Respacing carbs - for Chuck78

[GregT]

Many years back I bought a damaged set of 29mm Mikuni smoothbores. I cut them into a pair, initially for a Gilera Nordwest, then for a 600 yamaha single. Now respaced again for a GSX250 twin. New cross shaft made up for each application using 10mm silver steel rod. it's soft enough to tap easily and is precision ground as bought. Mounting plate made up in 5mm 5083 aluminium plate. Various cable brackets taken for the original backing plate for the set of four. The cross shaft in the original setup runs in bosses on the backplate so aluminium bearings have been machined and epoxied into the carb bodies - one bearing per carb. The fuel tee is one I had in the collection - from another Mikuni set I think. New O rings of course.
Still to put a choke mechanism on and an idle stop.

The RS carbs are much easier to do as the throttle and choke shafts run in the carb bodies and the cable anchors mount to the carbs too. All you need is aluminium angle 1/2in X 1/2in to make up new rails - and some 10mm silver steel rod.

The bellmouths I make from 6061 tube. Pressed over a former. A friend has just bought a piece of Australian roadrace history and didn't have bellmouths for the 29's he's putting on it - so I did a batch of them.

 

[GregT]

One pic per post.....

 

[Kiwi Canuck]

Greg, at first I thought that was a typo and that you were replacing the carbs.

Interesting looking project, well beyond my skill level to figure that stuff out.

David.

 

[GregT]

Interesting looking project, well beyond my skill level to figure that stuff out.

David.

No it's not...It's the Kiwi way, just get in and do it....

 

[Chuck78]

Very nice! Sounds like a lot more work on a set of VM carbs vs RS34's!
VM29 smoothbores on a GSX 250?!
What kind of bike is this, and what kind of cams are you running? I assume coming from you, that it is a road racing bike, especially with velocity stacks, & the fact that you are putting smoothbores on it.

 

[Chuck78]

Due to a serious knee injury at work, and surgery with a long-term recovery, I have not gotten to the serious mods on my GS425 that I plan for re-spacing a 4 cylinder rack of Mikuni RS34's into a 2-cylinder rack... but that is definitely the next of my street bikes that is getting major attention! I've been chatting with Rapid Ray about sending him a head and cylinders for full porting job, and resleeving to fit some pistons to boost its displacement up to just under 500cc @ 489cc.
502cc maybe attainable with really customizing it by using gs450 sleeves with the bottom outside diameter protruding into the crankcase being turned down smaller diameter for less clearancing needed of the upper crankcase, but I already have 3 used old school MTC Engineering 72mm pistons for 489cc's, from a blown up GS 750 /920cc engine that I had flogged for years and suffered from an amateur valve job from an automotive shop causing razor sharp tuliped edges on two of the eight valves which caused rapidly diminishing valve clearances and ultimately detonation which destroyed one piston and the combustion chamber...
Luckily I tracked down another set of long out of production 920 slugs for my next 750 engine, and have three good pistons left for this GS twin canyon carver / backroads twisties play toy / track day project! I may get into WERA vintage racing on a small scale basis in coming years with this, but at 41 & a serious debilitating knee injury (1st SERIOUS injury of my lifetime), my mortality and preserving my prolonged youthfulness is becoming much more obvious to me...but it is still very tempting, especially after my first ride back this past weekend, post-surgery. Ohio State Route 78, twisties heaven, 412ft tall ridgeline up and down twisting winding roller coaster for 11 miles on the best stretch of it... Rt 595, Rt 555, Rt 669 as well... Pure bliss...moto-nirvana

 

[GregT]

Very nice! Sounds like a lot more work on a set of VM carbs vs RS34's!
VM29 smoothbores on a GSX 250?!
What kind of bike is this, and what kind of cams are you running? I assume coming from you, that it is a road racing bike, especially with velocity stacks, in the fact that you are putting smoothbores on it.

Little pre 82 roadrace project. There's quite a lot of interest in small "vintage" racing locally. Our tracks suit them quite well. This engine has GSXR750 cam profiles and springs, ported head and the balance shaft removed. I've had one go at a frame for it already - a mini Harris copy - but wasn't satisfied at how it was turning out. Next version will be a little different. Tony Foale did a frame in period for the small Honda fours which will suit this engine well so I'll copy that.

Post my big op last year, I found that a project I could work at as I felt up to it, helped me get back to fitness. That was the EX500 resto. Sort out what you can do at this point and just do what you can as and when you feel up to it.