Topic: 1981 CB650 Performance Mods

[jpc002]

Has anyone made any performance modifications to their CB650? 

I've recently ported and polished the heads, and reseated the valves.  I also just bought a jet kit and K&N pod filters (they should be arriving in the mail shortly) I'll keep everyone posted on how well everything goes.

Now I'm looking into a MAC 4-1 exhaust.  But I'd like to hear others' opinions about such things.

If anyone has any helpful tips, or any experience with this stuff, please let me know! 

I've also heard that putting colder plugs on the inner 2 cylinders makes a bit of a difference- anyone have suggestions about what kind of plugs to use?

Thanks!

JP^speed

[Pinhead]

Lose the pods and stick with the stock airbox. Just remove the filter cover and up your mains to about 100's or so. That made a HUGE difference on my bike. Also, if you haven't already changed the exhaust, do this to your mufflers. Makes them a bit louder and deeper, and flows better.

Get a cam from a '79, which is a bit hotter than the later models. I think you could use an aftermarket cam that's designed for a 550, though you'd want to go "big" compared to the 550's specs.

[MRieck]

 I have used K&N individual filters for years on many older bikes with excellent results. The real world disadvantages are getting caught in the rain and getting a bit more particle ingestion. Modern airboxes work well because they have 5 or 6 times the volume of early boxes and generally incorporate ram air which allows for good fill. I think there is a definite lack of understanding regarding carb tuning especially in regards to fuel circuit overlap. I also think to many guys over fuel their engines finding the ability to say "I run 135 mains" macho. If you don't have a solid understanding of carb tuning you will have problems.

[jpc002]

I think you just about named off all the available mods you can buy without having to get parts made. Did you do the head yourself or send it out? The only other thing I can think of would be getting a three angle valve job while the head is off.

Canuck- I just did the head myself.  It made a noticeable difference in power.  What is a "three angle" valve job?  I reseated the valves with grinding compound?

Lose the pods and stick with the stock airbox. Just remove the filter cover and up your mains to about 100's or so. That made a HUGE difference on my bike. Also, if you haven't already changed the exhaust, do this to your mufflers. Makes them a bit louder and deeper, and flows better.

Get a cam from a '79, which is a bit hotter than the later models. I think you could use an aftermarket cam that's designed for a 550, though you'd want to go "big" compared to the 550's specs.

Pinhead- I previously removed the outermost baffle from a pair of extra exhausts I had, however I found that it didn't make much of a difference performance wise.  I put the old exhaust back on.  The bike was louder, however it sounded too harley-ish for my taste.  And again, I didn't notice any difference in performance.  I might try and put them back on after I put the jet kit in it.  I'll look into the '79 cam as well.  Thanks!

Does anyone have any tips or advice about spark plugs? 

I've been thinking about putting a larger toothed sprocket on the rear wheel.  Anyone ever tried this? 


JP^speed

[jpc002]

Here is a picture of the head I ported and polished.  I didn't take a "before" picture...  I should have to remind myself how bad it was.

You'll have to forgive me about the quality of the pictures- i'm new at this.

[mg1045]

I was told the earlier 650 head(79 and earlier) used the same intake spacing as the 750's. And that the older 750 carbs(69-76) would work on it. Please don't quote me on this, let me know if I'm wrong! I'm looking into this because I want to run dual mikuni carbs. Something like the cycle X carb kit. They might be a little to big for a 650. Need to do some more research.

Is there anything like a big bore kit available for the 650?

[fuzzybutt]

those cyclex carbs wont fit into a stock framed bike. ken the owner of cyclex told me there are ALOT of frame mods to be made to get them to work, not worth he said.

[mg1045]

I'll have to find out what kind of mods. I'm doing a rigid, a little rake, a little stretch. So a little more mods won't be a problem    But would they be too much carb for a 650? They have a kit available for the xs650. So I was hoping that it'd be oaky.

Not trying to steal this thread, but it goes along with the original question.

[paulages]

i'm planning on running PD series (i want the accelerator pump) 750 carbs  on my 718 project, which is using a '79 cb650 head. they require a little bit of finagling, as the carb mouths themselves are slightly larger, but they do fit. without any other head mods, i'm not sure why you would want to though.

[jpc002]

I've read that a good carb for the 650s is a 29mm smoothbore.  They are pretty expensive.  I found one for $450 on ebay a while back and they don't come around too often.  I'm not sure about fitting- the head for the '80 cb650 are different from the head of a '81 cb650 (i found that out the hard way)- the in-port spacing is a little different.  So carbs from an '80 wont fit the '81 without some weird shaped off-set boots.

[mg1045]

Bringing this back up.

I'll ask this here cause it's 650 related. Does anyone know where you can get raked triple trees? I need about 3 degree that'll fit our 35mm tubes? I found one custom place so far. Haven't called yet, but it's lookin like around $625 to make them!

Can you get money tree seeds on e-bay?

