That's what I get for bragging--idle problem

Just this morning I bragged about my bike running "perfectly" and damn if it didn't start having idle problems today. Seems to be losing one cylinder at idle and shutting down. Otherwise it runs perfectly. I'll try some new plugs first, and hopefully that will solve the problem--but the ones in there now only have a couple thousand miles on them. If I have to pull the carbs I guess I'll replace the seals, although I have no evidence that there is a problem with them. I've used propane around the seals with no change. Would that work to find leaks in the seals? Think that could have any connection with the idle issue?

 

Id check the plug caps first and see if you have "cold" cylinder ...My Honda CB750 did this to me drove me nuts replaced coils no help , plugs no help ...pulled the cap on #2 cylinder it was green in side put new cap on and vrooom no more problem .

 

Good idea. I'll check them before putting in new plugs.

 

Also, swap the spark plug from the mis-firing cylinder to another one, see if the problem "follows the plug"............

 

C

I don't think I can keep it idling long enough to figure which one --or ones--are missing. But I'll give it a try. Probably will be this weekend.

 

Did you just fill up your tank and get some crappie gas ?

 

This has been discussed before, and I am relatively new to motorcycles.
How do you know that you have 'lost' a cylinder?
Loss in power?
Sewing machine starts to sound like a weedwhacker against a fence post?

 

Idles rough. More evident though, the header pipe for the non working cylinder stays cold.

 

I have a general practice for not touching header pipes. Ever since my first trip to Rockerbox, parked my bike went to put my helmet on the ground between the front wheel and engine and my fore arm touched a pipe - gotta scar to prove it.

 

If one of the header pipes is cool or warm while the others are hot, it can mean a couple of things. One common problem is a bad carb sync and fuel to air mixture. Colortune it baby! Another is bad spark from the coils or the plugs are fouled up. Even with one cylinder not firing it should still idle.

when the bike is running how is the exhaust? does it smell different or was there a color change?

 

A clogged pilot jet/pilot curcuit on the dead cylinder perhaps? Does the cold cylinder kick in when driving with load?
If that's the case, you might have someting blocking your pilot jet. I had this issue as well (after I had cleaned my carbs and done the valve adjustment. I guess I wasn't
thorough enough cleaning/mounting the jets). A bit strange that your bike will not idle on 3 cylinders, though - mine did but rough of course.

Was not very keen upon breaking the carbs again (a nightmare to get the airbox boots on), so here is what I did in a desperate time.. This might be an option for you as well if you can access the pilot mixture screw easily, even though a complete carb cleaning/rebuild most likely will be the best option.
* took the tank off
* drained the bowl from that particular carb and let the drain screw left open
* took out the pilot mixture screw for that troubled cylinder (bottom down gently first, counting how many turns the screw are set) - At least in my bike, that screw consist in addition of a spring, a TINY washer and an TINY O-ring that you guaranteed has to "fish out" from the hole. This is perhaps the most difficult "operation" when carbs are mounted on the bike.
* Use carb cleaner with straw down the hole and compressed air repeatedly a few times.
* allowed the carb cleaner fluid to dry out - meaning let the bike sit for an hour before filling with fuel.
'*mount the pilot mixture screw (with all its small parts) and screw it back with the same turns out from bottom as before.

This actually fixed my cold cylinder at idle. But before you do this, be sure that you have checked the other possible culprits (coils, plug, plug cap, and perhaps compression).

; A

 

It will be this weekend before I can get back to it. Once off of idle it runs perfectly--kind of hate to use that word again--, that's why I first thought I would have to pull the carbs. But this came on so suddenly that I am now hoping that it is a loose plug wire, especially since I had just adjusted the valves and had tied the wires up and out of the way. Until yesterday the bike has been starting, idling and running great. Bummer.

 

Turns out that the spark plug cap on number 1 was loose, probably from being tied up when I replaced the valve cover gasket and adjusted the valves. Tightened it up and it starts and idles perfectly. Took a short ride with no problems. Real nice when the "fix" is that easy.

 

The KISS principal. Keep It Simple Stupid lol great that you figured it out. Now time to ride.

 

so there was a slight problem between the grips and the seat

 

I have been that. Errr had that happen a few times.