It is currently Sun Nov 18, 2018 4:41 pm

All times are UTC





Post new topic Reply to topic  [ 11 posts ] 
Author Message
 Post subject: REALLY stumped now
PostPosted: Sun Nov 04, 2018 12:03 am 
Offline
paso grand pooh-bah
User avatar

Joined: Wed Jan 19, 2005 12:00 am
Posts: 704
Location: CNY, US
model: 750 Paso
year: 1988
I've been having issues running properly for a while now. I thought it was fuel related, so I replaced all the lines, had the carbs (Mikuni 38s) cleaned, replaced the vacuum fuel pump with a Mikuni unit, tested the coils, the plugs & wires, the compression, checked the valves - all good. I'm at a loss, the shop that has it is at a loss. The only thing they can't test are the Kokusan ignition units. I don't know what else it could be. The shop suggested deleting the excess fuel line (the "Y" in between the pump & carbs that returns fuel to the tank), because they didn't think the vacuum system would send that so fuel that it'd be necessary.

What happens is it feels like the engine would start drowning; it wouldn't rev as quick as usual, it needed a lot of fuel and clutch feathering just to get moving from a stop. And then, every once ina while, there would be a brief flash of proper combustion. "Brief" like a snap of the fingers. Which makes me think it's electrical.

I was considering replacing the coils with the high output offering that California Cycleworks sells, but now I wonder if it's really the Kokusan unit I should replace? Is there any way to test that properly, or can anyone confirm if just replacing the coils with those HO coils would eliminate the Kokusan unit altogether?

At this point, I'll try anything, because even the shop is shrugging its shoulders at me. Thanks in advance, folks.

_________________
Just because you're not dead doesn't necessarily mean you're living, either.
1988 Paso 750 #753965
1997 Monster 750


Top
 Profile  
Reply with quote  
 Post subject: Re: REALLY stumped now
PostPosted: Sun Nov 04, 2018 9:02 am 
Offline
User avatar

Joined: Fri Jul 24, 2015 11:21 am
Posts: 165
Location: Belgium
model: 750 Paso
year: 1989
Hi,

Question: (how) did you test the ignition coils?
Coils can (only) be tested properly with special testing equipment most motorcycle workshops have, they sometimes stop working but most of the times they still give some output (spark) but just not enough for the engine to run properly under all circumstances.
If not available, you could try to test it by "making" a sparkplug with a gap of roughly 3/8 of an inch and it should still spark without hesitation.
On the other hand if you could exchange it with another (working) coil it is easy to feel possible differences.
This last method is easy snd can also be used for the kokusan units, but in that case you need someone who is willing to lend it yo you for a brief moment .....

Anyone near you who owns a Paso with kokusan units?

Hope it helps you somewhat.

Frank

_________________
Bimota SB4-S - 1984
Ducati Paso 750 - 1989
Suzuki SV1000S - 2008
Ducati Monster 796 abs - 2010


Top
 Profile  
Reply with quote  
 Post subject: Re: REALLY stumped now
PostPosted: Sun Nov 04, 2018 12:12 pm 
Offline
paso grand pooh-bah
User avatar

Joined: Sun Jul 18, 2004 12:00 am
Posts: 5255
Location: southern Germany
model: 750 Paso
year: 1987
I would almost bet it's not the Kokusan units. They rarely break down. However you have a Monster so you can try its units.
In what condition are the membranes in the Mikuni? Are they still soft or are they stiff? The throttle slider is vacuum operated and if the membranes become dry over the years the carb won't work properly. Worth checking. If you want to check be careful when removing the round covers as on the bottom there's a small O-Ring.
The fuel return line is not required with the vacuum pump but if you had that also before when the bike still worked properly it's not the issue.


Top
 Profile  
Reply with quote  
 Post subject: Re: REALLY stumped now
PostPosted: Sun Nov 04, 2018 1:42 pm 
Offline
paso grand pooh-bah

Joined: Thu Jun 21, 2007 12:00 am
Posts: 1445
Location: Gothenburg, SWEDEN
model: 907 I.E.
year: 1991
Quote:
The shop suggested deleting the excess fuel line (the "Y" in between the pump & carbs that returns fuel to the tank), because they didn't think the vacuum system would send that so fuel that it'd be necessary.


