CARB ADVICE NEEDED !!! MIKUNI ON 73 PINER

[gooey]

 OK OK OK I KNOW ! I am SUPPOSED to just leave this bike stock,, BUT I hate to,, so please help me !  Any advice on Mikuni carb size on my 73 'piner I really wanted to go with a 34mm ,,, but I have a parts bike with a GREAT 36mm mikuni (a Suzuki ... dont they make for a GREAT traction aid ) ... anyway ... any experience too much ?? i think probably so,,, but your input would help !  I know this bike was setup as an enduro bike when new,, and as an mx'er can stand more carb,,, but is this too much  THANX A BUNCH GUYS ! ! ( remember Im new at all this ... i dont want you ALL to lap me next year ... not all at once anyway !

"real" name Mark McGrew, friends call me Gooey,, we are all friends here I think !



Edited by - gooey on 10/16/2000  9:24:05 PM

[opiden]

gooey:
I'm wondering the same thing.  I bought a '77 175 GS-6 about a year ago.  The bike was not running, but had a 36mm mikuni on it all hooked up like the bike had been running with the carb.(throttle cable, intake, etc.)  I'm just now getting to rebuilding the engine and am getting close to needing some info. also.
Kurt


 

[gooey]

mine is the earlier ( black) motor .... different port work from the factory,,, or so Im told ,,, I am runnning a much modified,, shorter pipe,,, ports will be matched ,,, will have a lil lower gearing,,,    anyone out there can help either of us

[Chris Brown]

Test reply

 

[Chris Brown]

Guess this works.
I have a 73 Piner with the black KTM motor and a 34mm Mikuni carb. I bought the bike as a wreck (restorable core) now completely restored and pictured on the old pog site.
I don't believe it ever really ran after someone put that carb on. When I went to rebuild the motor it had a new top end on it! Imagine, a bike that hadn't run for 10 or fifteen years with a new top end.
Well, the carb was way too rich in the mid range and someone had tried to shave off some of the slide for more air. It ran great on the idle/pilot, and great wide open, but would just load up on any mid-range settings, and was un-rideable. I ended up going to a leaner slide needle (can post all jet #'s if needed) and it really screams now.
There should be no reason you can't make a Mikuni work. The 36mm seems a little large though. You may need to jet it leaner. Jetting can be a real pain. Sudco has all the jets and needles for them.
Chris

 

[gooey]

wow Chris ! THANX !

Let me start by saying ... AWESOME JACKPINER !  when I was looking at this thing,,, trying to decide if I wanted to pursue the project,, I saw a pic of yours,, and it convinced me ! NEAT BIKE ! nuthin like mine will be,, I am not nearly that skilled or patient,, a job well done !

Anyway,, back to the carb ... you are pretty much confirming what I already believed to be the case .. I was thinking 32-34 mm Mikuni would be realistic,, but I have a 36 and wondered if anyone had anyexperience ...

I think the Bing is probably a good carb (mine is on it's way to australia now),, but I have been away from bikes long enough that any famiarity I can achieve will be a good thing,, and the Mikuni is or at least was familiar to me at one point in what seems to be a previous life by now.

I would appreciate your 34mm jetting pointers,, and I realize that my final outcome will be different than yours,, with all the variables involved,, but a good starting point from someone who's been there will definately be a help !   I am NO WHERE near that stage yet,, so ,, no hurry ,, I am examining/ planning / replacing parts and mods as the bike comes apart this time ( in the past I have done it during re-assembly,, and that left a little to be desired ) .. so everything is backwards at this point !

Would appreciate the help !

Anyone wanna trade a 36mm round slide Mikuni for a 34mm

And,, thanx again !

