I need to pic your brain

[Dale Sonnenschein]

My 75 250 penton is close to being finished. I got it running a few weeks ago but now I'm having trouble. It has a new topend, new mikuni carb, new air filter, new petcocks and fuel lines. It starts hard, but if I let it sit for a few minutes after kicking it 15 or 20 times, it fires right up. But then it runs out of gas. The carb is just the way i bought it, new off ebay. It's a 36mm. I was having trouble with the gas flowing into the carb. You could see it would fill the line from the front petcock to the rear one but it wouldn't go down to the carb. I took the gas cap off and it still wouldn't flow. I took the carb apart and made sure the needle valve was clear. I put it back together and I could see the gas going into the carb. The bike started and ran for about 1  to 2 minutes and quit. It will run on whats in the bowl and then quit. The line still had gas in it.
What am I missing here?

Thanks for looking
Dale

74 puch 175 SD
73 Husky 360 WR/RT
75 Penton 250
10 ktm 250xc
02 bmw r1150r

[Kip Kern]

Try it with your gas cap removed as it may not be venting properly!

[Randy Kirkbride]

Hi Dale,
Does the float move free and is it adjusted properly?

[tomale]

Dale, I realize the petcock are new. Has the bike been sitting with fuel in the tank for a few weeks?  I am wondering if they are plugged. I had that happen to me after I started to ride my bike after it sat for a few years. If that tank has not been used in awhile, it could be lined with varnish that is starting to come off and plug stuff up. These old fiberglas tanks do not do well leaving gas in them, the gas will literally eat the tank. I always empty my tank after each time I ride my bike.
The other thing is that not all Petcocks are created equal. There are a few that look good but they really do not flow well. The problem is that the hole that the fuel runs through is too small to allow fuel to flow easily.  Some of the petcocks have a Reserve tube that sticks way up into the tank. Unless you are prone to running out of gas, I for one cut it short. I leave it at about 1/2 inch, that is tall enough so that a little bit of crud will not slow down the flow of the fuel.
I am not so sure about the jetting either. If everything is new and the fule flows right, the bike should start easier than that.  on a fairly nice day, it should kick over with just a few kicks, not 20 or so.. you might have too small of a pilot jet. Ask a few others what jets they are running on that bike too and use that as a base line. also, make sure that you set the idle as low as possible. If the idle is too high, it will make the bike start hard, The reason is that it leans out the mix coming through the idle circuit. You might want to check the air jets as well, the air jet restricts the amount of air coming into the pilot system. I have taken mine out and I rely on the air mixture screw to meter the air..  As for jetting spec, do a search any you will find a post a few years back where I posted my specs for my 76 250, that should get you close.
Email me and I will give you my phone number and we can talk if that would help.

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
74'250 hare scrambler (project)
74' 1/2 440 maico
78' 440 maico
72' cr125 Husky (project)
93' RMx 250 suzuki

[Big Mac]

If fuel is flowing free into carb and float needle isn't impaired, sounds like float is adjusted wrong, tang bent up too high. Might have been an ebay carb due to being someone else's problem.

[Dale Sonnenschein]

So far what I have done is take out the petcocks and made sure they are clear,they are new from Al B. I took the carb off and made sure the floats are free, and the needle is clean and free, there is a small wire clip holding the needle in the seat. The float arms are straight and it looks like if the arm is level it closes the needle. There has been a little gas that runs out of the over flow hose if I lay the bike over. I did have the gas cap off too.
As far as jetting, the bike ran good, but I only rode it for a few minutes a couple weeks ago. Thats the weird part too. It did run ok and now the gas won't flow.Hmmmmmmmmmmm, I'll keep you posted

74 puch 175 SD
73 Husky 360 WR/RT
75 Penton 250
10 ktm 250xc
02 bmw r1150r

[JCHubbard]

Dale, I had a similar condition like that once. Rebuilt an 82 Husky motor, new carb,good fuel flow, New Filter (key!!), etc...Put it all back together and it would start, and run for a couple of minutes then die...Sounded sort of like your situation Dale...I couldn't understand it...Then I remembered being at my local shop and watching my mechanic working on a modern bike with the same issue and remembered what he did to correct it.

