Rough Cold Start, High Idle When Warmed Up

[5twins]

Yes, that is the proper float setting for your carbs. When checking, measure from both sides. Many times the floats are twisted or tweaked and one side will sit different than the other. You want them the same so the float is sitting level.

Another method some use for leak detection is to use a propane torch, unlit of course. Hold it up to and move it around the rubber intake manifold with the gas (propane) turned on. If you have leaks, some propane will get sucked in and the RPMs will change.

Yes, the advance should snap back smartly on it's own. That one in the video is sticking and needs to be serviced. This is a common problem on these bikes. Many of the units haven't been touched since they left the factory. Besides cleaning and lubing the advance unit, you need to pull the advance rod out and clean and lube that too.

 

[ipmaham]

Thanks guys.

Unfortunately I do not have a propane torch, so I will have to go the carb cleaner route and look for the rpm's to change.

To clean and grease up the advanced rod, just remove the spring, clip, and nut on the advance unit and pull it straight out?

 

[5twins]

Remove the nut, lock washer, and little slotted disc from the advance unit side and withdraw the rod out the points side. The advance unit w/ it's arms and springs can all remain assembled and in place.

Once the rod is out, you'll notice that the 1st bushing in each end of the cam has grooves cut in it. These are for grease retention .....

Clean any old remaining grease out (chances are, you won't find much, if any) and re-fill with fresh stuff. The manual recommends a grease with moly in it .....

Lightly grease the rod and re-assemble.

 

[Ketis]

+1 on the floats like 5twins suggested. I also have a set of the 77 xs650d bs38s

I had the exact same symptoms that you listed and i carefully re-adjusted my floats (i thought i did this properly when i rebuilt them) and they were slightly twisted (one side higher than another) which caused a lean condition.

Made them exactly the same to the 77d spec and now it works great!

 

[ipmaham]

Just got new gaskets in for carb cleaning, but I was wondering...

I see a lot of people against soaking the carbs in cleaner because of parts inside that could be damaged by the strength of the cleaner. But after looking through my diagrams, manuals, and etc., I only see really four parts that could be damaged.

1. Float bowl gasket
2. Choke body gasket
3. Float valve/pin
4. Rubber/silicone diaphragm

If removed, will soaking be be a problem? Do you recommend?

-ipmaham

 

[Dastommy]

I used to soak mine on my sr but don't bother anymore. Hand cleaning does just as good a job plus you don't have to worry about forgetting to pull a rubber piece. I think it's more work then neccesary to me.

 

[ipmaham]

I used to soak mine on my sr but don't bother anymore. Hand cleaning does just as good a job plus you don't have to worry about forgetting to pull a rubber piece. I think it's more work then neccesary to me.

Did you just take off the bottom and top, brush clean w/ spray, spray more, spray air in crevasses, let dry, and reassemble? That was my plan, before the idea of soaking it.

 

[Dastommy]

You want to remove the jets and clean/inspect. There are little pin holes that feed the gas so you will want to locate them, spray carb cleaner then blow em clean with a air compressor or as I use air in a can for cleaning electronics. It can be pretty confusing and intimidating for first time. I got lucky that 5twins lives a couple miles away and walked me through it. He has a guide for carb cleaning he wrote up floating around this site. I'ld read it at least 3 times. Once you can identify each piece and what it does, it gets much easier. Another hint is keep the left and right piles of parts seperate. Makes putting it back together easy. I ended up with extra parts the first time and took a while to remember where they went. I also used kerosene that 5twins recommended and does get varnish off pretty good without damaging rubber parts as much.

 

[Dastommy]

Also should be rubber oring on your needle flute thingy, on your mixture screws and one other place I can't remember that you hadn't already listed.

 

[ipmaham]

Thanks man, I'll be digging into it tomorrow.

Love this forum.

 

[ipmaham]

Finally got around to messing with the carbs. Got some questions...

I was suprised when i finally got the floats off. the main nozzel, float, and float valve assembly look nothing like what I was expecting. Any tips on removing the main nozzle for inspection and cleaning? My Hanes manual says it should screw out from the base, but thats not happening. It will spin a few times and not come out a bit. I'm afraid that maybe the previous owners may have stripped it.

