I re-did the top end on my 175 XC, and I replaced the Mikuni with a new one. The bike use to start on the second kick when it was cold, and 1/2 a kick when it was warm. Now it takes 7 or 8 kicks when it is cold, and at least 4 when it is warm. I am running a 22.5 pilot jet and thinking of going down to a 20 to see if that helps. Any thoughts why the change?
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
That sounds like a lean condition to me. You may need to go up on jet sizes,not down. Mike
Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1978-1979 MX-6 175 & 250 KTM's
1976-78 125-400 RM's & 79 PE250 Suzuki & 2012 DR650
2007 CR125R Honda
1977 MC250 Maico
Thanks for the input Mike!
Quotequote:Originally posted by 454MRW
That sounds like a lean condition to me. You may need to go up on jet sizes,not down. Mike
Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1978-1979 MX-6 175 & 250 KTM's
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
1985 20' Hi Point trailer
That is extremely lean, I would not use smaller than a 35 pilot jet.
Brian
Well I went from the 22.5 to a 25 and the needle clip is in the middle. The bike is running really rich on the bottom. When I turn the throttle off the idle, and it is almost loading up; way too rich.
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
One time I reassembled my carb with the needle and clip inside the plastic cup rather than under it. It ran super rich and took me a while to figure it out. Any chance you did that?
Steve Minor
Steve, I don't understand your comment. What is the plastic cup? Anyway, I went to a 20 pilot jet and it rums much better. I think I need to adjust the clip on the needle for some fine tuning... Thanks for your input, well appreciated.
Quotequote:Originally posted by Steve Minor
One time I reassembled my carb with the needle and clip inside the plastic cup rather than under it. It ran super rich and took me a while to figure it out. Any chance you did that?
Steve Minor
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
Sorry....I should have read your first post more carefully. I just assumed you were using a Bing, not a Mikuni. Bings have a white plastic cup that the return spring sits in. It's sometimes easy to drop the needle and clip inside the cup rather than under the cup.
Steve Minor
Quotequote:Originally posted by skiracer
Well I went from the 22.5 to a 25 and the needle clip is in the middle. The bike is running really rich on the bottom. When I turn the throttle off the idle, and it is almost loading up; way too rich.
The range you are describing is not controlled by the pilot jet, it is controlled by the needle jet and the slide cutaway. On a Mikuni the pilot jet only controls idle when the slide is shut. What size Mikuni? Sounds like your needle jet is too rich, what needle jet is in it? I have Husky, Can-Am, Yamaha, and Penton 175s and the smallest pilot in any of those bikes is a 35, a 22.5 or even 25 pilot is really unusual, but as I always say, dont get hung up on the number and give the engine whatever jet size makes it happy.
Brian
Hey Brian,
The carb is a 34mm. I don't have any notes on the needle jet. I have never changed on before. Ii will take a look at it on Tuesday. Thanks for your input, it is well appreciated....
Quotequote:Originally posted by brian kirby
Quotequote:Originally posted by skiracer
Well I went from the 22.5 to a 25 and the needle clip is in the middle. The bike is running really rich on the bottom. When I turn the throttle off the idle, and it is almost loading up; way too rich.
The range you are describing is not controlled by the pilot jet, it is controlled by the needle jet and the slide cutaway. On a Mikuni the pilot jet only controls idle when the slide is shut. What size Mikuni? Sounds like your needle jet is too rich, what needle jet is in it? I have Husky, Can-Am, Yamaha, and Penton 175s and the smallest pilot in any of those bikes is a 35, a 22.5 or even 25 pilot is really unusual, but as I always say, dont get hung up on the number and give the engine whatever jet size makes it happy.
Brian
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
Spoke too soon. I have more notes than I thought... The needle is a 6D4H......
Quotequote:Originally posted by skiracer
Hey Brian,
The carb is a 34mm. I don't have any notes on the needle jet. I have never changed on before. Ii will take a look at it on Tuesday. Thanks for your input, it is well appreciated....
Quotequote:Originally posted by brian kirby
Quotequote:Originally posted by skiracer
Well I went from the 22.5 to a 25 and the needle clip is in the middle. The bike is running really rich on the bottom. When I turn the throttle off the idle, and it is almost loading up; way too rich.
