Four Stroking B+

[robert campbell]

Hello,
New to your site. Just finished a mild restoration on a 1972 Hodaka 100 B+. I am an old moto crosser from the early 70's and had a chance to acquire the B+ and could not resist! Never owned one before but saw a bunch of them. Got the book and the history is so cool and fascinating. what a neat chapter in small bore two strokes.

I am a good carb guy and rebuild and rebush all American muscle car carbs and do old school tuning. Have restored a 72 HI Kawai and own a 75 GT Suzuki 750 Lemans.

Anyway, my Hodaka "four strokes" at 1/8 to 14 throttle opening. I set the points with a break light and they open precisely at the factory timing mark. The cylinder was bored and an new piston and rings installed before I got it, but it has low miles on it. I serviced the gas tank, fuel system, air cleaner, and carb. The only mod that I see to this bike is the Bazani expansion chamber that I thoroughly cleaned and it has a new packing in the silencer. Bike runs great at 1/2 throttle and above. Pulls great with no missing at WOT. And pulling my 220 pound body is no easy task for a 100 cc bike! To much eating of the linguine!!

With the above I have a few questions for the group.

1. What is the main jet size for a stock B+ with a 20 MM Mikuni?
2. What is the stock setting for the slide needle groove?
3. Would you drop or raise the needle to help with the four stroking?

I do not know if the carb was rejetted for the expansion chamber or not.

Attached is a before pic. I will attach an after pic in a reply to the post

Rob

[robert campbell]

After pic! Please ignore the wrong seat foam. I ordered the wrong foam and Paul fixed me up!!

Many thanks to Paul and Bruce Young for helping me through this mild resto. I even laced and trued my first wheel from a used rim provided by Bruce!!

Rob

[robert campbell]

Pic with the new seat foam and my articulating coffee/bee holder!! I ride very slow and in the daylight only.

Rob

[robert campbell]

that would be a beer holder!!!

[Dale]

Rob,
Very nice bikes! My first Hodaka was a brand new B+ and about the same time that I purchased it, my older brother purchased the 500cc Kawi. Same year, orange. Scary fast and so much fun!

Your stock carburetor components would be a 95 main, 25 pilot, Needle 4F6 on the 4th notch, slide 2.0 and Air Screw 1 1/4 turns out. Some fine adjustment on your air screw might help. If not, the needle can be lowered (clip raised) to lean out the mid-range. It sounds like you have some good experience, but be careful not to get it too lean. A little rich until it is fully warmed up is a good thing...

Welcome to the world of Hodaka.
Dale

[Bullfrog]

1/8th to 1/4 throttle is smack dab where the slide cut-away is doing its thing to control mixture.

What slide do you have in your carb?

I may have a slide around here I could loan out for confirming tuning, I'll have to look. My carb parts tuning inventory is stronger for the 24, 26 and 28mm carbs - but I might have some stuff for the 20.

Ed

[robert campbell]

Dale/Ed,
Thanks for the responses! I will be with the bike this weekend. Idle screw If I remember is very close to 1 1/4 turn out, but I will try some adjustment there first. It is amazing how critical the idle circuit is to the transition to low speed operation!. If this does not cure it, I will go at the slide needle and see where it is at and if I can drop it down one step.

Ed,
I will bet it is a stock slide, but is there a number on it and if so where should I look?

If none of the above works, I will pull it off and catalog the stuff inside. By the way I am running Lucas 2 Stroke oil at a 40 to 1 mix. this was recommended by my local Suzi/Kawi/KTM dealer. One of the guys is a vintage moto crosser and he recommend this mix. Keep in mind that I am just putting around and not racing. I have yet to red line her and doubt I will unless by accident. I bet talking about oil and mixture ratios have been beaten like a dead horse on this site!! I removed the oil injection on the 1972 Kawi H1. Ran it on 40 to 1 Royal Purple Two Stroke oil and it worked great.

Rob

[Bullfrog]

The cut-away number is stamped on the bottom of the slide. Easy to see when you have it out. When you check the slide, examine it closely to assure that the bottom end of the slide has not been modified in any way.

If the diagnosis of throttle position (1/8th thru 1/4) problem range is precise, then a little bit of change can be achieved by adjusting the pilot air screw and/or needle position - but those changes will have other effects too.

As you know, the pilot circuit provides fuel at ALL throttle positions, so leaning it out WILL lean out the mix at ALL throttle positions. The effect of changes in the pilot circuit get smaller as the throttle opening gets bigger . . . but the effects are not negligible. (Noting that the current setting of 1 1/4 turns out for the pilot air screw is pretty much what we would want to see.)

