Topic: #2 Cylinder head pipe cooler than the other 3.

[72_350_FOUR]

My #2 head pipe is much much cooler when the bike is idling, and when I go out on the road and i give it some throttle you can almost hear it kick in...  I've done all the 3000 service and my carbs are clean and synced.  Would you guys look at a float level not enough fuel problem?  I'm getting spark so i know it's not the coil or ignition.   The bike just seems to "miss" and not have the power it should, and i know this is the reason i just cant figure it out.  can you help a brother out?

[Gordon]

Eliminate the easy things first.  Switch the spark plug to another cylinder and see if the problem follows it.  If not, there's a Carb problem. 

[trueblue]

A leaky valve can also give a miss at idle and run fine at higher revs.

[Terry in Australia]

I'd just about bet my left testicle that it's a blocked idle jet, just about the most common cause of poor idling on old bikes. I can't remember one bike that I've pulled out of a barn that hasn't had at least one blocked idle jet.

I bought a CB750K2 in 2005 that had been sitting in a barn for over 20 years, and it looked really rough. I removed the head and realised that the engine had been rebuilt with new pistons and rings, but due to a blocked idle jet the PO had given up on getting it running properly and parked it, because one piston was still shiny and new whilst the other three had carbon deposits on the crowns.

I cleaned the idle jet, replaced the head, and that engine pulled like a train! Cheers, Terry.

[72_350_FOUR]

Terry, that's the first thing i thought of but i know it's clean, i just rebuilt them,  although of course i wont discount it til i pull them back off and look again. I guess some sediment from the tank could of gotten in even though i cleaned it.   Now that i think of it I have always used carb #2 for my baseline for synching the carbs... could it be completely out of whack?  I'll use # 3 or something and see if that makes a difference.  If I had a bad valve would i see other signs like oil burning? or excessively rich plug on that cylinder? 

Thanks for your replies..

[Terry in Australia]

So when you say you cleaned it mate, you removed it from the carb, and looking thru it, you could see daylight, yeah? Then you blew the circuit out with compressed air, and you checked that it was totally unblocked too? Sorry if I sound like Lloyd, (Two Tired) but a lot of folks assume that they've cleaned everything when all they've really done is sprayed a bit of carb cleaner around?

If it's a valve problem, it'll most likely be a burned exhaust valve. Do you have a compression tester? If so, don't worry about firing the engine up to normal operating temperature, that is the best way, but if you do have a valve problem, even if the engine's cold, it'll still be obvious, as you'll have less than 100 psi pressure in that cylinder.

Check them all, and if you want to risk burning your pinkies on a hot header pipe run the engine by all means, (you'll never forget the pain, take it from me) but as I've explained above, not really necessary as the difference will be huge between a good cylinder and a bad one. I hope this helps! Cheers, Terry.

[trueblue]

It could also be as simple your valves being slightly too tight.  If the valve is really bad you will get a black plug, but if it is only minor you may not.

[matt mattison]

Is the inside of your tank clean and rust free? If its not, that alone will foul a clean carb up every time.

[72_350_FOUR]

Yes sir i completey took the carbs apart including the emulsion tubes, and cleaned with toothbrush bristles, and verified light coming through.  The tank is clean but not perfect, so i'll look for sediment too.  I dont have a compression tester but will get one.  I'll pull the carbs off and clean the slow jets again, and also switch the plugs around. i'll post back when i run put of things to try, thanks for the suggestions, Im almost betting on a slow jet, cause as soon as i get past 1/8 throttle you can hear the other cylinder kick in.  so it has to be in the slow system somewhere.         

[Teatimetim]

I would pull the carbs off again and re check..   and also so make sure you blow out the air passage ways for the idle jet at the mouth of the carb.

I had the same problem, patted myself on the back cause I thought I had done such a good job, found that I forgot to tighten an idle jet, and it had fallen out, lodged in the float and  cut flow to the carb.  We are humans and therefore we make mistakes.