The range you are describing is not controlled by the pilot jet, it is controlled by the needle jet and the slide cutaway. On a Mikuni the pilot jet only controls idle when the slide is shut. What size Mikuni? Sounds like your needle jet is too rich, what needle jet is in it? I have Husky, Can-Am, Yamaha, and Penton 175s and the smallest pilot in any of those bikes is a 35, a 22.5 or even 25 pilot is really unusual, but as I always say, dont get hung up on the number and give the engine whatever jet size makes it happy.
Brian
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
When I took the Bing off of my Can-Am 175 I put the standard generic Mikuni 34mm, probably the same one you have, and I had to lean the needle jet several sizes. That stock needle jet was close for the '83 Husky 175WR and the '82 Husky 125XC, but I had to lean the needle jet on my '72 Jackpiner and Yamaha 175s, just not as much as the Can-Am. You should have a Q-2, I think I put a P-4 in the Can-Am and a Q-0 in the Penton. Have you tried the needle clip in the top (leanest) position? Try a richer pilot jet (25 or 30) and the clip in the leanest position. Each needle jet is the equivalent of moving the clip form the middle slot to the bottom or top depending on if its richer or leaner so that will give you a feel for how much change you need.
Brian
Okay, it has a 159 Q-0. I will try moving the clip from the middle to the top to lean it out, and I will go from the 20 to a 25 pilot. Thanks for all your help and knowledge....
Quotequote:Originally posted by brian kirby
When I took the Bing off of my Can-Am 175 I put the standard generic Mikuni 34mm, probably the same one you have, and I had to lean the needle jet several sizes. That stock needle jet was close for the '83 Husky 175WR and the '82 Husky 125XC, but I had to lean the needle jet on my '72 Jackpiner and Yamaha 175s, just not as much as the Can-Am. You should have a Q-2, I think I put a P-4 in the Can-Am and a Q-0 in the Penton. Have you tried the needle clip in the top (leanest) position? Try a richer pilot jet (25 or 30) and the clip in the leanest position. Each needle jet is the equivalent of moving the clip form the middle slot to the bottom or top depending on if its richer or leaner so that will give you a feel for how much change you need.
Brian
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
Moving the clip only changes the timing of when you get fuel, if it is too lean or too rich from just of idle to mid throttle then the needle jet is where you need to look. Moving the needle may give you a clue as to what needs to change but once you change the size of the needle jet, put the needle back on the center clip. All of my bikes are set for sea level so if I ride above 2500 feet, I will sometimes change out the pilot and drop the needle one step.
Thom Green,Still crazy after all these years!
74' 1/2 440 maico
70' 400 maico (project)
93' RMx 250 suzuki
2004 Suzuki DL1000
1988 Honda Gl 1500
2009 KTM 400 XC-W
Thom is correct, you need to move the clip back to the middle when you change the needle jet, but by going to the leanest clip slot and a richer pilot it will tell you if that is the right direction to go further before you buy any jets. I am pretty sure that a richer pilot and a leaner on the needle jet is the right direction.
Brian
I have been reading this topic with interest. Now I am ready to chime in. Let's try the basics. Why did you replace your original Mikuni that ran good? Was it the same size as the new one? If so what was the old jetting? Have you put the old one back on and tried it?
ted
Tom, I had an older 34mm and thought I would but a new one; tighter clearances, etc. Yes it was the same size. The only change was a new top end. I had originally installed the same jetting new carb. It wasn't running right, so I started changing the jetting to get the bike running better. Okay new needle jet is ordered. Question: what is the advantage of a leaner needle jet and a larger pilot jet as opposed to a richer needle jet and a leaner pilot jet?????
And yes, I understand that the clip needs to go back to the middle.
Quotequote:Originally posted by t20sl
I have been reading this topic with interest. Now I am ready to chime in. Let's try the basics. Why did you replace your original Mikuni that ran good? Was it the same size as the new one? If so what was the old jetting? Have you put the old one back on and tried it?
ted
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
What size was the pilot in the old carb? Does the bike start with the old carb fine?
Ted
Quotequote:Originally posted by skiracer
Tom, I had an older 34mm and thought I would but a new one; tighter clearances, etc. Yes it was the same size. The only change was a new top end. I had originally installed the same jetting new carb. It wasn't running right, so I started changing the jetting to get the bike running better. Okay new needle jet is ordered. Question: what is the advantage of a leaner needle jet and a larger pilot jet as opposed to a richer needle jet and a leaner pilot jet?????