DIdn't want them to stay open for too long, afraid the diaphram may get dried out.

 

[Dastommy]

The "flute tube" (as I like to call it)? That should just pull out. Only thing holding it in is that oring at the base. Atleast that's on my stock 78 special. Don't know if different carbs have another setup.

 

[ipmaham]

OK. Here's another question for you guys.

I noticed the main jet was screwed in from the inside of the float bowl. From all the diagrams I've seen, it shows the main jet screwed in from the outside followed by a washer and plug (bigger bolt). Did the previous owner doing maintenance screw it in wrong?

 

[5twins]

I didn't think it was possible to screw the main in from the inside of the bowl. If that was done then yes, it's wrong like that. It should screw into the bowl from the outside, on the bottom in the hole capped by the drain plug bolt. Jeez, just when I think I've seen it all, something else totally off the wall comes along, lol. There seems to be no end to the strange things people do to these bikes.

Your needle jet is just a snug push fit into the carb body if the o-ring is good. If it's bad, the jet may be loose, so loose sometimes that it can fall right out when the float bowl is removed.

 

[ipmaham]

I didn't think it was possible to screw the main in from the inside of the bowl. If that was done then yes, it's wrong like that. It should screw into the bowl from the outside, on the bottom in the hole capped by the drain plug bolt. Jeez, just when I think I've seen it all, something else totally off the wall comes along, lol. There seems to be no end to the strange things people do to these bikes.

Your needle jet is just a snug push fit into the carb body if the o-ring is good. If it's bad, the jet may be loose, so loose sometimes that it can fall right out when the float bowl is removed.

Yeah it caught me off guard when comparing it to the service manual. Looks like the threads on the inside on one of the carbs was stripped a little and the screw wasn't coming out (snugged to tight). Ended up drilling it out from the inside and, still screws in on the outside just fine. So no biggy there.

Also looks like the previous owner put a pilot jet with no holes, rather than the a pilot jet with two holes. I'm thinking a variation of all these things was causing it to run badly.

Few questions:

Gasket doesn't quite match up with the floats. A little offsets occur over the circuits on the float. Should they be cut/modified to match the exact paths and circuitry of the float? I will try to provide a picture here in a bit to show.

 

[5twins]

The "no hole" pilots were stock on some of these BS38s. The side air bleed holes are actually not needed due to the way the pilots mount and flow in your carb set. Having the holes hurts nothing though so if you need to replace the pilots, the normal version with the side air bleed holes will work just fine.

Yes, I would need to see a pic of how the gasket is sitting to tell if it will impede the flow. The air feeds are quite large and would probably be fine if slightly covered by the gasket but you'll want the pilot inlet totally clear .....

 

[ipmaham]

My main concerns are...

Not sure if the gasket is supposed to leave an opening for the top passageway to the vents. Same for the tunneling near the pilot jet.

or

If they are supposed to be covered.

Because if the passageway is supposed to be covered, the gasket leaving a small area to the left of the tunnel open and is offset a bit.

 

[ipmaham]

Also, should I fill the carbs back up with a little gas before installing them? Instead of a dry install?

 

[ipmaham]

Just a follow up from where I was previously...

-Completely cleaned carbs and replaced old worn looking pieces.
-Readjusted valves correctly. Exhaust had no gaps small enough for feeler gauge.
-Can chain tensioner was fine.
-Added uni filter to clear up some clutter and bought new agm battery.
-Added Doorman brake check valve to one of the opened tube coming from block that originally went to air filter. Capped off other one.

Some problems exist.
-Upon start up bike ran flawlessly at idle. About 3 min in, the rpms raised from 1.2k to 3.3k. Immediately adjusted idle screw slightly and it restored back to 1.2k rpms. I have no idea what that was about.

-Bike revved up to 2k rpm (while at idle) and caused some nasty backfire out of left exhaust. Right exhaust seemed fine.


Any idea what the sudden rev up was about? Or about the backfire out of left exhaust?

 

[ipmaham]

Actually, going to check the rod that runs thought the cams, check the advance unit, and check/reset the timing tomorrow.

May invest in a PAMCO ignition system and ditch the points too.