Poor sparks on front cylinders

[MadDogRoger]

Thanks for the offer Red Baron, but a little ingenuity gets you a long way.
Got word from Topham that they don't have the floats listed. They asked for some pictures and measurements to see if any of their stock in the warehouse matches.
I hope they find some. I'm not looking forward to patching up the old ones.

Greetz,
Roger

[phildu31]

Why do you want to change the floats without testing them ???

[MadDogRoger]

Why do you want to change the floats without testing them ???

As I mentioned, the floats were pretty crooked when I opened the carbs for the first time. Obviously someone had had a go at them previously.
I straightened them out as good as I could and they do look straight, however the one thing that is very hard for me to check is the hole for the float axes. The hole consists of two pieces that have to be perfectly aligned. Bending on the float won't exactly help in the aligning department.
It only takes a tiny bit of misalignment to have the float stick. I don't think this can be detected by hand.
So I ordered 4 new floats and float axes today from Topham. If that doesn't solve the overflowing, then I don't know what will.

.
It's a matter of logical elimination. The only thing not changed between gas tank and overflowing carbs, are the floats.
Given the history of the floats (being bent to start with), the likelihood of them having to do something with the problem is pretty big..
The problem is not that they are leaking but that they are sticking on the axis around which they rotate. If a gentle tap with a wooden stick, shakes it loose, it isn't sticking much yet still enough. I don't think this can be felt by hand with the float bowl off, because I didn't feel the float sticking at any point. But then again, it's a very delicate balance.

Got word from Topham today that they looked through their entire warehouse and don't have any floats resembling the ones that I need.
Next route is the Yamaha dealer. Let's see if they still sell them and what they want for them.

Greetz,
Roger

[phildu31]

And what will you do if the overflow still occurs with new floats ?
You can't even be sure that your new valve sets are ok.
You have a carb overflowing, start by swapping parts between the leaking one and another one until you identify the faulty part !!
Or do as you want ! But I'm afraid this won't be the last part you'll buy to test and try...
We haven't even talked about the engine itself.

[MadDogRoger]

You can't even be sure that your new valve sets are ok.

Please explain. My philosophy is that when you use new, quality parts, you can assume, no expect that they work correctly. From your remark I take it you assume nothing works correctly until proven??
I'm not trying to be an asshole here, just trying to understand your point of view and learn from it.
I agree that swapping floats is a good way of testing whether they are the problem. It doesn't cost anything, it's reversible and it will always tell you something. One way or the other. I certainly will try it. I just don't understand your comment. If you can't trust quality parts then where does it all end???

Greetz,
Roger

[Brad Winchester]

I feel your pain with the leaking carbs. For what it is worth, these are my thoughts. I think you are spot on with your thoughts on the floats. My 4 floats were not identical in shape. I have replaced everything in the carbs except the floats and could not stop the overflow. I "experimented" with bending the floats until they seemed to work freely. Also if the floats are bent, the float adjustment as per the manual may not be right. I worked out that 50ml of fuel in each carb seemed to work OK. So I adjusted/bent the floats until they cut off at 50mls. I would like to replace the floats, but it seems OK at the moment. When the carbs were too full of fuel, I had intermittent firing of the cylinders and like you, chased a non existent spark problem. My next modification is to replace the original carbs with 28mm keihins.

[MadDogRoger]

Hi again,

It has been a while since the last post. Didn't do much work on the RD due to some house re-modelling that took a couple of months and it being too cold in the unheated garage to work on it.
But with better temperatures I picked up where I left off. Did some thinking in the meantime and decided to try a leak-test. So off with the carbs and pipes and on with the leak-test.
This is what I found:


This is at 4 psi, mainly on the left cylinder. The right cylinder is less but also shows a leak.

So I set to it to remove the intake rubbers. It took a lot of fiddly work but I managed to get both intakes off without taking off the upper intakes or the power valves support bracket. Of course the rubbers aren't very supple but there are no cracks in them.
The reeds valves look pretty good. If I hold them towards the sun I can't see any light at the tops, only on the sides there's a tiny slit of light. Should I be worried?
The reed valves have a protruding rectangle (tab) on one side of the housing (see video). Is there a preferred direction for mounting these? Both tabs were pointing to the left of the bike.

How should I proceed with the leaks. Does anyone have some experience with this? There's no gasket between inlet rubber and reed valve body. There's a metal plate worked into the foot of the inlet rubber. There's a smaller rectangle in the foot of the inlet rubber with some sort of sealing lip.
I have some gasket material from which I could make a gasket. I could mount this with some silicone sealant. Would that do the trick?

I will also have to change the oil supply lines because they have hardened over time and leak ever so slightly at the connection pin. That's why the foot of the cylinders looks so oily.

As ever, any thoughts on this is greatly appreciated.