And yes, I understand that the clip needs to go back to the middle.
It is not really an advantage, its understanding what part of the carburetor controls fuel in what range of throttle opening, which I did not understand it for a VERY long time and made a lot of mistakes jetting because I didnt understand and correctly identify which piece of brass I needed to change and changed the wrong one. What you are doing by changing the needle jet instead of the pilot is changing the part that actually controls the rich point you are having. Many times main jets or pilot jets are changed when the problem is the needle jet, I did it myself for many years as I said. Going leaner on the pilot is used to cure what is really a rich needle jet, but on the Mikuni the pilot jet ONLY controls fuel when the slide is completely closed, the instant the slide cracks open even the tiniest amount the needle jet and slide cutaway are what is controlling the fuel mixture. The pilot will continue to flow fuel after the throttle is open so it does effect jetting after the slide opens but the effect is extremely tiny and you cant really effectively use it to tune above the closed slide position. The only functional purpose for a pilot jet in a Mikuni is starting (closed throttle) and idling. You are having a rich condition right after you open the slide, but you are also having hard starting, which tells me the pilot is too lean trying to compensate for a rich off idle/mid range which is the needle jet.
Also, and some of this might be obvious to the more experienced folks but it was not obvious to me for a LONG time, the tuning parts of a carburetor function purely on the slide position, IE 1/4 or 3/4 throttle open, the carb does not know nor does it matter what RPM the engine is running, the carb only sees the vacuum signal coming from the engine. Many times in the past I would get slide opening and "engine low end or top end" mixed up. When you are test riding, ignore (or mostly ignore) the engine RPM and focus your attention on what the jetting feels and sounds like relative to the amount of throttle you have applied.
Brian
The pilot was a 22.5. Yes it does start, however, as the reasoning for all the changes is that it has become harder to start since I re-did my top end............
Quotequote:Originally posted by t20sl
What size was the pilot in the old carb? Does the bike start with the old carb fine?
Ted
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
Well said Brian! I learned more today than I have in a long time... Thank you! So, I went down two sizes on the needle jet. I am thinking that I will start with a 30 pilot.... Until Tuesday......
Quotequote:Originally posted by brian kirby
Quotequote:Originally posted by skiracer
Tom, I had an older 34mm and thought I would but a new one; tighter clearances, etc. Yes it was the same size. The only change was a new top end. I had originally installed the same jetting new carb. It wasn't running right, so I started changing the jetting to get the bike running better. Okay new needle jet is ordered. Question: what is the advantage of a leaner needle jet and a larger pilot jet as opposed to a richer needle jet and a leaner pilot jet?????
And yes, I understand that the clip needs to go back to the middle.
It is not really an advantage, its understanding what part of the carburetor controls fuel in what range of throttle opening, which I did not understand it for a VERY long time and made a lot of mistakes jetting because I didnt understand and correctly identify which piece of brass I needed to change and changed the wrong one. What you are doing by changing the needle jet instead of the pilot is changing the part that actually controls the rich point you are having. Many times main jets or pilot jets are changed when the problem is the needle jet, I did it myself for many years as I said. Going leaner on the pilot is used to cure what is really a rich needle jet, but on the Mikuni the pilot jet ONLY controls fuel when the slide is completely closed, the instant the slide cracks open even the tiniest amount the needle jet and slide cutaway are what is controlling the fuel mixture. The pilot will continue to flow fuel after the throttle is open so it does effect jetting after the slide opens but the effect is extremely tiny and you cant really effectively use it to tune above the closed slide position. The only functional purpose for a pilot jet in a Mikuni is starting (closed throttle) and idling. You are having a rich condition right after you open the slide, but you are also having hard starting, which tells me the pilot is too lean trying to compensate for a rich off idle/mid range which is the needle jet.
Also, and some of this might be obvious to the more experienced folks but it was not obvious to me for a LONG time, the tuning parts of a carburetor function purely on the slide position, IE 1/4 or 3/4 throttle open, the carb does not know nor does it matter what RPM the engine is running, the carb only sees the vacuum signal coming from the engine. Many times in the past I would get slide opening and "engine low end or top end" mixed up. When you are test riding, ignore (or mostly ignore) the engine RPM and focus your attention on what the jetting feels and sounds like relative to the amount of throttle you have applied.