Still need to call Ken at cycle X to find out about those carbs. It's lookin like the whole back half of the bike will need to be changed.

[jpc002]

Well, I finally installed the dynojet kit and air pod filters on the cb650.  It has a lot more power and the carbs run more smoothly. I recommend doing it (it'll put you about $200 in the hole, but it's worth it).  The kit comes with two main jets- a 110 and a 116.  The carbs I had already had 120 mains in them so I was kind of shocked to "downgrade."  But MRieck is right.

I think there is a definite lack of understanding regarding carb tuning especially in regards to fuel circuit overlap. I also think to many guys over fuel their engines finding the ability to say "I run 135 mains" macho.

*****One problem!!!!  The K&N air pods (there are 2 pods that come in the kit and "Y" into the carbs) do not fit perfectly!  The crome tip of the air filters, opposite of the inlet to the carbs, hits up against the frame.  The only thing you can do is send them back or do a little cutting on the boots that hook onto the carb.  The rubber is pretty easy to cut and it'll still clamp on well, but just a heads up if anyone was looking into K&N pod filters for their 650...

I'm still thinking about putting a MAC exhaust on: 4-1.  Also thinking about getting a cam from a '79 650 off of ebay to install on my '81.  They sell them for as cheap as 10 bucks so it is worth the shot.  Anyone have experience with these?

[Pinhead]

[mg1045]

JPC what carbs are you running? Well actually what carbs is everyone running? I've got the vb44a's on mine. I do have a full rack and half rack of 44c's, but they are completely gutted. Does anyone know where you can get carb parts? I'll need more than just a carb kit.

Is that a pic of the 79 cam? That's a pretty big difference on lift.

[Pinhead]

Is that a pic of the 79 cam? That's a pretty big difference on lift.

I THINK so.

[Buber]

This is a difference between the european cam and US cam. All european 650 had 50hp only.

[Ibsen]

I think it it was Germany that got the 50hp 650. In the rest of Europe, at least in the UK and Sweden, it got the 63hp cam.

[mg1045]

If that's true what about using a 550 performance cam? Does anyone know the specs of our cam?

Web Cam lists 2 cams, high performance street & hot street.

[cb650]

The "HOT" 550 is 1mm more lift than the stock 650.   Dont know what its worth but shouldnt need any mods to the rest of the 650 valve train.



                             Terry

[Soos]

The "HOT" 550 is 1mm more lift than the stock 650.   Dont know what its worth but shouldnt need any mods to the rest of the 650 valve train.



                             Terry

Can anyone confirm the fitment of a "HOT" 550 cam in a cb650('79) head?

l8r

 

[mg1045]

I found the megacycle cams while searching too. There was a thread on this also over on Hondacb650(I think that's it).

I was looking for 550 cams, but all I could find was stock. If I can get my hands on a decent priced hot/street cam I'll try it.

I do have a extra cam out of a 650(not sure what year) but it looks like the 2nd cam in the pic a few posts back. I need to measure the total lobe. I think I read somewhere that stock was 33mm and the better cam was 36mm. Does anyone have the specs of a 650 cam?

[paulages]

i forget who i talked to- either megacycle or webcams (think it was the latter)- who said that though they don't list the 650 cam, they have the numbers somewhere and can do it.

[Ibsen]

The 63 hp cam: Honda pn 14101-426-000, cam lobe diameter 35.6mm IN and 35.3mm EX.

The 50 hp cam: Honda pn 14101-426-690, cam lobe diameter about 33.1mm on both lobes.

[jpc002]

Too much tuning to figure out.

I didn't have any trouble tuning the 650.  I put the 116s in it (stage 3) because I had the K&N air filter & I took the baffles out of the pipes.  I don't know how the 110 is.  I'm sure it would run better though.  The kit comes with detailed instructions if you find that your bike is having trouble idle, whatever.  It takes some tinkering sometimes getting those jets tuned just right, but I think it is worth it.  I didn't even have to adjust anything when I installed the kit though.

The 63 hp cam: Honda pn 14101-426-000, cam lobe diameter 35.6mm IN and 35.3mm EX.

The 50 hp cam: Honda pn 14101-426-690, cam lobe diameter about 33.1mm on both lobes.

Ibsen- Where exactly did you find this info?

[Ibsen]

The 63 hp cam: Honda pn 14101-426-000, cam lobe diameter 35.6mm IN and 35.3mm EX.

The 50 hp cam: Honda pn 14101-426-690, cam lobe diameter about 33.1mm on both lobes.

Ibsen- Where exactly did you find this info?

This info was provided by a German CB650 owner who converted his bike from a 50hp to a 63 hp version. And the measurements for the 63hp cam are correct. I have measured the 63hp cam in my 650. I also have a spare 63hp cam that measure the same.
Also the carbs, or more correctly the carb internals like the jets and the needles were different on the 50 hp version. So the way I understand it those who have the 50hp cam and put in a 63 hp cam won't get the full effect before they have changed the carbs to fit the 63 hp carb specs.