If I throttle too fast or shift into 1st my bike DIES

1941 Views 12 Replies 8 Participants Last post by D-Fresh, 11 mo ago

mcd0minguez

Discussion Starter · Jan 21, 2022 (Edited)

So I installed the Mikuni VM34 from Murray's Carbs on my 1978 CX500

We cleaned out the gas tank and sealed it

Added new Honda NOS petcock (but the outlet fuel line is smaller than the Mikuni's)

New fuel lines and fuel filters (should I use 1/4, 5/16, 3/8? seems like these VM34s gulps)

New 2-1 quick throttle cables ran on top of frame spine under gas tank like recommended

If I throttle too fast the bike dies out.

After it warms up and I shift into 1st, the bike also dies if I don't give it a little throttle first.

These carbs are said to be pre tuned and jetted specifically for the CX500 w/o air box.

Any thoughts?

I attached a video, click link below:
iCloud

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1 - 13 of 13 Posts

SirFoxx

· #2 · Jan 21, 2022

you may need to up your idle speed a hair to fix the stalling issue.

also you cannot go 100% instantly. there was just a thread about this. you have to roll into the throttle. punching it immediately causes a huge drop in vacuum pressure, which the carb cannot immediately change with.

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jlbutler81

· #3 · Jan 21, 2022

What he said^ Murray's also a member here. I have to believe that somewhere on his site he warns people about how to throttle control his Mikunis vs the stock CV carbs.

But the thing with it stalling in 1st only after warming up, without knowing what your idle speed is, might indicate a problem with your clutch. Maybe just a simple clutch adjustment, or like Sirfoxx said idle speed too low. Warm clutches for me usually slip more, not less but maybe hot it's swelled and more grippy.

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Randall-in-Mpls

· #4 · Jan 21, 2022

Your first step should be to contact Murray.

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murrayf

· #5 · Jan 21, 2022

call me dont fiddle with the carbs don't adjust the idle or you will throw them out of whack
if you don't have my number look on the letter you got with the carbs or go to my website or pm me

and to those trying to help the mikunis idle faster than the stock carbs we set them to be idling at 1350 or so
if the bike is not idling there something is wrong PLEASE remember all of our carbs are tested and calibrated prior to shipping
ALL of them

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cbxmoe

· #6 · Jan 28, 2022

Well I guess I should introduce myself,-Jeff, east central mn. large mechanic background. I own an 80 CBX, 2 1100f's 2 V65 sabers. 5GL1200's which includes 2 84 naked's, one of each color, plus 3 GL 500's and 1 GL650, 2 VTR 250's, and an ST1300. I joined this group to get ideas for an off-road GL project. Soooo, my question is, why deviate from stock carbs? What is the performance gain? I mean these are 500cc bikes. From what I have read everybody complains about the performance once modified. "You have to roll on the throttle slowly" What? Really? And Murry- 1300 rpm idle? Do you really think you can improve upon those Japanese fellas in the white lab coats? I'm not trying to be a Debbie downer here, but my opinion is the minimal power gains are not worth the drivability issues. Please correct me if I'm wrong, throw me under the bus, whatever. Thank you all for listening?

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SirFoxx

· #7 · Jan 28, 2022

cbxmoe said:
Well I guess I should introduce myself,-Jeff, east central mn. large mechanic background. I own an 80 CBX, 2 1100f's 2 V65 sabers. 5GL1200's which includes 2 84 naked's, one of each color, plus 3 GL 500's and 1 GL650, 2 VTR 250's, and an ST1300. I joined this group to get ideas for an off-road GL project. Soooo, my question is, why deviate from stock carbs? What is the performance gain? I mean these are 500cc bikes. From what I have read everybody complains about the performance once modified. "You have to roll on the throttle slowly" What? Really? And Murry- 1300 rpm idle? Do you really think you can improve upon those Japanese fellas in the white lab coats? I'm not trying to be a Debbie downer here, but my opinion is the minimal power gains are not worth the drivability issues. Please correct me if I'm wrong, throw me under the bus, whatever. Thank you all for listening?

stock carbs are fine if you are wanting stock performance. between the different 500's ive ridden (cx500, vf500f, vt500c, etc) they are very lethargic, and have a less than exciting power curve.

performance gains is ~15hp. very, very noticeable. and yes, if you go from idle to 100% throttle instantly, its going to stall. its the nature of the slide carbs.

and yes, murray has improved these bikes. i wouldnt call the throttle rolling "driveability issues". its just a different characteristic of slide vs cv carbs.

if you dont want the hassle of power gains, then dont buy the carbs 🤷‍♂️

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jlbutler81

· #8 · Jan 28, 2022

cbxmoe said:
Well I guess I should introduce myself,-Jeff, east central mn. large mechanic background. I own an 80 CBX, 2 1100f's 2 V65 sabers. 5GL1200's which includes 2 84 naked's, one of each color, plus 3 GL 500's and 1 GL650, 2 VTR 250's, and an ST1300. I joined this group to get ideas for an off-road GL project. Soooo, my question is, why deviate from stock carbs? What is the performance gain? I mean these are 500cc bikes. From what I have read everybody complains about the performance once modified. "You have to roll on the throttle slowly" What? Really? And Murry- 1300 rpm idle? Do you really think you can improve upon those Japanese fellas in the white lab coats? I'm not trying to be a Debbie downer here, but my opinion is the minimal power gains are not worth the drivability issues. Please correct me if I'm wrong, throw me under the bus, whatever. Thank you all for listening?

