100cc reed valve

[chuck]

I put a reed valve on my Penton 100 and tried it for the first time today. At high rpm it spits and sputters. I wasn't able to try different jetting at the track. The plug looks a little rich but not too bad. I'm running a Mikuni 26mm. Is there a general rule of thumb with a reed valve that you go richer or leaner? Any ideas?


Thanks,


72 125 Six Days
72 100 Berkshire
74 250 Hare Scrambles
72 Wassel

[Larry Perkins]

Did you drill the reed holes in the piston?  

Larry P

[chuck]

Yes,the piston was dirlled. The work was done by a friend who is a motorcycle mechanic. He's done other reeds for me on other bikes. Unfortunately, he is out of town on vacation and I can't get a hold of him.

thanks,


72 125 Six Days
72 100 Berkshire
74 250 Hare Scrambles
72 Wassel

[john durrill]

Chuck,
We have installed a few reed kits over the years and what we have found is you usually need to go up in carb size 2 to 4 mm to get the benefit a reed can give you.
 You usually need to add boost ports to gain any performance on piston port engines. On engines like the Sachs , Zundapp you will probably loose HP and performance with out the added "boost " Ports.
 See this dyno chart on a 125 Zundapp that was modified with a reed kit below. It will give you some idea on what just a reed does on a high output piston port engine.



The size of the reed cage and how its mounted to the cylinder play a big part also.
 Rule of thumb on jets is richer every where 2 sizes or so on stock carb.
john d.

[chuck]

John,

Thanks for the info. The manifold has a place to add a boost bottle. I was trying without it first. That might make the difference, getting more air. I'll also go to a larger carb as you suggest.


Thanks,


72 125 Six Days
72 100 Berkshire
74 250 Hare Scrambles
72 Wassel

[Ron]

Hi Chuck,
If you plan to ride ARHMA events, the max carb size for 100cc bikes is a 28mm.
Also, I think boost bottles were really just a sales gimmick and have a minimal if any effect on performance.
John is refering to additional ports being added to your cylinder.
Boost ports open the intake port through the back wall of the cylinder (generally at an upward angle), creating additional transfer ports.
These ports are fed through the holes in the back of the piston from the crankcase.
Ron

[firstturn]

If the max size is a 28mm carb try and use a Bing as it actually flows more that any other brand of carburetor that I have used or tested (on a flow bench).  If anyone disagrees with this please let me know as I am always willing to learn new ideas?   ......I think it goes as old dogs can learn new tricks from smarter people.[]

Ron Carbaugh

[linglewn]

Ron,
When it comes to 2-stroke engines, experience trumps smart any day. Your advice is valuable.

Nelson Lingle
73 Jackpiner
74 Jackpiner
71 DKW 125

[brian kirby]

Uncle Ron is 100% correct of course. I have a 28mm model 84 Bing on my Berkshire and I can tell you its as fast as most reed valve 100s including the Suzuki TM and those $10,000 Hodakas are half a hair faster. Other than some very mild porting, a "Cranke" modded stock pipe and the 28mm Bing the engine is stock.

Brian

[john durrill]

chuck,
Ron C. and Brian are giving you very good advise.
 The Bings really  do flow more air than the Mikuni. The type 84 can still be found in 28 mm. Some Spanish bikes used the 28 mm .
If it were my cylinder from what we have seen over the years I would add 2 ports in the rear or one about the same size as a Zundapp bulletin shows. I have a fuzzy jpg that Speedy sent me years ago on the Zundapp Reed kit mod.
 I will post the Fuzzy jpg below. But an note to Speedy could get us a much better copy to look at if you decide to go with just one dead center in the rear port.
 The ring stop pins are what usually determine where we would add the " Boost " ports.
 
john d.

[firstturn]

John,
  Is this a map to the subdivision you live in?  Just kidding you are always so  complete in your descriptions and you pictures replace a thousand words.  Thank for the jpg.

Ron Carbaugh

[chuck]

Good adive from all. We did add two boost ports. I think I'll try the 28mm Bing and play with jetting before adding a boost bottle. I think they were a gimmick as well.

Thanks again for all the advice.

Chuck


72 125 Six Days
72 100 Berkshire
74 250 Hare Scrambles
72 Wassel

[john durrill]

chuck,
 Could you post the approx. angle the 2 ports were cut in at please?
The Sachs uses a off set dome in the combustion chamber. I think the Zundapp had a hemi type chamber. The angle could be important to anyone else that installs a kit.
Thank you,
john d.

[[email protected]]

All the guys racing the Hodaka's are using a 28mm Mikuni. I personally have not tried a Bing but if it is better flow than this should be a great improvement. Both John D and Ron C have great information here. Not sure if I had ever seen a $ 10,000.00 Hodie yet but when I do I will post a photo here first :-)
Most of our bikes are stock or slight mods like one of Dane and B.J's PVL ignitions ( a must to have !) new HT pipe and maybe a Clarke tank other than that stock, stock, stock...
Paul

[brian kirby]

LOL...I figured the $10k Hodaka comment would draw you out Paul! You know I'm just messing with ya.

I think you should try a 28mm Bing Paul. Look on eBay for a late model (74-76?) Bultaco Sherpa Bing, it was a 28mm even for the 250/350 and it has the cylinder side male spigot like a Mikuni to bolt into a rubber manifold and not the Sachs/KTM female style where the carb bolts directly to the cylinder. The Sherpa Bing would also be an ideal carb for a reed valve modified Sachs like Chuck's bike. They come up on eBay occasionally and usually go real cheap because they are so small. I bought a NOS 28mm Sherpa Bing a year ago for $25 just for the parts.

Brian