Restore 90%done, but carbs are still bogging her down

[jurgenkoppen]

Hi, good folks, so I restored a '76 with a PMA and got 5 out of 6 systems going as they should. This bike I am working on for my friend had been neglected and sat for 5 years, but she is running now, actually, with a lot of power, except it bogs down when I open the throttle, not so much when the choke is on. Obviously, it is running too lean; the spark plug shows a bright silver-grey on the left side, ie, lean, and black on the right. I had the carbs out no less than 4 times now, replaced the boots, the idle screws, and cleaned everything below the diaphragms. The weird thing is that it runs best right now with the idle screws all the way in....I am not clear what influence the idle screws have on overall lean or richness other than when idle. Other than that, it has pods, not stock air filters, which adds another layer of variables. I need help sorting out how to get the lean side to be less lean, basically to get the carbs to cooperate.....and to get input on the idle screws being all the way in when running best...please and thank you.

 

[spresser]

Both cylinders are actually firing?
Have the carbs been synced?
Compression?
Have you done timing chain and valve adjustment yet?

 

[jurgenkoppen]

Both cylinders are firing, they are both hot, and the bike runs and idles very smoothly after the carb cleaning I did. It just does not want to be cracked open after about 4000 rpm it seems to starve out. I will check compression and timing next.

 

[gggGary]

pull the pods check both diaphragms are rising as they should when you rev the motor.
good pods or cheapies? some/many pods have a thick square edge flange facing the carb that restrict the entrance to the diaphragm chamber.
Fuel float levels checked?
recheck the pilot jet on the lean side.
How does he diaphragm drop test go are the sides fairly even on drop rate.
Have the throttle shaft seals been changed?
Spray carb cleaner around when running to look for air leaks.

 

[jurgenkoppen]

Hi Gary, the pods are the regular generic type like these:

The slides appear to be moving freely when I tested them during the three cleaning processes I put the carb through, ie, I pushed them up and released them, they had the same amount of resistance going up, and returned with the same amount of slight delay. I will follow your advice and see how they behave when the bike is running and I open the throttle. That may give me more clues. I will also spray some WD-40 around the intake boots (new from Mike's) and post the results. I had been duking it out with the fuel supply needle in the right carb, which kept leaking gas until I micro-cleaned some crud off the needle valve and its seat, so that is behaving now. I am just about to gear up some means to read the fuel level by creating a nipple under the float bowl. I think you once wrote about making one to see the fuel level with a clear hose and a grease nipple...? If you have another method that doesn't require sourcing something to screw into the float bowl bottom, I would be keen to know. I dumped in a fair bit of Sea foam, and it seems to get better as time goes by, now that I am at least able to take it for test spins. Until now this bike was undrivable with all the issues it had (Starter gear, clutch, no front brake, PMA regulator miswired by some previous hack resulting in a fried regulator... etc, etc ) What really baffles me is how my new idle needles from Mike's 1.) did not go in an even amount, and 2. then want to be all the way in for the bike to be happiest in the below 3500 rpm range. Do the idle mixture set screws affect the mixture for all the other ranges as well? I.e., can I change how lean or rich the bike runs across all ranges by using those adjusting screws on the outside of the carb? Given that they are used to balance the carbs, it would only follow that they affect the overall fuel/air ratio, or am I missing something here?

 

[Tiggertoo]

I'd be VERY wary of using those filters, see the holes outlined in the pic below? The inner "lip" on those filters look like they would block them off, if the top holes are blocked then the slides will not fall quickly enough. That could be a big part of the problems you are seeing right there.

 

[Its been a long time]

I agree. If that picture's really the arrangement of the air filter, it's awful. I would try running it with no air filters to see what a difference it makes.

 

[gggGary]

I've taken an exacto knife and beveled off the square corner on that type filter before.
Did you keep the original idle screws? If so try them.

 

[jurgenkoppen]

Thank you guys, I will follow your pointers and report back. I have also been told that the carbs need to be put in an ultrasonic cleaner, then reassembled. A high-speed port is still plugged....So that also is on my agenda as I get a moment to get back to this stubborn restore.

 

[jurgenkoppen]

I've taken an exacto knife and beveled off the square corner on that type filter before.
Did you keep the original idle screws? If so try them.

I will do the exacto knife fix for sure, but I lost one of the idle screws on my first test run, because I had to back it out so far to get it to go semi OK, and the little rubber ring was already deteriorated and made it easier to vibrate out. I only have one of the originals. I am also just gearing up to measure the float levels with the clear hose method. Making the screw in port for the bottom of the carb out of epoxy is my approach, since finding an 8-1mm grease fitting proved impossible in my small town.

 

[5twins]

There's an eBay seller who sells a ready-made "special tool" for that .......

https://www.ebay.com/itm/274881260720

I have a couple and they work really well ......

 

[gggGary]

I will do the exacto knife fix for sure, but I lost one of the idle screws on my first test run, because I had to back it out so far to get it to go semi OK, and the little rubber ring was already deteriorated and made it easier to vibrate out. I only have one of the originals. I am also just gearing up to measure the float levels with the clear hose method. Making the screw in port for the bottom of the carb out of epoxy is my approach, since finding an 8-1mm grease fitting proved impossible in my small town.

I think you can just shove/twist/thread a 1/4"? OD clear fuel line in there.