cylinder running cool

[francoisloubser]

I am new to the biking scene and need some advice. I have a 1974 GT750 that I fixed up(restored). The bike is running beautifully, BUT I find that (when sitting on the bike) the right hand exhaust gets hot. the middle one a bit cooler. The lefthand cooler still. All this on idling. Spark is fine on all plugs. If you drive a bit they will all be very hot as expected.
It seems all is well, I am wondering about the left hand side running cooler at idling.
Any help will be appreciated.

[H2RICK]

If your sparks AND timing are fine at idle, then (assuming your compression is equal on all cylinders and there are NO air leaks) then it's got to be a carburator problem. Maybe carb
synchronization is off, maybe partially blocked pilot circuit, etc.

[francoisloubser]

Thanks h2rick. What is funny is that all the cylinders are smoking bur the left is cold, even though the the smoke seems the same. I am running my fuel at the moment 20:1 mixture as I want to make sure all is well in the 2 stroke oil delivery. Would it be best to first take the carbs out to see if there is anything cloging the jet. How would one test if feul is being delivered??? to the cylinder. Another thing I niticed is that if I disconnect the right hand plug the rev falls and it is the same with the middle one. If I disconnect the left one there is no real difference.

[markj]

with the crossover exhaust tubes you'll still get smoke from the running cylinders through the non running cylinder's exhaust pipe. I'm guessing this may be why you're seeing that even though it's not firing.

[francoisloubser]

What is the easiest way to check if petrol is going to the cylinder. Could one take the rubber of between the engine and carb. Should I get a spray of petrol??? and disconnect the plug of course

[h2okettle]

If everything Rick says is fine, another thing you can do is pull the airbox off. Then with the bike at idle you can take a spray bottle with fuel in it and spray/mist it in the back of the carb of the cylinders in question.. If the idle picks up then you probably (maybe) just have a slightly clogged pilot jet.. It will be starving for fuel at idle, but under throttle acceleration its getting fuel from the main jet.. This happened to my 74 GT750 coming home from Deals Gap once.. Running down the road it was perfect.. But when stopped idleing, it would drop the center cylinder.. Pulling the carbs off I found a piece of trash stuck in the pilot jet. Removed it and blew carb cleaner through all the jets to make sure they were clear.. After it ran perfect..

Allen..... Heavy smoker...... CCI !!!

[tz375]

I had the same problem on teh last GT that I built. I had rebuilt teh carbs so it could not be that and it had new plugs and electronic ignition.

In your case the left cylinder is not running at idle but is OK when you rev it out. Same as mine. That points to a blocked pilot jet or a blockage in that circuit.

First, drain teh fuel form all three float bowls through the small drain bolts.
Pull the carbs off and drop the float bowls. Remove the pilot jets and clean them out. I like to blow through them with a can of carb cleaner and that way I can see if they all allow the same amount to spray though. Then spray through all the small drillings in the pilot circuit especially around tehmixture screw.

If a pilot jet is blocked replace it with a new BS30/96. They look similar to other Mikuni jets but are very different.
http://pinkpossum.com/GT750/carb/BS40carbs.htm" onclick="window.open(this.href);return false; for more details

[francoisloubser]

Thanks all, it was a blocked pilot jet. The 3 small holes was basically not holes anymore, cleaned it and now idling perfectly.

[H2RICK]

Way to go, Francois !!! C'est de logique, n'est-ce pas ??
Now you have one more piece of troubleshooting knowledge stored away in your memory banks.....for next time.

[francoisloubser]

I cleaned the carbs properly today after fixing my idling problem. Now the bike revs at 2000pm +, I saw that if i twisted the throttel hard to the close position to the close position that the revs fall. So I adjusted the throttle cable to drop the revs to 1500 as I could not get it lower than 2000 with the idling screw. I assume the previous owner had the dirty carb and he pushed the revs up by adjusting the throttle cable, I assume this as with the dead carb the idling was around 1500. Once I got the carb running idling went up to a bit over 2000 and the idling screw could not lower this. Myquestion is this how do I know the tension on the throttle cable. I adjusted the throttle cable to Idling around 1500m and then fine tuned it with the idle screw. All with the motor warmed up nicely

[TLRam1]

Throttle cable should have some slack when in the idle position and the return mechanism resting on your idle adjusting screw.

[francoisloubser]

Thanks tlram1