It heats up and no longer runs right

bohalrantipol · Post by **bohalrantipol** » Thu Aug 10, 2006 3:40 pm

Hey,
I have a 87 750 paso, DCNF 44, I recently aquired this bike had loads of problems with the carbs on it and unfortunatley they continue. I rebuilt the carb and cleaned the ever loving bejesus out of it. Put a 60 idle jet because of info on here (even though all of my weber experience disagrees), and changed the fuel pump out for a facet 3-5psi pump (which fit flawlessly if anyone is interested). Did a once over on the valve train etc.. and here is my delima. When i begin the tune up process i can get the bike at just warm to idle and run very smooth, but after riding it and getting it up to "proper" operating temps it will not idle nor does the off idle acceleration work for a damn. once moving the upper RPMs lend a good deal of acceleration but nada down low, sounds and feels like it is running on one cylinder. any advice etc. would be nice. Also more if some one could give me a proper procedure for tuning DCNF i would appreciate it. All my weber exp. is with IDF's mainly, not that i think it is different just curious if i am missing anything.
Thanks guys.

Desmo_Demon · Post by **Desmo_Demon** » Thu Aug 10, 2006 5:06 pm

I've never claimed to be a carb expert, and just about loathe working on them. I know nothing about a Weber, so take this with a grain of salt. My first thoughts are that the main jetting is correct, but your idle/secondary (aka intermediate) circuit(s) are too rich. You know it isn't an electrical or fuel delivery issue, as it runs fine at higher rpm.

You don't mention anything about backfiring or exhaust smoke. If the bike backfires through the carb, that is typically a lean condition. Back, sooty smoke out the exhaust (sometimes followed by back-firing through the exhaust) is typically a rich condition. Any chance you have an air/vacuum leak?

If the idle circuit is rich, lower temps would have it acting like a choke, but then the rich mixture would want to kill the engine oncve it warms up....usually accompanied with black smoke. So.......questions...

1) Are you getting any backfiring through the carb or exhaust?

2) Are you experiencing any black smoke?

3) Have you taken a can of starting fluid or similar to check for air/vacuum leaks (usually leads to lean mixtures)?

4) Have you checked the color of the spark plugs (the color is not always beneficial in trouble-shooting)?

This is the way I'd start trouble-shooting it. Never know, someone here may be able to help out with a little more info.

streetsurfer · Post by **streetsurfer** » Thu Aug 10, 2006 8:40 pm

Your comment on it feeling like running on one cylinder struck a chord here. I had problems with the horizontal cylinder fouling the plug. Changing to Dyna-coils stopped it. My carb and jetting were stock (for the Limited). It would stumble and cough down low, or not start at all, but often after accelerating past a certain point it would wake up and fire on both and run fine for the rest of the ride. Other times it necessitated a plug change or cleaning.

bohalrantipol · Post by **bohalrantipol** » Fri Aug 11, 2006 4:18 am

all advice apreciated, i undertook some more tinkering and now have some new developments. I adjusted some more, and now its more baffeling then ever. At first i went on a nice long ride and nothing seemed to be wrong, then i throttled it up and by fourth gear it was boggging down, it did not recover and ran like crap untill i really hit the throttle. I am a bit frustrated and i am now entertaining the idea of some mikunis. Could this be an ignition thing? or do i just need to adjust some more?

bohalrantipol · Post by **bohalrantipol** » Fri Aug 11, 2006 4:21 am

Desmo_Demon wrote:I've never claimed to be a carb expert, and just about loathe working on them. I know nothing about a Weber, so take this with a grain of salt. My first thoughts are that the main jetting is correct, but your idle/secondary (aka intermediate) circuit(s) are too rich. You know it isn't an electrical or fuel delivery issue, as it runs fine at higher rpm.

You don't mention anything about backfiring or exhaust smoke. If the bike backfires through the carb, that is typically a lean condition. Back, sooty smoke out the exhaust (sometimes followed by back-firing through the exhaust) is typically a rich condition. Any chance you have an air/vacuum leak?

If the idle circuit is rich, lower temps would have it acting like a choke, but then the rich mixture would want to kill the engine oncve it warms up....usually accompanied with black smoke. So.......questions...

1) Are you getting any backfiring through the carb or exhaust?

2) Are you experiencing any black smoke?

3) Have you taken a can of starting fluid or similar to check for air/vacuum leaks (usually leads to lean mixtures)?

4) Have you checked the color of the spark plugs (the color is not always beneficial in trouble-shooting)?

