · « **Reply #7 on:** April 10, 2012, 06:30:22 AM »

I'd really like to hear from others who've done the 550 into a 500 swap and what gearing you used.
Did you change to a 37 tooth rear? Still using 34 tooth?

Also, a good place to get a 35 tooth?

Duanob · « **Reply #8 on:** April 10, 2012, 09:12:42 AM »

I just swapped out my old 37T for a 36 tooth rear for kicks and grins. Both sprockets needed replacing anyway. I rode to work this morning, but really didn't notice any difference. Same RPMS/Speed, maybe a bit of quicker accelleration but it could be that i haven't been on my bike in a while.

My 550 hasn't really ever gotten great mileage. If I get 45 MPGs I consider that great. 40 is more normal. 6000rpm@70mph but don't know how accurate my speedo is.

becken · « **Reply #9 on:** April 11, 2012, 07:38:52 AM »

I did a lot of the modifications from the FAQ section, on the thread titled "Thoughts of Hondaman." There are several posts there about the 500/550s. I did one thing at a time and then rode the bike before doing the next step. Modifying the ignition advance springs and advancing the idle timing helped the off idle performance a lot. When I lowered the needle clip, I noticed the cruising speed performance to be ratty and fuel mileage suffered. I then drilled out the emulsifier tube holes to .039, but I drilled them all figuring I would replace the tubes if I messed them up. This completely straightened out the steady speed running and brought my mileage back up to 45 - 50 mpg with very little if any flat spot. Bike was still pulling strong in high gear at 95 mph indicated. I bought my 550 new and it runs better now than new. Gearing is stock 17/37 and I am showing 5000 rpm at 60 mph indicated.

Scott S · « **Reply #10 on:** April 12, 2012, 02:39:35 PM »

Will the 500T sprockets fit the SOHC4's ?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260997953993&ssPageName=ADME:B:WNA:US:1123

LesterPiglet · « **Reply #11 on:** April 12, 2012, 02:47:33 PM »

That particular one will fit 350/400's according to this.

http://dixieinternational.com/store//publications/catalogs/2009vint/10_Sprockets.pdf

Duanob · « **Reply #12 on:** April 12, 2012, 04:36:08 PM »

Why not buy the one that fits from a reputable dealer?

http://www.powersportparts.net/JT-SPROCKET-REAR-36T-JTR282-36-p/55-28236.htm

chadbenson · « **Reply #13 on:** April 12, 2012, 07:10:45 PM »

My 550 was doing exactly what yours was. It was getting around 30ish mpg's and with a 37 tooth rear it wo uld do 60mph at around 5k rpms. I've talked to others with the same issue including a friend I ride with who has a '74 550. What others and I have done is to drop down to a 34 or 35 tooth rear sprocket to get the 5th gear revvs down a bit. You'll hear two things from people who ride 550's. Either they get like 40+ and can cruise 70 at 5k rpms or you get what I described before. My bike does run rich but I haven't changed anything from stock even when I've gone to refurbish and tune the bike.

Scott S · « **Reply #14 on:** April 13, 2012, 04:41:58 AM »

Chad, which sprocket did you choose, the 34 or 35? Other than lower revs on the freeway, any noticeable difference in performance? Especially in the lower RPM range?

Scott S · « **Reply #15 on:** April 13, 2012, 05:16:42 AM »

Quote from: Duanob on April 12, 2012, 04:36:08 PM

Why not buy the one that fits from a reputable dealer?

http://www.powersportparts.net/JT-SPROCKET-REAR-36T-JTR282-36-p/55-28236.htm

Thanks for the link. I asked earlier about a good place to find them. I'll call later and make sure they have one that fit's our bikes. The price is good, too!

Bailgang · « **Reply #16 on:** April 13, 2012, 05:46:51 AM »

I've got a 34 tooth rear sprocket on my 75 550 and yes there is a trade off between it and the original 37 tooth. In my case it hardly had any effect on fuel mileage which for me ranges anywhere between 38 to 42 mpg and it did cut my rpm's at highway speed to a more agreeable level but the trade off is that I have to do a bit more downshifting when passing. I've also recently installed a 650 cam and I'm not sure if the cam likes the 34 tooth sprocket very much but that could be because I haven't gotten the carbs tuned correctly yet.

chadbenson · « **Reply #17 on:** April 13, 2012, 06:18:09 AM »

Scott,
I went with the 34 tooth on mine. It does take a little more feathering of the clutch from a full stop, but not horribly. As far as the lower rpm range it doesn't change the feel too much except for 1st gear. Once your moving it revs through to 3rd just fine. It's worth the trade off to me as your not always searching for that elusive 6th gear on the highway. Mine pulls right at 5k rpms at 65 mph in 5th gear. I've also found it makes 4th gear a little more friendly in town/city areas.

I bought a 34 tooth JT sprocket from bikebandit.com by just searching for my bike ('76 550k) and looking under aftermarket parts. It was on clearance so there are probably plenty left.

Again you'll definitely notice a slight difference down low but to me and others the trade-off is well worth it.

