Crank Seals

[FZRichard]

Over the last few rides on my 3XV1, I have noticed when coming to a stop, the revs hanging at around 1700rpm then slowly dropping to 1300rpm taking 20 or so seconds. It never did this previously. Could it be the crank seals? Is there a way to test these seals without a leak down tester?

Is the best method to set the idle speed and mixture screws by isolating one cylinder at a time and tune each cylinder separately?

[JKV45]

Over the last few rides on my 3XV1, I have noticed when coming to a stop, the revs hanging at around 1700rpm then slowly dropping to 1300rpm taking 20 or so seconds. It never did this previously. Could it be the crank seals? Is there a way to test these seals without a leak down tester?

Is the best method to set the idle speed and mixture screws by isolating one cylinder at a time and tune each cylinder separately?

I'm not a 3XV expert, but that's typical of some kind of vacuum leak.

As far as tuning, I adjusted the idle mixture by deactivating one cylinder (ground a spare plug), bump up the idle a bit, and adjust to get the highest RPM.

For syncing the carbs, I turned the idle speed back-down, reactivated both cylinders, and read the exhaust temp at the manifold right at the head.

You have to match the temps and also get the correct idle speed at the same time.  Takes a bit of fiddling, but it seemed to work.

[ybk]

@FZRichard Yeah sounds like some sort of air leak. Leak down test is the only sure way to know.

Are you running the stock fuel tap? Maybe check the vacuum feed on the top carb first. If it's not sealing then it will leak air there. People have had issues with the YEIS bottles as well. They can split on the seam.

Idling as JKV45 said is done 1 cylinder at a time with the plug out.

Mixture screws just turns out as per manual.

[FZRichard]

When I take the plug out of one cylinder and set the idle on the functioning cylinder how many rpm do you set the cylinder to? Not sure where the mixture screws are at now so I will have a look at them.

I will also check the vacuum feed on the carb. I could also spray around the carbs with some starter fluid to see if I can find a leak.

Are the 3XV1 cylinders the Nikasil type or do they have steel sleeves, it is just an R model?

[JKV45]

When I take the plug out of one cylinder and set the idle on the functioning cylinder how many rpm do you set the cylinder to? Not sure where the mixture screws are at now so I will have a look at them.

I will also check the vacuum feed on the carb. I could also spray around the carbs with some starter fluid to see if I can find a leak.

Are the 3XV1 cylinders the Nikasil type or do they have steel sleeves, it is just an R model?

Don't remove the plug, just take a spare plug and insert it into the cap - then ground it.

I initially set the RPMs to 2000 when running on 1 cylinder, then adjusted the idle mixture to get the highest RPM.  It was easier to see with the initial idle at 2000.

You can set the idle mixture by the recommendation in the manual.  I ended up being pretty close.

The idle mixture screws are different, and in different locations on the carbs. Settings are different as well.

Download the service manual to help guide you.

[thump566]

Could you get access to a leak down kit from someone in your neck of the woods ?

[FZRichard]

I have ended up making my own leak down kit to test the crank seals.

I got a piece of tubing, 36mm I think, and welded a cap on one end. Installed a Schrader valve and a 3/16 barb. The tubing fits perfectly into the carb boots. I am not the best welder, but I got it airtight.

So, I can pump it up to 6 psi with a bicycle hand pump and run my pressure gauge from the barb fitting to see the pressure.

Also made a plate to block the exhaust, it's on the left in the picture.

It did need some epoxy around the Schrader valve for it to be able to seal properly. Tomorrow when the epoxy is dry, I will test it out on the bike.

Cost me $6 for the bike pump and $9 for the barb fitting, everything else I had lying around the shed.

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[thump566]

We also made our own kit in the UK and it evolved with each use. If you Google MotoToki you will find numerous videos, one is solely covering the leak down kit and it's functions. Possible food for thought.

[FZRichard]

I had a look at the MotoToki video. I had not considered the oil lines from the oil pump, will block them up.

[FZRichard]

Instead of removing the 2 stroke oil lines and blocking them I think I will just use some vise grips and pinch them to block them.