Hi everyone,

I have renovated my old TR1(5A8) engine and i am having troubles getting the mixture in idle dialed in.
I hope that some really clever people can help me out inhere

My problem is the front cylinder that is running really rich.
No matter how far I screw ind the mixture screw i get a really rich mixture. 13/14% on the gas tester, and a really yellow/orange color on the color tune.
My exhaust from the front cylinder also looks like an old British chimney.

I have checked the carburators multiple times, all the jets, needles, float height(many times), diaphrams and so on.

- The entire ignition system has been checked
- filters and air passages.
- carburetor mounts for leakage
- gasoline
- carbs has been synchronized several times.

When i drive it, it runs decent, but i am always worries it will turn of the engine.
The engines start really well and idles decent aswell, but in time the spark plug gets so black that it starts misfiring.

I am thinking now:
- could it be valve stem seals (but do they influence the co tester?)
- could it be worn piston rings? (The smoke is not white or grey but black)
- could it be a bad valve? (Would that influence the mixture? I guess that would be poor engine performance and behaviour)

I am really lost here and need some advice

Good morning Greg,

if you are inspecting your carburettors:
1) as nanno said before, check for proper installation of all jets to the corresponding carburettor.
2) check diaphramas for cracks or puntures in the rupper surface
3) check the stater plunger inserts for correct sitting in place, sometimes the rubberseals are old and not more so flexible. if you pull the Choke cable, watch for the moving of the stater plungers. After releasing the Cable, does the Starter plungers are going back to fully back (closed) positions? Check it by pushing the little piston on top of it. If they are able to push a little bit more in , they are open a little bit, that on the other side enriches your mixture.
4) Pilot Srew: basic setting is 2 evolutions out ( from the complete closed position. if you have turned out the Pilot screw, renew the little O-Ring, to prevent later problems. I mean, the older the Rubber material the more it goes harder. And hard Rubber is not usefull to seal sensitive adjustments.
5) after the Engine starts and warmed up perfectly let it run for a while with some raised rpm from time to time. After shot down check the colors of the ign-plugs to inspect how the adjusted mixture works. Color shout be between white-light grey and middle grey-brown. If your bike is in condition to take a ride on it, drive it for some miles and check the colors of the Ign-Plugs ceramic insulator, then.

Hope it helps you
Regards Anja

Is your engine ventilation connected to the front or rear cylinder? Normally it is connected to the rear, but i believe i have seen bikes where it was connected to the front. Mine had also high CO2 values on the rear cylinder, i removed the engine ventilation and then i could adjust the CO2 normally.

Hi Greg,

I have double checked the jets and diaphragms several times and I am sure they work and is in their correct position. Thank you.

Hi Anja,
I have also checked the starter plungers, actually disconnected the mechanism that opens them to be sure. The bike start really easy without this.
I have installed new renovation kit for the carburetors from keyster, and have also been aware on the different parts in each set for front and rear cylinder.
thank you for the input.

Hi Hornschorsch,
Mine is connected to the rear cylinder carburetor but the hose from front cylinder. will this impact the mixture you think?

Hi Ali,
I have not checked this, but i will definitely try it. I know my petcocks are rather old. I will keep you guys updated on this, during the week. thanks!


Thanks all for the help, really appreciate it  

Hi all, it's been awhile but that life when you have small children

I read another thread where someone had troubles with bad wires, so I checked my entire wire harness, I should not have done that... I now have a complete new installed  

I tried to bypass the vacumm pipe from the intake-manifold, and sadly without any luck.
Also did a compression test on a cold motor. The test showed approx. 12 Bar on each cylinder, so I assume the piston rings are fine.

My front spark plug is very black and rear very white(with black edge), any sparkplug expert that can say anything on behalf of this?

I have discovered a ticking noise from the front cylinder head, and also found that the front cylinder backfires/misfires at times, almost looks like it want to eject the front carburetor out of its manifold. When the engine is cold and I hold my hand to the exhaust pipe from the front cylinder, my hand catches some black matter.
could this be:

- Valve stem seals?
- Worn valve springs?
- Worn valve seat?