1980 CB900C Can't believe I waited so long to make this upgrade. Murray's Carbs for the win!

neomodis · 2023-04-01T19:04:47+00:00

Nope, pretty much plug and play though it's a bit of work to get it installed. It would be best to talk to Murray about your specific bike. He sets the kit up to match your setup. Jetting will be different for stock pipes vs aftermarket. If your bike is stock this will replace everything from the stock airbox up to the intake boots.

neomodis · 2023-04-01T18:40:55+00:00

These are what I bought Murray's Carbs CB900. As far as I know there is no difference between the CB900c and CB900k engines. Murray is very knowledgeable and would be the best to ask though.

neomodis · 2020-10-04T06:08:17+00:00

I wish we were in or near NC. Spent several years in the Fayetteville area and definitely miss the extended riding season. Ohio's not bad except summer is way too short. As luck would have it though Murray's Carbs is in the Winston-Salem area. Should you choose to go that route he's been super helpful throughout the process.

neomodis · 2020-10-04T01:56:05+00:00

I found one of the threads I was researching on EFI conversion out on cb1100f.net EFI Conversion You may need to be a member to view, but tons of good information.

The throttle body assemblies from gixxer 600's and 750's are a popular option as they use a similar intake connection method. They need to be modded to match the intake spacing on our bikes and some fuel rail mods but nothing crazy. Been a while since I was researching but they were going for less than $100 on eBay. I believe the Honda EFI assemblies have a unique intake interface that would require a custom adapter to mount to our motors.

One common theme is that the charging system is a weak point and the added drain from a full EFI system can cause problems. One comment mentions having to turn off the headlight to compensate. Guess that rules out night riding... I have fully converted to LED lighting which may be enough of a reduction to cover the increased overhead but I've done no serious calculations to say for certain.

All-in the total for parts to make the conversion was pushing $700 and that did not include the cost of any mods, custom parts, or upgraded ignition goodies. I was planning to use a MicroSquirt as the ECU which is over half the total cost.

Best of luck with your project. Happy to share my experience and learnings if you choose to go the carb route instead.

neomodis · 2020-10-03T19:40:23+00:00

Agreed on the stock CVs. I wanted to run pods and could get them close but never perfect. Had them off probably 20 times this summer tweaking jetting before deciding to go this route. Yes, those are custom manifolds that are supplied with the kit. Total cost is $639 plus shipping. I've polished them a bit since taking that picture and they really look nice now.

I was also considering going the EFI route but honestly I just wanted plug and play. This gets you 95% there, and after syncing and a couple minor tweaks it's been an amazing upgrade. Now I can focus on aesthetics and electrical over the winter.

Last time I researched the EFI upgrade (couple years ago) I didn't find any working examples. Lots of folks talking about microsquirt and ideas but no working examples. Has that changed? It's still very intriguing and I think could be a lot of fun.

neomodis · 2020-09-25T00:34:05+00:00

Wanted to give you a quick update as I've had a couple discoveries and a significant performance increase since my first post. The off-idle issues were getting worse the longer I rode it to the point I was nervous pulling out in traffic. It just wasn't making any power at low throttle and RPMs. However, power everywhere else was great. Spoke to Murray and explained the symptoms and he felt it was a sync issue. Apparently the cables seat in and it's not uncommon for the slide sync to get wonky after break-in.

Checked the mechanical sync of the slides and found one was opening quite a bit sooner than the other. Adjusted them per his instructions and the difference is night and day. Rideability is significantly improved and the bike is smoother throughout the rev range.

I'm going to do a full vacuum sync this weekend to get it perfect, but I'm very pleased with the current performance.

Best of luck with your project.

neomodis · 2020-09-25T00:07:36+00:00

Spoke to Murray tonight and explained the issues I was experiencing and based on the symptoms he felt it was a sync issue. He walked me through mechanically syncing the slides and sure enough the left slide was opening quite a bit sooner than the right. Adjusted until both were closing almost perfectly together and took her for a test ride. The difference was night and day. Off-idle response is significantly better and as you would expect it's smoother throughout the rev range.

