Topic: Yamiya Tank - Carb Linkage Clearance Issues

[celebutante]

Recently I've had a bunch of work done on my '74 CB750K4 by a high-end repair/restoration guy (he's almost overqualified to work on a SOHC CB - his shop is full of all manner of exotic European bikes). My tank and side covers were not the correct factory color (Boss Maroon) and I wanted everything to look stock, and I realized it was cheaper to buy Yamiya pre-painted replacements. I ordered them, they arrived quickly and the packaging was really well done (including Kanji-language newspaper!), and as others have said, they look amazing.

Unfortunately, the tank doesn't fit properly because the carb linkage hits the bottom. My repair guy sent pics of all the spots where it hits (marked with blue tape), as well as pics of the original and Yamiya tank clearly showing how the bottoms are shaped differently. I emailed Yamiya and included the pics. They didn't acknowledge the difference in shape, but they said the clearance issue was because the carb rubbers were turned incorrectly which would angle the carbs upward. They sent a diagram showing how they should be (all it really showed was that the carbs are supposed to be as horizontal as possible). My tech has been restoring high-end bikes for decades, so ... he already figured this out on his own, and no amount of reorienting the carb rubbers fixes the clearance issue. (BTW, the carb rubbers are brand-new Honda OEM replacements and carbs are stock)

This is where I need help - my mechanic says that Honda made changes to the linkage over the years, and he's pretty confident that later on, the amount it lifted was reduced, and that a solution would be to swap out my carbs for a later year (somewhere between '75-'78?). Does this sound right? Is he just thinking of DOHC versions, which I'm sure would be an entirely different ball of wax and not compatible?

I'm really hoping I can make this work, because the tank is super nice, Yamiya doesn't seem to want to take a return, and I can't resell it in good conscience if I know a buyer will likely have the same issue.

[69cb750]

Sometimes there is room between tank and frame for cables.
In situations like this you need to route the cables through the frame triangle and over coils like the factory did.

[pjlogue]

One thing you need to check is that the rubbers for the head intake nipple to carb body are positioned properly.  slight angle changes can cause big interference problems with the carbs and tank.  What I have found useful when putting these rubbers back on is to get a 2x4 and use it as a flat plane and adjust all the rubbers so they sit flat against the 2x4 and the 2x4 is not angled up or down.  When I restored my 750 I ran into the carb lifter/tank interference problem.  The 2x4 helped get things adjusted properly.

If this does not work I suggest using a spacer at the rear of the tank to raise it a small amount.  This may give yoou the clearance you need without interfeering with the seat.

-P.

[celebutante]

Thank you for you replies. Although the guy who working on it is a pro, everything has been kind of third hand because it's been 20 miles away at his shop. I have it back now and can fool with it myself.

[BenelliSEI]

Is the stock airbox in place? If your carbs are to high up, it won’t line up with the two mounting screws either…… This drove me nuts on my Sandcast project too, but it was because the carbs were too high.

[celebutante]

>> Is the stock airbox in place? If your carbs are to high up, it won’t line up with the two mounting screws either…… This drove me nuts on my Sandcast project too, but it was because the carbs were too high.

Not sure I'm understanding the question correctly, but it's currently back together with the original tank and airbox. (and running great, wish it wasn't so cold in CT right now!)

[newday777]

>> Is the stock airbox in place? If your carbs are to high up, it won’t line up with the two mounting screws either…… This drove me nuts on my Sandcast project too, but it was because the carbs were too high.

Not sure I'm understanding the question correctly, but it's currently back together with the original tank and airbox. (and running great, wish it wasn't so cold in CT right now!)

So you are in Connecticut? Your profile shows Las Vegas.
 
Are the numbers on the boots at 12 o'clock position and numbered left to right 1234?(as you sit on the bike)
Are the cabs setting level looking from the side profile? Pictures would be helpful.

[BenelliSEI]

>> Is the stock airbox in place? If your carbs are to high up, it won’t line up with the two mounting screws either…… This drove me nuts on my Sandcast project too, but it was because the carbs were too high.

Not sure I'm understanding the question correctly, but it's currently back together with the original tank and airbox. (and running great, wish it wasn't so cold in CT right now!)

The stock air box mounts to the frame with two bolts, one on each side of the top tubes. If the bolts are there and it all lines up fairly well, your carbs are likely angled correctly. Any error at the intake manifolds is magnified at the points further away from the head……. A few pictures would really help.

[MauiK3]

Yamiya tanks are pretty spot on, can you post the photo?

[pickleknuckles]

I've got a Yamiya tank on my K4 w the original carbs from '74. Zero issues w clearance. That said, before I had my frame straightened out, there were issues that I ended up partially solving by loosening all the engine mounts and letting the engine settle vertically. The shop that measured and straightened the frame suggested I do so before committing to them to see if it helped frame alignment. Carb/tank clearance increase was the unintentional result and actual frame straightening did not noticably increase the clearance beyond that.

[seanbarney41]

Also, perhaps the rear tank mount rubber is incorrect...there are at least a couple subtly different ones used over the years and differences would affect height and alignment of clearance zones.  Also, working on these bikes is significantly different from "high end European" bikes.

[celebutante]

I know it's been a long time, but I FINALLY got the Yamiya tank mounted - bit of a tail-between-legs scenario here, but it was indeed a carb boot alignment issue. Thought this info might be helpful to somebody.

[MauiK3]

No worries, a common problem and a bit fiddly to fix.