marlintec

Thanks for your explanation, Ishy. ;-) About your question, the use of rollers on the rocker arms is not related to the cam timing or valve elevation, but only with the lobes sizes. I have some math to show but this is not the place, better take two coins, fix one to the table with your finger and roll the other around the border. Imagine now that your fixed coin is lobed, then it's easy to see that as bigger are the rolling coin, smaller has to be the fixed coin to describe the same movement of your moving finger. Do you remember those children artifacts with "sprockets" inside a teethed circle, drawing flower-like forms? Is just the same. The use of rollers permits very tiny cams but also affect to the form of the lobes, being more acuted (steeped?) as bigger is the roller, being the valve timing the same. Another advantage is that lubrication could be less strict because there is no friction between surfaces but there are rolling points (like a bearing). A secondary advantage is that, being equals the rpm, the linear velocity of the lobes peaks is slower than in a traditional cam (the same angular velocity, but less radius = less tangential (linear) velocity) then the better following. The counterpart of this system is more noise and the more frequent setting of valve-rocker gaps. The problem of floating valves is more related to the weight of valves and the respective fractions of springs and rocker arm (so I use forged aluminium rockers in mi Bul4T). BUT if feel that our little TLR engines (I have also a TLR 200) don't suffer of this problem below 8000 rpm. Do you really go over this? Before the valve floating, we will suffer blowing problems at the valve ports (more diameter is needed and more valve overlap timing is needed): beyond certain velocity of gas (gas = gasoline + air) the flow becomes turbulent and almost is stopped at the entrance of valves. This may be felt as the symptom you explain. Respect to this, I like very much the Sherco design: it has a very reduced cam (in diameter and lenght) and also uses the vase-shim system to do the valve-rocker ajustment. I think Honda also uses roller rockers but only for 2 valves and uses the screw-locknut system (I was surprised to see "4-valves" in the Cota brochure, an error?). Well, anyway, I imagine that none of us is going to rev these bikes beyond 9-10.000 rpm. Cheers, JM.

Thanks Nigel, I didn't catch it. About reliability, sure we won't know anything until the first year of use. I would like to know more on these bikes. Technically, I mean. Cheers, JM.

"mont exhaust is on the wrong side" I had to flick it because Sherco's and Honda's photographers have different ways to see the best side of theirs bikes. Also, in relation to Bullfrog question, I used the diameter of both rims in both bikes to set the proper scale. Rim diameters are the only measurements that coincide in both bikes. Anycase, it was only an entertainment. Like the statistical analysis of the SSDT. If any of you are trying to see more than that (i.e. a malign attemp), please explain it clearly because English isn't my mother tongue. Cheers, JM.

Nigel, could you explain the "anti sherco stuff"? Thanks,

Montesa 4T vs. Sherco 4T (animated gif)

If the casting has high content in magnesium, the surface must be paint-protected to avoid corrossion (look at those "golden" parts on the GGPRORAGA). Probably, the impeller touched the paint and magnesium got exposed. Beta has changed ocassionally the casting compound of the cases in a constant fight against weight. Without much success, IMHO. Cheers, JM.

You could use the Dell'Orto angled-guide (sorry I can't find the word) and mantain all in the original status. When you sell the bike (or if you don't like the Keihin), it will be very easy to come back again. Cheers, JM.

Keihin has the PWK model in severals configuration, with the vent and overflow holes in different places. If your model has the vent hole at the right, it will touch the exhaust when tilting to save the fuel tap. It is very easy to drill out the other side of the carb and close the other vent. I did that on my Keihin (shown in the photo). Cheers, JM.

Hi G., sorry but I wrote the english version only for the Bul4T pages. If the new Sherco pages would consolidate, I'll write the english version (well, with all my limitations because English isn't my mother tongue) In the meanwhile, you may try a web translator like BabelFish or another one. Sorry for the inconvenients and many thanks for your interest. Cheers, JM:

Hi'all, I have just uploaded a page with a complete description about mounting keihin in a sherco. You coud reach it at http://www.terra.es/personal9/marlintec/taller/ In Spanish, by now. Cheers, JM.