I`d start w that. The other carbed Ducs don`t use return line so copy that setup.

What does the plugs tell you if you kill engine just as you feather it to take off?
Try to eliminate fuel starvation issue.
If you losen fuel hose at carbs, it should pulsate fuel if you run starter w ignition off.

_________________
Gert

907 I.E. -91
M900 -97
MTS 1100s -07


Top
 Profile  
Reply with quote  
 Post subject: Re: REALLY stumped now
PostPosted: Sun Nov 04, 2018 8:18 pm 
Offline
paso grand pooh-bah
User avatar

Joined: Wed Jan 19, 2005 12:00 am
Posts: 704
Location: CNY, US
model: 750 Paso
year: 1988
@Frank - the shop tested the coils, not me. The shop owner actually used to have a Paso, so he's familiar with them (and possibly therefore more sympathetic to me?). The tech was convinced it was jetting - although it had been running fine for years prior. So that's why we've moved into electrical.

Gerhard - you raised a good point with the Monster. I'll actually pulling the engine from mine because the output shaft bearing grenaded, so it won't miss its ignition. I'll bring that stuff to the shop, see if that fixes the problem. If that's the case, then in the meantime, I'll just look for a replacement while the Monster is a basket case.

Thanks, fellas - I appreciate the objective viewpoint. I'll keep you posted!

_________________
Just because you're not dead doesn't necessarily mean you're living, either.
1988 Paso 750 #753965
1997 Monster 750


Top
 Profile  
Reply with quote  
 Post subject: Re: REALLY stumped now
PostPosted: Sun Nov 04, 2018 8:25 pm 
Offline
paso grand pooh-bah
User avatar

Joined: Wed Jan 19, 2005 12:00 am
Posts: 704
Location: CNY, US
model: 750 Paso
year: 1988
paso750 wrote:
In what condition are the membranes in the Mikuni? Are they still soft or are they stiff? The throttle slider is vacuum operated and if the membranes become dry over the years the carb won't work properly. Worth checking. If you want to check be careful when removing the round covers as on the bottom there's a small O-Ring.
The fuel return line is not required with the vacuum pump but if you had that also before when the bike still worked properly it's not the issue.


They've had that carb apart a number of times over the past month, so I'm sure they would've seen any issues in it.

Good to know about the fuel return line. I kept that as a hold over from original pressured system, but I'll delete it if it's not necessary. Do I need to plug that tube on the tank?

_________________
Just because you're not dead doesn't necessarily mean you're living, either.
1988 Paso 750 #753965
1997 Monster 750


Top
 Profile  
Reply with quote  
 Post subject: Re: REALLY stumped now
PostPosted: Mon Nov 05, 2018 4:06 pm 
Offline

Joined: Thu Nov 29, 2007 2:38 am
Posts: 287
Location: UK
model: 907 I.E.
year: 1990
there are a couple of things that are often overlooked...

a are the fuel hoses OK? dont say they are new, have you actually checked them ? sometimes they come "defective" but because you think they are new " and therefore must be OK" then you do not check if they actually deliver fuel.

another thing is the fuel cap, are you sure the tank is properly vented? if the tank is not vented properly after a short wile it will create vaccum and starve the engine; when it starves try opening the cap, maybe it is just that simple.

as for the electrical side, the ignition key switch and the kill switch on the handlebar are also something that need to be checked, I had a Paso 750 with both issues and they were driving me nuts. You can disassemble clean and refurbish them, it takes patience but is feaseable.


Top
 Profile  
Reply with quote  
 Post subject: Re: REALLY stumped now
PostPosted: Mon Nov 05, 2018 9:03 pm 
Offline
User avatar

Joined: Sun Jul 30, 2006 12:00 am
Posts: 213
Location: Chicago-NW Suburb
model: 750 Paso
year: 1988
Check for a voltage drop to the coils. Sounds like how mine ran when there was, due to a fouled on/off/on switch. Dyna coils helped for a while, as they fired better under the lower voltage, but eventually the switch was found to have its contacts fouled so badly, even the Dyna coils couldn’t keep up. Cleaning the switch contscts corrected the regualar plug fouling of the forward cylinder, and intermittent stumbling from running on one cylinder.


