Hello everyone

This is my first post.,

I have a 1981 TR1 XV1000.

My rear cylinder is running very rich and fowling the spark plug.

I have replaced the inlet manifolds on both cylinders, checked the float bowl fuel level (it's spot on), adjusted the pilot jet to full lean (all the way in), fitted a brand new air filter and it still runs rich.

The front cylinder is fine.

Any ideas?

Thanks,

Chris.

Hey all,

Never mind.  I have sorted it.  It turned out to be the float level after all.  My workshop manual has two ways of measuring the float level.  One involves a clear length of fuel hose connected to the drain tap, the other involves removing the carbs and measuring the distance from the top of the float to the gasket mating surface.

Using the clear fuel hose method indicated that it was spot on.

Using the carb removal method showed that it was 4mm too high.

So I reset the floats and it runs perfect.

My workshop manual (Haynes 802) also has an error in it concerning the main jet sizes.  It says that the left carb main jet is a 126 and the right is a 124.

Every other XV model has the larger jet in the right side carb so I don't see why the TR1 should be the other way around.

My carbs had the 124 in the left and the 126 in the right and it runs perfect like that (now that the floats are sorted out).  It also seemed the wrong way to go to take the manuals advice and put the larger jet in the rear cylinder which was already running too rich.  Glad I measured the floats instead.

Is it just me or is it impossible to get the carbs out without taking the inlet manifolds off the heads?

Chris.

Sounds strange that the clear hose method should be wrong?? Worked great for me. Sounds like the float needle is not closing completely, perhaps there was some dirt trapped that messed things up?
Sometimes the choke plungers start leaking and the richer mixture fouls the plugs. The choke plungers have rubber tips that gets old and hard. Very hard to get new ones but an alternative is to buy used carbs and hope for the best... All Hitachi carbs for the XV:s are the same (1981-1983)

The left carb feeds the rear cylinder and should have a bigger main jet to keep the temperature down. Lean jetting runs hotter than rich.
No, It's not only you; you have to remove the inlet manifolds to take off the carbs.

ChrisACT wrote:

Using the carb removal method showed that it was 4mm too high. So I reset the floats and it runs perfect.

And how much is the distance between the floater and the sealing surface?


Quote:

My workshop manual (Haynes 802) also has an error in it concerning the main jet sizes.  It says that the left carb main jet is a 126 and the right is a 124. Every other XV model has the larger jet in the right side carb so I don't see why the TR1 should be the other way around.

You need the larger jet in the carb for the rear cylinder. That makes the mixture slightly richer when running with full open throttle, which gives more cooling to the rear cylinder. This is because the rear cylinder is behind the front cylinder and does not get so much cooling air.

Bye,
Georg

Quote:

And how much is the distance between the floater and the sealing surface?

15.8mm as my workshop manual states.


Quote:

You need the larger jet in the carb for the rear cylinder. That makes the mixture slightly richer when running with full open throttle, which gives more cooling to the rear cylinder. This is because the rear cylinder is behind the front cylinder and does not get so much cooling air.

Here's what my workshop manual says:

Main Jet            XV750(UK)    XV750(US)    XV920RH & RJ    XV920J    XV920K, MK    TR1

Left (rear)         122              122              126                    126         126                 126
Right (front)      122              122              124                    128         128                 124

According to this the XV750's have the same size main jets in both cylinders, the XV920J, K & MK have the larger jet on the front cylinder and the XV920RH, RJ and TR1 have the larger jet on the rear cylinder.

It seems a little inconsistent to support the theory that V-twins need the larger jet in the rear cylinder for cooling(even though that theory makes sense to me).

Does everyone elses workshop manuals say that the TR1 has a 126 in the rear cylinder and a 124 in the front?

Chris

Directly from the supplementary service manual from Yamaha:
Main jet; #1 cylinder #126, #2 cylinder #124.

N.B. ; #1 cylinder is the rear one and #1 carb is the left one.

OK, I'm convinced.  I've changed the jets so that the 126 is in the rear and the 124 is in the front.

One last thing.  When you refit the carbs, is everyone just using the gasket and O-ring to seal the inlet manifolds to the heads or should I use some kind of sealing compound as well to make sure there are no air leaks?

In other words, does the gasket and O-ring do the job or does it need some help?

Chris

No sealer should normally be used but if you don't get a good seal you could use silicone sealer.

now you have changed your jets I was going to suggest, if the rear is fouling the spark plug again, use a hotter running plug? I don't think a hotter plug would make a big deal to the general running temperature of the cylinder?