Author Topic: Advice needed on carb/intake/filter combo for SP  (Read 323 times)

Online berniebee

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Advice needed on carb/intake/filter combo for SP
« on: September 16, 2021, 10:48:22 PM »
Hi folks,

I'm hoping to get some suggestions as to which air filter, intake manifold and air intake tube I should be using. My present configuration doesn't seem to work right. Some background:

I finally started the engine for my '83 SP project. Weirdly, from cold it started without the enricher more easily than with it. Took a while for the first start but ran ok once started, for about three minutes or so. Shut it off but, now warm it would not start. I think I know why. The K& N pods slide on to a very long air intake tube attached to the PHF30 carbs:






Also, notice that the bike came with the less-curved-than-stock Delrin intake manifolds, so the left filter touches the frame: (the stock side panel doesn't fit.)





I've placed the right filter above the intake tube so you can see how far the tube intrudes inside the filter:



temporary image hosting


My theory is that the intake tube is partially blocking the airflow through these tiny pods, resulting in a rich mixture. And maybe these pods are just too small? To prove it, I started the bike a couple of hours later without filters (Engine was cold) and this time it started quickly with the enricher on. Once warmed up, the engine started easily without the enricher.  Also seemed to rev up more quickly when twisting the throttle.

All these parts came with the bike as I purchased it. But the frame was crabbed and the carbs were off when I bought it, so I don't know if it was actually run in this configuration. From my experience today, it doesn't seem likely.

I don't think I can fit a larger K&N (The oval one) with this configuration. It doesn't look like Delrin type manifolds with a sharper curve are available. (But please let know if you've found one.)

Ideally, I would like a solution that would allow me to A: use bigger air filters (Or a large shared one.) and B: not have to cut my left side panel to fit.  I want to keep my just rebuilt PHF30's. 

Any suggestions?




Online nc43bsa

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Re: Advice needed on carb/intake/filter combo for SP
« Reply #1 on: September 16, 2021, 11:52:23 PM »
You've found the problem;  the inlet stubs are strangled by the filters.

Either find shorter inlet stubs for the carbs or take them off and mount the filters to the carbs directly.
« Last Edit: September 16, 2021, 11:53:09 PM by nc43bsa »
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Offline not-fishing

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Re: Advice needed on carb/intake/filter combo for SP
« Reply #2 on: September 16, 2021, 11:56:17 PM »
I had a filter fitment problem with my V65SP resurrection.  K & N's never fit right.  Stock airbox was long gone.

So I got the socks and they fit.

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Online Tony F

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Re: Advice needed on carb/intake/filter combo for SP
« Reply #3 on: September 17, 2021, 12:06:32 AM »
Le Mans side covers, if you aren't seeking originality, give a more space for filters. You can also space the side cover mounting out further for a little more space. I'd remove the stubs entirely.

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Re: Advice needed on carb/intake/filter combo for SP
« Reply #3 on: September 17, 2021, 12:06:32 AM »

Online jwinwi

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Re: Advice needed on carb/intake/filter combo for SP
« Reply #4 on: September 17, 2021, 06:45:02 AM »
If you stay with those K&Ns cut the manifolds so there's just enough for the filters to attach to.   Maybe UNIs would work better in the space you have?
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Online John A

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Re: Advice needed on carb/intake/filter combo for SP
« Reply #5 on: September 17, 2021, 06:59:20 AM »
 the closed end of the filter needs to be at least two and a half  times the internal diameter of the carb throat away from the end of the carb opening according to “The Scientific Design and tuning of Intake and Exhaust Systems” or it will affect running, especially at wider throttle opening. It’s an effect I’ve experienced on Guzzi engines
« Last Edit: September 17, 2021, 12:23:22 PM by John A »
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Online berniebee

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Re: Advice needed on carb/intake/filter combo for SP
« Reply #6 on: September 17, 2021, 08:45:48 AM »
 The WildGuzziers come through again with great suggestions and tips.


Thanks, you guys are the best.  :bow:


Offline billgilbert

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Re: Advice needed on carb/intake/filter combo for SP
« Reply #7 on: September 19, 2021, 12:07:47 PM »
Same deal for me on my 83 SPNT. My rubber couplers cracked and are unobtainium. I went to the delrin couplers, had to cut out the side covers and move the slotted rubber bushing in the hangar brackets out as far as possible to get clearance for the filters. Those extension tubes will unscrew from the carb. Took some heat and finesse, large diameter, fine threads, but they came off. I removed them and have been running this way for years. The quoted tuning book is probably right about the 2.5 diameter thing, but good luck actually doing THAT. Don't worry too much about it, it'll work fine.

Just put a pair of Lafranconi Reservato Competizione mufflers on mine and it has noticeably more power at hiway speeds, if a bit louder.






Offline guzzista

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Re: Advice needed on carb/intake/filter combo for SP
« Reply #8 on: September 19, 2021, 12:59:38 PM »
With Guzzi or Malossi ally intake manifolds no hacking, cutting necessary.
I purchased some Delrin manifolds years ago , but never liked the angle as they aim the carbs out and cause interference
Some  bending inwards of side covers front  downwards edge, foam filters and a set of PHM 40's  will fit



 in there without any rubbing



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Offline Matt Story

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Re: Advice needed on carb/intake/filter combo for SP
« Reply #9 on: September 20, 2021, 07:10:04 PM »
Which bikes were cursed with the deteriorating rubber intake manifolds?  How many different rubber parts are we talking about that are no longer available?  I ask these questions as someone who could reverse engineer these no longer available parts and facilitate the production.  If nothing else, the parts could be scaled and 3D models could be resolved and published for others to produce from, either by 3D printing, machining or molding.

The more limited the number of different obsolete rubber manifolds, the more sense it makes to reproduce.

I am volunteering to scale a few of these up and attempt printing them.
« Last Edit: September 20, 2021, 07:11:32 PM by Matt Story »
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Offline rjamesohio

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Re: Advice needed on carb/intake/filter combo for SP
« Reply #10 on: September 21, 2021, 06:23:15 AM »
K&N's on an SP - it's been a few minutes since I arranged them on my SP but once on I had no issues....

I used the larger oval ones and was able to fit them but 'canting' them to each other; they did not look symmetrical but they fit.

But it sounds like you'd need to first buy the larger ones...
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Harper's Moto Guzzi
Harper's Moto Guzzi. Where we still answer the phone, use the highest quality parts, and also do Transmission, rear drive, and carb rebuilds fast. Call us at 816.697.3411 and get your problems resolved.
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Harper's Moto Guzzi
Harper's Moto Guzzi. Where we still answer the phone, use the highest quality parts, and also do Transmission, rear drive, and carb rebuilds fast. Call us at 816.697.3411 and get your problems resolved.
http://www.harpermoto.com
Advertise Here