I am having a problem starting my 76 175 GS with a Mikuni carb. When the motor is cold, it takes 15-20 kicks to get it started... every time. If I stop riding for five or ten minutes, it I have to use the choke, and 3 or 4 kicks to start it. New plug, good gas.... any suggestions? Thanks, James
i bet your pilot jet is clogged. did you leave any old gas in the bowl? chi jer
Every bike I ever rode with a Mikuni had the same problem (even new). Probably because most of them are reed valve bikes & it's hard to get a good draw across the choke circuit by kicking.
Huskies are notorious for it - we always just lean them over to force them to flood a little when cold. The old wives tale was that by pumping the choke lever several times it would flick a little fuel into the circuit & help. It never seemed to work for me.
But - thinking about it - for a piston port engine like yours Jerry is probably right.
Also make sure your air filter is clean & not over oiled and that you didn't leave a shop rag in the exhaust port last time you had the pipe off...... (can't tell you how many times I found this when a customer would bring a bike in that wouldn't run).
Is the motoplat getting old? Nice fat blue spark? Plug gap correct? Coil has a good ground? Decent compression?
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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
If it idles after it warms up, its not the pilot jet. If your using the choke after its warmed up to get it fired again, it sounds like a lean condition. make sure the carb and maniflod are tight. Also the slide in the carb hanging up will make it start hard. ( just a little open )
I'm not gonna tell you to check your valve adjustment !!:D
Too many variables to bench fix...
Raymond
Down East Pentons
Have the crank seals been replaced in the past few years? Typical Penton syndrome is that push starting works, but kicking doesn't indicating a low vacuum at kicking speed. Mike
Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S
1975 Can Am 175 TNT & 77 250 Black Widow
1979 Husqvarna OR390
1976-78 RM & 77-79 PE Suzuki's
1974 CR250M 07 CR125R 79 CR250R
Sounds like the pilot jet is too small or the Motoplat is weak.
Brian
Weak motoplat I agree with Brian. Take the plug out and as you are kicking it over, call me crazy. I hold onto the plug and see how hard it bites. This is the true way I check for good spark. Been doing this for years, maybe this is what is wrong with me.[:0][:0]
Ha! Gary, I am so chicken of getting bit I wont even hold a good plug cap with my fingers while I kick it over, I hold it with insulated extended pliers!
Brian
and that is another reason I always prefer the Bing carb with the trickle feature. Rarely ever needed to use the choke unless a cold Ohio Winter day. joe
Thanks guys! Fresh gas, good air cleaner, good compression, no rags.... NO I am not going to hold the plug while kicking...... I think I will start with the pilot jet. I will work on it after doing a little shoveling!!! Jl
your gonna do more than just a little shoveling today Mr.
I let my wife sleep in this morning, she's gonna be busy all day.
I got about 27" of snow right now. Looks like tomorrows rides out:(
Raymond
Down East Pentons
Jim, my penton 250 had the same problem. I put a bigger pilot jet and now it usually starts after a few kicks.
74 puch 175 SD
73 Husky 360 WR/RT
76 Husky WR360
75 Penton 250
10 ktm 250xc
02 bmw r1150r
Mikuni's will run well with a really lean pilot jet, but they will be very hard to start. When I took the Bing off my Can-Am 175 I had a 30 pilot in the Mikuni and it ran great when it was warm, but absolutely would not start cold unless I laid the bike over to flood the carb. The good thing about the Mikuni is once you get it dialed in you never have to spend another cent on it, unlike the Bing, which requires yearly parts replacement to keep it working if you ride it much. Those Bing parts, many times, cost more than a complete new Mikuni.
Brian
I have a Bing on a Husky and my Penton. I have an Amal on an Ossa. All three have ticklers and all three start great; one or two kicks. I have a Yamaha with a Mikuni that, when cold, you can kick forever with the choke on and it will start at some point. But if I lean it over until fuel comes out of the overflow, the bike will start in two or three kicks and run forever.
I would try that first James.
I agree with Brian, as far as parts go. The Bing parts wear out fast and are expensive to replace. But for some reason, I keep buying them.
