I have a friend who recently got a '78 175GS. He is having trouble with no low end power. I have not ridden the bike, so I dont know if it is normal and he is expecting too much or maybe his bike has some other issue. My question is, how does the stock power compare between the early 7 fin 175 cylinders and the 76+ 6 fin cylinders? Was the 76+ more pipey or wider or the same power compared to the 7 fin?
Brian
Gary Ellis would be the best person to answer that question, but the 6 fin engines were built more for and advertised as motocross type top end power, whereas the earlier style 7 fin engines were more of a broader Enduro power band. Depending on whether the bike has the Lectron or Bing carb will also make a difference, and proper timing and jetting play a big factor. Mike
Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1978 KTM 250'S
1975 Can Am 175 TNT 250 conversion
1976-78 125-400 RM's & 79 PE250 Suzuki & 2012 DR650
2007 CR125R Honda
1977 MC250 Maico
It had a Mikuni but he put a Lectron on it before he took it out for a real ride because the bottom end power was so poor. The Lectron made a big difference, but I suspect you are right that its designed as a mid-top engine. Will the 7 fin cylinder fit? The bottom ends are the same right?
Brian
I don't think it's a direct Bolt-on replacement due to the transfer ports and possibly even stud placement. Check with Gary. He might be able to put a 7 fin engine in by trimming some head fins for pipe clearance. I fit one into a 76 MC5 125 chassis with trimmimg, but that was with the non-torque style pipe. Mike
Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1978 KTM 250'S
1975 Can Am 175 TNT 250 conversion
1976-78 125-400 RM's & 79 PE250 Suzuki & 2012 DR650
2007 CR125R Honda
1977 MC250 Maico
I just looked closer at pictures of his bike, it has the older engine not the correct 6 fin engine. The plot thickens.
Brian
There is one for sale on eBay right now from Pampa TX. with the correct 6 fin engine and Bing carb that has not met reserve. I would like to have it, if I just had the spare $$$, It is not a GS6 as advertised, with a frame serial # starting 855- even in the serial # range, (10599/10650) that may have been a MX-6 early 79 with the white KTM decals on the fork legs. The MX-6's that I have found started around serial number 855-10315 and higher. Mike
http://www.ebay.com/itm/131671763847?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1978 KTM 250'S
1975 Can Am 175 TNT 250 conversion
1976-78 125-400 RM's & 79 PE250 Suzuki & 2012 DR650
2007 CR125R Honda
1977 MC250 Maico
I saw that eBay listing! Not many of those around for sure. Mike - did these new 6 fin motors come with Bings or Lectrons in 1978?
You DO have a mystery on your hands if it is the 7 fin motor, Brian.
I run both - a Bing-carbed 7 fin Jackpiner and a Lectron-carbed 6 fin MC5. Let's just say that the 7 fin motor is an easier time/more forgiving in the woods. The newer 6 fin motor - even with the Lectron - requires me to be ENGAGED. ;)
If your friend is at least an intermediate woods rider both motors should be fine. The seven fin may be a little better bottom end but not a night and day difference.
Dennis Jones
I believe the GS6 may have used Electrons on 175's, I know 77 did, but I will have to look up 78. MC5's used Bings. Mike
Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1978 KTM 250'S
1975 Can Am 175 TNT 250 conversion
1976-78 125-400 RM's & 79 PE250 Suzuki & 2012 DR650
2007 CR125R Honda
1977 MC250 Maico
If your friend is at least an intermediate woods rider both motors should be fine. The seven fin may be a little better bottom end but not a night and day difference.
Dennis Jones
I believe the GS6 may have used Electrons on 175's, I know 77 did, but I will have to look up 78. MC5's used Bings. Mike
Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1978 KTM 250'S
1975 Can Am 175 TNT 250 conversion
1976-78 125-400 RM's & 79 PE250 Suzuki & 2012 DR650
2007 CR125R Honda
1977 MC250 Maico
According to a 12-1-78 KTM Technical Service Bulletin that I have thanks to Donny Smith, the 78 & 79 models all used Bing Carbs. 125's used a 34mm, 175's used a 36mm, 250/400 used a 38mm, & 79 420's used a 40mm. The difference in the carbs for 250/400 GS VS. MC was the carb slide # 230 VS. 220 respectively, and the idle jet for 250 GS was 45 and 250 MC was 50.
