Anyone with CR carbs on their CB?

I am having endless carb issues and thinking of biting the bullet and buying fresh carbs. There are the CR carbs or the CycleX Mikunis (which are cheaper)

I asked on SOHC 4 forums if anyone had experience with the CycleX carbs and got no replies, so I want to try. If anyone has any sort of tips or suggestions they are all welcome!

The cost of new carbs is high, but i have odds and ends I can sell and will have 2 sets of stock carbs to sell which shold help offset it.

The bike is a 78 cb750

just a silly question but are you absolutely certain that the problem is with the carbs?...
what kind of issues/symptoms are you having?

Good question. My bike mechanic buddy is certain it is the carbs. As we keep cleaning them, we have different problems with cylinders firing. We adjusted the points at one point, and it helped to get the bike starting. However, now that it is starting, cylinders that were running properly before are not now. The plugs are new and look good when pulled, so he insists the carbs need more cleaning. I dont really understand why just a good cleaning once cannot solve the issues, but he is positive that he needs to take them off again. Compression is good across the board, he keeps saying it is fuel issues.

To make matters worse, so many people seem to be saying that the CR's do not necessarily make their bikes run better out of the box. I am also using a 4-1 with the big original muffler just jammed on for tuning, so maybe that has somthing to do with the issues, aside from the carb. I really really want a reliable bike because I am not mechanically inclined, and I have a couple grand in this now and still have yet to get it running top notch. These new carbs with shipping and exchange will cost me a grand, but if it can solve these issues so I can finish making my seat and get the custom muffler ideas sorted I will be as happy as the day we trailered the thing home in January.

Not to mention i will be able to drive it over to T.O. to meet up with some of you guys. Looking forward to that. I better learn to ride first, dont wanna be a poser :-\

Did you investigate if your coils are functioning well?

you said nothing about syncing the carbs.. have you done that?

Dumb question, but can the carbs be synched without gauges? I havent seen him use anything but wrenches. He was the sole mechanic at a bike shop for 4 years so he swears he has had a million carbs apart.

I did ask him about the coils, and he just said they were fine. Is there a way to test them? If the carbs are ok and upgrading ignition is all I need I will save a bunch thats for sure. Could rid of the points completely

Thanks guys for your input

hmmm...
If you are in the GTA area, you'd best call Tony... 647 888-1194

locO leoN said:

hmmm...
If you are in the GTA area, you'd best call Tony... 647 888-1194

Click to expand...

Ya i am in oshawa, but the bike is in Niagara on the Lake. If the project continues its slow crawl I will bring it up here and call Tony. I have noticed the posts online noting his skill.

Just 'cause you buy new $1000 carbs doesn't mean they're gonna work right outta the box. Some jetting will be needed....CR carbs are not for reliable town machines....stock carbs are for reliable town machines.
Again, what are the symptoms? So all cylinders are being intermittent? Any hissing and spitting from the carbs?(intake leaks)
Will it run on starting fluid? Meaning a short blast in each carb just before cranking it over.
I had a basically new CB350f(1200 miles) that I chased intermittent stuff around on for a while, only to find the ground lug for the wiring harness, not the battery, was loose and on a painted portion of the frame. Took care of that and all was good. Still had to flog the poor little thing to get it to move out. That's a 350Four for yuh!

Nate in PDX

Speaking from experience as a relatively new CB750 owner, I highly recommend getting a good set of carb synch gauges. I got mine on eBay for less than $100 from sportingforless. They come with four gauges, vacuum hoses and a variety of screw in spigots to fit most carbs. You can find them cheaper but this set had the most options for tuning other bikes.

Get the kit, learn how to do it, then recoup your investment by charging your friends, to synch their carbs! This is easy to do and takes less than 30 minutes start to finish. I think crazypj is correct, you don't need CR carbs. The CB's are fine if they are cleaned AND rebuilt with new gaskets, jets and needles.

Scott

Skyeye said:

Speaking from experience as a relatively new CB750 owner, I highly recommend getting a good set of carb synch gauges. I got mine on eBay for less than $100 from sportingforless. They come with four gauges, vacuum hoses and a variety of screw in spigots to fit most carbs. You can find them cheaper but this set had the most options for tuning other bikes.

