I'm looking to improve the low end on my 1976 175 XC. There is a big lag off the bottom, and then a big hit. I am running a 34mm Mikuni. Any suggestions?
1976 MC 5 Original Owner
1976 Penton 175 XC
A 32mm will help but you loose a bit of top. Lectron carb does better all in all also. Assuming your jetting is on and it is not that though.
Larry P
Why the 32? I understand loosing on the top end, but what does the smaller carb do for the bottom. Yes, I am very familiar with the Lectrons. I have one on my 250. I had a 34 on this bike and could never get it right; ended up going back to the Mikuni. As far as the proper jetting..... I think it ran better when I was in NY than it does here in FL. Maybe I need to revisit my settings.... Thanks for the input, always appreciated!
Quotequote:Originally posted by Larry Perkins
A 32mm will help but you loose a bit of top. Lectron carb does better all in all also. Assuming your jetting is on and it is not that though.
Larry P
1976 MC 5 Original Owner
1976 Penton 175 XC
Buy a 250!! Just kidding. On one of my bikes I geared it down to help the low end. It did help my problem.
Smaller carb per displacement will roll on the throttle or fast wick better is the deal on going down to a 32mm.
Larry P
I already have one! Problems? You have bike problems? Seems to me you just turn the throttle another notch!! lol.....
Quotequote:Originally posted by Dale Sonnenschein
Buy a 250!! Just kidding. On one of my bikes I geared it down to help the low end. It did help my problem.
1976 MC 5 Original Owner
1976 Penton 175 XC
Got it! Thanks Larry...
Quotequote:Originally posted by Larry Perkins
Smaller carb per displacement will roll on the throttle or fast wick better is the deal on going down to a 32mm.
Larry P
1976 MC 5 Original Owner
1976 Penton 175 XC
James, I have a 32 Mikuni on the '73 Jackpiner I ran all season with good results.
Mick
To add to what Larry said the reason is a smaller carb increases the air velocity which helps atomize fuel better. When rapidly opening a carb the air velocity drops too quickly which leans mixture causing flat spot. You might add flywheel weight if that is possible also to help low end but it also slows acceleration.
Thanks guys for the input. Before I go and change the carb, I am going to make some changes to my existing set up. I want to lean out the lower end. Here is what I have:
Main 220
pilot 27.5
Needle 6 DH-3
needle jet 159 P-6
the clip is on the top notch, so I am going to install a 159 P-4 needle jet, and lower the clip to the middle notch. From there, I will see which way to go. I am thinking the move from NY to FL has effected my settings. The bike ran very well in the past, so, lets see what happens.... stay tuned...
1976 MC 5 Original Owner
1976 Penton 175 XC
I've got a 32mm Mikuni I'm going to put on my 175 Penton. Due to my age and health I'm not looking for a lot get up and go as most of my get up has gone. The Mikuni I have, has very little #s are letters Just the #s 166 with 10 under the 166. Other then Mikuni the letters ISO. The jetting is "Main 190" "Pilot 50" "Needle jet 169 Q5" "jet needle 5FJ9" and a #2.0 slide. I have no idea what this carb is off of? Any ideas where to start with jetting? Also I have a lot of good to new Mikuni parts to get rid of and some carb's a 38mm and a 40mm. Dave
Hit up Mick Milakovic he has the 32 and his runs well. You might try the search too as it has probably been discussed in the past.
Larry P
Additionally you might want to revisit your ignition side of the bike. More than once carburetor problems have been traced to a weak ignition and/or improper timing settings. Spend an evening or two going over those two areas before buying another carburetor.