I pulled off the new (heavily oiled filter) and the bike started right up!...After I cleaned the "brand new and heavily" oiled filter, and put on a lightly saturated filter, the bike ran fine. I also forgot to mention that prior to installing the well oiled filter in question, it had been sealed (full saturated of course) in a ziplock back for about 2 months prior to me installing. I know seal them in ziplock bags with oil on them...Now, I only oil my spare filters right before I install them...Otherwise I leave them on the shelf, clean and dry.

What I've noticed on my vintage bikes (all of them have fresh, low hour rebuilt motors) is that when I've used modern filter oil (ie. belray or twinair airfilter oil) specifically on Unifilters (twinair filters seem to breath better IMHO) the way I would on a modern bike air filter, it seems to choke the engine and cause difficult starting and horrible running.  

So now instead of pouring filter oil from a bottle onto the air filter, I use PJ1 SPRAY AIR FILTER OIL.  Provides good coverage without over saturation.  Now, when I know that I'm not going to ride a bike for along time, I put a clean un-oiled filter on the bike and will only oil it when I'm ready to use it.  I find that sometimes when vintage bikes sit with a heavily oiled filter on them, the filters almost become hardened (almost like a shellac) and less breathable.

An old timer taught me this next item.  In order to rule out the gas tank being the issue, I'll take a spare tank or pull a tank from a same model bike that I'm currently using or have used and run a piece fuel line from it to the current erratic running bike in question.  If the "bike in question" runs well, revs freely after using a different or spare gas tank then I'll know my "bike in question" tank has an obstruction issue that needs to be resolved.

Hope this helps.

John

[454MRW]

If the bottom end crankshaft seals have never been replaced, it could be that running it for the first time has caused the Ignition side seal to tear or fail from drying out. I would remove the ignition and stator plate and inspect it, because with a leak there, the engine does not generate enough vacuum to pull fuel through the carb when attempting to start the bike. Normally when you turn the petcock on prior to start up, fuel should run for anywhere from 5 to 10 seconds then stop with the line mostly full with the exception of some trapped air in the line when the float bowl is full and the float shuts off. If you want to verify the float/needle/seat is not the culprit or is not adjusted high enough, remove the float bowl and operate the float by hand on the bike with the petcock on. Sometimes the angle that the carb sets is not properly taken into consideration when setting the float, and it may be too low. 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

[hankthecrank]

I know this probably sounds silly but I saw a jap carb once [looked like a mikuni] off a yamaha, the float was in upside down. The bowl went on a little tight but no fuel went thru. This carb float needed the flat side down and the hump up. It had been installed like a bing, flatup and hump down. Worked great turned over. Might have been a Kehien. Is that spelled right?


Hank Rinehart

[Dale Sonnenschein]

This carb has floats on pins in the bowl and there is an arm they contact and lift the arm and close the needle. The floats are in right, good idea though. I have another tank I want to try tonight and maybe some petcocks off my puch.
Mike, The bike seems to not have gas and after sitting for a few minutes with the gas on it will start with one kick. Then run fine for a minute or so and then you can tell is runs out of gas.

74 puch 175 SD
73 Husky 360 WR/RT
75 Penton 250
10 ktm 250xc
02 bmw r1150r

[454MRW]

Dale,
you say that the floats are in right. Are you sure? The small pins on the side of the floats pointing inward that contact the float arm should be at the bottom. The could just as easily be installed upside down and shut the needle valve off almost immediately when fuel runs in the bowl. 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

[Dale Sonnenschein]

Mike, Yes, the floats are in right. They actually say UP on the side near the top. But the arm? I'm not sure of how that is on. Thanks for that pic, I was looking for that. It looks like the arms have the bend up.If they were down I think they would close the needle too early too. I'll have to check that!!

74 puch 175 SD
73 Husky 360 WR/RT
75 Penton 250
10 ktm 250xc
02 bmw r1150r

[gooddirt]

# 5 could be upside-down

[454MRW]

Setting the float requires a small ruler, float guage, or a digital, verier caliper, as the float arm measurement is usually given in MM's. It is NOT a matter or getting it level, it is getting it the right distance from the bottom of the carb body to the arms of the float arms just as the needle valve makes contact with seat before it compresses the internal springed point in the needle its self. Have you measured the level? most any Honda/Suzuki/ JAP motorycycle shop would set if for you, or watch as you use their guage. My sons 2007 CR125R Honda is extremely sensitive to float level setting. You can do an online search for the Mikuni model carb you have for the proper float setting and instructions. 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