Fuel Delivery on '92 Seca II

It seems that the carbs on my '92 XJ600 are not receiving enough fuel, so I have been trying to narrow down the source of this problem.

When it was running, the engine would seem to bog down an increasing amount with the more I pulled back the throttle. This problem gradually became worse and worse until it would no longer even start up any more. And now, I can't even get it to sputter unless I manually feed the carbs with fuel or starter fluid upon start-up.

So now I'm trying to troubleshoot the fuel system, but I've realized I don't actually know how much fuel is supposed to be delivered to the fuel rail when the engine is trying to start. Upon disconnecting the hose feeding the fuel rail (coming from the fuel pump), I'm getting a fairly steady drip, but it is definitely not a stream of fuel. Is that about how much I should expect to see, or should it be feeding fuel faster than that when the engine is trying to turn over?

And presuming that is approximately the correct rate of flow, what factors might prevent all four carbs from being fed with enough fuel once the fuel has already reached the fuel rail?


Thanks in advance for any help.

 

I am not familiar with the seca II, but there are some general basics that apply.

The fuel flow when in normal operation should be a steady stream. If not. that would be an indication of a loss of vacuum. Double check the vacuum hoses to make sure they are not cracked/broken, and that they do not crush when vacuum is applied.

It appears from the parts schematics, and pics on ebay that the fuel pump is also vacuum operated. In which case you should be able to bypass the fuel pump and apply vacuum directly to the petcock for testing. You will want to use a vacuum pump for this.

If you get good fuel flow with vacuum applied to the petcock, but not when attached to the fuel pump. You could have a bad diaphram in the fuel pump.

If you do not get good fuel flow with vacuum applied to the petcock. You could have a bad diaphram in the petcock.

Hopefully this gives you something to start looking at until someone more familiar with the system drops in.

Ghost

 

Assuming the engine is in good shape (compression, valves in check) the fuel goes like this:

Tank -> petcock -> fuel pump -> fuel rail -> floats -> jets

If there's fuel coming out of the fuel pump line, then lets assume that's working. Since it's vacuum operated, the higher the engine RPM, the more fuel comes out. So if you are just sputtering, not much is going to come out at this point.

But let's rule out the fuel pump altogether. Take the tank off and plug the vacuum line that goes to the petcock. Find an auxiliary tank (or even the actual tank set on "prime" and hook it directly into the carbs. See if you get any different results.

If yes, and the bike idles, then your fuel pump is whak

If you get the same non-running results, I would suspect you need to give your carbs a thorough cleaning, make sure the jets are clean, and set both the floats and fuel mixtures properly.

In order to have a bike run properly, these things MUST be addressed, in this order, and without skipping a step. Skip one of these steps and you'll be chasing your tail trying to get the bike to run right.

1. Valve clearances within specifications

2. Carbs surgically eat-off-them clean

3. Floats set correctly

4. Fuel/idle mixtures set correctly

5. Carbs vacuum sync'd

 

Thank you both for offering advice that should definitely help me narrow down my issue(s).

When I have the chance to work on it tomorrow, I will start by feeding the fuel rail directly to see which side the trouble is coming from before proceeding to further rule out and/or fix the potential problem areas you have described.

 

Okay, so with the fuel tank elevated, connected directly to the fuel rail, and set in the "prime" position, I am getting lots of fuel pouring out of the overflow hose between the two carbs on the right side. I thought that the floats on one of those carbs might have been stuck, so I tried knocking it free by tapping on them with a rubber mallet (since I remember that worked once before). But that definitely didn't help this time.

Regardless, the engine still doesn't seem to even sputter unless I manually feed fuel into the tops of the carbs. This has me a little confused, because I feel that even if one or two of the carbs were having issues, the other ones would still try to do their thing and at least make the engine sputter a little bit while I try to start it.

Can I use any of this knowledge to further narrow down the source of the problem, or do I just need to begin taking the carbs apart?

 

You have deffinately narrowed it down to a couple problems.

First, you have a fuel pump problem in that it is not allowing the proper fuel flow.

Second, You have a carb problem in that the floats are not shutting the fuel off properly. With the float problems also comes blocked passages, and jets. I would deffinately say that it is time to pull the carbs for a good cleaning, and rebuild.

Ghost

 

If you don't want to buy an OEM fuel pump or take a risk on a used one, there is a Polaris fuel pump which is made by the same manufacturer, Taiyogiken. It's exactly the same.

Polaris PN: 2520227

They run about half as much as a new one from Yamaha. Why? I don't know. All I do know is that they work.

 

I went ahead and ordered that fuel pump along with some new float bowl gaskets & float needles (apparently full carb rebuild kits don't exist for the Seca II for some reason).

Hopefully everything will work itself out once I clean the carbs and piece it all back together.

Thanks again, guys.

 

With the age of the bike I would also suggest replacing those throttle shaft seals also.

256-14997-00-00 SEAL

You will need 2 per carb.

Ghost

 

Well, I replaced the fuel pump and cleaned out the carbs (which were very gunked up inside the float bowls), but I still can’t get the engine to run on its own.

I have verified that fuel is getting into each carburetor (and no longer spilling through the overflow hose), but the fuel doesn’t seem to be making it into the cylinders properly. I ended up taking the carbs apart again to make sure the jet aren’t clogged or anything, and they seem to be clear of any debris. And the new float needles appear to be functioning properly as well.

When I spray starting fluid into the intake, and the engine cranks up and runs just fine for as long as I continue to spray it. I assumed the carbs would take over at some point and would continue feeding it with fuel, but I can’t even get the engine to sputter once I stop manually feeding it with an external fuel source.

What is it that I’m missing here?