Brian
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
No problem, I am always happy to help especially since carburetor jetting can be counter intuitive and confusing. I didnt figure this stuff out by myself, everything I know about motorcycles and engines, or virtually everything, I learned from people much wiser than me. I listen to guys like Speedy, Ron Carbaugh, Gary Ellis, JP Morgen, Peter Villacaro, Bob Bean, Larry Perkins, and too many others to name. I try to remember what I learn from them and pass it on.
Brian
Same question. If you put the old carb back on does it help the starting issue?
Ted
What Ted is asking could solve a big piece of the puzzle. Probably worth the effort if doable.
Larry P
I agree, changing back to the old carb will eliminate some thing, for example if the old carb exhibits the same symptoms is something else causing the hard starting, like an air leak.
Brian
No, putting the old carb back on does not change the starting issue. I received a new needle jet over the weekend and will test it this evening..... stayed tuned!
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
If it started fine with the old carb before and does not now it is not a jetting problem in my opinion.
Larry P
I agree. Sounds like an air leak to me.
Brian
Where?
Quotequote:Originally posted by brian kirby
I agree. Sounds like an air leak to me.
Brian
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
Here is the update:
Went from a Q-0 to a P-6 needle jet
Changed the pilot jet from 20 to 32.5 Needle clip is in the middle.
Bike ran rich on the bottom; zero to 1/4 throttle, very rich.
Went to a 27.5 pilot running much better.
Moved the clip to the top, bike is running very well.
Mention of an air leak.... where? Would that not make the bike run lean, and idle very high?
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
The bike started well before re-doing the top end....
Quotequote:Originally posted by Larry Perkins
If it started fine with the old carb before and does not now it is not a jetting problem in my opinion.
Larry P
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
Quotequote:Originally posted by skiracer
Mention of an air leak.... where? Would that not make the bike run lean, and idle very high?
It could be anywhere there is a gasket or a seal. Those are classic air leak symptoms, especially the high idle.
Brian
But I don't have any of those issues......
Quotequote:Originally posted by brian kirby
Quotequote:Originally posted by skiracer
Mention of an air leak.... where? Would that not make the bike run lean, and idle very high?
It could be anywhere there is a gasket or a seal. Those are classic air leak symptoms, especially the high idle.
Brian
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
I thought you meant you had those symptoms. An air leak could also only cause hard starting and/or detonation or lean conditions without high idle.
The point I think Larry was trying to make is, if the bike exhibits the same symptoms with both new carb and the old carb, then its not the carb that is the problem.
Brian
Well, if both carbs have the same jetting, plus or minus, I think the results should be about the same, no? I thought the new carb, being a little tighter, would offer a better overall response. The issue came about after doing the top end; increasing the compression big time..... So, with the new leaner (by 2) needle jet, I have increased the pilot jet by 2 also; going from a 20 to a 27.5. Should I try going down another 2 or 3 sizes on the needle jet so that I would then increase the pilot another 2 or 3 sizes thus getting me up into mid 30's range on the pilot...
Quotequote:Originally posted by brian kirby
I thought you meant you had those symptoms. An air leak could also only cause hard starting and/or detonation or lean conditions without high idle.
The point I think Larry was trying to make is, if the bike exhibits the same symptoms with both new carb and the old carb, then its not the carb that is the problem.
Brian
1976 MC 5 Original Owner
1982 Suzuki PE 175
1976 Penton 175 XC
1985 20' Hi Point trailer
I would put the old carb on or... with new carb as last resort ....try spraying contact cleaner around head gasket, carb / cylinder junction / base gasket one area at a time with bike idling. You should see noticeable idle speed change if you spray where the air leak is. Could also be a leak unrelated to top end like crank seal. For now let's assume for now it is due to top end rebuild. Personally I would use old carb that ran good before so you aren't introducing to many variables.
Ted
I think you are on the right track James, but take is slow and one size at a time on the needle jets and pilot jets, make sure you dont go too far and seize it.
Brian
Hi James - very interesting reading. Need a favor if you could text me please at 315-297-2892.