750kat in 2 pistons

[random_kat_rider]

I have a `95 750 kat. After timing chain and gasket set replacement seems to not run as it should. The bike starts really easy even if cold and seems to run fine at idle but the exhaust pipes on pistons 3 and 4 are cold even after 20mins of running. If i unplug the spark plugs on 3 and 4 there`s no difference in idle speed.

piston rings installed gap 0.30-0.35mm (limit 0.70 in service manual).
valves grinded 2 weeks ago.
carbs sincronized (i have a sincronizing device installed on bike right now).
i have spark on all plugs.

i fully cleaned carbs 2 times with carb solvent and comperessed air. I tryed fuel/air screws at 1.7, 2.5, 3.5 turns out of maxim.
needle is set on 3/5.

thanks for any advice.

[stretched600]

First off, Welcome to the KR forum...Now you could be having one of several problems! Since, you did say you had the valves ground recently, it could be a seating issue...Also, I'm hoping you changed the plugs, even though you are getting spark! Check your plug order as well...My final thoughts are that you may not being getting fuel in those 2 carbs...The synchronizer will show only the vacuum (air) they pull! If your carbs have 2 separate inlets like mine does...that would be where I'd start!

[squiggy]

Try a compression test on those two cylinders. Since there is no noticeable difference when unplugging the spark plugs, I would suspect a no compression issue rather than a no fuel or spark issue. If there is proper compression, those two dead cylinders would hinder the rest of the engine; it would cause lugging in the engine. But since you state the engine runs fine as it is, those two cylinders are freewheeling with no resistance, i.e. compression. It could be a valve issue like Stretch said.

If it was fuel related then you should be able to smell unburned fuel coming out the exhaust; the exhaust would smell rich. If your not getting any fuel, that's typical of a stuck float in the closed position.

[random_kat_rider]

thanks for replys.

i tested the compression and cylinders:
1,2,4 - over 10 bars.
cylinder 3 - 4bars.

put oil in cy 3 and after new test - over 12 bars.

I`ll remove the head and cylinders to check.
should i replace base cylinder and head gaskets (like 30mins of running) or can i try use them one more time ?

[squiggy]

I`ll remove the head and cylinders to check.

If you have access to a "leak down tester" it will tell you where in the combustion chamber your having sealing issues. Whether it be a piston ring issue or an intake valve or exhaust vale issue or even a head gasket issue.

should i replace base cylinder and head gaskets (like 30mins of running) or can i try use them one more time ?

I could not say for certainty, however, when I replaced my cylinder head the gasket appeared to have the ability to compress when the bolts were tightened down to spec. Since the head gasket has already been installed and compressed, it may not want to seal a second time around. Again this is just an observation.

[steves]

My head doesn't operate in units "bar" but for a compression test I think you want something in the range of 100+ PSI. Did you hold the throttle wide open during your compression test?

I think that the head gasket is reusable so long as it hasn't been damaged.

A leak down test is the best way to figure out what's going on.

[tmk7c9]

should i replace base cylinder and head gaskets (like 30mins of running) or can i try use them one more time ?

Replace it. Those gaskets are meant to compress ONE time, and then they're basically shot. Same goes for the crush washers on the cylinder head nuts....those should be replaced too.

Can it be reused? well, technically yes, if you're a college student on a mac & cheese budget. I reused the same head gasket on my Bandit 12 multiple times back in the day, $70 for a new one was simply out of the question at the time.

To do it right, and make it last another 30,000 miles, replace it with a new one.

[ATOMonkey]

On a cold engine, without changing the petcock, crack the fuel bowl drains on 3 and 4.

Then crack the drains on 1 and 2.

See if there is any difference in how much fuel comes out.

Since 3 and 4 are paired with the same fuel inlet Tee, you may have a fuel delivery issue. Could be a line, the tee, or a petcock problem. Make sure the tank isn't crimping a line.

[squiggy]

My head doesn't operate in units "bar" but for a compression test I think you want something in the range of 100+ PSI.

I had to Goggle the conversion too.

1 Bar = 14.5 psi.

[random_kat_rider]

My head doesn't operate in units "bar" but for a compression test I think you want something in the range of 100+ PSI. Did you hold the throttle wide open during your compression test?

I had to Goggle the conversion too.

1 Bar = 14.5 psi.

Sorry for measurement units used. I`m from Europe. We usualy use metters and bars here . I`ll translate in next posts . This can also explain my poor english. Is not my native language.

I didn`t touch throttle during the compression tests. Can this be a reason for test results on cyl.3 ? Why the high compresion with oil inside ? Or maybe i put enough oil to fill the whole compresion chamber...

I`ll remove carbs tomorow and redo the tests.

[ATOMonkey]

If you put oil in the cylinder it will typically seal better than without. It makes a hydraulic seal on top of the compression ring.

There isn't supposed to be any oil near the compression ring, so it's not a good representation of the actual workings of the engine.

Typically you do a compression test with the throttle wide open so you don't get a bad reading from a throttle that is more or less open than it should be. Hole 3 could have been low because that's the way it was synchronized.

I still think it's a fuel problem.

[steves]

This link has some information on making a home-made leak down tester.

http://www.dootalk.com/forums/index.php?showtopic=132291

[random_kat_rider]

If you put oil in the cylinder it will typically seal better than without. It makes a hydraulic seal on top of the compression ring.

There isn't supposed to be any oil near the compression ring, so it's not a good representation of the actual workings of the engine.

Typically you do a compression test with the throttle wide open so you don't get a bad reading from a throttle that is more or less open than it should be. Hole 3 could have been low because that's the way it was synchronized.

I still think it's a fuel problem.

I put oil there only to check where`s the leak. If it still leaks after i put oil on top of piston most likely is a valve problem.
I see the point of throttle now. Must be opened so the engine can get cylinder full with air before compression.

You gave me hope. I can`t afford new gaskets right now, lost my job 3 months ago. That`s why i have time for my bike.
If is only a fuel problem i`ll be really happy.


Thanks steves, seems quite simple to build a home made leak tester.

[random_kat_rider]

Ok, i did compresion test with no carbs. Same results, cylinder 3 compresion is low.
Removed the cylinder head, i tested valves, 100% no leak.
Removed cylinders. Piston rings on piston 3 in perfect shape. Lower than 0.35mm installed gap.

Can this be a head gasket problem ? Was brand new torqued at 40Nm.

[steves]

Did you follow the procedure for tightening the gasket? There is a special pattern you are supposed to follow.

And you ensured the cams were lined up correctly, and had the correct number of links between the cams?

You didn't rotate the crank shaft while the cams were removed, did you?