Dropping the needle will have some slight effect below 1/4 throttle (which may help) - but it will also have some effect above 3/4 throttle (which may not be needed or wanted).
Ed

[taber hodaka]

Rob the throttle valve (slide) is stamped on the lower side . The smaller numbers are richer and the larger numbers are leaner. In the good old days we filed them if need be. Like Ed said the slide is for 1/8 to 1/4 throttle. ----------Clarence

[robert campbell]

I will look today at the slide. Might not respond until Sunday. Time for lake and beer time!!!

[viclioce]

Hmmm. Have you checked to make sure your choke is working correctly? You might verify that the starter plunger is not stuck short of being closed, and that also the rubber seat in the plunger is not torn or cut allowing an overly rich mixture at low speed. Not to mention that you may have clogged air passages in the idle circuit, which can be verified by unscrewing the air mixture screw to see if it makes a difference where it is set. If it makes no difference, it isn't getting any air. I had a similar problem on my B+ after running the tank down to empty. I kept stalling out & leaning the bike over to get more fuel into the petcock from the right side of the tank. At first I thought I had fouled the plug, but pulling the pilot jet showed me otherwise. ; D Victor

[robert campbell]

Went through the carb in carb cleaner, washed it down and blew it out with compressed air. Rubber seat was fine as well as the rubber cover on the choke. Choke seems to work great and it is needed only for about 2 to 3 minutes. Bike has the typical stuttering right after choke but a couple blasts and I cleans right out. Came back in from the lake but will be with the bike in the a.m. Going after the mixture screw and the slide needle in the morning. If that does not allow me to tune it in, then I will bring the carb in and catalog the parts.

Other than the low throttle opening stuttering, it runs awesome.

Thanks again for the responses. Many minds can figure out anything!!

Rob

[robert campbell]

Just got back from the lake. Started to get ready to remove the slide, but stopped and checked the air mixture screw. I spun it in gently and yup 3/4 turn out. I set it at 1 and 1/4 turn out and she started right up. Idled perfectly, so off we went for a spin. Almost all 4 stroking is completely gone. Woke up the low range a whole bunch and the bike runs very nice!! Great transition from idle to low speed to high speed. Nice and smooth

I may experiment a bit more, but one mo question. I assume that backing the mixture screw out leans the idle mixture on a Mukini? I got the car carbs figured out and some are the opposite of others.

Thanks for the help guys!!!

Rob

[Dale]

Rob,
The screw controls the air. So yes, opening it up provides more air thus leaning the mixture. There is some good reading available on Mikuni carburetor adjustments. If interested, I can find some links for you. The air mixture is adjusted to the best idle with the target to be between 3/4 to 2 turns out. If it idles best at more than 2 turns, then a smaller pilot jet is called for. Conversely, if it idles best when turned almost all the way in, then a larger pilot jet is called for.
Dale

[robert campbell]

Dale,
Went to the lake today and gave the B+ a good long ride with a common screwdriver in my pocket. Opened it to 1 & 3/8 turns. Ran even better!! Opened it to 1 & 1/2 turns and even better yet!! Amazing how much just a small turn makes. Idle picked up a bit too, so brought it back down.

First time I have really rode it for a long ride. Just around the two lakes near my lake cabin. Got her nice and warm for the first time and she runs so great. No 4 stroking anymore and the low end is a lot stronger! Runs like a top and starts first kick every time!

Thanks for the help guys!!!

Rob

[Dale]

Awesome

[Bill2001]

Be aware of this: I have a new Mikuni for my W'Bat 94 and I noticed that the slide cutout was freshly milled and the slide was marked "2.0" instead of the spec'd "2.5". The cutout dimensions were the same as my old 2.5 slide, so it seems that a spare 2.0 slide was remachined to 2.5 dimensions and not re-marked. So be careful.

On my carb, it runs so much better with a
#30 pilot jet instead of the stock #25. And I'm surprised with how sensitive and critical the Idle Air Screw adjustment is. Much more so than on the Bing carbs ony other bike.

[robert campbell]

when it comes to jets a set of "pin gauges" is a great tool. I run 48 IDA Webers on my high zoot 289 in a Mustang and the jets out there have been drilled many times. What they say is not what you get. Even the emulsion tubes may have been soldered up and re-drilled in another area.

If you seem to have a problem that conventional wisdom and the help of others cannot solve it may be a drilled out jet!!

Rob

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[Bill2001]

Jet drills are useful for R&D or troubleshooting if you don't have a full set of jets, but use factory jets for the final tuning.

[robert campbell]

Hot weekend in the Pacific NW!!! Going to enjoy my Hodaka at the lake!!! Thanks for the help guys! Almost feel like I could attend Hodaka Days next year! She ain't a museum piece but darn nice!!

Rob

[Dale]

Rob,
You must come to Hodaka Days next summer! You have the perfect bike to participate in every event that you wish. You will see every kind of Hodaka there from pieces in a box to the museum quality bikes. That vast majority are somewhere in between, just like yours.
Dale