You should maybe read up on his carbs and background before shitting on his product. His product serves a specific purpose that's very well documented here.

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reclinedrelic

· #9 · Jan 28, 2022

cbxmoe said:
Soooo, my question is, why deviate from stock carbs? What is the performance gain? I mean these are 500cc bikes. From what I have read everybody complains about the performance once modified. "You have to roll on the throttle slowly" What? Really? And Murry- 1300 rpm idle? Do you really think you can improve upon those Japanese fellas in the white lab coats? I'm not trying to be a Debbie downer here, but my opinion is the minimal power gains are not worth the drivability issues. Please correct me if I'm wrong, throw me under the bus, whatever. Thank you all for listening?

cbxmoe have you read through this thread? First impression of Murray's carbs

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Randall-in-Mpls

· #10 · Jan 28, 2022

cbxmoe said:
Well I guess I should introduce myself,-Jeff, east central mn. large mechanic background. I own an 80 CBX, 2 1100f's 2 V65 sabers. 5GL1200's which includes 2 84 naked's, one of each color, plus 3 GL 500's and 1 GL650, 2 VTR 250's, and an ST1300. I joined this group to get ideas for an off-road GL project. Soooo, my question is, why deviate from stock carbs? What is the performance gain? I mean these are 500cc bikes. From what I have read everybody complains about the performance once modified. "You have to roll on the throttle slowly" What? Really? And Murry- 1300 rpm idle? Do you really think you can improve upon those Japanese fellas in the white lab coats? I'm not trying to be a Debbie downer here, but my opinion is the minimal power gains are not worth the drivability issues. Please correct me if I'm wrong, throw me under the bus, whatever. Thank you all for listening?

Welcome, Jeff!
Jumping, apparently blindly, in to the deep end of this thread might not have been the best introduction.
To answer a couple of your concerns: The Honda engineers' goal was to strike a balance between performance, fuel efficiency, durability, emissions, etc. Any of those can be increased at the expense of the others. If you're unconcerned about economy, significant gains can be had in power output. For your off-roader, you probably want increased torque more than the high-end power these Mikunis provide. Improvements can be had in adjusting exhaust design and maybe rejetting. Murray can offer good insights on that as well.
Throttle sensitivity is in the nature of direct-slide carburetors. Constant-velocity carbs were developed so we can pretend to be more skilled riders than we are. The concession is a slight loss of precision in throttle control. That said, I'll admit I haven't ridden with direct-slides since I was a teenager. For my street riding, stock CVs are good enough.
Let's start a new thread regarding your off-road GL: CBXMoes's off-road GL
Also, as you're in east-central Minnesota, keep your calendar open the Saturday after Memorial Day. I'll be posting soon regarding the 15th Annual Twin Cities Spring Ride.

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cbxmoe

· #11 · Feb 10, 2022

Randall-in-Mpls said:
Welcome, Jeff!
Jumping, apparently blindly, in to the deep end of this thread might not have been the best introduction.
To answer a couple of your concerns: The Honda engineers' goal was to strike a balance between performance, fuel efficiency, durability, emissions, etc. Any of those can be increased at the expense of the others. If you're unconcerned about economy, significant gains can be had in power output. For your off-roader, you probably want increased torque more than the high-end power these Mikunis provide. Improvements can be had in adjusting exhaust design and maybe rejetting. Murray can offer good insights on that as well.
Throttle sensitivity is in the nature of direct-slide carburetors. Constant-velocity carbs were developed so we can pretend to be more skilled riders than we are. The concession is a slight loss of precision in throttle control. That said, I'll admit I haven't ridden with direct-slides since I was a teenager. For my street riding, stock CVs are good enough.
Let's start a new thread regarding your off-road GL: CBXMoes's off-road GL
Also, as you're in east-central Minnesota, keep your calendar open the Saturday after Memorial Day. I'll be posting soon regarding the 15th Annual Twin Cities Spring Ride.

OK, so I don't get on here a lot or often, so 1st I will offer my sincere apology, I am not trying to shit on anyone's product, although I will acknowledge that it certainly sounded like it. Also, no, I have not read the recommended threads but given time I will. I will also say that modifying these bikes to the extent of the thread I jumped blindly into does not interest me, at this time. If I want more power I simply get on a different bike. I do however respect everyone's choice to do as they see fit. Randall, I did see the links to the off-road projects that you posted and will look into them with great interest. I thank you for that. What I have read on this forum is a lot of very nice, knowledgeable people trying to help one another, and I can definitely get on board with that. Again, my apologies and I shall strive to be a better forum member. Thank you!

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mcd0minguez

Discussion Starter · #12 · 11 mo ago (Edited)

Update* My mechanic did tamper with Murray's pre-set adjustments messing everything up. In the end he ran the 2-into-1 throttle cable incorrectly. So Murray's allowed me to ship the carbs back to them for a FREE readjustment, then I ran the throttle cable on the back of the spine of my CX500 like instructed and everything now works as meant to.

However, the coil-over-plugs plastic connected to the coil boot thingy cracked. Murray's coil-over-plug upgrade bolts onto the valve covers, and my friend may have accidentally bumped into something. Does anyone know if I can just order a single replacement?