Gentlemen,

Since we are all thinking about carbs, please allow me to insert a general question regarding the ancient instruments:

I have Del'orto PHM 40s combined with Malossi intake manifolds and Malossi fire resistant (don't ask why) pod filters. The P750 runs great, accelerates like a jet airliner, and behaves beautifully throughout the entire rev range. Never an issue other than a vehicle fire (leaking gas tank in 2012) regarding fueling. I've since replaced that fuel tank and repaired all damage

However, on my last ride early last week, the motor started to come down from higher revs quite slowly. Not crisply as it has in the past. This certainly affects downshifting and engine braking significantly.

Gentlemen, do you think this symptom is indicative as a air/vacuum leak in a fuel line, or perhaps a timing issue?

Coils are in great shape (from a '99 M900) air gap just fine, but start-up aren't as natural and automatic as before. I had to be sensitive to the throttle position a bit more on the last two startups in December.

Thank you all for your time and attention and for any thoughts or suggestions.

Blessings & Happy New Year to All. :-)

you need to check few things :

- sparkplugs, check if both are the same color, the darker the richer; if one appear much paler in colour then you might have an airleak somewhere or the carb is delivering less fuel.
- engine off, check if the carbs shut completely when opening and closing the throttle; you should hear/feel a distinctive "clack" on each of the carbs, you need to check the cables are free and the carbs close together
- check for a bad seal in the manifolds and carbs.
- have the carbs been checked? maybe you got a loose jet or a damaged level float.
- do you have a Digiplex? if affirmative there are some vaccum pipes and a sensor worth checking, maybe the ECU is being fooled and keeps the advance timing "advanced"

My feeling is that there is an airleak somwhere, but fisrt start checking the cables, could be something silly.

it does sound like it's running lean. Have a close look at the rubber boots between carb and carb manifolds. Make sure that the carbs sit correctly and all clamps are tightened properly.

Thank you both! I am going to remove fairings today and have a look at throttle, cables, fuel lines, manifolds, plugs, boots. Luckily, I do not have the Digiplex, rather I have the Kukosan. Your expertise is so helpful for me and I am extremely grateful. I'll keep y'all abreast of my findings and any results from remedial actions. Best Wishes!

One minor additional item to consider, and I am very sure you are sharp enough to have already considered this, but to be sure: check the vacuum nipples that should be on each Malossi intake (mine has them) to ensure they are tight and leak-free. Mine have loosened in bygone years.

Thank you davidrose. I'll add that item to my list. Excellent advice much appreciated.

Greetings! I've been motivated by your helpful advice and done some work toward resolution.

Pictures after my tank and fairings removed reveal a dirty girl that needed to be sanitized, greasy pods, and degradation of the rubber booties at the manifolds and throttle cables. The hairline cracks on the manifold booties are not ruinous yet, but I will find and order new boots.

i could tighten the attachment bolts on the vertical cylinder's Malossi manifold about 1/16 turn, the horizontal's manifold was super snug. Vacuum plugs on the manifolds were snug. I turned the screws on the rubber boots's hose clamps 1/8 turn apiece. They feel very tight.

The 40's are perfectly synchronized. One clack on throttle release, and I could observe that synchronization visually as well. Fuel hoses are a 5 years old: not as pliable as new, but in good shape w/o cracks or holes. No weepage or wetness observable. As you see, the set-up is simple: no return lines.

The floats seem to work: no weepage or leaks from the bowls. Very dry and stays dry.

Plugs electrodes seem a nice enough brown. I'd say it was running a tad bit rich, pro'lly because I swapped out the F1 cans for stock muffs about 2 years ago 'cause they look so sweet. What do y'all think? Plugs are 5 years old, 10K miles from new. Should I replace them?

I've cleaned the foam filters and I've done a deep cleaning+reconditioning of the motor, frame, etc and I've waxed the fairings and tank. Before I completely reassemble, I will heed any advice given as well as take a 50 mile test ride with the front fairing and oil radiators secured to see if the symptom recurs.

Al in all I think this Paso looks pretty fine for 50,000 miles and 32 years of use. I'm still so in love...

Thank you all again for you interest and attention and advice. My Best Wishes to each of you. :-)

Throttle cables well lubed/smooth?

Thanks T-fan for the mention. The cables are 5 yrs. old in excellent shape custom made in Cali by MotionPro. They replaced fire damaged units. They are smooth, but I've not lubed them. I will take your prompt and use a MotionPro cable lube device to take care of the job.

Replacement rubber manifolds and clamps (US$25 ea.) and cable adjuster covers have been purchased from Bevel-Heaven in Concord, CA. I hope they arrive this week so I can reassemble and ride during the mild weather that's arriving tommorow.

Thank you again. Best Regards! :-)

Does your Paso sit for a few months at a time or more? The ethanol-rich Cali gas may be clogging or affecting your carbs. Mine become degraded with as little as 4 months of non use. Probably not the problem, as your symptom seems to indicate an air leak, however since your carbs are readily accessible and because you are already in contact with Steve at Bevel Heaven it is not much more trouble and one less thing to worry about to replace rubber components, ensuring the tiny carb passages are clear, and double checking all carb measurements. Does not take long and simple to do.

Thank you again davidrose. Excellent advice. I ride the P750 consistently every other week up into the East Bay hills (Redwood Rd, American Canyon, etc) on a 50 mile run to keep us both in shape. I always hope this will clear the carbs and circulate & heat the oil, etc. You're right in your observation however, it's been several years since a carb rebuild to replace the rubber components and certainly they must suffer from the doctored up petrol we fill our tanks with. I will order 2 rebuild kits from Steve and get that work on my schedule. While at it, I should order new fuel line as well and do a complete job...

I hope to ride the Paso as soon as the manifold boots arrive in the interim though because I'm impatient and I can't wait . Thank you!

Gentlemen:

One last bit of advice from the collective would be most helpful before I button up the Paso: I have new NGK DPR8EA spark plugs but I do not know the correct gap for the P750. What would Y'all recommend as the proper gap?

NGK
DPR8EA
9

Should I go with the .9mm gap? Thanks again for all your consultation.

I don't know if the 750 ignition is up to it but run as big a gap as you can get away with. 0.9mm is what I'd go for.

Many thanks Derek!

I just wanted to say thanks again to all who helped, especially Tamburinifan. I finally lubed the throttle & carb and cables with white lithium and while at it I noticed that the union where two cables to the carbs split from the throttle cable had sagged a centimeter and that seemed to be the cause of my issue. I supported it with a cable tie to the frame and am once again enjoying the Paso. :-)