Duanob · « **Reply #18 on:** April 13, 2012, 11:44:53 AM »

Quote from: Scott S on April 13, 2012, 05:16:42 AM

Quote from: Duanob on April 12, 2012, 04:36:08 PM
Why not buy the one that fits from a reputable dealer?

http://www.powersportparts.net/JT-SPROCKET-REAR-36T-JTR282-36-p/55-28236.htm

Thanks for the link. I asked earlier about a good place to find them. I'll call later and make sure they have one that fit's our bikes. The price is good, too!

That JT number is the one that fits. I just bolted it on last weekend.

Update on the 36T I do notice I get about 4ish MPH more at about 6000RPMS. I used to be at 70+ MPH at 6000. Now Im @ 74 75 MPH at the same engine speed. But my speedo isn't the most accurate. When I hit the throttle I get a pretty good response for passing. It zooms to 80 no problem and feels like it has more to go. I think I like the power range on the hiway with the new 36T sprocket. I would be careful going any less on the rear sprocket you might end up pretty sluggish around town and during take off.

chadbenson · « **Reply #19 on:** April 13, 2012, 04:38:55 PM »

Duanob,
I'm due for a sprocket and chain change myself. The 36T sprocket you put a link to: it will fit a 530 roller chain on the 550? Just wanted to make 100% before I order it!

Thanks!
Chad Benson

Scott S · « **Reply #20 on:** April 16, 2012, 03:43:16 AM »

I may try the 35 tooth, but it appears I still have some jetting to do.

260 miles of mostly hwy/5th gear and I still barely broke 30 mpg. I did a semi-plug chop as I was pulling into my neighborhood (Revved it up past 6K in 3rd gear, hit the kill switch and pulled the clutch lever in. Coasted in to my garage). The plugs still show rich.
That's odd to me since these are stock carbs and stock jets for this engine and I've already lowered the needles one clip. I don't have a jet gauge, but maybe someone has drilled the mains?
I'm thinking lower the needles one more clip and then try a smaller main if it's still rich.

dave500 · « **Reply #21 on:** April 16, 2012, 12:21:16 PM »

are you using d8 plugs?

Scott S · « **Reply #22 on:** April 16, 2012, 05:18:57 PM »

NGK D7EA plugs. Would one heat range on the plugs really make that big of a difference?

Duanob · « **Reply #23 on:** April 16, 2012, 05:28:33 PM »

Quote from: chadbenson on April 13, 2012, 04:38:55 PM

Duanob,
I'm due for a sprocket and chain change myself. The 36T sprocket you put a link to: it will fit a 530 roller chain on the 550? Just wanted to make 100% before I order it!

Thanks!
Chad Benson

Yes that is the JT sprocket number for the CB550K. I use a standard 530 100 link roller chein. It's easy to double check.

dave500 · « **Reply #24 on:** April 16, 2012, 10:01:28 PM »

i use 7,,i just thought perhaps you had colder and they speak with forked tongue when read?im running 38/100 4-1 and mine run just nice.

cwchan · « **Reply #25 on:** May 18, 2012, 07:39:44 AM »

hmm... reading this thread means i have a non-stock rear sprocket. I only get to 100kph at around 7-8000 rpm....>:\

lucky · « **Reply #26 on:** May 18, 2012, 07:50:59 AM »

Quote from: TwoTired on April 09, 2012, 06:48:33 PM

17/37 is stock and what my 550's have that get 45-50MPG on good gas. (I haven't measured with the ethanol contamination. I'd expect 3% down for that.)

Ethanol is not contamination.
Ethanol is ethyl alcohol.
Ethanol BTU=76,000
Gasoline (summer)=114,000 BTU

Ethanol makes gasoline burn cleaner.
Sometimes a 3% loss in MPG, and sometimes up to 40% less MPG!
Makes you wonder. Cleaner air though.

It takes .5 to 1.5 gallons of gas to produce 1 gallon of ethanol.

But direct fuel injection systems now use 65:1 ratio of air to gas!
Our old Hondas used about 14:1 air to gas.

Things are getting better.

TwoTired · « **Reply #27 on:** May 18, 2012, 05:06:54 PM »

Quote from: lucky on May 18, 2012, 07:50:59 AM

Quote from: TwoTired on April 09, 2012, 06:48:33 PM
17/37 is stock and what my 550's have that get 45-50MPG on good gas. (I haven't measured with the ethanol contamination. I'd expect 3% down for that.)

Ethanol is not contamination.

Yes it is. Look up the meaning of contamination. Ethanol gas is NOT pure gasoline, it is adulterated/contaminated.

Quote from: lucky on May 18, 2012, 07:50:59 AM

Ethanol makes gasoline burn cleaner.

Ethanol makes non-computer controlled engines burn leaner, and use more fuel per mile traveled.

Quote from: lucky on May 18, 2012, 07:50:59 AM

Things are getting better.

Politicians and tax collectors must love you.

We had a separate thread about gasohol. Did you miss it? Or, are you cross posting/stumping for the corn industry?

http://mystarbrite.com/startron//content/view/14/37/lang,en/

So, now we get to pay more for fuel, get less value from it, have to buy products to counter it's negative effects, and get taxed more for each portion of a "consumer solution" that didn't have a root problem in the first place. The government wins again. Aren't you proud?

News:

Author Topic: 550 rear sprocket question (Read 5522 times)