Hypercharger for K-68 Carburetors

The K-68 carburetor by Pekar needs to be balanced.  This is simply a small tube which runs from on carburetor to the other.  Much has been said about installing a hypercharger/balancer which is available from Europe on E-bay and other sites.  Ken Ulrich at U2 cycles has managed to sort out the problems with casting and finish and is offering them at a very reasonable price.  Ken can be reached at machrat@aol.com.

   The following is from a post by JBG on the Russian Iron forum (www.Russianiron.com) John rides a Ural but we wont hold that against him as the carburetors are the same on Dnepr’s.  Please ignore the fact that the photos show a Ural engine, and please don’t e-mail me to point out that it is not a Dnepr.  Its all about the carburetor and the hypercharger kit.

I had ordered a Ken Ulrich "U-2 Special" machined inertial hypercharger/balancer assembly last month, and today I finally got around to installing it on my 650 rig with the Pekar K-68 carbs.

Ken did a nice job with the machining, the surfaces are clean and flat and he expanded the mounting holes as needed so that they will fit the American import rigs (mine originally had Mikuni carbs with a slightly larger distance between the threaded mounting holes in the heads).

Ken's kit comes with the two machine adapters/flanges, some quality heater type rubber hose, hose clamps, longer threaded studs, and two gaskets.

I lost one of the gaskets that came with the kit. And I wanted to experiment making my own gaskets with some thick fiber exhaust manifold gasket material that Bill Glaser gave me. Maybe I'll post the gasket making part in another thread. So I did not use the gaskets that came with Ken's kit.

I also used different threaded studs than the ones that came in the kit. When I installed my K-68's about a year ago, I used studs that 8mm coarse threads on both ends. The studs that Ken sent are coarse threads on one side and fine threads on the other end. I probably could have just got some fine thread nuts to solve the problem, but I decided to pick up some 8mm x 50mm studs with coarse threads on both ends from the local Ace Hardware. I really like to torque these threads down to avoid a leak, and I just felt better torqueing the thicker threads. It probably doesn't matter; it's more of a "piece of mind" thing to me.

Installation was pretty easy, just remove the branch tube (I have CEET tubing on my rig), remove the fuel lines, pop off the carbs (I did not disconnect the cables or pull the slides, I just set the carb on the cylinder while working on it), put the longer threaded studs in, slide a gasket on, then the flanged adapter, then another gasket and then the carb. I taped open the throttle wide open, so I could peek down thru the carb and thru the flanged adapter to the head so I could make sure everything lined up OK. I also test fit everything before installing it. Once everything was in place, just put the lock washers and nuts on the ends on the studs and tighten them down. You will need a "stubby" wrench to tighten down the nuts on the inboard sides of the carbs. Once both sides are tightened down, just fish the hose between the two sides between the alternator and the air box, slide the clamps on each end of the hose and pope the hose ends on to the flanged adapters and tighten the clamps. Put the fuel lines back on the carbs and reconnect the air inlet branch tubes and you're done.

Again, I used some home-made gaskets out of thicker gasket material, and I even coated them with some copper high-temperature RTV sealant. Again, it might not be necessary to do this, but it probably wouldn't hurt and more fidgety old me "piece of mind" crap, since I’ve already done the "Holey Piston" thing once before due to a carb flange leak.

    

Now you are ready to do a standard carburetor adjustment.  A tip from Ken Ulrich “I don't try to pinch off the hose to synch the carbs, I do it by ear, a little more experience and I think I will have that down flat, maybe. But in my view using a vice grip and a couple pieces of thin plywood strips to protect the cross over hose , then set up as usual with a twin max or what ever, after you remove the vise grip, you will note an increase in rpm, back off both throttle idle screws evenly to suit your idle needs... The balance tube needs to be about 1/2 in I.D. to work right IMHO, a tiny tube will only affect the idle, if at all. In theory these work on a pressure pulse at low speed, as the speed gets higher there is less pulsing so the advantage goes away, off road and in city traffic they are in their element. As for cost, we will do up a set and mail them out for 50.00 post paid. They will do a couple of other things, if you break a throttle cable, the one operating cable will thru its carb, supply you enough mixture to the broke side to run you home, it did on mine, very nicely I might add, the other thing is it will mix the output of each carb with the other a bit at lower rpm...just seems to me to be a good thing, if you have a small air leak or maladjustment...that’s about it… Ken”

This from VW Nate… “To get the full effect of a balance tube, you should always pinch the hose shut when balancing the carbs as the tube will offset some minor unbalancing @ idle speeds.”

Finally this was posted by Christian Schneider on the Russian Iron forum in regards to the kit that he purchased from a European seller on E-bay. 

“At first, I was quit disappointed with the quality!

The casting was very poor, and the bore was not consistent at all.

I spent much of the day port matching and grinding, creating gaskets and making the appropriate longer studs.

When I finally had everything assembled I attempted to attach the most important part...... the hose!

Well I'll be, It didn’t fit! The hose was about 3 inches too short. A quick trip to the local pep boys and a 3 dollar purchase of a two foot long section of 5/8 heater hose fit the bill.

With it completely assembled I tickled the carbs, and started the bike. Amazingly, in 48 degree weather, with no choke, the bike started up instantly on the first kick. (Usually in this weather it required choke and about 5 kicks).

First immediate impression, wow first kick, and then hmmm idle was WAY high. I figure this has to do with the balance pipe drawing from both carbs???

I adjusted the screws for an appropriate idle and off I went.

I IMMEDIATELY felt an AMAZING increase in power. The increase is substantial (with sidecar).

Once the engine was wormed up I proceeded to make my way to a quite stretch of road and continued with some speed tests.

My little Neepr topped out at 135km/h, yes 135 km/h !!!!!!!

Top speed before.... a little over 110km/h.

I am very pleased.

And here are some photos that Christian provided showing his kit installed on his Dnepr.