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Ruined carb

Started by NYSingh, May 17, 2020, 10:43:33 PM

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NYSingh

Now that I got my RD400 running again, of course I had to do something stupid to screw it up.

On the right side carb, one of the float bowl screw holes was stripped so the screw wasn't tightening fully. Drilled and re-tapped for one size larger to "fix" it.  Then thought I might as well do all the screw holes so the same size screw is used.  Tried testing it and fuel spilled everywhere.  I must've drilled/tapped one or more of the holes crooked, because now the gasket surface of the carb is warped, making it impossible to get a seal on the float bowl - see photo.

Anything I can do to fix this, or did this screw fix screw me? Even if I managed to straighten out the carb again, I'd probably have to drill/tap even larger, and not sure there's enough clearance.

If it's ruined beyond repair, can I run them with the left OEM and the right a new replacement? Or will they not 'match'?

FYI I'm running stock carbs, Dave F modded.
1976 RD400C (SpecII pipes, K&N Y-boot, Dave F Mod, Team Scream Racing Stage-1 Porting)
Moto Guzzi V7III

SUPERTUNE

RD machine work, boring, porting, cranks and engine building.


Chuck 'SUPERTUNE' Quenzler III
Team Scream Racing LLC
1920 Sherwood St. STE A
Clearwater, FL. 33765
cqsupertune@tampabay.rr.com

NYSingh

Ignoring the price difference, and just considering performance, which is better to get:
(A) used OEM carbs
(B) new VMs

Also, for new VMs would a size up from s28mm improve performance with the TSR stage 1 porting?
1976 RD400C (SpecII pipes, K&N Y-boot, Dave F Mod, Team Scream Racing Stage-1 Porting)
Moto Guzzi V7III

Yamaha 179

I believe I have a NOS RD 400 right carb in a box on the shelf.  Contact me via email if you are interested in it.  vintspclty@aol.com
Lyn Garland

elliottles1

hi,

if it was me, firstly I would try standing the carb on four nuts, one in each corner and give the top a "slight press" whilst protected with wood. you might see it straighted out enough to seal with a good gasket. its bin fodder anyway!.

cheers
les

economan

Quote from: NYSingh on May 18, 2020, 01:53:32 AM
Ignoring the price difference, and just considering performance, which is better to get:
(A) used OEM carbs
(B) new VMs

Also, for new VMs would a size up from s28mm improve performance with the TSR stage 1 porting?
B & Yes.

Yamaha 179

#6
I checked and I do have a NOS Yamaha RD 400 right hand carb in the YMC box.  Part # 1A1-14102-00 is on the tag. 

As for needing a larger carb; for your use that is unnecessary.  The 28's supply all the fuel/air you will need.  I've road raced RD 400's in the Formula RD class with Stage 3 porting, turned cylinder heads, Swarbrick chambers, and PVL ignition systems and never had a problem with insufficient fuel supply.  Formula RD required we use production chassis parts (tank, seat, fenders, wheels,etc) and stock carbs with some type of air filter.  The VM 28s will also make the bike better behaved around town.
Lyn Garland

NYSingh

Thanks to Lyn for the part!  Looks like I'll be back in business sooner than I thought  :celebrate:

If anyone has any use for a warped right-hand carb, it's yours to take.
1976 RD400C (SpecII pipes, K&N Y-boot, Dave F Mod, Team Scream Racing Stage-1 Porting)
Moto Guzzi V7III

rodneya

I dont see how drilling could have warped the carb body.
I have drilled a few and installed helicoils after the previous owners had screwed them up and had no issues.

Got a few bikes really cheap because of things like that.