1973 400 CR

The carb nut hits the cases with no air bell at all.



In Fact, there's a pretty good groove where it has been hitting for a while. I noticed it while prepping the cases, but thought I'd wait until it was back together to see how things line up. The carb is a nice snug fit on the intake. My friend who does all my machining is copying the original and making a custom shallow bowl nut.

My only other thought is whether this carb originally came with one of the bowls that doesn't have a removeable nut. As the pics above indicate, some had a drop down well (which might also hit) and some were nearly flat across the bottom of the bowl.

it would have to be something like that, someone has replaced and not measured. must shake the crap out of the fuel when running...fizzy fuel diet..

you would think but alot of stuff is mounted solid like that. old mikunis on snowmobiles are same way..

It's not so much the solid mounting that foams the fuel. It's the vibration of carb against cases that does it, and it can cause a dangerously lean condition. That's why I'm being so picky about it. I'll post pics of the new part when it arrives.

id be right on to that, that's a high speed, no throttle seizure every day

'zactly.

Looks like you have a solution in progress. I am still stumped why this was happening in the first place though. Attached are 1/36/106 OEM parts pics for reference. Are they different from the 114?

Float Bowl Nut OAL - 18.3mm (Inside depth - 16.3mm)


Float Bowl Nut Head - 9mm


Float Bowl - 35.6mm


Main Jet in Float Bowl

If you end up using a different float bowl you may also need to reconfigure some parts inside your carb also . Looked thru Bing carb parts I have at home and found 2 different length main jet holders and jet needles . If your main jet is where Vinskord is showing his , it may be too long .

Couldn't post last picture

Wow. Those pics are above and beyond. So helpful. I measure the same bowl and nut. I did try to trim the nut to 17mm but it's still touching. Don't want to go any further.



The main jet in mine looks to be the same or slightly more recessed.



So, for now I'm going with the custom bowl nut from my machinist. Will be a while before I can get that back and follow up with photos. I am looking for the forward carb clamp if anyone wants to part with one.

Got the rear fenders lined up nicely. That's a little tricky when a) you've never seen one of these bikes before, and b) there are no holes to start with in the plastic. I'm happy with the fit. Bolts were trials and will be replaced with proper length and nylock's.

More pics to compare. It is hard to believe manufacturing tolerances would account for such a difference between 400's. If you think of additional pics you would like to see, let me know.

Carb Intake to Float Bowl Nut - 57mm


Intake Upper Length - 71.7mm


Distance from top of motor to bottom of intake:

Can't help but offer a small opinion... Are you using the correct gaskets and most importantly, red phenolic spacer between the cylinder and intake manifold? Do you have more than one manifold to be sure something hasn't been altered?
Been around a few of these bikes and don't recall any problems with the float bowl coming in contact with case....
Pat

I purchased gasket/fiber spacer/gasket from Hall's. It's not red, but the total stack is pretty thick. The only other thing I can think of is that my intake might have less angle at the cylinder mating surface. I wonder if the previous builder (it was a modified 70's race bike that "got bent" and was parked to rot) milled that surface for some reason to fit the original frame that they had modified.

My machinists has all the parts in his hands, and says he can easily get me a few mm clearance. I'll post pics when they're back.

Ordered a pipe. This is a ProForm.

You have to shave the fins to run this pipe. Oddly, this head was already shaved.

That's an interesting pipe configuration. The header is really long and the way the expansion chamber is incorporated into the final turn is also interesting. Did you happen to ask what the performance advantages were, any dyno graphs?

On another note, did you get your intake milled? The stock intakes had a 15 or 22 degree angle on the gasket surface to allow the carb to clear the cases.

I don't know anything about this pipe except that it was available. Tried for a long time to get a stock pipe, but dollars and condition didn't match.

The intake is already angled, and doesn't appear to have been machined flatter. I did consider having it milled at more of an angle, but I have a machinist friend who made a custom low profile bowl nut. It's a work of art. I'll try to get a photo up. Bottom line, I now have clearance between the nut and the case!

I was looking at your pictures and based on this one the intake isn't angled which is why the carb was hitting the cases but it sounds like you got her fixed by machining the carb nut.


Heres a pic of a stock intake. You can find them on ebay from time to time if you ever decide you need one.

What ? Really that's your garage workshop ? I envy it !