Can't get it running

[Gordon Brennan]

Ok, I can't help myself from checking out this thread every once in a while. 4 pages and nearly 3000 views on this subject has to be a new record.
What exactly is a "custom" float seat? On page 2 of this article, it looks like a Mikuni float seat. If so, I would pitch that and get the correct seat and new needle from Bing. Bing carburetor = Bing parts. 12 different combinations of components isn't going to help you until you fix the float situation. Positively gorgeous photos. But the picture of the upside down carb and your jets doesn't show us (me) anything. You have to lift the float and slowly let it drop until the tab just touches the pin on the float needle and see where you're at. Level is a good starting point. Also, stick to the slide that belongs in your carb for your bike. In my opinion, your slide looks fine. I've run slides much worse looking than that with smiles in them and it had no effect on how the bike started or ran. A new one just makes the bike run better and crisper.
I hope I don't come off as a smart alack. It could just be my New England, get to the point, upbringing. Or my Dad's "I broke it, let's fix it". mentality. And somehow we always did.
   

[454MRW]

Gordon,
This other thread explains what Andreas has gone through with the needle seat which was modified by Bing to fix his previously modified carb. Mike
http://pentonusa.org/forum/topic.asp?TOPIC_ID=15762&whichpage=3&SearchTerms=bing%2Cneedle%2Cseat

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

[Gordon Brennan]

Thanks Mike,
I must have missed that part of the saga.
Bing, pushing Mikuni parts, and fixing their own product with another companies hardware. First I've heard of that tactic. At least from them.

[Andreas Piepke]

Not really! Some unknown previous owner had modified the the Bing carb with a Mikuni float needle. That individual drilled the original seat away, opened the hole and equipped it with a thread to accomodate the Mikuni part. I didn't even realize this mixup until people on this forum identified the components for me.
The needle was leaking and there seemed to be no way to get this fixed. I sent the carb to Bing and they were nice enough to custom build a new needle seat and fit it into the carb body so I can use an original new Bing float needle with Viton tip. They figured out how to do that, hand made a new float needle seat and installed it into the old carb. All of that for very reasonable price. So the Bing people went out of their way to make a 40 year old product useful for their customer. I was quite impressed by this customer service I have to say!

Cheers

Andreas

[Andreas Piepke]

Hi POG,

Below find a picture of my new carburetor parts, acquired in response to your feedback:



I got a new (not quite new but in good conditions) set of black floats from a friendly POGer! People had pointed out that my original size 0 slide (right in the image) shows wear. It indeed does. If one touches the engine side of it, it has a perceptible step. I purchased a new size 5 2 slide (I posted an image of the original part earlier in this string) but found it has only a 4 mm high cut-out while the original slides cut-out is 7 mm. Test running with the 5 2 slide indeed showed very rich mix, a wet plug. Correspondence with Bing actually revealed that my Bing 54 2/36/102 carburetor, when installed on KTMs or Pentons, was equipped with a size 1 slide. I further understand that a size 1 slide should have an 8 mm cutout. In response to that I machined the cutout to 7 mm to match what I had. It is interesting that the size 5 2 slide has a different inner rim height. However, when measuring how far the needle sticks out below the lower edge I get 43.1 mm for both slides. I conclude the needle position is equivalent on both slides. Another difference is that the bottom of the original 0-slide is closed where the choke slot is, my new 5 2 slide is open. I'll need to see whether this makes a difference in air flow.
The Bing people where also nice enough to tell me that for correctly set floats the fuel level in the bowl needs to be 1/2" below the upper rim. This constraint will now allow me to check correctness of the float position setting, independent of assumptions on the correctness of the float needle's location.
Last week I made another test run video: https://www.youtube.com/watch?v=NQYNQS5UYlE
The bike certainly runs better than before but still not satisfactory. I'll try out the new floats and slide.

Happy Easter to everybody on the list!

Andreas

[454MRW]

I noticed that when starting the bike you did not hold the tickler down near long enough for the fuel to overflow the bowl vent lines. With a cold engine, hold the tickler down 3-5 seconds until you see fuel dribble out of those lines and it should start in a couple of kicks. 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

[Andreas Piepke]

Will try next time after putting the new parts into the carb. Maybe I should try to replace the 40 pilot jet with a size 50 exemplar (was initially installed).

Thanks for sharing your observation!

Andreas

P.S.: One more question: what percentage open do you hold the throttle when attempting to start the engine?

