175 low end improvements....

[skiracer]

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

[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

[skiracer]

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!

quote: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

[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.

[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

[skiracer]

I already have one!  Problems?  You have bike problems?  Seems to me you just turn the throttle another notch!!  lol.....

quote: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

[skiracer]

Got it!  Thanks Larry...

quote: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

[Mick Milakovic]

James, I have a 32 Mikuni on the '73 Jackpiner I ran all season with good results.

Mick

[t20sl]

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.

[skiracer]

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

[242]

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

[Larry Perkins]

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

[wfopete]

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

[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

[skiracer]

Dave, can you email me?  Thanks, James [email protected]

quote: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