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Discussion Starter · #1 ·

I saw this video and I'm curious what the benefit is, if any.

I feel like my carbs need to be adjusted differently because my CB400 doesn't have an air box, just two pods. Someone told me that it will change the mixture if there's no air box. As it is now, if you go more than halfway quickly on the throttle, it bogs down pretty bad. Any ideas?

Premium Member
254 Posts
The benefit to a single carb is the simplicity of it and that's about it in my opinion.
With your set up it is quite possible to need slightly differing adjustments but there are many factors that contribute. IN some ways you need to think that you essentially have two single cylinder engines. In other ways you need to think of the whole things as a complete "system".
Your description indicates you've got some anomaly in one or the other carb that needs to get sorted out. You also need to know the health of the "pump" side of your engine. Is one cylinder way off in compression, valves adjusted, etc etc.

While the owner/builder did a nice job on the single conversion and he obviously likes to tinker, my opinion is the intake manifold is of poor or at least far from optimal design (but I realize you can only do so much). And while it idles great, does it fill or expand the performance envelope of the engine design?
My 2 pence-

Premium Member
24,208 Posts
I see zero benefit from doing this other than the engineering exercise and the simplicity of tuning 1 carb. There is a 'sticky' on making pods work here in the SOHC section and there are any number of topics concerning it if you use the search function. Here's info on successful applications I've collected
1980 CB400N
I will find the carb number asap
I didnt shim the needle since I didnt like the idea of fixing the needle with glue or locktite.
So I jetted with 90 and 125 for the main jet - and extended the intake with 54 mm. Samco Silicone hoses - 76 mm long. ... 35c3bc390d
The filter are cheap pod filter, 60 mm (equals ca. to the 54 mm hose + 4 mm x 2 thickness)
Float level is stock.
The bike has a quick throttle response, but a lousy km/l- around 15 kilometres pr. liter, not sure what that is in mpg.
On the highway the intake are very noisy, almost like a vacuum cleaner

Firstly I couldn't get the carbs to work without stacks fitted before the filters - no problem cut some round 2" rain pipe at same length as the original rubber airbox ones (about 3") - warm the end with a hot air gun and pass the end over the carb bellmouth and let cool. Cut some slots and fasten to the carb with clips.

Fit the pods over these and clamp on with clips - note the cheap pods will need to be a bigger size as you must get the little rubber shelf that's inside over the stack otherwise it disrupts the airflow. Better quality pods don't have this rubber shelf.
The stacks smooth the flow and allow the cv carbs to work again as designed.

Now you need one washer under the needle to lift it - the needle is non adjustable so when you do this, screw the needle retainer all the way down until it just touches the needle but allows the needle to still move - you will see when you do it- if you screw it fully down the needle gets locked rigid which wont work.
Once your happy, that it moves but with no slack, spread varnish or glue at the top of the retainer to stop it coming loose.

Now leave float heights stock and slow running screws too - rejet to mains 95 and secondary 127.5. - yes that's a big jump but trust me it works - result is fantastic - absolutely no flat spots or hesitation, backfires or spitting and power is full on, yet you can still do top gear roll on.

Mine has a straight through pipe, so if stock you might have to drop to 90 and 125 if too rich. The midrange mains does need to be big though otherwise it will hesitate.

So pods and cvs do work - ignore the doubters, but you need the stacks! - good luck!

1980 CM400T
I'm using the K&N part number RC-2330 now, with good results. There's so many variables to this, I think. Engine condition, carbs, personal preference, etc. It took me around a year to get mine where it is now with a lot of experimenting. I see threads started about this all the time on several forums. Just referred someone to this over on do the ton, too.No stack right now. The filter is completely open, and doesn't appear to be blocking the port for the piston. Before I changed to the K&N, I jetted them at 125 and 78. I think that's where I left them anyway. With the cheapo pods, it cut out on the top end. I'm gonna guess 8k, cause I took my tach off. Now it pulls as long as I can hold the throttle. I have noticed a slight off idle hesitation since I changed filters, but it's very subtle. And I just checked my plugs. They're just a shade darker than light tan. I'm at around 50 mpg now. I honestly don't remember it ever getting that good with the airbox, but it's been a learning experience with getting he carbs right. I also probably need rings soon. I'm at 140 lbs dry on my compression tester. It isn't my every day bike, though. Especially not with the clip ons and rear sets. Simply isn't set up for long rides or every day conditions.
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