[454MRW]

None. Throttle closed until it fires. Opening the throttle defeats the choke operation. 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

[Andreas Piepke]

Hi All,

I installed a new modified slide, and the new black floats. Initially this put me back to square one: an overflowing carb when running the engine. Taking the carb back off revealed: the little safety wire (very stiff) on the tickler was a bit long, rotated upward due to the engine vibrations and then held down the floats. I cut the wire shorter and this fixed the problem.
After fixing this issue the bike certainly now runs better than ever before. It is till difficult to start and seems to kick back after I kicked it over a number of times. I have already taken the ignition point back to 2.25 mm before TDC.
I posted another test run video on YouTube and asking for you input:

https://www.youtube.com/watch?v=tp1zKGhN6sg

The engine certainly now runs and the bike accelerates alright. However, I am unsure as to the engine performance. Judging from the rate of rise of the revs is this a reasonable engine performance? I don't seem to be able to make the front wheel lift off. I expected a little more "pull".
The image below shows a 1981 KTM 250 GS I had rebuilt from three box bikes in the late 1980-ies (with me an my late dad). That bike lifted the front wheel in second gear without problem. Do I need to fiddle more or is this "good running"? And Mike: my carb doesn't have a choke.



Cheers and happy Easter for everybody

Andreas

[Daniel P. McEntee]

Well it sounds like you are definitely making good progress. Really hard to tell by the video sound, but sounded pretty clean. Since this is a "new" engine, I would proceed with caution from this point forward until you get some time on the bore and rings to let them seat properly. Have you checked your plug recently? Keep a close eye on it while you fine tune things. In this day and age with the laser temp gauges, I wonder how useful it would be to shoot a temp reading on a known, good running 250 to see what the temps are at the exhaust right near the cylinder? This might be a good way to help judge lean or rich.
  As you get closer on the carb settings, you may find that you have to tune the Super Trapp silencer also, more plates, less plates, looser night, or tighter nut. I don't have a lot of experience with these, and may be putting one on the 400 I'm trying to finish up and would like to here what others think on this.
  As as throttle on start up, I agree with Mike, especially since you have the Bing with no choke. Tickling the carb makes it over flow. Some goes into the engine, some flows out of the carb. Some engines like to be almost flooded when starting stone cold, and I'm guessing that you might not be tickling it long enough on a cold start. I keep the throttle closed, as this lets the slide block off the intake, and helps pull fuel through the idle jet. Cracking the throttle greatly lessens the effect. You had mentioned ,maybe trying the next richer idle jet, and you may want to do that. If you have to close the air adjusting screw  to less 3/4 of a turn to get it to idle at all, that may be an indication also. Make sure you get the engine to operating temperature when testing out all carb changes also. Cold starts are just one of the things you have to figure out for each bike.
  You have the internal flywheel motoplat on your bike, I think also, don't you? I think I saw that in one of your previous threads. That makes a big difference in how an engine responds and performs also. It will work hand in hand with the pipe/silencer combination.
   You certainly are being very thorough and methodical in your approach to solving your problems. And your pictures and videos are very helpful and will be a good record that will help others as they go through the same process, like ME!
  Good luck with the rest of the process,
   Dan McEntee
  PS to add;
   I was taught to check years ago the spark plug as follows: Find a place where you can run the bike out to full top end revs on as high a gear as possible. Preferably running toward your truck and tool box! When you hit top speed, pull in the clutch and hit the kill switch and coast to a stop, then check your plug. That will let you check the plug as it was performing at it's peak, and really see how it is on the main jet. Adjustments to the idle jet, needle and slide are transitional and shouldn't affect how the plug looks on top end, but will influence the reading if you let the bike slow down while running, idling and such. We have come to know these trial runs as "Rudder Runs" !

[454MRW]

Yes, throttle closed until the bike is running. Starting involves pulling fuel through the idle jet, often referred to as a pilot jet, and if the throttle is open, this will not happen regardless of choke or not. Again, hold the tickler down until fuel runs out the overflow first to almost flood the engine, KTM engines like a lot of fuel to start when cold. 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

[Andreas Piepke]

Hi Daniel and Michael,

Thanks for the useful suggestions. I'll try them out. Daniel, have a look at the first page of this string: the bike has an external fly wheel. I haven't tried to tune the super trap and doing so seems a good idea. I have already changed to a size 50 pilot jet. Today I tried flooding the carb to overflow and then attempted to start with a close throttle. This didn't work, the bike only started after multiple kicks with half open throttle. I'll try again. Maybe I need to flood even more.

Thanks again for your help on this!

Andreas

[454MRW]

Size 40 to 50 jet is a big jump, combined with the extra fuel by holding the tickler down. 1st rule of thumb is to do 1 change at a time or you never really know what helped. A 45 with slightly less tickler would be my suggestion ultimately. Try less tickler before changing the jet first just for starting. Once fully broken in the bike should loft the front wheel in all 6 gears. Take it out in the country and ride it for 30 minutes in one ride after taking a full throttle spark plug reading to make sure its not lean, then re-evaluate your settings, and even do another full throttle test with a new plug. 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

[brian kirby]

I still think all of your problems are with the modified float needle and seat in your Bing. I am even more certain of that since the new floats caused the carb to work differently, which should not happen.

Brian

[Andreas Piepke]

There was no problem with the new floats, the very stiff tickler wire (securing the seal plate on it) was too long and hung up when it rotated up. I think I fixed this issue. The bike definitely runs better now than before but just not really right yet.

Thanks a lot for your input!

Andreas