[Chris Brown]

The 400 has an old Bing, and it's okay but I like the Mikuni design is better and I think it works better. Both will flood the engine if the petcock is left open when the engine(s) is shut down. Perhaps a new needle and seat would correct that but it's a simple matter to [remember] to shut the cocks off when I stop. Neither will overflow when it's running although I've experienced that with Keihin(sp?) carbs.
The tickler on the Bing makes cold starting possible, but still difficult until enough gas gets to the combustion chamber. The Mikuni's choke makes cold starting mostly a first kick affair.
I ended up using a Uni air filter from an XR Honda in the Jackpiner. Seems to fit and work very well. Vintage Iron had a GP filter for the 400. I had to do quite a bit of glass repair on the airbox of the 'piner as it had cracked behind the expansion chamber. It has an EC Birt pipe that makes it better suited to MX style riding than for trails. There's a big hit on the top end with sufficient pull from low rpm's. Vintage Iron had an original air box to carb boot in great condition. Another problem solved.

A friend of mine has an aircraft parts plating company and hard-chromed the spokes, cad plated the nipples, axle spacers, brake arms and rod, and foot pegs. The frame was stripped and then primed and painted with automotive urathane paint (Dupont Centari with a cross-linker/hardner)as well as the hubs and body work. I didn't go with the expense of powder coating advised for durability, but I have not had a problem with chipping and wear with the epoxy type paint. The original shouldered steel rims were rusted out and bent square. Not wanting to spend $400 for wheels and spokes, I was able to find a couple of chrome steel Takasago rims from a salvage yard in decent condition that had the correct nipple cup angles. Vintage Iron had fenders, bars, throttle assy, new cables, front springs and seals, and Works shocks for the rear. Al had a repro tank strap, counter sprocket, and kick start and shift levers. I did have to replace the crank seal behind the ignition rotor.
It was a very satisfying project. The finished bike is actually ridable. Maybe one of these days I'll get to race it.
The 400 had nice alloy rims so I went with a set of Buchanan stainless spokes and nipples for it. Vintage Iron had new (Progressive) front springs and seals, the rears have pretty decent (still) Bilstein shocks. The side covers were missing and Rick found those for me as well. There was a rats nest (for real!) in the airbox and I doubt it had run for at least 10 years. Vintage Iron found me a new piston and barrel, Al had a new top end bearing and I used a carb boot from a Maico. I got new bars and fenders, and rest of the bike was finished the way I did the Penton.

Best of luck on your project.
Chris.



Edited by - Chris Brown on 11/01/2000  12:22:39 AM

Edited by - Chris Brown on 11/01/2000  12:23:25 AM

[gooey]

thats pretty neat ! your 175 especially looks awesome !

I could still use some jetting tips .. I will use the 34mm Mkuni ... thast been my experience on other bikes as well,, easy starting,, easy maintenance,, and crisp throttle response ... I threw away several amal's and replaced 'em w/ mikunis when I was riding triumphs,, and every time was a success!

I have sold my airbox,,, for the type of riding I am planning I think a K N style filter will work wonderfully ... although I am a LITTLE concerned about pipe clearance ,, I have obtained a much modified shorter pipe of unknown origin,, probably will use a wiseco piston ( the lesser of the evils at this point) .. the ports will be matched,, and it will be geared just a tad lower I think ... being able to forego some top end for some off the berm power,, modified KYB shocks in the rear,, and revalved forks ,,,  I have aquired a pretty decent pair of 70 vintage Akronts,, and even though they hold a lot of mud,, they are SO cool .. they SCREAM vintage MX !   paint will be a similar to the original color,, but metallic,, with orig decals ...  I have replaced the seat with a newer KTM ( 79 or 80 250) seat that is in being upholstered ... the one concession I am making STRICTLY for looks is "PENTON" embroideried on the rear sides of the seat in blue ... wont hold up,, but hopefully will look nice for at least awhile

My original goal was to build a period correct MX version of this bike,,, but has evolved into a new goal: too see if a guy that hasnt raced MX since about 75 or 76  can be competitive amongst the Novice 250 guys on a quick handling, somewhat well prepared bike of considerably smaller engine size !

but,, I still could use a lil jetting help !  ( hint hint )

I am not powdercoating either,, there are some paint coatings that hold up very well,,, I spent some time ( about 8 years ) in that industry .. and your choice for centari and hardener is a very good one indeed ...