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 Post subject: 750 Sport run issue
PostPosted: Mon Apr 23, 2018 12:03 pm 
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Joined: Mon Apr 16, 2018 8:37 pm
Posts: 16
Location: Finland
model: 750 Sport
year: 1989
Hello everybody,

I got my bike started for the first time after it's been sitting for 4 years. To my surprise it started right away with not much effort...WIN! :) However I noticed that when it being on no choke, idle revs are less than 1000rpm and battery light is on. When slowly touching the throttle to rev up I hear spitting from right side muffler and then suddenly engine revs up and then settles down again. What could this be about?

Here I have a video clip from the situation: https://youtu.be/1hBfxPTRn8E

My ideas: Either one of the carbs is stuck and not giving enough gas to the engine or spark plug is in the end of its life?
Next I'm going to try to add some gas system cleaner. If this is not helping then change for a new spark plug.

What could be the reason for low idle revs?


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 Post subject: Re: 750 Sport run issue
PostPosted: Mon Apr 23, 2018 1:49 pm 
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paso grand pooh-bah

Joined: Thu Jun 21, 2007 12:00 am
Posts: 1436
Location: Gothenburg, SWEDEN
model: 907 I.E.
year: 1991
Sounds abit strange, you sure it is running on both cylinders?
Check that both get spark and fuel.

Battery status?
When you raise RPM, do voltage over battery terminals rise to around 14V?

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Gert

907 I.E. -91
M900 -97


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 Post subject: Re: 750 Sport run issue
PostPosted: Mon Apr 23, 2018 10:12 pm 
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paso grand pooh-bah
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Joined: Sun Jul 18, 2004 12:00 am
Posts: 5206
Location: southern Germany
model: 750 Paso
year: 1987
Running on one cylinder is typical. The usual reason is low voltage at the coils. When throttle is opened voltage increases and the other cylinder will kick in. Since there's unburnt gas in the exhaust it will spit or backfire.

First of all: good that you got the oil screen filter out. ;)

Do measure the voltage at the coils when the ignition is on and at idle. If it's lower than battery voltage check the FAQs for the wiring modification. That should fix it.
Make sure the spark plugs are clean or better install new Champions. Did you drain the tank and use fresh fuel?

Quite sure it's ignition not carb related.


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 Post subject: Re: 750 Sport run issue
PostPosted: Tue Apr 24, 2018 9:33 am 
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Joined: Mon Apr 16, 2018 8:37 pm
Posts: 16
Location: Finland
model: 750 Sport
year: 1989
I see, that's a good point. I'll check does first. I was going to do the wire modification anyway, so hopefully it will help too :)

In the video battery light goes on when on low rpm. Is this normal or is it because of bad coil?


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 Post subject: Re: 750 Sport run issue
PostPosted: Tue Apr 24, 2018 6:25 pm 
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paso grand pooh-bah

Joined: Thu Jun 21, 2007 12:00 am
Posts: 1436
Location: Gothenburg, SWEDEN
model: 907 I.E.
year: 1991
Not normal, indicates low charging of battery.
But, after a first ride of 40-50 km`s, battery should be fully charged and no light.
Do check voltage over battery as mentioned.

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Gert

907 I.E. -91
M900 -97


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 Post subject: Re: 750 Sport run issue
PostPosted: Fri Jun 01, 2018 7:26 pm 
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Joined: Mon Apr 16, 2018 8:37 pm
Posts: 16
Location: Finland
model: 750 Sport
year: 1989
viewtopic.php?f=13&t=7920&p=62009#p62009

At least for now this issue is solved by changing bad accelator pump.


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 Post subject: Re: 750 Sport run issue
PostPosted: Mon Jun 11, 2018 4:08 pm 
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Joined: Mon Apr 16, 2018 8:37 pm
Posts: 16
Location: Finland
model: 750 Sport
year: 1989
Still some problems. Too much fuel. Running very rich and allways smelling the fuel. Ran on full choke this morning just for 1min and soon there was fuel leaking from exhaust pipe linkage. Found this on the forum’s FAQ topics:

”The biggest problem was that the fuel pump was too strong for the needle jet in the carb, thereby flooding it, all the time. Putting in a pressure regulator at 3psi improved things imensely. There were a few other tweaks you could make to get the stock carb working reasonably, but 'reasonably' was all you could expect. There was a whole lot more potential in the engine if you change out the carbs.