Greetz,
Mad Dog Roger

[Bengt Weil]

As for proper orientation of the reed cage assembly -

http://rzv500r.net/Workshop_Manuals/47X ... ge_114.jpg

The leakage you are experiencing is very common and shows up during leak-down testing. Problem can be solved with a thin coat of Yamabond on the leaking surface of the rubber intake manifold. Be sure to do another leak-down test after re-assembly, checking each crank assembly under vacuum as well as pressure. Air leaks will hinder proper jetting and can lead to complete engine failure - check all crank seals & gasket sealing surfaces again if vacuum/pressure doesn't hold.

[MadDogRoger]

Hi Bengt,

Thanks for your reply. A thin coat of Yamabond it is, no extra gasket.
Uhm, how do you check under vacuum?? I have a compressor so pressure test is not a problem. But I don't have a vacuum pump.
Do I need a vacuum pump or is there a home made setup that can do the trick?

Thanks,
Roger

[Bengt Weil]

Correct - no gasket, just the Yamabond. My apologies for not clarifying.
For the vacuum test, you can use a brake bleed hand vacuum pump with a gauge - induce the amount of vacuum and see that it holds or goes down no more than the minimum allowable amount. Always best to test the vacuum pump/gauge to see that it properly holds the vacuum on its own before trying it on your lower end.

https://www.harborfreight.com/brake-ble ... gKD_PD_BwE

[kpke]

Hi Bengt,

Thanks for your reply. A thin coat of Yamabond it is, no extra gasket.
Uhm, how do you check under vacuum?? I have a compressor so pressure test is not a problem. But I don't have a vacuum pump.
Do I need a vacuum pump or is there a home made setup that can do the trick?

Thanks,
Roger

Roger, I'm not sure that you want to use a compressor for your pressure test. You do not want to over pressurize your engine for fear of blowing seals out. I use a bicycle hand pump for pressure checking.

[Bengt Weil]

Absolutely do not use a compressor -

Look for 5 psi for 5 minutes for the pressure test. A loss of no more than 1 psi is considered acceptable (though I'd still see if you can locate the leak with soapy water). Exception is when the crank seal on the primary side leaks, it is hard to find until the engine runs and the primary/clutch oil starts disappearing.

Vacuum test should be 10 inHg of vacuum for 5 minutes with no more than 2 inHg loss.

Never exceed 6-8 psi or 12-16 inHG of vacuum

[MadDogRoger]

Absolutely do not use a compressor

NO NO don't worry, I just meant that I have pressurized air available. The video is at 4 psi.
But thanks for the figures on the vacuum, I didn't have them.

I know what I'll be doing this weekend

Greetz,
Roger

[MadDogRoger]

Hi all,

Something came up in the weekend so it took another week.
I managed to get the intake leak sealed with Yamabond. Checked with pressure test and they are sealed.
Didn't have access to the vacuum tester so put the bike back together and tried: .
Nope same story: lower pipes remain cold and the two cylinders not working.
Then I remembered my son has a brake bleeding kit with such a pump so borrowed that and did a vacuum test this evening.

With the vacuum pump not hooked up to the bike I can easily get it up to 12 inHg. However if I hook it up to the bike the highest I can get it is 7.5 inHg.
It almost immediately drops to 7. After 5 minutes it's still 6.5.
Does this mean the main crankcase seals are leaking? And would this explain the flooding of the cylinders?

Another thing, when I took the pipes off I again could pour some gasoline/oil mixture from the pipes. If this mixture ends up in the pipe, is it fair to assume that the crankcase will also be flooded?

Greetz,
Roger

[silverstrom]

Hi all,

Something came up in the weekend so it took another week.
I managed to get the intake leak sealed with Yamabond. Checked with pressure test and they are sealed.
Didn't have access to the vacuum tester so put the bike back together and tried: .
Nope same story: lower pipes remain cold and the two cylinders not working.
Then I remembered my son has a brake bleeding kit with such a pump so borrowed that and did a vacuum test this evening.

With the vacuum pump not hooked up to the bike I can easily get it up to 12 inHg. However if I hook it up to the bike the highest I can get it is 7.5 inHg.
It almost immediately drops to 7. After 5 minutes it's still 6.5.
Does this mean the main crankcase seals are leaking? And would this explain the flooding of the cylinders?

Another thing, when I took the pipes off I again could pour some gasoline/oil mixture from the pipes. If this mixture ends up in the pipe, is it fair to assume that the crankcase will also be flooded?

Greetz,
Roger

Sounds like your float valves (needle and seat) are leaking. This results in fuel getting into the cylinders and pipes. Are your lower cylinder spark plugs wet? That would also result in poor running on the affected cylinders. That could mean cold pipes when the lower plugs aren't firing because they are wet with fuel.