This is the way I'd start trouble-shooting it. Never know, someone here may be able to help out with a little more info.

in response, there is a little backfiring out the exhaust, no black smoke, i checked for air leaks and found none, the spark plugs are definately black and i need to replace them so prehaps it is the coils, seems suspect though.

Post by **paso750** » Fri Aug 11, 2006 10:22 am

what exhaust, airfilter and plugs are you using ?
All original or aftermarket ?
You may measure voltage at your coils at different rpm. If it`s under 12V the wiring mod you can easily find here will help.
Meaure also the voltage from your regulator, is it ok ?

I had similar symptoms when my voltage regulator starting to break down. I changed different t5hings at that time so I cannot say what it definetely was at the end.

G.

bohalrantipol · Post by **bohalrantipol** » Fri Aug 11, 2006 5:03 pm

Yeah i am really starting to think it is something with the electrics, another odd thing started happening were the starter would only run when the kill swith was off, then i had to switch it to on to get it to run. This is also sporadic. I dunno what the hell that is all about. Stock exhaust, K&N airfilter, normal plugs i.e. probally nippon.

bohalrantipol · Post by **bohalrantipol** » Fri Aug 11, 2006 5:04 pm

what else did you change beside the regulator? I will test it when i get home.

delagem · Post by **delagem** » Mon Aug 14, 2006 3:39 am

I'm staying outta that Weber discussion! But my Paso does the kill switch thing: It won't spin on the starter unless the kill switch is off, and then once you've got the starter spinning, you switch the kill switch back on.

Bruce Meyers says this is most likely the ground on the harness, under the gas tank. Just pull the bodywork, clean to bright metal, put some dielectric grease or vaseline on the contacts, and reassemble.

But since it's such a pain to pull the tank and bodywork, I haven't done it yet. So I look at it as an anti-theft device; who is possibly going to know that trick, except another Paso owner?

Post by **paso750** » Mon Aug 14, 2006 8:00 am

sorry for the delayed reply.

Here you find the regulator tests:

http://www.geocities.com/750paso/paso/faultfinding.pdf
(be sure the battery is ok)
As delagem said, clean all ground connections and the starter/killswitch.
Measure resistance of the coils and ignition cables.
Put in new plugs (Champion RA6HC recommended)
Measure voltage at the coils with engine off and running at different rpm. If it starts from lower than battery voltage try the wiring mod (check FAQs post)
Check if carb is synchronized correctly and fuel/air mixture is right.
Ensure that there are no air leaks

If one cylinder has drop outs try to switch CDI units and then the coils. Are the drop outs on the other cylinder then or is it as before ? (which I assume)

If all this doesn`t do any change it will be getting a bit more difficult.

(if you have the "thing" that the engine starts with the kill switch on, or you only get it running when you crank in off position and then while cranking switching to on. Try one thing next time after you`ve measured all lines. Keep the switch on on position, crank and gently hit the starter switch under the seat with the flat hand.
If it then catches and starts you might consider changing it)

G.

Post by **jcslocum** » Fri Aug 18, 2006 2:39 am

delagem wrote:But my Paso does the kill switch thing: It won't spin on the starter unless the kill switch is off, and then once you've got the starter spinning, you switch the kill switch back on.

Bruce Meyers says this is most likely the ground on the harness, under the gas tank. Just pull the bodywork, clean to bright metal, put some dielectric grease or vaseline on the contacts, and reassemble.

But since it's such a pain to pull the tank and bodywork, I haven't done it yet. So I look at it as an anti-theft device; who is possibly going to know that trick, except another Paso owner?

This is the fix for the starting problem; Paso 750 Wiring Upgrade: http://tinyurl.com/42xo9 . My Paso did exactly the same thing with the kill switch before fixing the wiring. It's not a dirty ground. The wiring is crap....

Desmo_Demon · Post by **Desmo_Demon** » Fri Aug 18, 2006 9:24 pm

delagem wrote:But my Paso does the kill switch thing: It won't spin on the starter unless the kill switch is off, and then once you've got the starter spinning, you switch the kill switch back on.

I think this is what the PO of my Paso was trying to tell me this one did. After checking about 90% of all the wires (some of it was really screwed up) and redoing a couple of grounds, it appears to be back as normal according to a multimeter when checking for continuity. I'm seriously thinking of doing the relay mod on this bike while I've got it apart, though. Shouldn't be difficult at all, compared to what I've just gone through electrically with this bike.