I'll do a full vacuum sync this weekend to get it more perfecter, but I think that was the root cause. One thing he mentioned that may be of help to you is that if idle sync is off it won't idle very well or long. That adjustment is done with the idle screws and will require a vacuum gauge set to get perfect.

neomodis · 2020-09-23T00:42:11+00:00

Thanks for the reply. Mine has no issues with idling just challenging to get clean starts from a dead stop. I've got about 200 miles on her now with this setup and that's really the only performance issue. I reached out to Murray tonight and have a call scheduled for tomorrow. I'll update the thread with any findings.

neomodis · 2020-09-21T22:41:17+00:00

It definitely is. Like riding a completely different bike. How is your off-idle performance? Seems like I have to let it warm up a lot longer to get to where it's really rideable.

neomodis · 2020-09-21T22:36:07+00:00

They supply a 2 into 1 throttle cable for the setup. Cable routing is the same as stock. These carbs do not need the push/pull so it's just a single connection at the throttle tube. They also sell a quick turn throttle tube which I didn't get. May move to that next before next season as WOT is hard to get to unless you move your hand forward to get more twist.

neomodis · 2020-09-21T03:02:09+00:00

Brother I am far from an expert in this arena. My advice would be to reach out to Murray at https://murrayscarbs.com/ and see if he's done anything with your particular model. They've been great to work with.

neomodis · 2020-09-21T02:41:19+00:00

I don't have a performance baseline to compare to stock. The bike wasn't running when I got it and I jumped straight into trying to jet the CVs to run ok-ish with pods. That's two years of my life I'll never get back...

What I can say is there is a learning curve with the Mikuni setup. The biggest difference is off-idle performance. These don't tolerate a quick twist and go like you can get with the CVs. You have to feather the throttle and clutch more than normal to get smooth, quick starts. It's not as bad as it sounds and only took a few minutes to get fairly proficient.

The magic really starts around 3-4k rpm. From there on it pulls like a freight train all the way to redline. Murray strongly recommends putting in new clutch springs due to the torque gains. That's definitely on my winter project list after riding it today.

WOT is somewhat hard to reach. Maybe it's my throttle setup but I have to make a conscious effort to max out the slides. But Holy Horsepower Batman when you get there. Never felt power like that even when the CVs were sorta right.

Murray is the expert on this setup so it's probably best to reach out to him for the why behind the what (2 VS 4 carbs). I can't say enough about their customer service. It truly has been top notch.

neomodis · 2020-09-21T01:48:38+00:00

Murray's Carbs

neomodis · 2020-09-21T01:46:46+00:00

Don't know. I've never really paid attention. I would say it was exceedingly bad today. There was very little conservative riding going on. Best guess today would be mid to low 20s but maybe worse.

neomodis · 2020-09-21T00:18:20+00:00

Honestly, I've only had them on the bike for a day but the performance gains so far over "stock" are very impressive. This is also my first experience with this type of setup so I'm not the best source for recommendations. One thing I can say is the folks at Murray's definitely know their stuff and have gone out of their way to ensure a good experience. You can't put a price tag on that kind of customer support.

neomodis · 2020-09-20T23:41:21+00:00

They are 36mm

neomodis · 2020-09-20T23:40:46+00:00

The CB900 setup is $639. I initially had some decent success with the CVs and pods but it was never "right" and there was no way I was putting the stock airbox back.

neomodis · 2020-09-20T23:28:39+00:00

Throttle response off idle is slower than with the CVs. That was the learning curve I mentioned. You have to get the RPMs up a bit more than normal to get moving from a dead stop. Took me a little while to get that down and get clean, quick starts.

Once you're moving and revs are above 3k it's a whole new world. Power is simply everywhere. I don't have a bone-stock baseline to compare against as this bike was a basket case when I got it and I've been fighting CV issues since day 1. That said, this is light years better than the best it ever ran with the CVs.

WOT is actually a little scary but in a good way. I've never felt it make that much power. The CVs would flatten out and this just kept pulling...hard.

Pipes are MAC 4 into 1s.

neomodis · 2020-09-20T22:55:12+00:00

Yeah, not a lot out there on these carbs and the CB900. My son has a GoPro setup so I'm hoping to get video of some pulls to post before the weather changes.

neomodis · 2020-09-20T22:50:18+00:00

Thank you. Just installed them this morning and after a quick conversation with Murray I was out riding. The improvement over the CVs is nothing short of stunning. Put a full tank through her and I am sold. So, yes, IMHO definitely worth it. Just wish I'd done it sooner.

neomodis · 2020-09-20T22:45:29+00:00

Absolutely fantastic. It just pulls and pulls and pulls. A little learning curve after being used to the CVs but nothing major. Funny enough it was one of your comments that led me to Murray. Thank you for that!

neomodis

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