In the Paso, you could bypass the fuel pump, but you can't do that in the Sport. The fuel lines in the tank are brazed in such a way that if you take out the fuel pump, you will only use 1/2 of the tank's capacity. Not a good option. Make sure your fuel lines have a T in them that returns to the tank. This keeps your fuel pressure reasonably low and won't flood your carbs. The return line is one of the stubs in the middle of the tank. One is a vent, the other is a return.”

As stock there should be T in fuel line already and so does mine. Should there be an additional one?

About the fuel regulator: where should one be implemented? Can’t I just close the fuel gate a little bit to lower the preasure?


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 Post subject: Re: 750 Sport run issue
PostPosted: Tue Jun 12, 2018 10:37 am 
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paso grand pooh-bah
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Joined: Sun Jul 18, 2004 12:00 am
Posts: 5206
Location: southern Germany
model: 750 Paso
year: 1987
your bike should run as it is w/o the need of any modification. Did you check the electrics as suggested before and is the Weber's float valve ok? The float needle's rubber tip can wear over time and let fuel through. When you've verified that and that's all ok you could try to remove the jet in the return line (#32).


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 Post subject: Re: 750 Sport run issue
PostPosted: Tue Jun 12, 2018 10:43 am 
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Joined: Mon Apr 16, 2018 8:37 pm
Posts: 16
Location: Finland
model: 750 Sport
year: 1989
I have checked the electrics and made the third wiring modification. I guess the float chamber gets flooded then. Also the rpm goes over 2000 when the bike is facing uphill when idleing.


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 Post subject: Re: 750 Sport run issue
PostPosted: Tue Jun 12, 2018 10:50 am 
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paso grand pooh-bah
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Posts: 5206
Location: southern Germany
model: 750 Paso
year: 1987
something else, breather hose and fuel return are connected correctly?


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 Post subject: Re: 750 Sport run issue
PostPosted: Tue Jun 12, 2018 11:00 am 
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Joined: Mon Apr 16, 2018 8:37 pm
Posts: 16
Location: Finland
model: 750 Sport
year: 1989
I have to double check, but yes they should be what I remember. When opening the fuel cap I can see fuel rush inside the tank when pump is running. Isn't this sign of correct connection?

You mean the number 6 rubber?


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 Post subject: Re: 750 Sport run issue
PostPosted: Tue Jun 12, 2018 11:15 am 
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paso grand pooh-bah
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Posts: 5206
Location: southern Germany
model: 750 Paso
year: 1987
as in your picture the return connection is the one on the outer side. It sounds ok.
If you open the carb do also verify that the floater actually still floats. If it isn't airtight anymore it can fill up with fuel, sink and leave the valve open.


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 Post subject: Re: 750 Sport run issue
PostPosted: Tue Jun 12, 2018 11:40 am 
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paso grand pooh-bah
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Posts: 5206
Location: southern Germany
model: 750 Paso
year: 1987
Quote:
You mean the number 6 rubber?

no I mean number 7 but I have to correct myself. Often valve needles have a rubber tip but the ones in the DCNF don't seem to. Still they can wear. On the bottom there's an example found on a website about Kawasakis. It's a worn vs a new jet. The marks can be minimal and only hard to see.


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 Post subject: Re: 750 Sport run issue
PostPosted: Tue Jun 12, 2018 4:33 pm 
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Joined: Thu Nov 29, 2007 2:38 am
Posts: 276
Location: UK
model: 907 I.E.
year: 1990
question... is the fuel pump "original"? I mean the one for carburated engines?

the IE version is exactly the same from the outsice but pumps @ over 3BAR and you will need a pressure regulator to make it work correctly with the Injectors.

in your case even 1.5 bar are too much, the carburated version should be less than 0.8 (I think) or it WILL push the float valve and flood the carb.

If the Pump was replaced (or the tank) you need to check you have the correct one.

then you need to check all fuel connections are correct and also check the return is free, if the jet in the return line (#32) is full of dirt then your return is not working causing the pressure encrease in the system.

you need to check also the float valve, it is a cheap component and is worth renovating it anyway.


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 Post subject: Re: 750 Sport run issue
PostPosted: Tue Jun 12, 2018 5:58 pm 
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paso grand pooh-bah
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Joined: Sun Jul 18, 2004 12:00 am
Posts: 5206
Location: southern Germany
model: 750 Paso
year: 1987
Quote:
question... is the fuel pump "original"?

Good point. You never know on such an old bike that may also have had a few owners tinkering with it :thumbup:


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