Get the kit, learn how to do it, then recoup your investment by charging your friends, to synch their carbs! This is easy to do and takes less than 30 minutes start to finish. I think crazypj is correct, you don't need CR carbs. The CB's are fine if they are cleaned AND rebuilt with new gaskets, jets and needles.

Scott

Click to expand...

+1 with Scott..

HOWEVER, that being said... if you absolutely insist on throwing away $700....my paypal address is: noelocol@rogers.com ;D

Cool guys, I hear ya. My buddy is the type that always thinks he is right, so he doesnt take my suggestions well. And I dont have anything to tow the bike away from his shop. I know he hasn't used any gauges to synch, thats for sure.

I was thinking earlier how the CR carbs are way to pricey for my first bike and first build, so I will try and get the others sorted.

I havent heard any kind of hissing. I know that the exhaust gaskets are leaking, as the header pipes dont flare like the stock 78's do, but I dont think that would have anything to do with fuel issues and he says we can double up the copper gaskets, so I bought more already. I did paint the whole frame, but this guy has done wiring from scratch on 100,000 dollar builds, and I have heard him mention how just a simple ground can cause havoc, so I can most likely rule that out.

So basically, it was super hard to start, and when we did get it running, one or two cylinders were not firing. So cleaned the carb, played with the points, and now it starts right up, BUT a different cylinder is not firing now, and the others are working properly. Thats where it stands now.

It has been great rebuilding the bike with a friend and free labour, but maybe I need to get it up here and pay for another mind to work on it....we will see what happens this weekend. He better not be busy, I can only even get to the bike on weekends since its in niagara and i am working in oshawa now. hurtin.

4-1= bigger main jets, right off the bat. You running pods too?

ahhh i did not know that about the 4-1 ...nope no pods. Any idea what jets would be best? I wanted to go with pods, but read a bunch of negative reviews about them.

For the pipe you are going to need to go up one size I think on that bike it would be a 115 but best to check. Another issue you might be having is that the accelerator pump probably needs to be cleaned out 78 cardbs are F model carbs and therefore have an accelerator pump just off of carb number 3 if that is not clean you can have different cylinders that will be starved for fuel and not run.

I don't have CRs on my Honda but I do have them on my Triumph . Good carbs but if you plan on running them invest in a carb synch tool . I synch my CRs at least twice a year and they behave differently when in cold weather to hot weather . I would think they're be a pain in the balls to get 4 CR carbs playing together tight all the time . I thought about CRs on my CB but changed my mind . Too much of a hassle . However they do look cool . 8) I had them on my SRX as well which was a tad easier . 2 carbs to 1 piston so one is certainly going to compensate . Not as fussy .
But for a CB750 4 I think would be okay if you can synch yourself . If you would have to rely on a shop get the stockers rebuilt or even look into Cycle-X's 4 into 2 Mikuni . But I think there would be clearance issues pending on how your bike is set up . I know for mine there would be .
And 4 Mikunis they want STUPID money for . Hope that helps .

Ya I read abit about the 4-2 Mikuni, that is an option, but will still cost me 6-700 bucks. I will talk to my friend about synching carbs. I know he has had the accelorator pump apart so I dont think that would be the issue, not sure.

ya i think if i buy another cafe, I will hunt for an XS650 and have less carbs to deal with .lol

a synch does do a lot of good, but you can actually mechanically synch those carbs pretty accurately. air leaks i think are one of the biggest sources of problems with those

Do you mean stock carbs get leaks?

PJ has this subject nailed! These are old bikes and prone to rubber parts hardening, particularly when they are subject to heat, like the carb to head rubber manifold.

Try this:

I replaced the hose clamps with some NORMA stainless ones I got from West Marine online. They're the same ones Carpy sells. These are 10mm wide versus the stock ones that are 9mm so you distribute the clamping force over a wider area. More important is that the stock hose clamps SUCK! They tend to concentrate the clamping load at a point, they corrode. Go stainless my man! Short of getting new rubber manifolds, this might be the best and cheapest way to give you some piece of mind.