CB450 Carburetor Needle for 723A

[Greybeard70]

My bike runs great except after I replaced the paper part of the OEM Air Cleaner with a free flowing foam it runs lean on high speed. It will easily get up to 80 mph and no faster. There was still quite a bit of throttle left which indicates it is running lean at full throttle. I then installed a larger main jet, 145 replaced with 150. Now it will easily reach 90 mph, problem now is that it seems to be too rich in the midrange causing it to have an intermittent miss at part throttle. Consistently intermittent in mid range operation. Idle is perfect , wide open is perfect. On any other carburetor I would raise the clip on the needle, dropping the needle so it will run leaner in the midrange. There is no clip on the needle with this carburetor. Are there any needles available with the clip option?
I have a spare set of needles from a rebuild kit and am considering removing a slight bit from the top of the retaining bushing to allow the needle to drop down slightly and try that. Any input from you knowledgeable guys would be appreciated.
I am pretty sure the mid range is running rich as it doesn't miss when the engine is not warmed up, but after riding a few minutes and it heats up it does exibit the issue.

I realized this is posted in the wrong forum would one of the moderators please place it in the 450 forum.

 

[ancientdad]

Moved to DOHC 450/500T Carburetion section.

Having a lot of throttle left at a certain speed does not necessarily indicate a lean mixture, gearing is a big part of why most Hondas have throttle left when they quit accelerating and are seemingly topped out. Honda intentionally geared their bikes for higher top speeds than the stock engine could attain, as a way of keeping the rpms lower at cruising speeds for better mileage and engine longevity. Plug chops at any specific rpm range or speed, where you hold the throttle at that specific speed in an upper gear for a few seconds before pulling the clutch and simultaneously hitting the kill switch to avoid the engine firing at any rpm or throttle setting lower than the rpm range you want to identify the mixture of. Then you coast to the side of the road, pull the plugs and check the color that occurred at that specific rpm.

As to your question about needles with clip adjustments available for the 723 carbs, AFAIK there are not due to the design.

 

[stl360+450]

I don't recall seeing anything about different needles for these carbs. I just took a look at CMSNL and one parts manual and didn't see anything, either. Still, that's not definitive because maybe there were revisions to the profile between different series, e.g., 14C, 14H, 723A/B, etc.

There were some other contemporary Keihin carburetors with the aluminum vacuum pistons and I wonder if you might find any helpful needle options by looking at those. I believe some Goldwings and some of the late 70s or early 80s 400 twins fall into this group.

1980 GL1000 needle $$$
1981 GL1100 needles (64A?)
1982 CM450 needle

Maybe you could even adapt another needle, whether Keihin or Mikuni, to fit in the holder.

My other thought would be to replace the foam with a paper filter element to hopefully return to where you were before the foam entered the picture. You could harvest the paper from automotive air filters and use a glue gun to seal it in place. It's not a lot of fun, but it's also very doable.

 

[RobMan]

If I remember correctly you have a 1972 CB450 like mine. I ordered the reproduction filters from from Scrambler Cycles and have been very pleased with them. Direct fit, I only had to loosen the battery box and shift it a bit for the mounting holes to line up. Comes with new filter to carb boots so eliminates any possible air leaks there. Cost a bit but worth it IMO.

Honda 72-74 CB450 72-74 CL450 Air Filter Set Left and Right - Reproduction

Honda 72-74 CB450 72-74 CL450 Air Filter Set Left and Right - Reproduction See installation steps below.The 1971 and earlier CB450 and CL450 used a different style of plastic filter housing. These filters fit the original housing on the models shown below.Original filters for the 450's have...

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