Top
 Profile  
Reply with quote  
 Post subject: Re: REALLY stumped now
PostPosted: Mon Nov 12, 2018 6:43 pm 
Offline
paso grand pooh-bah
User avatar

Joined: Wed Jan 19, 2005 12:00 am
Posts: 704
Location: CNY, US
model: 750 Paso
year: 1988
angelix & streetsurfer - you guys might be onto something.

I know the new fuel lines are ok, because I put them on and I put clear ones on because the first couple things I tried didn't fix the issue - and I specifically wanted to see what was going through the lines. ;)

But the ignition/kill switch ... for a while now, I've had this problem with my start switch: unless the battery was just fully charged, the starter wouldn't trigger when the switch was in the 'run' position. However, you can make the starter turn in the 'off' position - but the cylinders won't ignite. So I would turn the dial to off, hold the starter, and then flick the dial to run, and voila! Ignition!

So I wonder if that isn't causing some kind of issues when it's actually running? Luckily, I have a Monster that isn't running and doesn't need its right hand controls at the moment either ... (sigh)

More as it happens - thank you for input, folks!

_________________
Just because you're not dead doesn't necessarily mean you're living, either.
1988 Paso 750 #753965
1997 Monster 750


Top
 Profile  
Reply with quote  
 Post subject: Re: REALLY stumped now
PostPosted: Mon Nov 12, 2018 6:50 pm 
Offline
User avatar

Joined: Sun Jul 30, 2006 12:00 am
Posts: 213
Location: Chicago-NW Suburb
model: 750 Paso
year: 1988
fasterdammit wrote:
angelix & streetsurfer - you guys might be onto something.

I know the new fuel lines are ok, because I put them on and I put clear ones on because the first couple things I tried didn't fix the issue - and I specifically wanted to see what was going through the lines. ;)

But the ignition/kill switch ... for a while now, I've had this problem with my start switch: unless the battery was just fully charged, the starter wouldn't trigger when the switch was in the 'run' position. However, you can make the starter turn in the 'off' position - but the cylinders won't ignite. So I would turn the dial to off, hold the starter, and then flick the dial to run, and voila! Ignition!

So I wonder if that isn't causing some kind of issues when it's actually running? Luckily, I have a Monster that isn't running and doesn't need its right hand controls at the moment either ... (sigh)

More as it happens - thank you for input, folks!


That is the exact symptom I had. As you found, I could start the bike better by cranking in the off position then flipping it to on, without fail. Otherwise, very difficult to crank at enough speed and get enough voltage to the coils to fire. I think it was about a volt and a half lost across the swiitch too.


Top
 Profile  
Reply with quote  
 Post subject: Re: REALLY stumped now
PostPosted: Thu Nov 15, 2018 9:06 am 
Offline
paso grand pooh-bah
User avatar

Joined: Sun Aug 01, 2004 12:00 am
Posts: 1095
Location: siena, italy
model: 750 Paso
year: 1988
Quote:
And then, every once ina while, there would be a brief flash of proper combustion. "Brief" like a snap of the fingers. Which makes me think it's electrical.

This may happen because of fuel too. After a run, spark plugs look wet and black dirth or dry and light gray?
Moreover, as all other guys wrote, mikunis don't need return line at all.
Loss of voltage: Many of us made a wiring mod to solve it but you need to be sure about voltage regulator first of all!
Remember it must charge until 14,5 volt at about 4000 rpm and do not grow until rpm red line! A higher voltage blows kokusan units!!!
Then you can test the loss of voltage between +12 pole on the battery and the orange wire plugged on the coil. An OEM "used"wiring loses 1 or 2 volts, but gray coils need a voltage higher than 10 volt to run properly.
Once I experienced a damage to a wire under the main switch, it had a small contact when I turner right and it was interrupted when turning left! You can reach such wire introducing your hand under the dashboard and try to move it)
Hope it helps :)

_________________
have a nice ride, Nicola

Black "DUKE" 751582
ex...Red "smooth" 753349 :-(


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 11 posts ] 

All times are UTC


Who is online

Users browsing this forum: No registered users and 11 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to: