A A A A Author Topic: Air / Fuel Mixture Threaded  (Read 174 times)


Air / Fuel Mixture Threaded
« Started on: 09-Jun-20, 16:31 »
Hi all,
I have a 1980 cx500 - which i've owned for a couple of weeks now.

Bike is not running right. Bike starts to splutter at around 4k-5k rpm, but idles and starts fine.

I initially though it could be a blocked main jet - or poor a/f mixture.

I discovered on the weekend that the previous owner had stripped the air/fuel mixture screw on the RHS carburettor.

Do i have any chance to use a helicoil to repair this? Or is it prefferable to replace the carbs completely.

Does anyone have experience with this?

Cheers in advance!

PIC - for reference (my camera is busted at the moment)
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Re: Air / Fuel Mixture Threaded
« Reply #1 on: 09-Jun-20, 18:02 »
The problem you have is unlikely to be carburettor related.

Engine breaking down between 4,000 and 5,000 RPM is a problem with the Stator coils that feed the CDI.

There are several fixes for this BUT the best options are to replace the Stator or bypass it using a new electronic ignition system such as a Raesan unit from www.rae-san.com

As far as repairing your idle mixture screw thread goes CX Phreak from this site may have some info as he is the current carburettor guru.



Re: Air / Fuel Mixture Threaded
« Reply #2 on: 09-Jun-20, 18:05 »
The carb body likely needs to be replaced but I'll try to verify size and thread tomorrow.

You're not doing yourself any favours with those aftermarket mixture screws.


Re: Air / Fuel Mixture Threaded
« Reply #3 on: 09-Jun-20, 18:18 »
I just had a read through some other posts (very new member here) I'm going to perform the stator test this weekend also. Sounds exactly what problem ive got. Plus whatever my carb has got going on. thanks guys for getting back to me. Can't wait to get this thing running well


Re: Air / Fuel Mixture Threaded
« Reply #4 on: 10-Jun-20, 08:07 »
Thanks for looking in to this.

I'll definitely replace with an OEM screw - however, if the carb body is repairable - i'd rather go down that path.

Thanks again for your help with this - it's great to see such a community for these bikes.


Re: Air / Fuel Mixture Threaded
« Reply #5 on: 11-Jun-20, 13:07 »
Sorry, got busy when I went out to the shed last night and forgot to check this.

 The thread appears to be somewhat oddball at M6 x .75 mm pitch.

 I don't know if there's a helicoil for that size.

 I may have a stray carb body. Is it left or right and what are the carbs numbers?


Re: Air / Fuel Mixture Threaded
« Reply #6 on: 11-Jun-20, 16:23 »
Cheers for that - i had a quick look online - looks like there may be some kits available. However i've taken down the carb body no.

The carbs are still on the bike - so i couldnt see the RHS carb (the one with the problem) but the LHS carb no. is VB 36AQI9 - Let me know if that makes sense - it was hard to make it out.

Also I performed the stator test.

Here are my results - See attached photo ( i performed hot and cold - hot was worse

I had a look to - it seems that the previous owner has installed an ignitech (it looks identical to an ignitech to the photos online) - However the bike is still having the stumbling problem.

The results show that the ignitech should fix the issue - but obviously the problem persists.

1/5 - 121
2/5 - 103
3/5 - 232
4/5 - 120
6/5 - 104
7/5 - 0
9/5 - 360
9/8 - 192

A/B - 2.5
B/C - 1
C/A - 3

A/Grnd - nil
B/grnd - nil
C/grnd - nil

What do you guys think? Should i go for a rae-san? This is all pretty foreign to me - i'm alright at wrenching, but electronics is very foreiign to me.

Thanks in advance!



Re: Air / Fuel Mixture Threaded
« Reply #7 on: 11-Jun-20, 17:41 »
The ignitech units bypass some of the most common failure points in the 35 year old electronics BUT they require certain original parts to be working properly to get a stable system.

Do yourself a favour and install a Rae-SAN ignition as it uses all modern electronics and bypasses all of Texas 35 year old electronic ignition parts.

Interestingly you are the second person in the last couple of months to have a very similar problem where the installed ignitech unit was not working properly. The other bike had faulty pickup coils which the ignitech needs, to know when to generate the spark.

The Rae-SAN units are made by Rayman, a member of this forum, and he is always available to help if you have any problems along the way.

I would choose the Rae-SAN system that also supplies the Hall effect pickup as this is the most complete system and will bypass all the old ignition electronics in the Bike.



Re: Air / Fuel Mixture Threaded
« Reply #8 on: 11-Jun-20, 18:03 »
Hey Seagrass, Thanks for the response.

I was thinking as much - I had a look at the Rae-San webstire last night. Awesome to hear he's a member of this forum.

I'm not sure which kit should get? On the website theres a 12V conversion kit - A kit for ignitechs - and half and full kit - do you have any suggestions?

Maybe I should ask Rayman? Let me know what you think.




Re: Air / Fuel Mixture Threaded
« Reply #9 on: 11-Jun-20, 18:06 »
I was thinking this one - thaat interfaces with the ignitech.


( i dont know how to create a hyperlink haha )


Re: Air / Fuel Mixture Threaded
« Reply #10 on: 11-Jun-20, 19:11 »
William I am not familiar with all of the kits and I find the rae-san website a little confusing as the item in the "pick list" has a slightly different name than the listing on the web site.

There is a kit for $90 that can be used with a known working ignitech unit. This kit appears to replace the original pickups with a Hall pickup and then wires into the ignitech unit.

Personally I would choose the $180 kit (if it suits your bike) as this kit replaces all the old ignition electronics and the technology is newer than the ignitech units as Rayman only designed and built the units in the last five years or so, long after the ignitechs were being used. There have also been reports of failing ignitech units in certain conditions.

Send a PM (personal messsage) to Rayman and get his advice.



Re: Air / Fuel Mixture Threaded
« Reply #11 on: 11-Jun-20, 20:45 »
Thanks for the advice. I'm tossing up between those two options.

 I'll shoot Rayman a message.

If the problem could occur in the ignitech unit, it makes sense to swap it out.

I'll keep you posted .

Thanks again, I really appreciate it.


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