Hi C. I've never seen a PWK 26, it seems to me that Keihin has the PE model in 26 mm. but the minimum on PWK is a 28 mm bore. I'm not sure of this. The PWK 28 is a very common product and this is an advantage to get parts. Anyway, your Sherco will not be necessarly more powerful with a little wider diffusor, because YOU control the diffusor area with the throttle. More on, the boot connecting carb and reed cage has 26 mm of diameter, so if you don't touch it, the bigger diffusor will not affect almost. The best of Keihin is a very clean low end and also a very clean transition to 1/2 throttle, that means a better control on power delivery. As counterpart, it's a very sensitive carb that call for adjustement when weather or altitude changes. Cheers, JM.

Nigel, statistics can prove anything about 1 fantic, but can prove something about 67 Betas, or 62 Shercos. It's a question of numbers and significance. I'm not math teacher and this is not the appropriate forum, but ask one if you want. I just post the statistics for pure divertiment. Cheers, JM.

From SSDT data: Initial riders: 280 Final riders : 202 (72 %) i.e. one of four didn't finished. About bikes: Brand Initial Final ===== ======= ====== Beta 67 49 Sherco 62 41 GasGas 59 45 Montesa 52 42 Scorpa 21 13 Yamaha 6 5 Aprilia 1 0 Fantic 1 0 That gives the following ratios Brand Reliability ===== ======== Yamaha 83% Montesa 81% GasGas 76% Beta 73% Sherco 66% Scorpa 62% About average classification: Brand Pos.* ==== ======= Scorpa 77 Montesa 82 Yamaha 99 Beta 102 GasGas 109 Sherco 113 (* if 202 riders finished, the rider on the pos. 101 was in the middle classification) Time for comments, Cheers, JM.

Hi, G. The simplest way I found was to use a car-radiator hose, 45 mm diameter, 45 mm length, and remove the thin plastic bash that goes round the original rubber. Keihin carb will fit (50 mm diameter) and the air filter also (around 45 mm) in the new hose. Without the plastic, it's very easy to fit the airbox. About the needle, I had to machine my JNH because I didn't found the JJH in near dealers. You could do the same, if you are or know an effiecient machinist. Just remove 0.05 mm from the cilindrical section. Cheers, JM.

Hi all, Many thanks for your answers. As I thougt, my problem was the needle. I got the carb with a JHN needle from stock and I didn't notice it until followed the carburation ritual without success. I tested the 50 pilot jet but it was too rich for my riding style. Finally, I got the pwk chart (attached copy) and noticed that JHN needle was 0.05 mm thicker than JJH. Finally I sand-lathed the JHN to remove those 0.05 mm. Now the bike runs well (no pinging at all) with unleaded pump gas (98 octane) and Castrol R2 at 80:1. Cheers, JM.

Many thanks, Alan. This afternoon I've tested the a JHN needle modified in the cilindrical section (I sanded 0.05 mm in a lathe) and it cured the pinging I described before. The bike runs very clean, more than with the original Dell'Orto, but i feel that more can be made. I'm waiting to hearing from Wayne, many thanks again. JM.

More than fifty views, none answer? C'mon guys! Is this so hard for you? I'm progressing by myself, found some charts of PWK needles and feel that it is almost done, but I would know your opinion, or guess, at least. Cheers, JM.

I have just set up my old Keihin PWK 28 on my new Sherco 04. The best results were achieved with this settings: 45 low, 125 high, slide 3.5, air screw 0.75 to 1.25 turns... BUT I have a problem with the needle: with the clip in the middle position, the thing goes lean when chopped the throttle after a small opening. On the second position (from the bottom), the thing goes well but has blubbing (too rich) when throttle is open with load. I deduced I need other kind of needle. Actually is a JHN. Anyone in there has information about JJH needle (same taper than JHN, same lenght, but seems to be 0.05 mm narrow on the cilindrical section, and that could be what I need). I have experience with Dell'Orto but PWK is relatively unknown to me. Wayne, could you check the needle fitted on your Keihin? Any suggestion will be welcome. Cheers, JM.

Ipone probably is the more used oil in UE trials but, anyone has experimented with Castrol (R2 or Biolube)? Some riders use this last just to 100:1, apparently without problems.

Thanks, Johnny.

Bill and Martin, could you give the numbering of those needles? In Spain, the usual needle is D36, but in some cases we use D37 one (more gas:air ratio). Thanks, JM.