I agree 100% with you guys on the Mikuni's! That is why I have one on the bike. The performance is so much better than the stock Bing. I will go up a couple of numbers on the pilot jet to see what happens. Thanks again everyone for your input, I really appreciate it! Jl
I dont know that either one outperforms the other, once the bike is running, they are both excellent carbs. It is no doubt easier to start a big bore two stroke with a Bing, and there is no doubt the Mikuni is cheaper to maintain. People claim the Bing makes more power, and that may be true, but the difference, if any, is minimal and the far superior long term durability of the Mikuni makes it my choice.
Brian
I like the hit of the Bing not the Sewing Machine power band that MIC gives (100 and 125's )[:0]
Fought this same impossible to start gremlin this weekend on an old KTM I bought cheap because the seller gave up on kicking and a shop told him it was too old to service. Same lean condition you mention. Both the main jet and the pilot had a bit of scuzz inside.
Didn't have a bigger pilot to try, so I took a chance with reaming out the old pilot a bit with a sharpended wire. But the float height looked like it was shutting off fuel too soon. I bent the tang to set the floats so fuel was extra high...a hair past horizontal when held upside down and float arm resting on the needle. Starts today with two kicks when cold and choked, one kick no-choke when warm. Runs like a champ. Suggest you go big on the pilot and don't forget to keep fuel height plenty high in the bowl--should work better.
Float height is critical on a Mikuni, if it's too low it won't start.
Brian
Float height is critical on a Mikuni, if it's too low it won't start.
Brian
I get a bit nervous reading this thread. If the pilot jet is so lean that causes significant problems with starting (and it isn't plugged up), then it is lean enough to cause things to get extremely noisy then extremely quiet in quick succession whenever a low throttle position cruise situation is encountered with a Mikuni (and probably with a Bing or Amal).
A quick, though not completely conclusive, check for the Mikuni would involve:
1. Identify the pilot air screw setting. How many "turns out" is it?
2. Check to see if stable idle speed changes when the pilot air screw is adjusted "in" 1/2 turn. Do another check with the pilot air screw adjusted "out" 1/2 turn from the original starting position. Note that "in" richens mixture, and "out" leans mixture.
3. If pilot air screw adjustments do nothing . . . either the pilot jet or pilot air passage (or both) are plugged.
4. If best idle is achieved between closed and 1 turn out, this is an indication that the pilot jet is too lean - get a larger pilot jet.
5. If best idle is achieved at 2 turns (or more) out, this is an indication that the pilot jet is too rich - get a one step smaller pilot jet. (NOTE: it is not at all likely that a hard starting engine has a too rich pilot jet -- unless it is plugged.)
6. When the proper size pilot jet is installed, best idle will be achieved with the pilot air screw somewhere between 1.0 and 2.0 turns out.
Ed
PS: I don't know Pentons very well . . . but am pretty familiar with the innards and operation of the Mikuni.
PPS: Being lean on the pilot jet is not a good thing. No.
Keep the rubber side down!
Important to note, because the pilot jet feeds fuel in front of the slide, it flows fuel at all engine speeds.
If your extremely lean or rich in the pilot jet, changing the pilot jet will also change your air/fuel mixture in needle/needle jet combo, as well as your main jet. Get the pilot jet right first.
To be slightly more accurate, the pilot jet flows fuel at all throttle settings - so changing the pilot jet in a Mikuni has an effect on jetting at ALL throttle settings. To be sure, the effect at WOT of a 1 step change in the pilot jet will be small . . . but it could be very important if Wide Open Throttle was already on the ragged edge of being too lean and then the pilot jet was reduced by a step.
Yep, get the pilot jet right . . . and then check/re-check jetting at all other throttle settings.
Ed
Keep the rubber side down!
Thanks for all the help. I hope to work on the issue next week. Currently riding my 250 Herc in Fl.!
1976 MC 5 Original Owner
1976 Hercules 250 GS
1982 Suzuki PE 175
2002 KTM 200 EXC
1976 Penton 175 GS
I just wanted to thank everyone who responded to my request. I finally made the time to work on my Penton. I changed the pilot jet from 25 to 30, and adjusted the air screw to about 1.75 turns out. The bike started on the 4th kick after sitting since last October! Music to my ears! I really appreciate the help, thanks again. James