Pete Petrick
175 Jackpiner
Slow but Good
Thanks Larry and Pete, Ignition and carburetor OK. I'm just wanting to try a Mikumi. This is a 1978 MC-5 175 I got from Gary Ellis and just building a play bike. I'm using 1979 wheels to save weight, also welding up a set of 35mm Marzocchi forks for a disc brake. Planing on a hydraulic clutch. I have one on my Penton Motard, I change from hydraulic to stock in 10 minutes, I'm only 30 minutes from Magura and all parts are off there shelf plus it bolts right on, no modification to bike. I'm going over next week and have another one made up, I'll get all the #s and prices. Maybe we can get Al to sell them, they really work slick. Ol Dave
Dave, can you email me? Thanks, James
[email protected]Quotequote:Originally posted by 242
Thanks Larry and Pete, Ignition and carburetor OK. I'm just wanting to try a Mikumi. This is a 1978 MC-5 175 I got from Gary Ellis and just building a play bike. I'm using 1979 wheels to save weight, also welding up a set of 35mm Marzocchi forks for a disc brake. Planing on a hydraulic clutch. I have one on my Penton Motard, I change from hydraulic to stock in 10 minutes, I'm only 30 minutes from Magura and all parts are off there shelf plus it bolts right on, no modification to bike. I'm going over next week and have another one made up, I'll get all the #s and prices. Maybe we can get Al to sell them, they really work slick. Ol Dave
1976 MC 5 Original Owner
1976 Penton 175 XC
James, I can't e-mail at this time, something going on with my account,one of my grand kids got on it so??? My wifes phone # is 812-830-9918 and we can tex. Ol Dave
Hi James - you KNOW I will find this a fascinating topic. If you are talking about a 7 fin pre-76 motor, then I too might point to the carb. Gary set mine up with the 30 mm Bing and it is an electric motor, very good low to mid, actually makes me lazy to shift sometimes.
If you are talking about the newer 6 fin motor, is it just an entirely different animal. As you know I run a 34 Mikuni on mine, it's clean down low, but will never have anything resembling "bottom end" - it's a revver. My gearing is lower than the Jackpiner to account/help out a bit because of this.
Good luck, my friend.
Yes, it is the 7 fin top end. And yes, the carb settings did not like the change from NY to FL. Made some adjustments with the help of Kevin Donovan, and it runs much better, thanks for the input!
Quotequote:Originally posted by tooclose racing
Hi James - you KNOW I will find this a fascinating topic. If you are talking about a 7 fin pre-76 motor, then I too might point to the carb. Gary set mine up with the 30 mm Bing and it is an electric motor, very good low to mid, actually makes me lazy to shift sometimes.
If you are talking about the newer 6 fin motor, is it just an entirely different animal. As you know I run a 34 Mikuni on mine, it's clean down low, but will never have anything resembling "bottom end" - it's a revver. My gearing is lower than the Jackpiner to account/help out a bit because of this.
Good luck, my friend.
1976 MC 5 Original Owner
1976 Penton 175 XC
Can you say reed valve!! I am always amazed it took KTM so long to add reed valves, old KTM motors fly with the addition of a reed valve, but not an old GEM...
Quotequote:Originally posted by JP Morgen
Can you say reed valve!! I am always amazed it took KTM so long to add reed valves, old KTM motors fly with the addition of a reed valve, but not an old GEM...
JEFF BUSHEY
Quotequote:Originally posted by jbushey
Quotequote:Originally posted by JP Morgen
Can you say reed valve!! I am always amazed it took KTM so long to add reed valves, old KTM motors fly with the addition of a reed valve, but not an old GEM...
JEFF BUSHEY
Hi JP do you need to change the piston or porting if you add a reed?
JEFF BUSHEY
The piston needs holes and to get the full benefit you need some boost porting. JP has done this alot so he can probably give you specifics.
Larry P
You can put a reed valve on and nothing else, makes the bike more responsive, cleaner jetting, but to take full advantage if you want more HP, then you add/modify boost ports and add holes to the piston.
JP I sent you a brain picking question on FB.
Larry P
How do you fit a reed block, the carb, and the air boot in that area???? I have enough trouble dealing with a stock set up!!!
Quotequote:Originally posted by JP Morgen
You can put a reed valve on and nothing else, makes the bike more responsive, cleaner jetting, but to take full advantage if you want more HP, then you add/modify boost ports and add holes to the piston.
1976 MC 5 Original Owner
1976 Penton 175 XC
Just a follow up to my carb issue... I ended up changing the slide from a 2.0 to a 2.5, the needle jet from P-6 to a P-4, the pilot jet from 27.5 to 30, and lowered the clip one notch. Runs so much better off the bottom. Thanks for all the input, well appreciated!
1976 MC 5 Original Owner
1976 Penton 175 XC