1986 Radian with idling issues

[sodapopdave]

First build/bike. It's a 1986 Radian with 26k miles on it. When I bought it it was barely running. I've gotten it to the point where I think it's almost running right but I have an issue that I haven't been able to track down yet.

The issue (I believe) is only at idle. I would think it is something with the pilot circuit but I have pulled the carbs 3 times now, cleaned, replaced all pilot jets and air/fuel mix screws, plug out all passages, and they seem good. I've also synced them with a homemade manometer that seemed to work really well. Clean tank as well and checked fuel screen and it's all intact.

The bike, motor wise, is all stock. Stock air box, stock jet sizing, stock exhaust. The issue is that even after cleaning, syncing the carbs, and setting the idle speed, I still have to give it some throttle when I hit the start button to get it to keep running. Just a little throttle and just for a few seconds, but I want to hit the button and it just purrs. Once it is warmed up and ridden a bit, if I shut the bike down, it will start up on it's own (without giving it any gas), about 1/2 of the time.

I know there is something going on with the #4 cylinder as when it is just warming up, I can feel the other 3 exhaust headers heat up, except for the 4th one. Once I ride it a bit though it seems to get going and has full power throughout all gears/ranges. But when it's idling, I can pull the spark plug wire off and will only notice a slight change in engine speed, I pull any of the other 3 off and it barely runs.

Since I've bought the bike I've replaced all spark plugs, air filter, oil change, carb work, fixed a valve cover oil leak.. I think that's it on the motor side of things.

Hopefully this is enough info for someone out there to give me a few pointers of what to check out. I plan on checking the valve clearances soon, but I think they are going to be within spec because it seems the bike was well maintained before the owner passed and the bike sat for a while. I've also read that the valves on these motors don't need to be checked often (like 15-25k miles?), or something around those lines.

Thanks for any help, I'm limited on bike diagnosing specific tools and resources and trying to do this "on my own" so hopefully I can (with your help), get this figured out without having to take it to a shop. Here's a pic of it as it is now after I've installed the round headlight, drag bars, recovered the seat, bobbed front fender and eliminated rear metal fender and a ton of other small things just to get it road worthy if anyone cares ....

 

[hillsy]

How many turns out are the pilot screws? Sounds like #4 is running lean(ish) and needs an extra 1/4 turn or so.

 

[sodapopdave]

All the pilot screws are 2 and 1/2 turns out, I believe that's stock. Think I should give it a 1/4 turn and see how it does? That would be a 1/4 turn out, correct? (sorry, but I always forget and I'm just now getting used to carbs).

 

[hillsy]

Yes - the factory settings are to get you in the ballpark, but not all the screws and their ports are identical, so a bit of adjustment either way is sometimes necessary.

You could use a Colortune plug to help you get the mix right, but you've pretty much identified the problem and you will be able to tell if adjusting the screw will work by the exhaust pipe heat.

 

[sodapopdave]

Awesome, thank you! I knew that they should be fine tuned when I first cleaned the carbs but never thought about it after that. I will try it tomorrow or the next day and report back.

 

[sodapopdave]

Alright, I'm back, problem not solved but have more info that I think will help. I tried turning out the mixture screw with 1/4 more out to 2 3/4 turns, no change, header not heating up, pull the plug wire and no change in RPM. I turned it out another 1/4 turn and still nothing. I then turned the screw all the way IN and nothing still - no change.

Then, once the bike was warmed up, I had it back to 2 1/2 turns, turned off the choke, then the header finally started heating up and I can pull the plug wire and the motor definitely starts ti run rough.

So... it seems the issue I have is only when the bike is cold and with the choke on (I guess on these bikes it's called a 'enrichment cycle', don't know what the difference really is - they both essentially make it run more rich, correct?). So I guess that means it is running too rich when it is cold on that cylinder.

Any more ideas of things to check with this info? I feel I'm getting closer....

 

[BTF]

A cold pipe at idle can be plugged pilot jet or leaking carb mount.
I would take them back off. Also check out XJ bikes forum. They have some pretty smart guys concerning Hitachi carbs. BTF

 

[teazer]

Take off the float bowl and you should see a hole in the front face going down to the bottom of the bowl where there's a second hole. In the bottom of the well there is a small brass jet that gets clogged. That's the one that needs to be cleaned out. Try some clr and then after you flush it with water try to blast carb cleaner though it.

Your carbs are basically the same as these http://pinkpossum.com/GT750/carb/BS40carbs.htm

 

[sodapopdave]

When I pulled the carbs last I did not see any jets in the float bowl, I double checked by looking at a exploded parts diagram of the carbs and there is no jet there (Mikuni BS-30 carbs).

I replaced the pilot jets with new ones and also the boots going from the carb to the motor. Maybe something keeps clogging the new jets - I don't know, cleaned them real good and blew out all passages with compressed air. Thanks for the tip on the XJ bikes forum, I will check it out.

 

[teazer]

The jets in the float bowls are there but are pressed in and are not available and cannot be removed, but they are down there at the bottom of that hole. Did you check that web link for a better view of what I'm trying to describe?

if it runs OK at idle when warm but runs on 3 when cold, it's the enricher circuit that needs to be checked.

I have cleaned many racks of BS carbs - but none from your model - and they all get clogged enricher jets.

 

[sodapopdave]

teazer, you are THE MAN! 8)

I was able to pull that bowl this morning without removing the carbs, thank God, since it was on the outside. You were exactly right, the jet was clogged pretty good too. Blew some air through it and it came clean, put it back together and I feel the pipe heating up right away and seems to start much easier (no throttle needed)!

Thank you again for the help, sorry I doubted you - after re-reading your link I checked out the service manual for my bike and it shows it there, don't know how I missed it all the other times.

Makes me want to tear out the rack again and clean them all but I think I'm just going to ride for now and plan for a full rebuild sometime in the next few months.

 

[teazer]

No worries. Glad it's running again.

Those tiny jets are buried so deep that unless you know to look there, you would swear they aren't there. And once you know, you wonder how you ever missed them. Life is like that at times.

Have fun.