Another interesting item to note was that the 175 & 400 used a 2 ring piston with an L-shaped (Dykes) top ring, whereas the 125 & 250, used a single square ring. Use of a replacement single ring piston could impact the bottom end response possibly. The 79 420 used a single L-shaped (Dykes) ring.
Also according to the bulletin, late 77 MC5 Marzocchi 35mm forks had 240mm of travel vs. earlier 76-77's, which had 220mm of travel, equal to that of the 220mm travel Ceriani ribbed straight leg forks for 76. Mike
Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1978 KTM 250'S
1975 Can Am 175 TNT 250 conversion
1976-78 125-400 RM's & 79 PE250 Suzuki & 2012 DR650
2007 CR125R Honda
1977 MC250 Maico
Here's a picture of my brand new 1978 KTM 175. 6 fin motor & Bing carb. Wish I still had it.
(http://i928.photobucket.com/albums/ad130/eyemanrandy/Mobile%20Uploads/image_zpsyg70rcl9.jpeg) (http://s928.photobucket.com/user/eyemanrandy/media/Mobile%20Uploads/image_zpsyg70rcl9.jpeg.html)
Every new style KTM motored 125 and 175 I have owned I could never get to run clean. Approached it multiple times from the carb angle but nothing helped. I think it was a mismatch on the ignition but for whatever reason they were never correct. Ended up hating them all. Worst Pentons ever in my book.
Larry P
My 76 250 MC5 came with the longer Marzoke forks from the factory... The bike was a March build..
Quotequote:Originally posted by 454MRW
According to a 12-1-78 KTM Technical Service Bulletin that I have thanks to Donny Smith, the 78 & 79 models all used Bing Carbs. 125's used a 34mm, 175's used a 36mm, 250/400 used a 38mm, & 79 420's used a 40mm. The difference in the carbs for 250/400 GS VS. MC was the carb slide # 230 VS. 220 respectively, and the idle jet for 250 GS was 45 and 250 MC was 50.
Another interesting item to note was that the 175 & 400 used a 2 ring piston with an L-shaped (Dykes) top ring, whereas the 125 & 250, used a single square ring. Use of a replacement single ring piston could impact the bottom end response possibly. The 79 420 used a single L-shaped (Dykes) ring.
Also according to the bulletin, late 77 MC5 Marzocchi 35mm forks had 240mm of travel vs. earlier 76-77's, which had 220mm of travel, equal to that of the 220mm travel Ceriani ribbed straight leg forks for 76. Mike
Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1978 KTM 250'S
1975 Can Am 175 TNT 250 conversion
1976-78 125-400 RM's & 79 PE250 Suzuki & 2012 DR650
2007 CR125R Honda
1977 MC250 Maico
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1979 KTM 175 GS: FOR SALE
Sweet bike Randy, those shocks bring a bucket full of money these days.
Dennis Jones
I'm with you Larry, especially the 125. Never could get them to make any power, high or low end. Tried Lectrons, fiddling with the timing, all to no avail. It's like they just didn't want to breathe. Had a 2 day rider by the shop in the late 70's desperate to make his run right. The Lectron helped a smidge, but it just would not rev, almost like either the air box or exhaust was half plugged up.
In 78 I switched to a Husky and never looked back...
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"We the willing, led by the unknowing, are doing the impossible, for the ungrateful. We have done so much, for so long, with so little, that we are now qualified to do almost anything, with nothing."
1972 Penton Berkshire 100
1983 Husqvarna 250 XC
2011 Jayco 31.5 RLDS
2009 Chevy 2500 HD Duramax
Thats the way this bike is running, the Lectron helped but its definitely anemic.
Brian